Population structure and secondary productivity of Limnodrilus hoffmeisteri (Claparede) and Branchiura sowerbyi Beddard in the profundal zone of Lake Naivasha, Kenya

Abstract

Lake Naivasha has been well studied since the 1930s but attempts to understand its ecological functioning have had to wait until enough was known about its structure. The energetics of the lake has only been studied to date at primary producer level. Following the identification of the invertebrate components of the littoral and profundal benthos, this study was initiated. The absence of native fish species in Lake Naivasha, combined with a fishery based only on three, introduced species, added an applied dimension to the work. The introduction of additional fish species which will utilize unexploited ecological niches has been suggested. The benthic invertebrates form one such niche. Two oligochaetes dominated the community, Branchiura sowerbyi Beddard and Limnodrilus hoffmeisteri Claparade. The former had a productivity of 7.4 g m−2 ann−1 (as dry weight), the latter 0.6. These figures are not particularly high and do not support the introduction of a new fish species on their own