Coral Reefs
Drew Harvell
Ecology and Evol. Biology
Tropical Community Structure: Bottom Up vs Top Down?
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Over view of Reef Community
Population Biology Corals
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Hughes model
Predation
Acanthaster
¨ Cyphoma
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Competition and Sweeper Tentacles
Bottom Up
Nutrients
¨ Larval recruitment
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Phase Shift
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Hughes 1994
Whats wrong with reefs?
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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
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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:
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Acanthaster (coral predator)
Sharks
Big fish
Oligotrophic conditions (low nutrients)
Tools for SCUBA intensive projects
Underwater Aquarius habitat
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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
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Cyphoma and gorgonians
Acanthaster and corals
Jennaria and
Pocillopora
Acanthaster planci--Crown of Thorns
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-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?
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1.Natural cycle--paleo evidence suggests these outbreaks have occurred historically
2.Man-induced--more and bigger ones now
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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:
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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
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Predation on juveniles--
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Predation on adults
Corals compete with sponges
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Corals compete with sponges
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Slide deleted
Competition
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Sweeper tentacles
Induced sweeper tentacles
Not so healthy reefs…
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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
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Acanthaster (coral predator)
Sharks
Big fish
Oligotrophic conditions (low nutrients)
No disease,
eutrophic conditions
many coral/urchin diseases
What Caused the Phase Shift?
(Hughes 1994. Science 256: 1547)
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Disease killed dominant herbivore (Diadema)
Overfishing removed replacement herbivores
Nutrients stimulated algal growth
Hurricanes contributed
Recovery of Diadema
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Edmunds and Carpenter 2001
Graph showing corals recruit back into areas
With recovered diadema populations
Jackson et al. Where are the top predators
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J. Oliver
Management?
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Hughes et al--- Top Down Problems (herbivores gone)
Jeremy Jackson-- Top Down Problems (over-fishing)
Brian LaPointe-- Botttom up (Eutrophication)
Coral Bleaching
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Hoeghguldberg
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
Bruno
Wh. Plague
Wh. Plague
Australian coral diseases
Skeletal Eroding Band
(SEB)
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White Syndrome
Brown Band (ciliate)
Coral Reef Quiz
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Ecosystem services provided by coral reefs include
__________
-- __________
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Corals are
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________ 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:
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Over ______
A big _______
Increased _________
Danielle Dube, Laura Petes: Oceanography, Marine Ecology,
Akumal Course, Cornell Honors Research---> Top Grad Schools
Tropical
Tropical Marine
Marine Science
Science
Akumal,
Akumal, Mexico
Mexico
4 weeks Summer 2003, June 16-July 14
Apply through Shoals Marine Lab
Reef Ecology, Coral Biology, Coral Reef
Monitoring