Composition, Distribution and Density of Zooplankton in Randenigala Reservoir, Sri Lanka

Abstract

Randenigala is a hill country reservoir, constructed for hydroelectric power generation and irigation in 1982. Present paper deals with species composition distribution and density of zooplankton in the reservoir based on studies carried out from May to October 1992. Twenty-four species of zooplankton were recorded from the reservoir, out of which 12 species were rotifera, 8 species were c1adocera and four species were copepoda. Copepoda density was the highest throughout the investigation. The total copepod population consisted mainly of 34% of calanoid species, 6.7% of cyclopid species, 48.3% nauplii stages and 10.8% copepodid stages. Keretella tropica and Trichocera species formed more than half of the rotifers. The next abundant species were the Brachionus fulcatus, Filina opaliensis and Brachious caudatus. AspLanchopus and Lecane were very rare. Out of the eight species of c1adocera, Ceriodaphnia species was the dominant group contributing more than 69% to the total Cladoceran community. When the vertical distribution of zooplankton is concerned, the average highest density of zooplankton was Observed above 10m depth and highest numbers were generally recorded at surface waters. The densities were low bellow 10m reaching lowest density in the hypolimnetic region.