The ecology of Lake Nakuru (Kenya) IV. Biomass and distribution of consumer organisms

Abstract

Consumer biomass and spatial distribution in the equatorial alkaline-saline Lake Nakuru were studied from 1972-1976. These data will provide the basis for estimating feeding and production rates and for quantifying energy flow at the consumer level. Two of the main consumers, the Lesser Flamingo (Phoeniconaias re&or) and the Soda Tilapia (Sarotherodon alcalicus grahami), were covered by earlier papers. The biomass of the only planktonic crustacean, the copepod Lovenula (= Paradiaptomus) africana was very high (1.5 gDW (dry weight).m -3, mean in 1972/73) in comparison with other tropical lakes. Lovenula was absent in 1974 and 1975, and at very low levels (0.1-0.4 gDW.m -3) in part of 1976. Among the rotifers Brachionus dimidiatus dominated in 1972/73 (~0.2 gDW. m-3), but was outnumbered by B. plicatilis throughout most of 1974 to 1976 (mean total rotifer biomass 1.4 gDW. m -3, peak densities 7 gDW-m 3); during high salinity periods (>20%0) Hexarthra jenkinae occurred in very low numbers. For short periods rotifers can be the dominant species of L. Nakuru. Aquatic heteroptera (four species) played a minor role: they contributed 0.4% to total consumer biomass in 1972/73; in 1974-1976 the lake had no aquatic heteroptera. Benthic biomass (0.4 gDW-m-2) was within the range of other tropical lakes, it consisted almost exclusively of Leptochironomus deribae. Bird counts of the twelve most important species are given for the years 1972-1974: Pelecanus onocrotalus accounts for ~ 90% of the biomass (0.44 gDW.m -3, mean 1972/73) with peak densities of almost 20,000 birds. - The consumer organisms covered by this and the two preceding papers represent> 99% of L. Nakuru's consumer biomass. Population dynamics of various consumer species are discussed.