An Ecological Study Of The Zooplankton In Lake George In Uganda

Abstract

Lake George is a shallow tropical lake containing a high standing crop of phytoplankton, in which blue-green algae predominate. Although the temperature of the surface water may rise as high as 350C during the day, the water is normally mixed each night and the average lake temperature is 26.30C, with liutle variation throughout the year. Flow through the lake increases during the two ill-defined rainy seasons but other physico-chemical conditions are constant throughout the year. The zooplankton community is numerically dominated by the small cyclopoid copepod Thermocyclops hyalinus The carnivorous Mesocyclops leuckarti is also present but in small numbers. About fifteen species of Rotifera have been recorded and numbers, both of species and of individuals, are higher in the inshore regions of the lake, particularly on the West side, and appear to be highest at the beginning of the rainy seasons. Brachionus caudatus is numerically dominant and is recorded from All over the lake. Lecane"~bulla appears to be more abudant in the centre of the lake, where the phytoplankton is thickest. Ecological notes are given on the other species. Four species of Cladocera have been recorded from the open water of the lake, all in small numbers. Moina micrura is found more frequently inshore, Daphnia barbata more frequently in the centre of the lake. Ceriodaphnia cornuta has been measured and clutch sizes have been counted. It is smaller than other species of the same genus studied in Britain and the increase of clutch size with body length is slower. Neither body length nor clutch size shows any marked variation throughout the year. Alona poppei is a swamp species which appeared in the open water of the lake only when swept out during the rain