Population dynamics, ingestion, growth and reproduction rates of the invader Beroe ovata and its impact on plankton community in Sevastopol Bay, the Black Sea

The impact of the introduced ctenophore Beroe ovata on its preyMnemiopsis leidyi, another invader ctenophore voraciously feedingon mesozooplankton, and consequently on the mesozooplanktoncommunity, was evaluated by undertaking both laboratory andfield studies in the northern Black Sea. Ingestion and growthrates as well as the gross growth efficiency of B. ovata wereestimated from laboratory experiments. The daily ration of ctenophoreswas related to food abundance within a wide range of prey concentrationand never reached saturation. Beroe ovata required high foodrations (not less than 20% of body weight per day) for growth.The abundances, biomasses and population structures of thesetwo introduced ctenophore species were also monitored, alongwith mesozooplankton, in inshore waters of the northern BlackSea (i.e. Sevastopol Bay and adjacent regions) over a periodof 3 years (1999–2001) which is after B. ovata’sarrival. The annual dynamics of the M. leidyi population weresimilar for the last 3 years: very low abundances and biomassvalues were observed during most of the year (unlike the previousyears), with a sudden increase in summer–early autumn,but only for about a 2 month period. The B. ovata bloom duringthe peak M. leidyi biomass resulted in the M. leidyi biomassfalling sharply to extremely low values. The predatory impactof M. leidyi on prey zooplankton was found to be reduced duringthe period of study compared with before.