Influence of Agulhas waters on the population structure of planktonic Cnidarians in the southern Benguela Region
Francesc Pagès, J.M. Gili

During the Austral summer the southern Benguela system receives large inputs of warm, saline water from the Agulhas Current. These intrusions exert an enormous influence on the hydrographic structure in the region between Cape Infanta and Cape Columbine. The advection of Agulhas water coincides with coastal upwelling in the region, and together they strengthen a thermohaline front that extends along the entire continental shelf. This mesoscale hydrographic configuration in turn regulates the structure of the zooplankton populations. Siphonophore and medusae populations in January 1978 were compared to those in August 1977, when intrusions by Agulhas water and upwelling were minimal, in order to determine the extent of the influence of this configuration on the gelatinous zooplankton in the region. More species and individuals were collected in January 1978 than in August 1977, because of the penetration by Agulhas water. There was a distinct inshore-offshore gradient, with more species and individuals offshore, primarily concentrated between Cape Agulhas and Cape Columbine, close to the front, along the edge of the continental shelf. The distribution pattern was the same in both months, though species abundances were varied. The relationship between the distribution pattern and mesoscale hydrographic structures and the possible effects of the gelatinous zooplankton on the abundance of other zooplankton are discussed.

Keywords: Planktonic cnidarians, Zooplankton, community structure, southern Benguela, Agulhas waters.
Contents of this volume Sci. Mar. 56(2-3) : 109-123 Back PDF
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