Trophic Characteristics of Mnemiopsis leidyi and Its Impact on the Plankton Community in Black Sea Coastal Waters

Аннотация

The quantitative development of Mnemiopsis leidyi, the species structure of mesoplankton, and the food spectrum of ctenophores were studied in the shelf zone off the Crimean coast of the Black Sea during the summer seasons of 2013 and 2014. The feeding rate of the M. leidyi population and its predation pressure on the entire zooplankton community and certain species populations have been estimated from data on the diet composition, digestion time, and abundance of ctenophores. The volume of water cleared by M. leidyi varies by more than an order of magnitude depending on the systematic affiliation of the organisms consumed: it is maximum in the case of preying on Cladocera and Bivalvia veligers (up to 12 L ind.^–1 h^–1) and significantly lower for Copepoda (0.4–2.0 L ind.^–1 h^–1). The relationship between the value of the specific daily ration and carbon content in a M. leidyi body in the summer months of 2013 and 2014 is described by a parabolic equation with an exponent of –0.346 to –0.852. In 2014, the highest predation pressure, compared to other groups, was exerted on Copepoda and veligers of Bivalvia (on average 2.9 ± 1.5 and 2.2 ± 0.7% of biomass per day). The mean daily rate of predation on zooplankton in the Black Sea coastal zone was lower in 2014 (1.54 ± 0.58%) than in 2013 (3.94 ± 1.2% of zooplankton biomass) due to the low abundance of ctenophores. A comparative analysis of long-term data on the trophic role of the ctenophore in the plankton community has shown that the food spectrum, as well as the rate of predation on certain groups, varies from year to year. The low rate of predation on forage zooplankton by the M. leidyi population in recent years (2–5% of biomass per day) does not influence the interannual zooplankton dynamics in Black Sea coastal waters.