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 high and low degrees of wave exposure. The sampling program combined the following 4 environmental aspects: seasonal effects, wave action, vertical zonation and tide level Sixteen species were found, of which 7 occurred only at the exposed site. The lowest values of density and number of species corresponded to the protected site; high values characterized samples from the exposed site. Jassa falcata dominated at the exposed site but was absent at the protected mussel bed. The dominant species common to both stations were: Elasmopus brasiliensis, E. pectenicrus and Hyale sp. 1. The distribution of amphipods appeared to be a function of 3 main factors, as shown by correspondence analysis: structural heterogeneity of the mussel bed (related to wave action), vertical zonation, and desiccation. Accordingly, cluster analysis pointed out wave action and zonation as the 2 key factors affecting similarity of samples. The cluster analysis of species showed few cases of high similarity and when so, the amphipods differed in life style. This niche partition partially explains coexistence of the amphipod assemblage in the mussel beds. Direct effects of wave impact seemed less important than its side effects (e.g. sedimentation) as regards selection of species, and this was related to the physical protection of the mussel mats.