Lake Baikal is a natural reservoir of fresh water of unique and age. Its net zooplankton is represented by rotifers, copepods, and cladocerans. An integral part of the pelagic zone is the rotatoriofauna, which surpasses the most numerous group of planktonic animals Copepoda crustaceans in terms of abundance and biomass. Pelagic Rotifera can be used as an indicator of water quality: by consuming phytoplankton, accumulating energy and transferring it to the next trophic levels, rotifers influence other hydrobionts. The purpose of the study is to analyze the development of year-round, winter-spring and summer-autumn groups of rotifers in the pelagial of South Baikal from 2005 to 2014. The dynamics of number and species composition of planktonic rotifers was analyzed. The study revealed that in the 0–50 m layer, year-round species of rotifers dominate, the number of winter-spring rotifers was minimum. The highest numbers of rotifers were recorded in 2005, 2007, 2008 and 2014. Their shares in the total number of zooplankton were 16,50 %, 16,00 %, 28,30 % and 48,55 %, respectively. The minimum number of rotifers was observed in 2010–2013, when their shares were 2,12 %, 4,04 %, 2,62 % and 0,04 %. They were represented by 9–17 species. The diversity was more pronounced in the group of summer–autumn rotifers. In 2014, rotifers had an unusually high abundance and were diverse. They accounted for a large share in zooplankton. Over a ten-year period, the number of rotifers varied from 157,66 thousand ind. m-2 (2012) to 13 057,59 thousand copies m-2 (2014).
