The cryophilic habitat of micrometazoans under the lake-ice in Lake Baikal

An unusual micrometazoan community comprising bacteria, algae, rotifers, and copepods exists under the sea-ice as a type aufwuchs or periphytic community, but little is known of similar systems in freshwaters. Here we report on micrometazoans that comprise the lake-ice or cryophilic community in Lake Baikal (Russia). Our collections of the under-ice-water community were made using planktonic nets during a three-month period (February to April) in 2001 and 2004 and a volumetric syringe (March of 2004). We found that the species richness of this community was relatively high and comparable to that found in marine systems. Important members of the community include rotifers and copepods. In March 2001, we frequently observed endemic species of two genera, Notholca and Synchaeta. The community structure of rotifers appears to be driven by food availability. For example, in 2004, lake-ice diatom populations were relatively poor, which correlated with low rotifer abundance. We postulate that algal assemblages of the cryophilic community are important in structuring of these unusual communities by enlarging spaces within the ice and by providing food for zooplankton. This unusual habitat should be investigated further for two reasons: (1) The lake-ice habitat is the freshwater counterpart to that in the Arctic, and a comparison may provide insights into the structure of ephemeral zooplankton communities. (2) This community may be a source of energy for higher tropic levels during part of the ice-on period for Lake Baikal.