Effects of prey type and quality on Mnemiopsis leidyi feeding and carbon assimilation: a trophic biomarker approach

The invasive success of the ctenophore Mnemiopsis leidyi is partly related to its broad diet, which mainly consists of micro-, meso- and ichthyoplankton. Next to gut content analyses, which only provide a snapshot of the diet, grazing experiments and trophic biomarkers contribute to our understanding of M. leidyi’s feeding ecology. Grazing experiments were executed to determine the feeding rate of M. leidyi on Artemia salina and Acartia tonsa as small crustaceans, and on eggs and larvae of Dicentrarchus labrax. No significant differences in M. leidyi clearance rates (av. 0.2 ± 0.1 L.mLM.leidyi-1.h-1) were observed between prey types or sizes. Secondly, 13C tracer experiments were performed to determine carbon assimilation in M. leidyi, by offering enriched diatoms and the above mentioned animal prey as food sources. Highest carbon assimilation was observed for Acartia and sea bass larvae, and lowest for Phaeodactylum. To further elucidate prey-dependent variation in carbon uptake, the fatty acid composition was investigated, as a proxy for food quality. The consumption of sea bass larvae, characterized by higher levels of DHA (an essential fatty acid), resulted in significantly higher FA concentrations in M. leidyi. As M. leidyi does not convert excess food into storage lipids, it is likely that growth and reproduction will be enhanced when feeding on high quality food sources. A potential temporal overlap between the occurrence of M. leidyi and the high energetic fish larvae (e.g. due to global warming) may substantially impact the ichthyoplankton community in areas where M. leidyi has been introduced.