"Natural" Disturbances
Diadema antillarum
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The long-spined sea urchin is a major herbivore on reefs, particularly in the Caribbean. On rubble reefs that have already been severely degraded, its grazing activity can prevent larval coral recruitment. |
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On healthy reefs, however, it can serve as an important regulator or macroalgae growth. Mass mortality of Diadema in the Caribbean in 1983, probably caused by a waterborne pathogen, was partly responsible for the phase shift in Jamaica's reefs. These reefs were badly hit by Hurricane Allen in 1980, which changed coral communities from predominantly branching species to predominantly encrusting species. |
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These encrusting species were easily smothered by the algal bloom following the mortality of Diadema. Since Jamaica's reefs are also chronically overfished, no herbivores were available to graze macroalgae in the absence of Diadema. Even a second hurricane (Hurricane Gilbert in 1988) failed to redress the balance because algal communities recovered more quickly than coral communities. |
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