Patterns of Species Diversity in Caribbean Reef Corals

A method of counting chain links covering living coral is described and discussed as a means of calculating species diversity on coral reefs. Species diversity on San Blas coral reefs, Atlantic coast, Panama, shows two trends: diversity (H') increase from the surface to a peak of 3.2 at 5 m, remains between 1.5 and 3.5 down to 25 m, and then falls off to 0.0. Superimposed on this trend is an increase in diversity toward cliff edges. The cliff—edge diversity values are always higher than their corresponding back shelf values; this difference is significant at the 0.05 level for all but one of the ledges measured. In addition, the average cliff edge diversity (H' = 2.28) is significantly higher (P < 0.05) than the average back shelf diversity (H' = 1.89). Species diversity correlates strongly (P < 0.001) with both components of the species diversity formulation, species number and species evenness, indicating that both of these components are simultaneous properties of this coral reef community. Since the San Blas reefs are constructional, not erosional, in form and since corals have been shown to interact in definite competitive ways, the observed organization is under a considerable amount of biological control and the consistent, statistically significant diversity trends are indicative of an active form of coral community organization.