The community composition and biomass of pelagic ciliated protozoa in East African lakes

Abstract

The community composition and biomass of planktonic ciliates were studied in 17 tropical East African lakes varying from freshwater to saline, and from oligotrophic to eutrophic. The conductivity of the lakes varied from 207μS cm^–1 to 70 000μS cm^–1. Chlorophyll a concentration ranged from <5mg m^–3 to >50mg m^–3, while bacterial numbers were between 2.9 X 106 and 2.55 X 108 bacteria ml^–1. Principal components analysis based on environmental variables revealed a single strong environmental gradient across the lakes related to conductivity, alkalinity, bacterial abundance, chlorophyll a, and (negatively) to Secchi depth. Oligotrichs (e.g. Strombidium, Strobilidium, Halteria) and scuticociliates (e.g. Cyclidium, Pleuronema, Cristigera) dominated the ciliate communities numerically. The species-environment correlations, as revealed by canonical correspondence analysis, indicate a strong relationship between ciliate genera and the environmental gradient. Herbivorous oligotrichs were characteristic of oligotrophic and mesotrophic lakes, which were also freshwater to moderately saline lakes. On the other hand, scuticociliates, primarily bacterivores, were most abundant in alkaline and saline lakes with high chlorophyll a concentrations. Biomass of ciliates was related to chlorophyll, as has been observed in temperate and subtropical lakes, but was more strongly related to bacterial concentration.

African Journal of Aquatic Science 2007, 32(2): 175–183