Coral Reefs Drew Harvell Ecology and Evol. Biology

Tropical Community Structure: Bottom Up vs Top Down? Over view of Reef Community Population Biology Corals  Hughes model Predation  Acanthaster  Cyphoma Competition and Sweeper Tentacles Bottom Up  Nutrients  Larval recruitment Phase Shift  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 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 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 Cyphoma and gorgonians Acanthaster and corals Jennaria and Pocillopora

Acanthaster planci--Crown of Thorns  -individuals--eat 5-6 m2 coral/year  -populations--eat km 2 coral/yr  Guam % 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 a.remove top predators-the welks or larval predators b.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  Predation on juveniles-- Predation on adults

Corals compete with sponges

Competition Sweeper tentacles Induced sweeper tentacles

Not so healthy reefs… 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 Oligotrophic conditions (low nutrients) eutrophic conditions No disease, many coral/urchin diseases

What Caused the Phase Shift? (Hughes Science 256: 1547) Disease killed dominant herbivore (Diadema) Overfishing removed replacement herbivores Nutrients stimulated algal growth Hurricanes contributed

Recovery of Diadema Edmunds and Carpenter 2001 Graph showing corals recruit back into areas With recovered diadema populations

Management? Hughes et al--- Top Down Problems (herbivores gone) Jeremy Jackson-- Top Down Problems (over-fishing) Brian LaPointe-- 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

Bruno Wh. Plague Black Band Yellow band Wh. Plague Caribbean coral diseases

Skeletal Eroding Band (SEB) 65 X Brown Band (ciliate) White Syndrome Australian coral diseases

Coral Reef Quiz Ecosystem services provided by coral reefs include  __________ -- __________ Corals are  ________ organisms  Housing symbiotic _______ 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