Intro to Corals
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    Intro to Corals Intro to Corals Presentation Transcript

    • Introduction to Corals, Coral Reefs
      Dr. Mark A. McGinley
      Texas Tech University
      BIOL 5311
      Summer 2011
    • Great Barrier Reef
      The largest biogenic (made by life) stuctures in the world are coral reefs
      stretches over 2,600 kilometers (1,600 mi)
      area of approximately 344,400 square kilometers (133,000 sq mi).[
    • Great Barrier Reef From Space
    • Barrier Reefs
      Thickest reef almost 1 mile thick.
    • Coral Reefs
      Thick layer of calcium carbonate covered by thin layer of living organisms
      Built up over extremely long periods of time
    • Cnidarians
      Corals contain living animals from the Phylum Cnidaria
    • Some Members Of Phylum Cnidaria
    • Cnidarian Morphology
    • Coral Polyps
      A coral is a colony containing thousands of tiny polyps
    • Coral Polyps
    • Coral Feeding
      The coral polyps feed on either small living
      organisms or on dead material (detritus)
      that floats in the water.
    • Scleractinian Corals (reef building corals)
      secrete CaCO3
      external skeletons secreted by epidermis
    • Coral Skeleton
    • Hard Corals
    • Why Should You Care About Corals?
      Incredibly diverse
      Very important economically
    • Coral Ecology
      Corals are involved in a lot of interesting ecological interactions.
      Let me tell you about a few.
    • Energetics and Ecosystems
      Energy is required to do work
      Biological work
      Maintaining concentration gradients across membranes
      Active transport
      Breaking down and building up bio molecules
    • First Law of Thermodynamics
      Energy can not be created or destroyed
      It can only be converted from one form to another
      Forms of energy
    • Photosynthesis
      The most important energetic process taking place for life on earth
      Converts electromagnetic energy from the sun (released by fusion reactions in the sun) to potential energy stored in the chemical bonds of glucose
    • Cellular Respiration
      Energy stored in the chemical bonds of glucose is converted into energy stored in the chemical bonds of ATP
      ATP releases that energy
      Used to do biological work
    • Energy Flow Through Ecosystem
      Primary producers
      Primary consumers
      Secondary consumers
      Energy lost as heat to environment
    • Flow of Energy From One Trophic Level to the Next is Inefficient
      Only about 10% of energy captured by plants is passed on to primary consumers
      About 10% of energy captured by primary consumers is passed on to secondary consumers
    • Energy Pyramid
    • Biomass Pyramid
    • Forests
      In terrestrial ecosystems you see lots of plants.
      Forests are full of trees….
    • Prairies
      Prairies have lots of grasses.
    • Deserts
      You can even see lots of plants in the desert.
    • Coral Reef Video
      Schooling Fish
    • Coral Reef Video
      How many plants do you see on this video?
    • Coral Reefs
      Do not see many aquatic plants (algae) on coral reefs
      Yet coral reefs are teeming with life and are one of the most diverse communities on the planet
      How can this be?????
    • The Mystery of the “Inverted Energy Pyramid”
    • Missing Primary Producers
      Two possibilities
      Maybe plants are photosynthesizing but the plant material is eaten by herbivores as fast as it is produced.
      - Therefore we don’t see a build up of plants
    • Lots of Herbivores Living or Coral Reefs
      Parrotfish eat the algae living in corals by scraping
      off the outer layer using their very sharp teeth.
      They grind up the rocks, digest the algae, and
      poop out a lot of sand
    • Biogenic Sand
      So remember, when you are taking a romantic stroll down the beach with your
      sweetie much of the sand you are walking on is parrotfish poop.
    • Long-spined Urchin (Diademaantillarum)
      Long-spined urchins are important
      herbivores on coral reefs.
    • Results of Overfishing and Diadema Die-off
      About 20 years ago a disease entered the Caribbean
      Sea through the Panama Canal. This disease killed
      almost 90 percent of the urchins. In some places,
      fishing by humans has reduced the number of
      herbivorous fishes. The loss of the fishes and the
      urchins has allowed algae to grow. Because algae grows so much faster than corals algae is
      able to outcompete the corals so many corals have been covered by algae.
    • Missing Primary Producers
      In undisturbed reefs, primary productivity of algae is rapidly removed by the herbivores
      But calculations of rate of photosynthesis by algae was not enough to explain the energy and biomass at higher tropic levels
    • Missing Primary Producers
      Not looking in the right place.
      Scientists (and the video we just saw) looked all over the coral reef for primary producers
      Needed to look “inside” of corals
    • Symbiotic Zooxanthellae
      Little photosynthetic microorganisms called Zooxanthellae
      are found living inside of the coral polyps.
      --- Are group of algae called dinoflagellates (also form red tides).
      Symbiodinium spp.)
      --- Are different colors; brown, green, yellow.
      --- Dinoflagellatesmutualistic with other groups; sea slugs, giant clams, tunicates.
      --- Can live outside host
    • Mutualistic Relationship Between Corals Polyps and Zooxanthellae
      Mutualistic interaction
      Interaction between two species in which both species benefit.
    • Green polyp tissue, red zooxanthellae
      Coral – Zooxanthellae Mutualism
      Zooxanthellae provide corals:
      Energy (photosynthesis products) and as a by-product ability to grow and reproduce fast enough to produce reefs.
      Zooxanthellae can provide up to 90% of a coral’s energy requirements
      Corals provide zooxanthellae with:
      Protection from predators via Cnidarian nematocysts.
      Removal of dissolved organic material from water column (to keep water clear)
      Waste products useful for algal photosynthesis (nitrogen and phosphorous)
    • Coral-Zooxanthellae Mutualism
      Explains one aspect of the distribution of coral reefs
      Coral Reefs are found
      Shallow water
      Near continents
      Eastern sides of continents
    • Distribution of Corals
    • Coral reefs limited to the “photic zone”
      Zooxanthellae require light for photosynthesis
      Corals limited to relatively shallow water
    • Coral Reef Zonation
      There are consistent patterns of zonation on coral reefs with increasing depth
      Water absorbs light so there is less light as depth increases
      Thus, ability of zooxanthellae to provide corals with energy decreases with depth
    • Coral Species Change Growth Form at Depth
      Plating in Star Coral (Monastrea)
    • More Sponges and Fewer Corals at Greater Depths
    • Mutualisms
      Important for the two participant species to be able to find each other
      How do they do this?
    • Transmission of Zooxanthellae
      Maternally passed from parent
      to offspring
      -vertical transmission
    • Coral Life Cycle
      Corals can reproduce sexually or asexually
      Zooxanthellae easily passed from parent to offspring in asexual reproduction
      Corals also reproduce sexually
      Egg and sperm
      Mothers can place zooxanthellae in eggs
    • Sexual Reproduction in Corals
      Some species of corals release both eggs and sperm in the water
      Fertilization occurs in the water column
      Other species hold the eggs but release the sperm in the water
      Fertilization occurs in the Mom, later release larvae
      Maternal transmission of zooxanthellae occurs more often in brooders than spawners
    • Transmission of Zooxanthellae
      • Environmental transmission each new generation
      • Free-living Zooxanthellae enter new corals each generation
      This is very important for some of the issues we will talk about later
    • Benefits of Coral Reefs
    • Benefits of Coral Reefs
      Protect Shore
    • Benefits of Coral Reefs
    • Benefits of Coral Reefs
    • Many Coral Reefs Are Threatened
    • Decline of Caribbean Coral Reefs
    • Threats to Coral Reefs
      Storm Damage
    • Threats to Coral Reefs
      Crown of Thorns Starfish
      Occasionally, there are large population outbreaks of this big (and ugly) starfish. The starfish feeds on coral polyps and can kill large areas of coral reefs.
    • What Causes Such Large Increases in Population Size of the Starfish?
      One theory is that collecting Tritons to sell their shells has reduced the population size of the most important predator of the starfish.
      Without any predators the population size of the starfish increases greatly.
    • 63
      Threats to Coral Reefs
      When the land is disturbed by building or farming soil erosion can cause silt to be carried into the ocean.
      When the silt covers the coral the polyps can not feed and the Zooxanthellae can not photosynthesize so the coral dies.
    • Threats to Coral Reefs
      Algal Blooms
      The addition of nutrients to the ocean from fertilizer run off or human sewage can fertilize faster growth of algae.
      When the algae covers the coral it blocks the light to the Zooxanthellae.
    • Threats to Coral Reefs
      Blast fishing
      In some places fishermen capture the fish by stunning them with explosions.
      Obviously, these explosions to a lot of damage to the reef.
      I heard blast fishing for the first time while diving in Malaysia last year!
    • Threats to Coral Reefs
      Coral Bleaching
    • Coral Bleaching
    • Coral Bleaching
    • Coral Bleaching
      Environmental stress puts a strain on the symbiotic relationship
      fresh water dilution
      subaerial exposure
      solar irradiance
    • Coral Bleaching
      Fresh water dilution and sedimentation are local conditions so coral bleaching due to these factors is limited to certain small areas.
      Solar irradiance and especially temperature are stressors that cause coral bleaching on a global scale
      Potentially a much bigger problem
    • Coral Bleaching
      Coral bleaching is occurring all over the world!
    • Coral Bleaching
      Polyps can live for a while without the zooxanthellae, but growth rate is greatly reduced
      If stress is eliminated the zooxanthellae may return to the polyps and the coral recovers
      If stress continue for too long, then the polyps will die
    • New Guinea
    • Temperature and Coral Bleaching
      Coral reefs are vulnerable to increased temperature, which causes corals to lose their symbiotic algae in a process called coral bleaching.
      Small increase in water temperature is enough to trigger bleaching
      Over the last 30 years, average ocean temperatures have increased 0.3 to 0.4 degrees Celsius.
      Mass coral bleaching episodes have increased dramatically over the last 2-3 decades.
    • Temperature and Coral Bleaching
      El Nino events can change the pattern of ocean currents and bring warmer water to reefs
      16 % of the world’s coral reefs experienced bleaching in 1997-1998
      mortality approaching 90% in some places
      about half of damaged reefs have not recovered.
    • Mechanisms of Coral Bleaching
      Not well understood
      Often talk about polyps “expelling zooxanthellae”
      This may or may not be an accurate word choice
      This discussion might benefit from a better knowledge of about theories of mutualisms
    • Mechanisms of Coral Bleaching
      Zooxanthellae may be lost from polyps “unintentionally”
      Cell Adhesion Dysfunction
      High temperature shock could result in cell adhesion dysfunction between the cnidarianendodermal cells and the zooxanthellae cells.
      Cell adhesion dysfunction would cause the detachment and loss of zooxanthellae from the coral.
    • Mutualisms
      Mutualisms are interactions between two species in which both species benefit
      Often think of species behaving altruistically
      Probably more complicated then that.
    • Mutualisms
      Species are involved in mutualistic relationships because the benefits of interacting with the other species are larger than the costs of that interaction
      If something happens to alter the benefits and costs then species might “reconsider” whether or not they want to be involved in the relationship
      Whether or not they can do anything about it can vary from system to system
    • Zooxanthellae may “choose” to leave the polyps
      Stressed corals may give provide zooxanthellae fewer nutrients for photosynthesis
      - less benefit to the mutualism
      If the fitness of algae living independently is greater than the fitness of algae living in polyps then the algae may “decide” to leave the polyp and exist independently.
    • Polyps may “Expell” Zooxanthellae
      Coral polyps might “decide” to end the relationship with the zooxanthellae if
      The costs of hosting zooxanthellae increase
      The benefits received from the zooxanthellae decrease
    • Polyps may “Expell” Zooxanthellae
      Stress might alter the physiology of the zooxanthellaeand cause them to release compounds that are harmful to polyps (perhaps free oxygen radicals)
      Polyps will release the zooxanthellae rather than suffer the effects of the toxins.
    • Polyps may “Expell” Zooxanthellae
      Adaptation Mechanism
      If certain strains of zooxanthellae cannot function when stressed, the polyps expell these zooxanthellae to leave their tissues open to be recolonized by a different strain of zooxanthellaethat are better adapted to the current environment
    • Coral Diseases
      Coral diseases are another threat to coral reefs
      Coral diseases were first identified in the 1970s and their prevalence has increased since then
    • Black-band Disease
      Black-band disease is characterized by a blackish concentric or crescent-shaped band, 1 to 30 mm wide and up to 2 m long, that “consumes” live coral tissue as it passes over the colony surface, leaving behind bare skeleton.
    • Black-band Disease
      The disease is caused primarily by a cyanobacteria
      sulfide-oxidizing bacteria, sulfur- reducing bacteria, other bacteria and nematodes, ciliate protozoans, flatworms and fungal filaments also are present.
      The photosynthetic pigments of the dominant cyanobacteria gives the band its maroon to black color
    • Black-band Disease
      The dead skeleton will be attacked by boring algae, boring sponges, boring clams, and parrot fish which will gnaw away the skeleton
      remove about 1 cm per year.
      This means that in 100 years, a 1-meter high coral head will be completely consumed and converted to sediment.
    • White-band Disease
      White-band disease was first identified in 1977 on reefs surrounding St. Croix. It is now known to occur throughout the Caribbean where it is believed to only affect staghorn and elkhorn corals.
      This disease is characterized by tissue that peels or sloughs off the coral skeleton in a uniform band, generally beginning at the base of the colony and working its way up to branch tips
      The band ranges from a few millimeters up to 10 cm wide, and tissue is lost at a rate of about 5 mm per day
    • White-band Disease
      The cause of White-band Disease is unknown.
      unusual aggregates of rod-shaped bacteria were found in the tissue of corals affected by White-band Disease
      scientists have not determined the role of this microorganism
    • White-band Disease
      Since the 1980s, Acroporacervicornis has been virtually eliminated from reef environments throughout the Caribbean.
      In the U.S. Virgin Islands, populations of Acroporapalmata declined from 85 percent cover to 5 percent within 10 years
      White-band disease currently is the only coral disease known to cause major changes in the composition and structure of reefs
    • Yellow Blotch Disease
      Affects only star corals in the genus Montastraea and the brain coral Colpophyllianatans
      First identified in 1994 in the lower Florida Keys. It is now known to occur throughout the Caribbean
    • Yellow Blotch Disease
      Yellow blotch disease begins as pale, circular blotches of translucent tissue or as a narrow band of pale tissue at the colony margin, with affected areas being surrounded by normal, fully pigmented tissue.
      As the disease progresses, the tissue first affected in the center of the patch dies, and exposed skeleton is colonized by algae . The area of affected tissue progressively radiates outward, slowly killing the coral.
    • Yellow Blotch Disease
      The rate of tissue loss by corals afflicted with YBD averages 5 t 11 cm per year, which is less than that of other coral diseases.
      However, corals can be affected for many years, and the disease can affect multiple locations on a colony.
      Though the cause of Yellow Blotch Disease remains unknown
    • Red-band Disease
      Red-band disease consists of a narrow band of filamentous cyanobacteria that advances slowly across the surface of a coral, killing living tissue as it progresses.
      Affects massive and plating stony corals, and also sea fans throughout the wider Caribbean.
      exposed skeletal surfaces are rapidly colonized by algae and other competing organisms.
    • Sea Fan Aspergillosis
      Caused by the pathenogenic fungus Aspergillussydowii. 
    • Why has the prevalence of coral diseases increased so much in the last 40 years?
      One theory is that anthropogenic stresses on the environment have made corals more susceptible to infection by coral diseases
    • Dust Hypothesis
      Changes in global climate and land use in Africa resulted in severe droughts in the Sahara and Sahel of Africa starting in the 1970s.
    • Dust Hypothesis
      Hundreds of millions of tons of African dust are transported annually from the Sahara and Sahel to the Caribbean and southeastern U.S.
      A similar dust system in Asia carries dust from the Gobi and TakliMakan deserts across Korea, Japan, and the northern Pacific to the Hawaiian Islands, the western U.S., and as far eastward as Europe.
    • I’ve cleaned this dust off of boats in the Caribbean.
    • Dust Hypothesis
      African and Asian dust air masses transport nutrients (iron, nitrates, other nutrients), pollutants, and viable microorganisms that may adversely affect human health and downwind ecosystems such as coral reefs.
    • Dust Hypothesis- Mechanisms
      interfere with a coral's immune system, making it more susceptible to disease pathogens.
      induce pathogenicity in a microorganism in the reef environment.
      trigger a rapid increase in the number of pathogenic microorganisms.
      fuel macroalgae or phytoplankton growth
      has been shown for Red tides in the Gulf of Mexico
      directly deposit pathogenic microorganisms.
    • Lots of topics for future research about the role of microbes in coral reef ecosystems