Analysis of the influence of substrate variables on coral reef fish communities

A simple field technique to obtain a gross estimate of the surface area of a quadrat on a coral reef is described. This measure, termed the substrate rugosity index, was determined, in conjunction with two other substrate variables (vertical relief and coral species richness), in a series of 4 quadrats (10 to 40 m depth) along 4 transects. The mean substrate rugosity and vertical relief of a quadrat were highly correlated. A correlation analysis was made of the substrate variables and several reef fish community parameters (species richness, number of fishes and diversity). Species richness was highly correlated with substrate rugosity. This relationship was tested in two experimental quadrats and the results were generally in accord with those predicted. Stratification of the fish communities by body size revealed that the correlation with substrate rugosity was scale-dependent. The fish community parameters were poorly correlated with percentage substrate cover by corals (ramose and glomerate) and by sand. A significant area effect was determined for two species of sand-dwelling goby.