Interactions between native and invasive gelatinous zooplankton within the Baltic Sea food web (INIGEL)

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The proposed projects aims to study biotic controls of the ctenophore jellyfish Mnemiopsis leidyi which recently invaded North and Baltic Sea. The core experiments of the project should be performed by means of field mesocosms. The emphasis is put on experimental studies of the interactions with the resident scyphozoan jellyfish Aurelia aurita and on the effects of interfering chain-forming diatoms. The current seasonal growth pattern of M. leidyi is characterized by low abundance levels in early summer and sharp outbreaks in late summer. Thus, M. leidyi blooms do not co-occur with fish larvae, predation on fish-larvae being one of the most serious risk factor associated with M. leidyi invasions. The main hypotheses are that interference by chain forming diatoms and negative effects of A. aurita (competition and predation on juveniles) prevent outbreaks of M. leidyi during early summer, while the decay of A. aurita in late summer facilitates M. leidyi outbreaks by providing DOC (Dissolved Organic Carbon) for a microbial food chain supporting M. leidyi growth.