Short-term effects of coastal upwelling and wind reversals on epiplanktonic cnidarians in the southern Benguela ecosystem

Abstract

Patterns in the distribution of epiplanktonic cnidarians collected along the west coast of South Africa during June 1986 were examined. Upwelling-favourable south-easterly winds prevailed prior to sampling. These winds are believed to have transported coastal cnidarian assemblages offshore, resulting in a blurring of the inshore-offshore zonation of species. A wind reversal, to northerly winds in the north and north-westerly winds in the south, followed upwelling and persisted during sample collection. This resulted in the development of a distinct thermohaline front off Cape Columbine. Another consequence was the advection of oceanic water shorewards in the south, disrupting the original pattern of species zonation and redistributing cnidarian assemblages in a longshore pattern. Three different assemblages are differentiated: one north of Cape Columbine, consisting of coastal species, one south of Cape Columbine with a mixture of neritic and oceanic species, and one single-species community with coastal affinity inshore north of Cape Columbine. The effects of wind-driven onshore advection of offshore waters on the coastal communities of gelatinous zooplankters are discussed.