Changes in the crustacean community of a tropical rocky intertidal shore: is there a pattern?

A tropical rocky intertidal community in Montepio, southern Veracruz, Mexico, was sampled throughout a year to determine the extent of the changes in species composition and abundance. The study focused on the crustacean community, of which 49 species were identified. The community was characterized by a high species replacement rate, with 38.7% of the species appearing only once, 10% appeared twice, 16.3% were present in three different samples, and the remaining 34.7% were collected in 4 or more monthly samplings. Species diversity (H') varied constantly, while evenness remained relatively high and constant. An ordination analysis indicates that the crustacean community was dominated by the occurrence of rare species (47%). A cluster analysis, based on the Bray-Curtis similarity coefficient, shows that only a maximum of two consecutive samplings can have more than 50% similarity, reflecting the constant changes that occur in this community. When compared to the other numerically important phyla in the community, crustacean densities ranked third after annelids and mollusks. With such highly variable species composition and the absence of defined seasonal patterns, we propose that non-local processes, such as the strong winter winds ("northers") and a long season of tropical storms, are acting upon the community preventing the establishment of species for long periods of time and maintaining the biodiversity.