Plankton distribution on the Agulhas Bank between 20ᵒE and 22ᵒE Long.

Abstract

Monthly plankton samples taken with the Indian Ocean Standard Net by R.S. Africana II at a grid of stations on the Agulhas Bank during 18 months were studied and compared with the hydrographical data taken at the same time; a few samples taken off the bank were used for comparison. Average monthly distribution over the bank and the time/space distribution at the fixed stations were studied for total biomass, Copelata, Chaetognatha, Copepoda, fish eggs and larvae. The main conclusions point at a high productivity of the Agulhas Bank water, frequent formation of patches that drift west and southwards, a small seasonal fluctuation of biomass, patchiness of Copelata distribution, a similarity in the distribution of total biomass with Copepoda and to a lesser degree with Chaetognatha, and a very strong seasonal variation of the frequency distribution of fish eggs and larvae. High productivity of the Agulhas Bank water is considered to be brought about by horizontal mixing caused by eddies, mixing of water masses and upwelling.