Biogeography and community structure of the decapod crustacean fauna off Namibia (Southeast Atlantic)

Abstract

The communities of pelagic and benthic decapod crustaceans offNamibia (Southeast Atlantic) were studied. The samples comprised 97 species differing widely in their geographical and depth distribution. The analyses revealed distinct assemblages, with several well-defined boundaries. However, the barriers were different for pelagic and benthic species. The zonation of the pelagic species presented two clearly differentiated communities, an "inshore association" from the coast to about 70 miles (113 km) offshore, largely coinciding with the shelf, and an "offshore association" more than 70 miles off the coast. Both associations were present in the active (September-October) and quiescent (April) upwelling period, although during the active upwelling period the number of species clearly decreased. These results support the existence of different circulation patterns over the shelf and slope separated by a cross-shelf barrier. A third association seemed to be related to the seasonal intrusion of waters from Angola during the quiescent upwelling period. The communities of benthic species were mainly delimited by the depth, although several latitudinal boundaries exist. The bathymetric boundaries were well defined: the main boundary was located around 400 m, separating the shelf and slope-bathyal species. The latitudinal boundaries seemed to be related to different features of the Benguela upwelling and the circulation pattern in the region