DIEL DYNAMICS OF THE PLANKTON DISTRIBUTIO N IN THE NORTHERN BENGUELA UPWELLING SYSTEM

The plankton abundance was analyzed on the basis of net plankton sampl es collected vertically by layers during 24 h cycle at a station in th e northern part of the Benguela upwelling zone. The vertical distribut ions of plankton (seston) and zooplankton biomass were characterized b y the existence of surface and deep-lying layers of high concentration s and by distinct diurnal periodicity. The zooplankton biomass in surf ace layers showed the increase during the dark hours, exceeding the da y time biomass as much as 2 - 2.5 times. Diurnal pattern of plankton d istribution in deep layers was practicaly in the opposite phase to sur face waters. Obtained results are discussed in relation to diurnal pat tern of zooplankton distribution in different areas.