COMMUNITY STRUCTURE, DISTRIBUTION AND TROPHIC ECOLOGY OF ZOOPLANKTON ON THE AGULHAS-BANK WITH SPECIAL REFERENCE TO COPEPODS

The mesozooplankton of the western Agulhas Bank is largely an extensio n of the west-coast upwelling community, whereas one copepod species, Calanus agulhensis, dominates the eastern Bank community, comprising u p to 85% of the copepod biomass. Large populations of this copepod app ear to be maintained on the eastern Bank, particularly during spring a nd early summer, in association with a subsurface ridge of upwelled wa ter. This copepod appears to utilize efficiently the small cells which dominate the phytoplankton assemblage on the Agulhas Bank. Copepods m ay consume up to 50% of daily primary production. A low food-chain eff iciency of < 3% suggests that a large portion of the primary productio n moves through microheterotrophs. A variety of commercially exploited fish and other planktivores, including invertebrates, compete for cop epods as their primary food source. However, considerable research rem ains to be done to quantify the apportionment of copepods among their predators, and the effects of predation on copepod dynamics.