Mesozooplankton Communities in Deep-Water Areas of the Black Sea: Are Their Composition and Biomass Regulated by the Ctenophore Mnemiopsis leidyi A. Agassiz, 1865

The abundance, biomass, distribution, and feeding patterns of the ctenophore Mnemiopsis leidyi A. Agassiz 1865 were studied in the deep-water Black Sea in October 2019. The biomass of the ctenophore in the open sea areas was 100–200 g m^–2, and the abundance was 16–38 ind. m^–2. With the dominance of large individuals (≥30 mm) in the population, the activity of their reproduction remained extremely low. The specific daily ration varied from ~4 to 13% of body carbon in adults and juveniles, respectively, and exceeded the minimum food requirements of the ctenophore. The daily consumption of three species of copepods (Acartia spp., Calanus euxinus, and Oithona davisae) by M. leidyi reached 4.5–11% of their biomass, while that of appendicularians Oikopleura (Vexillaria) dioica was <1.6%. The predatory pressure of M. leidyi on the entire prey zooplankton attained 2–4% of the biomass of organisms per day.