Species Composition, Abundance and Distribution of Aquatic Oligochaetes in Colombo (Beira) Lake, Sri Lanka
H. H. COSTA, G. A. WEERASUNDARA and A. PATHIRATNE
Species composition, abundance and distribution of aquatic oligochaetes in Colombo (Beira) Lake were investigated from May 1993 to April 1994. Twenty two species of oligochaetes were identified representing 3 species of Aeolosomatidae, 17 species of Naididae and 2 species of Tubificidae. Seven species were recorded for the first time from Sri Lanka. These species are Aeolosoma truvancorense, Aeolosoma viridae, Allonais gwaliorensis, Dero dorsalis, Dero indica, Pristina synclites and Stephensiniana trivandrana. The populations of aquatic oligochaetes fluctuated considerably in size throughout the study period. Aulophorus michaelseni, Branchiodrilus semperi, Pristina longiseta and Aulodrilus pigueti were the most abundant species. Abundance of some species of oligochaetes was positively correlated with rainfall, organic matter content in the bottom sediment, pH, dissolved oxygen content, biochemical oxygen demand, nitrate and phosphate content in the bottom water whereas negative correlations were observed with salinity and conductivity in the bottom water (P<0 05). The number of species and the density of worms in the saline areas of the lake were comparatively low. Aulophorus michaelseni and Aulodrilus pigueti were the most abundant species in these areas.