MAJOR FACTORS THAT STRUCTURE THE BENTHIC FAUNA OF A SHALLOW, TROPICAL LAKE, LAKE KURIFTU, ETHIOPIA

The aim of this study was to determine the community structure of the benthos in Lake Kuriftu in relation to some environmentalvariables. Benthic samples were collected with an Ekman grab (0.0225 m 2 ) from three sites (littoral, sub-littoral and profundal zones) on a monthly basis from September 2009 to February 2010. Dissolved oxygen and temperature were measured with a probe at different depths of each site. Sediment texture was determined by the Bouyoucos hydrometer and organic matter content by loss on ignition method. Chironomids, EPT (Ephemeroptera, Plecoptera, Trichoptera), oligochaetes and coleopterans were abundant in littoral and sub-littoral zones, with EPT much higher in the vegetated littoral area. The mean density of benthic macro-invertebrates in littoral, sub-littoral and profundal zones was 20,443, 18,251, and 4,388 ind/m 2 , and that of Chironomids was 12,545, 14,003 and 3,215 ind/m 2 , respectively. The profundal zone had the lowest diversity with abundant oligochaetes but no EPT samples, despite the high oxygen content of the profundal zone (6.33 mg/l). Chironomids and oligochaetes were present in all zones which had negligible difference in dissolved oxygen and organic matter content. The littoral zone had highest diversity (H’=1.26) and richness (d=2.72). Our results indicate that abundance of benthic macro-invertebrates of Lake Kuriftu was best correlated with the presence of vegetation in the littoral zone and sediment texture (high clay) in the littoral and profundal zones. We conclude that benthic macro-invertebrate community structure in Lake Kuriftu is mainly influenced by spatial variation in vegetation, sediment texture and temperature, but not dissolved oxygen and organic matter content.