The response of zooplankton abundance in saline meromictic Lake Shira to a change in circulation regime

The long-term data (1996–2021) on the summer abundances of the dominant zooplankton species (copepod Arctodiaptomus salinus (Daday, 1885), rotifers Brachionus plicatilis (Müller, 1786) and Hexarthra sp.) in saline Lake Shira were used to analyze the response of zooplankton to air temperature and a change in the circulation regime of the lake: breakdown and reestablishment of meromixis. All groups of zooplankton responded to prolonged summer elevated temperatures by increasing their abundance. During the breakdown of the stable stratification of Lake Shira (2015–2016), zooplankton abundance increased on average by a factor of two and amounted to 9×10 5 inds./m 2 in the water column for copepods. That increase coincided with similar responses of other components of the lake’s mixolimnion ecosystem, whose biomasses increased approximately two-fold during that period. After the reestablishment of the meromixis, the abundance of zooplankton decreased to previous values. Thus, the abundance of zooplankton is largely determined by weather (the effect of temperature) and ecological factors (mixing regime).