Profundal oligochaete assemblages in Palaearctic lakes

The profundal oligochaete fauna is mostly formed of species present also in shallower waters. Endemic taxa have developed only in ancient rift lakes like Lake Baikal. "Common" lakes, mostly of glacial or volcanic origin, are too ephemeral for speciation. In the profundal of larger European oligotrophic lakes, there can occur about 10 tubificid and lumbriculid species. With a decline in dissolved oxygen in water, only 1-2 of them will remain, Tubifex tubifex often being the last survivor. In eutrophic lakes, Potamothrix hammoniensis is the climax species. In the Far East, the profundal is also inhabited by a small assortment of oligochaetes from surrounding waters. In the eutrophic lakes of Honshu (Japan), the widely distributed species Limnodrilus hoffmeisteri and T. tubifex dominate, while more species occur in the northern oligotrophic lakes. In the eutrophic lakes in China, L. hoffmeisteri or Branchiura sowerbyi dominates. The zoogeographical origin of the commonest profundal oligochaetes is discussed.