The Community Structure of Coral-Associated Decapod Crustaceans in Variable Environments

Abstract

The decapod crustacean community associated with the branching coral Pocillopora damicornis is described from two localities on the Pacific coast of Panama. The corals are of the same approximate geologic age but the physical conditions at one locality fluctuate unpredictably while conditions at the second locality are relatively constant. The species-area relationship does not differ between the two regions while the individuals-area regression of the constant environment has a higher intercept but the same slope. The dominance diversity curves for the two regions are similar in shape but dominance is greater in the constant environment. A generalist is dominant in the fluctuating environment while a specialist is dominant in the constant environment. There is no evidence for species packing as similar-sized coral heads have the same number of species in both regions and the species composition of individual coral heads suggests a random colonization process. There is no difference in the frequency of co-occurrence of congeneric species between the two regions; in both regions more congeners coexist than would be expected by chance. Comparison of species richness between the two areas based on either equal sample size or number of individuals demonstrates a greater total species richness in the fluctuating environment. It is suggested that a natural physical disturbance, upwelling, reduces dominance and increases species richness in the fluctuating environment.