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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).[
Why Should You Care About Corals? Cool Incredibly diverse Very important economically http://www.underseaproductions.com/demo_reels/marine_life_behaviour_video_footage.html
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 Biosynthesis Breaking down and building up bio molecules Movement Cilia Muscles
First Law of Thermodynamics Energy can not be created or destroyed It can only be converted from one form to another Forms of energy Electromagnetic Kinetic Nuclear Potential
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 Sun Plants Primary producers Herbivores Primary consumers Carnivores Secondary consumers Decomposers 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
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.
CORAL REEFS - ZOOXANTHELLAE --- 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 Tropical Eastern sides of continents
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 46
Coral Species Change Growth Form at Depth Plating in Star Coral (Monastrea) 47
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 Spawners Other species hold the eggs but release the sperm in the water Fertilization occurs in the Mom, later release larvae brooders Maternal transmission of zooxanthellae occurs more often in brooders than spawners
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 Siltation 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!
Coral Bleaching Environmental stress puts a strain on the symbiotic relationship fresh water dilution sedimentation subaerial exposure solar irradiance temperature
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
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.