Intro to Corals

Introduction to Corals, Coral ReefsDr. Mark A. McGinleyTexas Tech UniversityBIOL 5311Summer 2011

Great Barrier ReefThe largest biogenic (made by life) stuctures in the world are coral reefsstretches over 2,600 kilometers (1,600 mi)area of approximately 344,400 square kilometers (133,000 sq mi).[

Barrier ReefsThickest reef almost 1 mile thick.

Coral ReefsThick layer of calcium carbonate covered by thin layer of living organismsBuilt up over extremely long periods of time

CnidariansCorals contain living animals from the Phylum Cnidaria

Some Members Of Phylum Cnidaria

Coral PolypsA coral is a colony containing thousands of tiny polyps9

Coral FeedingThe 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

Why Should You Care About Corals?CoolIncredibly diverseVery important economicallyhttp://www.underseaproductions.com/demo_reels/marine_life_behaviour_video_footage.html

Coral EcologyCorals are involved in a lot of interesting ecological interactions.Let me tell you about a few.

Energetics and EcosystemsEnergy is required to do workBiological workMaintaining concentration gradients across membranesActive transportBiosynthesisBreaking down and building up bio moleculesMovementCiliaMuscles

First Law of ThermodynamicsEnergy can not be created or destroyedIt can only be converted from one form to anotherForms of energyElectromagneticKineticNuclearPotential

PhotosynthesisThe most important energetic process taking place for life on earthConverts electromagnetic energy from the sun (released by fusion reactions in the sun) to potential energy stored in the chemical bonds of glucose

Cellular RespirationEnergy stored in the chemical bonds of glucose is converted into energy stored in the chemical bonds of ATPATP releases that energyUsed to do biological work

Energy Flow Through EcosystemSunPlantsPrimary producersHerbivoresPrimary consumersCarnivoresSecondary consumersDecomposersEnergy lost as heat to environment

Flow of Energy From One Trophic Level to the Next is InefficientOnly about 10% of energy captured by plants is passed on to primary consumersAbout 10% of energy captured by primary consumers is passed on to secondary consumers

ForestsIn terrestrial ecosystems you see lots of plants.Forests are full of trees….

PrairiesPrairies have lots of grasses.

DesertsYou can even see lots of plants in the desert.

Coral Reef VideoSchooling Fishhttp://www.underseaproductions.com/demo_reels/schooling_fish_video_footage.html

Coral Reef Videohttp://www.underseaproductions.com/demo_reels/seascapes_video_footage.htmlHow many plants do you see on this video?

Coral ReefsDo not see many aquatic plants (algae) on coral reefsYet coral reefs are teeming with life and are one of the most diverse communities on the planetHow can this be?????

The Mystery of the “Inverted Energy Pyramid”

Missing Primary ProducersTwo possibilitiesMaybe 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 ReefsParrotfish 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 SandSo 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-offAbout 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 ProducersIn undisturbed reefs, primary productivity of algae is rapidly removed by the herbivoresBut calculations of rate of photosynthesis by algae was not enough to explain the energy and biomass at higher tropic levels

Missing Primary ProducersNot looking in the right place.Scientists (and the video we just saw) looked all over the coral reef for primary producersNeeded to look “inside” of corals

Symbiotic ZooxanthellaeLittle photosynthetic microorganisms called Zooxanthellaeare 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 ZooxanthellaeMutualistic interactionInteraction between two species in which both species benefit.

Green polyp tissue, red zooxanthellaeCoral – Zooxanthellae MutualismZooxanthellae 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 requirementsCorals 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 MutualismExplains one aspect of the distribution of coral reefsCoral Reefs are foundShallow waterNear continentsTropicalEastern sides of continents

Coral reefs limited to the “photic zone”Zooxanthellae require light for photosynthesisCorals limited to relatively shallow water

Coral Reef ZonationThere are consistent patterns of zonation on coral reefs with increasing depthWater absorbs light so there is less light as depth increasesThus, ability of zooxanthellae to provide corals with energy decreases with depth46

Coral Species Change Growth Form at DepthPlating in Star Coral (Monastrea)47

More Sponges and Fewer Corals at Greater Depths

MutualismsImportant for the two participant species to be able to find each otherHow do they do this?

Transmission of ZooxanthellaeMaternally passed from parent to offspring-vertical transmission

Coral Life CycleCorals can reproduce sexually or asexuallyZooxanthellae easily passed from parent to offspring in asexual reproductionCorals also reproduce sexuallyEgg and spermMothers can place zooxanthellae in eggs

Sexual Reproduction in CoralsSome species of corals release both eggs and sperm in the waterFertilization occurs in the water columnSpawnersOther species hold the eggs but release the sperm in the waterFertilization occurs in the Mom, later release larvaebroodersMaternal transmission of zooxanthellae occurs more often in brooders than spawners

Transmission of ZooxanthellaeEnvironmental transmission each new generation

Free-living Zooxanthellae enter new corals each generationThis is very important for some of the issues we will talk about later

Benefits of Coral ReefsFisheries

Benefits of Coral Reefs Protect Shore

Benefits of Coral ReefsTourism

Benefits of Coral ReefsBiodiversity

Many Coral Reefs Are Threatened

Decline of Caribbean Coral Reefs

Threats to Coral ReefsStorm Damage

Threats to Coral ReefsCrown of Thorns StarfishOccasionally, 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.

63Threats to Coral ReefsSiltationWhen 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 ReefsAlgal BloomsThe 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 ReefsBlast fishingIn 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 ReefsCoral Bleaching

Coral BleachingEnvironmental stress puts a strain on the symbiotic relationshipfresh water dilutionsedimentationsubaerial exposuresolar irradiancetemperature

Coral BleachingFresh 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 scalePotentially a much bigger problem

Coral BleachingCoral bleaching is occurring all over the world!

Coral BleachingPolyps can live for a while without the zooxanthellae, but growth rate is greatly reducedIf stress is eliminated the zooxanthellae may return to the polyps and the coral recoversIf stress continue for too long, then the polyps will die

Temperature and Coral BleachingCoral 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 bleachingOver 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 BleachingEl Nino events can change the pattern of ocean currents and bring warmer water to reefs16 % of the world’s coral reefs experienced bleaching in 1997-1998 mortality approaching 90% in some placesabout half of damaged reefs have not recovered.

Mechanisms of Coral BleachingNot well understoodOften talk about polyps “expelling zooxanthellae”This may or may not be an accurate word choiceThis discussion might benefit from a better knowledge of about theories of mutualisms

Mechanisms of Coral BleachingZooxanthellae may be lost from polyps “unintentionally”Cell Adhesion DysfunctionHigh 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.

MutualismsMutualisms are interactions between two species in which both species benefitOften think of species behaving altruistically Probably more complicated then that.

MutualismsSpecies are involved in mutualistic relationships because the benefits of interacting with the other species are larger than the costs of that interactionIf something happens to alter the benefits and costs then species might “reconsider” whether or not they want to be involved in the relationshipWhether or not they can do anything about it can vary from system to system

Zooxanthellae may “choose” to leave the polypsStressed 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” ZooxanthellaeCoral polyps might “decide” to end the relationship with the zooxanthellae ifThe costs of hosting zooxanthellae increaseThe benefits received from the zooxanthellae decrease

Polyps may “Expell” ZooxanthellaeStress 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” ZooxanthellaeAdaptation MechanismIf 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 DiseasesCoral diseases are another threat to coral reefsCoral diseases were first identified in the 1970s and their prevalence has increased since then

Black-band DiseaseBlack-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 DiseaseThe disease is caused primarily by a cyanobacteriasulfide-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 DiseaseThe dead skeleton will be attacked by boring algae, boring sponges, boring clams, and parrot fish which will gnaw away the skeletonremove 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 DiseaseWhite-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 tipsThe 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 DiseaseThe cause of White-band Disease is unknown. unusual aggregates of rod-shaped bacteria were found in the tissue of corals affected by White-band Diseasescientists have not determined the role of this microorganism

White-band DiseaseSince 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 yearsWhite-band disease currently is the only coral disease known to cause major changes in the composition and structure of reefs

Yellow Blotch DiseaseAffects 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 DiseaseYellow 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 DiseaseThe 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 DiseaseRed-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 AspergillosisCaused 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 HypothesisChanges in global climate and land use in Africa resulted in severe droughts in the Sahara and Sahel of Africa starting in the 1970s.

Dust HypothesisHundreds 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 HypothesisAfrican 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- Mechanismsinterfere 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 growthhas been shown for Red tides in the Gulf of Mexicodirectly deposit pathogenic microorganisms.

Intro to Corals

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Intro to Corals