CONTINENTAL-SHELF UPWELLING AND BENTHIC OSTRACODA IN THE BENGUELA SYSTEM (SOUTHEASTERN ATLANTIC-OCEAN)

The distribution of benthic Ostracoda (micro-crustacea) on the continental shelf off southwestern Africa is controlled by sea-floor physical and chemical parameters, which in turn can be correlated with the positions of quasi-permanent upwelling cells of the Benguela System. The linkage between benthic and surface physico-chemical environments (and consequently between benthos and surface parameters) is not direct, however, being modulated by equatorward motion in the upper water column, benthic poleward water-motion, fluvial input and cross-shelf advection of off-shelf water. These phenomena, and in particular the intensity of surface upwelling, show a sharp distinction about approximately 27 S, so that the ostracod faunas in the Northern Benguela Region are relatively sparse and dominated by Palmoconcha walvisbaiensis, (Hartmann) and Cytherella namibensis, Dingle, while in the Southern Benguela Region the faunas are more diverse and dominated by Pseudokeijella lepralioides, (Brady) and Ruggieria cytheropteroides, (Brady). When minor taxa are also considered, each cell in the Benguela upwelling system is shown to be associated with a unique ostracod fauna which can be related to its in particular environmental characteristics.