Coral Reefs Drew Harvell Ecology and Evol Biology
Coral Reefs Drew Harvell Ecology and Evol. Biology
Tropical Community Structure: Bottom Up vs Top Down? n n Over view of Reef Community Population Biology Corals ¨ n Hughes model Predation Acanthaster ¨ Cyphoma ¨ n n Competition and Sweeper Tentacles Bottom Up Nutrients ¨ Larval recruitment ¨ n Phase Shift ¨ n Hughes 1994 Whats wrong with reefs?
Corals are colonial invertebrates They grow by asexual propagation of polyps and can share nutrients among polyps O. Scleractinian corals O. Gorgonian corals O. Alcyonacean corals
Corals are cnidarians. The polyps are microcarnivores and feed On zooplankton. Symbiotic algae (zooxanthellae) in their tissues allow them to fix carbon autotrophically
Corals reproduce sexually
A healthy reef ecosystem n n n Tropical warm waters Corals and zooxanthellae fix carbon Algae fix carbon Herbivores (fish and urchins) graze algae, turf algae coexist with corals, Top predators exist in balance: Acanthaster (coral predator) ¨ Sharks ¨ Big fish ¨ n Oligotrophic conditions (low nutrients)
Tools for SCUBA intensive projects Underwater Aquarius habitat The luxury of an hour at 120’, unlimited time at 60’… Jen Ruesink, Brian Helmuth -- from Cornell honors student to Paine undergrad to Professor
Predation on reefs n n Cyphoma and gorgonians Acanthaster and corals Jennaria and Pocillopora
Acanthaster planci--Crown of Thorns -individuals--eat 5 -6 m 2 coral/year ¨ -populations--eat 0. 5 -6. 0 km 2 coral/yr ¨ Guam 68 -69 - 90% of coral killed along 38 km coastline ¨ Australia- outbreak travelled 100's of km, about 28% of reefs ¨
Why is Acanthaster such a problem? 1. Natural cycle--paleo evidence suggests these outbreaks have occurred historically ¨ 2. Man-induced--more and bigger ones now ¨ n n a. b. remove top predators-the welks or larval predators euthrophication--larvae do better (65 million larvae/season)
5 Hypotheses about control of population cycles: Nutrient Runoff-- higher nutrients suport more larvae ¨ Larval advection (due to currents)-- more larvae advected in to particular sites ¨ Predation on larvae-- sometimes predation released on larvae ¨ ¨ n Predation on juveniles-- Predation on adults
Corals compete with sponges
Competition n Sweeper tentacles Induced sweeper tentacles
Not so healthy reefs… n n n Tropical warm waters, climate warming Corals and zooxanthellae fix carbon bleaching Algae fix carbon too high a rate Herbivores (fish and urchins) graze algae, turf algae coexist with corals, macroalgae overgrow coral Top predators exist in balance: top predators gone Acanthaster (coral predator) ¨ Sharks ¨ Big fish ¨ n n Oligotrophic conditions (low nutrients) No disease, eutrophic conditions many coral/urchin diseases
What Caused the Phase Shift? (Hughes 1994. Science 256: 1547) n n Disease killed dominant herbivore (Diadema) Overfishing removed replacement herbivores Nutrients stimulated algal growth Hurricanes contributed
Recovery of Diadema n Edmunds and Carpenter 2001 Graph showing corals recruit back into areas With recovered diadema populations
Management? n n n Hughes et al--- Top Down Problems (herbivores gone) Jeremy Jackson-- Top Down Problems (over-fishing) Brian La. Pointe-- Botttom up (Eutrophication)
Zooxanthellae are damaged and leave corals Induced by elevated sea temperature Exacerbated by high irradiance Bleaching is one of several symptoms of (thermal) stress Hoeghguldberg
Caribbean coral diseases Black Band Yellow band Wh. Plague Bruno Wh. Plague
Australian coral diseases Skeletal Eroding Band (SEB) 65 X White Syndrome
Coral Reef Quiz n Ecosystem services provided by coral reefs include _____ -- _____ ¨ n Corals are ____ organisms ¨ Housing symbiotic _______ ¨ n n Bleaching occurs when coral expel _______ and is caused by _______ temp. _______ is caused by increased nutrients and is ______ for corals. A _____ diving habitat allows increased bottom time. A phase shift (______ replaced by _______) was caused by: Over ______ ¨ A big _______ ¨ Increased _____ ¨
Danielle Dube, Laura Petes: Oceanography, Marine Ecology, Akumal Course, Cornell Honors Research---> Top Grad Schools
Tropical Marine Science Akumal, Mexico 4 weeks Summer 2003, June 16 -July 14 Apply through Shoals Marine Lab Reef Ecology, Coral Biology, Coral Reef Monitoring
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