Variation in structural attributes of patch-forming corals and in patterns of abundance of associated fishes

There is increasing evidence that some of the spatial variation in characteristics of local assemblages of reef fish can be explained by variation in measurable features of the habitat. At Moorea, French Polynesia, several species of the coral genus Porites form patch reefs and provide an important source of habitat structure within the lagoons. One species, Porites rus, forms structurally complex patch reefs with surface branches and numerous holes and interior cavities. In contrast, reefs composed of colonies of Porites lobata-like species are less complex; they always lack branches and interior cavities and frequently lack holes. Surveys of these reefs revealed that, as expected, abundance and species richness of fish scaled with the size of the patch reef. However, for a given size, P. rus reefs had significantly higher species richness and overall abundance than P. lobata reefs. Further, abundances of fish, at the family level, varied among sets of reefs that had different combinations of key shelter microhabitats (i.e. holes, cavities, branches). This variation in relative abundances of fish families was predictable based on the microhabitat-use patterns of the fish; the greater the utilization of a microhabitat when available, the greater the difference in abundance between those reefs and others that lacked that microhabitat. Thus, spatial variation in the structure of the fish assemblages was strongly associated with variation among the types of patch-forming corals in the variety of microhabitat features each provided.