Winter is leaving: an eDNA-based assessment of marine vertebrate diversity in Svalbard coastal waters

Abstract The Arctic is undergoing rapid and spatially heterogeneous warming, with Svalbard among the fastest-changing regions worldwide. These transformations are reshaping coastal ecosystems and marine vertebrate communities, yet biodiversity assessments remain limited by logistical constraints and protection regulations. Environmental DNA (eDNA) metabarcoding offers a non-invasive alternative capable of capturing taxonomic and phylogenetic diversity across habitats. Here, we surveyed marine vertebrates along the western coast of Svalbard using continuous seawater filtration (16 transects of 2.5 miles each) from a dedicated sailing vessel, covering glacier fronts, walrus haul-out sites, harbors, and both shallow and deep-water areas. Across 31 samples collected at 16 sites, we detected 36 taxa, including 19 fish, 8 mammals, 8 birds, and 1 elasmobranch species. The congruence between eDNA, visual observations, and acoustic detections confirms the feasibility and robustness of eDNA sampling under Arctic conditions. Contrary to expectations of homogeneous assemblages across nearby sites, we observed marked taxonomic and phylogenetic turnover among habitats. Harbors and walrus haul-out areas showed particularly high taxonomic richness and phylogenetic diversity, whereas glacier-influenced sites were dominated by a few closely related taxa, suggesting that local conditions constrain community composition. Several detections, including Gasterosteus aculeatus , increased Phoca vitulina occurrence, and widespread Branta leucopsis , are consistent with biogeographic shifts linked to Arctic warming. The identification of Red List species and elusive taxa further illustrates the sensitivity of eDNA for conservation-focused monitoring. Overall, this study establishes eDNA metabarcoding as an effective tool for characterizing Arctic marine vertebrate communities and provides a valuable baseline for tracking ecological responses to rapid environmental change.