A belly full of jelly? DNA metabarcoding shows evidence for gelatinous zooplankton predation by several fish species in Greenland waters

The waters of Greenland harbour a high species richness and biomass of gelatinous zooplankton (GZP); however, their role in the diet of the many fish species, including commercially exploited species, has not yet been verified. Traditionally, GZP was considered to be a trophic dead end, i.e. with a limited contribution as prey for higher trophic levels. We applied DNA metabarcoding of two gene fragments (COI, 18S V1-V2) to the stomach contents of seven pelagic and demersal fish species in Greenland waters, to identify their prey composition as well as the occurrence of GZP predation. We detected GZP DNA reads in the stomachs of all investigated fish species, with frequency of occurrences ranging from 12.5% (for Melanogrammus aeglefinus) to 50% (for Argentina silus). GZP predation had not yet been reported for several of these species. GZP were found to majorly contribute to the diet of A. silus and Anarhichas denticulatus, particularly, the siphonophore Nanomia cara and the scyphozoan Atolla were of a high importance as prey, respectively. The use of multiple genetic markers enabled us to detect a total of 59 GZP taxa in the fish stomachs with several GZP species being detected only by one of the markers.