Species Composition and Abundance of Aquatic Oligochaetes in Ihalagama Reservoir, a Shallow Perennial Minor Reservoir in Sri Lanka
G.A. WEERASUNDARA, A. PATHIRATNE and H H. COSTA
Benthic oligochaetes were sampled from Ihalagama reservoir, Sri Lanka from May 1993 to April 1994 and examined together with the environmental characteristics of the reservoir. Oligochaete fauna in the reservoir was represented by two species of aelosomatids and eight species or naidids. The naidids, Dero zeylatnica, Pristina longiseta and Nais communius were the dominant oligochaete species. Abundance of total oligochaetes was positively correlated with pH, dissolved oxygen and nitrate levels of the bottom water and silt content or the bottom sediment (p < 0 05). Nitrate levels of the bottom water showed significant positive correlations with the abundance of most of the oligochaete species than the other measured environmental parameter in the reservoir. Species composition and densities of oligochaetes and low levels of organic pollution indicative parameters of Ihalagama reservoir indicate that the reservoir has not been subjected to severe organic pollution in comparison to highly polluted water bodies in Sri Lanka.