DIEL DYNAMICS OF THE PLANKTON DISTRIBUTION IN THE NORTHERN BENGUELA UPWELLING SYSTEM

The plankton abundance was analyzed on the basis of net plankton samples collected vertically by layers during 24 h cycle at a station in the northern part of the Benguela upwelling zone. The vertical distributions of plankton (seston) and zooplankton biomass were characterized by the existence of surface and deep-lying layers of high concentrations and by distinct diurnal periodicity. The zooplankton biomass in surface layers showed the increase during the dark hours, exceeding the day time biomass as much as 2 - 2.5 times. Diurnal pattern of plankton distribution in deep layers was practicaly in the opposite phase to surface waters. Obtained results are discussed in relation to diurnal pattern of zooplankton distribution in different areas.