THE ZOOPLANKTON OF LANGEBAAN LAGOON AND SALDANHA BAY

Summary The zooplankton of Langebaan Lagoon and Saldanha Bay are described on the basis of 127 plankton samples taken between 1946 and 1976. Hydrological conditions are described indicating a range from marine conditions in Saldanha Bay to hypersaline conditions at the head of the Langebaan Lagoon. Different zooplankton communities occur in different parts of the Saldanha-Langebaan system. In Saldanha Bay the plankton is composed predominantly of species which occur in the neritic plankton of the west coast. The plankton of Langebaan Lagoon is distinct but elements of the Saldanha Bay plankton community penetrate the lagoon to various extents. At the head of the lagoon the plankton community is estuarine in character which is remarkable as Langebaan Lagoon is not an estuary. The significance of this is discussed. Zooplankton biomass was highest in the middle reaches of Langebaan Lagoon ([xbar] = 41,80 mg/m3) and lowest at the head of the lagoon ([xbar] = 16,84 mg/m3) where the lowest diversity index also was recorded. Studies of diurnal variations indicate that the distribution of plankton in Langebaan Lagoon is essentially dynamic resulting from a complex interaction between vertical migration and tidal transport.