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Information about the dietary composition of a species is crucial to understanding their position and role in the food web. Increasingly, molecular approaches such as DNA metabarcoding are used in studying trophic relationships, not least because they may alleviate problems such as low taxonomic resolution or underestimation of digestible taxa in the diet. Here, we used DNA metabarcoding with universal primers for cytochrome c oxidase I (COI) to study the diet composition of the northern shrimp (Pandalus borealis), an Arctic keystone species with large socio‐economic importance. Across locations, jellyfish and chaetognaths were the most important components in the diet of P. borealis, jointly accounting for 40%–60% of the total read abundance. This dietary importance of gelatinous zooplankton contrasts sharply with published results based on stomach content analysis. At the same time, diet composition differed between fjord and shelf locations, pointing to different food webs supporting P. borealis in these two systems. Our study underlines the potential of molecular approaches to provide new insights into the diet of marine invertebrates that are difficult to obtain with traditional methods, and calls for a revision of the role of gelatinous zooplankton in the diet of the key Arctic species P. borealis, and in extension, Arctic food webs. [ABSTRACT FROM AUTHOR]

• Combining eDNA and trawl data increases the detected biodiversity. • Good reference databases are of vital importance for correct taxonomic classification. • We advocate that a combined sampling effort is a good strategy for future monitoring of biodiversity in the Arctic including the Barents Sea. Managing natural resources in a sustainable manner requires understanding the complexity of ecosystems and the species that are associated with the different parts of the ecosystem. Much of this knowledge is derived from traditional sampling methods (e.g., different types of trawls). The analysis of environmental DNA (eDNA) can provide increased knowledge, complementary to the traditional methods. In the present pilot study, we sampled eDNA from two geographical areas, north and west of Svalbard (NWS) and in the southwestern Barents Sea (SWBS). The combination of trawling, visual identification of mammals and eDNA collection facilitated a robust analysis of fish and marine mammal diversity and species composition. Through 12S MiFish metabarcoding of the eDNA samples, we found that incorporating eDNA data provided an additional level of information on both the diversity of fish and marine mammals in the study areas. By adding eDNA data to the trawl data, we found that richness increased from 32 to 49 fish taxa. Significant differences in diversity and composition of the fish communities were detected by eDNA between the two study areas. Considering degradation and dilution factors it is postulated that the results represent resident species to the Barents Sea and that long -transported DNA from other areas are less likely. [ABSTRACT FROM AUTHOR]

The Arctic is experiencing dramatic changes including increases in precipitation, glacial melt, and permafrost thaw, resulting in increasing freshwater runoff to coastal waters. During the melt season, terrestrial runoff delivers carbon- and nutrient-rich freshwater to Arctic coastal waters, with unknown consequences for the microbial communities that play a key role in determining the cycling and fate of terrestrial matter at the land-ocean interface. To determine the impacts of runoff on coastal microbial (bacteria and archaea) communities, we investigated changes in pelagic microbial community structure between the early (June) and late (August) melt season in 2018 in the Isfjorden system (Svalbard). Amplicon sequences of the 16S rRNA gene were generated from water column, river and sediment samples collected in Isfjorden along fjord transects from shallow river estuaries and glacier fronts to the outer fjord. Community shifts were investigated in relation to environmental gradients, and compared to river and marine sediment microbial communities. We identified strong temporal and spatial reorganizations in the structure and composition of microbial communities during the summer months in relation to environmental conditions. Microbial diversity patterns highlighted a reorganization from rich communities in June toward more even and less rich communities in August. In June, waters enriched in dissolved organic carbon (DOC) provided a niche for copiotrophic taxa including Sulfitobacter and Octadecabacter. In August, lower DOC concentrations and Atlantic water inflow coincided with a shift toward more cosmopolitan taxa usually associated with summer stratified periods (e.g., SAR11 Clade Ia), and prevalent oligotrophic marine clades (OM60, SAR92). Higher riverine inputs of dissolved inorganic nutrients and suspended particulate matter also contributed to spatial reorganizations of communities in August. Sentinel taxa of this late summer fjord environment included taxa from the class Verrucomicrobiae (Roseibacillus , Luteolibacter), potentially indicative of a higher fraction of particle-attached bacteria. This study highlights the ecological relevance of terrestrial runoff for Arctic coastal microbial communities and how its impacts on biogeochemical conditions may make these communities susceptible to climate change. [ABSTRACT FROM AUTHOR]

The two congeneric hyperiids Themisto libellula and T. abyssorum provide an important trophic link between lower and higher trophic levels in the rapidly changing Arctic marine ecosystem. These amphipods are characterized by distinct hydrographic affinities and are hence anticipated to be impacted differently by environmental changes, with major consequences for the Arctic food web. In this study, we applied DNA metabarcoding to the stomach contents of these Themisto species, to comprehensively reveal their prey spectra at an unprecedented-high-taxonomic-resolution and assess the regional variation in their diet across the Fram Strait. Both species feed on a wide variety of prey but their diet strongly differed in the investigated summer season, showing overlap for only a few prey taxa, such as calanoid copepods. The spatially structured prey field of T. libellula clearly differentiated it from T. abyssorum, of which the diet was mainly dominated by chaetognaths. Our approach also allowed the detection of previously overlooked prey in the diet of T. libellula , such as fish species and gelatinous zooplankton. We discuss the reasons for the differences in prey spectra and which consequences these may have in the light of ongoing environmental changes.

As a result of ocean warming, the species composition of the Arctic seas has begun to shift in a boreal direction. One ecosystem prone to fauna shifts is the Northeast Greenland shelf. The dispersal route taken by boreal fauna to this area is, however, not known. This knowledge is essential to predict to what extent boreal biota will colonise Arctic habitats. Using population genetics, we show that Atlantic cod (Gadus morhua), beaked redfish (Sebastes mentella), and deep-sea shrimp (Pandalus borealis) recently found on the Northeast Greenland shelf originate from the Barents Sea, and suggest that pelagic offspring were dispersed via advection across the Fram Strait. Our results indicate that boreal invasions of Arctic habitats can be driven by advection, and that the fauna of the Barents Sea can project into adjacent habitats with the potential to colonise putatively isolated Arctic ecosystems such as Northeast Greenland.

During a recent marine biological expedition to the Northeast Greenland shelf break (latitudes 74-77 °N), we made the first discovery of Atlantic cod (Gadus morhua), beaked redfish (Sebastes mentella) and capelin (Mallotus villosus). Our novel observations shift the distribution range of Atlantic cod >1000 km further north in East Greenland waters. In light of climate change, we discuss physical forcing and putative connections between the faunas of the Northeast Greenland shelf and the Barents Sea. We emphasise the importance of using real data in spread scenarios for understudied Arctic seas.