The benthic invertebrates of Lake Khubsugul, Mongolia

Abstract

Abstract Based on an examination of all relevant literature and including new information from the most recent studies in the lake, the first comprehensive survey is presented of the benthic invertebrate fauna of ancient Lake Khubsugul, a mountainous, cold-water, oligotrophic lake. Lake Khubsugul is located in Mongolia, in the Baikal rift zone, and is connected to Lake Baikal via a river system. The diversity and degree of endemicity of the benthic macroinvertebrate faunas of these two ancient lakes are compared. The modern Khubsugul fauna comprises at least 287 species and is believed to have resulted from colonization by riverine fauna during the Quaternary period. This is considerably less diverse than the fauna of Lake Baikal. This difference is especially apparent within the Gammaridae, Mollusca, Oligochaeta and Tricladida, which are represented in Baikal by complexes of endemic species. Thos taxa found in both lakes are predominantly representatives of General Siberian and Euro-Asian faunas. One species of nematode, two species of oligochaete, three species of chironomid and one species of halacarid are endemic to both lakes. Among the 19 species newly described from Lake Khubsugul, three species of Mermithidae belong to the Baikalian endemic genus Baicalomermis and one species of mollusc belongs to the Baikalian endemic subgenus Achoanomphalus . These four species, and also perhaps two species of the genus Gammarus , are probably endemic to Lake Khubsugul. The remaining 15 newly described species probably also occur in other water bodies.