Recent changes in the spring microplankton of Lake Baikal, Russia

Lake Baikal is facing several environmental stressors, including climate change and nearshore eutrophication. To assess recent ecological changes in Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the pelagic zone of the lake in 2016 and compared these data with unpublished and published historical information going back to 1990. In 2016, one pelagic long-term monitoring station was sampled in early spring (March) during ice cover and 21 long-term monitoring stations located throughout the lake were sampled in late spring (May-June). We measured water chemistry parameters at most stations and the abundance, taxonomic composition and biomass of bacteria, ciliates and phytoplankton at several locations in different areas of the lake. Biotic parameters from 2016 were compared with historical data, showing significant changes in the spring pelagic microbial community since the 1990s. We show increased quantities of small species, mixotrophic ciliates, and the appearance (or increasing number) of small coloured and colourless flagellates. We also show substantially decreased densities of formerly dominant heavily silicified diatoms such as Aulacoseira spp. Since 2007, Synedra acus subsp. radians, a smaller and weakly silicified diatom, has dominated the spring plankton of the lake. These results suggest that Lake Baikal's pelagic plankton community may be changing, with climate likely playing a dominant role in these changes.