Ctenophore Mnemiopsis leidyi A. Agassiz, 1865 Population and Its Impact on Zooplankton in Open Areas of the Black Sea in July–August 2017

The state of the population of the invader Mnemiopsis leidyi (A. Agassiz, 1865), the concentration and composition of mesozooplankton, and the trophic relationships and predatory impact of M. leidyi on the prey populations in the western and eastern sectors of the open Black Sea were studied in July–August 2017. The average biomass of M. leidyi at the peak of its seasonal development in these areas was 92–258 g m –2 . The food spectrum of M. leidyi was dominated by copepods Acartia spp. and Calanus euxinus (Hulsemann, 1984). Spatial differences in the quantitative development of M. leidyi and zooplankton, the intensity of food consumption, and prey grazing were found. A high rate of food consumption (specific daily ration of 45.50 ± 8.31% C of body) and intensive grazing of M. leidyi (up to ~50% of the biomass of Acartia spp. per day) in the western offshore part of the sea should be accompanied by a decrease in mesoplankton biomass. On the contrary, predation by M. leidyi did not significantly affect the plankton community in the east, where M. leidyi consumed about 6% of the biomass of Acartia spp.