Abstract
This work aims to analyze the interannual variability of zooplankton in Lake Alakol during different periods of the hydrological cycle based on our own (2002, 2004–2007) and literature data. In zooplankton composition, 132 taxa were recorded, from 15 to 64 taxa over the years. The average long-term abundance of zooplankton was 172.5±58.2 thousand specimens/m3 , with a biomass of 0.9±0.2 g/m3 . In the long-term aspect, zooplankton abundance changed 36 times and the biomass 10 times. A tendency has been revealed for the quantitative variables of zooplankton to increase in high-water years (1954–1968, 1996–1997, 2005) and to decrease during low-water periods (1983, 2000, 2002, 2004, 2006, 2007). During all research periods, rotifers dominated, with a more minor role of crustaceans. The dominant species complex included rotifers Brachinus plicatilis, Brachinus quadridentatus, Keratella quadrata, crustaceans Arctodiaptomus salinus, Mesocyclops leuckarti. The relative stability of the composition of background species of planktonic invertebrates for more than half a century is due to their broad ecological plasticity.