The Species Composition and Distribution of Free-Living Nematodes (Nematoda) in the Area of the Methane Seep Posolskaya Bank of Lake Baikal

The Posolskaya Bank methane seep (southern Baikal, depths of ~300–500 m) is characterized by weak metha-ne discharge and the deep occurrence of gas hydrates. The species composition and distribution of nematodes from 44 samples of meiozoobenthos on the seeps (gas unloading point and gas hydrate) and background stations were analyzed. 31 species of nematodes from 12 genera, 8 families and 6 orders were identified; 94% of them were found at background stations and/or in other areas of the lake. The ratio of Baikal endemic and Siberian-Palearctic species was 6 : 1. Endemic species of the genera Paratrilobus and Tripyla dominated occurrence frequency and population density. The data obtained on 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 the habitation of worms with different types of food. These data are discussed.