Species Composition and Distribution of Free-Living Nematodes (Nematoda) at the Posolskaya Banka Cold Methane Seeps, Lake Baikal

Abstract—The Posolskaya Banka cold methane seep area (southern Lake Baikal, depths ~300–500 m) is characterized by weak methane discharge and the deep occurrence of gas hydrates. The species composition and distribution of nematodes from 44 meiozoobenthos samples have been analyzed at seep (plume and gas hydrate) and background stations. In total, 31 species of nematodes belonging to 12 genera, 8 families, and 6 orders are identified; 94% of them are found at background stations and/or in other areas of the lake. The ratio of Baikal endemic and Siberian-Palearctic species is 6 : 1. Endemic species of the genus Paratrilobus and Tripyla dominate by frequency of occurrence and population density. The heterogeneous distribution of nematodes; the relationship between the density of their population; and the presence of filaments of sulfur bacteria, copepod detritus, and ferromanganese crusts in the bottom sediments, as well as different feeding strategies of the free-living roundworms inhabiting the seeps, are discussed.