Annual assessment of the predation of Mnemiopsis leidyi in a new invaded environment, the Kiel Fjord (Western Baltic Sea): a matter of concern?
author: Dr Jamileh Javidpour PhD jjavid@ifm-geomar.de IfM-GEOMAR experimental ecology [+49431 6004408] Duesternbrooker weg 20 Kiel Germany 24105; Dr Juan Carlos Molinero PhD jmolinero@ifm-geomar.de Ifm-GEOMAR - Kiel Germany; Dr Thomas Hansen thansen@ifm-geomar.de Ifm-GEOMAR - Kiel Germany; Dr Ulrich Sommer usommer@ifm-geomar.de Ifm-GEOMAR - Kiel Germany; Dr Andreas Lehmann alehmann@ifm-geomar.de Ifm-GEOMAR Ocean Circulation and Climate Dynamics Kiel Germany
language: en

Abstract

The sudden occurrence of the comb jelly Mnemiopsis leidyi has been reported recently from different sites over the Baltic Sea and it has been suggested that the species has invaded the whole basin. Here we provide the first set of quantitative data of seasonal diet composition and life history traits of M. leidyi and its predatory role in the pelagic ecosystem of the Western Baltic Sea. The size structure of the species appeared dominated by small size classes and only a few adults were as large as those reported in the native region of the species and in other invaded sites. We show that the species has a high preference for small sized and slow swimming prey, mainly during the low temperature period of winter. Barnacle nauplii appeared as the main source of carbon for the over-wintering population of M. leidyi. A preference for copepods was only found during August when these prey contributed up to 20% of the gut composition. In summer, planula larvae of the jellyfish Aurelia aurita, were the most abundant prey in the gut content (feeding rate of 621 ind. ctenophore-1day-1). We further found that at highest densities of the species, in summer, a significant predation on its larvae occurs, being this the major carbon source of adults. Overall these results are discussed in the context of trade-offs M. leidyi face in the new environment and adverse environmental conditions, which are likely forcing the species toward reduced sizes and likely reducing its potential predatory impact in the Baltic Sea.