Hurricanes and coral reefs: the intermediate disturbance hypothesis revisited

A review of research on the effects of hurricanes on coral reefs suggests that the intermediate disturbance hypothesis may be applicable to shallow reef zones dominated by branching or foliaceous coral species that are especially susceptible to mechanical damage from storms. Diversity (H') increases because of an increase in evenness following destruction or removal of the species that was monopolizing the space. The intermediate disturbance hypothesis as presented by Connell focuses on changes in number of species, but should be expanded to include diversity (H') and evenness. It should also be modified to incorporate changes in living cover and the time elapsed since disturbances of varying intensities. This hypothesis predicts that when cover is high, diversity will be low. However, research on coral reefs does not consistently demonstrate an inverse correlation of coral diversity and coral cover. An increase in cover and decrease in diversity with depth would also be expected because deeper reef zones generally experience less disturbance. However, higher diversity (both H' and species richness) is often associated with deeper zones. The effects of hurricanes on coral reefs will depend on the temporal and spatial scales under consideration, the life history characteristics and morphology of the dominant species, the depth of the reef zone, the ecological history of the site, and the influence of any additional natural or human stresses.