ИСТИНА

The goal of the present study was to investigate the potential mechanisms of excretion and mucus release by the jellies Mnemiopsis leidyi and Beroe ovata on the low trophic levels of Black Sea ecosystem. Two types of experiments were conducted jointly by SIO- RAS and IO-BAS as part of PERSEUS WP1 and WP2 research program – in lab aquaria and in situ mesocosms in the coastal area of Gelendzhik (2013) and Varna (2014). The laboratory (aquaria) experimens were designed to analyze the effects of exotic ctenophores on bacteria, ciliates, heterotrophic flagellates, phytoplankton taxonomic composition and chemical parameters of the environment, while in the mesocosms experiments, one more trophic level mesozooplankton as the main prey of M. leidyi was examined in addition to the same set of parameters. Here the results of the Gelendzhik experimental phase are reported. Under controlled laboratory conditions both Beroe ovata and Mnemiopsis leidyi induced changes in chemical properties of the media – pronounced increase of nutrients (P04 and NH4) and a decrease of pH, but the nutrients release was much higher in the aquaria with Beroe ovata. Autotrophic flagellates and heterotrophic flagellates demonstrated an increase on the 2nd day and dropped to the initial level on the 5th day of the experiment. The growth of Diatoms, Dinoflagellates and Euglenidae also was stimulated by the two ctenophores. While diatoms and euglenophytes proliferated to a similar level, Dinoflagellates outburst was marked in the B.ovata experiments. Possible reasons of the observed changes in the structural and functional traits of heterotrophic and autothrophic plankton communities are discussed.