The First Data on Harpacticoid Copepod Diversity of the Deep-Water Zone of Lake Baikal (Siberia, Russia)

Lake Baikal (LB) is the only freshwater ancient lake on Earth where animals inhabit all bathymetric zones down to the deepest sites (approximately 1640 m). However, there is very little data on the composition of their abyssal harpacticoid fauna. On the basis of the samples collected in LB in 2010-2017 at a depth of 270-1632 m, analysis of the fauna composition and species diversity of harpacticoids in the deep-water zone is presented. Studies were conducted in all parts of the lake, including areas of a hydrothermal, oil-methane seeps, and mud volcanoes. Nineteen Baikal endemic morphological species of the genera Bryocamptus, Attheyella, and Moraria (Baikalomoraria) were found. A brief description of the taxa morphology is presented. The genus Bryocamptus was the richest by species number at the studied sites, and Bryocamptus smirnovi Borutzky was the most frequent. The most diverse (8 species) was the fauna of the Saint Petersburg methane seep. Studies have shown that the taxonomic diversity of harpacticoid copepods in the deep-water zone of LB is lower than in its littoral zone. According to two non-parametric species estimators (Chao 2 and Jackknife 1), a 1.5-fold increase of species richness of harpacticoids of the LB abyssal is expected.