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  • 1. DYNAMIC AQUARIA
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  • 3. DYNAMIC AQUARIA BUILDING AND RESTORING LIVING ECOSYSTEMS Third Edition Walter H. Adey Karen Loveland National Museum of Natural History Smithsonian Institution Washington, D.C. AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Academic Press is an imprint of Elsevier
  • 4. Academic Press is an imprint of Elsevier 84 Theobald’s Road, London WC1X 8RR, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA 525 B Street, Suite 1900, San Diego, California 92101-4495, USA First edition 1991 Second edition 1998 Third edition 2007 Copyright © 2007 Walter H. Adey and Karen Loveland. Published by Elsevier Inc. All rights reserved The right of Walter H. Adey and Karen Loveland to be identified as the authors of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science and Technology Rights Department in Oxford, UK; phone: (+44) (0) 1865 843830; fax: (+44) (0) 1865 853333; e-mail: permissions@elsevier.co.uk. You may also complete your request on-line via the Elsevier homepage (http://www.elsevier.com), by selecting “Customer Support” and then “Obtaining Permissions” British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalog record for this title is available from the Library of Congress ISBN-13: 978-0-12-370641-6 ISBN-10: 0-12-370641-6 For information on all Academic Press publications visit our web site at http://books.elsevier.com Typeset in 10/12pt Palatino by Charon Tec Ltd (A Macmillan Company), Chennai, India www.charontec.com Printed and bound in the USA 07 08 09 10 11 10 9 8 7 6 5 4 3 2 1
  • 5. Contents Preface xi Acknowledgments and Dedication xv C H A P T E R 1 C H A P T E R Introduction 3 The Origin of Life: Microcosm Earth 2 Microcosms and Mesocosms of Aquatic Substrate: The Active Role of Rock, Mud, Ecosystems 5 and Sand Restoration of Damaged Ecological Systems 8 The Solid Earth and Life 44 Summary 8 Chemical Relationships Between Rocks, Taxonomic Notes 8 Sea Water, and Organisms 48 References 9 The Solid Earth, Rock, and Model Ecosystems 50 Sediments and Model Ecosystems 51 P A R T Geological Storage 59 References 60 I PHYSICAL ENVIRONMENT C H A P T E R 4 C H A P T E R Water Composition: Management of 2 Salinity, Hardness, and Evaporation The Envelope: Physical Parameters and Water Structure and Characteristics 62 Energy State Ocean Salinity 63 Hardness of Fresh Waters 67 Temperature 17 Water and Model Ecosystems 71 Water Motion 23 Algal Scrubbing and Water Composition 71 Tides: Simulating the Effects of Sun Marine Microcosms and Aquaria 72 and Moon 35 Quality of Top-up Water 73 References 41 References 73 v
  • 6. vi Contents C H A P T E R C H A P T E R 5 8 The Input of Solar Energy: Organisms and Gas Exchange: Oxygen, Lighting Requirements Carbon Dioxide, pH, and Alkalinity Photosynthesis and Its Origin 75 Oxygen Exchange 118 Solar Radiation and Water 79 Oxygen, Model Ecosystems, and Ecosystem Light Absorption by Water Plants 82 Restoration 120 Light Intensity and Plants 82 Carbon Dioxide Exchange 121 Photorespiration 88 Carbon Dioxide and Global Aquatic Light and Model Ecosystems 89 Restoration 122 Light and Physiological Considerations 91 Managing Carbon Dioxide and pH in Microcosms Summary 91 and Mesocosms 124 References 92 Gas Exchange and Selected Model Ecosystems 125 C H A P T E R References 128 6 C H A P T E R The Input of Organic Energy: Particulates and Feeding 9 Particulates, Energy Supply, and Aquatic The Primary Nutrients – Nitrogen, Ecosystems 93 Phosphorus, and Silica: Limitation and Inorganic Particulates 95 Eutrophication Organic Particulates 95 Humic Substance 97 Nutrients in Natural Waters 131 Particulates and Aquatic Models 97 Eutrophication and Hypereutrophication of Biofilms 98 Natural Waters 134 Particulate Import in Aquatic Models 100 Nutrients and Model Ecosystems 136 Aquatic Ecosystem Restoration 100 Summary 139 References 100 References 140 P A R T C H A P T E R II 10 BIOCHEMICAL ENVIRONMENT Biomineralization and Calcification: A Key to Biosphere and Ecosystem Function C H A P T E R The Process of Biomineralization 143 7 The Carbonate System and the Formation of Calcite and Aragonite 143 Metabolism: Respiration, Photosynthesis, Halimeda: Photosynthesis-Induced and Biological Loading Calcification 145 Calcification in Stony Corals 146 Metabolism 105 Calcification, Stony Corals, Coral Reefs, and Respiration 106 Global Warming 148 Bacterial Metabolism 110 Calcification in Mesocosms and Aquaria 150 Photosynthesis 112 Coral Reef Aquaria and Stony Coral Biological Loading 114 Calcification 151 References 115 References 154
  • 7. Contents vii C H A P T E R Food Webs in Model Ecosystems 195 Establishment of Food Webs 196 11 Trophic Structure in Aquaria 201 The Organisms 202 Control of the Biochemical Environment: References 202 Filters, Bacteria, and the Algal Turf Scrubber Sterilization Methods 156 C H A P T E R Bacteriological Filtration 156 Reef Systems 157 14 Denitrification 157 Foam Fractionation (Protein Skimming) 158 Primary Producers: Plants That Photosynthetic Methods 158 Grow on the Bottom Algal Turfs 159 The Algal Turf Scrubber (ATS™) 161 Benthic Algae 203 Algal Scrubbers and the Modeling of Algae in Model Ecosystems 219 Ecosystems 165 Submerged Aquatic Vegetation 222 Summary 168 Marine SAV and Model Ecosystems 229 References 169 Freshwater SAV and Model Ecosystems 231 Emergent Aquatic Vegetation 234 P A R T EAV and Model Ecosystems 242 Plant Communities and the Restoration of III Wild Ecosystems 250 References 251 BIOLOGICAL STRUCTURE C H A P T E R C H A P T E R 12 15 Community Structure: Biodiversity Herbivores: Predators of Plants and in Model Ecosystems Omnivores, Predators of Plants and Animals The Framework of Biodiversity 173 Types of Herbivores 254 The Community 175 Plant Defenses 256 The Biome 175 Modifications of Marine and Freshwater Features of Communities 181 Herbivores 257 The Magnitude of Biodiversity 183 Herbivores and Model Ecosystems 263 Community Structure and Ecological Models 186 References 265 Scaling and Reproduction 186 Model Diversity 187 Summary 189 References 189 C H A P T E R 16 C H A P T E R Carnivores: Predators of Animals 13 The Carnivore Predator 267 Trophic Structure: Ecosystems and the The Prey 268 Dynamics of Food Chains The Dynamics of Predation 269 Marine and Freshwater Predators 269 Energy Capture and Flow 192 Predators and Synthetic Ecosystems 275 Food Webs 193 References 279
  • 8. viii Contents C H A P T E R P A R T 17 IV Plankton and Planktivores: Floating Plants ECOLOGICAL SYSTEMS IN and Animals and Their Predators MICROCOSMS, MESOCOSMS, AND AQUARIA Plankton Size and Composition 282 The Bacteria 282 Phytoplankton 282 C H A P T E R The Planktonic Food Web 286 Mechanisms of Filter Feeding 288 20 Plankton, Particulates, and Model Ecosystems 293 Wild Ecosystem Restoration 300 Models of Coral Reef Ecosystems References 302 Modeling Coral Reef Ecosystems 344 Caribbean Coral Reef Microcosm at the C H A P T E R Museum of Natural History 345 Coral Reef Microcosm at the Smithsonian 18 Marine Station 353 Great Barrier Reef Mesocosm 353 Detritus and Detritivores: The Dynamics of A 130-Gallon Reef Microcosm 356 Muddy Bottoms Summary 368 References 368 The Deep Ocean 307 Bacteria 307 Fungi 307 C H A P T E R Protozoa 309 Meiobenthos: Protozoans 309 21 Meiofauna: The Multicellular Invertebrates 311 Macrobenthos 313 A Subarctic/Boreal Microcosm: Test of a Deposit Feeding in Saltwater Soft Bottoms 317 Biogeographic Model Deposit Feeding in Freshwater Soft Bottoms 319 Carnivores and the Detritivore Community 321 The Rocky, Embayed Coast of the Northwestern Detritus and Its Role in Model Ecosystems 321 Atlantic Geological History 371 References 327 The Gulf of Maine 376 The Core Subarctic 387 Core Subarctic vs Mixed Subarctic/Boreal 393 C H A P T E R A Maine Shore Microcosm 395 An Opportunity to Test Biogeographic Theory 403 19 References 404 Symbionts and Other Feeders C H A P T E R Zooxanthellae and Their Animal Hosts 329 Biology and Ecology of Corals 332 22 The Positive Feedback Loop between Photosynthesis and Calcification 334 Estuaries: Ecosystem Modeling and Anthozoans and Microcosms, Mesocosms, and Restoration Aquaria 335 Parasitism 336 Where Fresh and Salt Waters Interact 405 Environment, General Health, and Disease 337 Chesapeake Bay in Mesocosm 406 Biodiversity 337 A Florida Estuary in Mesocosm 416 Quarantine (Prevention of Transmission) 337 Nutrient Dynamics in Estuarine Models 439 Disease Treatment in Model Ecosystems 338 Estuarine Restoration 439 References 339 References 441
  • 9. Contents ix C H A P T E R Nutrient Removal from Agricultural Wastewaters (Nonpoint Source) 474 23 Nutrient Removal from Rivers 479 Bioenergy and Solar Energy Recovery Using ATS Freshwater Ecosystem Models Systems 480 Aquacultural Wastewaters 481 A Florida Everglades Stream and Wetland 443 Industrial Wastewaters and ATS Systems 484 A Blackwater Home Aquarium 450 References 489 Restoration of Freshwater Ecosystems 452 References 452 P A R T P A R T VI V SUMMARY THE ENVIRONMENT AND ECOLOGICAL ENGINEERING C H A P T E R 26 C H A P T E R Microcosms, Mesocosms, and Macrocosms: 24 Building and Restoring Ecosystems, a Synthesis Organisms and Natural Products: Commercial Ecosystem Culture Principles of Ecological Modeling 494 Ecosystems in Home Aquaria 498 The Aquarium World 458 Applied Model Ecosystems 499 Pharmaceutical Culture 462 References 499 References 463 C H A P T E R Index 501 25 Large Scale: Water Quality Management with Solar Energy Capture The Quality of US Surface and Ground Waters 467 Nutrient Removal from Domestic Wastewaters 468
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  • 11. Preface By the mid-20th century, widespread concerns were being top priority of all human society. It seems highly expressed for the way in which modern human popula- unlikely, no matter what our scientific and technical tions and their industrial endeavors and products were prowess, that humans can survive on this planet, with affecting both the environment in which they lived and our few domesticated species, in the midst of a radi- the planet’s wild populations and their ecosystems. Some cally altered atmosphere and hydrosphere and a dys- predictions for the future were dire, and enough environ- functional biosphere. It is most discomforting to hear mental activism developed so that some of the more of new plans to purposefully inject pollutants into the conspicuous problems (e.g. raw sewage, oil spills, DDT, stratosphere, to act like a volcanic eruption, or to spray PCBs, chlorofluorocarbons, and atomic power radioac- iron dust on the oceans, hopefully to increase photo- tive materials) were subsequently ameliorated or at least synthesis, and thereby, at least temporarily, reduce subject to management (though never fully corrected). global warming effects. Why is it that so much of our However, the larger, more widespread, and chronic efflu- educated humanity cannot conceive of working with ent problems of human society (e.g. nutrients, CO2, and our biosphere, using processes that we know well, to moderately toxic hydrocarbons) have continued to expand solve multiple environmental problems? their reach into every corner of the biosphere, atmosphere, Ranging from the domestication of a few wild and hydrosphere. The ever-growing global human popu- species by chance beginning 10 000 years or more ago lation, the continuing process of habitat destruction, and to that by design in the last few centuries, human the ever-expanding desire of that population for a western efforts to extend utilization of our biosphere beyond lifestyle, rich in fossil energy use and synthesized products, hunter-gathering have almost always been at the level using abundant raw materials, suggest that these prob- of an individual species. Limited polyculture, as farm lems, already built up over a century or more, and now ponds, is practiced in some countries, and in the latter growing geometrically with population expansion, are not half of the 20th century “permaculture,” following going to be so easily ameliorated. some ancient practices on land, advocated polyculture; Atmospheric CO2 increase, with its concomitant however, by and large, our domesticates remain mono- global warming, already seems beyond correction to a cultures. Compared to the global biodiversity (even the large percentage of scientists, engineers, and educated already greatly reduced biodiversity of today), the public. Yet, the degradation of our natural waters, and numbers of domesticated species remain vanishingly especially our oceans, the latter being of considerably small. The intensive management of farms and aqua- greater mass than the atmosphere, is slower to be rec- cultures provides one of the most extensive elements ognized; and orders of magnitude more difficult to cor- of coastal and oceanic pollution and wild ecosystem rect. In many coastal waters, decades of environmental loss. Unfortunately, especially in western cultures, it effort backed by large financial expenditures have remains deeply ingrained that only by optimizing all failed to prevent a continuing and serious reduction in aspects of single species culture, often at great environ- water quality. Although, in many countries, regula- mental cost, can we hope to support current human tions to contain the widespread pollution of the atmos- populations. It also does not help that most economic phere and natural waters have been initiated, habitat models call for ever-continuing growth, when this is destruction continues and increasing population and clearly the root of our failure to meet environmental advancing prosperity have overcome most efforts to problems. stem the tide of environmental degradation. As some This book focuses on efforts to interact with and writers have so succinctly stated, we are slowly begin- effectively “domesticate” at the ecosystem level, to ning to stew in our own toxic brew. build experimental ecosystems to learn, and to under- We are hardly alone in expressing our grave concern take ecological engineering, as interaction with “wild” for the future of the human race if the full understand- ecosystems. Ultimately, we propose to optimize bio- ing and correction of these issues does not become the geochemical function and biodiversity, and to reform xi
  • 12. xii Preface our relationship to our biosphere. As we explain in this degradation, and the waters of the Baltic Sea and book, symbiosis has been a critical part of organic evolu- Chesapeake Bay are considerably more altered than tion. Likewise, humans have formed a number of sym- those around Tierra Del Fuego. However, as we shall bioses with plant and animal domesticates. Some very point out in our following text, numerous studies and influential and critical scientists have recognized that reports declare a global scale alteration of species the human symbioses collectively called farming have and community function that is likely to continue and been a mixed blessing for the human race. Nevertheless, deepen. We have written this 3rd edition on the basic current human populations are demanding an ever- premise that most aquatic ecosystems are no longer expanding intensive global scale farming that typically “wild,” being subject to significant and negative uses monocultures to optimize a single return; usually unplanned and uncontrolled human effects. We now this return is biomass for food, materials, and, more must treat wild ecosystems as controlled systems that recently, energy. However, the human race also requires must be managed, and human effects ameliorated, just ecosystem/biosphere level atmospheric and hydros- as in our “captive” ecosystems. We have expanded our pheric cleaning, soil structuring services, and general earlier treatment of “Building Living Ecosystems” to biogeochemical stabilization that our farming sym- “Building and Restoring Living Ecosystems,” applying bioses do not and probably cannot provide. Global much of the original methodology, where appropriate, warming is only one example of human overpowering to “wild” systems management. We show that large- of those global ecosystem services. As we describe in scale ecosystem cleaning of human pollution, using depth in this book, the experimental study of living solar/algal techniques, can also provide considerable ecosystems can lead to “domesticated” ecosystems that usable energy to replace the fossil fuel use that is are far more efficient at solar energy capture than farm responsible for much of the global environmental monocultures, without providing the inevitable envi- degradation. Just as we have organized in the past to ronmental degradation of those monocultures. We industrialize, we must now re-organize to more fully demonstrate that use of such systems can clean up much integrate with the Earth’s biosphere while switching to of the damage already visited on our planet. renewable energy sources. Significantly increased energy and materials conser- It has been 15 years since the 1st edition of Dynamic vation is essential to current and future generations. Aquaria was completed; it has gone through several While this has been locally necessary in the past, as printings, and the response, especially in the academic many communities and even civilizations have found and professional world, has been quite favorable. out to their detriment, our great numbers and increasing Some of the model or controlled ecosystems described individual requirements have now expanded the con- in the 1st edition are still in operation. One system, servation requirement to a global level. Unfortunately, with its mechanical–electrical systems re-built, has we are unlikely to achieve the level of conservation now been in operation for over 25 years. A few have needed to stop the global warming “steamroller,” and been extensively researched, and we can now report ultimately coastal and oceanic depletion, unless we in depth on their function. Those long-term systems expand the scale and depth of our photosynthetic sym- that have been carefully studied have shown complex bioses to both the landscape and the ecosystem level. community and trophic structuring and extraordinary Some environmentalists will find the thought of domes- biotic diversities based on reproductively maintained ticating high-diversity, high-efficiency ecosystems as populations. undesirable, perhaps even encouraging human society The scientific context in which our approach to living to neglect conservation and population reduction. systems modeling has developed has changed signifi- Indeed, this is a potential dilemma. However, even if a cantly. In the year Dynamic Aquaria was first published broad spectrum of human society could be brought into (1991), the journal Ecological Engineering also appeared. an extensive conservation mode, the inertia of global It has now completed its 15th year and has published population and degradation provides environmental over 500 articles. Several scientific studies describing the problems that are realistically beyond a simple conser- approaches of other scientists to living systems model- vation solution. ing have also appeared during the same time frame, and In the earlier editions of this book, we presented a more peripherally, but of considerable interest, the methodology for re-creating functioning wild aquatic Society and journal Restoration Ecology have matured. ecosystems for research and education. The underlying In the public display/education arena, the philosophy centered on the notion that many of those Smithsonian exhibit conveying the principles of ecosystems remained in the “wild state” and that it ecosystem operation to the public at large has now was possible to re-create or model them experimen- moved to and become the “Smithsonian Marine tally. Clearly, there is a broad gradient of ecosystem Ecosystems Exhibit” at Fort Pierce, Florida. However,
  • 13. Preface xiii very few large public aquaria built during the past 20 the many millions of species in the world, most have years, unless adjacent to a good and abundant source evolved chemical/ mechanical systems that are of of high-quality water, have chosen to take an ecological potential use to the human race. Yet, we are forcing route – for most, the graphic design and artistic back- them into extinction at ever-increasing rates, every day drop may be ecologically oriented, but the organisms losing forever invaluable information. displayed are specimens isolated from a real ecology. Maybe one day we will know so much about genetic This is most unfortunate, because it is only with codes and cellular and organism development that we broader public understanding that the massive loss of can create de novo any organic possibility; and, on the diversity, so characteristic of today’s biosphere, can be other hand, maybe that day will be as far away as halted. This must be accomplished through steward- atomic fusion and artificial photosynthesis. In the ship of the environment and the ecosystems in which meantime, it behoves the human race to develop as organisms live by most of our population. The concept many symbioses with species and their ecosystems as that species can be saved one by one at best applies we can manage. We are an integral part of organic evo- only to mammals and a few birds and fish, if at all. lution and organic complexity. If we try to escape that Finally, the hobby world of aquaria remains in fer- fact, a fact as deeply and broadly based as any of our ment with ideas that still exceed the funding capability scientific and engineering knowledge, and a narrow of scientific and information systems to test and convey parasitism of a few species, the rest be damned, we reality. Unquestionably, many new “hobby” techniques, are likely to commit ourselves to early extinction. both those tested in the garage and those provided by Multimillions of species in the past have failed to adapt enterprising businesses, are increasingly capable of and traveled that well-worn route. Sooner or later, an culturing many species under optimum conditions of astronomical event may well cause our extinction. growth and sometimes reproduction. The recent Reef However, we will just as likely survive a few more mil- Aquarium “bible” by Delbeek and Sprung is a shining lion years if we will use our intellect to adapt to the example of progress in the hobby. However, hobby sys- reality of our base in organic evolution. tems mostly remain polycultures, and real ecosystems, This edition is divided into five broad sections, consisting of diverse communities of organisms in an each containing two to seven chapters. Most chapters environment approaching that of a wild analog and begin with a review of the subject matter relative to the processing energy and nutrients through food webs, larger picture of ecology, ecosystems, and the Earth’s are rare. biosphere as a whole. Part of our appreciation of In this edition, we greatly expand on the use of the complexities of smaller ecosystems comes from ecosystem modeling techniques to clean natural waters understanding the more universal context in which all and the atmosphere. We also show how large rivers, ecosystems operate. Where appropriate, the remainder bays, and even the ocean and atmosphere can be man- of each chapter deals with the building of microcosms aged in a far healthier state, and kept that way, if and mesocosms of ecosystems for research and also we will only adapt a more conservation-minded and gives examples of the unique aspects of small home ecosystem-centered approach to the human future. aquarium systems. Finally, where appropriate, we dis- We briefly discuss a critical area of aquatic ecosys- cuss how the information presented relates to the tem modeling that is especially ripe and far overdue larger concern of environmental restoration. for development, namely systems for identification Part I discusses the physical environment, elements and extraction of pharmaceutical drugs already devel- of which at the ecosystem level have often been mis- oped by a host of wild species. In our anthropocentric understood by environmental scientists and ignored arrogance, humans tend to conclude that with our by aquarists and hobbyists. We discuss our further brains, tool use, and language we are far beyond other understanding of the shapes, material, and construc- organisms. Humans have long thought of harnessing a tion of the envelope that will hold various size aquaria; few animal species to “work” for us, and have tried to the temperature, water composition, and motion; solar co-opt the energy storage of a number of plant species; energy; and the substrate, or rock, mud, and sand, that however, for many, most life is thought of as useful makes up the floor of the system and in part provides only to “tree-huggers” and in the way of our for all critical geological storage. We also examine the “progress.” We tend to forget the story of penicillin, critical role of suspended particulates, inorganic and and the parallel stories of many lesser known drugs. organic, in aquatic ecosystems. Since it is based in the Up to a half century ago, serious bacterial infections physical factors discussed in this section, we also pres- often meant death or dismemberment. Then we ent a biogeographic model for the world’s ocean learned of and eventually co-opted the chemical coasts. Much ecosystem modeling is likely to be carried “invention” of penicillin by the fungus Penicillium. Of out within the framework of this model.
  • 14. xiv Preface In Part II, on the biochemical environment, we dis- commensurate with the many years of extensive moni- cuss the mechanisms of gas and nutrient exchange, as toring data now available. Calcification and biodiver- well as the management of animal wastes in small sity investigations of the latter, 130-gallon coral reef models. We particularly examine “ecosystem metabo- system, are covered in Chapter 20. lism” contrasting the interlocking functions of plants Efforts are now under way to apply the concepts pre- with animals needed for the successful operation of sented in this book to commercial-scale culture of organ- these dynamic ecosystems. We continue to describe our isms and the production of human food. Both concepts primary means of controlling the biochemical environ- will assist in protecting endangered wild communities ment by using managed communities of algae, and to by greatly reducing wild harvest. Both concepts will cir- thereby achieve the simulation of larger volumes of cumvent the increasing tendency for wild harvests to open water and where appropriate export to other com- lose their economic viability. Equally important, the munities or geological storage. Because biomineraliza- basic water quality control methodologies described in tion, especially calcification, represents an internal sink this book are applicable to relatively inexpensive and and needs special treatment in semi-closed ecosystem high-quality treatment of a broad spectrum of both models, we provide a chapter reviewing what is known human wastewaters and the streams, rivers and bays, as about this complex subject, and we relate this to the well as coastal waters that are impacted by those waste- management of controlled ecologies. One of our longer- waters. In Part V, we describe some of the ongoing lived coral reef models was used to extensively research efforts to make these endeavors commercially viable this subject. Much of this has been published in scientific and environmentally successful at large scale. journals, and the basics are presented in Chapter 10. HydroMentia, Inc. of Ocala, Florida, provides the princi- The ecosystem concept remains a subject of ani- pal commercial effort to expand these methodologies to mated scientific debate. However, most scientists landscape scale. Some of HydroMentia’s engineering would accept for a definition something approaching processes are proprietary, including the use of ATS™ for “diverse communities of organisms, supported and phosphorus and heavy metal removal. Commercial constrained by a given physical–chemical environment, endeavors should examine the HydroMentia organiza- interacting to capture and process energy and nutrients tion website and contact their representatives for further in food webs.” In Part III, we deal with the organisms, information. their diverse communities, and their food webs. It has Finally, in Part VI, we present a series of principles been clearly and repeatedly demonstrated that given a for establishing and operating living ecosystems. This reasonable facsimile of the wild environment, with is where the real scientific learning process begins, in appropriate imports and exports, and a diverse mix of reducing our endeavors to core concepts, each of which introduced species of the wild biota, the species of we strive to better understand in the framework of the ecosystem models will self-organize communities and ecological function of the natural world. Most impor- food webs to process energy and nutrients. Finally, in tant, we come to understand that the key element to Chapter 19 of Part III, we introduce symbiosis, and dis- success lies in boundaries, the open end of the defini- cuss the considerable role that this process has played tion of an ecosystem. No ecosystem stands alone. in organic evolution. As humans continue to push other Understanding the conditions at the boundaries, the species “out of our way” and drive ever more of them imports and exports, knowing which species must be into extinction, it is essential to remember that a sym- simulated by human action because scaling factors biosis or joining together of organisms has often pro- effectively place them across the boundaries, and, vided a highly successful evolutionary strategy. finally knowing where to draw the boundaries to make In Part IV, we present case studies of numerous the modeling effort practical, will determine the mag- microcosms, mesocosms, and aquaria. Treatment of nitude of success. Restoration of human-impacted wild the Florida Everglades Mesocosm and the authors’ ecosystems differs primarily in scale; the concepts are 14-year-old 130-gallon coral reef is greatly expanded quite similar.
  • 15. Acknowledgments and Dedication It has been nearly 30 years since we initiated the develop- have been many and their wisdom and effects are ment of the concepts presented in this book and began always helpful, Pat Kangas has been ever behind the the long process of R&D that produced the very promis- principles and broader goals. And among our long ing array of ideas and working systems now in motion. time friends, Susan Bradley has always been ready to For those who will open their eyes and minds, we speak come to our rescue, whether for a creative design or of the methods of a new rapprochement with nature. A technical computer problems, while Addie Moray and generation ago, neither the method of experimenting Mary Ellen McCaffrey gave unselfishly of their time for with captured ecosystems nor the concept of learning some of the administrative tasks. We say again, a book from, and then “domesticating” ecosystem processes must teach, and while text is paramount, a picture is was widely accepted either in the aquarium hobby ever “worth a thousand words.” Again in this edition, world or in the science and ecological engineering com- photographers Nick Caloyianis and Clarita Berger munities. As exhilarating as these years have been for us, worked their superb magic to provide what only they have not been without physical, emotional, and photography can convey. financial struggles, especially for our far-flung families, The erratic path to knowledge in natural history sci- students, colleagues, business associates, and financiers. ence is, in the end, ever exciting, and because of the So many people have helped us, we are losing count, and “ivory tower” environment in which it is carried out, here we can single out only those who were strikingly we would not wish to lose a moment of it. The applied important in more recent years. We apologize to the far world, and finding the funding to make it happen, can more numerous helpers and facilitators that we do not be more brutal. To those engineering colleagues and specifically mention but without whose assistance the financial and business associates who have not only accomplishments we present would be far more lim- traveled with us in our efforts to bring the solar energy- ited. The contributions of many of these individuals are capturing and water and atmosphere cleansing process mentioned in the earlier editions. of ATS to a very needy world, but also have picked up To all the members of our families, who have the ball and run up-the-mountain when we have tired, inevitably lived with Dynamic Aquaria and its precedent we feel a gratitude and comradeship that is inexpress- research for decades, we thank each of you for your ible. At a time when algae was still a bad word, a cousin patience (and guidance). Special tribute goes to Nathene to red tide and the failed food promise of the 1950s, Loveland, Karen’s mother for her encouragement in ini- Don Panoz and Richard Purgason started the ball rolling tiating the R&D endeavor, and for her enthusiasm and with Aquatic BioEnhancement Systems. We are espe- multifaceted support, and to Walter Adey Sr., Walter’s cially indebted to the HydroMentia crew, especially father, for a guide to life that lives on. Whitcomb and Margaret Palmer on the business and Science and engineering is meant to be questioned, financial side, and Allen Stuart and Mark Zivojnovich tested and re-tested, but the road of true progress can on the engineering side. The engineering innovations be long, convoluted and tiresome. To our numerous and managerial devotion of the HydroMentia staff students and assistants, the energy of youth always to solving these serious environmental problems is made up for whatever we lacked, and we are deeply extraordinary by any measure; HydroMentia picked conscious of the gratitude we owe you. We are espe- up the ball when it was slowing and we are now cially indebted to our longtime friend, colleague, and approaching the goal posts, at least the ones most visi- student, Sue Lutz; she came to our rescue, to help us ble in the fog of time. Whit especially had the vision, meet the various deadlines, while we needed to be on interest, and resources to take the chance on this jour- our research vessel in the Canadian Maritimes; without ney, even when the walls in the fog soared out of sight. her multifaceted talents we could not have completed We are particularly grateful to both Mark and Allen this edition. In recent years, Allegra Small and Don who provided their consistent support in supplying Spoon additionally provided the dedicated support that editing, current data and information for this edition. was a requirement for success, and while our colleagues Above all, we thank all of you for your friendship and xv
  • 16. xvi Acknowledgments and Dedication ongoing, stimulating interchanges and discussions. especially Melissa Read, Project Manager, of Elsevier HydroMentia, this edition of Dynamic Aquaria, is dedi- Book Productions in Oxford, England, Gregory Harris, cated to you. the Designer for Elsevier, who stuck with us to create a Organism culture, by sustainable and non-polluting new cover design, and Pat Gonzalez of Academic Press means, is essential to our future use of organisms from in San Diego, who helped guide us in the initial process our hydrosphere. However, the “tragedy of the com- of this endeavor. mons” haunts us, and as long as there are “fish in the The global environment is under siege by an explod- sea”, the ability to make this shift will be illusory. On ing human populace driven by pre-historic genes. the ornamental culture side, we have to take our hats However, we can think and reason; we are not the deer, off to Morgan Lidster for his “green thumb.” However, rabbits, and lemmings who cannot know they are the financial mountain was overpowering, and we destroying the environment that they depend on and now put our hopes in SeaQuest of Utah for further are heading for population collapse. We can learn and motion in this very challenging arena. respond to the challenges. We surely must try, because, Finally, we thank our publisher Dr. Andy Richford, with our technical prowess and global influence, Senior Acquisition Editor, Life Sciences Books of humans will hardly be alone in this collapse. We salute Elsevier and Academic Press in London, for providing all of those who have helped us, and often carried us the opportunity to expand and broaden our scope in us on our way; we think the ideas expressed herein this edition, and for the unending enthusiasm and will help in our “coming to terms” with the realities of encouragement of the Elsevier/Academic Press staff, nature.
  • 17. C H A P T E R 1 Introduction This book presents the process of building, managing, in these endeavors and concepts (e.g. Osmond et al., and restoring living aquatic ecosystems (in microcosms, 2004). However, critically important at this juncture, mesocosms, and macrocosms) and its background, Petersen et al. (2003) have had the resources to demon- rationale, status, and future. We argue that there is no strate a scaling rationale that demonstrates veracity qualitative difference between a rationally constructed thresholds. In general, as might be expected, larger ecosystem in microcosm and mesocosm and that in a models can more accurately depict the function of their macrocosm. In this book, we use the term macrocosm for analog. However, as Petersen et al. (2003) demonstrate, a wild ecosystem that has been altered or constrained by large microcosms and moderate-sized mesocosms human endeavor. Human constraints are largely degrad- have already begun to pass those thresholds; and we ing in effect because they have mostly been performed expand that concept by greatly increasing the biodiver- with little concern for the continued function of the sity and ecosystem linkage of these models. ecosystem. However, they can be constructive, such as a In our view, no longer are there aquatic ecosystems scientific or restorationist effort at repair, revitalization, (including the oceans) on planet Earth that have not and even optimization. been significantly altered directly or indirectly by There has been a tendency on the part of some sci- human activities. Many species have been driven to entists to regard the modeling of living ecosystems as extinction, some as large as the Steller sea cow, and impossibly complex; that is, they view true ecosystems many more have had their ecological role greatly as beyond human construction. The tendency in meso- reduced and whole ecosystems altered (e.g. the North cosm research today is to restrict efforts to a few Atlantic codfish). Many fresh and coastal waters have species interactions, to keep control and limit the vari- been radically altered, some to a nearly “dead” state ables, but producing a result that most ecologists (e.g. upper Chesapeake Bay); even the open oceans would hardly accept as an ecosystem. In the aquarium have been degraded by food-chain concentrated toxic world, the feeling is widespread that total control over compounds that have rendered some organisms infer- very limited diversity (gardening rather than ecology) tile and others subject to organ malfunction and can- is necessary to achieve anything but an explosion of cers. Finally, simply to encompass what would be a weeds and parasites. Yet, as we shall discuss in this very long list, a global girding biome, coral reefs, are book, since the first edition was published, it has been facing drastic reduction, if not practical extinction. It possible for many years to operate in “aquaria” the has long been accepted by ecologists that ecosystem most complex ecosystems in the sea, coral reefs; these supports are critically important to the survival of microcosms of a few cubic meters, behave chemically human societies; the advent of concern for the effects as wild reefs, and have a biotic diversity per square of global warming, and the clearly impending collapse meter exceeding that known for the wild. Similarly, we of our access to clean water has spread the ecosystem demonstrate the ability to produce whole estuaries, for support concern far more widely. We feel that much of periods of up to a decade, with much of their biotic the ecosystem damage can be corrected, and our basic complexity intact. These estuaries were first attempts standard of living maintained if we greatly increase and the future bodes well for those willing to move on our efforts now. We have the tools, but time is running to larger, more sophisticated, systems. We are not alone out for their application. 1
  • 18. 2 1. Introduction We start our discussion by demonstrating that the In addition to the millions of stars in our galaxy, development and evolution of life is very likely an composed mostly of hydrogen and helium, there are inevitable part of the chemistry of the universe. We enormous masses of interstellar gas and dust. This inter- demonstrate that the definition of an ecosystem becomes stellar gas and dust is enriched in the heavier elements a functional reality given the right physical/chemical (i.e. formed in the cooling, nuclear furnaces of dying stars ecologically engineered) framework, and an appropri- and then blown into space in supernovae. The prevailing ately inserted, food web-based collection of species. In chemistry in these interstellar regions has been called this scenario, inserted organisms self-organize into a com- an “organic cosmochemistry” (Oró, 1994). It has been munity of species interacting to process energy and nutrients shown that the numerous hydrogen, carbon, nitrogen, through a complex of food webs (i.e. an ecosystem). Since no and oxygen compounds, identified both in interstellar ecosystem stands alone, the key element becomes under- space and in the comets and meteorites that arrive standing and re-creating the boundary conditions, the on Earth, can be abiotically combined in the laboratory imports, and the exports. The ecosystem is the most to provide water and a number of critical pre-biotic complex end-point of biotic evolution, and when the compounds (Table 1.1). A large proportion of cometary experimental method is applied, and disassembly and material is frozen water and some scientists have reassembly utilized, progress in understanding is most demonstrated that the volume of incoming comets has rapid. Scaling becomes our primary difficulty in model- been more than sufficient to provide the Earth’s oceans ing, because almost by definition, some species are too (Frank and Huyghe, 1990). “Furthermore, a large array big or wide ranging for microcosms and mesocosms of proteinic and nonproteinic amino acids, carboxylic and others have been fished out or otherwise damaged acids, purines, pyrimidines, hydrocarbons, and other in macrocosms. We need to know enough about these molecules has been found in the relatively primitive car- ecosystems to interact with them to replace or provide bonaceous chondritic meteorites” that have landed on the effects (e.g. grazing or predation) of the missing Earth (Oró, 1994). species; the process is continuously heuristic. Most theories of the origin of the solar system (e.g. Because we are inextricably enmeshed in our bio- Brown et al., 1992) start with condensation out of a solar sphere and its ecosystems, and because we process nebula. In these models, the inner planets (including global-scale quantities of energy and nutrients, human Earth) had all of their volatiles (including the principal endeavors must seriously consider the effects those elements and molecules of life) blasted out of them by endeavors will have on our ecosystems and how they the sun as they formed. Newer concepts of the forma- can be ameliorated. Microcosms and mesocosms are tion of the Earth–Moon system (e.g. Redfern, 2001), ideally suited for this task (see also Osmond et al., 2004). mostly evolve around the impact of a Mars-sized object with the early Earth, resulting in the Moon being ejected with many of the planetary dynamic characteris- THE ORIGIN OF LIFE: MICROCOSM EARTH tics (orbit, spin, and wobble) formed or altered by the impact. In either case, the Earth started as a rocky “cin- The four most abundant chemical elements (99%) of der” (like the planet Mercury today). It became revital- most living organisms, by number of atoms, are hydro- ized with oceans and gases, most likely, from cometary gen, oxygen, carbon, and nitrogen. The elemental com- and meteorite introduction. We now know that at the position of the universe (Figure 1.1) compared to that of outer margins of the solar system, there are a large num- the crust of the Earth (Figure 3.6) suggests that living ber of ice objects that form the Oort Cloud. These pro- organisms have more in common with the universe as a vide the comets that are sometimes perturbed into the whole than with the Earth alone. Even the relative pro- inner solar system, where they can impact the planets portions of these elements are about the same in living bringing water and organic compounds (Redfern, 2001). organisms as they are in the universe (although hydro- The key to the next step was a planetary mass and tem- gen is lower), but very different from that in the Earth’s perature environment in which the already omnipresent crust. Including the oceans (which are one-sixteenth the water components could be present in their liquid phase. mass of the crust) with the crust, in this elemental analy- While this may have happened on Mars and Venus as sis, has very little effect on the relationship. In the Earth’s well as on planet Earth, it is only on Earth that the con- crust, by weight, oxygen, silica, aluminum, and iron, fol- ditions for life have remained for 4 billion years. Later lowed by sodium, magnesium, potassium, and calcium, cometary and asteroid impacts snuffed out some of that are far above the very small percentages of hydrogen, life when they impacted, but so far none have reset the carbon, nitrogen, and phosphorus. If the whole Earth is life clock. considered (as an estimate), the big four, at 93%, are iron, Chemically, water is a most unusual material. oxygen, silica, and magnesium. By accepted physical/chemical rules, under normal
  • 19. The Origin of Life: Microcosm Earth 3 FIGURE 1.1 Relative abundances of the chemical elements in the universe (based on silicon as 104). Note that except for the very unreactive helium, the three most abundant elements of life are the same as those in the universe with the critical nutrient nitrogen next in line. From The Biological Chemistry of the Elements by Fraústo da Silva and Williams (1993). Reprinted by permission of John Wiley & Sons, Inc. pressures, one would expect this ubiquitous compound compound to form a “semicrystalline” liquid at mod- to exist only as a solid or as a gas, depending on tem- erate temperatures, water appears in its most familiar perature. However, due largely to the polarization of liquid form over a relatively wide temperature range. individual water molecules and the tendency of this At the same time, it becomes a “universal” solvent.
  • 20. 4 1. Introduction TABLE 1.1 Biomonomers, Biopolymers, and Chemical Properties That Can Be Derived from Interstellar and Cometary Molecules Molecule Formula Biomolecules and chemical properties Hydrogen H2 Reducing agent Water H2O Universal solvent Ammonia NH3 Catalysis and amination Carbon monoxide CO ( H2) Fatty acids (Linear nitriles) H(C)nCN (Fatty acids) Formaldehyde CH2O Ribose and glycerol Acetaldehyde CH3CHO ( CH2O) Deoxyribose Aldehydes RCHO ( HCN NH3) Amino acids Hydrogen sulfide H2S ( as above) Cysteine and methionine Hydrogen cyanide HCN Purines (e.g. adenine) Cyanacetylene HC3N ( cyanate) Pyrimidines Phosphate* (PN) PO3 ( nucleosides) 4 Mononucleotides (e.g. ATP) Cyanamide H2NCN (condensation) Biopolymers: peptides and oligonucleotides * Detected in interplanetary dust particles of possible cometary origin and in meteorites. From Oró (1994). Reprinted by permission of Cambridge University Press. Almost every chemical element that occurs in the Thus, while it seems that cellular structures with Earth’s crust dissolves in water, ultimately finding its simple organic compounds would be just “everyday” way into the sea. Water also has one of the highest chemistry in a pre-biotic world, is there an “external” capacities of any compound for storing and exchanging information component required to kick-start life from heat, and it has great surface tension. Thus, this almost there? Very long polymers, strings of smaller organic miraculous material is a basic stabilizing element, resist- molecules, are the everyday “magic” of organic chemists ing temperature variations. and industrial plants today, but they are also part of the Most of the above are debated only in the details by critical stuff of life. Some scientists would have it that scientists today. The critical step, from simple organic the ordered, endlessly replicating structure of inor- molecules, abundant in the colder parts of the uni- ganic clay minerals could provide a template against verse, to life is where the debate lies. Indeed, this may which many simple organic compounds could become have not been a step, but rather a flickering, on-and-off polymers. This can be done in the laboratory, and it process, happening millions of times before taking is an intriguing idea that in the pre-biotic world this hold. Was it enough that physical energy inputs, is where carbon and silicon chemistry come together. whether from lighting at the surface of the sea or Carbon and silicon are chemically similar, as elements: hydrothermal energy at ocean spreading centers (van they form multiple bonds with themselves and many Dover, 2000), into the primitive ocean soup (water plus other elements – silicon, one step up on the periodic simple inorganic compounds) created the next level of table, is roughly twice as heavy as carbon. complexity of organic compounds? This has been Could it be that silicon, the key chemical element in repeatedly accomplished in the laboratory. It may be the crust of cinder Earth, and carbon, coming with that anywhere in the universe, except near stars, when water from the cold outer solar system to bring poten- the temperature is right and water is liquid, then the tial life to a later, temperature-moderated Earth, pro- organic soup is ready to brew. vided the next step up the ladder to full-blown life? In Water has a tendency, because of its surface tension, the contact between the primordial water, rich in a wide to create membranes and “bubble” structures. Lipids, variety of simple organics and cellular bubbles, and present among the universal, simple, organic com- abundant clay minerals formed from erosion of rocks, pounds, spontaneously accumulate on these “bubbles” polymers could have formed from all the types of sim- to form membranes and cellular structures. This can be pler organics, including nucleic acids. Possibly formed abiotically accomplished in the laboratory (Hanczyc in much the same way, RNA is the basic message carrier and Szostak, 2004). Membranes can isolate, structure, of life today, and could well have preceded DNA. This and locate organic reactions making them more effi- is the so-called RNA world that some researchers see as cient than they would be in the greater “soup.” an essential phase (Orgel, 2004).
  • 21. Microcosms and Mesocosms of Aquatic Ecosystems 5 Such RNA in the ammonia, carbon dioxide rich and over the last 3 billion years. Photosynthesis “invented” anaerobic early world, could theoretically exist and repli- by early life has kept the Earth from the fate of Venus – cate itself, becoming more complex, based on natural a boiling, runaway greenhouse – by continually lock- selection. Eventually, the RNA molecules would have ing a large part of this carbon into semi-permanent found themselves inside developing cellular bubbles, storage. By releasing carbon from geological burial to where they could have co-opted those structures, to the atmosphere, we are courting both human and bio- spontaneously produce what one would have to call life. sphere disasters every bit as much as we were (and are) This very basic life probably began “soaking up” the with our nuclear arsenals. Many scientists are more organic chemicals of the soup. However, until regular immediately concerned with a global warming that energy sources and a means of synthesizing carbon and will disrupt many human societies creating global fric- nitrogen compounds from CO2 and NH3 (and eventually tion. Photosynthesis may be somewhat more effective N2) were tapped to bring reproduction and growth with higher levels of CO2 (there is still much debate on together, the future of this “life” had to be uncertain, and this point). However, most scientists have concluded perhaps frequently snuffed out. Eventually, several path- that this natural increase of photosynthesis cannot ways for fixation of carbon and nitrogen evolved in what keep up with our destruction of forests and tundra and could be called primitive bacteria, leading to the highly the release of fossil fuels carbon. Desertification and successful Calvin cycle of cyanobacteria (Raymond, the reduction of more efficient land photosynthesis by 2005). Tied to solar energy capture by the early photo- rising sea level, with human societies putting more and synthetic bacteria, some 3.5 billion years ago, life became more CO2 into the atmosphere in a struggle to obtain firmly established on Earth. From there, with occasional energy to survive the harsher conditions, could push disruptions, as large comets and asteroids continued to us to the high temperatures and sea levels of the arrive, life was on its way to creating the modern, com- Cretaceous with far less land area. Perhaps then mod- plex Earth, so fully integrated, at least from its crust to ern human societies would collapse (Diamond, 2005) the atmosphere, with life. and save the biosphere from a runaway greenhouse Today, the overwhelming geochemical evidence is tumble. that cellular life formed very quickly in the pre-biotic Today, all the Earth is a microcosm, or at least the con- soup (at 3.6–3.8 billion years ago) within at most a few cepts of microcosm, mesocosm, macrocosm, and bio- hundred million years of the formation of a liquid ocean sphere lie a spectrum of overlapping scale. No one on Earth (Gedulin and Arrhenius, 1994). Furthermore, doubts any longer that we can affect our Earth on a it is difficult not to conclude that life will form quickly global scale. The principles that we describe in this book (on a geological scale) anywhere in the universe where for microcosms and mesocosms are very much the same the physical conditions for liquid water develop as what we would use for macrocosms and the oceans. (National Research Council, 1990). We cannot return to a more simple state where the bio- The Gaia concept was popular several decades ago sphere can be counted on to “cover up” for us. We must and has now faded. The basic premise of Gaia, that quickly learn to properly manage the biosphere. some life made more life easier, even possible for more advanced life, is certainly correct. The primordial soup was necessary for the development of cellular systems MICROCOSMS AND MESOCOSMS OF and the earliest molecular complexes that could be AQUATIC ECOSYSTEMS called life. The early bacteria that survived on the soup were a necessary condition for photosynthesis and Over the last third of the 20th century, scientists in a eventually the symbiotic incorporation of photosyn- variety of laboratories around the world have been mak- thetic bacteria into early protists to greatly expand the ing significant advances in keeping marine, estuarine, process of pulling CO2 out of the atmosphere and and freshwater organisms in aquaria-like simulations replacing it with oxygen. And so on it went to life on of wild environments; they have generally been referred land, eventually to primates and humans. to as model ecosystems or microcosms. Some of these Whatever is to be made of these arguments about the become quite large, and when they exceed a few thou- development and expansion of early life, one thing sand gallons in water volume, they are sometimes called is very clear: photosynthesis eventually came to be mesocosms. There is no sharp line between the micro- the key to most life on Earth. Also, it is likely that the cosm and the aquarium. Perhaps it is best to draw the Earth’s crust, biosphere, oceans, and atmosphere line at the point where the desire for strict ecosystem together hold more carbon than ever before because of simulation is relaxed because of size, cost, or interest. continual outgassing of CO2 from the Earth’s mantle The older literature on “ecological microcosms” or
  • 22. 6 1. Introduction “controlled ecologies” was reviewed by Adey (1987; universal waste products urea and highly toxic ammo- 1995), Adey and Loveland (1998), and Kangas and Adey nia to the less toxic nitrite and thence to the least toxic (1996). Petersen et al. (2003) point out that mesocosms nitrate; and more recently (3) either in special anaero- have become as numerous as field studies and they pro- bic chambers, or in open-aerated trickle systems, the vide citations that would allow an extensive review of denitrification of nitrate nitrogen to atmospheric gas recent literature. Osmond et al. (2004) discuss the use of nitrogen. Either separately or in conjunction with the a very large mesocosm (Biosphere II) in the context of above systems, oxygen input into the aquarium and car- global climate change, and argue for the much wider use bon dioxide release from the aquarium are maximized of mesocosms to understand and solve our global to support not only the organisms being maintained, change problems. but also the essential respiration activity of the bacteria. In the Earth’s biosphere no ecosystem stands alone. The respiration of the bacteria in these filters releases Indeed, as we noted above, the primary energy source considerable carbon dioxide, which can significantly for the biosphere itself is derived externally from the acidify the culture. Thus, buffering with calcium car- sun; the remainder internally, from the Earth’s heat. bonate in a wide variety of forms is often used. Hendal Most of the original biotic materials came from outside (2006) and Delbeek and Sprung (2005) provide recent the Earth and, to some extent, are still arriving; the reviews of these methods for aquaria. In most cases, remainder derive by erosion from the Earth’s crust. these methods are sufficient to maintain many organ- External solar and lunar cycles are also important isms. However, they rarely achieve the quality of unpol- sources of information. The boundaries of an ecosystem luted wild waters. are entirely arbitrary. However, whether carrying out The basic principles of bacteriological filtration (and pure field research or drawing boundaries for modeling sewage treatment) lie in the assumption that microbes purposes, drawing those boundaries so that cross- have been the dominant force controlling water quality boundary interchanges can be known and measured or in the wild. However, this is likely to be incorrect, since estimated is a key to success. All ecosystems have cross- far more organic material is stored in soils and geologi- boundary interchanges, and the microcosm builder cal sediments than exists in the biosphere. In addition, must know what those interchanges are and simulate the Earth’s atmosphere is rich in oxygen and, prior to them accordingly or the model ecosystem will have little human involvement, was very poor in carbon dioxide. relationship with the wild analog. Higher plants and algae have created far more organic When modeling boundaries are established for most matter than microbes have degraded, with a concomi- aquatic ecosystems, water inflow and outflow are impor- tant production of oxygen and removal of carbon diox- tant parameters. In many cases (e.g. coral reefs and rocky ide from the biosphere. Thus, plants have been and shores), where local biomass exceeds diurnal recycling (until humans started burning coal and oil and using capabilities, incoming water quality is crucial to ecosys- rivers to dump their wastes) remain the dominant force tem function, and when it is not possible to provide that controlling Earth’s water and atmospheric chemistry flow from an undamaged wild source ecosystem, a and particularly the needs of higher animals. Humans water quality management system is established. There assume that lack of raw materials to maximize produc- are three basic approaches to the management of water tion is a basic need that must be managed; thus, the pri- quality in aquatic models (i.e. to match the lack of high- mary requirement is rapid breakdown of all organics to quality incoming water). One approach is abiological, in basic mineral elements (carbon, nitrogen, phosphorus, which chemical methods such as ozonation and physical sulfur, silica, etc.). We disagree with this concept. methods such as physical filtration, protein skimming, Primary productivity in the wild is sometimes limited and ultraviolet radiation are used to offset the effects of a by the lack of “nutrients.” On the other hand, excess poor water quality. These methods are almost always nutrients usually result in unstable (bloom) conditions. used with the second, more generalized, approach of Farming and aquaculture almost invariably add nutri- bacteriological filtration, which is employed in various ents to drive productivity of a single organism. How- forms and has been used in virtually all aquarium sys- ever, the result is either unstable or semistable, requiring tems (and sewage systems) of the past 50 years. continuous careful management to avoid a variety of The bacteriological (or biological) filter is a device of “crash” scenarios. Biospheric, and ultimately ecosys- almost infinite variety used to maximize surfaces with tem, stability lies not in the rapid breakdown of organ- bacterial cultures (i.e. bacterial films) in close contact ics but rather in emphasis on their storage as either with flowing water of the system being managed. The plant biomass or geological materials. Stability in the purpose is threefold: (1) the trapping and breakdown biosphere, in most wild ecosystems, and in microcosms of organic particulates; (2) the degradation of the and mesocosms must lie in competition for scarce
  • 23. Microcosms and Mesocosms of Aquatic Ecosystems 7 resources including carbon and nutrients. In aquacul- of organisms in the commercial aquarium trade. The ture systems designed to produce food, these require- suffering of the animals is deplorable, and there exists ments are reduced locally to maximize growth, but the very real possibility that intensive collection will must be managed in a broader context, or they will deplete the environment and upset the balance of be passed onto wild ecosystems where degradation is natural communities. While large numbers of plants inevitable. It is probably best to recycle all human and animals may die in the wild during environmental organic wastes, but the next best approach would be to extremes, in general, human impacts are becoming pump them into sealed oil wells or deep mines (geolog- severe enough to shift the delicate survival balance ical storage). Had that been done for the last century, we negatively for many species and even for ecosystems. would be faced with neither global warming nor pol- For recreation and education purposes, we cannot luted rivers and coasts and could perhaps tap the accept subjecting organisms to stressful conditions resulting methane gas for energy. We have not taken beyond their normal environmental range. Even for that approach and, at this stage, we need to quickly research purposes, it is crucial that scientists be sensi- organize to emphasize the locking up of nutrients, tive to the health of the organisms involved and to the including carbon in plant (including algal) biomass. potential negative impacts of collecting. The third approach, which we describe in this vol- Open water culture can help in some situations, and ume, is to match an undegraded analog wild ecosys- are increasingly important in coral reef culture. How- tem as closely as possible with the microcosm or ever, through the use of ecosystem techniques, culture mesocosm of interest, in terms of physical and chemi- systems can produce most of the organisms (and live cal characteristics, cross-boundary exchanges, and as rock) used in the aquarium trade, and distributors, deal- many organisms, with their food webs, as possible. In ers, and hobbyists can maintain functioning systems some cases, especially for smaller systems, human and reduce losses dramatically. Indeed, experimental manipulation must account for the cross-boundary ecosystems and their organisms can be maintained sep- exchanges of organisms that have a significantly larger arately from wild ecosystems and endangered organ- territory in the wild than is available in the model. isms can be nurtured for return to the wild. Zoological Water quality control of high biomass of benthic sys- parks have made a strong entrance into this arena in tems usually involves open water exchange with recent decades, and now public aquaria, with sufficient phytoplankton-dominated communities in the wild. We financial and scientific expertise, can do likewise. Many simulate this process with algal photosynthetic sys- freshwater fish have been bred in aquaria, and in the tems, allowing production and export or recycling of past decade increasing numbers of marine species of biomass (and nutrients) as appropriate. Foam fraction- fish have been also. Because of our success in breeding ation, filtration, and engineered bacterial systems are hundreds of species of marine invertebrates and plants not generally employed because they remove plankton in our ecosystem tanks, the prognosis for greatly reduc- and swimming or floating larvae on the one hand and ing wild collecting is encouraging, and we describe sys- unbalance water chemistry on the other. tems for accomplishing this objective. We also describe In Chapter 25, we describe several large-scale systems culture systems that can be used for identifying organ- for the closed or semi-closed aquaculture of food fish. isms that have potential for the production of pharma- These systems use the same Algal Turf Scrubber (ATS™) ceutical drugs and for initial harvest culture until the systems described in this book for controlling water synthetic equivalents can be produced. quality in microcosms and mesocosms. Technically these As we have pointed out, there is already a large aquaculture operations are quite successful, and indeed applied world that uses microcosms as tools for testing one system is still operating as a commercial endeavor the fates of pollutants in wild ecosystems and hopefully after 10 years. However, until truly sustainable wild fish- developing standards for lessening pollutant loads as a eries, without habitat degradation, can become the rule, result. These testing procedures use either highly simpli- and a cost is levied on nutrient release from aquaculture, fied ecosystems or a few species without a real ecology. it will be difficult for these sustainable methods to be However, the results derived would be more applicable truly cost competitive. to the real world if the models used were the more com- The hobby aquarium industry, in its public educa- plex systems that we describe in this book. Of equal tion effects, can have an incalculable positive effect on interest, it has long been known that up to a certain level, the need for public understanding of biology and ecol- ecosystems have a considerable capability for accepting ogy. Since it is “hands on” per unit effort it is probably polluting elements and degrading or detoxifying and far more effective than text book/lecture education. storing them. We have much to learn from ecosystems in However, as practiced today, there are enormous losses this respect, as we detail in Part V. However, what is most
  • 24. 8 1. Introduction relevant in the real world, where efficiency counts, is that (microalgae). The ATS™ was derived from mesocosm knowledge gained, through models, of ecosystem R&D, and is itself a biodiverse ecosystem that provides processes can lead to more economic means of handling multi-solutions. It demonstrates the great potential of large quantities of pollutants and keeping those pollu- microcosm and mesocosm research, but in the solution tants from degrading wild ecosystems. of grave problems of mankind. SUMMARY RESTORATION OF DAMAGED ECOLOGICAL SYSTEMS It is quite reasonable that we wish to understand in depth the complex ecosystem processes in which we We have used the term macrocosm for wild ecosys- are enmeshed. It may well be essential to our contin- tems that have come under the significant influence of ued existence as a species. To develop ecosystems in human activities and are in need of restoration to pre- microcosms, mesocosms, and aquaria, and to control vent loss of biodiversity and the degraded provision of their relationship to the rest of the world is simply the “ecological services” to human society. It may be that experimental method of science at the most complex most ecosystems on Earth are now macrocosms, but scale of biology. The ecosystem is the exquisite poten- there is certainly a broad gradient between those in tial of the universe, and we can capture it and look at it great need of repair and those minimally affected. logically for understanding or for its intrinsic beauty. There is no lack of understanding of the current, seri- To build and control ecosystem models and to use the ous nature of our loss of ecosystem function and sup- knowledge and techniques gained to restore damaged port. We cite two recent authors: Jared Diamond (2005) ecosystems is an essential endeavor. calling notice to the global level of ecosystem degrada- tion that can lead to social collapse, and Robert Livingston (2006) calling notice specifically to serious TAXONOMIC NOTES aquatic ecosystem degradation. There is considerable scientific consensus that human society, in its alteration As we have noted, the biological world is far more of the biosphere, is approaching a number of thresholds complex than the chemical world. While the core chemi- beyond which ecosystem supports will begin to fail and cal elements and compounds have a standard terminol- potentially cause social collapse. There are many ogy that has long existed for chemistry, the biological dimensions to the loss of ecosystem supports: for exam- world remains in flux. The Linnean system has been ple Diamond (2005) lists 12 key problems. As we dis- backed up by a formal, international system for the stan- cuss in Chapter 25, a number of these relate to a need to dardization and stabilization of nomenclature, but the restrict human population growth and human demand result is hardly stable. Some of these changes are for continued resources as well as the increasing num- reflected in advances in our understanding of organis- ber of invasive species caused by globalization (see also mic evolution, prodded on by a rapidly advancing Ruiz and Carlton, 2003). However, better than half of knowledge of what is called “molecular biology,” the the basic problems relate to water and atmospheric documentation of genetic coding. Unfortunately, some quality control and to fisheries. We describe in Chapter change also comes from nomenclatural wrestling. For 25 how in working with numerous microcosms and basic reference we provide a modern “tree of life” (Figure mesocosms, we have identified a practical methodol- 1.2) from Knoll (2003); the volumes of Parker (1982) can ogy for solving these problems using large-scale solar continue to fill in that framework down to family and energy capture through algal photosynthesis. These genus. In our descriptions of microcosms and meso- ATS™ systems have already been scaled up to a mod- cosms, as one part of the demonstration of “success” or ule size of up to 5 acres and 40 Mgpd by HydroMentia, veracity of modeling of an analog wild ecosystem, we Inc. of Ocala, Florida. HydroMentia offers nutrient, tox- provide species lists. Since these lists were accomplished, ics, and atmospheric carbon removal with water oxy- some genus and species names have changed. In this edi- genation and bioenergy supply as by-products at the tion, we have not “updated” these changes because it scale of large rivers (formal designs for ATS™ systems would have meant returning to the specialists that iden- up to 1500 acres, processing billions of gallons per day, tified the flora and fauna in the first place, or in some have been developed). There are numerous other cases finding new specialists, and this would have approaches to bioenergy, which are also carbon neutral, changed the basic function of the volume very little. In but they either add to nutrient problems (e.g. corn, soy, most situations, field guides will provide the older and switchgrass) or are monocultural in their solution names along with their newer versions.
  • 25. References 9 FIGURE 1.2 Family tree of eukaryotes and ancestral bacteria (there are other, more distantly related bacteria, such as the Archaea, that are minimally shown). All of the major lines of eukaryotes, including the five major groups, had already formed well back in the pre-Cambrian, probably before the major animal groups evolved. After Knoll (2003). Diamond, J. (2005) Collapse: How Societies Choose to Fail or Succeed. References Viking Penguin, New York. Adey, W. (1987) Marine microcosms. In: Restoration Ecology. Frank, L. and Huyghe, P. (1990) The Big Splash. Birch Lane Press, W. Jordan, M. Gilpin, and J. Aber (Eds). Cambridge University Secaucus, New York. Press, Cambridge. Fraústo da Silva, J. and Williams, R. W. (1993) The Biological Chemistry Adey, W. (1995) Controlled ecologies. In: Encyclopedia of Environmental of the Elements. Clarendon Press, Oxford. Biology. W. A. Nierenberg (Ed.). Academic Press, San Diego. Gedulin, B. and Arrhenius, G. (1994) Sources and geochemical evo- Adey, W. and Loveland, K. (1998) Dynamic Aquaria: Building Living lution of RNA precursor molecules: the role of phosphate. In: Ecosystems, 2nd edn. Academic Press, San Diego. Early Life on Earth. S. Bengston (Ed.). Columbia University Press, Brown, G., Hawkesworth, C., and Wilson, R. (1992) Understanding the New York. Earth. Cambridge University Press, Cambridge. Hanczyc, M. and Szostak, J. (2004) Replicating vesicles as models of Delbeek, C. and Sprung, J. (2005). The Reef Aquarium, Science, Art and primitive cell growth and division. Curr. Opin. Chem. Biol. 8: Technology, Vol. III. Ricordea Publishing, Coconut Grove, Florida. 660–664.
  • 26. 10 1. Introduction Hendal, J. (2006) Advanced Marine Aquarium Techniques. TFH research: scaling up in experimental ecosystem science. Glob. Publications, Neptune City. Change Biol. 10: 393–407. Kangas, P. and Adey, W. (1996) Mesocosms and ecological engineer- Parker, S. (1982) Synopsis and Classification of Living Organisms. Vols 1 ing. Ecol. Eng. 6(1–3): 1–224. and 2 McGraw-Hill, New York. Knoll, A. (2003) Biomineralization and evolutionary history. Rev. Petersen, J., Kemp, W. M., Bartleson, R., Boynton, W., Chung-chi Chen, Mineral. Geochem. 54: 329–356. Cornwell, J., Gardner, R., Hinkle, D., Houde, E., Malone, T. H., Livingston, R. (2006) Restoration of Aquatic Systems. Taylor and Mowitt, W., Murray, L., Sanford, L., Stevenson, J. C., Sundberg, K., Francis, Boca Raton, Florida. and Suttles, S. (2003) Multiscale experiments in coastal ecology: National Research Council (1990) The Search for Life’s Origins: Progress improvising realism and advancing theory. Bioscience 53: 1181–1197. and Future Directions in Planetary Biology and Chemical Evolution. Raymond, J. (2005) The evolution of biological carbon and nitrogen National Academy Press, Washington, DC. cycling – a genemic perspective. Rev. Mineral. Geochem. 59: 211–231. Orgel, L. (2004) Prebiotic chemistry and the origin of the RNA world. Redfern, R. (2001) Origins: The Evolution of Continents, Oceans and Life. Crit. Rev. Biochem. Mol. 39: 99–123. The University of Oklahoma Press, Norman. Oró, J. (1994) Early chemical stages in the origin of life. In: Early Life on Ruiz, G. and Carlton, J. (2003) Invasive Species. Island Press, Earth. S. Bengtson (Ed.). Columbia University Press, New York. Washington, DC. Osmond, B., Ananyev, G., Berry, J., Langdon, C., Kolber, Z., Gunghai, L., van Dover, C.-L. (2000) The Ecology of Deep-Sea Hydrothermal Vents. Monson, R., Nichol, C., Rascher, U., Schurr, U., Smith S., and Princeton University Press, Princeton, New Jersey. Yakir, D. (2004) Changing the way we think about global change
  • 27. P A R T I PHYSICAL ENVIRONMENT
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  • 29. C H A P T E R 2 The Envelope Physical Parameters and Energy State The shape and size of an aquatic ecosystem relative 1–2 meters. The construction of molded fiberglass to its controlling physical and energy parameters can tanks or poured concrete or concrete block tanks sealed determine the basic character of the system. This is with a wide variety of commercially available sealants especially true of the thickness of the water mass and its has considerable advantages for systems larger than relationship to the bottom. A 100-meter-deep lake of about a thousand liters. This is also true when the meso- several square kilometer surface dimensions, all other cosm modeler departs from the purely aquatic systems factors aside, would be dominated by true plankters, and enters the realm of wetlands, marshes, and swamps, normally living most of their lives suspended in mid where the key species are either large individuals or the and surface waters, with little benthic (or bottom) influ- very nature of the community (e.g. a marshland) requires ence, whereas the shallow stream or narrow lagoon of a a large area compared to water and sediment volume. few meters in depth is very much benthic dominated. Each of the aquaria, microcosms, and mesocosms Light enters only through the air–water interface of a described in Chapters 20–23 illustrates the process of water ecosystem, and the shape of the containing body designing envelope (tank) shapes to fit the functional of water relative to depth, as well as water turbidity, requirements of the enclosed ecosystems. Whether they determines the basic photosynthetic vs heterotrophic are fully successful or not is limited only by the ingenu- (nonphotosynthetic feeding) character of the ecosystem. ity and financial resources of the human builders The direction of current flow and wave action through (Figure 2.1). an aquatic system relative to the position and orienta- Ideally, the microcosm or mesocosm envelope would tion of the communities present is critical to simulate in be like that of the boundary of the mathematical modeler, any ecosystem model, or else the character of the com- a theoretical boundary controlling access but not having munities and the abundance of its various species will any inherent characteristics. Of course, that is not possi- change in the microcosm or mesocosm. ble, for two primary reasons. First, walls, whatever their The all-glass aquarium, ranging from about 40 liters nature (unless rather esoteric measures are used to pre- (10 gallons) to 1000 liters (250 gallons) is a standard vent organisms and organic molecules from using their and highly reliable piece of equipment in the aquarium surfaces) are effectively hard bottoms. In an aquatic industry (Color Plates 1 and 2). Likewise, because of its model of an ecosystem dominated by hard bottom com- low cost and availability, every effort is generally made munities that may not make a difference (remembering to use all-glass aquaria for microcosm work. Indeed, by however, that especially in marine and estuarine systems drilling holes to attach pipes and linking all glass tanks that some species have larvae that must escape into the in complex arrays, many aspects of wild ecosystems plankton for the early part of their lives). The important can be modeled with reasonable accuracy. of the walls is less, as is often the case in an all-glass sys- We talk about the issue of scaling later, but anyone tem, if the walls are frequently scraped. However, for wishing to simulate the planktonic aspects of an ecosys- a small model of a planktonic system, the presence of tem, not overwhelmed by the benthic communities, uncleaned walls may prevent the system from being is likely to be seeking tanks with radii greater than plankton dominated. Second, walls of living models 13
  • 30. 14 2. The Envelope FIGURE 2.1 Diagrammatic illustrations of two very different types of ecosystem models (a coral reef and a mangrove/swamp sandy shore) showing spatial configurations, water movement, controls, and energy supply as well as the basic materials used in construction. Both of these models are streated in considerably more detail in Chapters 20 and 22. consist of real materials. To some degree, they interact characterized environmentally by their long-term stabil- with the water of the ecosystem they contain. For most ity and a lack of leachable compounds. purposes, glass and many plastics are ideal in this respect. There are few aquatic systems in which the slow Glass leaching of silica into the water column would be a prob- lem, and barring the significant presence of ultraviolet Glass tanks constructed commercially offer many radiation, most plastics that one might use for walls advantages to the hobbyist and even to the scientist (polyester, polyvinyl chloride (PVC), polyethylene) are and aquarium distributor. Technically, a glass is any
  • 31. The Envelope 15 molten rock that has cooled so rapidly that crystals We have used heat-strengthened, laminated glass suc- have not had a chance to form. In the context of this cessfully. With three 0.5-inch panels and two 0.030-inch book, glass is silica (SiO2) or uncrystallized, amor- plastic laminate layers, little visual distortion occurs phous quartz. In practice, commercial glass is an alloy and cost is minimal. typically also containing oxides of sodium (Na2O) and calcium (CaO). This soda and lime glass is the oldest, Acrylic cheapest, and easiest to fabricate. Many other glasses now exist. For example, borosilicate (borax, sodium The primary competitor with glass for small aquar- borate, plus silica) is the base of chemical and kitchen- ium construction or for ports in larger tanks is acrylic ware glasses such as Pyrex and Kimax. Lead is used in sheet (Plexiglas, Lucite, etc.). Acrylics are made of syn- “crystal” glasses. Some commercial “glasses” for spe- thetic hydrocarbons and can be colorless and transpar- cialized uses do not even contain silica (see e.g. Bansal ent (see e.g. Levy and DuBois, 1984). Like glass, their and Doremus, 1986). strengths in actual practice are significantly lower than Soda–lime glass (simply glass in the rest of this dis- the theoretical values. The strength of acrylic is gener- cussion) is quite transparent and very hard. Very few ally taken to be somewhat less than that of glass. Where minerals, such as diamond and carborundum, are weight is a factor, acrylic is about 40% the density of harder or more resistant to weathering and most chem- glass, a feature readily apparent to anyone who has car- icals. Theoretically glass is stronger than steel even in ried glass and plastic aquaria. Using the same care as tensile strength. Also, most glass components (silica, for silicone cement attachment of glass, acrylic-soluble calcium, and sodium) in microquantities not only are cements can be used to fuse acrylic sheets together. nontoxic, but they are also needed micronutrients for While some brands of acrylics are harder than others, almost any ecosystem. Most of these points are well all acrylics are more or less subject to intensive scratch- known and along with the viewing characteristics are ing by organisms with shells or teeth. Also algal, bacter- the primary reasons for the traditional aquarium use of ial, and protozoan growths (aufwuchs) are inevitable glass. It is the theoretical qualification in the strength (and desirable) on available surfaces of all ecosystems. characteristics of glass that is puzzling and sometimes If visibility is to be maintained, the glass or acrylic sur- leads to the choice of other materials. Glass is brittle. faces must be regularly cleaned either by organisms or It shows little plastic deformation or give before frac- by hand. In time, this process tends to reduce the trans- ture. A very carefully drawn rod of glass can have parency of the hardest acrylic. Care also has to be taken extraordinarily high strength and, theoretically, could in construction of complex structures to allow for the replace steel in rigid steel cable. However, it flaws eas- considerable flexibility of acrylic sheets. In public view- ily and cracks can start at flaws, greatly reducing ing areas, where absolute safety is demanded, and strength. Also, even though glass has great weathering where unplanned impact from a hard object, such as a resistance, it does in fact react slowly with water (some tool or a bottle, is possible, acrylics have much to offer. SiO2 groups being replaced by SiOH). This effect is par- Nevertheless, in the past we have chosen safety glass ticularly seen at flaw points on the glass surface from (multilayered glass with thin acrylic sheets molded which crack development is accelerated. between) in these situations. This laminated glass prod- Glass is relatively cheap. Silicon is one of the more uct provides the advantages of both materials in aquaria abundant elements of the Earth’s crust. As long as and microcosm construction. weight is not a significant factor (and this is likely true in aquarium situations because of the proportionally Fiberglass-Reinforced Plastics large weight of water), 10 to 1 safety factors placed on normal working strengths will easily solve the indeter- In the mid-size enclosure range of 300–10 000 gallons, minant strength characteristics. There is a considerable composite plastic tanks are preferable to all-glass or literature that relates glass thickness to dimension char- acrylic units. The base material for these tanks is poly- acteristics currently in use in the commercial aquarium ester resin, usually with glass cloth or mat reinforcing. field (see, e.g. Adey and Loveland, 1991). This applies to Polyester resins have good strength, toughness, and all glass tanks or glass in steel or concrete structures. chemical resistance characteristics. Most importantly, Generally, in all glass tanks it is the sealant that begins polyesters adhere well to other materials, particularly to fail with minor leakage long before there are glass glass and wood. The composite material of polyester problems. In very sensitive situations, safety glass or resin and glass cloth or matting has a flexural strength of tempered glass can be used as an extra safety factor, nearly 10 times the practical strength of glass and can although safety glass eventually delaminates and tem- exceed that of magnesium alloys. Equally important, the pered or “heat-strengthened” glass can fail explosively. polyesters are catalyzed resins, and setting time as a
  • 32. 16 2. The Envelope function of temperature and catalyst quantity (which is controlling elements of biological function. DDT is a on the order of drops per gallon) is relatively uncritical. classic case, and Silent Spring (Carson, 1962) presents As in all plastics, avoiding contamination, especially a grim reality that could have been (and may yet by oils and greases, in mixing and application is critical. be – PCBs followed and now a new generation of syn- Although almost any technique will “work,” strength thetic herbicides, pesticides, and hormones are escap- and longevity will be severely compromised by any, but ing into our streams and rivers). DDT was, hopefully, a technique of scrupulous cleanliness and reasonable caught in time (it is still found in whales and birds adherence to time, temperature, and catalyst quantity in the remote reaches of oceans). Also, many pesticides tables. Fiberglass unfortunately is not transparent, and banned or highly controlled in the United States are therefore glass or acrylic panels must be used where used in massive quantities elsewhere (including DDT). side viewing is required. Chlorine used for water “purification” in swimming pools, sewer outflows, and drinking water supplies deserves close attention. We may yet destroy ourselves Reinforced Concrete and our higher animal and plant associates through Where weight and space are not factors, and tank size chemistry intended for “better living” if we do not rap- exceeds 10 000 gallons, reinforced cement block or con- idly learn more care in this regard. These matters we crete is the material of choice. Particularly in larger discuss further in Chapter 4. dimensions, these structures should be designed by The aquarist operates mini ecosystems that, because experienced engineers. However, it is essential to convey of their small size, are particularly susceptible to contam- the special problems of water, salt water, and ecosystems ination by external and internal pollutants. In Chapter 4, to the responsible engineers. An engineer will easily we discuss the potential problems that can derive from appreciate the corrosion problems, but the sensitivity of the water source. Here, we briefly discuss potential mate- ecosystems to contamination by metals must also be con- rial problems that apply equally to the envelope, plumb- veyed. Also, concrete is porous and blocks can gradually ing, heating and cooling, tide creation, and light supply disintegrate when constantly submerged. The inside sur- elements as well as to the substrate. These involve mostly faces of these construction materials must be coated with structural elements and thus primarily metal contamina- an impervious layer. Because this is the same problem, in tion, though many other possibilities exist. reverse, as the leaking of building foundations in wet Glass, acrylics, epoxies, polyesters, polypropylenes, areas, engineers and contractors will understand the polyethylenes, nylons, Teflon, and silicones, among sealing problems. However, the final internal coatings others, are structural materials commonly used in aquar- should be epoxy or butyl rubber to prevent any water ium construction. When properly cured these materials contamination. The function of one of the largest meso- are generally inert, nonbiodegradable, and nontoxic. In cosms attempted to date was severely compromised by some cases fungicides might be added to the materials in unsealed concrete (Marino and Odum, 1999). use, and these should be guarded against. Many metals find their way into construction processes and must be avoided. Except for perhaps lead, mercury, cadmium, Toxic Elements and Compounds chromium, nickel, and silver, metals can have micronutri- Many chemical elements and compounds are toxic ent uses in organic processes (e.g. iron, zinc, and copper) to life. Some of these are only mildly poisonous and are and are not a problem in small quantities. Nevertheless, often required by organisms as elements in small quan- in abundance even these can cause severe problems. tities and only become toxic in excess. Others are Copper is one of the most insidious of metal problems always toxic and only concentration determines effect. for the aquarist. In ionic form it is placed in municipal Many organisms have evolved the ability to produce water systems to kill algae; it is also abundant around poisonous organic compounds, primarily as a means human and aquarium situations as copper wiring and of defense or to facilitate food capture. piping. Stainless steel, in addition to iron (which is prob- Humans have been highly successful at learning the ably the most acceptable of metals, often a micronutri- chemical possibilities of the Earth, both inorganic and ent), has alloy metals such as chromium and nickel. organic. Some of the toxic productions of humans are While possibly acceptable in fresh-water use, stainless solely for industrial purposes, but in many cases have steels should be avoided around salt-water ecosystems. been allowed to leak into the wild environment. Other Titanium may be acceptable, especially in cooling sys- elements and compounds have been developed specifi- tems, though the final environmental word has not been cally to kill undesirable organisms. Unfortunately, many received on this metal. chemicals that are directed toward specific pest species Zinc as “galvanizing” is often used to coat iron and work their way through ecosystems and become major steel to reduce corrosion. It is particularly toxic when
  • 33. Temperature 17 dissolved, and in abundance, and should be strictly gradual uptake and storage of carbon dioxide (CO2) as avoided. Galvanized and stainless steel will be recom- well as the release of oxygen (O2) by plants, over geo- mended by engineers to solve structural problems where logic time, has created an atmosphere and biosphere corrosion is a potential difficulty; however, they should that greatly limits temperature extremes on planet not be allowed into aquatic life processes in abundance. Earth. The vegetated surface itself limits temperature Many plants take up metals and incorporate them variation because of its large water content and indi- into their structure. Some geological prospecting can rectly through the control of water movement. In part, be carried out by looking at the plants that either con- this phenomenon is the basis of the Gaia concept: the centrate the element of interest or show a characteristic presence of life on Earth has progressively made a rel- response. If algal turf scrubber (ATS™) control systems atively inhospitable environment ever more conducive are used, the algal turfs, also take up many metals to even more sensitive and complex life. (including heavy metals) preferentially, and with the ultraviolet component of especially metal halide Physiological Factors lamps, many toxic organics are also broken down. We discuss these issues in Chapter 25. Under water, the temperature extremes are much smaller than they are on land. However, some very important temperature-controlled factors are operating Plumbing and Electrical in addition to direct temperature effects. For example, PVC piping has become a standard part of western oxygen solubility, and thus the amount of oxygen avail- human society, and once manufactured appears to able to the gills of an aquatic animal, is quite tempera- offer no toxicity concerns either to aquatic systems or ture dependent (low at tropical temperatures and nearly humans. PVC pipe does have surfaces that are ideal for twice as high near 0°C). Tropical and temperate zones the attachment of many organisms. If this is a problem have existed for billions of years on the Earth. Arctic and either ecologically or from a maintenance concern, subarctic zones, on the other hand, have come and gone. then design and construction must allow ports or sim- Only a few million years have been available for the evo- ilar devices for regular cleaning. lution of new organisms, and cold-water mechanisms Likewise, electrical systems should be designed as and ecology, in the most recent set of glacial cycles they would be for wet areas in general, using equip- (Pleistocene, Quaternary). This basic limiting factor, along ment for exterior and all-weather use as well as ground with the strong seasonal cyclicity, is the main reason fault interrupters (GFIs) or breakers. GFIs are relatively why colder regions have fewer species and thus less expensive and prone to random failure and short life. complicated ecologies than the tropics. However, they are necessary to preserve human life. The most important factor limiting the majority of Thus, the consequences of their unreliability must be organisms to relatively narrow temperature or biogeo- avoided by design; for example, critical pumping, graphic zones is a basic chemical limitation. Rates of lighting, or heating functions must consist of dual units chemical reactions, including those characteristics of on separate breakers. organic processes, are a function of temperature, and the thousands of different reactions that occur in any organism are mutually tuned to a limited temperature TEMPERATURE range. Chemists and physiologists say that Q10 ranges from 2 to 3, meaning that any given chemical reaction While the temperature of stars ranges from about doubles or triples its rate for every 10°C rise of temper- 3000°C to 20 000°C, the mean temperature of the uni- ature. Since many mutually dependent chemical reac- verse is about –235°C. The surface of most of the plan- tions in an organism are not likely to have the same Q10 ets of the solar system generally ranges from below values, relatively small temperature changes can quickly –100°C to 100°C, beyond the range of most life as we unbalance an organism’s critical chemistry. Thus, organ- know it. The Earth is in a narrow range of distance isms are at a constant risk of poor health and death when from the sun that allows liquid water to be present, and the temperature exceeds the ranges, too high or too low, the size of the Earth ensures that it can be present in the to which they have become genetically and environmen- atmosphere. tally adapted. Abundant water is a major element in limiting the There are two generally applicable subrules that temperature range on Earth from about –50°C (–68°F) apply to the physiological temperature extreme capa- to about 50°C (122°F). However, to a large extent this bilities of organisms. First, most organisms can accli- extremely small temperature range also results from matize considerably given the time to do so. This rule the activities of organisms over billions of years. The applies to both individuals (within a time frame of
  • 34. 18 2. The Envelope FIGURE 2.2 Activity and mortality of marine/aquatic organisms is much more sharply tied to higher rather than lower temperatures. (A) Intertidal barnacle activity (upper inter- tidal, solid line; lower intertidal, dotted line). (B) Mortality rates of a number of marine crus- taceans as they approach their upper temperature limits. After Levinton (1982). Reprinted by permission of Prentice Hall, Englewood Cliffs, New Jersey. days to months) and populations (many years). Thus, a in Chapter 21, Strongylocentrotus drobachiensis, the green subarctic clam that might quickly expire given a tem- sea urchin, an algal grazer, is a keystone species in the perature of 15°C in March would find that same tem- North Atlantic Subarctic. At higher temperature levels, perature quite optimal in August. A second rule of but still well below its lethal temperature, S. drobachien- thumb is that individual organisms, as well as whole sis is subject to a protozoan disease. Because of this, at populations, are typically nearer their lethal point at temperatures only a few degrees above optimum, pop- the high-temperature end of the scale of survivorship ulations are subject to alternate build-ups and crushes, than at the colder end (Figure 2.2). Temperatures sev- as peak summer temperatures vary from year to year. eral degrees above the normal high temperature range An even bigger issue concerns the very future of coral of a population would likely be more dangerous than reefs. Temperatures just a few degrees higher than temperatures several degrees below the normal low normal in tropical waters cause corals to lose their temperature. zooxanthellae, with many dying. With global warming This relationship can be both complex and far- coral reefs will likely radically change their community reaching. For example, as we will discuss in more depth structure and combined with additional atmospheric
  • 35. Temperature 19 would show something similar for the use of a gardener, though not usually with the natural water supply component. Although perhaps more muted (as is temperature change), the same kinds and ranges of life zones or biomes occur under water. These biomes are partly determined by temperature, and substrate becomes more crucial and rainfall only indirectly of interest. In general, fresh-water streams follow a temperature pattern similar to that of the terrestrial life zones. How- ever, small spring-fed, especially forested area streams are more controlled by ground-water temperature and therefore have a small temperature range (Figure 2.5). Passing downstream, as branches meet and the flow grows, streams warm or cool according to air tempera- ture and range becomes quite large. Finally in larger streams and rivers, temperature fluctuations tend to reduce again as the greater volume is more subject to long-term factors. Rivers can become complex biomic entities as they flow for hundreds or thousands of miles changing radically in temperature characteristics, and therefore in the organisms that make up their biological FIGURE 2.3 Gonad development in the starfish Pisaster ochraceus communities. from the intertidal of northern California. Note that while some sea- sonal reproductive cycles are tied to day length, this animal reaches its peak reproduction shortly after average temperatures reach their min- imum for the year [1955 (•); 1956 ( )]. After Levinton (1982). Reprinted Temperature Characteristics of Lakes by permission of Prentice Hall, Englewood Cliffs, New Jersey. If they are large enough, lakes can have a consider- able ameliorating effect on the local terrestrial climate. In temperate and colder regions, the lake climate itself CO2 (and lower ocean pH) may stop growing alto- is always considerably more moderate than the sur- gether (see Chapters 10 and 20). rounding terrestrial climate. Because the maximum Beyond concern for the extreme ranges and the density of water (including the ice phase) lies at about short-term survivorship of organisms and their popu- 4°C, cold-climate lakes in the winter have relatively lations, there is also a need to consider normal life cycles, warm deep water (the hypolimnion) while the surface whether temperature determines breeding (as it often is frozen and the upper few meters lie near 0°C (Figure does) (Figure 2.3), and whether feeding patterns (and 2.6). During the summer, lake surface waters warm the availability of feed) and migration are also deter- considerably and, barring strong winds or other fac- mined by temperature. tors, become stable and stratified. The surface layers (or epilimnion) become nearly as warm as the average monthly terrestrial air temperatures, while the bottom Temperature Characteristics of water temperature typically ranges from 6°C to 15°C, Biomes and Rivers in temperate climates. The temperature change from Most people are aware that the major biomes (ter- shallow to mid depths, called the thermocline, is often restrial life zones) of characteristic terrestrial plants sharp. Because the hypolimnion is often relatively iso- and animals change radically with temperature. From lated, in lakes excessively rich in organic material, bot- the polar north southward, the polar south northward, tom waters can become anaerobic in summer if they lie and downward from the tops of high cold mountains, beyond the maximum penetration of light. In the fall, the tundra, taiga (conifer forests), and hardwood forests as surface temperatures chill and the water becomes form circumpolar or circummountain bands. Around heavier, these lakes “overturn,” mixing the water and the warm equatorial and subequatorial bands of the taking on the same temperature from top to bottom. Earth, water supply rather than temperature is the pri- Tropical lakes, on the other hand, while showing the mary factor determining biome type. These bands, same basic tendency to stratify, may have a surface to generalized for all continents, are shown in Figure 2.4. bottom temperature difference of only a few degrees A standard plant hardiness map for North America centigrade. Similarly, though much colder, Arctic lakes
  • 36. 20 2. The Envelope FIGURE 2.4 Idealized terrestrial biomes or large areas of similar climate, mostly determined by temperature and to a lesser extent rainfall. I. Tropical zones: (1) equatorial rain forest; (2) tropical rain forest with trade wind, orographic rain; (3) tropical-deciduous forest (and moist savannas); (4) trop- ical thornbush (and dry savannas). II. Extratropical zones of the Northern Hemisphere: (5) hot desert; (6) cold inland desert; (7) semidesert or steppe; (8) sclerophyllous woodland with winter rain; (9) steppe with cold winters; (10) warm-temperate forest; (11) deciduous forest; (12) oceanic forest; (13) boreal coniferous forest; (14) subarctic birch forest; (15) tundra; (16) cold desert. III. Extratropical zones of the Southern Hemisphere: (17) coastal desert; (18) fog desert; (19) sclerophyllous woodland with winter rain; (20) semidesert; (21) subtropical grassland; (22) warm-temperate rain forest; (23) cold-temperate forest; (24) semidesert with cushion plants, or steppes; (25) subantarctic tussock grassland; (26) inland ice of the Antarctic. After Walter (1979). can have the same temperature from top to bottom in temperature range throughout the world’s oceans, out- summer. side of very restricted salt ponds or tidal pools, is about 32°C (58°F), as opposed to about 100°C (180°F) in the land environments. The yearly ranges in any one locality, Marine Biogeography even coastal localities, are much more restricted, rang- Even more than in lakes, the marine environment ing from as much as 20°C (36°F) in some temperate or varies relatively little in temperature, and marine subarctic coastal areas to as little as 3–5°C (5.5–9°F) in organisms have evolved to be able to withstand only some tropical, boreal, and arctic coastal zones. In gen- small changes in ambient temperature. The maximum eral, the daily and weekly changes at a given depth in
  • 37. Temperature 21 FIGURE 2.5 Maximum daily temperature range as a function of stream order (0 spring, then numbered as streams join). The smallest, spring-fed streams and larger rivers are least affected by local climate. Mid-level streams can change radically on a day-to-day basis and fol- low atmospheric climate closely. From Vannote and Sweeney (1980). coastal and ocean waters are measured in no more than Coastal marine ecosystems have characteristic tenths of a degree centigrade (Thurman and Webber, yearly temperature ranges, usually following a more 1984). or less sinusoidal pattern with a peak and a minimum Most organisms in the biosphere are “cold” or following solar peak and minimum by 1–2 months. “cold-blooded,” poikilothermic in scientific terminol- Marine temperature patterns are related to ocean cur- ogy. Unlike birds and mammals (homeotherms), which, rents, the orientation of coastlines, and the relative with adequate energy or food supply, can handle a wide “continentality” of the coast, as well as to latitude. range of temperatures, invertebrates, most fish, amphib- Figure 2.7 shows a contour plot of miles of coastland ians, reptiles, and plants can do little or nothing to con- for the world’s oceans. Clearly, there are extensive trol their temperature. They function in accordance with lengths of coastline for some summer/winter tempera- the temperature provided to them by the ecosystem ture signatures (what we will loosely call shore climate) or ecosystems to which they are adapted. Some of and very little or none at other signatures. these species function over relatively wide temperature The last 2–5 million years has been characterized by ranges (eurytherms); others are much more limited alternating glacial and interglacial stages. Fortunately, (stenotherms). Any given species is subject to a wide the ocean surface temperatures, summer and winter for range of environmental variables, and the regional tem- the last glacial stage at 18 thousand years, have been peratures over which a species ranges are not all likely determined by studying the fossil planktonic commu- to be optimum for growth and reproduction. Those opti- nity that has rained into the extensively core-drilled mum temperatures are narrow and generally changing ocean sediments (Climap Project Members, 1976). Using with time, but lie within the regional range. a similar plot for 18 thousand years overlain on the plot Embedded in the terrestrial biomes shown in of Figure 2.7, it has been possible to estimate what shore Figure 2.4, which depend on temperature and rainfall climate signatures were constant over the last several (more generally climate), are biogeographic regions. million years (Adey and Steneck, 2001). Shown as a con- For example, the narrow equatorial zones are charac- tour plot in Figure 2.8, these are the shore climates to terized by tropical rainforest which has similar physi- which most current existing rocky shore species have cal, chemical, and ecological characteristics around the evolved. These are the biogeographic regions of the world. However, South American, South African and rocky shore biome and they are shown geographically South Asian, and the Australasian rainforests are occu- in Figure 2.9. They correspond closely with the classic pied by different species; they have developed in tune biogeographic regions determined from the distribution to the same kind of environment, but the genera and of marine fish and invertebrates (Briggs, 1974). In species that have resulted from evolution over the last Chapter 21, we discuss in more depth what this means 100 My, largely in isolation, are quite different. to the modeler of ecosystems. Marine ecosystems have the basic equivalent of the biomes; e.g. oceanic plankton/nekton systems, deep- Model Ecosystems and Temperature water benthic or bottom systems, and a wide variety of coastal muddy, sandy, rocky, and coral reef shores, all Matching the temperature pattern of any given under a wide variety of temperature conditions. Here, ecosystem model with that of its wild analog is not a we will concentrate on the shore systems, the rock difficult technical problem given the enormous diver- shores, and coral reefs most likely to be modeled. sity and sophistication of the equipment available. To
  • 38. 22 2. The Envelope FIGURE 2.6 Yearly temperature (°C) ranges surface to deep water in arctic to tropical lakes. (A) Arctic; (B) tropical; and (C) temperate, continental. After Hutchinson (1957). Reprinted by permission of John Wiley & Sons, Inc. achieve a high precision of measurement, recording in the long term, to be the controlling cost element. Since and controlling can be a significant cost factor. However, the situations are likely to vary widely, for each of the it is the resulting requirement for heating and especially myriad systems to be considered, we discuss heating and cooling, depending on the circumstances, that is likely, cooling for each of the examples given in Chapters 20–23.
  • 39. Water Motion 23 FIGURE 2.7 Distribution of temperature characteristics of rocky ocean shore in the world’s oceans. Each contour repre- sents one nautical mile square (1 minute of latitude; a nautical mile 6080 feet or 1870 meters). Note that overlapping coast patterns (e.g. Indo-Pacific and tropical East Pacific; New Zealand and Australia) are separated by the amounts shown to reduce confusing overlap. This diagram shows that large areas of coastline occur under certain temperature regimes. For example, hundreds of nautical miles of coast (in the Mediterranean) have a temperature regime of 24–26°C in summer and 10–16°C in winter; on the other hand there is virtually no rocky shore that is 20–24°C in summer and 6–10°C in winter. From Adey and Steneck (2001). This will give the modeler a perspective on the heating WATER MOTION and cooling problems likely to be encountered in a spe- cific case (Table 2.1). Natural waters, to varying degrees, are very much Temperature sensing and control units can provide chemical soups. The possibilities for chemical interac- significant contaminating problems; for example, cop- tions on a large scale are greater in water than in any other per heating or cooling coils are rarely acceptable. environment on the Earth. They are probably greater than Beyond contamination issues, for the simplest situa- anywhere else in the universe, except where water might tions, we suggest the control heating/cooling equip- be present. On the other hand, simple diffusion of an ment available at larger, more sophisticated aquarium element or an ion through water can be very slow. As we outlets or the options suggested by Spotte (1995). For discuss in Chapter 4, even though water allows most ele- more sophisticated systems with greater precision of ments and many compounds and gases into its loose control, especially when daily and seasonal ranges are chemical structure, often as weakly charged ions, the rate to be matched, the equipment offered by most of the of mixing and interacting can be limited in the short term larger scientific and laboratory supply or medical com- by the rate of diffusion. Indeed, the very structural factors panies provides a full range of options. Glass, plastic, that allow water to be the ultimate solvent, and thus the or ceramic surfaces in contact with water are almost chemical soup, also provide significant limitations to dif- always preferred to metal surfaces or contacts. fusion and therefore to the rates of reactions.
  • 40. 24 2. The Envelope FIGURE 2.8 Distribution of average temperature characteristics of rocky ocean shores in the world’s oceans for the past 3 million years (Pleistocene). This diagram is derived by obtaining the glacial coastal temperature range (after Climap Project Members, 1976) and multiplying (for each degree square) times existing coastal temperature range (Figure 2.7). Basically it shows expected species concentrations for rocky coasts. From Adey and Steneck (2001). Organisms are rarely static? (though resting It is now recognized that wave action and the orbital overwintering, overdrying stages, and seeds can be water motion it creates in the upper layers of oceans amazingly long lasting). The basic unstable nature of and lakes can increase phytoplankton photosynthesis individual life requires a constant flow of energy and (Marra, 2002). materials to keep the biological and ecological processes Figure 2.10 shows the contrast between the muddy operating. Whether it is the stirring of water in the bottom infaunal biomass, with depth, in fresh and home or laboratory, the wind blowing across a lake, marine waters. Nixon (1988) relates the approximate waves crashing on a rocky shore, or tides coursing in one-half order of magnitude difference between marine and out of a bay, all significantly contribute to ecologi- and fresh waters to the driving effects of tide and wind cal and ecosystem processes. These physical energy (waves and current). Note that the one lake that inputs force the mixing required to varying degrees by approaches marine situations in benthic biomass is the living organisms to carry out an active life. Scientists large Lake Michigan. have been examining the direct effects of waves and All forms of mixing accelerate chemical and there- currents on physical variables such as oxygen and tem- fore biological processes up to a certain saturation perature and directly on individual species for a long point beyond which other factors (light intensity, tem- time. These forms of physical energy have a major perature, chemical concentration, etc.) begin to be lim- impact on primary ecosystem processes such as photo- iting. Thus, waves, currents, and tides should not be synthesis and respiration (Leigh et al., 1987; Nixon, omitted from the ecosystem model any more than from 1988; Adey and Hackney, 1989; Carpenter et al., 1991). the wild community (Color Plates 9, 41, and 46). They
  • 41. Water Motion 25 FIGURE 2.9 Major biogeographic provinces of rocky shore in the world’s oceans. These are the coastal areas that one would expect to have strongly distinctive flora and fauna; the unhatched areas between the provinces are transitional. From Adey and Steneck (2001). TABLE 2.1 Heating and Cooling of Selected Model Ecosystems Described in Chapters 20–22 Heating Cooling System (Normal temperature Type Heat Type Heat range) exchanger exchanger Coral reefs 3000-gallon reef, Smithsonian 2000 W, titanium coated, None Two titanium immersion None (25–28°C) immersion heater (Process water chillers, 1 hp each Technology, Inc.) (Aqua-Logic) 130-gallon reef, home system Two 100-W glass aquarium None Air-conditioned room held at (25–28°C) heaters for winter minimum 23°C; no supplemental cooling 750 000-gallon reef Great Barrier Open air at Townsville, QLD, Water chiller Plastic tubing Reef Marine Park Australia; supplemental heating coils in tidal (25–29°C) from scrubber lights and immersion reservoir heater if necessary Estuaries Chesapeake estuary Temperature-controlled room; no Air-conditioned room and (20–28°C, summer) supplemental heating input sea-water cooled (4–6°C, winter) with an immersion chiller Florida Everglades estuary Propane-heated greenhouse None One titanium water chiller, Plastic tubing (25–28°C, summer) Three 4000-W immersion 2 hp (Universal Marine coils in water (18–21°C, winter) heaters (Process Technology, Industries) distribution Inc.) tower Florida Everglades fresh water Propane-heated greenhouse None One titanium water chiller, Plastic tubing (25–28°C, summer) Immersion heater as necessary 2 hp (Universal Marine coils in (20–22°C, winter) Industries) upper pool Maine coast 2500-gallon Maine rocky shore None needed Three titanium immersion water None (12–15°C, summer) chillers, 1 hp each (Aqua-Logic) (4–6°C, winter)
  • 42. 26 2. The Envelope FIGURE 2.10 Comparison of the biomass of soft bottom infauna in marine, estuarine, and fresh-water environments. After Nixon (1988), with mean curves fitted by eye. Weights are shell-free, ash-free dry weights. The wider curve to the right represents salt and brackish water. The narrow curve to the left/center represents fresh water. need not be, and often cannot be, of the great force and in colder climates, by autumn and spring overturns energy that they sometimes are in the wild. However, (Figure 2.6). Overturns result from surface cooling in wild levels during storms are often far above satura- the autumn (or heating in early spring) when the sur- tion levels in terms of their effects on ecological face waters become heavier than deeper waters. Under processes. On the other hand, storm or even weekly or some conditions, particularly in warmer and less monthly high waves or currents may determine com- windy seasons, or in the tropics where lakes can be munity structure in many cases. If these high-energy warm at the surface year round, the surface waters communities are to be simulated, at least in a localized become warm, light, and strongly stratified. When this way within a model system, then steps need to be taken happens, mixing with deep-water stops. If the bottom to provide strong point sources of physical energy. sediments are even moderately rich in accumulated organic material, bacteria, worms, and clams in the mud can use up all of the available oxygen and leave Currents in Fresh Waters the bottom sediments and even some of the bottom Currents, sometimes extreme, occur in streams and water virtually dead. This is more likely to happen in rivers. Those currents control mixing and circulation, lakes with greater nutrient input, and therefore higher as well as the nature of bottom sediments (see below). productivity levels (Figure 2.12). Lake Tanganyika in That currents also occur in lakes and are of great East Africa is a well-known example of such a lake, importance is not as widely recognized (Figure 2.11). with about 90% of its total volume being permanently As we noted above, lakes are also mixed by wind and, devoid of oxygen.
  • 43. Water Motion 27 FIGURE 2.11 Surface current patterns in Lake Constance, Switzerland. Average rates in shallow water are 10–20 cm/s and reach 27 cm/s at some localities. After Hutchinson (1957). Reprinted by permission of John Wiley & Sons, Inc. FIGURE 2.12 The relationship of stratification (as shown by temperature curves) and oxygen in different types of lakes (Feforvatn: biologi- cally sterile; Breiter Lucin: intermediate; Green Lake: highly productive). [O2] oxygen observed; [O2]s saturation level at temperature; temperature; bottom. From Hutchinson (1957). Reprinted by permission of John Wiley & Sons, Inc. It is also not unusual for even quite large lakes and and the dead zone has continued to grow (Price, 2005). estuaries to become unnaturally anaerobic due to the Unfortunately in these cases, since phosphorus does nutrifying effects of human activity. Chesapeake Bay in not diffuse easily through oxygenated sediment, slight eastern North America, one of the largest estuaries in deoxygenation releases stored phosphorus in large the world, is just such an example. A deoxygenated quantities. This triggers more surface productivity and layer began to appear in deeper waters during the sum- a “snowballing” of deoxygenation. Many lakes in pop- mer in the 1950s. In spite of great effort and expense to ulated or heavily farmed areas have reached a similar reduce nutrient loading over the last 30 years, popula- state, and now the northern Gulf of Mexico, off the tion growth in the watershed has offset improvements Mississippi River, has developed a large, hypoxic zone.
  • 44. 28 2. The Envelope Currents in the Marine Realm primarily by density as established by salinity and tem- perature (Figure 2.14). As in lakes, the limited circulation In open, shallow-water marine environments con- in deep water results in oxygen depletion (Figure 2.15). stant and relatively rapid turnover of living biomass is However, in this case because of the enormous depths the rule, longevity the exception. Organic-rich sedi- involved, the organic material raining from the surface is ments, equivalent to marshes on land, can form in deeper largely broken down within the upper 1000 meters. The water, in the extensive shelf environments and in pro- oxygen minimum occurs in the 500–1500-meter range, tected lagoons and bays. These organics can become geo- and oxygen concentrations generally increase in even logically stored for hundreds of thousands or millions of deeper water. The deep and bottom waters are generally years. However, the short-term in-situ storage of biomass very cold and relatively oxygen-rich, being derived from as in terrestrial forests and swamps does not readily very slow-moving bottom currents from the surface occur in the near-coastal marine or aquatic realms. A waters of the Arctic and Antarctic. rapid exchange of gases (oxygen, carbon dioxide), metabolites (food, nutrients, nitrogenous wastes), and Wave Action salts and minerals between aquatic organisms and their watery environment is the normal state in high-energy While the larger-scale circulation of the ocean is in environments. On the other hand, these low-biomass, large measure driven by long-term wind stress, wave high-water quality zones remain in that state in large action more directly and strongly mixes the surface measure because of export and storage of organics else- layers of water. Figure 2.16 shows how a wave, whether a where, whether in deeper water or in lagoons and bays. wind wave or swell, disturbs, and mixes surface waters The world’s oceans develop major surface currents by its motion. Waves driven for several hours or more (Figure 2.13). These currents are created primarily by by any wind over 12–15 knots and for a distance of over prevailing winds, modified by Coriolis (Earth rotational) several miles can have large effects on the shore and the and density forces as well as by land geography. While biological and ecological processes of that shore. Most moderate in rate, ocean currents can, however, reach sev- oceanographic text books provide tables or graphs for eral knots (e.g. the southern Gulf stream). Ocean currents predicting wave heights, wavelengths, and their fre- provide mixing and heat transfer for the entire ocean, quency. Marine literature, including sailing directions, and consequently the atmosphere. They are major factors and maritime forecasts, provide similar information. in determining weather patterns. Below several hundred Waves can accomplish more than circular internal meters, circulation generally is slower and is driven motion and turbulance when they are driven against FIGURE 2.13 Surface circulation of the world’s oceans. After Kennett (1982).
  • 45. Water Motion 29 FIGURE 2.14 Primary vertical circulation in the Atlantic Ocean. Temperature in °C. After Thurman and Webber (1984). Copyright © 1984 by Scott, Foresman and Company. Reprinted by permission of Addison-Wesley Educational Publishers. FIGURE 2.15 Oxygen concentrations with depth in the Atlantic and Pacific Oceans (ml oxygen per liter). After Kennett (1982). a shore. For example, a rich shallow-water coral reef, trade wind seas that drive water across the reefs and with its extraordinary respiration and primary produc- prevent serious oxygen depletion over the reef com- tivity, resembles a city in that it requires continuous munities. exchange with the adjacent ocean and lagoon. With a greater concentration of plants and animals than it can Water Motion and Model Ecosystems support within itself, the wild coral reef experiences rapid oxygen depletion of the strongly inflowing, oxygen-rich The role of wave surge as an important mixing ocean water during the night (Figure 2.17). It is the element is easily seen in a reef microcosm where a
  • 46. 30 2. The Envelope FIGURE 2.16 Motion of water particles in wind-driven waves. The circles describe the extent of orbital movement of individual water particles. After Thurman and Webber (1984). Copyright © 1984 by Scott, Foresman and Company. Reprinted by permission of Addison- Wesley Educational Publishers. well-defined flow and surge are present (Figure 2.18). While wave period can be simulated easily in an This irregularly oscillating inflow across the reef closely aquarium or mesocosm, wave height, except in the matches that measured by the same means in the wild. largest mesocosm (see Figure 2.20) will not likely be Removal of the surge component alone markedly fully matched. Consideration of the wild environment reduces photosynthesis and oxygen production (Figure in this respect should at least lead the scientist and 2.19). On quiet nights in a high-biomass wild reef, low aquarist to attempt a partial match and to consider the current and surge can result in low oxygen concentra- effects of reduced wave energy. tions. A well-developed reef community would quickly Traditional aquaria often employ bubblers or aera- expire under the stagnant conditions of a nonflowing, tors to achieve water motion with its resulting atmo- unaerated, closed-system aquarium because of oxygen spheric exchange. Although a bubbler can induce some drawdown and carbon dioxide and ammonia pollution; water movement when set up as an airlift, it is rela- this can occur rapidly with any appreciable animal load. tively inefficient at creating currents and cannot create
  • 47. Water Motion 31 FIGURE 2.17 Oxygen reduction at night in water driven over a Caribbean coral reef by the trade wind sea and swell. 1, Front of fore- reef; 2, back of forereef; 3, front of backreef; 4, back of backreef. Note the oxygen increase at night between forereef and backreef (i.e. 2–3), in the surf zone, due to input from the atmosphere. After Adey and Steneck (1985). FIGURE 2.18 Wave surge and current in the Smithsonian coral reef model. See Figure 20.1. The mean inflow (across the reef) is about 0.1 ft/s, but the oscillation (or surge) is very marked. a surge. Filter devices usually have associated drive (though see our discussion on the effects of bubblers and pumps. However, they are rarely used to establish cur- centrifugal pumps, below). In shallow coastal and shore rent or waves, although that possibility sometimes communities, marine or fresh water, on which this book exists. Even a pump of very high rating could provide focuses, water motion occurs as a result of simulated little flow if the filter unit itself is partially clogged. tides, currents, wave action, and its resulting surge. Newer pumping devices often include “power heads” Many devices have been constructed to create and are capable of producing locally high current zones waves in tanks for experimental purposes, including
  • 48. 32 2. The Envelope FIGURE 2.19 Reduction of oxygen production with reduced wave action in coral reef microcosm algal scrubber (Adey and Hackney, 1989). FIGURE 2.20 Pneumatic wave drive system used in Australian Great Barrier Reef aquarium at Townsville.
  • 49. Water Motion 33 push boards and large pistons. Most recently a pneu- strong wave action. It is often necessary in models of matic device has been extensively used for creating these systems, especially in the smallest microcosms and waves in swimming pools, and a version of this device aquaria, to create occasional unusual turbulence either has been used on several large mesocosms (Figure 2.20). by hand or with apparatus designed for this purpose. For most mesocosms and aquaria a variation of the sim- ple dump bucket (Figure 2.21) is the most reasonable approach in terms of cost and maintenance. If the dump Pumps rate is matched to the natural frequency of the tank (determined by “rocking” or seiching the tank water Among the wide variety of pumps available for mov- mass by hand), a high surge rate can be created. Often, ing water in microcosms, mesocosms, and aquaria, the however, it is desirable to slightly mismatch wave dump most commonly used is the centrifugal/impellor pump. with natural frequency to avoid waves that become These can be inexpensive, reliable, and quiet, and a wide excessive. If diaphragm pumps are used (Figure 2.22), a choice exists to fit almost any system design. Submersible surge or seiching motion can also be created by periodic impellor pumps are readily available and can be quieter suction. and esthetically more desirable than those designed Moderate waves, created by the techniques described for operation in air as they can be hidden within a tank. in this chapter and in Chapters 20–23, are normally suf- However, with plumbing failure they also have the ficient to maintain community structure on the scale of potential for pumping a tank virtually dry unless the days and perhaps weeks. However, many ecological intake is placed very high. Submersible pumps also tend communities, especially those of rocky shore and reef to raise system temperatures, and some varieties have environments, are partly structured by occasional the potential for leaking oil. FIGURE 2.21 Photographs of dump-bucket wave maker. Note that these devices are highly sensitive to weight shift and easily become unbalanced with algal growth. Proper setting of the hinge axis and the use of friction-minimum bear- ings that will not corrode are essential. We have found that Teflon against Teflon is the only foolproof method, although Teflon against other plastics is usually acceptable. We have also used Nylatron, as the axis against a Teflon bearing.
  • 50. 34 2. The Envelope FIGURE 2.22 The 30-rpm, 5-gpm diaphragm pumps as installed in a 130-gallon scrubber-operated reef aquarium (see Figure 20.18). The dark area to the right is a refugium. The scrubber unit is off the photo to the right (see Color Plates 8A and 8B). Photo by Nick Caloyianis. The unfortunate difficulty with most impellor extensively used the bilge pump system shown in Figure pumps is that their internal turbulence, pressure, and 2.22 on many small aquarium systems (see Chapters shear forces kill many plankters and the swimming or 20–23). Sophisticated engineering and manufacture for a floating reproductive states of plants and animals. We mass market could make these pumps “standards.” have been able to demonstrate a greater than 90% mor- Archimedes’ screw pumps are ancient devices used tality of large zooplankters, such as Artemia salina, on centuries ago, particularly in irrigation. Today, they passing through such a pump. Impellor pumps select still merit usage in sewage plants where a simple, vir- plankton populations in a system, killing some and tually uncloggable pump to move large quantities of effectively enhancing others. This is the basis for the water at minimal height is desired. development of tinted waters (yellow or green) in We have had experience with several, large some systems and not in others (see also discussion in Archimedes’ screw pumps in mesocosm systems. They Chapter 6). are unexcelled at lifting large quantities of water without We have experimented with alternatives to the ubiqui- significantly disturbing plankton, or even larger inverte- tous impellor pumps. Among the possibilities are rela- brates and fish (typically they lift to a distribution reser- tively large diameter diaphragm pumps that contain voir). However, Archimedes’ screw pumps have a “flapper valves” and alternate relatively slowly from a tendency to burn out drive motors, during restart (under slight suction to a slight pressure (Color Plates 2, 4–6). heavy water loading) during power outages. Also, the Some compressed-air-driven types for transferring cor- primary lower bearing is subject to corrosion and wear. rosive slurries in the chemical and other industries work Both of these issues are minor engineering problems. quite well and are easily available. However, they are Recently, a promising “bubble-lift” pump that uses expensive and often quite noisy. We have designed and large bubble “bursts” injected into a chamber from a
  • 51. Tides: Simulating the Effects of Sun and Moon 35 low-pressure, high-volume compressor has been devel- Many factors determine actual pumping rate com- oped. This is basically a smaller version of the wave gen- pared to the rate given on the pump or pumps. Besides erator shown in Figure 2.20. Because a single bubble on the pump rating, water delivery rate is a function of the order of several hundred milliliters to a liter or two both suction and delivery heights, length of flow, and (depending on pump dimension) will lift a relatively the size of the pipe, as well as any restrictions to flow. large volume of water, the bubble surface that traps Bacterial filtering devices can greatly reduce actual out- plankton is greatly limited. Thus, the “skimming effect” put, as well as destroying plankton. It is inappropriate of standard aerators or bubblers, which removes plank- to use such filters in model aquatic ecosystems unless ters, particulates, and large organic molecules, is partly they mimic a desirable feature of a wild system (e.g. a avoided. large filter feeder). In our discussions below we refer to Centrifugal pumps that lack impellors and have sim- actual flow. ple discs, or discs with grooves or ridges, called disc- In general, if algal scrubbers are used to control flow pumps, are used in the food-processing industry to water quality, a minimum rule-of-thumb flow rate over pump a wide variety of foods. These pumps are an the scrubbers is 40 liters (10 gallons) per minute per acceptable alternative to the impellor pump replace- one square meter (10.6 square feet) of scrubber surface. ments described above when the values of a centrifugal If this rate is not acceptable for achieving the currents pump are needed. Since disc-flow pumps are not yet desired, then a separate recycling pump can be used, being built for the mass market, they tend to be rela- either on the primary tank or on the scrubbers. A sim- tively expensive. On the other hand, we have found ple device that combines scrubbing with current, wave them to be highly reliable (see Chapter 22) and accept- action, and wave surge is shown in Color Plate 9 and able in maintaining diverse plankton communities. Figure 2.1. This “dump scrubber” is particularly effec- Pumping rates vary from system to system. At the tive when minimum space is available in a small system Smithsonian, the coral reef system overturned approx- and the desirability of mounting all apparatus directly imately every 60 minutes, and the Maine rocky-shore, on top of the tank is a foremost consideration. mud-flat tank overturned approximately every 45 min- It is best to split up the pumping among as many utes. The small, home, 130-gallon reef described in small pump units as economically and physically feasi- Chapter 20 overturned every 20 minutes. The 750 000- ble, thereby lessening the threat to the whole system gallon reef system at Townsville, Australia (Chapter when a pump breaks down, as it inevitably does. There 20), is completely pumped around every 2.9 hours should always be backup pumps readily available. (Jones, 1988). There is no way to arrive at an ideal rate Beyond the inevitable contamination, we remind the without taking oxygen measurements in the fully func- modeler, whatever the level, that the single most fre- tioning system (see Chapter 8) and comparing actual quent source of massive failure is catastrophic leakage currents and surge, depending on design, with the usually from plumbing. Also, pumps and electricity wild analog. The mean flow rate across the St. Croix will fail. If there is a dynamic water mass (i.e. water in analog coral reef is 10 cm/s, three times as high as that transit) in a system, adequate sump volume (e.g. the in the Smithsonian model at 3 cm/s. On the other hand, tank itself) must be allowed. turnover time (ocean water replacement) on the wild reef averages about 6 hours compared to 1 hour in the model mentioned above. Thus, these related parame- TIDES: SIMULATING THE EFFECTS OF ters are both within the right order of magnitude, but SUN AND MOON displaced in opposite directions because of critical size restrictions in the model. A secondary and related The ebb and flow of tides is one of the most fascinat- parameter, water quality in the model as measured by ing aspects of the sea. Even though lakes show sea- dissolved oxygen concentration, is remarkably close to sonal or meteorological changes in level, tidal effects that in the wild (see Figure 8.9). This kind of give and are virtually absent, and on some ocean coasts (e.g. the take matching is crucial to the modeling process. In southwestern coast of Norway), tides are small enough general, warmer and smaller microcosms and aquaria to be more or less negligible. However, as we pointed should turn over more frequently than larger and out above, bottom biomass in lakes is generally less colder systems. Oxygen solubility in cold water is than in the sea, probably in large part due to tidal almost twice that in tropical waters (see Chapter 8). effects (Figure 2.10). Many biological communities (e.g. Therefore, drawdown for a given biological load is less salt marshes and rocky intertidals) depend entirely on critical in cold water. Also, smaller systems will usually tides, and it has been demonstrated that the mixing be more overloaded than larger ones. Thus, greater cir- effects of tides provide an energy subsidy to ecosystem culation in proportion to volume is desired. function (Figure 2.23). In addition, many organisms
  • 52. 36 2. The Envelope FIGURE 2.23 Energy flow diagram developed for the Narragansett Bay ecosystem. Note that tide has been given a major controlling role both on solar input and on export from the bay. The boxed form of tidal attachment also indicates tidal effects driving all levels of the ecosystem. After Kremer and Nixon (1978). key important elements of their life cycles, particularly before being washed out to sea, it provides a more pre- reproduction, to the tides and to the moon (Palmer, cise way to ensure fertilization of large numbers of 1995). Sophisticated lighting control systems for home eggs. Also, the tide pool situation is one that is difficult aquaria have begun to include a moon component. for many fish to occupy. Wrasses, for example, would As an example of the complex ways in which tides otherwise eat the eggs as they are released. Thus, the and moon, together and separately, can affect an organ- tide pool provides relative freedom from fish predation ism (and therefore a community), we cite the case of and it seems likely that in part this also has resulted in the Caribbean/West Indian magpie shell, Cittarium the evolution of this curious pattern. A similar repro- pica. This large, rocky intertidal and upper subtidal ductive keying to spring – higher high tides on sandy snail, characteristic of exposed wave-beaten shores, California beaches – is practiced by a fish, Leuresthes achieves some gastronomic use in the Caribbean. Three tenuis, the grunion. Thurman and Webber (1984) to five days after the new moon (i.e. during the darkest describe this process and its relationships to tide in nights of the month), the males and females crawl into some detail. exposed tide pools at high tide. When tide level lowers The intertidal zone itself is truly the interface between sufficiently to isolate the pool, the snails start releasing the terrestrial and the marine, and this area is the most eggs and sperm into the water. (It is not known easily accessible of marine environments. Many scientific whether elevated temperatures, hydrostatic pressure, studies have been carried out in the intertidal zone and lack of wave action, or some other factor alerts the ani- some excellent books describe it (Raffaelli and Hawkins, mal that the pool is isolated.) Fertilization takes place 1996; Haywood, 2004). One of the finest of the classic in the pool and the developing larvae are washed into works is Between Pacific Tides (Ricketts et al., 1985), first the ocean as the rising tide floods the pools. This com- written in 1939 and now in its fifth edition. In particular, plex and multi-keyed reproductive pattern offers the rocky intertidal and salt marshes, restricted to the many advantages. To an animal living on a wave- intertidal zone, are important subjects for model ecosys- beaten shore where eggs and sperm released into the tems and we describe several of these models in later water would have a difficult time coming together chapters.
  • 53. Tides: Simulating the Effects of Sun and Moon 37 Ocean Tides semidiurnal tide, the Gulf of Mexico, a diurnal tide. The southwest Florida coast is where they meet. Every Average ocean tides measure 2–3 feet (0.6–1.0 meters) 2 weeks when the sun and moon are on the same side from high to low water, but they can range from virtu- of the Earth, and also when they are on opposite sides, ally nothing to 50 feet (15 meters), depending on special the Earth has large “spring” tides. Roughly 7 days after geographic features. Generally, any body of water has a a spring tide, when the sun and moon form right angles natural frequency of oscillation as a standing wave. This to the Earth, “neap” tides occur. These are a third to a can be demonstrated in an aquarium by “pushing quarter smaller (Figure 2.25). down” on the water on one side in a pulsing manner until the entire mass starts “rocking.” When the natural frequency of a body of water is close to that of the The Intertidal Zone sun/moon-created tidal wave, tide heights can become much larger than those in the open ocean. The English The intertidal band of bottom or shore between high Channel, the Gulf of Maine, the St. Lawrence River and low tides is a difficult region for living organisms Estuary, and the semi-enclosed waters north of Australia to occupy. Relatively few plants and animals have are well known for their extraordinary tides. adapted to this zone. It is alternately cooled and wetted Tides are typically semidiurnal, with two high points with salt water, sometimes frozen in the winter, dried and two low points a day, each one about 6 hours and and baked by the sun in the summer, and sometimes 10 minutes apart and more or less equal in height. flooded with totally fresh water during heavy rains at However, diurnal tides of one high and one low daily, or low tide. Depending on tidal range and slope of the combinations, mixed tides, somewhere in between, are shoreline, it can be quite narrow or many miles wide. It not uncommon (Figure 2.24). The Florida Everglades is neither marine nor terrestrial. On rocky shores it is coast, for which we discuss modeling in depth in dominated by relatives of primarily marine groups, on Chapter 22, has a nearly perfect mixed diurnal/ marshes and swamps mainly by terrestrial-derived semidiurnal tide. In this case, the Atlantic Ocean has a species. Environmentally difficult as the intertidal zone FIGURE 2.24 Distribution of tide heights around North America. After Thurman and Webber (1984). Copyright © 1984 by Scott, Foresman and Company. Reprinted by permission of Addison-Wesley Educational Publishers.
  • 54. 38 2. The Envelope FIGURE 2.25 A variety of tidal curves from ports scattered around the Earth, September 1958. After Gross (1982). can be, for those organisms able to withstand its rigors tides); (2) a periwinkle snail or littorinid snail zone successfully, competition and predation are generally (roughly the upper half of the tide zone); (3) a white reduced and for the plants both maximum light and a and very rough barnacle zone (the lower half of the reg- very reliable water supply can be achieved. ular tide); and finally (4) a mussel zone between neap The intertidal zone itself is often strongly subzoned, and spring low tides. Specific areas have even more char- and such zonation can be related to patterns of tidal acteristic communities, such as the rockweeds (brown form and height. Typically, worldwide, the basic pat- algae) and Irish moss (red algae) of the North Atlantic tern of zonation from top to bottom in the rocky inter- (see Chapter 21). Some of the most interesting marine tidal is: (1) a black band of blue green algae and lichens and estuarine plants and animals richly occupy the inter- (in the spray zone or just at or above the highest regular tidal zone and form unique and highly productive
  • 55. Tides: Simulating the Effects of Sun and Moon 39 communities (Figures 2.26 and 2.27). In more protected Whether tides should be considered a factor in a areas salt marshes and mangrove swamps cover many microcosm depends on the marine community being square miles and provide extensive habitats for inter- simulated. None of our coral reef tanks, all based on tidal organisms, insects, and birds. These too are Caribbean reefs, has had a tidal element. While in some strongly zoned to the tide (see Color Plate 40), even places of very high wave energy the intertidal algal ridge when beyond the limit of salt water (Odum et al., 1984). is one of the most fascinating communities on Caribbean Extensive mud flats, often found in protected areas reefs, for most reefs in this region tides are relatively having extreme tide ranges, can become rich reservoirs unimportant. On the other hand, on the Australian Great of organic particulates. These organic-rich, muddy bot- Barrier Reef, tides of 3–10 feet (1–3 meters) are an toms are largely derived by wash-in from more extremely important ecological element. The Great exposed areas and from streams and rivers. Tidal flats Barrier Reef Marine Park reef aquarium in Townsville, are occupied by a host of small invertebrates, including Australia, provides a moderate tide range. In the simula- many clams prized as human food. tions of the rocky Maine coast and Chesapeake Bay and the Florida Everglades described in this book, tides were too important to ignore and are critical elements. Tides and the Model Ecosystem Developing a tidal system in a closed microcosm is While a few research systems have been built partic- in part a matter of time-regulating higher and lower ularly to investigate the effects of oil on rocky shores water levels. This is most easily accomplished by tem- and marshes, and some of the more progressive public porarily storing water at times of low tide in a separate aquaria have constructed ecological models to show reservoir (Figure 2.28, and Figures 22.8 and 22.9). The the effects of tides in appropriate tanks, tidal models tidal reservoir can also serve as a fine-sediment settling are rarely constructed. This situation is peculiar since trap and refugium for the numerous worms and small accomplishing a rather accurate intertidal simulation is crustaceans that characterize deeper-water mud bot- not difficult. toms. As we discuss throughout this book, refugia and FIGURE 2.26 The vertical zonation of organisms occurring on intertidal rocky shores on the Pacific coast. Reprinted from Ricketts et al. (1985), revised by David W. Phillips, with the permission of Stanford University Press.
  • 56. 40 2. The Envelope FIGURE 2.27 The vertical zonation of intertidal organisms on hard bottoms of the Atlantic coast. Modified after Gosner (1978). Reprinted by permission of Houghton Mifflin Co. FIGURE 2.28 Photograph of tidal controller attached to a tidal reservoir on the Maine coast microcosm. The center motor rotates approximately twice a day to create the semidiurnal component. The outer motor rotates once every 2 weeks to create neaps and springs.
  • 57. Tides: Simulating the Effects of Sun and Moon 41 settling traps are critical elements of model ecosystems submergence) times in the microcosm are the same as in that allow the simulation of much larger wild environ- the wild. Marsh vertical ranges are always much smaller ments. If it is desirable to save space, two separate than the total tide, generally occupying only the upper reservoir systems or two separate parts of the same half of the tide range. tank can be operated on alternate tide cycles. In our Florida Everglades mesocosm, the estuary served as the tidal reservoir for the Gulf of Mexico portion of the system. Pumps first pumping in one direction (to the References reservoir) and then in the other direction (back to the Adey, W. and Hackney, J. (1989) Harvest production of coral reef main tank) can also be used; however, unless a compli- algal turfs. In: The Biology, Ecology and Mariculture of Mithrax spin- osissimus Based on Cultured Algal Turfs. W. Adey (Ed.). Mariculture cated multiple pump arrangement is employed, the Institute, Washington, DC. result is a sawtooth tidal pattern rather than the sine- Adey, W. and Loveland, K. (1991, 1998) Dynamic Aquaria: Building type curve of the wild. The sawtooth curve reduces by Living Ecosystems, 1st and 2nd edn. Academic Press, San Diego. about 25% the total times of high and low tide. Adey, W. and Steneck, R. (1985) Highly productive eastern We have designed a water-level tidal management Caribbean reefs: synergistic effects of biological, chemical, physi- cal and geological factors. In: The Ecology of Coral Reefs. M. Reaka system based on interval timer control of stepping (Ed.). NOAA Symposium Series on Underwater Research, Vol. 3. motors (Figure 2.28 and Color Plate 41; see also Figures Washington, DC. 22.7–22.9). This method creates pure semidiurnal tides Adey, W. and Steneck, R. (2001) Thermogeography over time creates and provides for biweekly springs and neaps as well as biogeographic regions: a temperature/space/time-integrated for the 50 minutes’ daily timing advance to “follow the model and an abundance-weighted test of benthic marine algae. moon.” The approach is generally trouble-free and J. Phycol. 37: 677–698. Bansal, N. and Doremus, R. (1986) Handbook of Glass Properties. inexpensive. The system can easily be adapted to a Academic Press, Orlando, Florida. diurnal tidal cycle simply by changing the timing on Briggs, J. C. (1974) Marine Zoogeography. McGraw-Hill, New York. the primary stepping motor drive. Stepping motor Carpenter, R., Hackney, J., and Adey, W. (1991) Measurements of pri- control can be modified to simulate virtually any tidal mary productivity and nitrogenase activity of coral reef algae in a cycle, even a mixed diurnal/semidiurnal tide. chamber incorporating oscillatory flow. Limnol. Oceanogr. 36: 40–49. Carson, R. (1962) Silent Spring. Fawcett Crest, New York. Mud flats and rocky shores are relatively easy to Climap Project Members (1976) The surface of the ice-age earth. establish and manage in an intertidal microcosm. Some Science 191: 1131. care should be taken to stock organisms at their proper Gosner, K. (1978) A Field Guide to the Atlantic Seashore. Petersen Field zonal level, and this can be quite difficult when a large Guide Series, Houghton Mifflin, Boston. vertical tidal zone in the wild analog is reduced to a rel- Gross, M. G. (1982) Oceanography: A View of the Earth. Prentice Hall, Englewood Cliffs, NJ. atively narrow zone in the model. However, commu- Haywood, P. (2004) A Natural History of the Seashore. Collins, London. nity adjustments in the microcosm generally develop Hutchinson, G. E. (1957) A Treatise on Limnology, Vol. 1. Wiley, New slowly over many months without detrimental effects. York. Rocky intertidals in particular are adjusted in the wild Jones, M. (1988) The Great Barrier Reef Aquarium: A Matter of Scale. Northern Reg. Eug. Conf. (Australia), Townsville, June 10–13. to wave action, with given zonal bands being higher Kennett, J. (1982) Marine Geology. Prentice Hall, Englewood Cliffs, NJ. with increased wave action (Figure 2.27). Also, rocky Kremer, J. and Nixon, S. (1978) A Coastal Marine Ecosystem Simulation intertidals are notoriously patchy, with the effects of and Analysis. Springer-Verlag, Berlin. settlement, wave action, local terrain, and local preda- Leigh, E., Paine, R., Quinn, J., and Suchanek, T. (1987) Wave tion varying widely. These effects have been favorite energy and intertidal productivity. Proc. Natl. Acad. Sci. USA 84: 1314–1318. subjects for studying the dynamics of community Levinton, J. (1982) Marine Ecology. Prentice Hall, Englewood Cliffs, NJ. structure (see Haywood, 2004). In an aquarium or Levy, S. and DuBois, J. H. (1984) Plastics Product Design Engineering small mesocosm, the available shore can become a sin- Handbook. Chapman and Hall, New York. gle patch changing from time to time. The process can Marino, B. D. V. and Odum, H. T. (1999) Biosphere 2, Research Past and be altered and directed by the “disturbance” of the Present. Elsevier Science. An Elsevier Science Publication, Ireland. Reprinted from Ecological Engineering Spec. 13(1–4). aquarist. Algal, mussel, and barnacle zonation on the Marra, J. (2002) Approaches to the measurement of plankton produc- rocky intertidal of an aquarium system, with the graz- tion. In: Phytoplankton Productivity. P. J. leB. Williams, D. Thomas ers and predators that occupy the same environment, and C. Reynolds (Eds). Blackwell Science, Oxford. can be an exciting model to manage. Nixon, S. (1988) Physical energy inputs and the comparative ecology Marsh communities are considerably more sensitive of lake and marine ecosystems. Limnol. Oceanogr. 33: 1005–1025. Odum, W., Smith, T., Hoover, J., and Mclvor, C. (1984) The Ecology to tidal levels than rocky intertidals. In microcosms of of Tidal Freshwater Marshes of the United States East Coast: A small or microtidal ranges (less than 2 feet in the wild), Community Profile. U.S. Fish and Wildlife Service OBS-83/17. it is important to place the sod surface of marsh grasses Palmer, J. (1995) The Biological Rhythms and Clocks of Intertidal Animals. at the equivalent tidal level so that total exposure (and Oxford University Press, London.
  • 58. 42 2. The Envelope Price, J. (2005) Chesapeake Bay an Undeclared Ecological Disaster. Thurman, H. and Webber, H. (1984) Marine Biology. Addison-Wesley Chesapeake Bay Ecological Foundation. On-line piece, Sunday, Educational Publisher, Menlo Park, CA. October 23, 2005. Vannote, R. and Sweeney, B. (1980) Geographic analysis of thermal Raffaelli, D. and Hawkins, S. (1996) Intertidal Ecology. Chapman and equilibria: a conceptual model for evaluating the effect of natural Hall, London. and modified thermal regimes on aquatic insect communities. Ricketts, E., Calvin, J., Hedgpeth, J., and Phillips, D. (1985) Between Am. Nat. 115: 667–695. Pacific Tides, 5th edn. Stanford University Press, Stanford, CA. Walter, H. (1979) Vegetation of the Earth, and Ecological Systems of the Spotte, S. (1995) Captive Seawater Fishes. Science and Technology. Wiley, Geo-Biosphere. Springer-Verlag, New York. New York.
  • 59. C H A P T E R 3 Substrate The Active Role of Rock, Mud, and Sand In the first two editions of this book, we emphasized last decade to bring the relatively new science of plate the construction of living models or microcosms and tectonics into a modern framework that includes the mesocosms of aquatic ecosystems. Our logic at that life sciences (e.g. Redfern, 2001; Marshak, 2004). That time in presenting a background chapter on geology, review should be followed by a more detailed examina- including the origin of the rocks that provided the base tion of local geology and sedimentation. of some aquatic ecosystems and the sediments that pro- Lithospheric activity, centered on plate tectonics, vided the base of other ecosystems, was that the nature determines the shapes of seas and oceans and greatly of the substrate was critical to the character and func- constrains open ocean currents. The position of conti- tion of the ecosystem being modeled. Also, the salinity nents, also constantly moving, relative to the Earth’s of the oceans and coasts and the chemical composition axis, along with the major ocean currents, over geolog- of fresh waters is determined by the nature of the rocks ical time is a very important factor in global climate. over and through which the water flows. This might Even more directly, along coastlines and mid-ocean have seemed quite remote for the oceans, but now we ridges, and of course in fast-moving streams and along know more about the hydrothermal vents along ocean the shores of larger lakes, rock provides a surface to ridges and how sea water is constantly circulating and which organisms attach and from which they interact chemically interacting with hot and even liquid ocean in myriad ways with the aquatic environment. crust (van Dover, 2000). Also, with human mining, and The processes of weathering, transportation, and coal and oil extraction from the Earth’s crust, we have sedimentation, whether on continental shelves or in become aware of the extensive changes to streams and the deep ocean, result in the constant geological-scale rivers, the Earth’s atmosphere and even the chemical sequestering of carbon and other nutrient and mineral character of the oceans (e.g. Kleypas et al., 1999). (i.e. elemental) requirements used in the building of In this edition, we have changed our focus some- living cells and tissues. Thus, ultimately, the underly- what and argued that all ecosystems on Earth are con- ing lithosphere or rock, in its interaction with the trolled by human activity and are in effect macrocosms. atmosphere and the hydrosphere, or liquid water enve- It is simply a matter of scale between the microcosms lope, determines the concentrations and thus the avail- and mesocosms that we build for research, education or ability of many of the basic chemical building blocks of hobby, and those macrocosms, altered by human activ- life in the ocean. Except in closed basins and areas of ity, that we seek to restore to a pre-industrial state (or at high evaporation relative to precipitation, fresh waters least rehabilitate). In ecosystem restoration, it is even are transient sites for elements, mostly in low concen- more important that the restorer understand the geo- trations, on their way to the sea. logical background and framework of the ecosystem It is perhaps not unreasonable for the modeler or being treated. Although here we present a basic back- aquarist working on an oceanic plankton community ground in geology and sedimentology, we recommend to regard the ocean characteristics, for all practical pur- that the modeler and restorer, before initiating work, poses, as independent from the lithosphere. For the review one of the broader texts that have evolved in the ocean restorationist, however, that would not be the 43
  • 60. 44 3. Substrate case, for most ocean and coastal pollution today Our planet still has considerable heat (from gravita- derives from land/river/bay run-off. And for benthic tional collapse and radioactivity) in its hot, liquid or (bottom), shoreline, and of course stream, river, and semi-liquid interior. The hard, semi-plastic crust of the lake shore situations, the presence and nature of the Earth caps a slowly churning mantle cauldron. This has rock bottom, and the sediments derived from those given rise to a rather remarkable evolution of the surfi- rocks, can be crucial to the function of both a wild cial crust that has been a major catalyst to the evolution ecosystem and its model. It might make the modelers’ of life and in many ways determines and constrains its endeavors easier to regard that surface of rock as a the- ecology today. The “boiling up” of this mantle cauldron oretical boundary, an attachment but nothing more, has gradually concentrated relatively light minerals par- like the glass of the model’s wall. Perhaps in some ticularly rich in silica, aluminum, and potassium in scat- cases, a smooth basalt bottom for example, this might tered “floating mounds” called continents, which are actually be the case. In most cases, however, the geo- raised above the generally heavier calcium-, magne- logical world is less remote from the needs of the sium-, and iron-rich crust of the Earth (Figure 3.1). The modeler or ecological restorer than a preliminary look oceans, occupying primarily the deeper parts of this two- might suggest. level surface (Figures 3.2 and 3.3), have a mean depth of 3730 meters, while the continents are slightly raised (above sea level) to an average height of 870 meters. THE SOLID EARTH AND LIFE Through the process of plate tectonics (continental drift), the boiling up of the Earth’s cauldron is constantly split- The Earth, as viewed from space, with approximately ting the crust, changing the shape of both continents and 70% of its surface covered with water, would be most oceans (Figure 3.4). When pieces of the crust driven by appropriately called “planet water.” The size of the the cauldron collide, earthquakes, mountain chains, and Earth, its distance from the sun, and its moderate level sometimes very active volcanoes are created and ocean of internal energy production have allowed it to retain a levels are changed (Marshak, 2004). massive volume of water (in the liquid state). This water, Thus, there has been throughout much of the Earth’s as we described in Chapter 1, was probably brought to history, and is certainly on-going today, a very active Earth early in its development by comets. However, the relationship between the Earth’s lithosphere, with its retention of the water, more than any other single factor, minerals and elements, and the hydrosphere, the origi- has led to the development and evolution of life. nator of life. This relationship is strengthened by the However, if the hard surface of the Earth, the litho- continuous formation of limestone and other sedi- sphere, were smooth (i.e. nearly spherical), then the ments in which living or recently dead organisms play solid Earth would be covered uniformly with approxi- a crucial role. Sedimentary rocks or structures include mately 2600 meters (8000 feet) of ocean. Although life those that are formed largely by the skeletons or even probably would have developed and evolved under the organic matter of dead organisms (coal, oil shales). such a regime, without a more active inclusion of the The Earth’s crust is a melange of rocks created by tec- lithosphere in the atmosphere–hydrosphere interaction, tonic and volcanic activities, and the results of the it would certainly be far less diverse. Probably it would reworking of those rocks by atmospheric and hydros- still be very primitive, as it was several billion years ago. pheric processes. FIGURE 3.1 Schematic section of the crust of the Earth at about 3.8 billion years BP. Prior to this point most of the crust was oceanic (basaltic), and creation of crust at ocean-spreading centers (a) was followed by subduction back into the mantle with little change. At the time shown, the fractionated lighter material of future continents (b) has been minimal and usually subducted with the basaltic crust (1). However, larger pieces (2) are beginning to survive, even- tually leading to full continent formation. From Lowe (1994).
  • 61. The Solid Earth and Life 45 FIGURE 3.2 Hypsographic curve of the distribution of the amount of Earth surface at different elevations. After Kennett (1982). FIGURE 3.3 Worldwide plate system showing the placement of “raised” continents and oceanic crust with its deep ocean. Continental margins are shallow coastal areas, presently submerged but belonging to continents, and are shown cross-hatched. The ocean ridges form over hot up-flowing areas in the underlying mantle and are sites of new ocean crust formation. Ocean crust slides away from the ridges and sinks and melts in the subduction zones. Volcanic hot spots are mostly on ridges or sub- duction zones, though a few (like the island of Hawaii) are isolated beneath either ocean crust or continents. After Gross (1982).
  • 62. 46 3. Substrate FIGURE 3.4 Development of oceans through seafloor spreading: (A,B) formation of rifts; (C) rift valley with lakes stage (see Figure 3.5); (D) “Red Sea” stage; (E) young ocean stage, subduction started on right; passive margin on left. After van Andel (1985). Crucial additions to an already active rock, water, in solar radiation and the orbit and rotation of the Earth, and atmosphere interface, changing mostly on the scale and partly due to the change of the positions of conti- of many millions of years, are major alterations of over- nents and sea bottom relative to ocean currents, cooling all Earth climate on the scale of tens to hundreds of of the poles results in large-scale glaciation. These “con- thousands of years. Partly due to slight cyclical changes tinental” glaciers produce both radical alterations in
  • 63. The Solid Earth and Life 47 FIGURE 3.5 Formation of large continental lakes by rifting of the Earth’s crust. After Burgis and Morris (1987). rock weathering (by ice) and sea-level changes. Even in North America are an example of this process. in mid-latitudes, sea-level changes resulting from the Elsewhere, a variety of local factors such as volcanism, locking of water in ice caps near polar regions and the beach drift along the shore, rivers that change their bending of the Earth’s crust as weight distribution of ice course, and of course human activities result in lake and water changes result in marked alterations of both and estuary formation. Stream formation results from coastal areas and, as the gradient changes, the lakes and the run-off of rain working against tectonism, that is, streams that drain into them. In addition, while some major Earth movements, and the relative resistance of lakes and rivers can result from tectonic effects, for the underlying rocks to stream erosion. Clearly human example, the African Rift Valleys (Figure 3.5) and the activity can radically alter many of the above described Andean lakes, the majority of lakes and drainage in relationships and ecological restoration is equally pos- high latitudes results from either the scouring or the sible as long as these relationships are understood and mounding-up of sediment by glaciers. The Great Lakes managed.
  • 64. 48 3. Substrate CHEMICAL RELATIONSHIPS BETWEEN logarithmic curve. In small planets near the sun, such as ROCKS, SEA WATER, AND ORGANISMS the Earth, the lightest elements are lost to space. The net result for the crust of the Earth (Figure 3.6) is a skewed The universe is heavily dominated by the very light logarithmic, normal curve of abundance with the lightest elements of hydrogen and helium in the atomic fires of elements depleted, the light to mid-weight elements from the stars (see Figure 1.1 in Chapter 1). As the tempera- oxygen to iron most abundant, and heavier elements tures of these fires degrade, as a star ages or as frag- scarce to rare. The very unreactive noble gases, helium, ments are spun off in collisions or super novae, heavier neon, argon, etc., are anomolously low in abundance. elements are formed. In general, with increasing atomic Pure water, possibly fractionated from the crust weight, elements decrease in abundance according to a early in the Earth’s cooling cycle, was more likely FIGURE 3.6 Diagram showing the abundance of chemical elements in the Earth’s crust in relation to the use of those elements by living organisms. The principal elements of life (CHON) are light, relatively abundant, and also form water and the Earth’s atmosphere. It is signif- icant that nitrogen is the least abundant of the principal life elements in the crust, requires energy to remove from the atmosphere, and is the most critically limiting nutrient in the aquatic environment. The remaining organic macronutrients are drawn from the elements that form the salts of the sea, which in turn are the next heavier and most abundant elements of the Earth’s crust. The micronutrients (with the outliers molybdenum and iodine) are the lesser abundant and/or heavier elements of the main group. Note that aluminum, titanium, chromium, and nickel lie within the main group and are essentially unused by organisms. Modified after Bricker and Jones from Salbu and Steinnes (1995) and Parker (1967).
  • 65. Chemical Relationships between Rocks, Sea Water, and Organisms 49 FIGURE 3.7 Concentration of some elements of sea water in relation to residency time of those elements in sea water. Data derived from Millero and Sohn (1992) as mean of river input and sediment rate calculations. “rained-in” from space later. Virtually all chemical ele- react more with the water cycle than the igneous rocks. ments occur in the sea, as we shall see in Chapter 4. Ultimately, the concentration of elements in sea water However, the heavier elements are poorly represented. is a function of their residence time (Figure 3.7) as The dominant elements dissolved in ocean water are determined by rate of incoming (from rivers) and out- mostly those that are also moderately abundant in going (to sediments). the Earth’s crust. However, the proportions are not Thus, of the top 12 elements, by weight, in the salts the same primarily because in the Earth’s crust most of sea water, chlorine at 19 000 mg/liter in sea water elements appear as components of minerals. As the forms only about 0.03% of the Earth’s crust, while sil- minerals of a rock exposed to atmosphere, rain, and ica, the dominant element of the Earth’s crust (28.5%) is inorganic and organic acids dissolve in water, some an important, but minor component of sea water elements are very mobile and move easily into streams (4 mg/liter). The top six elements of sea salt (chlorine, flowing to the sea. Others tend to be re-bound in new sodium, magnesium, sulfur, calcium, and potassium) minerals and stay in the crust or in sediments. To make are all “conservative.” They are required by organisms matters more complex, sedimentation tends to further and concentrated to some degree, especially calcium. fractionate some elements (e.g. calcium, carbon, and However, their relative requirement is minimal and the magnesium) into new sedimentary rocks, and these concentration of the large quantity in the sea is not rocks, common in terrestrial environments, tend to affected by the activities of organisms. Many of the
  • 66. 50 3. Substrate primary chemical components of organisms (carbon, mesocosm. However, because of the scaling factor the nitrogen, and oxygen) relate more to the Earth’s atmos- substrate can be crucial when interfacing with a small, phere (and are gases dissolved in sea water) than to sea enclosed body of water. Of course, rocks (or gravel) salts. Oxygen and hydrogen can enter the biosphere that are iron-rich, lead-rich, arsenic-rich, etc., particu- through the splitting of water in photosynthesis. larly in a small system, cannot be used without an However, phosphorus, iron, and silica, ultimately understanding of the export mechanisms of those ele- derived from dissolution of the Earth’s crust, are ments from the system (see, e.g. Chapter 11). It is par- organically required elements in sea water that can be ticularly important to ask what rock substrate is in very limiting to the production of plants and therefore contact with the ecosystem to be modeled in the wild: animals. In very pure (oligotrophic) waters, other ele- for example, carbonate rock for a reef, marine, or any ments can also limit plant production, though such hard-water system, or a silica-rich hard rock for a black limitation usually relates only to calcium, magnesium, or other soft-water ecosystem. Buffering and the car- or potassium. bon dioxide/pH cycle in relationship to carbonate sub- In general, the chemistry of life utilizes light elements strate are specifically discussed in depth in Chapter 8. (less than atomic number 35) that are also abundant and Rock substrate is often crucial in structuring a com- reactive. However, elements that tend to form insoluble munity in that it supplies a secure base for those organ- compounds or become locked up by mineralization isms able to tightly attach. In addition, the spaces of processes have generally been “avoided” by organisms. cracks or voids, sometimes abundantly available, pro- In the universe, aluminum is more abundant than vide greatly increased surfaces for attachment and sodium and calcium, and in the Earth’s crust it is lesser spaces for hiding. The aquarist should try to match the only than oxygen silica in abundance. However, it configuration, or spatial heterogeneity, of the wild ana- approaches being rare in sea water, having a residence log as closely as possible, and the restorationist may time of about 100 years, and is unused by organisms. need to consider the changes that could have occurred Iron is also one of the more abundant elements in the due to human activity (e.g. a sediment coating on rock universe and in the Earth’s crust. Because it readily oxi- surface). However, the sediments, in themselves, are a dizes to insoluble forms, its abundance in the sea is very more critical concern, and that is what we concentrate low. However, it is crucial to all organisms. It can be sur- on here. mised that before algae provided oxygen gas (dioxygen) Generally, whether dealing with a fresh- or a salt- in abundance to the Earth’s atmosphere (and ocean) iron water environment, there is a strong relationship was abundant and it became key to many life processes. between current and wave energy and the coarseness or It is possible that “life” nearly extinguished itself, a few fineness of the bottom sediments (Figure 3.8). In micro- billion years ago, by producing oxygen, which then cosms, mesocosms, and aquaria, sediments that have combined with iron (as iron oxide) to deplete this ele- the same physical characteristics as those in the systems ment from the seas. Some scientists have suggested that being modeled should be used. Strong wave action or replacing iron in the open ocean, through a massive, currents, whether on exposed lake or ocean coasts or in human industrial chemistry-type operation could solve a mountain stream, give rise to exposed bedrock or large the problem of excess atmospheric carbon dioxide by cobbles or boulders providing a bare (or usually algal- increasing open ocean photosynthesis now limited by colonized) rock. In an aquarium or mesocosm environ- lack of sufficient iron. More recent field research has ment, if these surfaces are to be preserved as in the wild, indicated that the effects are minimal and the costs high, equivalent or at least sufficient wave or current action and as we discuss in Chapter 25, there are other routes to must be present. Otherwise the surface will become increasing photosynthesis at large scale that are more coated with fine sediment and will fail to recreate the efficient and provide additional benefits (see ATS). wild ecosystem. There is a major difference between a However, this is the kind of global scale restorationist bare rock bottom to which organisms must attach (or thinking that is required to solve our overwhelming bore as in softer rocks), and over which water must have dominance of the biosphere. considerable motion, and a sediment bottom. As we dis- cuss further in Chapter 23, in fresh-water environments, human changes have often meant changing the water THE SOLID EARTH, ROCK, AND energy/sediment relationships, and these are the first MODEL ECOSYSTEMS corrections that need to be made. In Chapters 20–23, we discuss a variety of ecosystems It may seem remote to equate the activity of the lith- in mesocosms and aquaria with and without bare rock osphere with the Earth’s water on a geological scale to and coral rock substrate. It is best to discuss these on that relationship over a few years in an aquarium or an individual basis, because the very layout of this
  • 67. Sediments and Model Ecosystems 51 FIGURE 3.8 Relationship between the movement of sediment and the grain size of the sediment as a function of water velocity. After Davis (1983). substrate often provides the primary habitat for the sandy beach between a dune and a wave-broken sandy ecosystems. This chapter mostly deals with finer sub- bottom within a few meters. It does not work in the strate, and although there is considerable overlap with wild, as many coastal landowners have found to their Chapters 6 and 18, the generalities will be discussed here. chagrin, and it does not work in an aquarium or meso- cosm (Figure 3.11; Chapter 22). With difficulty, sandy beaches can be simulated in mesocosms. In aquaria SEDIMENTS AND MODEL ECOSYSTEMS and microcosms, it is extremely difficult, unless it is the only community included. As quieter water is approached, whether in widened As we discuss in Chapter 12, the break between areas or billabongs (ox bow lakes) in a stream, in a lake high-energy shores with rock or mobile sand substrate small enough to prevent large waves, or in a bay or and a quieter mud or sandy-mud bottom is ecologi- coastal lagoon along a sandy coast, the sediment cally great. We treat them as separate biomes, the high- becomes progressively finer from gravel, to sand and silt, est community level differentiation. Generally, algae to a soupy, silty-clay mud. Coarse sands or gravels are occupy the highly disturbed but stable rocky shores perhaps the most difficult benthic environments for and higher plants (marsh plants and submerged aquat- organisms to adapt to, and there are relatively few ics) dominate the finer, less energetic shores. Even in a species within sand and gravel habitats. To remain sand, lake this differentiation is apparent. Large lakes lack the bottom must stay in motion (and clay and silt remain reed beds on most shores (except in protected coves), suspended), and therefore special adaptations are and very small lakes are usually continuously rimmed required by any organisms that will inhabit such bot- with emergent aquatic flowering plants. In the ocean, toms. A few larger animals, such as the Donax clam and this relationship is also apparent. The outer shores, the amphipod Neohaustorius have developed rapid bur- depending on sediment supply, range from rock rowing techniques (Figure 3.9). The mole crab familiar to with more or less abundant macroalgae to bare sand. beach naturalists along the extensive mid-Atlantic US Mostly, the only plants from the high-water line sea- outer banks is another example. Otherwise, organisms ward on rocky bottoms are algae (including lichens). must be small (less than 0.5 millimeter) and worm-like, On the other hand, in deeper waters, in protected bays, so that the sand grains appear large to them, and have or behind reefs and barrier islands, mud bottoms pre- the capability to rapidly burrow: these are the relatively vail and the marsh communities and their flowering poorly known meiofauna (Higgins and Thiel, 1988) plants dominate the landscape. (Figure 3.10). Even bacterial numbers tend to be limited Finer sediments, sandy-silt to silty-clay mud, typi- in sand and gravel since their organic substrates are often cally have a very rich fauna, usually richer than a rock “washed out” (Table 3.1). or boulder surface, though probably not richer than a Sandy shores have a rather long profile in the energy coral reef. On a typical rocky shore, there are dozens of regime required to keep them sandy. In model con- common species of algae, barnacles, snails, and small struction there is little use in trying to sandwich a crustaceans in what appears to be an extremely rich
  • 68. 52 3. Substrate FIGURE 3.9 Two moderate-sized invertebrates from a sandy surf zone. The sand dig- ger (Neohaustorius) (D) and the clam Donax (A–C) are among the few macrofauna to adapt to the sandy surf zone. After Thurman and Webber (1984). (A–C) Copyright © 1984 by Scott, Foresman and Company. Reprinted by permission of Addison-Wesley Educational Publishers. (D) After Lippson and Lippson (1997), The Johns Hopkins University Press, drawing by Alice Jane Lippson.
  • 69. Sediments and Model Ecosystems 53 scattered around the world yielded figures from 722 to 30 000 individuals/m2, the mean number being 7400 individuals/m2 (Maurer et al., 1978). Some of the life habitats of these organisms are shown in Figure 3.12. The communities of such bottoms can also change radically with time and location over several miles. Sometimes they can be quite patchy even on a local scale (Figure 3.13). Functionally the same kinds of organisms occupy muddy bottoms in fresh waters. However, here the insects, particularly larval forms (Figure 3.14), almost absent from the marine environ- ment, become extremely abundant, while the domi- nant worms are oligochaetes (earthworm relatives) rather than polychaetes. Muddy bottoms are typically collection areas for FIGURE 3.10 Meiofauna (small invertebrates, less than 1 mil- large quantities of fine organic material from “pro- limeter and greater than 42 µm) in relation to fine sand grains. Three ducer ecosystems” such as coral reefs and rocky shores phyla are represented: (A) polychaete worm; (B) mollusk; (C) arthro- pod; (D) polychaete worm; (E) arthropod mite. After Thurman and to mud flats and lagoons, or from terrestrial sources Webber (1984). Copyright © 1984 by Scott, Foresman and Company. such as forests and fields to streams and lakes. This Reprinted by permission of HarperCollins Publishers. abundant food source gives rise to the rich diversity of species and feeding types that typically occupy the mud or sandy-mud bottom. In spite of the very active reworking of the mud by the infauna, or by fish, crabs, TABLE 3.1 Numbers of Bacteria in Sediments of and even diving birds seeking food, the abundant bac- Differing Grain Sizea terial activity on the organic particulates provides for Grain size Water content Bacteria strong oxygen utilization. Anaerobic conditions typi- (µm) (%) ( 10–3/g 1) cally exist close to the surface, and hydrogen sulfide production occurs within a few centimeters (Figure Sand 50–1000 33 22 3.15). This sediment chemistry is very different from Silt 5–50 56 78 that of most soils in the terrestrial environment and Clay 1–5 82 390 Colloidal sediment 1 98 1510 provides a strong control on the structure and function of the biological community. This leads in turn to a lim- a itation of the fauna to those animals that can reach the After Rheinheimer (1985). water/sediment interface or can pump oxygen-rich water through their tunnels. Some animals in this situ- ation have high levels of oxygen-carrying compounds in their bloodstreams or in a few cases have the capa- bility of surviving anaerobically, at least partially, through fermentation. In fresh waters (see Chapter 23), large numbers of submerged aquatic flowering plants tend to dominate over the algae on shallow sediment bottoms (Table 3.2). Although in proportion to terrestrial environments, few species of flowering plants occur in the sea (Figure 3.16), FIGURE 3.11 Generalized characteristics of sandy beaches and those that do occur can occupy very large areas of shal- of wave action on those beaches. After Kennett (1982). low, well-lighted bottoms. In the tropics, mangroves (aquatic trees) form very extensive swamps in muddy rocky intertidal and subtidal flora and fauna. On the marine or brackish intertidal zones (see Chapter 22). In other hand, in the very uniform and often vacant- colder waters, grasses and sedges develop broad wet appearing muds on the bottom of adjacent bays, hun- grasslands, or marshes, in the same habitat. dreds of species of worms, amphipods, and clams, to As we have reviewed above, fine sediment bottoms mention a few, are largely hidden beneath the surface. in the wild are typically very active and rich communi- An examination of numbers of macroinvertebrates ties that are important components of their ecosystems. occurring in the soft sediments of 13 estuaries and bays This flora and fauna should also be equivalently
  • 70. 54 3. Substrate important in mesocosms and aquaria. If enough light is organisms are able to work the rich organic load by present, algae and flowering plants (particularly in drawing in oxygenated water from above the mud. fresh water) are able to photosynthesize and to provide Traditionally, aquarium practice has been to avoid new production directly to grazers or to detritus in the the natural detrital processes and to keep the equiva- community. Algae derive most if not all of their nutri- lent bacteria in filters that to some extent act like a very ent supply directly from the water. Many of the higher reduced bottom community. However, in a filter the plants, however, extract their nutrient needs from the sediments (as on land). This provides an important link between buried organic materials and their nutri- ents and the overlying water. Equally important, the algae, and especially the flowering plants, act to trap and thereby increase sedimentation processes that are often needed in model ecosystems. In general, this is an extremely important issue for the aquatic restorer. A good example are the processes that are leading to the loss of wetlands in the Mississippi delta. With levees transporting fresh water directly to the Gulf of Mexico and cut channels bringing salt water into the fresh/brackish marshes, the extensive silt-trapping submerged and emerged aquatic plant marshes are disappearing making the entire region vulnerable to destruction by hurricanes. As we have noted, whether shallow or deeper, fine sediment bottoms are generally receivers of abundant organic detritus, plant fragments, dead animals and animal parts, and animal feces (Figure 3.17). Much of this “waste” organic material tends to be infractile to higher animals. On the other hand, it is easily utilized and fully broken down to carbon dioxide, water nutri- ents, and minerals by a host of bacteria. Most of the bac- teria are, in turn, utilizable as food by many inhabitants of the sediment bottom, particularly clams, worms, and insect larvae. Even though the sediment tends to be anaerobic at or immediately below the surface, many FIGURE 3.12 Selected infauna from muddy marine bottoms. (A) left to right Macoma clam, cockle, polychaete worm, Mya (soft shell clam), polychaete worm, and snails; (B) Arenicola, a polychaete worm – the food is organic particulates in the sediments, water moved through is used to receive oxygen; (C) Chaetopterus polychaete worm – a feeder on detritus particles suspended in the water column; (D) Amphitrite, a polychaete worm that feeds on surface deposits of organic particulates. After Thurman and Webber (1984). Copyright © 1984 by Scott, Foresman and Company. Reprinted by permission of HarperCollins Publishers.
  • 71. Sediments and Model Ecosystems FIGURE 3.13 Results of the analysis of the soft bottom macroinvertebrate (greater than 1 µm) communities from Delaware Bay in two successive years (1972; 1973). Although most of the same species occur in the 2 years, none of the “community” groupings is obviously the same. This analysis includes 169 species: 40.8% annelid worms; 28.9% arthropods; 17.8% molluscs; 7.1% bryozoans; and 5.4% miscellaneous phyla. By feeding types the species could be grouped as 45% deposit feeders; 24.8% suspension feeders; 18.3% carnivores; 10.7% omnivores; and 2.2% miscellaneous. After Maurer et al. (1978). 55
  • 72. 56 3. Substrate FIGURE 3.14 Life cycle and predators of mayflies. The flying stage is reproductive only and lasts for quite a short time. The larval stages of many species are burrowers in soft sedi- ments of lakes, ponds, and streams. After Burgis and Morris (1987). FIGURE 3.15 Distribution with depth of oxygen and hydrogen sulfide in a muddy bottom. This profile typically occurs over a few to at most a few tens of centimeters from the mud/water surface. After Levinton (1982). Reprinted by permission of Prentice Hall, Englewood Cliffs, New Jersey.
  • 73. TABLE 3.2 Plants Dominating Sediment Bottoms in Temperate Lakes and Their Patterns of Change with Time (Succession)a The English (Cumbrian) lakes Trout Lake (Wisconsin) Successions in deep water Successions in shallow water Exposed to slight waves; Severe wave Very fine, rich, Stony and sandy Fine inorganic Sheltered silted and action; rather inorganic silted Increase in substrates poor in soils with Largely organic soils rich in sandy soils coarse gravelly Soil substrates with fineness and basic silts, and continued Increase in soils with silt and with some and sandy type little organic matter richness of silt eventually organic silting organic content sparse silting organic sediment organic sediment substrates Najas (Nitella) Isoetes Littorella Lobelia Ceratophyllum Linear-leaved Potamogeton spp. Submerged linear- Potamogeton (Nitella) Potamogeton Myriophyllum Funcus Overall line succession and decrease in leaved association pusillus bulbosus (especially var. Potamogeton spp.) fluitans Myriophyllum– (Chara)– Potamogeton– Najas– (Nitella) Potamogeton Potamogeton Potamogeton Potamogeton Funcus (Chara)– obtusifolius praelongus perfoliatus bulbosus Najas– var. Vallisneria depth of water fluitans Sparganium Potamogeton Nymphaea Potamogeton Nymphaea– Elodea– minimum alpinus or Nuphar natans Potamogeton– Najas– Sagittaria Potamogeton Isoetes– Funcus– Lobelia Nymphaea Potamogeton Typha Schoenoplectus– Carex Sagittaria– Eleocharis– and natans Phragmites or Sparganium– Equisetum– Nuphar Equistum Typha Schoenoplectus Barren a In all the above successions, only the dominant(s) of each community is indicated. Algal dominants are enclosed in brackets. After Sculthorpe (1985).
  • 74. 58 3. Substrate 5 mm FIGURE 3.16 Characteristic marine flowering plants from muddy sand and muddy bottoms: (A) the tropical Thalassia testudinum (turtle grass), a dominant of many reef lagoons; (B) the cold-water Northern Hemisphere Zostera marina (eel- grass). Note that neither species is a true grass. After Dawes (1981). Reprinted by permission of John Wiley & Sons, Inc. variety and capability of the bacteria are limited. Few pathway for recycling nitrogen and phosphorus. or no animals are present to eat the bacteria and, in Another pathway is through the root hairs, rhizomes, turn, fish and larger invertebrates do not have a rich, and up into the leaves of higher plants, to be eaten by smaller invertebrate bottom on which to browse. Thus, fish or snails or become more detritus. Some nitrogen aquarium procedures in the past have tended to short- in the anaerobic sediments is denitrified to a gaseous circuit the natural cycling processes. This results in loss form and lost to the atmosphere. of valuable energy to the many larger members of the As long as the sediment surface is aerobic, phospho- community. Microcosms, mesocosms, and aquaria that rus tends to remain locked in the sediments, since iron by design do not have a fine sediment community oxides under these conditions link up with and trap should have a separate sediment trap that periodically phosphorus. When, because of excess organic material, can be partially drained of sediment. Particularly if a the normally subsurface zero-oxygen levels extend system needs to be driven faster than normal for scal- into the water column, producing dead zones, stored ing reasons, or if import and export are desired because phosphorus tends to be released. Sulfur also is utilized of the size and coverage of the model ecosystem, by bacteria and becomes the very odiferous hydrogen organic sediments can be used as an export tool. sulfide that one associates with anaerobic conditions. In the wild, nutrients are exchanged between sedi- In nutrient-poor lakes, phosphorus tends to become ments and the water column in a variety of pathways. the limiting nutrient because it is locked in sediments Detritus to bacteria to worms to fish is an important by high oxygen levels. In richer lakes and estuaries
  • 75. Geological Storage 59 FIGURE 3.17 Generalized feeding patterns in a typical shallow-water, soft-bottom community. with large amounts of sediment in contact with the 26, we discuss large-scale, photosynthetic procedures water, phosphorus tends to be released in abundance for solving these problems, combining nutrient removal and is responsible for algal blooms if nitrogen is avail- with oxygen injection. able. In the open ocean where fine organic sediments are deep and to a large extent out of reach of the shal- low water column, nitrogen and phosphorus tend to be closer in importance with the final limitation usually GEOLOGICAL STORAGE belonging to nitrogen. For the restorer of degraded lakes and estuaries, this Bioturbation (or bottom disturbance) by animals and is frequently the first and foremost issue to be the rooting and shooting activities of flowering plants in addressed. Once human eutrophication has allowed shallow water are processes that continuously return the spring planktonic algal blooms to increase bottom energy and chemical elements of organic sediment to the organic biomass and bring the anaerobic zone up to the water column. However, in many cases sedimentation is sediment surface and into the water column during the rapid enough to bury organic materials out of reach of summer, previously stored phosphorus is released living processes for geological time. This could be thou- causing a further cascade of degradation. Simply cut- sands of years for lakes or fresh-water environments or ting off the nutrient supply will no longer work in millions of years for marine situations. On the Earth, a these cases, and radical methods such as chemical pre- significant part of the plant primary production that has cipitation or sediment dredging are extremely expen- occurred in the past 500 million years has been stored as sive and sometimes prevent full restoration. In Chapter coal, oil, gas, and oil shales.
  • 76. 60 3. Substrate Limestone production likewise is indirectly related destroyed by increased run-off, with heavy sediment to the photosynthetic process. As we shall discuss fur- loadings, related to logging and shore development. If ther in Chapter 8, virtually all carbon on the Earth’s this is past activity, and significant sedimentation is no surface and in its crust has been cycled through organ- longer present, then transplantation of a new commu- isms, yet it has been estimated that greater than 1600 nity of reef organisms from a viable host reef is proba- times as much organic carbon is buried in the Earth’s bly appropriate (Precht, 2006). If moderate run-off is crust as exists in the biosphere proper. Most of this still occurring, then it is possible that the ATS system buried carbon was derived from the process of photo- described in Chapter 25 can assist in ameliorating the synthesis and was removed, as carbon dioxide, from effects. Heavy sedimentation will have to be blocked by the atmosphere. Photosynthesis, in the first few billion physical settling ponds or lagoons or any restoration years of Earth’s history, also resulted in the evolution efforts on coral reefs are likely to be unsuccessful. of oxygen into the atmosphere. During the past century, most human management of the Earth’s organic resources (historically including References sewage treatment and aquarium management) is Burgis, M. and Morris, P. (1987) The Natural History of Lakes. philosophically based on rapid recycling of readily Cambridge University Press, Cambridge. available raw materials (nutrients). In more recent pre- Davis, H. (1983) Depositional Systems: A Genetic Approach to Sedimentary Geology. Prentice Hall, Englewood Cliffs, New Jersey. human history of the Earth’s biosphere, organic stor- Dawes, C. (1981) Marine Botany. Wiley Inter-Science, New York. age and great limitation of available nutrients has been Gross, M. G. (1982) Oceanography: A View of the Earth. Prentice Hall, the rule. This is undoubtedly a major factor providing Englewood Cliffs, New Jersey. long-term stability to our biosphere. Likewise in mod- Higgins, H. and Thiel, H. (1988) Introduction to the Study of the ern organic waste management, it is important to keep Meiofauna. Smithsonian Institution Press, Washington, DC. nutrients locked in biomass, either active or stored. Kennett, J. (1982) Marine Geology. Prentice Hall, Englewood Cliffs, New Jersey. In addition to algal turf scrubbing (or other plant Kleypas, J., Buddemeier, R., Archer, D., Gattuso, J.-P., Langdon, C. removal) to simulate model communities characterized and Opdyke, B. (1999) Geochemical consequences of increased by organic sediment burial, a storing or exporting sedi- carbon dioxide on coral reefs. Science 284: 118–120. ment trap is necessary. There are many ways to do this, Levinton, J. (1982) Marine Ecology. Prentice Hall, Englewood Cliffs, and several units are described in Chapters 20–26. New Jersey. Lippson, A. J. and Lippson, R. L. (1997) Life in the Chesapeake Bay, 2nd Sometimes, when export, in the time frame of the model edn. Johns Hopkins University Press, Baltimore. planned, is not desired, and bottom disturbance is not Lowe, D. R. (1994) Early environments, constraints and opportuni- excessive, the basin of the tank itself becomes the sedi- ties for early evolution. In: Early Life on Earth. S. Bengtson (Ed.) mentation trap and organic storage facility. Separate set- Columbia University Press, New York. Marshak, S. (2004) Essentials of Geology. Norton and Company, tling traps, within the model plumbing, with tap-off New York. valves, can also be used as refugia (Chapter 12). Maurer, D., Watling, L., Kinner, P., Leethem, W., and Wethe, C. (1978) Benthic invertebrate assemblages of Delaware Bay. Marine Biol. 45: 65–78. Aquatic Ecosystem Restoration and Parker, R. (1967) Data of Geochemistry, 6th edn. USGS Prof. Paper Sedimentation 440-D. Precht, R. (2006) Restoration of Coral Reef Ecosystems. Coral Reef In several subsections in this chapter, we have noted Restoration Handbook Taylor and Francis, CRC, Boca Raton. the relationship of anthropogenic sedimentation, both Redfern, R. (2001) Origins: The Evolution of Continents, Oceans and Life. increased and decreased on the health of wild ecosys- University of Oklahoma Press, Norman. tems needing restoration. In general, ecosystems domi- Rheinheimer, G. (1985). Aquatic Microbiology, 3rd edn. Wiley, New York. nated by submerged aquatic vegetation (SAV) tend to Salbu, B. and Steinnes, E. (1994) Trace Elements in Natural Waters. CRC be damaged by excessive siltation from land develop- Press Boca Raton, FL. ment and farming and ecosystems dominated by emer- Sculthorpe, C. (1985) The Biology of Vascular Plants. 1985 reprint of gent aquatic vegetation (EAV) tend to be damaged by 1967 edn. Koeltz Scientific Books, Konigstein. the removal of periodic sedimentation (see also Chapter Thurman, H. and Webber, H. (1984) Marine Biology. Merrill Publishing, Columbus, Ohio. 14). However, other aquatic ecosystems can also be van Andel, T. (1985) New Views of an Old Planet. Cambridge highly sensitive to sedimentation processes. Among the University Press, Cambridge. most important of these are coral reefs. Frequently these van Dover, C.-L. (2000) The Ecology of Deep-Sea Hydrothermal Vents. tropical systems have been damaged or virtually Princeton University Press, Princeton, NJ.
  • 77. C H A P T E R 4 Water Composition Management of Salinity, Hardness, and Evaporation Virtually, all chemical elements dissolve in water. overall course of organic evolution, cell walls developed Many are rare in natural waters and of little conse- very early, perhaps 3.5 billion years ago, perhaps in a quence; most of the more common elements occur in pre-life chemical process; they would have provided an ionic form and often in element combinations. Some efficiency advantage to many organic processes that elements are fairly common in many natural waters previously had to compete in the larger oceanic soup. and sea water has a suite of elements that are largely Likewise, the first closure of vascular or blood systems, fixed in their percentage composition. Many chemical some 1 billion years ago, took the previously open sea elements occur in aquatic organisms; some are essen- water that used to carry food and oxygen to each cell tial to organism function and are highly concentrated and isolated it, as a transporting medium, in blood ves- over their concentration in the ambient water. Those sels and body cavities. This isolating device provided that are concentrated more than about 104 times can be more control and allowed the development of larger limiting for the growth of organisms; however, when organisms. However, to obtain oxygen from water, these elements greatly exceed normal concentrations in gills, devices basically arranged to bring water in as ambient water, they can also lead to the disruption of close a contact as possible to the flowing blood, had to community structure and function. These latter ele- be developed. ments are called nutrients (mostly nitrogen, N; phos- Even more recently, in a geologic sense, perhaps 400 phorus, P; iron, Fe; and silicon, Si); they require special million years ago, fish entering fresh waters for the first attention and we treat them in greater detail in Chapter time evolved kidney glomeruli. Once the salt balance 9. The conservative elements provide those salts that between inside and outside changed, these were neces- change little in abundance except for freshwater dilu- sary to constantly pump out the fresh water that now tion. Here we also cover the micronutrients and the continuously flowed into the blood through the gills relationship of all chemical elements of the hydros- (Evans, 1993). These bony (teleost) fish then returned phere and the Earth’s crust. In our view, “natural to the sea, millions of years later, having evolved to a waters” significantly unaffected by human activity lower level of salts in the blood. Then, for the marine have virtually ceased to exist, and in this chapter we teleost, the problem changed to a need to continually introduce the more important nonnutrient additions of drink water and excrete salt. Gills and bladders also industrial and agricultural societies. became involved in this need for osmotic balance The chemistry of the aqueous medium or hydros- (Jobling, 1995). While kidneys have gradually evolved phere as a whole is highly variable over the face of the to become much more complex and varied structures, Earth. Even the ocean, the most constant of waters, the problem of sensitivity to the aqueous medium varies considerably in some aspects of its chemical remains. Many algae and small invertebrate animals, composition as coasts and rivers are approached. At being essentially isotonic (same internal salinity) with the same time, aquatic organisms are much less chemi- sea water, remain extremely sensitive to changes in cally removed from the water medium than their ter- the chemical composition of water. Others, such as restrial counterparts are from the atmosphere. In the anadromous fish, can move salts or water in or out as 61
  • 78. 62 4. Water Composition required, and thus have adapted to manage enormous ameliorate the effects of human pollutants on the natu- changes in salinity. Yet, they remain quite sensitive to ral environment, an understanding of the basic nature acidity changes and it is unfortunate that one of the more of the chemical composition of water and its effects on routine human additions to the atmosphere, industrial organisms is essential. stack emissions that result in acid rain, has devastated In the pages that follow we will provide a basic fish populations in the streams and lakes of thousands understanding of that water chemistry and present a of square miles of Scandinavia and northeastern North rationale for dealing with human pollutants (the macro America. nutrients are treated separately in Chapter 9). In addition, human additions of heavy metals, espe- cially Mercury, into the aqueous environment has resulted in government warnings about the edibility of WATER STRUCTURE AND fish such as tuna. Also, pesticides, herbicides, antifoul- CHARACTERISTICS ing agents (tributyltin), industrial chemicals (PCBs, for example), and hormones have had significant effects Water is a most extraordinary compound. Because on flora and fauna. These effects extend to the open of its unusual molecular structure (Figure 4.1), it has ocean, and it has been widely documented that PCBs a number of unexpected chemical characteristics that and dichlorodiphenyltrichloroethane (DDT) occur in are generally favorable to life on Earth (Table 4.1). penguins, whales, and polar bears at the northernmost Its change of density with temperature (most dense at and southernmost reaches of the sea. These matters 3.98°C) is crucial for freshwater ecosystems to function we discuss further below. In the establishment and in cold climates. If it were a more normal chemical operation of model ecosystems, and in any attempt to compound, more dense below zero, all but the largest FIGURE 4.1 Molecular structure of water at different temperatures and in different states. Liquid water is a “semisolid” because of the asym- metric and charged nature of the molecule. It is this “mixed” state that gives rise to most of its “miraculous” qualities (see Table 4.1). (A) After Thurman and Webber (1984). Copyright © 1984 by Scott, Foresman and Company. Reprinted by permission of HarperCollins Publishers. (B) Pauling’s self-clathrate water model. (C) Frank and Wen’s flickering clusters model. B and C after Horne (1969). Reprinted by permission of John Wiley & Sons, Inc.
  • 79. Ocean Salinity 63 bodies of water in colder climates would freeze to the (Na at 30.61%) and chlorine (Cl at 55.04%) make up bottom, and only the surface would melt in summer. over 85% of this salt, and only four additional elements, Even more important to life as we know it is the dis- 2 sulfur as sulfate (SO4 at 2.71%), magnesium (Mg2 at solving power of water. Allowing virtually every natu- 2 3.69%), calcium (Ca at 1.16%), and potassium (K at rally occurring element and most compounds into its 1.10%), bring the composition to over 99%. As we dis- semi-open liquid structure, in the natural environment cussed in Chapter 3, the residence time of an element in water becomes the universal soup in which a very large sea water (between river delivery and sedimentation number of chemical interactions become possible. The removal) determines the ultimate concentration in sea clusters or “spheres of hydration” shown in Figure 4.1 water. When sea water is diluted by rivers and streams, also form around many ions and minerals and organic along an ocean coast, the proportional chemical compo- aggregates providing for most of the extraordinary sition remains essentially unchanged, though the total characteristics. quantity of salts drops with dilution. Evaporation, pre- cipitation, and river supply certainly affect sea-water salt composition, and for that reason the surface waters OCEAN SALINITY of the major oceans and seas can vary slightly in salinity. Also, variation can occur on a geologic time scale. For The salinity of the open oceans has a rather uniform example, it is known that epicontinental or enclosed chemical composition in both time and space (Tables 4.2 seas have often dried up, leaving large salt beds. In the and 4.3) that ranges from about 34 to 37 parts per thou- case of the Mediterranean in the late Miocene epoch, 5–6 sand (ppt) or 3.4% to 3.7% by weight. In the chemist’s million years ago, repeated isolation and complete evap- language, this is 34 000–37 000 mg/liter (ppm). Sodium oration probably also affected salt composition of the TABLE 4.1 Unusual Physical Properties of Water and Their Importance in Biological/Ecological Systemsa Property Comparison with other substances Importance in physical/biological environment Heat capacity Highest of all solids and liquids except liquid Prevents extreme ranges in temperature NH3 Heat transfer by water movements is very large Tends to maintain uniform body temperature Latent heat of fusion Highest except NH3 Thermostatic effect at freezing point owing to absorption or release of latent heat Latent heat of evaporation Highest of all substances Large latent heat of evaporation extremely important in heat and water transfer of atmosphere Thermal expansion Temperature of maximum density decreases with Fresh water and dilute sea water have their maximum increasing salinity. For pure water it is at 4°C density at temperatures above the freezing point. This property plays an important part in controlling temperature distribution and vertical circulation in lakes Surface tension Highest of all liquids Important in physiology of the cell Controls certain surface phenomena and drop formation and behavior Dissolving power In general dissolves more substances and in Obvious implications in both physical and greater quantities than any other liquid biological phenomena Dielectric constant Pure water has the highest of all liquids Of utmost importance in behavior of inorganic dissolved substances because of resulting high dissociation Electrolytic dissociation Very small A neutral substance, yet contains both H and OH ions Transparency Relatively great Absorption of radiant energy is large in infrared and ultraviolet. In visible portion of energy spectrum there is relatively little selective absorption, hence is “colorless.” Characteristic absorption important in physical and biological phenomena Conduction of heat Highest of all liquids Although important on small scale, as in living cells, the molecular processes are far outweighed by eddy conduction a From Sverdrup et al. (1942). Reprinted by permission of Prentice Hall, Englewood Cliffs, New Jersey.
  • 80. 64 4. Water Composition TABLE 4.2 Elements Present in Sea Watera (at greater than 6.10 6 mg-atoms/liter) Element mg/kgb Cl 19.00 0/00 mg-atoms/liter Cl 19.00 0/00 Atomic weight (1940) 1/atomic weight Chlorine 18980 548.30 35.457 0.02820 Sodium 10561 470.15 22.997 0.04348 Magnesium 1272 53.57 24.32 0.04112 Sulfur 884 28.24 32.06 0.03119 Calcium 400 10.24 40.08 0.02495 Potassium 380 9.96 39.096 0.02558 Bromine 65 0.83 79.916 0.01251 Carbon 28 2.34 12.01 0.08326 Strontium 13 0.15 87.63 0.01141 Boron 4.6 0.43 10.82 0.09242 Silicon 0.02–4.0 0.0007–0.14 28.06 0.03564 Fluorine 1.4 0.07 19.00 0.05263 Nitrogen (ionic) 0.01–0.7 0.001–0.05 14.008 0.07139 Aluminum 0.5 0.02 26.97 0.03708 Rubidium 0.2 0.002 85.48 0.01170 Lithium 0.1 0.014 6.940 0.14409 Phosphorus 0.001–0.10 0.00003–0.003 30.98 0.03228 Barium 0.05 0.0004 137.36 0.00728 Iodine 0.05 0.0004 126.92 0.00788 Arsenic 0.01–0.02 0.00015–0.000 74.91 0.01335 Iron 0.002–0.02 0.00003–0.000 55.85 0.01791 Manganese 0.001–0.01 0.00002–0.000 54.93 0.01820 Copper 0.001–0.01 0.00002–0.000 63.57 0.01573 Zinc 0.005 0.00008 65.38 0.01530 Lead 0.004 0.00002 207.21 0.00483 Selenium 0.004 0.00005 78.96 0.01266 Cesium 0.002 0.00002 132.91 0.00752 Uranium 0.0015 0.00001 238.07 0.00420 Molybdenum 0.0005 0.000005 95.95 0.01042 Thorium 0.0005 0.000002 232.12 0.00431 Cesium 0.0004 0.000003 140.13 0.00714 Silver 0.0003 0.000003 107.880 0.00927 Vanadium 0.0003 0.000006 50.95 0.01963 Lanthanum 0.0003 0.000002 138.92 0.00720 Yttrium 0.0003 0.000003 88.92 0.00125 Nickel 0.0001 0.000002 58.69 0.01704 Scandium 0.00004 0.0000009 45.10 0.02217 Mercury 0.00003 0.00000001 200.61 0.00498 Gold 0.000006 0.00000002 197.2 0.00507 10 Radium 0.2 3 10 0.8 12 10 13 226.02 0.00442 a Virtually all the gases of the atmosphere are also present, and together these provide a wide variety of organic and inorganic chemical compounds. Adapted from Sverdrup et al. (1942). Reprinted by permission of Prentice Hall, Englewood Cliffs, New Jersey. b The salinity for which these element concentrations are tabulated is 34.3 ppt. Each value should be multiplied by 1.043 to obtain an equivalent to a salinity of 35.8 ppt, a level more appropriate for coral reef systems. world’s oceans by several parts per thousand. (This in algae. The concentration of other mostly very minor ele- turn may have affected world climate by increasing sea ments can also be affected by chemical reactions, espe- ice formation because of general lowered salinities.) cially in sediments. Sea water near sea floor spreading Marine chemists have traditionally separated the zones where there is active interchange between hot, chemical elements dissolved in sea water into conserva- forming ocean crust and sea water can be locally altered tive and nutrient categories. The conservative elements (van Dover, 2000). are relatively abundant in sea water, particularly in pro- Table 4.4 shows the relationship between the princi- portion to their requirements by organisms. The nutrient- pal elements in oceanic phytoplankton (excluding car- type elements are relatively low in concentration in sea bon, hydrogen, and oxygen) and the mean sea-water water and are needed in proportionally large quantities concentrations of those elements. Clearly, limiting sta- by organisms, particularly phytoplankters and other tus is conferred both by the functional requirements of
  • 81. Ocean Salinity 65 TABLE 4.3 Ionic Composition of Sea Watera (at greater than 10 12 M) Element Chemical species Molar µg/liter (ppb) H H2O 55 1.1 108 9 He He (gas) 1.7 10 6.8 10 3 5 Li Li 2.6 10 180 4 B B(OH)3, B(OH)4 4.1 10 4440 C HCO3 , CO2 , CO2 3 2.3 10 3 2.8 104 2 N N2, NO3 , NO2 , NH4 1.07 10 1.5 105 O H2O, O2 55 8.8 108 5 F F , MgF 6.8 10 1.3 103 9 Ne Ne (gas) 7 10 1.2 10 1 1 Na Na 4.68 10 10.77 106 Mg Mg2 5.32 10 2 12.9 105 8 Al Al(OH) 4 7.4 10 2 5 Si Si(OH)4 7.1 10 2 106 P HPO2 , PO3 , H2PO4 4 4 2 10 6 60 S SO2 , NaSO 4 4 2.82 10 2 9.05 105 1 Cl Cl 5.46 10 18.8 106 7 Ar Ar (gas) 1.1 10 4.3 2 K K 1.02 10 3.8 105 Ca Ca2 1.02 10 2 4.12 105 8 Ti Ti(OH)4 2 10 1 V H2VO 4, HVO 2 4 5 10 8 2.5 Cr Cr(OH)3, CRO2 4 5.7 10 9 0.3 9 Mn Mn2 , MnCl 3.6 10 0.2 8 Fe Fe(OH) 2, Fe(OH) 4 3.5 10 2 Ni Ni2 2.8 10 8 1.7 9 Cu CuCO3, CuOH 8 10 0.5 Zn ZnOH , Zn2 , ZnCO3 7.6 10 8 4.9 As HAsO2 , H2AsO 4 4 5 10 8 3.7 Se SeO2 3 2.5 10 9 0.2 4 Br Br 8.4 10 6.7 104 9 Kr Kr (gas) 2.4 10 0.2 6 Rb Rb 1.4 10 120 Sr Sr2 9.1 10 5 8 104 Mo MoO2 4 1 10 7 10 9 Cd CdC12 1 10 0.1 9 Sb Sb(OH) 6 2 10 0.24 Te HTeO3 7 I IO 3, I 5 10 60 10 2 Xe Xe (gas) 3.8 10 5 10 9 Cs Cs 3 10 0.4 Ba Ba2 1.5 10 7 2 U UO2(CO3)4 2 1.4 10 8 3.2 a From Spotte (1979). Reprinted by permission of John Wiley & Sons, Inc. the phytoplankton and by the abundance of the Nitrogen, phosphorus, and iron are the classic limit- element in sea water. Sodium and chlorine have ing nutrients. Nitrogen and phosphorus (also the prin- higher concentrations in plankton than any other ele- cipal eutrophication nutrients) we treat in depth in ment except carbon, nitrogen, and oxygen. However, Chapter 9. Iron requires special mention, not because it because of the high concentration of these elements is likely to be either limiting or superabundant in in sea water, neither can ever be limiting. Silica, on the microcosms and mesocosms, but because it has been other hand, is moderately abundant in sea water. Yet, suggested that it is limiting for photosynthesis, far its great requirement by diatoms for their cell walls, from shore in the large southern ocean; some scientists when they explode in spring blooms, results in frequent have suggested that it might be possible to counter limitations. global warming by introducing iron into the southern
  • 82. 66 4. Water Composition TABLE 4.4 Relative Abundances of Elements in Marine Phytoplankters and in Sea Watera Concentration in Concentration in phytoplankton sea water Concentration (wt./100 g) (wt./m3) factor SW/Plankton 1.6.105 N u t r i e n t Nitrogen (N) 5g 300 mg 0.06* Phosphorus (P) 0.6 g 30 mg 2.105 0.05* Silica (Si) (diatoms) 10 g 500 mg 2.105 0.05* Iron (Fe) (other than diatoms) 1g 500 mg 2.105 0.05* Vanadium (V) 3 mg 0.3 1.105 0.1 Silica (other than diatoms) 0.5 g 500 mg 1.104 1.0 Carbon (C) 30 g 28 g 1.07.104 1.0 Iron (diatoms) 40 mg 50 mg 0.8.104 1.3 5.103 — — Copper (Cu) 5 mg 10 mg 2 Cobalt (Co) 0.05 mg 0.1 mg 5.103 2 Manganese (Mn) 2 mg 5 mg 4.103 2.5 Zinc (Zn) 20 mg 5 mg 40.108 4 C o n s e r v a t i v e Aluminum (Al) 1 mg 120 mg 83 120 Magnesium (Mg) 0.4 g 1.3 kg 3.07 300 Potassium (K) 1g 390 g 25.8 390 Calcium (Ca) 0.5 g 416 12.02 830 Sulfur (S) 1g 900 g 11.1 900 Fluorine (F) 1g 1.4 g 7.15 1400 Boron (Bo) 2 mg 5g 4 2500 Sodium (Na) 3g 10.75 2.8 3600 Chlorine (Cl) 4g 19.3 kg 2.07 4800 Bromium (Br) 2.5 66 g 0.37 26 000 (Rejected) * Frequent limitations a Modified after Millero and Sohn (1992). ocean. This we discuss in more depth later in this chap- outer ring of the atom, thereby dictating basic chemical ter. Even the elements most frequently limiting pri- reactivity. The elements in each column have a chemi- mary production by algae, nitrogen, and phosphorus are cal similarity, but the atoms are progressively heavier not limiting in very low-nutrient coral reef environments. and larger lower in the table. Thus, cadmium (Cd) and In most reefs, strong current flow from the open ocean mercury (Hg) chemically react like zinc (a minor nutri- constantly brings a new supply of low-concentration ent) but being larger atoms are likely to replace zinc in nutrients. Many algae are quite capable of obtaining an organic molecule but then twist the molecule out of those nutrients even at very low concentrations; this is shape. Thus, the general toxicity of these elements. so as long as there is abundant physical energy (current Likewise, arsenic (As) below phosphorus and nitrogen and wave action) that prevents microzones of low con- is a general biotic poison. centration against cell walls, where there is an active Most important for the modeler, who is typically uptake gradient. In addition to carbon, nitrogen, and working with a relatively limited volume of water, any phosphorus (and of course hydrogen and oxygen as element present in organisms could theoretically be water and ions), another six elements (sodium, potas- limiting and thereby function as a nutrient-type ele- sium, calcium, magnesium, sulfur, and chlorine) are ment. For example, in the operating of coral reef envi- essential to all life. Ten other elements, including iron, ronments in aquaria or mesocosms, due to potentially manganese, silica, copper, zinc, and boron, are required high calcification rates in those systems, calcium can by most organisms and another ten by a few organisms. enter “geological” storage. Even though it is returned Figure 4.2 shows diagrammatically the relationship from geological storage by boring organisms net calci- between the chemical elements, in the standard frame- fication rates can be very high, resulting in depletion in work of the periodic table, and their function in living the water column. In some reef systems, we have also organisms (see also Frausto da Silva and Williams, 1991). seen reductions in strontium and potassium, though Here, it is possible to see the role that some toxic ele- those reductions in concentration were probably not ments play in the basic chemistry of life. Each column of concern. However, any element on the upper two- in the table signifies the number of electrons in the thirds of the list in Table 4.4 could be a problem at
  • 83. Hardness of Fresh Waters 67 FIGURE 4.2 The chemical elements of living organisms and their primary function in relation to the periodic table of the elements. Modified from Frausto da Silva and Williams (1991). model scale and should at least be occasionally moni- above 0.2 ppt, barring human effects or the localized tored. The primary nutrients, including nitrogen, phos- leaching of salt beds. The River Jordan reaching 7.7 ppt phorus, silica, carbon, and calcium, we treat in depth in is an example of salt bed leaching and evaporation later chapters. In practice, in any model system in effects. which import and export of organics is similar to that in The ionic composition of fresh waters, even those of the wild analog and, in the case of salt- or hard-water far less extreme characteristics, can have significant systems, it is necessary to maintain a minimal water effects on biota. Hutchinson and Edmonson (1993) offer exchange to prevent salt drift. Chemical elements can numerous examples of control or rejection of some be lost to the atmosphere, as anyone who has operated species because of water composition. In the modeling salt-water systems in a greenhouse can attest. of freshwater systems, basic considerations of design, in Fresh waters, on the other hand, vary widely in most cases, will include salinity or hardness. salinity (generally called hardness) from those of virtu- ally pure water to very high levels for lakes with no outflow, that is, endorheic lakes (Table 4.5). The Dead HARDNESS OF FRESH WATERS Sea (226 ppt) and the North American Great Salt Lake (203 ppt) have salinities far above that of the ocean and Water hardness is handled a little differently from chemical compositions that vary considerably from salinity in that in some countries the degree is the unit those in the ocean. On the average, rainwater has a of measure. One German degree of hardness equals salinity of about 0.008 ppt and is slightly enriched in 10 mg/liter (ppm) of calcium and magnesium oxide or calcium and sulfate, though near sea coasts a consider- 17.8 ppm of CaCO3 in the USA. This is not at all equiv- able increase in chlorine can be found (Hutchinson, alent to salinity in that a relatively low salinity water 1957). River waters average 0.1–0.16 ppt, though those rich in calcium and magnesium could have a relatively draining predominantly igneous rock areas are high degree of hardness. On the other hand, a fresh water typically below 0.05 ppt. Rivers usually do not extend rich in sodium chloride alone could have a very low
  • 84. 68 4. Water Composition TABLE 4.5 Chemical Composition of Selected Lakes Dominated by Different Anions (%)a Na K Mg Ca CO3 SO4 Cl SiO2 (AlFe)2O3 Salinity (mg/kg) Chloride waters Bear River Upper, Wyoming 4.49 6.86 23.69 52.68 5.76 2.68 3.84 – 185 Lower, Utah 20.54 4.76 10.12 21.53 8.16 32.36 – 2.53 637 Great Salt Lake, Utah 33.17 1.66 2.76 0.17 0.09 6.68 55.48 – – 203 490 Jordan at Jericho 18.11 1.14 4.88 10.67 13.11 7.22 41.47 1.95 1.45 7700 Dead Sea 11.14 2.42 13.62 4.37 Trace 0.28 66.37b Trace – 226 000 Sulfate waters Montreal Lake, Saskatchewan 4.9 2.3 10.8 16.8 56.5 1.8 2.5 3.9 0.5 150.5 Redberry Lake, Saskatchewan 12.0 0.85 12.3 0.56 2.58 70.5 1.1 0.03 0.07 12 898 Little Manitou Lake 16.8 1.0 10.9 0.48 0.47 48.4 21.8 0.019 0.21 106 851 Carbonate waters Silvies River, Oregon 10.42 2.45 3.13 12.88 34.76 7.35 2.88 25.13 0.08 163 Malheur Lake, Oregon 24.17 5.58 4.13 5.58 44.63 7.64 4.55 2.89 Trace 484 Pelican Lake, Oregon 29.25 3.58 2.62 2.27 30.87 22.09 7.97 1.21 0.02 1983 Bluejoint Lake, Oregon 37.70 2.62 0.63 0.53 38.68 5.67 13.85 0.55 0.02 3640 Moses Lake, Washington 19.86 7.25 8.41 51.56 2.87 3.88 5.06 1.11 2966 a After Hutchinson (1957). Reprinted by permission of John Wiley & Sons, Inc. b And 1.78% Br. TABLE 4.6 Hardness Scales for Fresh Watersa of the standard hardness test kit. If one is creating a synthetic system, the best manuals describing standard dGH dKH pH aquaria fish usually provide optimum numbers for each GH total hardness (dGH German total hardness) KH carbonate hardness (dKH German carbonate hardness) species. Many fish species can adapt to a wide range of PH permanent hardness hardness, particularly if it is changed gradually. Gener- Carbonate hardness based on bicarbonate is not permanent because ally, with freshwater systems, as long as evaporation is the CO2 can be driven off by boiling. The remaining calcium and not excessive and the hardness of the replacement magnesium by definition determines permanent hardness. water is not too high, occasional small volume changes Total hardness can be illustrated as follows: Degrees of hardness (1 gallon a week for a 70-gallon system) are sufficient to 0–4° dGH very soft 12–18° dGH fairly hard prevent salt buildup and the effective development of 4–8° dGH soft 18–30° dGH hard an endorheic or salt lake in the aquarium or mesocosm 8–12° dGH medium hard over 30° dGH very hard environment. As discussed below, algal scrubbers tend One degree of hardness 10 mg/liter of CaO or MgO to adjust disproportionate elements as long as the system is not allowed to become too unbalanced. The a Partly after Riehl and Baensch (1987). difficulties arise in fresh- or salt-water microcosms or aquaria when the fresh water being used to replace evaporated water is excessive in certain ions, typically hardness. Nevertheless, the mean river of Hutchinson those of the elements calcium, iron, sulfur, or magne- (1957) with a salinity of 0.13 ppt would have a hardness sium. Even in models of soft to medium-hard water of about 1.9° (i.e. very soft). The standard terminology ecosystems, it is important to occasionally carry out an relating degrees of hardness to descriptive elements is analysis of the spectrum of inorganic elements. A stan- given in Table 4.6. dard commercial test for tap or drinking waters will Unfortunately, hardness through calcium is tied to usually suffice. the very nonconservative carbonate system, as meas- We have worked with a hard water on the Atlantic ured by pH. The pH is very much affected by organism Coastal Plain that is rich in both iron and sulfur. Even respiration and photosynthesis and is treated at length though a standard water softener is used on the well in Chapters 8 and 10. In practice, these two can be han- water, the taps and sinks have excessive iron staining dled separately as long as one remembers that there can and water out of the tap has a sulfurous odor, particu- be a connection. Hard waters usually have a high pH. larly in dry years. The water softness, as an ion exchange The status of a wild freshwater community that one system, also introduces a small amount of sodium chlo- wishes to simulate can be determined within the range ride. We have successfully solved this problem by using
  • 85. Hardness of Fresh Waters 69 TABLE 4.7 Concentrations of Selected, Analyzed Chemical Elements, Ions, and Compounds from a Variety of City Water Suppliesa Parts per million, mg/liter Element, ion, San Washington, or compound Boston Chicago Dallas Baltimore Los Angeles Francisco DC *Aluminum ? 0.45–0.5 ? 0.08–0.16 ND–0.2 0.02–0.08 0.042–0.2 Arsenic 0.005 0.005 0.005 0.005 ND–0.02 ND 0.000–0.001 Barium 0.1 0.05 0.05 0.021–0.03 ND ND–0.01 0.028–0.07 Cadmium 0.002 0.001 0.001 0.001 ND ND 0.0–0.00 *Chlorine-free ? 2.12–2.29 ? 0.4–0.7 1.6–2.1 *Chloride 12–44 10.9–11.1 15–27 18–22 18–127 2–19 15.6–29.0 Chromium 0.005 0.003 0.01 0.001 ND ND–0.001 0.0–0.006 *Copper 0.01–0.08 0.003 0.01–0.02 0.004–0.006 ND ND–0.015 0.001–0.110 *Fluoride 0.06–0.98 0.92–0.93 0.77–0.78 0.9–0.97 0.1–0.7 0.3–1.2 0.93–1.14 *Iron 0.02–0.16 0.010 0.01–0.01 0.02 ND–0.07 ND–0.06 0.001–0.07 Lead 0.002 0.003–0.010 0.005 0.001 ND ND–0.001 0.0–0.001 Manganese 0.01–0.05 0.001–0.002 0.005 0.01 ND ND–0.01 0.001–0.004 Magnesium .5–2.4 12.3–12.5 3–5 4.4–6.2 5.7–27 ? 6–11 Mercury 0.001 0.0005 0.001 0.0005 ND ND 0.0000–0.0003 Nickel ? 0.003 0.01–0.01 ? ? ? 0–0.003 *Nitrate (as N)b ? 0.25–0.26 0.22–0.45 1.7 ND 0.04–0.1 1.29–2.67 *Phosphate (as P)b ? 0.010–0.018 0.03–0.09 0.01 0.02–0.07 0.002–0.017 00–0.14 Potassium 0.9–2.3 1.5 3.7–4.8 2.2–2.6 3.6–4.8 0.2–0.8 2.11–3.27 Selenium 0.005 0.001 0.001–0.001 0.005 ND ND 0.0–0.002 Silver 0.005 0.001 0.01 0.005 ND ND 0.0 *Sodium 7.2–26.3 5.8–6.0 11.0–28.5 7.1–8.3 37–86 1.0–15.5 4.8–15.6 Strontium ? 0.119–0.142 0.10–0.25 ? ? ? 0.093–0.24 *Sulfate 8.3–14 26.4–27.5 31–50 13.6–15 28–232 1.6–3.6 22.1–48.9 Zinc 0.02 0.004–0.005 0.01–0.02 0.028–0.038 ND ND–0.010 0.0–0.005 Total trihalomethanes ? ? 0.0227 41 13–72 0.063–0.075 26–137 Endrin (pesticide) ? ? ND 0.04 ND ND ND 2.4-D (pesticide) ? ? ND 0.05 ND ND ND Note: Tap waters can have additional or increased contamination levels. ND, not determined. These data are from the 1980s. Few, if any, large metropolitan water systems would lack free chlorine or trihalomethanes today. a Sources: Indicated metropolitan water authorities. b Reactive. *Added in treatment, in part or whole. a separate water softening algal scrubber system. Excess that of an endorheic, or closed basin lake, if topping up calcium, iron, and sulfur are either taken up by the algae for evaporation continues for some time and water or precipitated out on the surfaces of the cells and exchange with waters of the character of the analog of the removed at harvest time. A reverse osmosis (RO) unit model is not carried out. However, the primary prob- can be used following a water softener if the volume lem with city tap water is the additives used to control requirements are not too great. human pathogens, to adjust the taste, to control algae in The character of well waters varies widely, and it artificially eutrophic reservoirs, or to reduce corrosion would be impossible to cover the problems of micro- in pipes (Table 4.8). The addition of chlorine is well cosm and mesocosm water supplies for all cases. In known and is the primary characteristic that renders general, if a standard water softener does not solve the tap waters objectionable to humans. It is added to kill problems, we have found that a separate algal turf pathogens, but the chlorine also would kill most of the scrubber (ATS) managed water reservoir (see Chapter animals that one would wish to maintain in an ecosys- 11) adjusted for nutrient levels and pH can remove tem. Fortunately, being in the gaseous state it is more almost any contaminant including heavy metals. or less easily removed by bubbling or allowing the In general, city or town waters provide more serious water to stand for several days. problems. While rarely are city tap waters saline or Since chlorine in combination with organic com- hard compared to average natural waters (Table 4.7), pounds occurring naturally forms compounds (tri- the salinity of an aquarium or microcosm can become halomethanes; see Table 4.7) that have been shown to be
  • 86. 70 4. Water Composition TABLE 4.8 Chemicals Typically Used in the Treatment of City Water Suppliesa Chemical Purpose Aluminum as aluminum sulfate (Al2(SO4)3, 18 H2O) Clarification Ammonium hydroxide (NH4OH) Taste and odor control Carbon, activated (C) Taste and odor control Chlorine or chloramines (Cl2) (NH2Cl, NHCl2, NCl3) Sterilization Copper sulfate (CuSO4) Algal reduction Fluorosilicic acid (H2SiF6) Dental decay reduction Ferric chloride (FeCl3) Clarification Hexametaphosphate (PO3)6 Reduce corrosion in metal pipes Lime (CaO, Ca(OH)2) pH adjustment Sodium chlorite (NaClO2) Taste, odor, and algae control a Sources: Metropolitan water authorities as given in Table 4.7. carcinogens, some cities have started to add chlor- these and other anthropogenic organic compounds amines instead of chlorine to control human pathogens. (which are now banned in the USA) are extremely low Unfortunately, chloramines are more toxic than chlorine in sea water, they tend to be concentrated “up food to fish and invertebrates and are more slowly lost to the chains,” especially in fatty tissues, until very toxic levels atmosphere than chlorine. are developed in top predators (e.g. Laws, 1993). While Copper sulfate is added to many drinking water the half-life of many of these compounds in the sedi- systems that include reservoirs to prevent the excessive ments of lakes and estuaries may be only 10–15 years, algal growth that sometimes results from artificially in the biosphere they can be 150 years or more. For high nutrient levels. Unfortunately, the copper is also example, while 7–16 ppm of PCBs in milk is highly toxic to the algae that is necessary to maintain virtually toxic to infant monkeys, Beluga whales were found in all natural, aquatic ecosystems. Finally, a major prob- the St. Lawrence estuary (which is a highly mixed body lem of many city tap waters is that they are eutrophic, of water with extensive deep water oceanic injection) that is, excessive, particularly in dissolved nitrogen with 575 ppm PCB in their livers and 1750 ppm in their and phosphorus. While additional chemical treatments milk (Laws, 1993). are available to remove all of these contaminants, we Heavy metals from industrial activities and sewage prefer physical (RO) and plant production (algal scrub- (e.g. mercury, Farago, 2000), and organometals like trib- bing) methods for cleaning tap waters to levels accept- utyl tin (a now banned antifouling agent) tend to be able for ecosystem management. Scrubbers utilized in thought of as local pollutants, mostly in harbors where this way are typically dominated by blue-green algae. boats are concentrated and mixing minimal (and We have limited our discussion of water composition where very serious and lethal effects on mollusks have to the inorganic elements, mostly those existing in solu- been documented). However, years after use was dis- tion as charged ions, either alone or in combination with continued in the USA and Canada, the livers of Beluga oxygen and sometimes hydrogen. However, natural whales in the St. Lawrence estuary (again, a very large waters also include abundant particulates both inorganic and well-mixed body of water) were still contaminated and organic, and aquatic ecosystems cannot function with tributyltin (Preston, 2002). normally without the particulate “soup” that is often The problem of toxic compounds has gone well present in the wild. Many of the smaller organic particu- beyond immediate solution in the ocean. Only time lates can be regarded as dissolved organics, the bound- (probably measured in decades and centuries) and ary between particulate and dissolved being quite future prevention of release of toxic compounds to natu- arbitrary. In this book we treat the particulate compo- ral waters can eventually solve this problem. Even when nents primarily in Chapters 3, 6, 17, and 18. concentrations of many of the newer industrial, agricul- Finally, anthropogenic pollutants, inorganic and tural, and pharmaceutical compounds are not directly organic, cannot be ignored in any natural waters that lethal, they can function as endocrine disrupters pre- might be used for source or exchange. POPs (persistent venting or reducing reproduction and having drastic organic pollutants), like DDT and its breakdown prod- effects on invertebrate and fish populations (Pellerito ucts, and PCBs have reached every corner of the globe et al., 2002). As we discuss in depth in Chapter 25, most (Turosov et al., 2002). Penguins, seals, and whales in if not all of these compounds can be removed from lake Antarctica and polar bears in the Arctic have DDT and and river waters along with nutrients, though consider- PCBs in their tissues. Although often concentration of able public and political will is required to do so.
  • 87. Algal Scrubbing and Water Composition 71 WATER AND MODEL ECOSYSTEMS disease and toxic introduction, and a pre-treatment water system with ATS clean-up is desirable. In earlier editions, we discussed our preference for Once a microcosm, based on the principles discussed using natural waters from unpolluted habitats to initiate in this book, is established, water changes should be min- model ecosystems. On occasion, in the 1980s and 1990s, imal and aimed primarily at preventing evaporative we went as much as 50 miles offshore in the mid-Atlantic “salt drift” in sea waters and the change in the propor- region to obtain water suitable for starting large model tional salt content caused by evaporative accumulation coral reef systems. However, for most aquarists, includ- in fresh waters. In short, very minor water changes ing university researchers modeling ecosystems, high- should be made to avoid drift in conservative elements quality natural waters may simply not be available. that would create a “Great Salt Lake” or endorheic basin. To emphasize the magnitude of the problem, we cite As we discuss in Chapters 7–11, nonconservative or Turosov et al. (2002) (National Library of Medicine). nutrient-type elements should be maintained dynami- “Due to its stability and its capacity to accumulate in adi- cally by balanced system loading. pose tissue, it (DDT) is found in human tissues, and there is now not a single living organisms on the planet that does not contain DDT.” PCBs, mercury, and probably ALGAL SCRUBBING AND WATER numerous other compounds of modern civilization have COMPOSITION already achieved or are approaching the same state. However, the microflora and microfauna appropri- In both our mesocosm and aquarium endeavors, we ate to a model system is likely to be obtained only from have emphasized the use of plants, mostly algae, to natural waters. The rational approach today is to use manage water quality. This is part of a broader tendency RO water adjusted to salinity with the highest-grade in environmental water management today called phy- sea salts, or prepared with reagent, or better, analytical toremediation, and we treat the subject in some detail grade chemicals appropriate to the type of hardness in Chapter 25. As we discuss in many places in this desired (for fresh waters) to fill the system. Once an book, the key to ecosystem management is stability aquarium, microcosm or mesocosm is operating as a achieved by locking nutrients up in biomass rather physical plant, algal scrubbers (see Chapter 11), and than by using bacterial filtration to rapidly reduce all 5–10% additions of natural water can be added to intro- nonliving organics and organism excretions to freely duce microflora and microfauna and clean up micro available elements and ions. The algal scrubber is the contaminants. The gradual introduction of macro organ- principal technology in this management system and is isms to build up community structure can then be car- discussed in depth in Chapter 11. ried out with the occasional natural water aliquot. As we Algal scrubbing is used primarily to maintain a bal- describe in depth in Chapter 11, if the ATS methodology ance, to simulate the effects of the larger body of low- is employed (with routine harvest), heavy metals will be animal biomass water that balances out the requirements captured by the algae and most organic pollutants will of high-biomass systems. This might be smoothing out be broken down and the carbon removed from the water the differences between day and night in small model column of the system along with the algal harvest. ecosystems or between seasons in large mesocosms. If When substrate and organisms from the natural envi- there is no import to a system, because it is large ronment are introduced, as we describe above, micro- enough and rich enough in photosynthetic plants to organisms will be brought in with them. They cannot be provide sufficient energy to the community of organ- avoided, unless one wishes to select all organisms, isms maintained, then export is not required. The algae including protozoans and microbes, individually (a vir- are removed by scrubbing as a daily, weekly, or seasonal tually impossible task) and then pass them through sub- requirement and are dried and eventually returned to lethal or other baths selective for the desired organisms. the system. Thus, there is little chance for the removal of The sterilization approaches of modern medicine are not critical elements from the water medium. However, applicable to the synthesis of most ecosystem models. when the aquarist is running a dynamically balanced Quarantine of fish, especially those purchased, and par- system with significant input (usually dried or live ticularly those from fresh water, is essential to avoid food) and export, either because the model has exces- occasional serious disease problems. On the other hand, sive biomass and is being driven hard or because the if the organisms are in a healthy environment and the input and export simulate similar features in a wild ecosystem is managed properly, disease will be mini- ecosystem, then imbalances are theoretically possible. mal. We discuss these matters further in Chapters 19 and The algal turfs of scrubbers are communities, typi- 26. However, as we have recently learned from hard cally with many species from most algal divisions, and experience, today, any coastal waters are suspect for thus tend to be self-balancing. Algae and other aquatic
  • 88. 72 4. Water Composition plants synthesize a wide variety of organic compounds including many vitamins (Ragan, 1981). It is unlikely in diverse communities of fifty to several hundred species of plants that contain many herbivores, even in relatively small models, that lack of algal-synthesized organic compounds would hinder ecosystem development. On the other hand, many algae have requirements for inor- ganic micronutrients, such as iron, calcium, manganese, molybdenum, boron, cobalt, copper, and iodine that could theoretically provide such limitations by locking up elements of concern. Moe (1989) discusses removal of trace elements particularly by ozonation and protein skimmers, but also through uptake by algae. Iodine, particularly needed by crustaceans for molting, was cited as a characteristic problem. We refer to a general pattern of crustacean success in our systems (Chapters 20–23), where extensive algal scrubbing has been used for many years. For one particularly successful coral reef model, we describe more than 9 years of continu- ous molting in a single individual of rare reef lobster. In addition, after 10 years of continuous operation that never included a mass water change (beyond a standard 2% per month to prevent salt drift), the Smithsonian Coral Reef contained concentrations of iron, manganese, silica, copper, and strontium that remained very close to or slightly above concentrations in Delaware coastal waters (the source of top-up water at that time). FIGURE 4.3 Conversion graph for obtaining salinity from specific On the other hand, as we describe in detail in gravity and temperature. Chapters 10 and 20, in coral reef models with abundant calcifiers, high temperatures and light levels with extensive photosynthesis, the “sinking rate” of calcium living and dried foods; (3) in the long term utilize small and carbon in carbonate skeleta and shells is very high water changes (constant “new water” exchange is (see also Chapter 3, re: geological storage). This can a feature of wild ecosystems); and (4) where calcifica- lead to calcium and alkalinity depletion followed by tion is an important and extensive feature of a model slower growth rates of calcifying organisms. It is essen- ecosystem, be certain that calcium carbonate, espe- tial in this situation to maintain calcium and alkalinity cially as aragonite, is readily available and alkalinity is concentrations at or above levels typical for the open within normal range (see also Chapters 8 and 10). For ocean (420 mg/liter and 2.43 meq/liter). The addition the latter, standard, inexpensive test kits are available. of calcium and bicarbonate in this case simulates deliv- However, especially for calcium, the accuracy and pre- ery to wild reefs by equatorial and tidal currents as well cision are marginal. as trade wind seas, and cannot be regarded as “undesir- able”; if one’s purpose is modeling, these additions are equivalent to that in the wild and are required for ecosystem function. MARINE MICROCOSMS AND AQUARIA In a research laboratory, the limiting or potential limiting of chemical elements in ecosystem models can An attempt to faithfully re-create a marine system be extensively monitored and appropriately adjusted. must include monitoring of salinity levels and a knowl- For the researcher with more limited resources or a edge of daily, weekly, and monthly salinity variations in hobbyist, a commercial water analysis service may do, the wild. Normal ranges of salinity for most nonestuar- although sufficient accuracy and precision needs to be ine coastal situations are 28–34 ppt for colder waters demanded. Following a few simple rules (that are, in (with a variation of no more than several ppt a day) and effect, what happens in the wild) will avoid most prob- 34–37 ppt for tropical oceanic situations (varying no lems: (1) do not run import and export highly out of more than 0.5 ppt daily). (The idiosyncrasies of brackish balance (see Chapter 11); (2) use a wide variety of water aquaria are discussed in Chapter 22.)
  • 89. References 73 provides about the same precision. Both devices require very careful observation and conversion for effective use on reef systems. For other coastal communities and estuaries, either device is quite adequate. The infrared-level sensors, now easily available, are generally quite accurate. The sensors themselves need to be wiped off every few weeks to avoid failure. Failure of a water-delivery system can be just as disastrous as the jamming of a heater. A check of the tank twice daily can prevent the problem from becoming critical. However, continuous pumping of fresh water for hours can destroy a sensitive marine microcosm. We use manually filled freshwater reservoirs for replacement water. The reservoirs contain the maximum amount of water that can safely be pumped in between checks. QUALITY OF TOP-UP WATER For coral reef systems, high-grade distilled water is recommended for evaporative replacement water, because many contaminants continually placed in a closed tank are generally not removed by evaporation. Poor input water quality is a key element tending to degrade model ecosystems. As we discuss in depth in Chapters 11 and 25, many pollutants are broken down and removed from ecosystem models through the use of algal turf scrubbers. The reverse osmosis and laboratory- grade deionizer system that we used for the Chesapeake mesocosm are illustrated in Figure 4.4. In this case an FIGURE 4.4 Tap water cleaning system consisting of a laboratory- algal scrubber unit is also used because it produces lower grade RO unit, a reservoir, and an algal scrubber. nitrogen input levels than the reverse osmosis unit. Such a system will also remove heavy metals and synthetic organic contaminants where that is necessary. City tap waters and many private well waters are unsuitable Evaporation is an on-going process with all open for direct long-term evaporative water replacement to tanks, and generally at least daily replacement of evap- ecosystem models. orated water is necessary. Manual topping up to a The long-term result of intensive evaporation of mark is acceptable for cold-water or brackish systems water is an alteration of the salt composition of a sys- that normally experience wide salinity swings. But for tem. A 0.5–1.0% per day exchange with a high-quality controlling salinity in tropical reef tanks, precision lev- “make-up” water of appropriate salinity or hardness eling devices now available from most aquarium stores (as we discussed above) will generally avoid this prob- and laboratory supply houses should be used. The lem. Hardness in fresh water is usually much less of a hydrometer measures salinity by specific gravity (or problem than salinity maintenance in salt waters. density) and is the least expensive and most trouble- Nevertheless, in special cases it can be critical, and the free device of this type. A conversion is required (Figure 0.5–1.0% exchange may also be appropriate. 4.3) because temperature is also an important parameter relating salinity to specific gravity. Also, hydrometers must be calibrated for reading variation as a function of References temperature away from the standard for which they are calibrated at the factory. However, even the larger Evans, D. (1993) Osmotic and ionic regulation. In: The Physiology of Fishes. D. Evans (Ed.). CRC Press, Boca Raton, Florida. hydrometers are difficult to read with a consistent effec- Farago, M. E. (2000) Mercury in Marine Environments. In: Chemical tive precision of better than ±0.2 ppt. A refractometer Processes in Marine Environments. A. Gianguzza, E. Pelizzetti, costs a little more and is easier to use. However, it and S. Sammartano (Eds). Springer, New York.
  • 90. 74 4. Water Composition Frausto da Silva, J. and Williams, R. (1991) The Biological Chemistry of Preston, M. (2002) Endocrine-disrupting chemicals in the marine envi- the Elements. Oxford University Press, Oxford. ronment. In: A. Gianguzza, E. Pelizzeti, and S. Sammartano (Eds). Horne, R. (1969) Marine Chemistry. Wiley, New York. Chemistry of Marine Water and Sediments. Springer, New York. Hutchinson, G. E. (1957) A Treatise on Limnology, Vol. 1. Wiley, Ragan, M. (1981) Chemical constituents of seaweeds. In: The Biology New York. of Seaweeds. C. Lubban and M. Wynne (Eds). University of Hutchinson, G. E. and Edmondson, Y. (1993) A Treatise on Limnology, California Press, Berkeley, California. Vol. IV. Zoobenthos. Wiley, New York. Riehl, R. and Baensch, H. A. (1987) Aquarium Atla. Mergus-Verlag, Melle. Jobling, M. (1995) Environmental Biology of Fishes. Chapman and Hall, Spotte, S. (1979) Seawater Aquariums. Wiley-Interscience, New York. London. Sverdrup, H., Johnson, M., and Fleming, R. (1942) The Oceans, Their Laws, E. A. (1993) Aquatic Pollution, An Introductory Text, 2nd edn. Physics, Chemistry and General Biology. Prentice-Hall, Englewood John Wiley and Sons, New York. Cliffs, New Jersey. Millero, F. and Sohn, M. (1992) Chemical Oceanography. CRC Press, Thurman, H. and Webber, H. (1984) Marine Biology. Merrill, Boca Raton, Florida. Columbus, Ohio. Moe, M. (1989) The Marine Aquarium Reference. Green Turtle Pub- Turosov, V., Rakitsky, V., and Tomatis, L. (2002) Dichlorodiphenyl- lications, Plantation, Florida. trichloroethane (DDT): ubiquity, persistence and risks. National Pellerito, L., Barbieri, R., DiStefano, R., Scopelliti, M., Pellereito, C., Library of Medicine, Pub. Med. Environ. Health Perspect. 110: 125–128. Fiore, T., and Triolo, F. (2002) Toxic Effects of Organometallic Van Dover, C.-L. (2000) The Ecology of Deep Sea Hydrothermal Vents. Compounds Towards Marine Biota. Ibid. Princeton University Press, Princeton, NJ.
  • 91. C H A P T E R 5 The Input of Solar Energy Lighting Requirements In many ways, this is the key chapter in this book. they are rather rare, requiring an anaerobic environ- Photosynthesis not only provides virtually all the energy ment in conjunction with abundant solar energy, a that drives ecosystems, it provides our food and the envi- somewhat unusual situation on today’s Earth ronment in which humans have evolved. This has not (Rheinheimer, 1985). always been so. Finally, about a billion years later, the blue-green The early atmosphere and ocean, rich in carbon algae (treated today as cyanobacteria since they lack a dioxide, ammonia, and perhaps hydrogen sulfide and well-defined nucleus) developed the ability to use the without oxygen or ozone, was bombarded with short- most abundant compound available in the Earth’s wave radiation. Possibly the radiation impacting the oceans (water) in this same basic process of energy elemental soup created a wide variety of physically supply (Figure 5.1). Photosynthesis eventually became synthesized simple “organic compounds,” or possibly a highly sophisticated chemical process of two basic they “rained in” with comets that also provided the steps, the first requiring light and using chlorophyll water. The earliest proto “organisms” evolved from and associated pigments, as antennae or catalyzers, to chance combinations of these compounds, perhaps capture light energy and to split water to provide elec- with the involvement of the intense energy of lightning trons and hydrogen ions (and incidentally release oxy- strikes. Some researchers think that the structural pat- gen). The second step can take place in the dark. It uses terns of clay minerals, which can replicate, may have the energy carried by excited electrons from the first provided the proto-genetic organization, while the sur- step and the hydrogen ions to build simple sugars or face tension of water combined with simple “organic” alcohols (C6H12O6 or 6CH2O) from carbon dioxide, created cellular-like bubbles. These developing “organ- thereby providing the basic chemical energy supply for isms” likely made direct use of simpler, energy-rich the plants, and for the animals that eat them. compounds, much as many present-day heterotrophic It is still true that in oceans, at sea floor spreading bacteria are able to do, and were able to grow. This pat- zones and on anaerobic mud flats, as well as in hot tern of energy supply continued for perhaps a billion springs on land, some biological sources are chemo- years or more and probably could have been effective autotrophic and probably not even indirectly derived only in the absence of oxygen. from solar energy. A prime example, discovered in the early 1980s, is provided by the thermal vent communi- ties and their ecosystems, along mid-ocean ridges. These PHOTOSYNTHESIS AND ITS ORIGIN ecosystems are based on energy supplied from the Earth. However, interesting as these systems are, and as inter- About 3 billion years ago, some bacteria developed esting as they would be to bring into a microcosm, it is the ability to absorb sunlight and to split a variety of sunlight that drives the vast majority of ecosystems abundantly available noncarbon compounds with likely to be of interest to the ecologist and the aquarist. hydrogen and an available electron, such as H2S and Also, in environments such as deep soft bottoms where H2. The same or similar bacteria still exist today though no light is present, the ecosystem’s driving energy is 75
  • 92. 76 5. The Input of Solar Energy FIGURE 5.1 Evolution with time of the major groups of organisms, the process of photo- synthesis, and the composition of the atmosphere. After Mathews and van Holde (1996). Reprinted by permission of Addison Wesley Longman. obtained through the rain of organic matter from shal- more complex life forms on Earth. Since the dawn of the low water or possibly through turbidity or other cur- industrial revolution, human society has been massively rents. Tropical jungle streams survive largely through extracting energy from fossil fuels and forests (both the breakdown of leaves that fall into them or are made stored carbon) and simultaneously releasing nutrients to available to the community during floods of the adja- surface waters with little regard for the consequences. To cent forest floor. In simulating such systems one would prevent a collapse of human civilization when the fossil perhaps wish to “feed” them with appropriate organic oil runs low (see e.g. Diamond, 2005; Lovins et al., 2004) particulates or leaf litter rather than primarily with and the Earth overheats, we need to greatly expand our light through a second model ecosystem. However, the solar energy capture systems (including photosynthesis most interesting systems for aquaria, and microcosm bioenergy). At the same time we need to de-nutrify and models, as well as wild aquatic systems currently need- de-toxify our surface waters. In the second edition of this ing restoration, are high light systems. Even the source book, we reasoned that while we could build ecosystem water for blackwater streams might be best “scrubbed” models that operated in pre-industrial environments, we first, as we described at the end of the last chapter, and could not economically repair the existing damage to our then acidified to rain level pH with CO2 bubbling. atmosphere and natural waters. The principal focus of We examine the light-driven reactions of photosyn- the earlier edition was to provide enough public and sci- thesis in greater depth, because they provide the keys to entific understanding of the workings of aquatic ecosys- the operation of model ecosystems, as well as to the tems to redouble conservation efforts at preventing restoration of most damaged ecosystems. The evolution, further damage. Conservation is essential, but a more increasing sophistication and globalization of photosyn- pro-active approach is now necessary. In this edition, we thesis, and its corollaries, an oxygenated, low carbon replace that more pessimistic, but hopeful view, with atmosphere and mostly low nutrient-shallow waters, one of greater optimism. We describe how our natural provided the basis for the further evolution of higher, ecosystems can be recovered with economic advantage.
  • 93. Photosynthesis and Its Origin 77 FIGURE 5.2 Electron microscope and diagrammatic view of chloroplast structure. After Keeton and Gould (1986). Reprinted by permission W. W. Norton & Co., Inc. This optimism is based in an understanding of chloro- constructors of most coral reefs. These coelenterates phyll and photosynthesis, and in an application of that build reef “infrastructure” that is then colonized by the understanding to environmental restoration. highest diversity of animals and algae in the oceans. Chlorophyll is the basis of photosynthesis. The This feat of calcification and growth is accomplished magnesium-centered chlorophyll molecules, porphyrin- by a photosynthesis-enhanced metabolism that accrues ring structures (like the iron-centered hemoglobin) were from the capture of algal cells (zoothanthellae), and no doubt the end result of hundreds of millions of years the combining of the physiologies of both animal and of improving the biochemical processes of photosyn- alga. There are many animals in coral reefs that are thesis. The cellular synthesis of the chlorophylls and herbivores of free-living algae, and many that hide in hemoglobin is part of the same biochemical complex of the free-living algae that grow on the reef surface, but processes that synthesizes the cytochromes (electron- only the symbiosis of an animal and an alga could transferring molecules of photosynthesis), the phyco- create the largest and most diverse ecosystem in the bilins (light capturing accessory pigments of red and shallow ocean. brown algae) and cobalt-centered vitamin B12, among In algae and higher plants, the chlorophyll mole- many others. Some photosynthetic bacteria have chloro- cules are held on the lipid membrane surface of the phyll pigments that are zinc-centered porphyrins. These granae by a convoluted protein and have long hydro- are all molecules configured to easily pick up and lose carbon tails embedded in the membrane. As shown in excited electrons and to bind oxygen. In the algae and Figure 5.3, chlorophyll “a” (the primary photosyn- higher plants, chlorophyll and photosynthesis occur in thetic molecule) is tuned to light capture in two differ- chloroplasts, membrane enclosed cellular organelles ent ways. Photosystem II, absorbing light at 680 nm that contain membrane-bound platelets (granae) (Figure (red), produces excited electrons that escape from the 5.2). Chloroplasts have their own DNA, quite different chlorophyll molecules, and then, in a poorly understood from the cell’s nuclear DNA, and many researchers process (Pace, 2005; Melis, 2005), replaces those elec- think that these represent cyanobacteria, first captured trons from water molecules resulting in the “splitting” over a billion years ago by algal ancestors (Lee, 1999). of water and the production of oxygen. In the light, the Thus, algal (and now higher plant) photosynthesis was lipid membrane surface of the granae, which is studded the result of a symbiosis similar to the coral symbiosis with molecules like cytochrome and ferredoxin, that with zooxanthellae that we describe later. The light pick up and lose excited electrons easily, is a “sea” of capture process occur on the surface of the granae. The moving, excited electrons. Some of the cytochrome mol- so-called dark reactions of the synthesis of sugar ecules, as an electron attaches and detaches, use elec- (Chapter 7) occur in the intergranae spaces, the stroma. tron energy to pump hydrogen ions into the internal As we will discuss in greater depth in Chapters 19 spaces of the granae. Employing the hydrogen ion gradi- and 20, stony corals are the primary framework ent, enzymes, also embedded in the membrane, function
  • 94. 78 5. The Input of Solar Energy FIGURE 5.3 Process of photosynthesis and the sequence and location of light-sensitive phases on the membranes of plant chloroplasts. After Keeton and Gould (1986). Reprinted by permission of W. W. Norton & Co., Inc. as hydrogen-ion-driven pumps to attach phosphorus much as 80%; Melis, 2005) by the chemical storage ions to ADP to in turn create the energy transporting process. Nevertheless, the overall process of photosyn- ATP in the intergranae spaces. The membrane also has thesis and primary production remains considerably chlorophyll “a” molecules that are tuned slightly dif- more efficient than current industrial methods of solar ferently, to 700 nm (Photosystem I), and serve to simply energy capture. re-excite electrons traveling along the membrane with- Many scientists are attempting to find the keys for out splitting more water. Finally, ferredoxin molecules, carrying out photosynthesis industrially, physically on picking up excited electrons, are able to attach those independent of algal or plant cells. This is certainly logi- electrons to NADP to produce the energy carrier cal. The chemical process of photosynthesis is highly NADPH. efficient and produces electrons, oxygen, and hydrogen. In the light, activated NADPH and ATP molecules In the laboratory, some algae have been induced to pro- are constantly released from the surface of the granae duce hydrogen gas, which could be used in fuel cells membranes into the stroma (intergranae spaces) where (Melis, 2005). Hopefully, if this can be accomplished they are available to drive sugar synthesis (Chapter 6) without negative side effects (as in atomic energy), then and then return to the granae surface for reactivation. perhaps with a more or less inexhaustible energy source This process of photosynthesis, evolved over a billion we could concentrate on environmental recovery. How- years or more, is highly efficient at solar energy capture ever, as we have shown, photosynthesis is a highly com- and also supplies energy storage in chemical bonds. plex process, and chlorophyll does not function when Solar cells and wind generation also capture energy in it is stripped from its supporting protein molecules the form of moving electrons, albeit far less efficiently and lipid membrane. Perhaps the new science of nano- than photosynthesis. However, storage of energy technology (the physical manipulation of molecules and acquired with these devices is far more problematical, atoms) can help us out with this problem. While human requiring expensive, inefficient batteries, or more eso- understanding of physical and biological processes, and teric methods. It is interesting to note that the highly our achievements at engineering that knowledge for efficient chlorophyll, energy capturing process of algae practical human use, is phenomenal by any measure, and higher plants is greatly reduced in its efficiency (as not all natural processes can be reduced to practical
  • 95. Solar Radiation and Water 79 human use, especially in the time frame we may require. As we discussed in the Introduction, our approaching socio-political collision with the exhaustion of oil energy, coupled with an ever-growing pollution of the Earth’s atmosphere and water, and increasing disruption of nat- ural ecosystems gives us little lead time. We cannot wait on the engineering of photosynthesis to solve these prob- lems. In this book, we describe how we can achieve that “symbiosis” with photosynthesis, not only for the man- agement of aquaria and ecosystem models, but also for the restoration of wild environments and the recovery of our socioeconomic system. However, above all, it requires an understanding of photosynthesis, both in algae and in the higher plants. SOLAR RADIATION AND WATER Any atom or physical mass, including the sun, radi- ates electromagnetic energy in accordance with its tem- perature. Beginning at about 800 K (degrees centigrade plus 273), visible light in the red end of the spectrum begins to be radiated. As the temperature increases, emit- ted wavelengths (and the amount of energy radiated) increase. An incandescent bulb has a color temperature of 2800 K and is quite red; a cool-white fluorescent bulb radiates at about 4000 K and is strongest in the red- FIGURE 5.4 Attenuation of PAR in different types of water. After orange. Daylight fluorescent bulbs and the sun radiate at Kirk (1994). Reprinted with permission of Cambridge University about 6000 K. Unfortunately, the magnitude of visible Press. radiation is measured in many ways. Wherever possible, we use an energy measure: microeinsteins per square meter per second (millimoles). For rough comparison, 2000 µE/m2/s is approximately 100 000 lux or 10 000 foot-candles. In the middle of a bright sunny day, early summer at high latitudes and year-round in the tropics, approxi- mately 2000 µE/m2/s of visible or photosynthetically active radiation (PAR) is received at the Earth’s surface. Depending on the clarity of the water in question, this radiation can extend to great depth or be limited to a few meters (Figure 5.4). The total solar radiation received per day over the Earth is shown by month for various lati- tudes in Figure 5.5. The yearly total is shown in Figure 5.6. Generally, higher latitudes have greater seasonal vari- ability in incoming light. While progressively north and south of latitude 40 total yearly radiation is consid- erably reduced, in a broad range of mid-latitudes total incoming radiation is mostly a function of cloudiness or atmospheric clarity. Light incoming to the Earth’s outer atmosphere has roughly the spectrum shown by the top curve in Figure FIGURE 5.5 Change in incoming solar radiation at the top of the 5.7. By the time it passes through the atmosphere and atmosphere calculated seasonally and for different latitudes. After reaches the sea surface through clear sky or clouds, it Kirk (1994). Reprinted with permission of Cambridge University looks more like the second or third curves. Shaded areas Press.
  • 96. 80 5. The Input of Solar Energy FIGURE 5.6 Mean annual insolation (solar radiation) on the surface of the Earth (calories/cm2/year 103). Note that the greatest yearly totals occur in the horse latitudes rather than in the tropics proper. However, the seasonality is considerably greater in the horse latitudes, with higher levels in summer and considerably lower levels in mid-winter (see also Figure 5.5). After Gates (1980). FIGURE 5.7 Spectral quality of incoming solar radiation, light reaching the Earth’s sur- face (through clear and clouded sky), and light transmitted through terrestrial vegetation. After Gates (1980).
  • 97. Solar Radiation and Water 81 without significant local reflection and those under The resulting attenuation at different wavelengths green foliage are the fourth and fifth curves. Further, varies greatly depending on depth and water character. attenuation in lakes or the sea provides a color balance Curves for light distribution with depth for open ocean, that is even more removed from the original spectrum. clear coastal water, and a lake are shown in Figure 5.8. FIGURE 5.8 Spectral quality of solar radiation transmitted through natural waters (marine and fresh) of varying character. After Kirk (1994). Reprinted with permission of Cambridge University Press.
  • 98. 82 5. The Input of Solar Energy In general, pure water absorbs longer wavelengths above 550–600 nm and thus, given enough depth, will appear green or ultimately blue. Suspended particu- lates and dissolved substances absorb the shorter wavelengths, and typically as one passes from open ocean to coast, to estuary, and then to river and lake, more of the wavelengths below 500 nm and eventually even 600 nm are absorbed. Thus, depending on the extent of matter in the water, one passes from blue, to green, to yellow, to red or brown in making such a tran- sect. This is also an indication of the kind of light that is available at depth. Further upstream, into mountain lakes and streams (at least when they lack glaciers), the number of particulates usually decreases along with FIGURE 5.9 Spectral absorption of the freshwater macrophyte nutrients and planktonic algae. Under these condi- (flowering plant) Vallisneria spiralis. After Kirk (1994). Reprinted with tions, water clarity and the blue-green character of the permission of Cambridge University Press. water return. community, particularly an algal community, the pho- tosynthetically active pigments cover the visible spec- LIGHT ABSORPTION BY trum. As stated by Mathews and van Holde (1996) WATER PLANTS “scarcely a photon can come through that cannot be absorbed by one chromophore (pigment) or another.” Plants, including algae, utilize a wide variety of acces- Heldt (2005) demonstrates how the red and blue pig- sory energy-absorbing pigments in addition to the all- ments of red algae and cyanobacteria, phycoerythrin, important chlorophyll. Each of these pigments requires and phycocyanin (structural relatives of chlorophyll) specific wavelengths to be photosynthetically efficient. are in effect “extra antennae” that are arranged on the Plants are generally classified into evolutionary group- surface of the granae membranes on top of or near ings, most easily designated by color and therefore by chlorophyll “a” Photosystem II reaction centers. Photons their photosynthetically active pigments. The green are captured by the accessory pigments and subse- plants include the flowering plants such as marsh quently the energy transferred (as a fluorescence process grasses and all submerged aquatic vegetation as well as or excitons) to the chlorophyll “a” reaction centers, green algae including Ulva (sea lettuce) and Enteromorpha. allowing these algae (and cyanobacteria) to use light The brown algae, with virtually no fresh water or terres- thru the middle of the visible light range where the trial representatives, include large marine plants such as chlorophylls are inactive. Laminaria (kelp) and Sargassum. The red algae, mostly marine with a few species in fast-running streams, include Chondrus (sea moss) and Rhodymenia (dulce). LIGHT INTENSITY AND PLANTS The blue-green algae (Cyanobacteria) are filamentous or unicellular plants that form slimy crusts, ribbons, or In addition to color balance or spectrum of solar cushions of varying hues (green, red, black, etc.) that radiation, a major concern in photosynthesis is the total are common in most lighted wild environments as well intensity of the radiation. Many plants including as in many fresh- and saltwater aquariums. Finally, marine and aquatic plants are highly adaptive to avail- a number of widespread algal groups particularly able light. Plants of a given species grown at high light important as plankton include golden-brown algae intensity will perform more poorly under low light (diatoms) and yellow-brown algae (dinoflagellates). than plants raised at low intensity. It is characteristic of The chlorophylls and the accessory pigments used by many algae that with a major change in solar radiation higher plants, and marine and aquatic algae absorb light the plants will die or die back and develop new growth for photosynthesis at particular wavelengths or groups adapted to the new light levels. of wavelengths. These absorption peaks tend to be in Terrestrial plants from normal sunny habitats typi- the blue-green and the far-red wavelengths. However, cally show a pattern of photosynthesis with available the actual absorbance by plants and the action spectra light similar to that of the bean (Figure 5.11). At cool (or photosynthetic activity) of those plants, including temperatures leaves of this plant show a more or less the major phyla of marine algae (Figures 5.9 and 5.10), direct and strong increase of photosynthesis up to are more smoothed or spread out. In general for a plant about one-third of full tropical sunlight. Above that
  • 99. Light Intensity and Plants 83 FIGURE 5.10 Action (- - - -) and absorption (—) spectra of photosynthesis in vari- ous marine algae. While the two curves usually coincide and light absorbed is utilized in photosynthesis, that is not necessarily the case, particularly at the ends of the spec- trum. (A) Ulva (green); (B) Coilodesme (brown); (C) Delesseria (red); (D) Chlorella (green); (E) Skeletonema (diatom). After Kirk (1994). Reprinted with permission of Cambridge University Press. level up to the strongest natural light possible, photo- surface light, and at higher intensities it is actually synthesis continues to increase but at a slower rate. On inhibited. The same results are obtained in more recent, the other hand, at high midday leaf temperatures pho- sophisticated computer modeling (Behrenfeld et al., tosynthesis considerably increases up to the most intense 2002). On the other hand, benthic plants, both flowering solar light possible on Earth. Most physiological studies plants and algae, do not show an obvious inhibition of plants are carried out on small specimens or pieces of (Figure 5.14). those plants. As shown in Figure 5.12, there is a major One might conclude from these data that while difference between the photosynthetic performance of many land plants, given no limitation by other factors whole plants compared to their parts. The relationship (e.g. carbon dioxide or temperature), can use all of the between light and photosynthesis for entire trees is possible solar radiation available for photosynthesis, almost direct to the full intensity of sunlight. marine and freshwater plants saturate or even lose pro- An often quoted pattern of underwater photosyn- duction at levels of one-quarter to one-half of available thesis is that of phytoplankton, as shown in Figure 5.13. surface radiation. However, if one looks at production Here, photosynthesis peaks at about one-quarter of by entire benthic plant communities in the wild, almost
  • 100. 84 5. The Input of Solar Energy FIGURE 5.13 Photosynthetic rates of Sargasso Sea (•) and Lake FIGURE 5.11 Light response at different temperatures of the Windemere (• ) phytoplankton as a function of light levels (labora- • bean Phaseolus vulgaris, a tropical plant characteristic of sunny sites. tory experiments). After Kirk (1994). Reprinted with permission of At lower temperatures photosynthesis is limited by molecular and Cambridge University Press. chemical processes controlled by temperature, rather than by light itself. After Gates (1980). FIGURE 5.12 Photosynthesis rate for two terrestrial, woody plant species – individual leaves as compared to the entire trees. After Oliver and Larson (1990). Reprinted with permission of John Wiley & Sons, Inc. invariably primary production (or water purification, if While 50% of production is achieved when 500 µE/m2/s one is thinking in those terms) is limited seasonally and is reached (a few hours after dawn), full production is daily by the available solar radiation (Figures 5.15–5.18). only achieved at noon, at light intensities close to full Figure 5.15 illustrates the relationships particularly well. tropical sunlight. Below maximum intensity (and down
  • 101. Light Intensity and Plants 85 FIGURE 5.14 Photosynthetic rates of (A) various submerged macrophytes (flowering plants) and (B) algae as a function of light levels. After Kirk (1994). Reprinted with permission of Cambridge University Press.
  • 102. 86 5. The Input of Solar Energy FIGURE 5.15 Photosynthesis (day) and respiration (night) as measured on a Caribbean coral reef (Panama): (A) oxygen exchange vs time; (B) oxygen exchange vs light in situ on reef; (C) oxygen exchange vs light for an in situ microcosm of the reef. After Griffith et al. (1987). Reprinted with permission of The American Society of Limnology & Oceanography. to about 500 µE/m2/s) every 10% reduction in intensity causes a 5% reduction in production. Likewise in a cold- water kelp community (Figure 5.16), light and tempera- ture are not in phase. Yet yearly photosynthesis closely follows available light independent of temperature. Factors other than light may also limit plant produc- tion. Plankton production in higher latitudes in lakes and oceans, for example, typically rises sharply in the spring, as the light returns and no nutrient limitation exists. There may be dips in production in midsummer, but this is usually due to nutrient limitation or grazing by zooplankton. Phytoplankton production and more FIGURE 5.16 Photosynthetic rates of kelp as related to light lev- rarely benthic plant production can be limited by ultra- els (at depth of growth) throughout a 1-year cycle. After Kirk (1994). violet (UV) radiation near the surface. This limitation is Reprinted with permission of Cambridge University Press. minimal, however, and likely more than made up for
  • 103. Light Intensity and Plants 87 FIGURE 5.17 Diurnal oxygen exchange of a tropical coral reef community by season. After Adey and Steneck (1985). FIGURE 5.18 Gross primary productivity of four sections across a well-developed shallow-water tropical coral reef community (St. Croix, U.S. Virgin Islands) as a function of light, season, available surface, and biomass. After Adey and Steneck (1985).
  • 104. 88 5. The Input of Solar Energy FIGURE 5.19 Generalized spectral characteristics of natural water bodies and the artificial light typically required to provide underwater light in aquarium and mesocosm models of those water bodies. by increased plant production in deeper water, particu- Calvin cycle and reduce CO2 to make the sugar phos- larly in benthic communities. phoglyceraldehyde and eventually glucose (a process called carbon fixation). The simplest way to determine the magnitude of photosynthesis is to measure oxygen PHOTORESPIRATION release. All of the measures of photosynthesis dia- grammed above were based on determining oxygen As we pointed out above, photosynthesis involves release. However, primary production refers to the two primary steps: (1) the capture of solar energy in completion of the process and the net fixation of carbon electron excitation, with the electrons derived from the (from carbon dioxide) in simple carbohydrates. splitting of water molecules (with the release of Ribulose 1,5-bisphosphate (RuBP or Rubisco) carboxy- gaseous oxygen, O2) and (2) the transfer of electrons to lase is a critical enzyme in the fixing or incorporation of NADP and ADP, the energy transfer molecules, on the carbon dioxide in the dark phase of photosynthesis (the granae of chloroplasts. The resulting NADPH and ATP Calvin cycle). It has been known for some time that in are then available in the chloroplast stroma to drive the many higher plants, under some conditions (especially
  • 105. Light and Model Ecosystems 89 high temperatures and low carbon dioxide availability) 1978). Algal turf communities in exposed reef flats reach RuBP carboxylase acts as an oxidizer, “respiring” the peak production at midday light intensities of about intermediate products of photosynthesis without provid- 1500 µE/m2/s (Adey and Hackney, 1989). Small and ing net energy or biomass to the plant. Adey (2001) demonstrate system calcification rates equal Some groups of higher plants, particularly the to the faster growing coral reefs in the wild, as well as grasses or C4 plants, have developed mechanisms to the fastest, published Acropora growth rates, using six, avoid the effects of photorespiration. Others, with the C3 160-W VHO fluorescent lamps on a 130-gallon coral or standard Calvin cycle, simply perform poorly when reef system (see Chapter 20). At the distance involved matched with C4 plants in intense light at high tempera- in the formal coral growth studies, light received would tures. Although all or most algae appear to have C3-like have been about 1500 µE/m2/s. pathways, photorespiration seems to generally be sup- When planning light simulation in microcosms, pressed in algae (Lobban and Harrison, 1994). In algal mesocosms, and aquaria, our rule of thumb is to match turfs under coral reef environmental conditions, which both light spectrum and light intensity as closely as we discuss at some length in later chapters, studies have possible to those of the wild ecosystem being modeled. shown no evidence of photorespiration (Hackney and In general, if desired for reasons of economics, light Sze, 1988). It has been assumed that bicarbonate (HCO3) intensity may be reduced by 20–30% of that in the wild under normal conditions in aqueous environments, without major effects, but greater reductions would especially in the sea, is available to algae as a carbon seriously compromise the system biologically and eco- source and this prevents the significant occurrence of logically. Likewise, if there were considerable benefits photorespiration. It is unlikely that carbon, as a nutrient, to be derived, one might omit some of the green-yellow can ever be limiting in marine environments (see coral part of the light spectrum, but it is likely that some part calcification, Chapter 10). However, this may not be so of the ecosystem would be compromised. in highly productive freshwater environments (see A great number of artificial light sources are now Chapter 25). available for use in model ecosystems. Delbeck and Sprung (2005) provide an excellent summary of the more recent lighting developments as they apply to the build- LIGHT AND MODEL ECOSYSTEMS ing of coral reef aquaria. These produce a diverse range of intensity and spectra (Color Plates 7 and 8). Tungsten- Until the 1980s, because of the rule of thumb that filament lamps produce light useful to plants. However, aquatic plants used only a fraction of available sun- a tungsten lamp produces little green and blue light, light, model ecosystems tended to be operated with whereas it is in the blue-green end of the spectrum that relatively low light levels. In the aquarium world, light aquatic plants carry out a major part of their photosyn- was largely considered to be solely for the viewer and thesis. They are also relatively inefficient in terms of PAR perhaps for the activities of fish. Particularly in marine produced compared to heat. On the other hand, the gas tanks, if algae were present, they were primarily the lamps – fluorescent and metal halide – produce a wide encrusting blue-greens that could manage the low light variety of light spectra, much of it within the photosyn- levels (and low water quality). Because these algae thetically useful range (Color Plates 7 and 8). In addition, were often black (and slimy), even such a minimum they are quite efficient in terms of power usage. Many presence was not desired. spectral types of fluorescent lamps are available and, Moe (1989) documents this history and provides an with appropriate mixing of color types, the spectrum of excellent review of the changes in attitude among incoming sunlight to a marine or aquatic community aquarium hobbyists, particularly those specializing in can be reproduced. The intensity of the standard fluo- reef tanks. In the reef aquarium world, the approach rescents is, however, relatively low and, although they has shifted radically, and now we find many of the are strong enough to supply the light requirements of more advanced hobbyists seeking out the various the deepest-water or heavy-shade communities, they are actinic, 10 000 K or even 20 000 K, lamps. These lamps not generally suitable for most sun-dependent ecosys- have a spectrum that is shifted far to the blue. If the pri- tems, especially those from shallow tropical areas. mary interest is to culture deeper water corals or a deep High-output (HO) and very-high-output (VHO) flu- reef ecosystem, this approach is perhaps warranted. orescent lamps can be found in most of the spectral On the other hand, most Acropora, Millepora, and Porites types of standard fluorescents. The same size as stan- species, among many others, grow most rapidly where dard lamps, they put out approximately twice and four they receive greater than 1000 µE/m2/s, at the equivalent times as much radiation, respectively. (Output is roughly of 5000–7000 K (i.e. little shift from the natural spectrum proportional to wattage.) For most small systems (less of sunlight), through the middle of the day (Adey, than 200 gallons), especially fresh- and cold-water coastal
  • 106. 90 5. The Input of Solar Energy microcosms, these lamps are suitable. For coral reef or effective depth of the microcosm. The light at the bot- similar brightly lit communities it is possible to use tom of the reef tanks at 6 feet is equal to that measured VHO lamps, particularly if the tank is relatively shal- at 40–60 feet in the natural reef environment. The result low. However, the light levels of the shallowest coral is that the microcosm contained in this tank is essen- reefs cannot be effectively produced by this means, and tially a scale model, relative to light, and includes the number of lamps that have to be used require major 40–60 feet of reef profile (relative to light) in only 6 feet wiring efforts. of water. Many opportunities and problems are pre- For large (deeper) microcosms and mesocosms, and sented by this compression of depth zones. even larger coral reef aquaria, only the high-intensity dis- The cold-water and temperate microcosms, as we charge lamps, which can be obtained from 250 to 1000 W, have arranged them, are also lighted at least partially by provide sufficient light to simulate shallow-water inten- metal halide lamps. The bottom in the Maine tank slopes sities. For larger systems, of all commonly available light steeply, and the turbidity is moderate. The community sources, metal halide lamps have been found to provide represents a cross section that reaches from the intertidal the best combination of spectrum and intensity for zone nearly to the limit of the photic zone. While sum- simulating natural sunlight (Color Plates 7 and 8). These mer radiation in the Maine intertidal zone can be close to lamps are now available in 2000–6000 K and much that received by an exposed reef, or algal ridge, in the higher models, solving the most acute spectrum prob- tropics, even during times of strongest sunlight, the lems. However, achieving an even distribution of 6000 K energy that reaches the subtidal organisms in the coastal light at 1000 µE/m2/s for a shallow reef flat requires a Gulf of Maine is much less than that in the clear water of dense aggregation of the highest wattage lamps. the tropics. Turbidity is caused by runoff from the land, In ecosystem models, the intensity and period for tidal stirring of sediments, and the bloom of planktonic which artificial lighting is used can be varied to suit organisms responding to high nutrients and the sea- conditions in the native environment of the commu- sonal increase in light. A light measurement equivalent nity being supported. For instance, the microcosms to a depth of about 50–60 feet is registered at the bottom holding the coral reef communities (see Chapter 20) are of the Maine tank, while the intertidal zone receives modeled after areas in the tropical Caribbean between light levels close to those found in the wild. As we dis- 10° and 25° north latitude. Day length at those locali- cuss in Chapter 21, the lights are raised and the daylight ties (photoperiod) ranges from about 11 to 13 h over the period shortened to simulate winter light levels. year, and incoming light intensity at noon, just beneath In the Smithsonian Chesapeake estuarine meso- the water surface, measures about 1800 µE/m2/s in cosm, the shallow and emergent marshes required summer and 1400 µE/m2/s in winter. The “cold tank” maximum intensity, and we used four 1000-W metal (Chapter 21) represents the Maine coast, 2000 miles to halides, at a height of about 3 feet above the soil sur- the north, where photoperiod and light intensity change face, for about 20 square feet of marsh area. It is inter- significantly with the season. In summer the sunlight is esting to note that while radiation of 1200–1800 µE/m2/s almost as strong as that of the tropics and the day is is characteristic of the upper third of the marsh plants, even longer. However, in the winter, light intensity many will grow well into the high-intensity cone of drops dramatically to about 800 µE/m2/s just below light, exceeding 4000 µE/m2/s, with apparent healthy the water surface at noon and there are only 6–7 daylight color ceasing only when temperatures finally become hours. Lighting for these microcosms was planned with too high. On the deeper end of the Chesapeake tank, these conditions in mind, and the diagrams of the eight 160-W VHO lamps are used to simulate reduced arrangements that reproduce them are shown in light in the highly turbid bay analog. Thus, for the Chapters 20 and 21. Clear 500–1000 W lamps are used marsh, a maximum equivalent intensity of 200 W/ft2 is to light the tropical tanks, the brighter lamps over the used whereas in deeper water levels drop to 32 W/ft2 deeper areas. Although output directly beneath indi- (electrical rating). vidual bulbs exceeds the intensity of natural sunlight The period of illumination of each mesocosm, micro- in the tropics, the light level decreases rapidly with dis- cosm, and aquarium that we have constructed (i.e. the tance from the center of concentration. The physical “day length”) is controlled automatically by timers that size of the light units prevents there being more than open and close the light circuits according to a preset one bulb for every 3 square feet of tank surface; thus program. However, full intensity is not delivered to the the mean light intensity per unit surface is lower than microcosms for the entire period of illumination, but that found in the tropics. Peak intensity is, however, changes gradually to imitate the periods of dawn and stretched out over a longer period each day. On the other dusk. This is accomplished by lighting or extinguish- hand, lower intensity in midday results in a rapid dwin- ing parts of lights in sequence over a period lasting up dling of light as it penetrates the water and increases the to 2 h between each light and dark cycle. This allows
  • 107. Summary 91 the tank inhabitants a transition period between day can be greatly reduced before morning. Many shallow and night activities. Most marine organisms are sensi- marine and aquatic environments have relatively dense tive to light changes. Some animals are nocturnal, func- populations. However, in the wild, during the night, tioning only during dark periods, while others are the constant flow of water from less populated areas of active in the daytime. In some cases, these transitions the open ocean, lake, or river supplements the supply are striking. Parrotfish, for instance, rest in a secreted of oxygen and removes wastes. bag of mucous in the dark hours and feed continuously This situation where one ecosystem supplies the during the day. A reasonable twilight or changeover needs of another is common in the wild and can be time is desirable. adopted to preserve the nighttime balance in an aquar- The total light energy available to a microcosm is a ium. Rather than using a large reservoir to replenish the function of period as well as intensity, the length of water at night, a method of ensuring continuous water time as well as the brightness. To a limited extent, a conditioning by plants can be utilized. Our microcosm deficiency of light intensity can be compensated for by systems are connected to separate units that are reserved lengthening the period, but probably with some loss of for the cultivation of a specialized community of algae. accuracy in simulation results. Many plant and animal These units are lighted at night when the microcosms responses are related to day length, especially in popu- are in darkness, and they supply a constant flow of lations from higher latitudes where seasonal variation oxygenated, decontaminated water. This process (algal is significant. Often growth and reproductive cycles turf scrubbing) and the mechanisms built to support it can be closely connected with light period. are described fully in Chapter 11. As Delbeck and Sprung (2005) discuss, there are a Light measurement is an important part of micro- multiplicity of new lighting shapes, sizes, and color cosm management. It is also one of the most difficult of temperatures, as well as increasingly sophisticated con- physical factors to quantify. A number of instruments trolling systems available to the aquarist and modeler. are available for sensing intensity. Examination of However, the basics have not changed over the last spectral characteristics, while not difficult, requires decade. There is great hope for the potential of LED light- even more sophisticated instrumentation. In general, if ing, but the intensities required for coral reefs or most proper light measuring equipment is not available, the shallow-water ecosystems are not yet available. It is guidelines provided above will suffice if the bulbs are hard to imagine how one could use a metal halide replaced on a regular basis (every 6 months). lamp of 10 000 K, except possibly for a very large deep- water ecosystem. Those authors do point out that with the now available lighting, it would be possible to pro- vide harmful UV light to corals and they suggest SUMMARY means for measuring and avoiding the problem. The approach we have shown in Figure 5.19 can be adapted The light phase of photosynthesis is highly efficient, to some of the newer lighting types. perhaps more so than any other process in nature (and certainly far more than industrial creations, Barter et al., 2002). However, the second or dark phase is limited LIGHT AND PHYSIOLOGICAL in several ways by the basic inefficiencies of the key CONSIDERATIONS enzyme Rubisco. The light phase in many planktonic algae is inhibited by high light levels and is therefore The reprocessing of animal and bacterial metabolic reduced in production capability. This may in part be a wastes and oxygen production occur as natural parts result of the UV that accompanies the useable part of of algal metabolism in well-lighted situations. However, the light spectrum, but is more likely the result of a sufficient biomass of plant material must be main- excess O2 production, and oxidation of the photosyn- tained to provide the production of plant food needed thetic centers. In most benthic algae and the higher to accommodate the full requirements of plant-eating plants, it is the dark reactions that are more limiting. animal populations. It is possible to balance this inter- In the higher plants, “photorespiration” (basically a action within a single large tank, but usually this requires chemical “confusion” between CO2 and O2) can be a that the number of animals be limited to their average problem especially when temperatures are high. Some abundance in the natural environment, especially if desert and tropical plants (C4 and C5 plants) have herbivorous species that might deplete the algae are developed mechanisms to concentrate CO2 at reaction included. When the lights go out at night the plants centers and thereby avoid photorespiration. However, stop producing oxygen and, if the animal population is this reduces the efficiencies of those plants under more large, the oxygen supply dissolved in the tank water equable conditions. Benthic algae are at least mostly C3
  • 108. 92 5. The Input of Solar Energy plants and rarely have to deal with excessive tempera- Barter, L., Bianchietti, M., Jeans, C., Schilstra, M., Hankamer, B., tures and photorespiration. Diner, B., Barber, J., Durant, J., and Klug. D. (2002) Biochemistry 40: 4026–4034. The process of ATS (algae turf scrubbing) that we Behrenfeld, M., Esaias, W., and Turpie, K. (2002) Assessment of pri- describe in this book, is a way to optimize photosynthe- mary production at the global scale. In: Phytoplankton Productivity. sis for ecosystem modeling and environmental restora- P.J. Williams, B. le, D. Thomas, and C. Reynolds (Eds). Blackwell tion. This solar–algal process removes many of the Sci, Oxford. deficiencies of “wild” photosynthesis, and could well be Delbeck, C. and Sprung, J. (2005) The Reef Aquarium, Science Art and Technology, Vol. 3. Ricordea Publishing. Coconut Grove. a critical tool to stabilize the earth’s environments until Diamond, J. (2005) Collapse, How Societies Choose to Fail or Succeed. the scientific community can create a viable artificial Penguin. photosynthesis without negative side effects. ATS Gates, D. M. (1980) Biophysical Ecology. Springer-Verlag, Berlin. avoids both photorespiration and photo-oxidation/ Griffith, P., Cubit, I., Adey, W., and Norris, J. (1987) Computer auto- inhibition. By forcing water/cell contact through surg- mated flow respirometry: metabolism measurements on a Caribbean reef flat and in a microcosm. Limnol. Oceanogr. 32: ing, it also avoids the additional serious problem of 442–451. nutrient deficiency that occurs in most benthic and GTE/Sylvania (1987) Color Is How You Light It. Catalog. Sylvania planktonic algae (as well as higher plants). “The same Lighting Center, Danvers, Massachusetts. surging motion provides for light flashing on cells, Hackney, J. and Sze, P. (1988) Photorespiration and productivity avoiding inhibition due to “over-lighting” and shading. rates of a coral reef algal turf assemblage. Marine Biol. 98: 483–492. Heldt, H.-W. (2005) Plant Biochemistry. Elsevier, Amsterdam. The latter problem is so severe in the more typical algal Keeton, W. T. and Gould, J. L. (1986) Biological Science, 4th edn. reactors, that some groups of scientists are working to Norton, New York. genetically engineer planktonic cells to both operate at Kirk, J. T. O. (1994) Light and Photosynthesis in Aquatic Ecosystems, lower light levels and to reduce light absorption (Melis, 2nd edn. Cambridge University Press, Cambridge. 2005). ATS is a planar, rather than a volume system, ren- Lee, R. (1999) Phycology, 2nd edn. Cambridge University Press, Cambridge. dering harvest an efficient process of scraping or suction Lobban, C. and Harrison, P. (1994) Seaweed Ecology and Physiology. rather than filtering. In the terrestrial plants, primary Cambridge University Press, Cambridge. production has a basic limitation resulting from the cou- Lovins, A., Datta, E. K., Bustnes, O.-E., Kooney J., and Glasgow, N. pling of CO2 uptake and water loss. When carbon diox- (2004) Winning the Oil Endgame. Rocky Mountain Inst. Snow- ide uptake and energy production is being considered, mass. CO. Mathews, C. and van Holde, K. (1996) Biochemistry. Benjamin/ water for enhanced terrestrial production (irrigation) is Cumming, Menlo Park, California. rapidly becoming a serious issue; this is not a factor in Melis, A. (2005) Bioengineering of green algae to enhance photosyn- large-scale ATS systems. thesis and hydrogen production. In: Artificial Photosynthesis. A. Collings and C. Critchley (Eds). Wiley-VCH, Weinheim. Moe, M. (1989) The Marine Aquarium Reference. Green Turtle References Publications, Plantation, Florida. Oliver, C. and Larson, B. (1990) Forest Stand Dynamics. McGraw-Hill, Adey, W. (1978) Coral reef morphogenesis: a multidimensional New York. model. Science 202: 831–837. Pace, R. (2005) An integrated artificial photosynthesis model. In: Adey, W. and Hackney, J. (1989) Harvest production of coral reef Artificial Photosynthesis. A. Collings and C. Critchley (Eds). Wiley- algal turfs. In: The Biology, Ecology and Mariculture of Mithrax spin- VCH, Weinheim. osissmus Utilizing Cultured Algal Turfs. W. Adey (Ed.). Mariculture Rheinheimer, G. (1985) Aquatic Microbiology. Wiley, New York. Institute, Washington, DC. Small, A. and Adey, W. (2001) Reef corals, zooxanthellae and free- Adey, W. and Steneck, R. (1985) Highly productive eastern living algae: a microcosm study that demonstrates synergy between Caribbean reefs: synergistic effects of biological, chemical, physi- calcification and primary production Ecol. Eng. 16: 443–457. cal and geological factors. In: The Ecology of Coral Reefs. M. Reaka (Ed.). NOAA Symposium Series on Underwater Research, Vol. 3, Washington, DC.
  • 109. C H A P T E R 6 The Input of Organic Energy Particulates and Feeding The treatment of suspended particulates has been flagellated microalgae, by removing the larger plank- largely ignored in most aquatic models used for ters from the water column. Depending on the exact research and in virtually all aquaria. Unfortunately, in nature of the filter involved, and the turnover time of most cases standard filtration methods remove, or at the system (all the water in the system passing through least attempt to remove, the particles, radically altering a pump or filter several times an hour will have a far their size and quality distribution and rarely is this greater effect than a turnover of once in several days, quantified. Traditionally, the filters employed by aquar- particularly on reproductive stages), filters are likely to ists have been standard bacterial (biological) types, have far more significant effects than pumps alone. As though more recently trickle filters, protein skimmers, we describe in Chapter 20, we have had repeated coral and in some cases resin columns have been used. These larval settlement out of the water column in systems devices are designed to trap particulates as well as sup- without centrifugal pumps and with very low turnover, port biofilms. Less obtrusive “nonfiltration” methods and we have not seen significant coral settlement in such as rotating drums employing bacterial or algal systems with impellor pumps. films have also been employed in aquaculture, though rarely in aquarium or ecosystem models. In this book, we emphasize the use of algal turf scrubbers (ATS) PARTICULATES, ENERGY SUPPLY, AND to control water quality (oxygen, pH, nutrients, etc.). AQUATIC ECOSYSTEMS Some capture of particulates occurs in these devices (see e.g. Adey et al., 1993); however, relative to particu- All organisms and therefore their ecosystems require lates, ATS act more like biofilms than filters. energy to function. For most higher plants and algae, Particles, whether of inorganic or organic material, that energy source is solar, through the process of pho- are an integral part of all aquatic ecosystems. In some tosynthesis. Energy from chemosynthesis, and particu- cases, the use of bacterial or simple physical filtration larly from volcanic vents along mid-ocean ridges, is (or better biofilm capture) might be a valuable compo- quite interesting, but globally is very small as compared nent of modeling, for example, to simulate the sinking to photosynthesis. For many animals and bacteria, the of plankton and other particulates out of an open, sur- energy source, through food webs, is based directly in face-water system. However, when such methods are higher plants and algae. However, for some very large used, the modeler or aquarist needs to insure that the water ecosystems (e.g. the deep ocean and deeper parts filters are functioning in the manner intended and are of lakes), most of the direct organic energy supply is not radically altering the model to a state very different derived from particulates originally created by photo- from that desired. Although we have not studied the synthesis and primary production in shallow water. effects of a variety of filtration systems on a commu- It is well known that small, planktonic algae, proto- nity of plankters (including reproductive stages), we zoa, and bacteria (which can be considered particulates) have examined the effects of standard impellor pumps. are fed on by a wide variety of larger filter feeders, and In general, an impellor pump will select the very small provide the base of open-water food webs. It is not as 93
  • 110. 94 6. The Input of Organic Energy FIGURE 6.1 Diagrammatic representation of the “mass balance” of particulates in a bottom- dominated aquatic ecosystem. Modified after Johnson et al. (1990). widely recognized, at least in aquatic systems modeling, from the capture of oceanic plankton (Chapter 20). In that the ocean, lake, or river “soup” is in large measure some very large ecosystems (e.g. the mid-ocean and made up of suspended particles, in part inorganic, but deep ocean), the only energy supply is through in large measure organic but nonliving. This is the the organic particulates or “marine snow” from surface detritus of the more obvious organisms and their food waters. This particulate transport route is so important webs; it consists of the body parts of animals and higher to biosphere function that it can determine ocean plants, algal fragments, and fecal material, usually chemical composition (Stumm, 1987; Boyd et al., 2000; coated with fungal hyphae and/or bacteria, and is called see also Chapter 3). Finally, marine snow is probably particulate organic material (POM). As it degrades, the “sink route” for about one-half of the anthropoge- POM ranges down to the state of dissolved organic nic carbon as carbon dioxide that is currently released material (DOM). These particulates are not, by any yearly into the atmosphere. means, the end point. They continue to be an energy The “sinking” of organic material in the open ocean, source in mid-water detrital food webs. Even in the after both trophic (food web) and microbial loop dissolved or extremely small particulate state, these reworking, can be quite substantial. Because of this, in organic materials can be absorbed by bacteria, some the 1990s a plan was developed and eventually tested animals, and algae, they can aggregate to form larger to increase planktonic photosynthesis in the Southern particulates again, or they can be adsorbed onto larger Ocean (Boyd et al., 2000), hopefully to greatly increase particles and organic films that have developed on sur- carbon dioxide removal from the atmosphere. In this faces (Figure 6.1). global-encircling ocean, where land contact is mini- In addition, ecosystems are rarely closed in the mum, the potential for iron limitation of photosyn- sense that the energy supply is only directly from solar thesis (Table 4.4) becomes a reality. The concept was to sources. Almost invariably there is an input from an greatly increase photosynthesis by spraying very fine adjacent ecosystem of living or dead organisms and iron particulates on the ocean surface from freighters. organic particulate materials that are derived from Theoretically, this iron would dissolve and be uptaken dead organisms, including fecal materials. Coral reefs by phytoplankters previously limited in production are among the strongest and most efficient photosyn- potential. Eventually, the increased organic material thetic communities on Earth, and yet a significant developed would form “marine snow” that would fall ( 10%) part of a typical reef’s energy supply is derived to the deep ocean, taking carbon out of the atmosphere
  • 111. Organic Particulates 95 semi-permanently and reducing the effects of global moving waters. Particularly in large and very deep warming. After several trials, this “ocean-seeding” waters, such as the open ocean, clays can provide the process did not turn out to be as effective as first primary source of bottom sediment. Ocean sediments thought, and because of additional environmental con- are dominated throughout much of the shallow open cerns, the idea is on hold. ocean by calcium carbonate provided by the rain of Carbon is often used as a proxy for bioenergy tests or shells from coccolithophore planktonic algae; exchange and storage. However, the largest volume at more moderate depths, sediments become domi- of stored carbon near the surface of the Earth lies in nated by shells of foraminifera and pteropods, and inorganic limestones and dolomite, bearing no energy deeper by the siliceous particles derived from diatoms storage. By far the largest proportion of organic (energy- and radiolarians. Both calcium carbonate and siliceous bearing) carbon on Earth is in coal, oil, gas and kero- particulates slowly dissolve as they sink. In the deepest gen, stored over the last 300–400 million years. Only ocean waters only the red clays remain. 1/3000 of the organic carbon on Earth occurs in the Many groups of animals, particularly some biosphere, and only 1/20 000 occurs in the atmosphere. foraminifera (and other protozoans), and many poly- The current scientific evidence strongly indicates that if chaete worms in the sea and chironomids (mayfly larva) a fraction of this stored carbon were to be released into and caddisfly larva in fresh water build their external the atmosphere, especially considering that human skeleta by “glueing” together primarily inorganic par- society is continuously reducing the potential for pho- ticulates. Although organism-derived, these are mostly tosynthetic production and accumulation in the bios- inorganic and do not bring an energy component; we phere, the Earth would be driven into a super-heated, treat these particulates in Chapters 3 and 18. dead Venus-like state. Why wouldn’t it just return us to To chemists and atomic scientists, all matter includ- the “ocean soup” of billions of years ago? Probably ing atomic and subatomic materials is particulate, and because the Earth’s mantle is out-gassing and continu- dissolved inorganic elements and ions we treated in ously producing “new carbon.” While that rate is very Chapter 4, under water chemistry. This was done, even small, over the more recent 300–400 million years it has though we recognize that there is no sharp line, relative produced much of the organic carbon currently on to organism function, between dissolved and particu- Earth. In addition, it is generally thought that the sun late. Here, as is standard in the field, we use 0.45 µm in produces more radiation now than it did during early diameter as the practically useful boundary between Earth time (see e.g. Figure 5.1). In short, we cannot go particulate and dissolved. For a greater depth of treat- back; we must keep the stored carbon out of the atmos- ment we recommend the book by Roger Wotten (1990a), phere, but managing oceanic particulates alone is The Biology of Particles in Aquatic Systems. unlikely to accomplish this need. Assuming that some of the energy supply remains unconverted to organism function and low-level heat, ORGANIC PARTICULATES material input to an ecosystem must be balanced by internal storage of organic materials. This will happen In terrestrial stream–river systems, large logs can be by the buildup of nutrients and other elements, by a displaced by bank erosion or beaver activity and even- temporary buildup of living biomass (e.g. a newly set tually carried into the open ocean. In time, these become mussel bed), or by equivalent export. We discuss the water logged and sink to the ocean floor, where they storage and export equivalents in model ecosystems in continue to be broken down into smaller and smaller Chapters 3, 9, and 11. The form and magnitude of pieces. Maser and Sedell (1994) describe this process of organic particulate input is the primary subject of this mass transfer and degradation of organic materials that chapter. encompasses virtually all aquatic environments. The source of a much greater mass of organic partic- ulate and dissolved material is that of wood and leaf INORGANIC PARTICULATES fragments that enter streams or lakes as larger particu- lates, either from soil erosion or simply by being blown In many aquatic environments inorganic particu- in. These fragments are continually reduced through lates are derived from the terrestrial erosion of rocks clipping, shredding, masticating, and partial digestion and the soils produced by the precipitation and atmos- by a host of invertebrates, particularly insect larvae pheric weathering of rocks. Sand to silt-size particles in fresh waters, as they “spiral” through the food webs do not remain suspended for long (Figure 3.8). of freshwater complexes, and finally into estuaries and However, fine clay particles do remain in suspension the sea. Particularly along rocky or coral coasts, algal for long periods and can be carried great distances by production adds to the detrital/food-web loops and
  • 112. 96 6. The Input of Organic Energy FIGURE 6.2 The movement of particulates (POM) and dissolved organic (DOM) and inorganic (DIM) matter through aquatic systems from the terrestrial realm to the open ocean. Modified after many sources (see especially Kranck, 1984). the suspended and dissolved supply of particulates. In larger streams and rivers, as tree shading is Mud flats and muddy bay bottoms, rich in organic reduced and sufficient light reaches the water column, detritus mostly derived from elsewhere, are rich dumps stream banks, and bottoms, phytoplankton populations of energy as particulates. A host of invertebrates work with zooplankter grazers develop in the water column. these muddy flats and bottoms for their food supply In addition, bacterio-algal surface biofilms (epilithon, (see Chapter 18). periphyton, or aufwuchs) begin to form on substrates
  • 113. Particulates and Aquatic Models 97 freshwater, and soil organic degradation. As polymer compounds, they are highly varying combinations of organic molecules (carbohydrates, amino acids, and fatty acids) and are also highly resistant to further microbial degradation. Terrestrial and freshwater humic substances generally contain recognizable lignin, while marine humic substances do not. Also, marine and ter- restrial humic substances differ in isotopic composition, so that it has generally been assumed that terrestrial organics are largely trapped by the estuarine “filter” or at least do not make it across the shelf in any significant proportion (Millero and Sohn, 1992). Although the process is poorly understood, it is widely accepted that humic substances are gradually integrated into sediments and become the kerogen or “oil” of oil shales, probably the largest single reservoir of carbon on Earth. Kerogen, in turn, subject to appro- FIGURE 6.3 Relationship of the “microbial loop” to the standard open-water food chain. The reality is far more complex than this dia- priate geological heating and pressure, is thought to gram. However, it is useful in emphasizing that even at the level of develop into crude petroleum. Kerogen formed in the dissolved organics the biochemical energy originally formed in pho- marine environment is often called algal kerogen. This tosynthesis continues to be aggregated and inserted back into the organic “waste” is largely derived from humic sub- food chain. Dissolved organics in an aquatic ecosystem, wild or stances originating in phytoplankton production in the modeled, can be an important aspect of function. Modified after Wotten (1990). ocean, especially along continental shelves and in shal- low epicontinental seas. (Figure 6.2). Both of these communities can interact with the terrestrially derived organic particulates, degrading PARTICULATES AND AQUATIC MODELS them physically and chemically, and can even uptake DOM. Wood and leaf particles are not a high-quality food Microcosms, mesocosms, and aquarium models have source. However, as they are worked over, a new and largely ignored the existence of particulates and their higher quality organic particulate with feces and body relationship to equivalent processes in the wild analogs. parts mixes with the wood and leaf-derived detritus. Often particulates and unfortunately any plankton, As the rivers reach estuaries, the flocculating effect of including reproductive states, are removed by a wide salt ions causes much of the DOM and smaller POM to variety of filtration processes. Sometimes, particularly in aggregate into irregular masses and sink to the bottom. display systems, dissolved organics and humic sub- At the same time, laterally, sometimes very extensive stances are oxidized or greatly reduced by ozonation or marshes and mangroves develop that are both trapping resin column and charcoal treatment. Since very few river-derived particulates and massively producing ecosystems operate exclusively by direct primary pro- woody and leafy detritus of their own. In the extensive duction, with degradation up a food web and all par- tidal channels of marshes and among the prop roots of ticulates exported to another ecosystem (and none the mangroves, the same basic organic conversion and imported), an important element of internal recycling is cycling occurs as in the rivers that feed the system. omitted. If bacterial filtration is the reason for the cap- Passing out to sea, much of this material is reduced ture of particulates, the filtration system acts like a single in abundance by sedimentation, incorporation in large and often very important filter feeder and removes organisms through the microbial food web (Figure 6.3) or greatly reduces normal filter-feeding populations and of bacteria, ciliates, and plankton, or simple dilution. their energy contribution to the model. As Tables 6.1–6.4 Further offshore, phyto- and zooplankton come to demonstrate, many filter feeders are able to extract con- dominate the organic particulate spectrum. siderable food value from detritus as well as from dis- solved organics. While the food value in leaf and wood fragments and humic (refractory) substances is very HUMIC SUBSTANCE low, the food value in mucus, organic films, and some detritus can be as high as that of phytoplankton. Humic substances, in the past called “gelbstoff” As we discussed in Chapter 2, pumps can have a or yellow compounds, are the end points of marine, considerable effect on plankters and reproductive
  • 114. 98 6. The Input of Organic Energy TABLE 6.1 Assimilation Efficiency (AE) of Freshwater TABLE 6.3 AE of Freshwater and Marine Shredders Filter and Deposit Feeders on Organic Particulatesa Feeding on Organic Materialsa Taxon AE (%) Food Taxon AE (%) Food Annelida Insecta Oligochaete worms 3–6 Particulates in sediments Pteronarcys 9–16 Detritus Insecta Crustacea Hexagenia 68 Detritus Asellus 23 Decayed leaves Simulium (8) 17–25 Organic particulates Asellus 26–44 Decomposing leaves including plankters Gammarus 10 Decaying leaves Crustacea Gammarus 73–96 Fungal protein Cladocera (2) 10–30 Detritus Hyalella 22 Elm leaf protein Daphnia 2–18 Detritus Hyalella 7–15 Lake sediments Daphnia 50 Bacteria Hyalella 14–23 Sediment protein Ostracoda cypridopsis 85 Detritus Palaeomonetes 91 Detritus Ostracoda dolerocypris 73 Decomposed blue-greens Ostracoda dolerocypris 27 Decomposed green algae a After Wotten (1990b). Reprinted with permission from CRC Press. a After Wotton (1990). Note: In this and following tables – repeated citations of a taxon TABLE 6.4 AE of Freshwater and Marine refer to different experimental trials with usually somewhat Browser/Scrapers Feeding on Organic Particulatesa different results. Reprinted with permission from CRC Press. Taxon AE (%) Food TABLE 6.2 AE of Marine Filter and Deposit Feeders on Insecta Organic Particulates (Including Dissolved Organics)a Spaniocerca 69 Surface organic layer Pycnocentrodes 18 Surface organic layer Taxon AE (%) Food Helodid beetles 30–31 Surface organic layer Mollusca Coelenterata, Gorgonian Potamopyrgus 4 Detritus Coral 22 Coral mucus Potamopyrgus 74 Surface organic layer Mollusca 14 Refractory particulates Hydrobia 5–19 Dead green algae Geukensia Crassostrea 1 Refractory particulates a After Wotten (1990b). Reprinted with permission from CRC Crustacea Press. Acartia 47 Mucus and microorganisms Acartia 50 Coral mucus systems of small volume compared to the wild analog. Mysidium 44 Mucus and In Chapter 11, we discuss ATS, a process emphasizing microorganisms primary production that is designed to control nutrients, Corophium 82–92 Surface of particles oxygen, and carbon dioxide/pH without significantly Echinodermata 30 Organic sediments affecting the particulate spectrum. When low-oxygen Stichopus Parastichopus 17 Organic sediments and low-pH environments are desired, rotating drum Chordata 42 Kelp detritus units can similarly provide a large bacterial film sur- Pyura face for removing ammonia and DOM. DOM, including humic substances, can probably be controlled for view- a After Wotten (1990b). Reprinted with permission from CRC ing situations, where extreme clarity is necessary, by Press. using ultraviolet light at high oxygen levels. The nega- tive effects of ultraviolet light on plankton can be stages, drastically altering ecosystem function. While reduced by limiting application to either a small part of the direct effects of pumping on nonliving or bacterial- the model or only a small part of the pumped overturn coated POM and DOM are probably small, the effect of of system volume. preventing flocculation (coagulation) and thus the building of organic particulates to a size that is utiliz- BIOFILMS able by many filter feeders is a serious issue for many model ecosystems. Bacteria in the environment have generally been Bacterial or algal films (Figure 6.4), in which trap- regarded as primarily planktonic in nature, free in the ping of particulates is minimal, provide a solution to water column or attached to organic particulates until the need to control water quality and nutrient export in those particles are broken down. A newer view regards
  • 115. Particulates and Aquatic Models 99 FIGURE 6.4 The relationship of a river biofilm to dissolved (DOM), colloidal (COM) and particulate (POM) organic matter in the water column. These dynamic interactions apply to all biofilms, to varying degrees, in all ecosystem models. From Lock et al. (1984). Reprinted with permission of Munksgaard International Publishers, Ltd. bacteria as primarily components of a mini but extremely cleaned. In reef and rocky shore models, this may not widespread set of “benthic” ecosystems called biofilms matter, and these surfaces can be regarded as additional (Harrison et al., 2005). In this latter view, biofilms are “bottom” or pore space. However, in many models, diverse communities of bacteria (and protists) in which these surfaces may well provide a significant biologic/ species are “organized” into consortia to perform differ- ecologic presence, with their biofilms, that cannot be ent functions in community maintenance, including the ignored. This is also true of the inside surfaces of piping. releasing of the polysaccharide and protein slime that In general, piping is minimized in the design of any provides the matrix and protection to the communities. ecosystem model for hydraulic and energy reasons. Individual bacterial cells within a biofilm exchange However, biofilms will form wherever such surfaces metabolites and even DNA (Figure 6.4). “Reproductive,” exist and these biofilms will capture particulates, organic free-swimming cells, of bacteria as well as protists, are and inorganic, and become a part of microcosm/aquar- released into the water column to colonize other surfaces ium metabolism. Petersen et al. (2003) describing scaling extending the biofilm. work on mesocosms demonstrate how system volume In the construction of enclosed marine/aquatic must be above a certain level so that wall benthic com- ecosystems, piping and walls add surfaces that do not munity does not overwhelm a plankton community. appear in the wild example or type system. While these However in many systems, the inner surface of piping surfaces are initially neutral, they soon acquire biofilms. with its biofilm could easily exceed tank wall surface. If The glass walls of tanks are usually present to provide this is to be avoided, piping should be of large diameter visibility and are likely constantly cleaned to prevent and short. In Chapter 25, we discuss a specialized situa- biofilm formation. However, especially in larger systems, tion of high ammonia loading where biofilms in piping there may well be significant nonglass walls that are not became a very serious issue of water quality control.
  • 116. 100 6. The Input of Organic Energy Whether this process is significant or not in any given sit- Particulate processes in model aquatic systems are uation is up to the modeler to determine. poorly understood. We make a plea for more research In lower-energy environments, even on shallow, in this area to test against design concepts. While many well-lighted surfaces that contain photosynthesizing of the model systems described in this book have an algae, biofilm communities can become very complex organic input based on known inputs in wild analogs, autotrophic or subautotrophic ecosystems (Burkholder, none have made a serious effort to develop a reason- 1996). We discuss this issue in many chapters, espe- able size or quality spectrum for that input. cially the higher energy variant algal turfs, and the eco- logically engineered subset ATS. AQUATIC ECOSYSTEM RESTORATION PARTICULATE IMPORT IN In Chapter 3, we discussed the role of inorganic sed- AQUATIC MODELS imentation in the problems of restoration of damaged aquatic ecosystems. While inorganic and organic sedi- In most ecosystems, particulate import or export to mentation can occur together, generally the problem of or from external sources (other ecosystems) is normal. excess organic sedimentation is more likely correlated It can be at very high levels, as in tidal mud flats, or with excess nutrient loading. These issues we discuss it may be moderate, as in coral reefs. In a model this in depth in Chapter 25. provides the opportunity to control organic input by “feeding.” As we discuss in Chapter 20, inputs into References coral reef models were based on fine mesh plankton Adey, W., Luckett, C., and Jensen, K. (1993) Phosphorus removal from tows upstream (in the trade wind current) of the reef natural waters using controlled algal production. Restor. Ecol. systems in St. Croix, US Virgin Islands. Unfortunately, 1: 1–11. these tows did not include very fine organic particu- Boyd, P. W. et al. (2000) A mesoscale phytoplankton bloom in the lates, or DOM, and import to these models at roughly polar southern ocean stimulated by iron fertilization. Nature 15% of total organic energy supply may have been low. 20: 695–702. Burkholder, J. (1996) Interactions of benthic algae with their On the other hand, export from the model systems was substrata. In: Algal Ecology, Freshwater Benthic Ecosystems. in the form of algal filaments from scrubbers (POM in J.R. Stevenson, M. Bothwell, and R. Lowe (Eds). Academic Press, the wild), so DOM was also not exported. San Diego, California. Some coral reef microcosms and mesocosms have a Harrison, J. J., Turner, R. J., Margues, L.L.R., and Ceri, H. (2005) faint yellow color at lighting levels less than 5000 K. Biofilms: a new understanding of these microbial communities is driving a revolution that may transform the science of microbiol- However, careful microscopic examination has indicated ogy. Am. Sci. 93: 508. that this coloration is provided by very small suspended Johnson, B. D., Kranck, K., and Muschenheim, D. K. (1990) algae rather than significant humic substances. The sys- Physicochemical factors in particle aggregation. In: The Biology of tems that have this coloration are impellor pump-driven Particles in Aquatic Systems. R. S. Wotton (Ed). CRC Press, Boca units. Even in a situation where waters and organisms Raton, Florida. Kranck, K. (1984) The role of flocculation in the filtering of particu- are mixed between two separate tanks, one with impel- late matter in estuaries. In: The Estuary as a Filter. V. Kennedy (Ed). lor pumps another with bellows pumps, only the impel- Academic Press, San Diego, California. lor pump unit has the yellow coloration. It is very likely Lock, M. A., Wallace, R. R., Costerton, J. W., Ventullo, R. M., and that the impellor pumps select out the small algae by Charlton, S. E. (1984) River Apilithon (Biofilm): Toward a Structural killing off their larger predators and competitors. Functional Model. Munksgaard International Publishers Ltd., Copenhagen, Denmark. There is considerable question whether refractory Maser, C. and Sedell, J. (1994) From the Forest to the Sea, the Ecology of humic substances have any negative effect on system Wood in Streams, Rivers, Estuaries and Oceans. St. Lucie Press, function, though esthetic issues might be of concern. Delray Beach, Florida. At the Great Barrier Reef Marine Park Authority reef Millero, F. and Sohn, M. (1992) Chemical Oceanography. CRC Press, aquarium in Townsville, Australia (see Chapter 20), Boca Raton, Florida. Peterson, J., Kemp, W. M., Bartleson, R., Boynton, W., Chen, C. C., ozone is used periodically to reduce yellow coloration, Cornwell, J., Gardner, R., Hinckle, D., Houde, E., Malone, T., solely for esthetic reasons. This is probably having detri- Mowitt, W., Murray, L., Sanford, L., Stevenson, J. C., Sundberg, K., mental effects on the microbial and planktonic popula- and Suttles, S. (2003) Multiscale experiments in coastal ecology: tions, though no study has been carried out to determine improving realism and advancing theory. Bioscience 53: 1181–1197. whether ozone is a factor in system function. Large Stumm, W. (1987) Aquatic Surface Chemistry. Wiley, New York. Wotten, R. S. (1990a) The Biology of Particles in Aquatic Systems. CRC impellor pumps are utilized on this system and since the Press, Boca Raton, Florida. planktonic microflora and fauna have not been studied, Wotten, R. S. (1990b) Particulate and dissolved materials as food. it is quite possible that the coloration observed has the In: The Biology of Particles in Aquatic Systems. R. S. Wotten (Ed). same origin as the systems described above. CRC Press, Boca Raton, Florida.
  • 117. P A R T II BIOCHEMICAL ENVIRONMENT
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  • 119. C H A P T E R 7 Metabolism Respiration, Photosynthesis, and Biological Loading To maintain a human being or almost any terrestrial can provide us with a good supply of water, we need mammal or bird, the “hotel” requirements seem rela- to worry only about the temperature, salinity, light, tively simple, at least on the surface. Unfortunately, it is space, and food needs of those few species. But what this apparent simplicity that has placed the human about good water quality? That is hard to get from race in its present increasingly difficult environmental most municipally supported taps and many river, lake, situation. As long as there were relatively few of us, and ocean shores these days. When the authors were and our tools and access to the Earth’s great store- young, tap water was still mostly drinkable, and, on a houses of short- and long-term “fossil” energy were hike, one could drink from most streams. Now that is limited, we took for granted many essentials that the rarely the case, and reverse osmosis (RO) created bot- natural ecosystems of the Earth’s surface provided. No tled water is carried by most of us wherever we go. But longer can we assume that good-quality water and RO is very expensive at large scale, and many profes- atmosphere will automatically be available or that the sional production aqua-culturists are increasingly find- products of our daily activities can simply be discarded ing themselves in great controversy because of the for “processing” by nature. With our increasing num- pollution of natural waters that their intense and mas- bers and intense energy use, we are massively chang- sive cultures are producing. ing our planet. With a thorough understanding of In ecosystems, modeled or wild, we do not neces- organism metabolism at the ecosystem scale, particu- sarily want organisms to grow fast, as if we were going larly plant metabolism, and the conditions under to eat them, like a herd of cows in a feedlot or chickens which solar capture by photosynthesis can be opti- in a coop, but we do want them to behave normally. mized in engineered systems, many of these problems This is the context in which we have passed more than can be solved (Chapter 25). However, with time, if 99% of our evolution, one in which thousands of human numbers remain uncontrolled, relative to our species around us behaved “normally” in a mutual large-scale ecosystem management capabilities, our environment or biosphere. Water quality is even more future looks dim indeed. important to an aquatic organism than it is to us. When For the hobbyist and scientist the problem of main- our primary water requirement is for drinking, at least taining aquaria, microcosms, and mesocosms is similar in much of the world we can collect rainwater, use on a small scale to the global environmental problem solar stills, or use a variety of filtering and de-ionizing for the environmental restorationist. Several extremely devices. However, the entire bodies of underwater ani- important wild ecosystem-based fisheries have col- mals are immersed, including their gills and, effec- lapsed. We have had a spectacular example in the loss tively, their internal vascular or blood transfer systems. of what was at one time the largest fishery in the world, So far in this book, we have discussed physical and in the northwest Atlantic. The Atlantic cod fishery is environmental factors, factors that to a large extent still heavily restricted by the Canadian government 15 modern humans immediately understand as part of life years after closure. We can operate aquacultures for a in an industrial society. Now we approach life in a bio- few species, and assuming local aquatic ecosystems chemical context. We also come to a most appropriate 103
  • 120. 104 7. Metabolism question that should precede our attempts to re-create our planet’s surface. The oxygen-rich atmosphere that or restore living ecosystems based on hundreds of living allows the rapid time scale of animal life, and has in species. In the introduction to this volume, we asked part given us equitable temperatures for several billion the question: “How did life originate on planet Earth?” years, the very soil that supports so much terrestrial As we discussed, the scientific community is gradually biomass, and the organic-rich sediments that become piecing together a “most likely” scenario. However, we an integral part of Earth’s geology (perhaps, as some did not entertain the question of: “What is life?” A typi- would have it, even allowing continental drift and the cal dictionary definition would be “a quality that dis- essential features of the Earth’s geology) are all part of tinguishes a plant or animal from the inanimate such the accomplishments of life. These are the unique fea- as rocks, earth, or water,” sometimes followed by “espe- tures of the “living Earth” and probably other living cially characterized by reproduction and growth by planets scattered through the cosmos. They are con- accreting materials from the surroundings.” To say that trary to what the physical evolution of the solar system something alive is not dead is rather circular reasoning; offers when life does not evolve. in any case, many mineral crystals not only reproduce The ability to reduce entropy and produce highly and grow; they often “look alive,” at least in the plant unlikely levels of organization through energy capture sense. Life, of course, is rich in complex molecules of might be the modern physicist’s answer to the nature of carbon, hydrogen, and oxygen, but that is also true of the basic entity that we call life. One biologist’s answer the plastics that we now routinely manufacture. Viruses seems different (see Mayr, 1988): life is uniquely charac- are not alive; they are packets of information that can terized by information, the information encoded in the utilize living cells to make more information. So, what genes. If that is so, then a virus is alive, and so is a clay is the state of “alive”? mineral. Also, a cell from which a nucleus has been Beginning nearly 40 years ago, the U.S. National extracted is already dead, even though it might func- Aeronautics and Space Administration began to have tion as any cell in that state for some time. Perhaps, for this problem when they proposed to find out, as their now, we should retain the ability to store and process space probes and landers touched down elsewhere in energy definition, recognizing that information from the solar system, whether life was present. Dr. James the distant past is required to do this. Lovelock, the author of Gaia (1979) and The Ages of Gaia Several billion years ago life evolved the process of (1988), proposed an answer, outlined below, that is still respiration. The information that allows, through both workable and instructive relative to how we energy conversion, the structural and functional ele- approach life both on Earth and in our mesocosms. ments required to do this has been passed through In a physical context, the science of thermodynamics countless generations of organisms. Every cell in our tells us that energy is always moving to a lower level body has the age-old code for respiration. Hundreds of of intensity or organization. The disorganization of this millions of years ago our distant relatives added energy in the form of the bonding and motion of mole- another level of respiratory complication. Oxygen and cules and atoms (entropy) is always increasing. Thus, carbon dioxide are exchanged in the lungs from the in Earth’s time frame, the universe has been running ambient atmosphere or water to the bloodstream. The down like a battery, as matter flies out from the big blood in turn meets each cell to provide the raw bang. Some billions of years from now this almost materials for respiration. Every cell in our bodies also inconceivable collection of matter and energy is head- “knows” this. Whether a cell acts to “pull its weight” at ing for death close to absolute zero. Perhaps once it has this level depends on whether it is part of this higher- converted all its energy to the gravitational form, it will level respiratory pathway. collapse to another big bang and a rebirth. Our concern Life has what we can call a self-organization capabil- here, however, is the running-down process. On the ity that occurs at many levels. While we humans may time frame of hours to years rather than a few billion well be very bright as animals go, we still do not fully years, life temporarily reverses this apparent process of understand the intricacies of most ecosystems. Yet most senescence. It is capable of collecting small amounts of of these complex systems preceded us by many millions mostly solar energy and chemically organizing, stor- of years, without the benefit of our brains and powers of ing, and directing that energy to rather intensive usage. organization. Throughout this book we suggest that On the scale of the individual, life can literally store since we know only vaguely how to internally organize and concentrate solar energy, eventually to defy grav- and operate ecosystems in a long-term stable fashion, or ity; on the scale of the community, life can store and even in the short term, we should let those ecosystems concentrate energy to be released as heat a few or mil- be “free” to do what they are more than capable of lions of years later; on the scale of the biosphere, life doing. They “know” because they consist of organisms has been and still is capable of massive alterations of with information that dates back millions of years,
  • 121. Metabolism 105 encoded in their genes. Thus, broadly, but in the context transfers the energy of sunlight to hydrogen and elec- of this book, the modeler or the restorationist should trons obtained by the splitting of water and the release supply the right environment as closely as possible, sup- of oxygen (see Chapter 5). Thus, in an ecological sense, ply the right genetic material, then sit back and watch or given light, plants are purifiers: they are constantly begin the experiment as one’s endeavor directs. It is removing nutrients, including carbon as carbon dioxide, often necessary, because of the small scale and location from their surroundings and adding oxygen. Plants are of a given mesocosm or wild ecosystem needing restora- purifiers in many other ways, such that their use in an tion, for the human operator to participate to supply environmental sense is now known by the general term energy, to fill the role of missing larger organisms, or phytoremediation. to offset patchiness. However, given the right outside Animals, on the other hand, eat plants or other ani- parameters (light, temperature, salinity, nutrients, as mals. When they are no longer growing they return all well as appropriate import and export), the “captured” intake materials in reduced form to their environment. ecosystem will generally take care of itself. Even while growing, food-transfer efficiency is low With this statement of philosophy, let us move on to and therefore a large part of the ingested materials is the nitty-gritty of the chapter. A basic understanding of released to the surroundings for breakdown by bacte- metabolism in living organisms and how it relates to ria. As long as the delivery rate of animal plus bacterial the chemistry of the environment is required to develop wastes to the local environment is no faster than the a husbandry capability for captured or managed uptake of the plants that require those “wastes,” then a ecosystems, what Adey (2006) called the “operational balance is present. imperative.” The references will provide the interested An idealized model of animal vs plant requirements reader with a more in-depth treatment of the subject. is shown in Figure 7.1A. If excess plant production occurs, and direct-feeding animals as well as detritus feeders are not available to consume all of plant pro- METABOLISM duction, assuming plenty of water, light, and carbon dioxide from the atmosphere, and some nutrient input, Life in the whale, the tree, the alga, or the protist sur- then plant material accumulates. Given the right condi- vives by the same very basic process: the chemical tions, as in a swamp, this excess organic material could “burning” or oxidizing of organic matter (food) at the go into geological storage as coal for tens of thousands cellular level. Although it is possible to obtain some to millions of years. As we described in Chapter 6, algal energy without oxygen (e.g. by fermentation), cellular remains, as complex and refractory unreduced organic respiration using oxygen is the most efficient pathway. molecules called humic substances, give rise to the very The food, a carbon, hydrogen, and oxygen complex, large quantity of petroleum and kerogen (oil shales) sometimes with nitrogen, phosphorus, sulfur, and stored in the Earth’s crust. Under natural conditions, minute quantities of other elements, is produced inter- excess animals occur only under unusual conditions nally (by plants) or is taken from another organism. that do not last long, usually because the food supply The energy stored biochemically in the food is directed runs out or predators arrive to enjoy the excess. In a cul- to the production of chemical compounds that are ture or human-operated environment, as in a human city, transferred to specific sites in the cell for release as heat where plants do not or cannot balance animals, and or motion or to the building of structural materials for food is artificially introduced, something entirely differ- reproduction or growth. ent happens. Here waste products accumulate (carbon Generally, plants are producers of food and capturers dioxide, as well as nitrogenous, phosphorus, and sulfur- of solar energy. Whether bacteria, algae, or nonvascular rich compounds). Bacteria use the excess waste products. or vascular plants, through photosynthesis and acquisi- However, bacteria, which in most cases metabolically tion of solar energy, photosynthetic organisms build act like miniature animals, when in excess can also rad- sugars, starches, and oils. By this means, plants, algae, ically alter environmental chemistry. In addition, when and photosynthetic bacteria store the captured energy atmospheric access is slow, in water and muds, for for building the even more complex structural and example, oxygen can be used up, creating an anaerobic chemical compounds needed, such as cellulose, lipids, situation that few higher plants and animals can toler- proteins (including the enzymes that drive reactions at ate. This metabolism, occurring out of environmental biological rates), and the informational nucleic acids. context, or organic pollution, is the primary subject of The needs of photosynthetic organisms are great: water, this chapter. carbon dioxide, nitrogen, phosphorus, and many The basic picture of metabolism in a generalized micronutrients. On the average, growing photosynthetic plant cell is shown in Figure 7.2. If the segment involv- organisms are also oxygen producers. Photosynthesis ing photosynthesis in the lower right is removed, and it
  • 122. 106 7. Metabolism FIGURE 7.1 (A) Simplified schematic diagram of the movement of essential compounds by organisms in an idealized closed ecosystem. (B) “Unbalanced” community of plants in which excess plant production is being stored (e.g. in sediments). (C) “Unbalanced” commu- nity of animals in which food is provided. is assumed that glucose and basic nitrogen (and other molecules of a cell are stable with time and can even be nutrients) are derived from digested food not from the stored in excess of immediate need, proteins tend to be water column, then the diagram also applies to a typi- unstable, constantly breaking down and being replaced cal animal cell. Much of the structure of an animal cell by new synthesis. is built up from sugars digested from plant or other animal foods. Some amino acids, for protein construc- tion, are derived directly from food; others are synthe- RESPIRATION sized from ammonia derived from the simultaneous bacterial breakdown of food (in a stomach or intestine). Animals come in a wide variety of sizes and com- In general, the construction or anabolic reactions or plexities. They range from unicellular protozoa (now steps do not occur at the same site in a cell as the break- typically placed in a separate kingdom, the Protista), a down or catabolic reactions. Also, while most complex fraction of a millimeter long, to elephants and whales
  • 123. Respiration 107 FIGURE 7.2 Generalized process of metabolism in a living cell. Plant cells normally add the photosynthetic component on the lower right and dispense with the nitrogenous excretory function on the lower left. Modified after Mathews and van Holde (1996). Reprinted with permission of Addison Wesley Longman. in which tons of complex tissues and multimillions of (Mathews and van Holde, 1996) for a discussion of all cells work together. The basic pattern, based on the cell components. Here we concentrate on the cyto- cell, is the same in all cases. In the more complex ani- plasm and the mitochondria, because it is in these mals, individual cells become highly organized parts locales that the basic respiration and glycolysis processes of tissues and organs specialized in one or a few of the take place. many functions of cells. A generalized animal cell is When an animal eats a plant or another animal, a shown in Figure 7.3. The reader is referred to texts on complex digestive process begins. In the stomach and biology (e.g. Keeton and Gould, 1986) or biochemistry small intestine or their equivalents, digestive acids and
  • 124. 108 7. Metabolism FIGURE 7.3 Idealized animal cell with its multiplicity of internal organelles. After Keeton and Gould (1986). Reprinted by permission of W. W. Norton & Co., Inc. numerous enzymes break down food particles to their ammonia. The blood stream delivers these basic mole- molecular constituents and then the large organic mole- cules directly to each cell in the animal body where res- cules to smaller, simpler molecules. These small mole- piration and the collective anabolic and catabolic cules can be absorbed through the walls of the intestine processes (as in Figure 7.2) can occur. Within each cell, and then enter directly into either the blood stream or the basic energy removal is that of the oxidization or the lymph system. The blood vessels along the small “burning” of sugars. Simplistically, this is C6H12O6 6O2 intestine return directly to the liver where glucose is 6CO2 6H2O 670 kcal/mol of energy: the cell cannot stored and re-released to manage constant levels in the simply burn the sugars. Instead, it uses a small-scale bloodstream, and amino acids are broken down to chemical transfer process. Respiration of glucose
  • 125. Respiration 109 FIGURE 7.4 Simplified diagram showing the process of the complete breakdown of glu- cose, in respiration, to achieve 36 ATP for energy transfer elsewhere in a cell. After Keeton and Gould (1986). Reprinted by permission of W. W. Norton & Co., Inc. produces adenosine triphosphate (ATP) and CO2. ATP and some tissues within organisms to live in an anaero- carries away small packets of energy in chemical bonds bic or partially anaerobic environment. (about 1/100 that of an entire glucose molecule) and When an animal feeds on a plant or another animal, delivers that energy throughout the cell for many pur- it obtains many organic chemicals more complex than poses. Figure 7.4 shows a very condensed version of the sugars for digestion. Proteins and fats are essential to entire process of breakdown of a simple sugar and con- the animal in many ways, providing vitamins, miner- version of its energy to ATP. Carbon dioxide and water als, and other important compounds. However, much are the by-products. One critical feature to note in this of the protein and fats is also simply digested and diagram is that some ATP can be produced without oxy- respired to produce energy, much as sugars (Figure gen. The amount is small, but this primitive process 7.5). Herein lies a crucial element of the effects of ani- (glycolysis or fermentation), probably the dominant one mals on their environment: the production of nitroge- in the early eon of life on Earth, allows some organisms nous wastes and, to a lesser extent, phosphorus.
  • 126. 110 7. Metabolism In more complex organisms, water control and excre- tion have tended to be joined together. In a sense, the unit of the mammalian kidney, the nephron (Figure 7.8), is an advanced flame cell. Because water loss can be cru- cial in land animals, the nephron and the kidney came to reabsorb much water, leaving more concentrated nitro- gen compounds as urea. In fish, on the other hand, the primary excretory product remains ammonia and, par- ticularly in fresh water, large quantities of water and ammonia are excreted through the kidneys (Bond, 1979). The kidneys are by no means the only site of excretory activity. The liver, in addition to being a digestive organ, excretes waste compounds. Also, the digestive system itself excretes, along with the nondigested wastes of the feces, nonabsorbed nitrogen- and phosphorus-rich com- pounds that have been broken down both by the animal itself and by bacteria in the gut. In animals with gills, including fish, much ammonia is excreted through the gills, along with carbon dioxide. FIGURE 7.5 Generalized process of breakdown of proteins and fats to achieve introduction of these compounds into the respiration BACTERIAL METABOLISM process. After Keeton and Gould (1986). Reprinted by permission of W. W. Norton & Co., Inc. Bacteria are neither plants nor animals and today are placed in a separate kingdom called the Monera. Some In many of the tiny protozoans, digestion and excre- bacteria (including the very important cyanobacteria or tion can be seen in their basic form. For example, in blue-green algae) are capable of photosynthesis, thereby Figure 7.6, a small plant or animal is shown being cap- acting like plants. Most bacteria act like animals and tured, engulfed and enclosed in a vacuole (phagocyto- break down dead organisms or are predators acting as sis). The golgi apparatus, through the lysosomes, parasites in living organisms. Bacteria are very simple provides digestive enzymes to the food-filled vacuole. cells, filaments, and colonies. They lack a nucleus and After the food is broken down, undigested particles other cellular organelles enabling them to carry out the (e.g. a diatom silica wall), along with ammonia and complex cellular digestive/excretion process we dis- phosphoric acid, are transported to the cell membrane cussed above. Bacteria excrete their digestive enzymes and simply excreted to the exterior of the cell by exocy- into their surroundings and absorb through their cell tosis. Sugars, amino acids, and nutrients needed are membranes the simple sugars and reduced nitrogenous taken into the cytoplasm through the vacuolar mem- and phosphorous compounds that they require. Nitroge- brane. Also shown in Figure 7.6 is the more general nous and other wastes develop at least partly external to process of recycling of organelles by capture in lyso- the cell. In a sense, when bacteria are abundant, because somes and eventual excretion (B) and even the destruc- dead organic material is abundant, the external environ- tion of a whole cell (D). Pathway (A) refers to the ment locally becomes like that of the stomach or small excretion of digestive enzymes to the surroundings, intestine. We discuss this in depth later, but excess dead such as would occur in some protists. organic material free in a relatively closed space pro- Early in evolutionary history another process vides an environment like a stomach: acid, rich in carbon entered into the excretory picture. In any water less dioxide, methane, and ammonia, devoid or nearly devoid than full ocean salinity, outside fresher water continu- of oxygen, and having many enzymes capable of organic ously moves into the cell by diffusion. The resulting breakdown. This is a specialized environment, which in cell dilution is called osmosis, and it often results in a the open world could be the subsurface of an organic-rich pressurized internal environment. To avoid dilution of mud flat; however, it is not one that many higher organ- the cell to the point of death, some vacuoles (contrac- isms can tolerate. It is also an unsatisfactory environment tile) function to collect this water, eventually expelling for the open water of most aquaria, microcosms, and it to the exterior. A more advanced form of this process, many wild ecosystems. including a specialized cell, the flame cell, is seen in the And now we briefly return to Figure 7.1 and the simple planarian (Figure 7.7). basic ecological point of this chapter. Animals and
  • 127. Bacterial Metabolism 111 FIGURE 7.6 Digestion of food by idealized protozoan cell. After Mathew and van Holde (1996). Reprinted by permission of W. W. Norton & Co., Inc. most bacteria require complex organic foods, plants, produced. In the more-or-less restricted localities and other animals, dead or alive. The principal require- where wastes do accumulate, in some cases entering ment is simple sugars for energy. While a small amount into geological storage, they create a special environ- of vitamins, amino acids from protein, and many other ment in which a few specialized organisms are capable micronutrients are required, only a small part of the of functioning. The biosphere/lithosphere combina- nitrogen, phosphorus, and sulfur in complex com- tion has the means of storing the components of excess pounds is needed. The rest becomes organic waste, organic production – organic-rich sediments and even- some of which is toxic, when concentrated in quantity, tually coal and oil, for example. The same basic storage to many organisms. On the other hand, these wastes equivalent can be accomplished in a mesocosm, and, are required by living, photosynthesizing, and grow- with a little more difficulty, in the aquarium. When one ing plants and algae to build their tissues. In a balanced is dealing with restoration of an aquatic ecosystem that system and in most natural ecosystems, organic wastes is receiving excess anthropogenic waste products, the do not accumulate; they are used as fast as they are storage option may not be possible without changing
  • 128. 112 7. Metabolism the entire character of the ecosystem. However, as we discuss in Chapter 25, prevention of organic import may be possible. PHOTOSYNTHESIS Nearly all the organic energy stored in the Earth’s crust and held as biomass in the biosphere, as well as that used by humans since they have evolved, has been solar energy, captured in the process of photosynthesis. Most of this solar energy has been captured within the chloroplasts of plant cells (Figure 7.9). Nuclear energy remains a miniscule portion of energy used by humans and is likely to also remain problematic. In Chapter 5, we discussed how that energy capture occurs and how, through oxygen release, the process has changed the surface of the Earth, making life possible for more than just microbes. The light reactions of photosynthesis are highly efficient and produce energized electrons and hydrogen ions that end up energizing two transport compounds ATP and NADPH . However, this is just the beginning – the chemical energy built into these compounds has to be efficiently stored and used to build more complex organic compounds and cell struc- ture, plant and eventually animal bodies or it will quickly be lost as heat to the environment. Early in the development of the biosphere, roughly from 2.5 to 3.5 billion years ago, a number of chemical FIGURE 7.7 Planaria flame cell. A cell specialized for water reg- pathways evolved that would allow the anaerobic bac- ulation – a primitive kidney. Keeton and Gould (1986). Reprinted by permission of W. W. Norton & Co., Inc. teria of the time to use the energy of ATP, NADPH , and perhaps other energy carriers, to capture, or fix, CO2 (or possibly –HCO3 in some cases) and build organic compounds (Raymond, 2005). Some of these ancient pathways still exist in more or less rare, anaero- bic bacteria. However, at about 2.5 billion years ago, cyanobacteria evolved the Calvin cycle (see Heldt, 2005 and Figure 7.10). Probably by symbiotic “capture” of cyanobacteria cells by protists, this has been passed on to all algae and eventually to higher plants. The basic Calvin cycle produces fructose and other sugars in the stroma of chloroplasts (see Figure 5.2), and these sugars, mostly translocated throughout the cells or to other cells in tissues, become the building blocks for more complex compounds. The uptake of CO2 in the Calvin cycle, as shown in Figure 7.10, is catalyzed by the highly abundant but very inefficient enzyme Rubisco. Much as in animal cells, the energy-rich sugars pro- duced by plant cells are respired as needed to produce ATP. The ATP-stored energy derived from photosyn- thesis is then transferred throughout the cell and used FIGURE 7.8 Diagram of the principal cellular element of the to build walls (cellulose), nucleic acids, proteins, phos- human kidney. After Keeton and Gould (1986). Reprinted by permis- pholipids (on cell membranes), and more chlorophyll, sion of W. W. Norton & Co., Inc. to name a few. All of these are needed as cells grow and
  • 129. Photosynthesis 113 FIGURE 7.9 Idealized plant cell. To compare essential similarities and differences to an animal cell see Figure 7.3. After Keeton and Gould (1986). Reprinted by permission of W. W. Norton & Co., Inc. divide. These building processes result in a need for these compounds are left for bacteria degradation, the nitrogen, phosphorus, sulfur, and other micronutri- result will be lower water quality, perhaps even an ents, which are primarily taken up as dissolved salts anaerobic environment. (phosphate, nitrate, sulfate, etc.). Ammonia, at least in Plant cells also respire, much as animal cells, and at small concentrations, is a preferred source of nitrogen. night generally require oxygen and release carbon Often, especially in algae and aquatic plants, higher dioxide. In some cases, both in the wild and in closed forms of the most essential requirements, such as urea, ecosystems, the combination of animal and bacterial can also be taken up. In the aquatic environment respiration in the dark can be crucial to ecosystem removal of these compounds by plants can be crucial, function. The practical aspects of this situation are dis- as, in abundance, they are toxic to most animals. If cussed in Chapter 8.
  • 130. 114 7. Metabolism for all the various elements of organic function. Carbon dioxide is produced by this process, and a typical measure of respiration is O2 use or CO2 production. Most important in this context is that the use or production of O2 and the use or production of CO2 are among the most critical and obvious ways in which marine or aquatic organisms change the chemistry of their sur- roundings and the most immediate factors to be dealt with in an enclosed system. In a closed ecosystem, the respiration process is basically no different than that in the wild community, but several factors have to be kept in mind. For example, a high-biomass (and high-metabolic-rate) rocky-bottom community typically relies on constant movement of water from the overlying or off-lying water mass, often a planktonic community, which normally has much lower loading effects. The community in a tank might FIGURE 7.10 Movement of photosynthetic productions in a very well be functioning exactly as in the wild and yet typical plant cell, including most marine and aquatic plants (C3). not have sufficient oxygen to survive at night because After Mathews and van Holde (1996). Reprinted by permission of of lack of contact with the equivalent larger adjacent Addison Wesley Longman. Note that in most algae (other than green body of water. Indeed, this basic situation happens nat- algae) the storage products are often not starch, but a wide variety of oils, alcohols, and starch-like compounds. urally in the wild in a mud-flat environment where the oxygen needs of the community as a whole cannot be met because of inadequate oxygen-exchange mecha- nisms for the large metabolic requirement. A mud-flat BIOLOGICAL LOADING community is adapted to this situation. A rich rocky- bottom community would probably not survive, either As must be very clear from the above discussion, in the tank or in the wild, if this need is not met. living organisms can radically change the chemistry of There are many other metabolic effects of marine their surroundings. From the study of geology and and aquatic organisms that lead to changes, buildups, atmospheric chemistry, we know that global-scale or exhaustion, of elements or compounds in the water changes have been introduced over billions of years by in which they live. Chief among these are the variety of living organisms. In shorter time frames, the same compounds that result from nitrogen metabolism. The effects are very obvious during a red tide, or near an primary problem in this case is the excretion of ammo- odiferous mud flat, and become particularly noticeable nia and related products, toxic compounds in large when one “walls off” a piece of that environment. quantity, that results from the constant breakdown of When scale modeling a living ecosystem, the buffer proteins in animal cells and by some bacteria. In a effect of the larger surroundings is gone and one loses broadly considered wild marine ecosystem, ammonia the normal dynamic balances that result from commu- is very much needed by the photosynthetic organisms, nity-level patchiness in the larger ecosystem. Biological whether phytoplankton, algae, or higher plants that loading is the term that we use to describe the effects of inhabit the community. Thus, it should never be a crit- the organisms present on the physical and chemical ically toxic element either in the wild or in a micro- environment. In a simulation system, biological load- cosm. However, in both cases potential imbalances ing can be classified in two general categories: chemi- exist. On an organic-rich muddy bottom, animal bio- cal exchange and its requirements, discussed in this mass often greatly exceeds plant biomass, which in chapter and the remainder of Part II, and behavioral deeper waters could be totally absent. While bacteria requirements and interactions, discussed in Part III. may then take over the role of plants in taking up and While there is some connection between the two, they utilizing ammonia, the levels of ammonia present are are largely independent of each other. likely to be much higher than those in a community Metabolism refers to the complex of chemical reac- frequented by plants. tions that occur inside a living organism. Respiration Thus, in aquarium science, when a bacterial filter is refers specifically to the basic energy-exchange mecha- used to break down ammonia, not only is more oxygen nisms that involve the use of oxygen to “burn” (chemi- used, but the ammonia concentrations are likely to be cally) the appropriate organic matter to provide energy considerably higher than they would be in a plant-rich
  • 131. References 115 community like a shallow-water coral reef or a rocky of its organic production in the reef itself, and there is shore. Also, dilution plays a major role in potentially major loss of plant fragments to lagoons by most reefs. transferring toxic ammonia from an animal-rich site of This potential organic loss to a reef is partially made up production to a broad area of dilute but more than suffi- for by the capturing of zooplankton swept in by cur- cient plant production. There are many other ways in rents from the open ocean. which use of a bacterial filter can negatively affect many Such mass balances need to be carefully considered marine organisms and communities, and that relates to in microcosm work. For example, in a coral reef micro- a tendency in aquarium science to turn to other method- cosm, if 1 g of dried shrimp is fed to the system each ologies, especially foam fractionation. The same prob- day to simulate the planktonic input from the open lem applies to wild communities, especially streams, ocean in the wild, then more than 1 g (dry) of algae or lakes, and bays with large adjacent human communi- other organics must also be removed from the tank. ties. Sewage plants are nothing but large bacterial filters, This may not necessarily be carried out daily or even and large bodies of water can be destroyed by the ill- weekly – the import/export schedule is a function of considered use of these systems (e.g. Chesapeake Bay). how much imbalance a system will normally take. In some cases, use of a foam fractionator can remove There are several ways in which this can be done, as we excreted particulates and even large molecules, but they discuss in depth later: cannot remove ammonia and CO2 already formed and, in addition, remove the plankton and reproductive 1. weeding of macroalgae; stages that are key elements of most aquatic ecosystems. 2. sediment settling traps that include organic particu- Trickle filters, basically water trickling over abundant lates and foam fractionators that remove those par- surfaces with bacterial biofilms, are a great improve- ticulates as well as large molecules of dissolved ment over the more traditional bacterial filters in that organics (see Chapter 3); atmosphere exchange is greatly improved; however, the 3. removal of larger organisms that have grown in the same basic problems remain. These matters are dis- systems (fish, invertebrates); or cussed in detail in Chapter 9. 4. the use of an algal turf scrubber (Chapter 10). The basic concept under discussion here can be It is also possible to scrape the diatoms or other algae extended to carbonate metabolism, silica metabolism, that grow on the walls of the microcosm or aquarium, and all of the potential water chemistry-altering activi- and to mechanically filter out those scrapings for a short ties of organisms. When one is considering microcosm period. However, a major part of the algae removed or mesocosm simulation of a community, the question tends to be diatoms, and the net result after periods of should be asked: “How does the wild community in several months can be silica depletion. While this might question avoid the problems created by metabolic not be undesirable in some cases, generally it results in imbalances?” If they are solved within the community considerably reduced numbers of both planktonic and on a daily as well as hourly basis, then faithful repro- benthic diatoms. duction of environment and community in microcosm In the next three chapters we discuss the primary will produce the same result. However, if the problem chemical problems of biological loading, respiration, of metabolic imbalance in a wild situation is solved by and nitrogen metabolism, and the generalized means of interaction with another community, or effectively by simulating the required adjacent ecosystem effects. In dilution, then either the alternate community or the Chapters 20–23, in discussing the major types of micro- dilution must be supplied or its effects simulated. cosms and mesocosms on which we have worked, Another aspect of biological loading is long- or other generally less crucial aspects of biological loading short-term storage of organism tissues or organic mate- are considered further. Finally, in Chapters 24 and 25, rials derived from those tissues. Some entire ecosys- we discuss the landscape and global implications of tems, such as bogs, are accumulating storage biomass. human loading on wild ecosystems and the biosphere, In these situations, some high-level organic com- and discuss large-scale methods for dealing with those pounds that could be available to organisms are not problems. being used for a variety of reasons. Fossil fuels derive from long-dead ecosystems that functioned in this manner. Other biological communities, such as reef References lagoons, mud flats, and temperate forests are charac- Adey, W. (2006) Lessons learned in the construction and operation of terized by the accumulation of organic detritus in part coral reef microcosms and mesocosms. Chapter 17 in: Coral Reef of the system (e.g. the soil or lagoonal sediment), Restoration. Handbook. W. Precht (Ed.). Taylor and Francis Group where it is gradually used by organisms specialized to CRC Press, BocaRaton. the environment. A coral reef system stores very little Bond, C. E. (1979) The Biology of Fishes. Saunders, Philadelphia.
  • 132. 116 7. Metabolism Heldt, H.-W. (2005) Plant Biochemistry, 3rd edn. Elsevier, Amsterdam. Mathews, C. and van Holde, K. (1996) Biochemistry. Benjamin/ Keeton, W. T. and Gould, J. L. (1986) Biological Science, 4th edn. Cummings, Menlo Park, California. Norton, New York. Mayr, E. (1988) Toward a New Philosophy of Biology. Harvard Lovelock, J. (1979) Gaia: A New Look at Life on Earth. Oxford University Press, Cambridge, Massachusets. University Press, Oxford. Raymond, J. (2005) The evolution of biological carbon and nitrogen Lovelock, J. (1988) The Ages of Gaia: A Biography of Our Living Earth. cycling – a genomic perspective. Rev. Miner. Geochem. 59: 211–231. Norton, New York.
  • 133. C H A P T E R 8 Organisms and Gas Exchange Oxygen, Carbon Dioxide, pH, and Alkalinity The metabolism of living organisms affects water water body lacks organisms and organic materials, an chemistry in two basic ways: (1) gas exchange (mostly equilibrium or saturation is established that is a func- oxygen and carbon dioxide) and (2) exchange of dis- tion of temperature, salinity, and pressure. Nitrogen is solved nutrients (nitrogen, phosphorus, and a variety of the most abundant gas in the Earth’s atmosphere. micronutrients). However, animals also release undi- However, while it is abundantly present as a dissolved gested food in the form of feces and plants lose or detach gas in water, it is largely inert (as a gas) and is little parts, which relative to the environment are dead organic affected by biological activity. We discuss nitrogen fix- materials undergoing further breakdown primarily by ation and denitrification (exchange from the gaseous microbes. They also excrete organic compounds such as state to the organic or dissolved state and the reverse) ammonia and urea that undergo further microbe degra- in Chapter 9. Here, our concerns are primarily for the dation. All of these processes ultimately use oxygen, next most abundant atmospheric gases, oxygen and release carbon dioxide, and produce nutrients. carbon dioxide. The concentration of these gases is rad- In this chapter and Chapter 9, we discuss gas and ically and constantly altered by organic activity in nutrient exchange, respectively. In Chapter 10, we exam- aquatic and marine environments. The carbon dioxide ine the issue of biomineralization, the formation of bone of the Earth’s Northern Hemisphere atmosphere varies and shell, and particularly the crucial subject of calcium seasonally due to the activity of plants (about 5 of almost carbonate formation by organisms. Calcification is 380 ppm today, it was 320 in 1965). Indeed, so great is important to the entire biosphere, as well as to many the potential for exchange of these gases by biological ecosystems and thousands of abundant species, and is activity that the Earth’s atmosphere has been drasti- inextricably linked to carbon dioxide and its reaction cally changed (over billions of years) primarily by plants. with water. For perspective, we briefly discuss selected In addition, a considerable percentage of the rock on wild aquatic and marine environments followed by the Earth’s surface is limestone or marble (primarily examples from a variety of captured ecosystems. In CaCO3), ultimately derived from carbon dioxide through Chapter 11, we examine methods of controlling gas, the shell-creating or environment-changing activities of nutrient exchange, and calcification in microcosms, plants and animals. Other rocks, such as shales (derived mesocosms, and aquaria. In these model ecosystems, from muds), can also be very rich in organic carbon control or compensation is needed because of the small derived from the bodies of ancient organisms. size of the system in a day–night cycle, the presence of Tables 8.1 and 8.2 give the saturation values, that is, an unnaturally large biomass, or the lack of compensat- concentration at equilibrium, for oxygen and carbon ing larger adjacent body of water. Finally, in Chapter 25, dioxide, respectively, at different temperatures and we show how these same methodologies, at landscape salinities. These values apply to surface waters, and, and even global scale, can lead to the repair of ecosys- for “nonliving” waters, they are good reference points. tems damaged by human organic overloading. However, they hardly ever occur in nature because Gases from the atmosphere diffuse into and out of of the constant exchange activities of organisms. In any water body that the atmosphere contacts. If the aquatic and marine ecosystems oxygen is generally the 117
  • 134. 118 8. Organisms and Gas Exchange TABLE 8.1 Saturation Levels of Oxygen Gas Dissolved such as many submerged aquatic plants and mangroves, in Water as a Function of Salinity and Temperaturea are adapted to living on oxygen-deficient soils or sub- Salinity (ppt) strates and have spaces within their tissues for the storage Temp. and transport of oxygen. Nevertheless, an oxygenated (°C) 0 5 10 15 20 25 30 35 40 water column or atmosphere is required. Some animals and plants can temporarily use nonoxygen-requiring 5 14.8 14.4 13.9 13.5 13.0 12.5 12.1 11.6 11.2 metabolic pathways to derive energy from food. These 10 13.0 12.6 12.2 11.8 11.4 11.0 10.6 10.2 9.8 15 10.3 10.0 9.7 9.4 9.2 8.9 8.6 8.3 8.1 pathways can be utilized in low-oxygen environments 20 9.4 9.1 8.8 8.6 8.4 8.1 7.9 7.6 7.4 or to carry out “extra” metabolism (e.g. the emergency 25 8.5 8.3 8.0 7.8 7.6 7.4 7.2 6.9 6.7 heavy use of muscles) over and above oxygen transport 30 7.8 7.6 7.4 7.2 7.0 6.8 6.6 6.4 6.2 capabilities. Such pathways are, however, much less a efficient than those using oxygen. Recalculated from data of Home (1969). Reprinted by permission of John Wiley & Sons, Inc. Values given as mg/liter. Unicells, or simple filaments, such as bacteria, proto- zoa, and fungi, take up oxygen directly from the envi- ronment through their cell membranes. Multicellular aquatic animals have evolved a variety of organs called TABLE 8.2 Solubility of Carbon Dioxide in Water as a gills to remove oxygen from the water column. They Function of Salinity and Temperaturea have also evolved a number of blood pigments to carry Salinity (ppt) oxygen in the bloodstream (Table 8.3) so that cells situ- Temp. ated deep inside their bodies receive oxygen. In gen- (°C) 0 5 10 15 20 25 30 35 40 eral, it is the microbes, bacteria, yeasts, and some fungi, 0 3.39 3.31 3.22 3.15 3.07 2.99 2.90 2.83 2.75 protozoans, and certain parasites that are adapted to 6 2.72 2.65 2.59 2.52 2.46 2.39 2.34 2.28 2.21 the anaerobic environment. 12 2.21 2.16 2.11 2.07 2.02 1.97 1.93 1.88 1.83 A number of alternate energy, “chemosynthetic,” 18 1.83 1.80 1.75 1.72 1.67 1.64 1.60 1.57 1.53 and nonoxygen-using carbohydrate breakdown path- 24 1.54 1.51 1.52 1.45 1.42 1.39 1.36 1.33 1.30 ways exist. Some produce compounds like hydrogen 30 1.32 1.29 1.27 1.25 1.22 1.20 1.17 1.15 1.13 sulfide, which are quite poisonous to most animals. a Recalculated from data of Richards (1965). Values given as g/liter. Many organisms are adapted to aqueous environments in Note that oxygen (in Table 8.1) is given in mg/liter. Effectively, the which anaerobic sediments are overlain by oxygen-rich solubility of CO2 is hundreds of times greater than that of O2. water or the atmosphere. However, where oxygen depletion is permanent and extends up into the water column, along with the concomitant H2S, the envir- onment becomes largely “dead” except for anaerobic most important and straightforward of the two gases. microbes. This can happen on a very large scale, such Carbon dioxide reacts with water to form carbonic acid as in the Black Sea where deep waters are isolated by and its ionic forms. It is also involved with both inor- the shallow sill at the Bosporus and the rain of organic ganic and organic calcification. We discuss carbon diox- material to deep water exceeds the diffusion and cur- ide second. Note that in a water body not significantly rent transport requirements for oxygen. Unfortunately, affected by the activity of organisms, much more carbon today such oxygen depletion is also happening in dioxide will be dissolved (including its ionic forms) than many lakes, bays, and even coastal waters, ultimately oxygen. due to human eutrophication. In the surface waters of the open ocean, oxygen is generally supersaturated (Figure 8.1). While extensive OXYGEN EXCHANGE surface exchange (wave action) under conditions of low biomass would not allow a large negative difference The vast majority of organisms, animals and plants, from saturation values, either seasonally or diurnally, living on the surface of the Earth and within its waters excess plant biomass and photosynthesis in the well- require an oxygenated environment. While plants pro- lighted zones tend to keep ocean surface waters above duce oxygen, often in great overabundance (to their saturation levels. The ocean is a major original and con- immediate needs), photosynthesis requires light, which tinuing source of oxygen to the atmosphere. It can be is rarely continuous. Most algae and higher plants can- argued that before humans evolved and utilized oxygen not store oxygen and must remove some from their in the burning of forests and fossil fuels, maximum environment at night (even if they produced a great atmospheric oxygen levels had been attained. The use of overabundance during the day). More complex plants, fire in hunting by Stone Age humans probably already
  • 135. Oxygen Exchange 119 TABLE 8.3 Respiratory (Oxygen-Carrying) Pigments in the Animal Kingdoma Hemocyanin: Copper-containing protein, carried in solution. Molecular weight 300 000–9 000 000 Mollusks: Chitons, cephalopods, prosobranch, and pulmonate gastropods: not in lamellibranchs. Arthropods: Malacostraca (sole pigment in these): Arachnomorpha: Limulus, Euscorpius Hemerythrin: Iron-containing protein, always in cells, nonporphyrin structure. Molecular weight 108 000 Sipunculids: All species examined Polychaetes: Magelona Priapulids: Halicryptus, Priapulus Brachiopods: Lingula FIGURE 8.1 Oxygen saturation levels of the surface waters of the Chlorocruorin: Iron-porphyrin protein, carried in solution. South Atlantic Ocean. After Richards (1965). Molecular weight 2 750 000 Restricted to four families of Polychaetes: Sabellidae, Serpulidae, Chlorhaemidae, Ampharetidae Prosthetic group alone has been found in starfishes, Luidia and Astropecten Hemoglobin: Most extensively distributed pigment; iron- porphyrin protein, carried in solution or in cells. Molecular weight 17 000–3 000 000 Vertebrates: Almost all, except leptocephalus larvae and some Antarctic fishes (Chaenichtys, etc.). Echinoderms: Sea cucumbers Mollusks: Planorbis, Pismo clam (Tivella) Arthropods: Insects Chironomus, Gastrophilus. Crustacea Daphnia, Artemis Annelids: Lumbricus, Tubifex, Spirorbis (some species have hemoglobin, some chlorocruorin, others no blood pigment). Serpula, both hemoglobin and chlorocruorin. Nematodes: Ascaris Flatworms: Parasitic trematodes Protozoa: Paramecium, Tetrahymena Plants: Yeast, Neurospora, root nodules of leguminous plants (clover, alfalfa) a After Schmidt-Nielsen (1975). significantly lowered oxygen concentration and raised that of carbon dioxide. The domination of Australian FIGURE 8.2 Dissolved oxygen levels in the sea (in ml/liter). After forests by eucalyptus and the abundance of parklike Dietrich (1963). grasslands and sedge lands in place of the previously dominant Nothofagus and Araucaria forests were proba- bly caused by the aborigines’ burning activities (Flood, trigger glacial periods (reverse global warming) and set 1983). Atmospheric oxygen levels prior to human influ- another kind of limit on photosynthesis. ence were in part limited by the natural combustion In somewhat deeper water (100–700 meters) in the levels of forests. In short, “the world is (or at least was) open ocean, oxygen levels reach their minimum (Figure green.” Plants probably have the capability to raise 8.2). This is below the lighted or photic zone of plant atmospheric oxygen concentrations higher than they activity. It is also a level at which the rain of algal and ani- are, perhaps to 22%. The potential for subspontaneous mal waste material from the surface provides relatively combustion of forests on land, the release and oxidation high animal and bacterial activity. Finally, in the lower of methane from anaerobic deposits, and perhaps the half of the deep ocean, oxygen concentrations return reduction of carbon dioxide to the point where photo- to near-surface values. These deep waters are cold synthesis becomes very slow set the limit to atmospheric and largely derived by deep currents from Arctic and oxygen levels (see Lovelock, 1979). Although there is Antarctic zones. At their high-latitude sites of origina- much debate on the subject, low CO2 levels could also tion, oxygen saturation levels were initially high. Also, at
  • 136. 120 8. Organisms and Gas Exchange cold temperatures plant photosynthesis is relatively biomass (Stumm and Morgan, 1981). Also, in oxygen- more efficient than either plant or animal respiration. poor environments, glycolysis and fermentation result Open coastal waters are similar to the open ocean, in the partial breakdown of plant-produced organics though fluctuations are greater. without the use of oxygen. This is how oxygen derived Lakes and rivers tend to operate under similar oxygen from the photosynthetic splitting of molecular water has distributions but, on the average, show a shift to lower gradually built up to high levels in the atmosphere. oxygen levels. This situation derives from the addition of Even if the Earth has now reached a balance (independ- terrestrial organic matter from the surrounding water- ent of humans) in oxygen production, and levels are no shed. There are almost as many oxygen distribution and longer building up in the atmosphere, the excess oxygen exchange patterns as there are lakes. For more detail see required by methane, coal, and oil as they are exhumed Chapter 2 and the extensive discussion by Hutchinson on the surface of the Earth is not generally recycled by (1957) and Dodds (2002). In summary, oxygen concentra- organisms in aquatic environments. Thus, most natural tions in the surface waters of most lakes are near satura- water ecosystems not made eutrophic by humans, par- tion levels. Relatively clear, unproductive lakes in which ticularly shallow-water environments, will tend to be a more ordered organic and oxygen exchange occurs can supersaturated or at least rich in oxygen. average supersaturated levels of oxygen at the surface and moderate oxygen levels at depth. At the other extreme, in eutrophic or nutrient-rich lakes, variations in OXYGEN, MODEL ECOSYSTEMS, AND oxygen concentration can be very large. Under the right ECOSYSTEM RESTORATION conditions in the spring or summer, such lakes bloom with intensive plant growth. In these cases, oxygen In microcosms and mesocosms where one is attempt- supersaturations of 50% or more are eventually followed ing to simulate all aspects of a particular environment by a “crash” in oxygen levels by late summer. Such and ecosystem, presumably one provides enough light eutrophic lakes build up biomass to the point where and the appropriate plant community to simulate wild oxygen diffusion at night is not sufficient to prevent levels of photosynthesis. If diurnal and season oxygen anaerobic conditions resulting from the very large oxy- measurements show oxygen levels below those in the gen requirements. Extensive fish kills often result. Unlike natural community then there is a serious problem that the oceans, lakes, and rivers acquire significant organic should be corrected. This is often the simplest proxy loads from the terrestrial environment. Where depths measurement for the overall model veracity. Assuming extend well below the photic zone, mean oxygen deficits that community structure is more or less correct and can exist, and a lake will use more oxygen than it pro- photosynthetic plant biomass and animal biomass are duces or can diffuse through its surface. properly balanced, a problem of low oxygen levels is Estuaries lie between lakes and rivers and the ocean likely to be caused either by inadequate light or by a fail- with regard to mean oxygen concentration and can be ure to simulate water flow from areas of higher oxygen more like one or the other depending on the nature of concentration, particularly at night. The first problem the organic and nutrient input of the fresh waters and was discussed in depth in Chapter 5. We discuss the the amount of exchange with the ocean. In lakes, rivers, solution to the second problem in Chapter 11. and estuaries, organic and nutrient inputs by humans In microcosms and mesocosms, even if the builder are crucial to oxygen levels and organic stability. Indeed, and operator are attempting to maximize equivalences oxygen depletion often becomes the most essential ele- between the wild environment and the aquarium, scal- ment of human degradation of aquatic environments – ing and inadequate ratios of water surface to water vol- more on this below. Mesocosms and aquaria are similar. ume can provide great difficulties relative to oxygen Photosynthesis and respiration are often summed up concentration. In the aquarium, where display is a pri- as CO2 + H2O + energy (light/chemical) CH2O + O2. mary function and volume is small, animal biomass is Ecologically, this implies a balance in which all energy- likely to be higher than normal, particularly for the rich organic compounds created by the photosynthesis marine environment. Also, artificial feeding in excess of of plants are either metabolized by the plants them- wild equivalents is almost invariably provided to an selves or metabolized by animals through a food chain. aquarium. Thus, except for the relatively unusual envi- However, this is not the case. Much plant and some ani- ronments normally low in oxygen that one might try to mal organic material goes into geological storage, even- model, it is difficult to simulate a proper oxygen envi- tually becoming peat, organic-rich shale, coal, gas, and ronment by simple aeration. While trickle filters and oil. It is estimated that over 14 000 times as much organic foam fractionaters may improve oxygen exchange, with- material and other carbon of organic origin lies in geo- out using bottled oxygen, they cannot achieve the super- logical storage as presently exists in the biosphere as saturation of wild systems.
  • 137. Carbon Dioxide Exchange 121 Many lakes and ponds have become hypoxic or down photosynthesis to some degree. However, in most anaerobic and unaesthetic and useless for recreation due aquatic and virtually all marine environments there is to nutrient overloading by sewage plant outfalls, farm usually a very large supply of this essential compound runoff and runoff from urban/suburban development (as bicarbonate ion, HCO3 ) available for all biological (Livingston, 2006). This widespread problem has activity. On the other hand, excess carbon dioxide tends expanded and moved downstream, so that in recent to increase the acidity of an environment and renders the decades one of the largest estuaries in the world calcification requirements of an organism more difficult. (Chesapeake Bay – Blankenship, 2005) and even coastal As shown in Figures 8.3 and 8.4, the proportion of the areas (Gulf of Mexico – USGS, 2005) have developed primary components of the carbonate system (carbon large “dead” (anaerobic) areas during the summer. In a dioxide, bicarbonate, and carbonate and hydrogen ion, case of minimum overload (e.g. a pond with human-fed pH) present in any given water mass is a function of the ducks), a water fountain aerator might temporarily interaction of several chemical equilibria dependent on solve the problem. Restoration of these large-scale envi- temperature, salinity, and pressure. The status of the ronments can be accomplished, and we discuss the oxy- entire system under any given set of conditions can be genation and denitrification methodology in Chapter 25. determined by measuring any of two of the following 2 components: pH, total alkalinity, total CO2 (CO3 + HCO3 + CO2), and the partial pressure of CO2 (e.g. CARBON DIOXIDE EXCHANGE Millero and Sohn, 1992). In practice, this is usually done by measuring pH and total alkalinity. Total alkalinity for The other major gas involved in exchange between sea water consists of bicarbonate (HCO 3, approximately 2 organisms and their environment is carbon dioxide. The 89%), carbonate (CO3 , approximately 6.7%), borate activity of CO2 is, in a sense, the inverse of oxygen, the (B(OH)4, 2.9%), and several minor components (includ- two being primarily cross-exchanged between plants ing OH ) adding up to less than 0.5%. In most meso- and animals (Figure 8.3). However, it is also very differ- cosm work, where great precision is not needed, ent from oxygen in that it reacts chemically with water. inexpensive analytical kits are available to measure total Also, CO2 is intimately bound to calcification or shell and alkalinity or carbonate alkalinity. However, pH should wall formation in many organisms (bacteria, protists, be measured with high-quality probes and meters using plants, and animals) and to the chemical precipitation of high-quality buffers for standardization. limestones. Photosynthesis and calcification by organ- Calculating the expected changes in the carbonate isms are intimately linked through carbon/carbonate system of any body of water can be done using the chemistry (McConnaughey, 1994; Small and Adey, 2001). equations discussed in depth by Millero and Sohn (1992). In synergistic fashion the two processes enhance each In field work on coral reefs, for example, alkalinity deple- other and have thus given rise to many animals/algal tion from ocean water pouring over a reef has been symbioses in the ocean. Unlike oxygen, relative to respi- used repeatedly to determine rates of community calci- ration, the lack of carbon dioxide in special terrestrial and fication. In practice, in mesocosm and aquarium work, aquatic environments (including greenhouses) may slow Figure 8.4 can be used to estimate magnitude and direction of change due to biotic effects, and actual measurements of pH and alkalinity can be taken to verify the expected changes. With some minor modifi- cation, the nomographs for evaluating bicarbonate and carbonate alkalinity and carbon dioxide given in the seventeenth edition of Standard Methods for the Examina- tion of Water and Wastewater (Cleseri et al., 1989) can be used to quickly and precisely evaluate the status of the carbonate system in both wild and captured systems. Note that while removing carbon dioxide through pho- tosynthesis, in a closed system, raises pH with little effect on alkalinity, calcification lowers both pH and alkalinity. Thus, photosynthesis supports calcification by removing the excess CO2 produced and preventing acidification. Calcification, in turn, supports massive FIGURE 8.3 Chemical and biological movement of carbon diox- photosynthesis (and oxygen production) by preventing ide in aquatic and marine ecosystems. After Horne (1969). Reprinted depletion of the carbon supply. We discuss these matters by permission of John Wiley & Sons, Inc. in greater depth in Chapter 10. A specific example
  • 138. 122 8. Organisms and Gas Exchange FIGURE 8.4 The distribution of dissolved compounds in the carbonate/water reaction chain as a function of pH. Note that sea water is buffered and occurs only over a limited pH range, while pure water can range widely. After Home (1969). Reprinted by permission of John Wiley & Sons, Inc. applied to a coral reef microcosm is given in Chapter 20 the surface where, partly through the atmosphere, and described in depth by Small and Adey (2001), with organisms can again turn over that stored carbon. All of the primary elements of the carbonate system shown in the carbon on the surface and in the continental crust, Figure 8.5. except for a small amount of new carbon arriving from In the CO2–CaCO3 system, the oceanic parallel to deep in the Earth, mostly through volcanoes, has been high photosynthesis, high levels of oxygen in the sur- cycled through organisms several times. At least prior to face photic zone, is seen in calcium carbonate satura- the use of fossil fuel by humans, it is likely that the tion (Figure 8.6). In tropical oceans, ultimately due to storage of “organically derived” carbon in the Earth’s photosynthesis, there is a great excess of calcium car- rocks was continuing to grow slowly as the continents bonate in crystalline form as shells. However, in deeper enlarged (Chapter 3). water, carbonate concentration rapidly falls and calcite becomes undersaturated (i.e. shells begin to dissolve as they sink). Where the oxygen minimum and the carbon dioxide maximum meet, sea water has only 70% of sat- CARBON DIOXIDE AND GLOBAL uration levels. Finally, below about 4500 meters the AQUATIC RESTORATION rate of supply of calcium carbonate from the surface is exceeded by dissolution and carbonate shells are virtu- Most people are aware of the concept of acid rain ally absent from sediments. and understand that many lakes in largely igneous and Most of the carbon on the surface and in the crust of metamorphic regions such as New England and the Earth does not occur in organisms or in the atmos- Scandinavia, where there is little carbonate buffering, phere. At any one time, carbon occurs mostly in lime- have had their fish populations radically altered by stones, in coal and oil, and in other organic rock such rain from upwind industrial areas. Carbon diox- derivatives (Figure 8.7), mostly deposited in shallow ide in the atmosphere does make rain acidic, as we waters. However, the exchange rate, primarily through describe below; however, in the case of lakes it is excess carbon dioxide, is very large. For example, carbon SOX from coal-fired power plants, effectively sulfuric turnover between the atmosphere and organisms occurs acid in the rain that is the primary problem. However, on the order of every 20 years. Also, as large as the reser- the ever-increasing CO2 in the atmosphere, resulting voir of carbon is in the rocks, on a time scale of about 400 from the burning of all fossil fuels, is also having a seri- million years, geological processes bring the carbon to ous effect on the pH of natural waters.
  • 139. Carbon Dioxide and Global Aquatic Restoration 123 FIGURE 8.6 Factors affecting the distribution of calcium carbon- ate as calcite, with depth, in the equatorial Pacific Ocean. After Kennett (1982). Sea water is strongly buffered for pH and generally ranges from 8.00 to 8.40. Because of the ions present, great changes in carbon dioxide are necessary to effect a small change in pH. Nevertheless, most marine organisms are particularly susceptible to small pH changes, and in this respect, environmental status is crucial. Despite the buffering, the pH of sea water can be reduced as a function of the interaction of sea water with the CO2 in the atmosphere as well as photosyn- thesis and calcification in shallow water. Roughly one half of the anthropogenic CO2 released into the atmos- phere does not show up in the many standard meas- urements taken of the atmosphere. It has generally been thought that this was a good thing, as it has so far saved human civilization from the worse complications of elevating atmosphere CO2. However, researchers FIGURE 8.5 The daily state of the carbonate system and pH in a have now begun to document drops of pH in oceanic coral reef microcosm. (A) mean pH levels during a 24-hour cycle for one year; (B) mean Talk (total alkalinity) during a 24-hour cycle for waters. This process is expected to reduce calcification one year; and (C) mean state of daytime carbonate system calculated by 14–30% by mid-century (Kleypas et al., 1999; Osmond, by nomogram from Talk and pH. From Small and Adey (2001). 2004). While there is little question that this will have
  • 140. 124 8. Organisms and Gas Exchange of sand- or silt-size aragonite, the least stable form of cal- cium carbonate, is invaluable. The shells of some cal- careous algae (e.g. Halimeda) or crushed coral skeleta can provide the aragonite (when clean of organic material). Oolitic or nearly pure Bahamian aragonitic sand is mar- keted in bulk in the United States. Spotte (1992) has argued that in an aquarium system, such carbonate (as calcite) has its potential dissolution surfaces “blocked” by magnesium overlays. Organic material can have the same effect. Thus, even though boring and scraping constantly make new surfaces available in a high diver- sity, properly functioning mesocosm, it is good practice to use a fine aragonite sand or silt and to arrange for frequent delivery of fresh sand. In part, by reducing carbon dioxide production and removing carbon dioxide through “excess” photosyn- thesis one can achieve a status of the pH/carbonate complex that is equivalent to most shallow sea waters. FIGURE 8.7 The carbon cycle on Earth showing the approximate However, if significant calcification is occurring in a quantities of carbon and relative exchange between compartments. closed system and maintaining the rate of such calcifi- Mass exchange rates are given as microgeomoles/year (1014 moles/ cation is a primary feature of the model, it will likely be year). Carbon mass is given as geomoles (1020 moles). After Stumm and important to replace alkalinity depletion with an out- Morgan (1981). Reprinted by permission of John Wiley & Sons, Inc. side source, much as occurs in the wild. This process is discussed in greater depth in Chapters 10 and 20. However, it is important to emphasize that many prop- disastrous effects on already damaged coral reefs world- erly operated shallow water microcosms, especially wide, the more dangerous effects on biosphere health coral reef systems, will have calcification rates that are may be in changing the role of calcifying coccolithores, so high that both alkalinity and calcium ion need to be the dominant phytoplankters in tropical and temperate monitored and re-supplied, just as in the wild. shallow ocean waters. As we noted above, the exchange rate of carbon Fresh Water dioxide between the biosphere and the atmosphere is very high, overturning on the order of 20 years. This is Rainwater from an unpolluted atmosphere typically a good thing, in that it means that the undesirable has a pH of less than 5.6 (i.e. moderately acidic due to changes that we have brought about in our atmosphere the interaction of atmospheric carbon dioxide with the can be reversed relatively quickly, by reducing fossil water while it cycles through the atmosphere. On lime- carbon export and increasing photosynthesis. We dis- stone and related substrates, this natural acidity can be cuss just such a scenario in Chapter 25. Here, we simply strongly buffered. In some cases, however, particularly note that for a fraction of the cost of going to war we can on largely unbuffered granitic rock basements, and with solve one of our most serious environmental problems. the addition of organic acids from some vegetation, the natural acidity of the rainwater can be significantly increased in the surface and groundwater. Freshwater lakes, ponds, and rivers typically vary from slightly MANAGING CARBON DIOXIDE AND pH IN acidic (pH 6) to moderately basic (pH 9). Extremes occur MICROCOSMS AND MESOCOSMS from acid volcanic lakes (near pH 1) to soda lakes (at pH 12), though these would be of concern only to a few Sea Water aquarists. Because of great concern over the polluting Within a model system it is possible to increase the effects of acid rain and the resulting environmental acid- buffering effect of sea water using calcium carbonate ification, considerable study has been directed to the chips or substrate. Since most shallow marine waters are negative effects of acidification on flora and fauna highly supersaturated with calcium carbonate, this is an (Figure 8.8). The interested reader is referred to Cresser essential fail-safe feature for any marine microcosm or and Edwards (1987). aquarium. In small and difficult situations with heavy In the modeling of freshwater systems, the aquarist animal loads or high calcification requirements, the use seeks to simulate waters of a given pH. For basic
  • 141. Gas Exchange and Selected Model Ecosystems 125 geologically and biologically, and has been studied in some detail. The water moving onto the reef due to wave and current action typically has an oxygen concentration close to 6.5 mg/liter, a level that varies by only a few tenths day and night (Figure 8.9). This is essentially the saturation point. As this sea water flows in over the reef, driven by the constant trade winds, it picks up extra oxy- gen, becoming highly supersaturated during the day because of excess photosynthesis, that is, photosynthesis that exceeds respiration. On the other hand, at night the same water loses oxygen, due to the respiration (without photosynthesis) of both plants and animals in the reef. The effect of extensive wave breaking on the exchange of oxygen can also be marked on rough days and causes oxygen loss during the day and oxygen gain at night, the net effect being to smooth out metabolic effects on the gas concentrations. This is not an unusual pattern for a well-developed, open-water coral reef, whether Indo- Pacific or Caribbean (see Chapter 20). To simulate this typical reef environment in a micro- cosm system, the aquarist would need to obtain a night-to-day oxygen concentration range from 5.5 to FIGURE 8.8 Lower pH tolerance limit of common molluscs and 8.5 mg/liter, 6.3 mg/liter being the approximate satura- crustaceans found in Norwegian fresh waters. After Cresser and tion level. The traditional marine aquarium, with its Edwards (1987). Reprinted with permission of Cambridge heavy animal oxygen requirement, increased by bacter- University Press. ial action in biological filters, cannot achieve supersatu- ration. Trickle filtering and foam fractionation release waters, above pH 8.0, the same rules previously dis- oxygen from the water and actually prevent supersatu- cussed for salt waters apply. On the other hand, if neu- ration, though oxygen rather than or mixed with air tral or acidic waters are desired, the situation becomes might produce the appropriate effect. Even if well more complex. Certainly if a high-nutrient, low-pH lighted, such a system is likely to remain undersaturated environment is desired and oxygen levels are not a for oxygen and may well go below 5 mg/liter at night. concern, then bacterial filtration is an ideal approach to The lower limit of oxygen for water overlying a reef com- system management, preferably using a rotating drum munity is probably typically about 4 mg/liter under or trickle system instead of a “filter” unit to avoid exceptionally calm conditions. Extensive periods lower removing plankters. On the other hand, if a low-nutrient, than this level in the main mass of overlying water low-pH (e.g. a black-water stream) environment is would likely be detrimental to reef plants and animals, needed, the situation becomes considerably more diffi- especially because oxygen concentration would be con- cult. In mesocosm and microcosm simulations of siderably lower in the interstices of the reef. Intensive air black-water streams where fish and invertebrate bio- bubbling carried out in well-kept and reasonably loaded mass are kept appropriately low and where energy traditional tanks could produce minimum oxygen levels input is derived largely from slowly breaking down at or above 4–5 mg/liter. However, without intense light- leaf litter, minimum mechanical filtration or, prefer- ing and abundant photosynthetic plants (or an oxygen ably, settling traps may be all that is required. For sim- bottle) it would not be possible to raise oxygen concen- ulating highly acidic natural waters, acidification can trations above 6.5 mg/liter and likely not even to that be derived from CO2 bubbling. level. The “dry”-type trickle filter is excellent for raising oxygen levels from the lower potential values. However, it too loses oxygen during the day. A dry trickle filter GAS EXCHANGE AND SELECTED could be attached to the system at night and separated MODEL ECOSYSTEMS during the day to overcome this problem. The oxygen concentration in a Smithsonian coral reef The southern bank barrier coral reef on the Caribbean microcosm compared to that in the wild reef is shown in island of St. Croix can be regarded in many ways as a Figure 8.9. As described in Chapter 11, by using an algal generalized tropical reef. It is mature, well developed turf scrubber rather than a bacterial filter, even during
  • 142. 126 8. Organisms and Gas Exchange FIGURE 8.9 Comparison of oxygen levels in the open sea and on a St. Croix coral reef with levels in a coral reef microcosm (see also Chapter 20). After Adey (1983). –, Oxygen saturation. the dark hours oxygen levels are stabilized just below thereby lowering pH even while oxygen remains at sat- saturation levels. During the day oxygen levels in this isfactory levels; therefore both O2 and pH levels through- well-lighted reef tank (see Chapter 20) rise well above out the day should be checked at least occasionally. saturation and in most respects match wild reef values Equally important, as discussed in Chapter 9, nitroge- closely. nous exchange between plants and animals is not sig- Using an oxygen meter, one can measure the rate of nificantly affected by atmospheric exchange. Even if oxygen uptake in a mesocosm or aquarium system oxygen is artificially kept above 5 mg/liter by physical during the dark at near saturation levels to determine atmospheric exchange methods, it does not mean that if the community respiration load is equivalent to that water quality is not otherwise rapidly degenerating. It is in the environment one wishes to simulate. This meas- wise to have either adequate water buffer to carry a sys- urement must be taken at or near saturation so as not to tem through the night or a plant-compensating system. have to account for exchange with the atmosphere. The critically important variable of photosynthesis, In one of the early 1800-gallon reef tanks, for example, or primary production, is treated in several chapters. the dark respiration rate was about 2 g O 2/m2 of reef However, it is so inextricably linked to oxygen, carbon surface/hour or about 24 g O 2/m2/day. This is only dioxide, pH, and system loading that its role is repeated about one-half of the wild St. Croix reef rates, which again here in the context of a coral reef model. Net pri- presumably means that we could have doubled our mary production (in terms of oxygen) for the St. Croix animal respiratory load, assuming that wave or other reef is shown in Figure 8.10. If oxygen loss due to respi- exchange keeps oxygen concentrations at a minimum ration, which we presume to be roughly constant at all of about 4 mg/liter. Later tanks have had rates of times, is removed from the data (by dropping the zero 3–5 g O 2/m2/h, rather closer to rich reef levels. line approximately 2.5 g O 2 /day), a curve of approxi- Oxygen is relatively soluble in water and exchanges mate total photosynthesis is derived. Several important rapidly with the atmosphere in bubbling or wave action. pieces of information can be derived from this diagram. However, carbon dioxide exchanges more slowly and First, total photosynthesis is very high, at approximately even though sufficient oxygen may be supplied to a 40 g O 2/m2/day. If this is converted to actual plant pro- microcosm, CO2 concentration may well increase rapidly, duction (leaving out what the algae themselves use),
  • 143. Gas Exchange and Selected Model Ecosystems 127 FIGURE 8.10 Mean yearly diurnal oxygen exchange for several reef transects on the island of St. Croix. After Adey and Steneck (1985). one finds a rate of about 25 g ( dry weight)/m2/day. In activity for short periods in the summer and essentially the laboratory, measured rates of actual algal production shut down for the colder, darker part of the yearly consistently achieve 10–20 g ( dry weight)/m2/day on cycle. However, examination of primary production in flat screens. Since a typical reef has several times the Gulf of Maine rocky-bottom kelp and rockweed com- mean surface of a flat screen, the reef value measured munities shows that this is hardly the case (Figure by oxygen seems not unreasonable. Also production 8.11). Photosynthetic efficiency, or available light con- (photosynthesis) continues to increase during the morn- verted to biological use, on a wave-beaten rocky shore ing, peaking around 12:00 h when sunlight is at its great- is about the same, in proportion to available light, as on est intensity. In summer, it appears that there is a slight a coral reef. Interestingly enough, on the rocky shore drop by noon, but this is probably at least partly due to itself, grazing rates are relatively low and thus there is saturation of metabolites. Unlike what most scientists an actual excess of production. In the wild, roughly have thought with regard to other marine algae, the reef three-quarters of the plant production is eventually lost plants (primarily algal turfs) can use most of the avail- from the rocky bottom to beach drift and finally deliv- able sunlight and as a community do not seem to be ered by tides and currents to the inshore mud flats. In inhibited by the intense light (see Figure 5.15). The high short this community is a strong net exporter of biologi- respiration and biomass levels of a shallow-water reef, cal production, and this must be taken into account and a well-designed and operated reef microcosm, are when designing such a system. internally driven by a high level of plant production that In the rocky Maine shore microcosm, oxygen levels needs full sunlight to fully perform. averaged higher than on a coral reef, as a reflection of We have based our discussion of oxygen and carbon this system as a net producer and exporter of plant bio- dioxide exchange to this point on field studies and mass. At 8.5–9.5 mg/liter of dissolved O2, average oxy- models of coral reef systems. However, the points gen concentration remains above saturation for most of made are equally true in other model ecosystems. One the year. This occurs in spite of the fact that considerable tends to think of cold-water northern ecosystems as wave action was present, continuously, in the model highly seasonal ones that may reach high levels of (see Chapter 21).
  • 144. 128 8. Organisms and Gas Exchange FIGURE 8.11 Yearly productivity of benthic algae (in wet weight) in rocky intertidal and sub- tidal zones in the northern Gulf of Maine. After Adey (1982). References Cresser, M. and Edwards, A. (1987) Acidification of Freshwaters. Cambridge University Press, Cambridge. Adey, W. (1982) A resource assessment of Gouldsbaro Bay, Maine. Dietrich, G. (1963) General Oceanography. Wiley-Interscience, New York. Report to NOAA, Marine Sanctuary Program. NA81AA-D-Cz076. Dodds, W. (2002) Freshwater Ecology. Academic Press, San Diego, Adey, W. (1983) The microcosm: a new tool for reef research. Coral California. Reefs 1: 194–201. Flood, J. (1983) Archaeology of the Dreamtime. Collins, Sydney. Adey, W. and Steneck, R. (1985) Highly productive eastern Horne, R. A. (1969) Marine Chemistry. Wiley, New York. Caribbean reefs: synergistic effects of biological, chemical, physi- Hutchinson, G. E. (1957) A Treatise on Limnology, Vol. 1. Wiley, cal and geological factors. In: The Ecology of Coral Reefs. M. Reaka New York. (Ed.). NOAA Symposium Series on Underwater Research, Vol. 3, Kennett, J. (1982) Marine Geology. Prentice Hall, Englewood Cliffs, Washington, DC. New Jersey. Blankenship, K. (2005) Bay experiences largest recorded anoxic zone Kleypas, J., Buddemeier, R., Archer, D., Gattuso, J.-P., Langdon, C., this summer. www.bayjournal.com. and Opdyke, B. (1999) Geochemical consequences of increased Cleseri, L., Greenberg, A., and Prussell, R. R. (Eds) (1989) Standard atmospheric carbon dioxide on coral reefs. Science 284: 118–120. Methods for the Examination of Water and Wastewater, 17th edn. Livingston, R. (2006) Restoration of Aquatic Ecosystems. Taylor & Francis, American Public Health Association, Washington, DC. Boca Raton, Florida.
  • 145. References 129 Lovelock, I. (1979) Gaia: A New Look at Life on Earth. Oxford Schmidt-Nielsen, K. (1975) Animal Physiology. Cambridge University University Press, Oxford. Press, Cambridge. McConnaughey, T. (1994) Calcification, photosynthesis and global Small, A. and Adey, W. (2001) Reef corals, zooxanthellae and free- carbon cycles. Bull. l’Inst. Ocean. Monaco 13(Specl.): 137–161. living algae: a microcosm study that demonstrates synergy between Millero, F. and Sohn, M. (1992) Chemical Oceanography. CRC Press, calcification and primary production. Ecol. Eng. 16: 443–457. Boca Raton, Florida. Spotte, S. (1992) Captive Seawater Fishes. Wiley-Interscience, New York. Osmond, B. (2004) Changing the way we think about global change Stumm, W. and Morgan, J. (1981) Aquatic Chemistry. Wiley, New York. research: scaling up in experimental ecosystem science. Global USGS. (2005) Resource Data Base for Gulf of Mexico Research. Change Biol. 10: 393–407. www.gulfbase.org. Richards, F. (1965) Dissolved gases. In: Chemical Oceanography. J. Riley and G. Skirrow (Eds). Academic Press, London.
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  • 147. C H A P T E R 9 The Primary Nutrients – Nitrogen, Phosphorus, and Silica Limitation and Eutrophication Open ocean sea water contains about 35 parts per to primary production in ocean waters far from land. thousand (ppt; 35 000 ppm) by weight salts and other This situation is highly unlikely in model ecosystems elements, in addition to the hydrogen and oxygen that and human-controlled aquatic ecosystems because of make up the remaining 965 ppt (mostly as water). Over the abundance of iron in human environments. Carbon 99.6% of the “salt” weight is made up, in order of abun- (as CO2 and alkalinity) could also be limiting in some dance, of chlorine, sodium, magnesium, sulfur, calcium, community models (e.g. coral reefs). This potential and potassium. These elements are conservative. They problem is treated in Chapters 8, 10, and 20. vary little in their proportions over the entire world’s oceans and even into most estuaries. Several gases, nitrogen, oxygen, and carbon dioxide, are also more or NUTRIENTS IN NATURAL WATERS less abundant; these we discussed in Chapter 8. Most of the remaining chemical elements occur in sea water, in A typical tropical open ocean distribution pattern extremely small quantities. However, there are a num- of dissolved (reactive) nitrogen and phosphorus ber of elements, required by some or all plants, that with depth is shown in Figure 9.1. Surface values of occur normally at concentrations of a small fraction of a these essential compounds are typically less than 1 µM ppm to perhaps as much as 0.2 ppm. The most impor- (0.014 ppm) nitrogen as nitrite plus nitrate and less tant of these elements to organisms are nitrogen, phos- than 0.1 µM (0.003 ppm) phosphate. Below the photic phorus, and silica. See Table 4.4 for a summary of these zone, and a little below the oxygen minimum and car- relationships. bon dioxide maximum, where phytoplankton and zoo- In fresh waters, the conservative elements are gener- plankton are being eaten or are breaking down without ally present in very small quantities with salt lakes in light for recycling, nutrient levels climb to about 20–30 basins without an outflow being striking exceptions. In times surface values. In the deepest waters, which are salt lakes, the dominant salts vary widely, depending on cold with very slow currents derived from Arctic and the rocks present in the drainage basin (see Chapter 4). Antarctic surface waters, nutrient levels are moderate However, the same basic nutrients as in the sea tend to be at all times. Largely inaccessible to plants except at limiting to plant production in the Earth’s fresh waters. unusual points of current upwelling, reactive nitrogen In this chapter we discuss the primary nutrients, and phosphorus remain in storage for hundreds to nitrogen, phosphorus, and silica. After the basic physi- thousands of years in the deep ocean. cal parameters, temperature, light, etc., the abundance In relatively shallow coastal waters the picture is rather of these elements is critical in determining the character different, especially outside the tropics where surface and function of an aquatic ecosystem. Other nonconser- warming in the summer tends to prevent mixing. The vative elements might be limiting in special cases. Iron yearly cycles of nitrogen and phosphorus levels for has recently been under heavy investigation as a limiter the English Channel are shown in Figure 9.2. Here, the 131
  • 148. 132 9. The Primary Nutrients – Nitrogen, Phosphorus, and Silica oxygen reverses this reaction and allows reactive phos- phorus to escape into the lower water column. How- ever, being generally below the photic zone except in the smallest lakes, it remains largely unavailable for plant growth. Silicon is one step up from carbon in the periodic table of the elements. Thus, chemically it is quite similar to carbon, but is a little over twice as heavy. Forming an enormous number of compounds as minerals in the Earth’s crust, it is to the lithosphere what carbon is to the biosphere. Diatoms are the only primary producers that make an ecologically important use of the element. FIGURE 9.1 Distribution with depth of phosphate and nitrate in Diatoms use silicate, instead of cellulose or related com- the tropical and subtropical portions of the oceans. Microgram atoms pounds, to form cell walls. They are essentially alone in per liter µM; concentrations of N as nitrate with depth are this use, although a few other heterotrophs (secondary 0.3–0.6 ppm; P as phosphate are 0.06–0.09 ppm. After Sverdrup et al. producers) such as radiolarians and some sponges make (1942). Reprinted by permission of Prentice Hall, Englewood Cliffs, silica skeletons. Radiolarians can be extremely abundant New Jersey. both in the plankton and on the bottom in specialized localities. While silicon (as silicate) is moderately abun- dant in water environments (about one-tenth of carbon mixing of tides and winter storms accompanied by low and six times that of reactive nitrogen), it can sometimes light allows moderate levels of nutrients to build up in be limiting to plant production when that production is winter. Note, however, that in the winter at 5–8 µM dominated by diatoms (see Table 4.4). nitrogen as nitrite plus nitrate, levels are still well below Today human influence on the biosphere is massive deep ocean levels. Most aquatic animals excrete ammo- and rapidly growing; thus, it is critical for the modeler, nia. This very toxic compound is metabolized by bacte- the aquatic restorer, and the hobbyist to keep the above ria to the mildly toxic nitrite and finally to the relatively described relationships in mind. Under pre-human benign nitrate. Both ammonia and nitrite occur at a conditions, in all aquatic and marine environments, fraction of the concentration of nitrate in the water except relatively rare naturally eutrophic situations, columns of most aquatic ecosystems. Algae and bacte- the low concentrations of nitrogen, phosphorus, silica, ria both compete for these compounds as sources of and sometimes iron provided considerable restrictions nitrogen and energy, and if it is possible to measure on the level of plant activity and therefore on the level ammonia and nitrite by any but the most sophisticated of total biological activity. An upwelling zone with of chemical analytical processes, that is, if either is over a prevailing offshore wind, a whale washed up on about 0.5 µM (0.0007 ppm), they are probably much too the shore of a restricted inlet, a marshy basin on a high, as we discuss in some depth below. recently burned slope, organic detritus concentrated The nutrient picture in fresh waters not subject to on a beach or a mud flat by a storm – these were natu- intensive human activity is similar to that of the ocean, rally eutrophic or nutrient-rich situations. However, but different in some critical ways. First, nitrogen has they were restricted in space and time. In the plank- many potential sources of atmospheric bacterial fixa- tonic environment, the flow of nutrients to the algal tion on the land. The equivalent process is not available cells could also be greatly limited by the diffusive for phosphorus, and thus phosphorus tends to be lim- boundary layer (DBL); understanding the conditions iting for plant production, rather than nitrogen. It is under which the effect of the DBL is reduced is a sci- phosphorus that operates on a yearly cycle to limit pri- ence by itself (Riebesell and Wolf-Gladrow, 2002). mary production. Figure 9.3 shows typical summer Much of the practical and operational water quality patterns on several lakes with low levels of phospho- control measures discussed in this book will deal with rus at the surface markedly increasing below the ther- ways of reducing the effects of the DBL. mocline. On the other hand, near the bottom, additional Some heterotrophic bacteria, primarily under anaero- mechanisms quite different from those applicable to bic conditions, but as we now know also under some nitrogen are active (Figure 9.4). Under aerobic conditions, aerobic conditions (Sprent, 1987), utilize nitrate or nitrite phosphate combines with ferrous iron in the sediments. and produce the gases nitrous oxide and nitrogen. This The precipitate that forms remains locked in those sed- process of denitrification removes nitrogen from an iments until they approach anaerobic conditions. Thus, aqueous medium or sediments to the atmosphere. In the under stratified and stagnant summer conditions, low water column of most lakes and the oceans, this process
  • 149. Nutrients in Natural Waters 133 FIGURE 9.2 Yearly cycles of nutrients in the English Channel. Milligrams per cubic water µg/liter; for nitrate, 100 µg/liter 7µM; for phosphate, 30 µg/liter 1 µM. After Gross (1982). Reprinted by permission of Prentice Hall, Englewood Cliffs, New Jersey. is negligible. However, in the anaerobic sediments of when that is achieved largely by macrophytes or eutrophic bodies of water (enriched by human activi- attached algae. ties) denitrification rates can be considerable, in some In summary, below about 15–20 µM (N as NO2 cases at the levels of primary production (Seitzinger, NO3) (0.2–0.3 ppm) denitrification is negligible. Below 1988). On the other hand, in noneutrophic shallow about 1–2 µM (N as NO2 NO3) (0.014–0.03 ppm) nitro- waters, low in nitrogen, denitrification, mostly from gen fixation from gaseous N2 begins to be a significant underlying sediments, occurs at rates an order of mag- factor (Lucid, 1989; Chapter 20). The net effect is that in nitude or more below primary production, particularly most modeling and restoring efforts, where achieving
  • 150. 134 9. The Primary Nutrients – Nitrogen, Phosphorus, and Silica FIGURE 9.3 Phosphate concentration in several temperature lakes during the summer. , temperature °C; phos- phorus: PT, total; PS, soluble; PST, in particulates. After Hutchinson (1957). Reprinted by permission of John Wiley & Sons, Inc. the original, nondegraded, ecological environment is bacteria (including H2S) provides environmental condi- desired, denitrification (nitrogen loss to the atmosphere) tions that are suitable for very few organisms. is not a significant factor and a small amount of nitrogen As we discuss under Bacteriological Filtration in fixation (from the atmosphere) is likely. Chapter 11, it has become customary for modern human societies to avoid the most serious problems of excess concentration of organics (generally sewage) by provid- EUTROPHICATION AND ing large bacteria-operated industrial plants to break HYPEREUTROPHICATION OF NATURAL down these organics. A sewage plant releases carbon WATERS dioxide to the atmosphere, reducing biochemical oxygen demand (BOD) in the water effluent (but adding to Excess concentration of organics and nutrients by global warming). The bacterial biomass that develops human activities leads to a variety of problems in wild (sludge) is hauled away to environments of less concen- ecosystems that are not adapted to such excesses. Most tration. Ocean dumping is rarely allowed today; how- critical for marine and freshwater environments is ever, spreading or spraying sludge on farm fields simply ammonia. When this very toxic nitrogenous excretion of moves the problem to another location. Most of the nutri- many waterliving organisms (see Chapter 7) is available ents in solution, as nitrites, nitrates, and phosphates, are in abundance, and sufficient plant or microbe activity is then dumped into estuaries, lakes, and streams. While not present to remove it, it can become deadly. A number this process has avoided the most immediate difficulties of bacteria and fungi also perform nitrification, or break- of mass sewage, namely disease transmittal and local down of ammonia to nitrite and nitrite to nitrate, though low oxygen, when carried out with large human popula- they generally require oxygen and release carbon diox- tions it only extends the basic problem a few years. After ide. Excess organic material without consequent plant a half-century of adding and upgrading sewage plants, return to the stored “fixed” carbon state also leads to a as a “half solution,” the nutrients have simply built up drawdown of oxygen and eventually anaerobic condi- downstream in lakes, bays, and now the ocean. tions. The combination of anaerobic conditions in the Many algae and some aquatic plants are adapted to water column and the often-toxic products of anaerobic make use of the temporary mass availability of nutrients
  • 151. Eutrophication and Hypereutrophication of Natural Waters 135 FIGURE 9.4 Seasonal cycling of oxygen, iron as Fe2 , and phosphate just over the deepest mud, at 14 meters in an English lake. After Hutchinson (1957). Reprinted by permission of John Wiley & Sons, Inc. in wild ecosystems (the dead whale, for example, or the moderate levels increases the growth rates of many school of fish on the beach). The life strategy of these plants (other factors being equal) and most animals “opportunists” is extremely rapid growth, given ade- including corals are not directly affected by this increase. quate light, temperature, and a large peak of nutrients. Thus, in human cultured environments, it may be desir- Given summer long or permanently high nutrients, able to elevate nutrients (as in farming). However, at the these plants multiply rapidly, choking bodies of water risk of overstatement, we note again that such increases and eventually reducing oxygen, killing themselves as almost always change ecosystem community structure, well as many invertebrates and fish at the same time. sometimes radically. Direct control methods (e.g. weed- Given elevated nutrients and typically higher tempera- ing, light control) can affect these changes; however, this tures some blue-greens (cyanobacteria) in fresh water can be very difficult and costly to achieve. It has not been and dinoflagellates in coastal waters can bloom, pro- unusual to apply herbicides (to kill off the offending duce abundant toxins, and provide mass kills of fish and submerged aquatic vegetation (SAV) or algae), but this sometimes birds and humans (e.g. Livingston, 2006). is a very short-term solution. Also, dredging of eutrophic To many humans, it is the fast-growing algae or the sediments merely puts the problem off a few years and equivalent macrophyte such as Hydrilla or water hyacinth can rarely return an ecosystem to its original state. that is the problem, not ourselves who have created the In wild ecosystems, this is not simply a matter of unnatural high nutrient situation. Increasing nutrients to esthetics. The loss of major fisheries and their associated
  • 152. 136 9. The Primary Nutrients – Nitrogen, Phosphorus, and Silica jobs, and the impending loss of recreational value, in problem in traditional aquarium management, and in Lake Okeechobee, Pensacola Bay, Chesapeake Bay, and most model ecosystems for that matter, has been pre- now the northern Gulf of Mexico (to name just a few) venting the “pollution” of the system by these excre- is only a prelude of things to come. Serious fish and tory compounds. It is primarily to solve this very basic invertebrate diseases, and red tides that cause human problem that the biological filter was developed. illness and even death, are not far behind. Chemical and Unfortunately, in many cases reliance on the bacterial or bacterial methods of dealing with human-concentrated “biological” filter is counterproductive in that the solu- nutrients have been developed (BNR: biological nutri- tion to the ammonia problem is accompanied by a num- ent removal), and are beginning to be used in the US ber of negative side effects that render natural ecosystem (Zickefoose, 2004). However, they are difficult, erratic, management difficult or impossible to achieve. and costly (Chesapeake Bay Commission, 2004). After Marine and freshwater planktonic algae actively roughly 25 years of major effort by governments and photosynthesizing and growing have a continuous and NGOs, and billions of invested dollars, Chesapeake Bay, often production-limiting requirement for nitrogen and for example, is more eutrophic than when the effort other nutrients. Approximately 1 nitrogen atom is needed began. Nutrient inputs in the rivers of the Bay have not for every 7 carbon atoms built into plant tissue and 1 been reduced, and the dead zone in the Bay in the sum- phosphorus atom for every 100 carbon atoms. Benthic mer of 2005 (Blankenship, 2005) was larger than ever. algae, on the other hand, are capable of producing at a Some of this degradation can be put down to increasing considerable deficit when nutrients are low (Figure 9.5). population in the watershed, and indeed this cannot go Likewise many fleshy algae are noted for their “luxury” on indefinitely. Mostly, however, it is a failure to recog- or excess consumption of nutrients when they are avail- nize basic biology and ecology, and to develop counter- able. Most algae accept ammonia as a nitrogen source ing methodologies. In Chapter 25, we bring together the and are capable of rapidly taking it up. The nitrification rationale and methodology for a full solution to this products of ammonia, nitrite, and nitrate, as well as ever-increasing problem. more complex nitrogenous excretory products such as NUTRIENTS AND MODEL ECOSYSTEMS Basically, the organic pollution problems are the same for the aquarist as they are for human society at large. Only the scale is different. It is instructive to compare wild ecosystem nutrients discussed above with those for traditional aquaria. We quote from Spotte (1979): “It is inevitable that seawater aquariums will become eutrophic . . . inorganic nitrogen levels in aquarium water can be staggering.” Great improve- ments in culture techniques have been made since the first edition of this book was written. However, these improvements apply to a limited set of organisms, in a garden-like environment; in an ecological context, con- siderable improvement is still needed. As we discussed in Chapter 7, animal tissue that has become food for other animals or for bacteria or fungi undergoes a continuous process of breakdown and assimilation. Carbohydrates and most fats in this breakdown process are metabolized using oxygen and result in the release of carbon dioxide. On the other hand, proteins, nucleic acids, and phospholipids (along with other compounds) provide an excess of nitrogen and FIGURE 9.5 Carbon, nitrogen, and phosphorus ratios in marine phosphorus in addition to the basic carbon, hydrogen, plants. Note that temperate algae were apparently not nutrient defi- and oxygen of organic tissues. The net result is a require- cient, tropical algal turfs were not nitrogen deficient (due to nitrogen fixation) but were slightly phosphorus deficient, and larger tropical ment for the excretion of nitrogen-rich and phosphorus- algae were deficient in both nutrients. Productivities as measured by rich compounds into the ambient water. Chief among biomass increase were approximately equivalent in all groups (Adey, these excretory compounds is ammonia. The central 1987).
  • 153. Nutrients and Model Ecosystems 137 urea, can also be used by many algae. In reef tank radiation or equivalent light levels can induce disas- ecosystems, with dense algal and higher plant commu- trous planktonic algal blooms at the nutrient concentra- nities, nitrogen salts, measured with autoanalyzers, tions of traditional aquarium tanks. It has been typically occur at a concentration of less than 1–1.5 µM demonstrated that moderate nutrient levels ( 5 µM (14–21 ppb). This is equivalent to the situation nor- N–NO3, 70 ppb) are not directly damaging to some reef mally encountered in a wild reef and yet is at great corals (Atkinson et al., 1995). However, experiments variance with traditional aquarium systems in which have shown calcification disruption in corals by even nitrogen levels of over 100 ppm are acceptable. The lower nutrient levels (Marubini and Davies, 1996). At limiting of sensitive organisms in aquarium systems the very least, excess nutrients can allow benthic algae by ammonia, nitrate, and nitrite, as well as the unsta- to outcompete corals. Even if grazing levels are greatly ble environment these nutrients create in excess, is a increased, this can provide a level of disturbance that is major element in the erratic nature of the traditional destructive to stony corals. aquarium. Maine rocky shore and temperate estuarine systems Tropical reef communities in particular are character- such as the Chesapeake Bay, as well as other communi- ized by low nutrient levels. Nitrate levels in incoming ties that have been involved in microcosm or mesocosm ocean water in St. Croix reefs are about 0.4 µM (6 ppb). simulation, have relatively high concentrations of dis- More open ocean or equatorial current situations (such solved or reactive nitrogen (Figures 9.6 and 9.7). Those as Grand Turk, for example) are even lower, on the order naturally rich ecosystems, however, at 5–10 µM of 0.1 µM. Blue-green algae in reef waters are known to (N–NO3 ) for unpolluted waters, and 10–80 µM (NO3 ) fix gaseous nitrogen much as the bacteria of the root for polluted waters, are still far below the older type nodules of legumes do in the terrestrial environment. aquaria at 5000 µM (N–NO3 ) or higher. Note that in However, these blue-greens are either not present or Figure 9.7, 25 µM (0.38 m/liter) N–(NO2 NO3 ) and unable to fix nitrogen in any but the most nutrient- 13 µM (0.38 mg/liter) (total phosphorus as PO3 ) are 4 minimum environment. High nutrient levels cause a noted as critical levels, above which algal or aquatic shift in algal community structure, a shift that can be plant blooms occur with disastrous consequences. Both very detrimental to an attempt to simulate an ecosys- systems are also characterized by having both a sediment tem. It has long been known that perhaps next to silta- sink and an open ocean sink for such nutrients. If rocky tion, elevated nutrients (or eutrophication) is one of the shore and estuarine communities are managed properly, primary factors causing degeneration of wild reefs. with considerable nutrient importation, then a “nutrient A serious problem for coral reefs as well as most open sink” is required to prevent eutrophication and radical shallow-water ecosystems is the relationship of such alteration of the biological communities. Most such high nutrient levels to the growth capabilities of some coastal marine communities are characterized by run- species of both planktonic and benthic algae. Solar off from the adjacent land. Without the ocean sink to FIGURE 9.6 Nitrate concentration as a function of salinity in the Sheepscot estuary (Maine), September 1986. After Fefer and Schettig (1980).
  • 154. 138 9. The Primary Nutrients – Nitrogen, Phosphorus, and Silica 3 FIGURE 9.7 Nitrate plus nitrite and total phosphorus as PO4 concentrations on the upper Potomac estuary, summer, 1972–1975. After Lippson et al. (1979). eventually dilute and remove those nutrients, eutrophi- Some aquarists have advocated using the process of cation would result. The data given in Figure 9.7 shows denitrification in special anaerobic traps to remove the Potomac River leading into the upper-mid Chesa- excess nitrogen from mesocosm and aquarium environ- peake Bay, as it was in the 1970s – already eutrophic. As ments. Indeed, this process probably occurs to a limited we discussed above, this eutrophic character, in 2005, has extent in virtually all closed systems and in many wild extended to the entire upper half of this 200-mile-long systems. In eutrophic aquaria with rich sediment bot- Bay. In the simulations of Chesapeake Bay and the rocky toms, it will certainly be an important process. However, Maine shore described in Chapters 21 and 22, dissolved in sediments and their overlying waters that are not nitrogen concentrations are normally maintained in the enriched far beyond natural levels, denitrification rates 1–10 µM range, far below presently existing levels in the are likely to be below 30–50 µM N/m2/h (Seitzinger, wild ecosystem, but probably slightly above pre-human 1988). This is one to two orders of magnitude below the levels. removal rates of nitrogen in primary production or
  • 155. Summary 139 photosynthetic removal of nitrogen. In addition, denitri- SUMMARY fication does not remove the balanced array of nutrients that are taken up in primary production. A number of The handling of nitrogenous and phosphorus schemes have been developed to enhance denitrification wastes in aquarium simulations of ecosystems can be (NO3 to N2) in coral reef systems, and these have been summed up by several critical requirements: reviewed by Delbeek and Sprung (2005). Some of these 1. An animal load that is at least close to that in the methods add sulfur so as to use sulfur bacteria to drive wild (an excessive load technically can be managed; the process, and they can then work efficiently. however, it makes the system more equivalent to an However, all of the other criticisms remain, and one is aquaculture or farming unit and presents numerous operating a potentially deadly system in tandem with ecological balancing problems). the highly oxygenated system desired. The chance for 2. A built-in system for rapidly exporting ammonia disaster is always present, and one has to ask: why not and other waste compounds. In most aquarium sys- stick with the primary production processes that work tems this is the bacterial or “biological” filter. In so well in the wild? most natural shallow-water ecosystems, and in the In recent years perhaps the most favored methodol- examples in this book, this requirement is accom- ogy for maintenance of high water quality in aquarium plished directly by plants or by export/mixing with systems is foam fractionation, more commonly known an adjacent community (a larger open body of in the aquarium trade as protein skimming. This water). process provides a fine stream of bubbles in a vertical 3. A means of ultimately exporting added nutrients. In column with a means for collecting the foam generated the wild this is partly accomplished by oceanic dilu- (Delbeek and Sprung, 2005) and has numerous varia- tion and sinking to deep water, although burial in tions and methods for increasing efficiency. The pri- marshes, sediments, and soils acts as a primary, mary purpose is to remove dissolved organics and short-term sink. thus, unlike denitrification “filters” and similar to algal “filtration” systems, it will remove a cross section of The first requirement, that of an appropriate animal nutrients. Foam fractionation does not directly remove load for the area and volume involved, is discussed in dissolved nutrients and therefore cannot achieve the depth in a number of the following chapters. The second oligotrophic levels of open ocean waters, although requirement can be met by providing the appropriate schemes have been developed to enhance water col- photosynthesizers for the system being worked, and the umn bacterial action (e.g. by adding alcohol – vodka) right environmental factors, light, and water motion to to enhance bacterial production and therefore increase enable those plants to function. These elements are dis- skimmer removal of nitrogen and phosphorus. How- cussed primarily in Chapters 12 and 14. Finally, the ever, most important as a consideration for a technology effects of an open-water sink relative to nutrients can for operating closed ecosystems, foam fractionation also be provided by plants and algae (MAPS: managed cannot differentiate between dissolved and particulate aquatic plant systems), given a proper control mecha- organics and the planktonic and reproductive flora and nism. Several mechanisms, particularly algal turf scrub- fauna. While foam fractionation cannot be used to bing (ATS), have been devised and are discussed at accurately model most ecosystems, it could have been length in Chapter 11. used where a more limited result of the culture of indi- The management and restoration of wild ecosystems vidual organisms does not directly or indirectly utilize subject to human eutrophic degradation differs only as a a natural planktonic or particulate community (see matter of scale. Sewage plants at cities and towns and Chapters 2, 6, and 17). If a “garden” is desired, this buffer strips and best management practices (BMPs) on could be an excellent way to go, one for the aquarist farms are essential at the primary, particulate level and and one for the aquarium (i.e. vodka). for disease control. New BNR methods have been devel- Ion exchange media, including charcoal and newer oped for nitrogen and phosphorus, but they are batch, resins and plastic materials with great porosity and ion one nutrient at a time, processes and are very sensitive absorption characteristics, can also be used to reduce to minor environmental changes. Computer control and nutrients as well as dissolved organics. These media all expert staff are necessary to achieve success. However, suffer from difficulties of control and balance in the only solar-capture, photosynthetic (MAPS) methods can chemical soup that is a “living” water, especially sea efficiently solve the eutrophication problem at land- water. Also, as in all filtration methods, plankton and scape scale. These low cost methods have been demon- larval stages are trapped and mostly destroyed (see strated at large scale (20 mgd modules) and are also Chapters 6, 11, and 17). discussed in Chapter 25.
  • 156. 140 9. The Primary Nutrients – Nitrogen, Phosphorus, and Silica References Lucid, D. (1989) Effects of Dissolved Inorganic Nitrogen Concentrations on Primary Productivity, Nitrogen Fixation, and Community Composition Adey, W. (1987) Food production in low-nutrient seas. Bioscience 37: of Coral Reef Algal Turf: A Microcosm Study. M.S. Thesis, University 340–348. of Maryland. Atkinson, M., Carlson, B., and Crow, G. (1995) Coral growth in high Marubini, F. and Davies, P. (1996) Nitrate increases zooxanthellae pop- nutrient, low pH seawater: a case study of corals cultured at the ulation density and reduces skeletogenesis in corals. Mar. Biol. 127: Waikiki Aquarium, Honolulu, Hawaii. Coral Reefs 14: 215–223. 319–328. Blankenship, K. (2005) Bay experiences largest recorded anoxic zone Riebesell, U. and Wolf-Gladrow, D. A. (2002) Supply and uptake of this summer. www.bayjournal.com. inorganic nutrients. In: Phytoplankton Productivity. P.J. le B. Chesapeake Bay Commission (2004) Cost effective strategies for the Williams, D. Thomas, and C. Reynolds (Eds). Blackwell Science, Bay. www.chesbay.state.va.us. Oxford. Delbeek, C. and Sprung, J. (2005) The Reef Aquarium: Science, Art, and Seitzinger, S. (1988) Denitrification in freshwater and coastal marine Technology, Vol. 3. Ricordea Publishing, Coconut Grove, Florida. ecosystems: ecological and geochemical significance. Limnol. Fefer, S. I. and Schettig, P. (1980) An Ecological Characterization of Coastal Oceanogr. 33: 702–704. Maine, Vol. 2. US Fish and Wildlife Service, Boston, Massachusetts. Spotte, S. (1979) Sea Water Aquariums: The Captive Environment. Wiley, Gross, M. C. (1982) Oceanography, 3rd edn. Prentice Hall, Englewood New York. Cliffs, New Jersey. Sprent, J. (1987) The Ecology of the Nitrogen Cycle. Cambridge Hutchinson, C. E. (1957) A Treatise on Limnology, Vol. 1. Wiley, University Press, Cambridge. New York. Sverdrup, H., Johnson, M., and Fleming, H. (1942) The Oceans: Their Lippson, A. J., Haire, M. S., Holland, A. F., Jacobs, F., Jensen, J., Moran- Physics, Chemistry and General Biology. Prentice Hall, Englewood Johnson, R. L., Polgar, T. T., and Richkus, W. A. (1979) Cliffs, New Jersey. Environmental Atlas of the Potomac Estuary. Environmental Center, Zickefoose, B. (2004) Improving the Design of the BNR Process in Martin Marietta Corp., Baltimore, Maryland. Wastewater Treatment Plants from an Operations Perspective. M.S. Livingston, R. (2006) Restoration of Aquatic Systems. CRC Press, Taylor Thesis, Engineering Department, Florida State University. and Francis, Boca Raton, Florida.
  • 157. C H A P T E R 10 Biomineralization and Calcification A Key to Biosphere and Ecosystem Function Under very special circumstances of burial and Muscles certainly greatly pre-date the Cambrian as preservation the soft tissues of animals and their part of multicellular organisms. However, muscles are imprints in sediments can be preserved in the fossil more efficient, the required distance of movement record. Woody plants of the last 400 million years have being less, if they are attached to and pulling against been preserved, especially under swamp conditions. something hard. Thus, whether for capture or escape, However, the tremendous library of organic evolution mineralized skeleta for muscle attachment provided of fauna over the last 543 million years, the paleonto- major advances in evolutionary “races.” Finally, sens- logical record, is primarily written in mineralized ing and balance systems gain greater precision, in many skeleta. This is a complex record of comings and goings, cases, if they are not jell-like in texture, and instead are of changes in the kinds of organisms that are dominant, heavier than water and “rock-firm.” Many organisms that depends, at least in part, on small changes in the developed mineralized otoliths or their equivalent. chemistry of the sea (Knoll, 2003). Thus, mineralized hard parts have become an indelible For nearly a century, geologists drew the practical line and critical element of many organic lines, both aquatic between living and nonliving at the pre-Cambrian/ and terrestrial. Cambrian boundary, about 500 million years ago. The The realm of geology is dominated by silicate chem- principal paleontological question of the first half of this istry. However, except in science fiction, this is the century was: why did a large, complex fauna suddenly province of geology, the lithosphere, rather than the show up at the Cambrian? Intensive paleontological biosphere, where carbon is the key element. The ele- work through the middle and later part of the 20th cen- ment silicon is used by many living organisms to form tury has demonstrated life over 2 billion years further hard parts, and diatoms are a very abundant example back, with numerous complex, taxonomic lines at least in aquatic environments; however, such use is as amor- several hundred million years before the Cambrian. The phous silica (SiO2) not as a crystalline silicate. Silica is event that changed apparent life on Earth so radically an important biomineral; however, it follows the car- was the widespread development of an ability on the bonates in abundance. Of the hundreds of minerals part of many evolutionary lines to make mineralized known, nearly half are not silicates, and about 50 have hard parts. That these fossils were easily seen in sedi- been developed by many phyla of living organisms as mentary rocks, and their predecessors were not, formed hard parts (skeleta, teeth, and sensory devices). Table the principal character of early paleontology. 10.1 shows the more important minerals of aquatic sys- The development of mineralized hard parts was an tems and the phyla in which they occur. inevitable step in evolution. Protection by external For very good reasons, as we shall see, carbonate skeleta in aqueous environments was an obvious way minerals overwhelmingly dominate the biominerals. to lessen predation pressure, though, almost as quickly, Nevertheless, a dozen phosphatic minerals are also predators upped the ante of the arms race (Chapter 16) extremely important in the biosphere, for example as by developing mineralized teeth and radula. In reef vertebrate bone (calcium hydroxyapatite), and iron systems, calcification by many organisms also became oxides and calcium oxalates come into play in a few a competitive device to obtain space and light. groups (especially as teeth and skeleta, respectively). 141
  • 158. 142 10. Biomineralization and Calcification TABLE 10.1 Principal Mineral Formation by Aquatic Organisms Rhodophyta (including Corallines) Chlorophyta (including Halimeda) Chordates (mostly bony fish) Cyanophyta (Cyanobacteria) Coccolithophores Platyhelminithes Zygnematophyta Echinodermata Dinoflagellata Foraminifera Coelenterata Brachiopoda Rhizopodea Phaeophyta Charophyta Arthropoda Ciliophora Radiolaria Ectoprocta Sipuncula Annelida Mollusca Heliozoa Diatoms Bacteria Porifera Phylum Carbonates Calcite (Ca(Mg)CO3) * * * * * * * * * Aragonite (CaCO3) * * * * Vaterite (CaCO3) Monohydrocalcite Amorphous hydrated carbonate Phosphates Dahllite * (Ca10(PO4)6(OH)2) Francolite (Ca3Mg3(PO4)4) Brushite Amorphous dahllite Amorphous brushite Amorphous whitlockite Amorphous hydrated ferric phosphate Halides Fluorite Amorphous fluorite Oxalates Whewellite Weddelite Sulfates Gypsum Celestite Barite Silica Opal (SiO2) * * * Fe-oxides Magnetite Goethite Lepidocrocite Ferrihydrite Amorphous ferrihydrates Note: *Biomineralization of widespread occurrence and of special significance to mesocosm and aquarium operation. Modified after Simkiss and Wilbur (1989). Since such a large number of minerals of quite dif- conditions under which biomineralization occurs. ferent chemical composition are used in such a large Before entering into our principal concern in this chap- percentage of phyla of living organisms, it seems likely ter, biomineralization that is potentially controlled or that there are some basic physiological and biochemical limited by the basic parameters of living models and
  • 159. The Carbonate System and the Formation of Calcite and Aragonite 143 degrading ecosystems, we examine biomineralization the framework of a more complex hard-part structure in general. (such as a tooth or bone). In some species, mineralization occurs simply because Thus, the basic principles for the construction of of the chemical changes caused in the surrounding organism hard parts, with minerals both known in the waters by the metabolism of the organism. This occurs lithosphere and specific to organisms, whether skeletal, most often in bacterial and blue-green algae (cyanobacte- sheathing, or sensory, are known. The minerals employed ria) films and can involve the precipitation of sulfides in are numerous, with undoubtedly more to be discovered. the first case and carbonates in the second. See also the In general, the process of membrane formation followed discussion on the green algae Halimeda below. Mostly, by ion pumping requires energy and can therefore work however, biomineralization is under some direct control against considerable environmental gradients. In the end, (and at some energy expenditure) of the organisms however, a basic ecological trade-off must apply. The sur- involved, as is the case for most skeletal hard parts, such vival benefits provided by the skeleta or sensory appara- as vertebrate bone, mollusc shells, and a wide variety of tus must exceed the survival losses inherent in the energy tooth-like structures. given up. Also, in many cases, behavioral aspects requi- site to the use of hard parts can have considerable bearing on survivorship. A very striking example in the aquatic THE PROCESS OF BIOMINERALIZATION environment is the required molting phase of crus- taceans: during the soft intervals, while the skeleta are Control of the production of hard parts by an organ- being “calcified,” individuals of many species are in large ism involves two key elements: measure defenseless and subject to considerable losses due to predation. 1. The enclosure of a very small volume of water by tis- sues, cells, a membrane-bound vacuole, or a macro- molecular sheath produced by the organism. This THE CARBONATE SYSTEM AND space can be totally surrounded by organic material THE FORMATION OF CALCITE or it can be created against a substrate or an already AND ARAGONITE formed mineral base. 2. The capability of bounding cellular membranes The construction of hard parts of silica and phosphate to pump ions (typically Mg2 , Ca2 , Si4 , CO3 , 2 2 is very important to biosphere function. However, they PO4 , H , etc.). do not begin to compare in magnitude to the importance The enclosure of the mineralization space allows of calcium carbonate. The direct or indirect formation of the membrane-pumping function to build up high con- calcite and aragonite by organisms has massively centrations, generally greatly supersaturated, of the altered the Earth’s atmosphere, hydrosphere, and lithos- appropriate mineral components. The ion pumping phere and moved about 70 000 gigatons of carbon from capabilities of phospholipid membranes are well known the original atmosphere primarily to the oceans and (Figure 10.1) and are typically the subject of whole thence to the lithosphere. Limestones and lime-rich rocks chapters in modern biochemical texts (e.g. Mathews and are among the principal elements of the Earth’s crust. van Holde, 1996). Typically, the pore of an ion-channel Yet, they were virtually absent before the activities and is formed by a protein, embedded in the phospholipid numbers of organisms became significant on a global membrane, and, especially in plants, the structure and biochemical basis. rapid function of these channels have been extensively The reason for this tremendous biogeochemical pro- studied (Heldt, 2005). Some ion-channels pump ions to cessing is more or less obvious: the carbonate ion is create an electrical gradient (e.g. the strong pH gradient oxidized carbon, the basic building block of living between stroma and thylakoid in photosynthesis; see organisms. Through carbon dioxide, the basic respiratory Chapter 5); however, generally the electrical gradient is product of most of Earth’s organisms, and the primary avoided by exchanging ions of equivalent valence and substrate for the building of biomass in photosynthe- this is likely critical in coral calcification (see below). sis, carbonate mineralization is directly linked to the Other components of greater sophistication may or core chemistry of living organisms. Furthermore, as we may not be present. The most common of these are discussed in Chapter 8, carbon dioxide does not simply nucleation sites created by organic molecules (often dissolve in water, remaining in its gaseous state (e.g. acidic glycoproteins) that attract and hold the cation like nitrogen); it also reacts with water to develop a (e.g. Ca2 ) from which mineralization can initiate. series of ions linked directly to the acidity/basicity of Another component that can provide more control to the aqueous environment, a key element in organism biomineralization is an organic matrix that provides function. Finally, although there are other biological
  • 160. 144 10. Biomineralization and Calcification FIGURE 10.1 Generalized cell membranes showing pumping organelles and function. (A) Typical cell and membrane; (B) bicarbonate pumping; (C) sodium–potassium pumping. The and refer to the specific protein that form the pore (in channel) and with adenosine triphos- phate (ATP) energy drive the pumping process. From Mathews and van Holde (1996). Reprinted by permission of Addison Wesley Longman. carbonates, calcium is abundant in the Earth’s crust and with a saturated aqueous solution. Particularly in oceans and forms several key crystalline minerals that, warm, tropical seas where the surface waters are highly under the physical/chemical conditions at the surface supersaturated with calcium carbonate, calcification of the Earth today, are approximately in equilibrium would be expected to happen massively sometimes
  • 161. Halimeda: Photosynthesis-Induced Calcification 145 incidentally to the normal functioning of many organ- isms and their ecosystems. Oolitic (aragonite) sands are abundant on shallow, tropical banks and can be important rock-formers where the environmental conditions are too extreme for corals and calcifying algae. While many attempts have been made to implicate algae (as cyanobacteria) directly in this process, the consensus today is that the warm, calcium- saturated, very high pH conditions of the water over these banks (probably due to phytoplankton) results in aragonite crystallization out of solution without direct biological control. Because an understanding of the calcium carbonate biomineralization process is crucial to the design and operation of many microcosms, mesocosms, and aquaria, we examine two key calcifying organisms of coral reefs: the green alga Halimeda and scleractinian, hermatypic corals in general. Halimeda calcifies almost incidentally to the photosynthesis processes. Stony corals have more direct biotic control over mineralization. However, they also rely not only on their internal symbiotic photosyn- thetic system with zooxanthellae but also on the reef community of algae in general to provide conditions that are favorable for competitive calcification. Adey (1998) reviews, in depth, the role of algae in coral reef calcification. HALIMEDA: PHOTOSYNTHESIS- INDUCED CALCIFICATION Halimeda is a well-known tropical benthic genus of green algae. Fairly large, of centimeter to several decime- ter dimensions, species of this genus consist of strings FIGURE 10.2 Halimeda favulosa, drawn from a 10-inch-high plant of flattened or sometimes crinkled, calcified discs con- collected in the Bahamas. This green alga is constructed of filaments nected by flexible joints. They are abundant in shallow without cross walls (coenocytic). In the segments, the filaments branch and end in swelled-tip utricles that lay down a matrix of aragonite. seas around the tropics especially on “coral” reefs and in Between the segments, the filaments are not calcified, giving the plant their lagoons, although some species range down reef the flexibility and the capability of withstanding moderate water drop-offs to great depths. During the 1950s when large motion. From Taylor (1960). numbers of deep boreholes were drilled into Pacific atolls, geologists found that the dominant element of the carbonate structure of these atolls was not stony coral but rather a lithified sand made up of the lobes of swollen to form a continuous surface as a kind of cellular Halimeda. The members of this genus rank as one of the pavement. Just below the surface of the lobe, there are most important calcifiers of the biosphere; it is likely considerable spaces between the utricles (Figure 10.3). that their CaCO3 production over all tropical seas is The calcification, mostly of aragonite needles, occurs considerably greater than that of the stony corals. almost entirely in these interutricular spaces. Thus, as Halimeda (Figure 10.2) is a member of the green algal we described above, through the anatomy of their utri- order Siphonales and is further described in Chapter 14. cles, these algae have provided one of the basic require- In brief, anatomically, members of this genus are con- ments for biomineralization, confined spaces in which structed of tubules, with very few cross walls. Thus, critical supersaturation can occur. individual cells are extremely long and narrow. At the When a Halimeda disc is sectioned (some are soft surface of the discs or lobes, the “bat-like” surface enough to be cut with a razor blade), it is possible to see expression of these tubules (called utricles) is slightly under a dissecting microscope that the chloroplasts are