Oligochaeta from the abyssal zone of Lake Baikal (Siberia, Russia)

Abstract

Lake Baikal is unique because the water circulation carries oxygen to its deepest point (1637 m), which makes it the only freshwater lake in the world with an inhabitable abyssal area. The sampling of the abyssal of the Lake was recently made possible, allowing a study of the bathymetric and vertical distribution in the sediment of Oligochaeta. Samples were taken with a Reineck box corer and subsamples were extracted and subsequently divided into slices. Factors likely to affect oligochaete abundance with depth and in the sediment were then evaluated. Identification to the species-level allowed discussion of the possible role of the abyss of Lake Baikal in the origin of oligochaete taxa and to assess if genuine deep-water taxa exist. Abundance of Oligochaeta generally follows an exponential decline with depth. An exception was one station located near a deep hot vent. In the abyssal area, all families of Oligochaeta are concentrated near the surface of the sediment. While there are generally no Naididae below 50 m, Tubificidae, Lumbriculidae, Propappidae, Enchytraeidae and Haplotaxidae are present at all depths. Evidence suggests, for the first time, that food abundance is a limiting factor of oligochaete distribution. The possibility of a genuine deep-water oligochaete fauna in Lake Baikal cannot be excluded but the low densities and the very small sizes of animals in this environment might have caused biased samples.