Coral Reefs
Drew HarvellEcology 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?
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Corals are colonial invertebrates
They grow by asexual propagationof polyps and can share nutrientsamong polyps
O.Scleractinian coralsO.Gorgonian coralsO.Alcyonacean corals
Corals are cnidarians. The polyps are microcarnivores and feedOn 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)
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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 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
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
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Corals compete with sponges
Competition
Sweeper tentaclesInduced 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 1994. 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 areasWith 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 temperatureInduced by elevated sea temperatureExacerbated by high irradianceExacerbated by high irradianceBleaching is one of several symptoms of Bleaching is one of several symptoms of (thermal) stress(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 ScienceAkumal, MexicoTropical Marine ScienceAkumal, Mexico
4 weeks Summer 2003, June 16-July 14Apply through Shoals Marine LabReef Ecology, Coral Biology, Coral Reef Monitoring
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