Faunal and ecological aspects of aquatic oligochaetes (Annelida, Clitellata) in Japanese lakes

The faunal composition and ecology of aquatic oligochaetes(Annelida, Clitellata)in Japanese lakes have been summarized based on a literature survey. Since Annandale’s initial benthological research in Lake Biwa in 1915, aquatic oligochaetes in Japanese lakes were studied, mainly in terms of lake typology, until the 1970s. Subsequent taxonomic and faunal studies have recorded 40 oligochaete species belonging to five families in the profundal bottom of freshwater lakes on Japanese islands. The profundal forms are generally widely-distributed species, with parallel replacement with European species. A variant form of Branchiura sowerbyi, which is almost devoid of posterior gill filaments, is restricted to the profundal bottom in the North basin of Lake Biwa, and is the only unique representative of lake profundal oligochaetes in Japan. Limnodrilus hoffmeisteri and Tubifex tubifex were the most common oligochaete species in profundal bottoms, both occurring irrespective of the trophic status of the lake. Unique oligochaete compositions were found in the bottom of several deep and oligotrophic lakes in northern Japan, and often comprised subterranean species. The taxonomic position of Tubifex(Peloscolex)nomurai, which was described from deep profundal bottoms in Lake Tazawa, and became extinct in the 1940s has been discussed. The composition and abundance of oligochaete communities in Japanese dam-lakes are comparable to mesoand eutrophic natural lakes in Japan. Azoic zones occurred in four lakes owing to the acceleration of artificial eutrophication and global warming recently. Oligochaete diversity in Japanese lakes is poorly understood in littoral zones and brackish lakes, and taxonomic studies will reveal many additional species.