Primary production and rates of algal growth in Lake Tanganyika1

Abstract

In October–November 1975 the mean rate of integral primary production in Lake Tanganyika was 1.4 g C·m^‒2·d^‒1 (for cloudless weather). The range of values for daily integral primary production observed at this time of year over the whole lake could occur at a single station in the course of a day. Small‐scale spatial variability was equally extreme. There was no consistent pattern of diurnal variation. The mean annual daily rate of primary production for the lake was estimated to be 1 g C·m^‒2·d^‒1, assuming cloudless weather. Because phytoplankton biomass was low in October–November the rates of primary production observed imply very high algal growth rates, ranging from 0.1 to 3.0·d^‒1 with a mean of 0.9. This mean rate and the range of growth rates are the highest so far known for tropical lakes. High growth rates combined with persistently low algal biomass require tl: at loss rates be high also. The high fish production of the lake requires either very high trophic efficiency based on the measured pelagic primary production or an additional source of energy derived from the perenially anoxic deep water.