FEATURES OF THE STRUCTURE AND DYNAMICS OF THE ZOOPLANKTON IN LAKE NERO (YAROSLAVL REGION) DURING CLIMATE WARMING

Data on the abundance, biomass, and composition of the dominant complex of zooplankton in the shallow hypertrophic lake Nero (Yaroslavl region) from 2007 to 2017 are present. The spatiotemporal distribution of zooplankton is analyze. The high zooplankton species richness is characteristic of Lake Nero (>100 species in the general list and up to 22–27 species in the sample). 2007 to 2011, a low amount of zooplankton was noted (<37.9 thous. ind./m3 and 0.15 g/m3), with a relatively high proportion of copepods (up to 83%). Since 2012, the abundance of planktonic animals has increased (313 thous. ind./m3 and 1.20 g/m3). In 2007–2017 the composition of dominants remained close to that in previous years; small crustaceans (Bosmina longirostris, Chydorus sphaericus, Mesocyclops leuckarti), rotifers (genera Asplanchna, Brachionus, Keratella, Trichocerca and Anuraeopsis) dominated the zooplankton community. Rotifer-dominated communities (with a high abundance of thermophilic Brachionus diversicornis) formed during abnormally warm summers. Two species groups are determined: the first dominates in spring, early summer, and autumn, and the second in the second half of summer. The high abundance of zooplankton (>5 mil. ind./m3 and 10 g/m3) is in the thickets of macrophytes, which is 8–9 times higher than in the open littoral and pelagic zones. In the western littoral zone, the low abundance of zooplankton (<1 g/m3) may be associated with local pollution, high concentration of chlorophyll a, high phytoplankton biomass, represented by low food cyanobacteria. The center part and the adjacent open littoral zone differed in composition and abundance of dominant species from the southern bays occupied by macrophytes. The trophic status of the lake ecosystem in terms of zooplankton is hypertrophic since the 1980s. The abundance, composition and structure of the community in the long-term aspect are stable with interannual fluctuations common for a high-trophic shallow lake.