Coral Reef EcosystemsMARS 34508 October, 2013Great Barrier ReefAustraliaThe Sapelo Island Field TripRed dots = GCE LTER sampling sitesUGAMICoral Reefs•Phylum: Cnidaria, Class: Anthozoa•Ahermatypic: corals that don’t precipitate CaCO3•Hermatypic: corals that precipitate CaCO3Calcium carbonate deposits laid down by biological processesand gradually accretingThese makereefsWhich organisms build coral reefs?1) CoralsSea Fans, Sea Whips(Nybakken 2001)HermatypicCorals•Polyp imbedded in “corallite”•Polyps within a colony are clones;arise from single polyp that divides asexually•Connected by a layer of tissue•Feed on zooplankton/particles but…•Symbiotic algae in gastrodermis(Nybakken 2001)Zooxanthellae•Dinoflagellate•Genus Symbiodinium•Typical morphology in free-living stageCoral-Zooxanthellae symbiosis•Coral provides CO2, nutrients•Alga fixes CO2to carbohydratesSolar Powered!(Castro & Huber 2003)Efficient Recycling!Coral-Zooxanthellae symbiosis•Previously thought to be one species of Symbiodinium;“one host-one symbiont” obligate relationship•But molecular data suggest otherwise•18S rRNAs from symbiont show variability within a colony of Montastrea•Is there a “community” of symbionts selected for light exposure? (Rowan et al. 1997)Position on colonyCulturesABCFragment Length(Rowan et al. 1997)Coral-Zooxanthellae symbiosis•Tested the light hypothesis by looking at patterns of symbiont occurrence relative to light levels•Types A and B found in high light situations within a coral and along depth transects•Type C found in low light situationsA=grayB=whiteC=blackWill this improve understanding of coral bleaching?Who Cares?Fine-tuning the symbiosis(Castro & Huber 2003)Coiled tubes attached to gut wallExtruded through mouthExcrete digestive enzymes for feeding and defenseMesenterial filamentsMucus sheets- Corals excrete mucus on surface- For feeding and sediment removalMucus as a source of energy for the reef?•Australian coral Acropora•Exudes 4.8 liters of mucus/m2/day•Mucus traps additional POC and DOC•Serves as source of organic matter for reef organisms(Wild et al. 2004)Large mucus float Part of complex food web?Coral Reefs•Coral morphology•Reef structure•UV protection for zooxanthellae(Castro & Huber 2003)What organisms build coral reefs?1) Corals2) Coralline Algae3) Organisms with CaCO3 shellsRed algaeGrow in sheets across reef surface“Cement” reef into continuous surfaceIncorporate rubble and sediment Bivalves, gastropods, urchins, spongesBeach Rock – an authigenicmineral deposited at high tide lineCa2+ + CO32- CaCO3CO2+ H2O  H2CO3 H++ HCO3- 2H++ CO32-Corals (and other organisms) have mechanisms for concentrating Ca2+ and CO32-(Nybakken 2001)Distributionof Coral Reefs•Light •Temperature: >20oC•Salinity: 32-35 psu•Low sediment loading•Low N and P loading20oC IsothermEffect of upwellingEffect of low salinityHighnutrientsfavorweed algaeParticlesblock lightReefs(Castro & Huber 2003)Types of coral reefs: Fringing•Develop adjacent to shore•Best example: Red Sea(4000 km long!)(Castro & Huber 2003)Types of coral reefs: Barrier•Develop several km from shore•Shallow lagoon forms•Best example: Great BarrierExamples of Barrier Reefs(Castro & Huber 2003)Types of coral reefs: Atoll•Found in deep water•Ring-shaped reef enclosingshallow lagoon• Primarily Indo-PacificHow do they form?Begin as fringing reef on volcanic islandPrimary Production in Marine EcosystemsSystem gC/m2/y apples/m2/yOpen ocean <100 1Benthic deep sea* 0 0Coastal upwelling 300 6Kelp Systems 1300 26Tropical forests 1200 24Seagrass beds 800 16Coral Reefs 3000 60(+200)Who are the primary producers? •Zooxanthellae•Algal turf•Coralline algae•Seagrasses and macroalgaeMost are “cryptic”Corals, giant clams, sponges, gastropods- Not detritus-based! (except maybe mucus)- Herbivores,- Corallivores,-PlanktivoresDeep Water Coral Reefs•First discovered ~20 years ago•Mounds of corals ~300 m high x 1000 m diameter•But located well below light level for photosynthesis(200-2000 m); no zooxanthellae!•Temperatures of 4-12oC•Found where particle supply is high•Corals less diverse than shallow reefs(Roberts et al. 2006)Not requiredfor reef building10 species comparedto 800 for shallow reefsDeep Water Coral Reefs(Roberts et al. 2006)Deep Water Coral Reefs(Roberts et al. 2006)(Gardner et al. 2003)Coral Reef DeclinesIntense stormsSea star outbreaksIncreased runoff from landsedimentnutrientsTemperature increasesEl Niñoglobal warmingDiseaseWhat is causing mortality?number of studiescoral coverCaribbean Basin Coral CoverClearly it is the number of studies!Reef fish•Parrotfish feeding•Carnivorous