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