Spatial and temporal distribution of Amphipoda associated with mussel beds from the Bay of Santos (Brazil)

Abstract

Effects were determined of some abiotic factors on the patterns of abundance and diversity of amphipods associated with Perna perna (L.) beds. Observations were conducted at 2 sites subjected respectively to h g h and low degrees of wave exposure. The sampllng program combined the following 4 environmental aspectsseasonal effects, wave ac t~on , vertical zonation and tide level. Sixteen species were found, of which 7 occurred only at the exposed slte. The lowest values of density and number of species corresponded to the protected site; high values charactenzed samples from the exposed site. Jassa falcata dominated at the exposed s ~ t e but was absent at the protected mussel bed. The dominant species common to both stations were: Elasmopus brasiliens~s, E. pectenicrus and Hyale sp. 1. The distribution of arnphipods appeared to be a function of 3 main factors, as shown by correspondence analysis. structural heterogeneity of the mussel bed (related to wave action), verbcal zonation, and desiccation. Accordingly, cluster analysis pointed out wave action and zonation as the 2 key factors affecting similanty of samples. The cluster analysis of s p e c ~ e s showed few cases of high similarity and when so, the amph~pods differed In 11fe style. Thls niche partition partially explains coemstence of the amphipod assemblage in the mussel beds. Direct effects of wave impact seemed less important than its side effects (e.g. sedimentahon) as regards selection of specles, and t h ~ s was related to the physical protecbon of the mussel mats