Effectiveness of eDNA metabarcoding to reconstruct biodiversity of fisheries catches in the Adriatic Sea

Monitoring the status of marine resources is a key activity in biodiversity conservation and fisheries science, but most scientific surveys still largely rely on costly and time-consuming traditional visual and capture-based methods. Recent advances in DNA sequencing allow species detection from trace DNA in the environment - environmental DNA (eDNA), which is increasingly becoming a primary source of biodiversity information in every habitat. For this study, eDNA samples were collected through a low-cost and low-effort sampler, a hollow perforated spherical probe (the ‘metaprobe’) filled with gauze rolls, associated with fishing gear; metaprobe-based eDNA sampling was implemented in two scientific fishing surveys in the Adriatic Sea: a demersal longline survey in the southern Adriatic Sea and a trawl survey within the MEDITS framework in the northern Adriatic Sea. By applying a standard eDNA metabarcoding pipeline and filtering procedure, it was possible to molecularly identify using a 12S barcode 11 taxa to species level for the longline survey and 70 taxa for the MEDITS trawl survey, 61 to species level and 9 to genus level. In both cases, when compared to catch data, eDNA metabarcoding data also provided a biodiversity ‘bonus’ of species not otherwise catchable, allowing an overall better qualitative estimation of species composition. Further investigation is however needed to overcome some challenges inherent to eDNA metabarcoding techniques, in order to ultimately upscale this promising approach and use fishing vessels as widely ranging data-collecting platforms.