Ecosystem

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Aquatic Ecology-Plankton:
Dilip Kumar Jha, PhD
Professor and Chairman
Department of Aquaculture
Agriculture and Forestry University, Rampur, Chitwan
dkjha@afu.edu.np 9845155154; 9804273475
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ARM 602: Advances in Aquatic Ecology

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Ecology- Relevance to Humankind
• The word ecologi is derived from rhe Greek oihos,
meaning "household," and logos, meaning "study."
Thus, the study of the environmental house includes
all the organisms in it and all the functional
processes that make the house habitable.
• Literally, then, ecology is the study of "life at home"
with emphasis on "the totality or pattern of relations
between organisms and their environment," to cite a
standard dictionary definition of the word (Merriam -
Webster's Collegiate Dictionory, 1Oth edition, s.v.
"ecology").
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Levels of 0rganizationHierarchy
• Hierarchy : “an arrangement into a graded series”
• System : “regularly interacting and interdependent
components forming whole”
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Figure: Ecological levels of organization spectrum emphasizing the
interaction of living (biotic) and nonliving (abiotic) component

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Figure: Ecological levels of
organization hierarchy;
seven transcending
processes or functions are
depicted as vertical
components of eleven
integrative levels of
organization (afier Barrett
et al. 1997).

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Figure: Compared with the strong
set-point controls at the organism
level and below, organization and
function at the population level
and above are much less tightly
regulated, with more pulsing and
chaotic behavior( but they are
controlled nevertheless by
alternating positive and negative
feedback-in other words, they
exhibit homeorhesris as opposed
to homeostasls. Failure to
recognize this difference in
cybernetics has resulted in much
confusion about the balance of
nature.

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Basic Terminology
• Autotrophy :The ability of organisms to grow and
reproduce independent of external sources of
organic carbon compounds.
• Eukaryote :An organizational state of cellular
organisms in which the genome of the cell is stored
in chromosomes enclosed in a membrane-bound
nucleus; all protists (algae and protozoa), fungi,
plants, and animals are eukaryotes.
• Euphotic :The top layer of a water body through
which sufficient light penetrates to support net
photosynthesis. Rarely more than 100 m in depth,
the euphotic layer can be as little as 1 m in turbid
waters.
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Basic Terminology
• Heterotrophy :The ability of organisms to grow and
reproduce on organic carbon sources, taken in
dissolved or particle form.
• Metazoan :Literally, a multi-celled animal.
• Mixotrophy :The ability of a normally autotrophic
organism to switch, circumstantially, to phagotrophy,
or to support an otherwise meager food supply by
resorting to the ingestion and assimilation of bacteria
or their products.
• Phagotrophy :A type of heterotrophy that involves
the consumption of protists, plants, or animals as
food.
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Basic Terminology
• Photoautotrophy : A type of autotrophy in which
organisms gather light energy in order to reduce
carbon dioxide to organic carbon; characteristic of
green plants, most algae, and some prokaryotes.
• Picophytoplankton :The smallest (o2 mm) size class
of photoautotrophic plankton.
• Prokaryote :Organizational state of cells lacking a
membrane-bound nucleus and certain other
organelles. Bacteria, including the cyanobacteria, are
typically prokaryotic.
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Plankton
• The name plankton was coined by German marine
biologist Victor Henson in 1887.
• ‘‘Plankton’’ is a collective term for organisms
adapted specifically for a life in suspension in the
open waters (the pelagic zone) of the sea and of such
inland waters as lakes, reservoirs, and rivers.
• Planktonic organisms include protists (allegedly
simple, unicellular, or colony-forming algal primary
producers and their protozoan consumers),
microorganisms, and certain types of small metazoan
animals, all sharing a common liability to passive
entrainment in water currents, generated by tide,
wind, convection, gravity, and the rotation of the
earth.
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Figure: Plankton
(organisms that drift
with water currents)
can be contrasted
with Nekton(organis
ms that swim against
water currents),
Neuston (organisms
that live at the ocean
surface) and benthos
(organisms that live
at the ocean floor).
Source: Wikipedia

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Planktonic ways of life
• The planktonic ways of life have evolved to
accommodate the several problems and drawbacks
associated with living in open water.
• These concern (1) remaining in suspension, (2)
exploiting nutrient resources, and (3) energy.
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Plankton- Types
• On the basis of broad functional groups or trophic
level Plankton are primarily divided into :
1. Phytoplankton: which include the plantlike
chlorophyll-containing primary producers, E.g.,
Autotrophic prokaryotic or eukaryotic algae
(Diatoms, Cyanobacteria, dinoflagellates etc
2. Zooplankton: which include the animal-like
consumers, E.g., small protozoans or
metazoans that feed on other plankton
3. Mycoplankton: which include fungi or fungus like
organisms
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Plankton- Types
4.Bacterioplankton: which include bacteria and archaea
play an important role in remineralising organic
material down the water column
5. Virioplankton: which include viruses
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Figure: Diverse planktonic organisms- Micro and meso-plankton

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Mixoplankton
• Mixoplankton: which include mixotrophs
Plankton have traditionally been categorized as
producer, consumer and recycler groups, but some
plankton are able to benefit from more than just one
trophic level.
In this mixed trophic strategy—known as mixotrophy—
organisms act as both producers and consumers, either
at the same time or switching between modes of
nutrition in response to ambient conditions.
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Mixoplankton
This makes it possible to use photosynthesis for growth
when nutrients and light are abundant, but switching
to eat phytoplankton, zooplankton or each other when
growing conditions are poor.
Mixotrophs are divided into two groups; constitutive
mixotrophs, CMs, which are able to perform
photosynthesis on their own, and non-constitutive
mixotrophs, NCMs, which use phagocytosis to engulf
phototrophic prey that are either kept alive inside the
host cell which benefit from its photosynthesis, or they
digest their prey except for the plastids which
continues to perform photosynthesis.
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Plankton types on the basis of size
• Macroplankton – their size ranges from 2 to 20 cm.
• Mesoplankton – includes organisms with size 0.2 to 20 mm.
• Microplankton – their size varies from 20 to 200 𝝁m, e.g. most
of the phytoplankton, protozoans and large protists.
• Nanoplankton – size ranges from 2 to 20 𝝁m, e.g. protists,
diatoms and algae.
• Picoplankton - size ranges from 0.2 to 2 𝝁m, e.g. small
eukaryotic protists, bacteria, Chrysophyta
• Femtoplankton - <2 𝝁m e.g. marine viruses
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Figure: Distribution of different taxonomic-trophic compartments of plankton in a
spectrum of size fractions, with a comparison of size ranges of zooplankton and
nekton. Solid rectangles denote size of most organisms in each size group, bars denote
approximate minimum/maximum size range of group. Blue bars, heterotrophic
microbes; green bar, autotrophic microbes (phytoplankton); purple bars, animals.
Figure is updated from a figure published by John Sieburth and colleagues in an article
in Limnology and Oceanography in 1978.

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Figure: Plankton sizes by taxonomic groups

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References
• Fundamentals of Ecology by Eugene P Odum
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Thanks for your endurance
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