In 1983, an unprecedented, Caribbean-wide dieoff of the urchin Diadema antillarum occurred. Densities of this herbivore decreased drastically in reef environments throughout the region. The resulting reduction in grazing pressure has been implicated in an observed increase in fleshy algal cover on coral reefs. The actual relationship between reduced urchin grazing and increase in algal cover is still open to debate.
I. Introduction: Diadema ecology and life history
a. Habitat
b. Behavior
II. The Mortality Event
a. First observations
b. Symptoms
c. Geographic progression of epidemic
d. Intensity of mortality
III. Apparent Ecosystem Effects
a. Increase in fleshy algae
i. Diadema grazing studies
1. Carpenter 1981
b. Loss of coral cover.
IV. Questions Remaining
a. Cause of disease
b. Recovery of Diadema populations
c. Top down versus bottom up control
i. Lapointe 1997.
1. overfishing was severe long before recent blooms
2. Time line inconsistencies
3. Fore reef involvement
ii. McClanahan and Muthiga 1998
d. Disease-related coral loss
e. Jackson’s ideas
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McClanahan, TR and NA Muthiga. 1998. An ecological shift in a remote coral atoll of Belize over 25 years. Envir. Conserv. 25: 122-130.
Woodley, JD. 1999. Sea-urchins exert top-down control of macroalgae on Jamaican Coral Reefs. Coral Reefs 18:192-193.
Yoshioka, PM 1996. Variable recruitment and its effects on the population and community structure of shallow-water gorgonians. Bull. Mar. Sci. 59: 433-443.
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