Composition and Abundance of Zoobenthos in the Profundal Zone of Lake Oze-numa in Central Japan

Composition and abundance of zoobenthos in the profundal zone of Lake Oze-numa (36° 56′N, 139°18′E) were studied at two sites, Lake Center and Off Nushiri, from May to September 1986. Among the eight taxa recorded, three species (Tubifex sp., Limnodrilus hoffineisteri, and Chironomus sp.) accounted for more than 95.5% of the macrobenthos in number. Species diversity, density, and biomass of macrobenthos were lower at Lake Center (8.8m deep in average) than those of Off Nushiri (6.8m). Oxygen content was probably an important factor in these differences between the sites. At Off Nushiri, Tubifex sp. and L. hoffineisteri reproduced throughout the study period but with low proportions ; pupae of Chironomus sp. were found only in late June.