Abstract
Changes in metazooplankton productivity and the pressure of invertebrate predators in the Rybinsk Reservoir are analyzed on materials of long-term studies (1956–1995). The production of the plankton community was shown to be twice as high (72.5 kcal/m2) in 1990–1995 as in 1950–1970, i.e., typical for aquatic ecosystems of the eutrophic type. About 70% of the production (33.7 kcal/m2 of nonpredatory cladocerans; 7.3, rotifers; 3.9, nonpredatory copepods; 3.2, predatory cladocerans; and 1.4, omnivorous and predatory cyclopoid copepods) was available to meet the food demands of fish. In summer (June–July), strained trophic relations were registered between predatory and nonpredatory zooplankters. A strong effect of Mesocyclops and Thermocyclops on the abundance and structure of the community was revealed: for a season they consumed 11.6 kcal/m2 of the metazooplankton production, and the index of their total impact was 0.21–0.22. The limitation of the number and productivity of the small fraction of metazooplankton (especially of rotifers) by invertebrate predators is discussed.
Published Version
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