The evaluation of the role of pelagic invertebrate versus vertebrate predators on the seasonal dynamics of filtering Cladocera in a shallow, eutrophic reservoir

An evaluation of the role of invertebrate (Leptodora kindtii) versus vertebrate (juvenile fish) predators in the dynamics of filtering zooplankton (Daphnia sp.) in the pelagic zone of the Sulejow Reservoir was conducted during summer from 1994 to 1996. Leptodora kindtii appeared in high densities (mid-July: 2-6 ind. l^sup -1^) in the pelagic zone. Its predation impact on the dominant filtering zooplankter population Daphnia cucullata, expressed by consumption, was significant and accounted for a reduction of 10 to 51% of Daphnia biomass. Although D. cucullata was a preferred food of juvenile pikeperch in June, due to low biomass, these fish were able to eliminate daily only 0.1-5.4% of Daphnia biomass in the pelagic zone. Thus, the role of juvenile fish in the midsummer decline of D. cucullata density in the pelagic zone seems to be much smaller than that of Leptodora kindtii.[PUBLICATION ABSTRACT]