Feeding pressure on meroplankton by the invasive ctenophore Mnemiopsis leidyi

After its bloom in the Black and Caspian Sea in the late 1980s and early 90s, there has been an increased interest in understanding the ecology of the invasive zooplanktivorous comb jellyfish Mnemiopsis leidyi and its potentially severe impacts on the functioning of marine systems. In the last decade, M. leidyi has colonized most of the Mediterranean Sea, including the Adriatic Sea, and in 2016 it was recorded in the Venice Lagoon (Malej et al. J Sea Res 124:10–16, 2017). The impact M. leidyi could have on a semi-enclosed ecosystem like the Venice Lagoon is of concern as it is an important nursery and foraging area for several fish species as well as an area of mussel, clam, and crab fishery and aquaculture. Historically, the feeding preference of M. leidyi was determined by morphological identification of gut contents. This is the first study investigating the in-situ gut contents of this species using DNA metabarcoding, which overcomes the limit in identifying partially digested prey. In this study, M. leidyi ’s gut contents collected in the Venice Lagoon were evaluated by metabarcoding and compared to the in-situ mesozooplankton community. The results indicate that its blooming period is in the late summer and that it feeds on a variety of prey, mostly coinciding with the zooplankton assemblage. Notably, some groups, like decapod larvae and the slow-swimming larvae of gastropods and bivalves, appear to be favored. Conversely, the relative abundance of copepods was higher in-situ than in the gut contents.