Species-area relationships for coral reef fish assemblages of St. Croix, US Virgin Islands

Since the early 1920s, ecologists studying a variety Of taxa have observed a positive relationship between the number of species and area sampled. The purpose of this study was to examine species-area relationships in coral reef fish assemblages in a tropical marine ecosystem and to determine what factors influence this relationship on isolated patch and continuous reefs. A positive relationship between the log (species richness of reef fish) and log (coral reef area) was observed, where area explained 66 to 96 % of the variation in species richness, At smaller spatial scales patch reefs contained significantly more, approximately 35 % more, species than continuous reefs. However, the slope was significantly greater for continuous reefs, and consequently at larger spatial scales the number of species was similar to that of patch reefs. Explanations are given for the observed variation between the slopes of species-area curves reported here and those of other studies, These include an influence from the 3-dimensional nature of reef systems, the lack of quantification at sufficient spatial scales and the potential role of habitat richness. Multiple forward stepwise regressions indicated that 80.2 % of the variation in species richness on continuous reefs was explained by a suite of microhabitat variables, whereas for patch reefs only 55.7 % of the variation was explained by these same variables, Of the Variables, microhabitat richness was found to explain the greatest amount of variation in species richness for both continuous and patch reefs even though the species-area relationships differed significantly.