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Coral Reefs Drew Harvell Ecology and Evol. Biology

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

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Coral Reefs Drew Harvell Ecology and Evol. Biology

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  1. Coral Reefs Drew Harvell Ecology and Evol. Biology

  2. 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?

  3. 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

  4. Corals are cnidarians. The polyps are microcarnivores and feed On zooplankton. Symbiotic algae (zooxanthellae) in their tissues allow them to fix carbon autotrophically

  5. Corals reproduce sexually

  6. 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)

  7. 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

  8. Predation on reefs • Cyphoma and gorgonians • Acanthaster and corals Jennaria and Pocillopora

  9. Acanthaster planci--Crown of Thorns • -individuals--eat 5-6 m2 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

  10. 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)

  11. 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

  12. Corals compete with sponges

  13. Competition Induced sweeper tentacles • Sweeper tentacles

  14. 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: toppredators gone • Acanthaster (coral predator) • Sharks • Big fish • Oligotrophic conditions (low nutrients) eutrophic conditions • No disease, many coral/urchin diseases

  15. What Caused the Phase Shift? (Hughes 1994. Science 256: 1547) • Disease killed dominant herbivore (Diadema) • Overfishing removed replacement herbivores • Nutrients stimulated algal growth • Hurricanes contributed

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

  17. Management? • Hughes et al--- Top Down Problems (herbivores gone) • Jeremy Jackson-- Top Down Problems (over-fishing) • Brian LaPointe-- Botttom up (Eutrophication)

  18. 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

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

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

  21. 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 _________

  22. Danielle Dube, Laura Petes: Oceanography, Marine Ecology, Akumal Course, Cornell Honors Research---> Top Grad Schools

  23. Tropical Marine ScienceAkumal, 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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