What happens to the reef when the top predators disappear?
The top predators on coral reefs, such as sharks and barracuda, help to control the number of omnivorous and herbivorous organisms. If sharks and barracuda were to disappear from reef ecosystems, herbivore populations would increase. At first, one would think that this would be a good occurrence for a coral reef given the importance of grazing in the control of algal populations. Unfortanately, this presupposition is false. First, large predatory and herbivorous fishes have been severely overfished for centuries. This, in turn, explains the high densities of the long spined sea urchin, Diadema antillarum, on Caribbean reefs prior to the early eighties. In the absence of predators and competing herbivores, D. antillarum became a keystone specie in the control of macroalgae abundance. In late 1982 an unknown pathogen killed well over 90% of D. antillarum in the Western Atlantic. An explanation that has been put forth for the ecological extinction of this keystone specie is that due to se
