MESOZOOPLANKTON COMMUNITY STRUCTURE AND GRAZING IMPACT IN THE REGION OF THE SUBTROPICAL CONVERGENCE SOUTH OF AFRICA

Mesozooplankton distribution and community structure in the region of the Subtropical Convergence (STC) south of Africa were investigated du ring the SAAMES III cruise in austral winter (June-July) 1993. Both th e STC and an associated warm-core eddy (WCE) exhibited enhancements in zooplankton abundance, compared to the Subantarctic waters. Particula rly, elevated zooplankton densities were found in the centre of the ST C and in the region north of it as well as at the edge of the WCE. Cop epods (mainly Pleuromamma abdominalis and Metridia lucens), euphausiid s (Euphausia spinifera, E. similis and E. recurva),pteropods (Limacina spp.) and chaetognaths (Eukrohnia hamata and Sagitta spp.) dominated numerically and accounted for >60% of the mesozooplankton community. B oth cluster and ordination analyses indicated the occurrence of two ma jor plankton communities located north and south of the STC. These res ults confirm that the STC is one of the strongest regional zoogeograph ical barriers, but south of Africa,WCEs may represent the most importa nt source of disturbance in the meso-/macroscale zonation of the zoopl ankton assemblages. The daily grazing impact of the epipelagic communi ty was estimated to remove similar to 1-18% of phytoplankton standing stock and 20-165% of daily primary production. The highest rates of ph ytoplankton consumption were found in the centre of the STC and within the WCE, suggesting that the zooplankton assemblage transferred by th e WCE may enhance substantially the mesoscale carbon flux in the Suban tarctic zone south of Africa.