Thomas Gunnar Dahlgren

Deep‐sea and Arctic soft‐bottom organism communities remain severely underexplored. Sediment environmental DNA (eDNA) metabarcoding can complement existing survey methods, but its ability to discriminate among habitats and to reliably assign taxa must be critically evaluated. Here, we analyzed sediment samples from 10 areas in the Nordic Seas and adjacent Arctic, including the Arctic Mid‐Ocean Ridge (AMOR), continental slope habitats, and abyssal environments. Four genetic markers targeting different organism components were used: prokaryotic 16S and eukaryotic 18S (V1‐V2 and V4 regions) rDNA, and the metazoan cytochrome oxidase subunit I (COI) gene. Our aims were to gain biodiversity insights for these habitats by (1) comparing markers for characterizing and discriminating between samples and habitats, and (2) evaluating the potential for extracting low‐rank (family to species) animal taxa to complement taxonomic inventories. Alpha diversity varied substantially between markers and sampling areas, reflecting ecological variability and methodological differences. In contrast, beta diversity patterns were robust and consistent. Multivariate analyses showed clear separation by area and depth: the included AMOR seamount constituted a distinct community, and Arctic samples showed strong structuring with depth. Depth and geographic position explained significant fractions of community variability across metabarcoding markers. Taxonomic assignment revealed complementary performance of 18S rDNA and COI: 18S rDNA excelled in meio‐ and macrofauna coverage and intermediate‐rank performance. Conversely, COI yielded higher resolution at species rank. In total, 479 unique metazoan taxa were identified at family rank or below, highlighting both current limitations and future potential of metabarcoding for biodiversity inventories in the region. Overall, we find that multi‐marker eDNA metabarcoding can reliably discriminate between soft‐bottom organism communities. When combined with taxonomic validation and standardized workflows, this provides a powerful complement to existing survey methodology for understudied assemblages in the Nordic Seas and on the AMOR and should be integrated with future surveys in the area.

Improving environmental management in the offshore Oil & Gas sector requires approaches that capture the ecosystem services (ES) provided by marine sediments, particularly their roles in carbon and nutrient cycling. Microbial communities are central to these processes, and molecular tools offer new opportunities to assess their functional diversity. To explore how different sequencing approaches inform environmental impact assessment, we compared taxonomic and functional prediction based on 16S metabarcoding, shotgun metagenomics and messenger RNA-based metatranscriptomics, targeting prokaryotic communities. Our aims were to evaluate the ability of each approach to detect impact and to determine how well they captured functions relevant to ES. All approaches revealed clear differences in community composition between impacted and non-impacted sediments at both taxonomic and functional levels, with impact significantly associated with hydrocarbon and barium content. Functional inventories showed substantial overlap across the three approaches, and 48-55 ES-related processes were detectable in all datasets. While metagenomics provided the strongest statistical discrimination between impact groups, metatranscriptomics resolved the actively expressed pathways underpinning ES, yielding the most biologically meaningful functional profiles despite its lower statistical power. All approaches indicated that Oil & Gas activity drives shift towards anaerobic, hydrocarbon-degrading, and sulfur-respiring microbial communities, with hydrocarbon degradation, sulfur cycling, and metal detoxification being the dominant ES processes in impacted sediments. Metabarcoding was confirmed as a cost-effective option for impact assessment when focused on taxonomic composition. However, functional prediction from metabarcoding data proved less reliable, as several ES showed contrasting associations to impact category between metabarcoding and shotgun sequencing approaches.

DNA metabarcoding offers prospects to assess benthic biodiversity in a more scalable and comprehensive way, but processing methods remain insufficiently standardized and calibrated against traditional morphology‐based approaches. Here, we evaluated four processing strategies for DNA extraction from North Sea sandy and muddy sediments. These included two bulk DNA approaches (sieving and elutriation) and two direct environmental DNA (eDNA) approaches (3 × 0.5 g with homogenizer and 10 g with vortex). Animal and microbial diversity were assessed using mitochondrial cytochrome c oxidase subunit I (cox1) and small subunit ribosomal RNA markers (16S and 18S). Bulk DNA methods recovered more macro‐ and meiofauna Operational Taxonomic Units (OTUs) than direct eDNA approaches. However, effect sizes were small (< 0.4), while sample processing times were substantially longer (3–6 times slower), highlighting trade‐offs between biodiversity recovery and scalability for monitoring programs. Notably, the performance of size‐class sorting through sieving (1 mm) varied significantly with sediment grain size, recovering more macrofauna OTUs in sandy sediments but performing worse than direct eDNA methods in muddy sediments, thereby decreasing comparability across geographic regions. Both bulk approaches also led to increased detection of nontarget planktonic protists and reduced recovery of benthic prokaryotes, limiting their suitability for holistic biomonitoring. Both direct eDNA methods recovered similar OTU numbers and phylum‐level community compositions across markers, confirming that sample homogenizers enable efficient diversity recovery from small sediment volumes, also for animals. Sample completeness curves indicated that ~80% animal biodiversity coverage can be achieved with eDNA when spatial replication is increased to ~20 stations. Morphotaxonomy and metabarcoding datasets showed poor concordance at family and genus levels, with better levels of overlap for cox1 (20%–30%) compared to 18S (18SV1V2: 12%–20%, 18SV4: 6%–15%). Consequently, correlations between morphotaxonomy‐ and metabarcoding‐derived biotic indices were weak across all extraction strategies, highlighting the need to adapt biotic indices to metabarcoding data.

In marine environments, nonindigenous species (NIS) are especially difficult to manage since they are often first detected when fully established and near impossible to eradicate. The development and implementation of effective monitoring methods for marine NIS are therefore crucial for early detection valuable to management. In this study, we develop and evaluate environmental DNA monitoring using quantitative digital PCR (dPCR) to assess the presence of the euryhaline round goby (Neogobius melanostomus) in a seascape environment close to Scandinavia's largest shipping port. We developed a dPCR assay for the species, targeting a region of the 12S gene, and verified its specificity compared to other locally common species from the gobiid family. Using captive live fish, we also experimentally determined the decaying rate of N. melanostomus DNA in water to a half‐life of 9.8 h in 15 ppt salinity and 15°C. Finally, we sampled 10 sites within a 400 km² area using eDNA, fyke nets, and baited remote video to validate the accuracy of the water samples to predict the presence and abundance of the species. We found that the number of DNA copies extracted from the water samples varied strongly at sites where N. melanostomus were caught in nets or on video, but the average value from four water samples significantly correlated with an average value from four video samples and also with the total catch at each site. The eDNA assay also detected signals from the species at sites where no fish were caught by fishing or on video. These results show that this method is sensitive for the species at low abundance, and with enough replicates, it can be possible to determine the relative abundance between sites.

More than 7000 demosponge species have been described to date globally but Plenaster craigi, the most common and abundant species in the eastern CCZ, represents a new family, and possibly in a new order. Interestingly, P. craigi and members of the families Polymastiidae and Hamacanthidae, all filter‐feeding demosponge species, are far more abundant in nodule fields than the carnivorous sponges (Cladorhizidae) which were widely known to be the most dominant demosponge group in the abyssal depths. Lastly, it is highly likely that such tiny demosponges are present in other habitats. They might have been overlooked and/or ignored by sponge researchers in the past due to their tiny size and nondescript habitus. These demosponges could be distinct new species, not juveniles or indeterminates and warrant full taxonomic treatment.

0.0 Non-indigenous species (NIS) is one of the five most global concerns when it comes to ecosystem services and threats to native biodiversity. This is especially true in aquatic environments which are harder to monitor than terrestrial environments, and NIS are often found first when they are fully established and basically impossible to eradicate. In marine environments, this is further complicated due to the connectivity and difficulty of eradication. The development and implementation of effective monitoring methods for marine NIS are therefore crucial to enable early detection useful for management strategies. In this study, we develop and evaluate environmental DNA monitoring using quantitative (q)PCR as a means to assess presence of the euryhaline round goby fish ( Neogobius melanostomus ) in a seascape environment close to Scandinavia’s largest shipping port. We developed a dPCR assay for the species, targeting a region of 12S gene, and verified its specificity compared to other common species from the gobiid-family in the region. We also experimentally determined the decaying rate of round goby DNA in water to a half-life of 9.8 hours in 15 PSU and 15°C with live fish in captivity. Finally, we sampled 10 sites within a 400 km ² area for eDNA and presence of the species using fyke-nets and baited remote video to validate the accuracy of the water samples to predict presence, and abundance. We found that the number of DNA copies extracted from the water samples varied strongly at sites where round gobies were caught in nets or on video, but that the average value from four water samples significantly correlated with an average value from four video samples, and also with the total catch at each site. The eDNA assay also detected signals from the species at sites where no fish were caught by fishing or on video. These results show that this method is highly sensitive for the species even in low abundance, and with sufficient amounts of replicates, it can be possible to determine the relative abundance between sites.

We present a checklist of annelids from recent United Kingdom Seabed Resources (UKSR) expeditions (Abyssal Baseline - ABYSSLINE project) to the eastern abyssal Pacific Clarion-Clipperton Zone (CCZ) polymetallic nodule fields, based on DNA species delimitation, including imagery of voucher specimens, Darwin Core (DwC) data and links to vouchered specimen material and new GenBank sequence records. This paper includes genetic and imagery data for 129 species of annelids from 339 records and is restricted to material that is, in general, in too poor a condition to describe formally at this time, but likely contains many species new to science. We make these data available both to aid future taxonomic studies in the CCZ that will be able to link back to these genetic data and specimens and to better underpin ongoing ecological studies of potential deep-sea mining impacts using the principles of FAIR (Findable, Accessible, Interoperable, Reusuable) data and specimens that will be available for all. We include genetic, imagery and all associated metadata in Darwin Core format for 129 species of annelids from the Clarion-Clipperton Zone, eastern abyssal Pacific, with 339 records.

The DNA taxonomy of six species of the annelid family Lumbrineridae collected from the Clarion-Clipperton Zone (CCZ) in the Central Pacific, an area of potential mining interest for polymetallic nodules, is presented. Lumbrinerids are an ecologically important and understudied annelid family within the deep sea, with many species still undescribed. This study aims to document the taxonomy and biodiversity of the CCZ using specimens collected from the UK-1, OMS, and NORI-D exploration contract areas and Areas of Particular Environmental Interest. Species were identified through a combination of morphological and molecular phylogenetic analysis. We present informal species descriptions associated with voucher specimens, accessible through the Natural History Museum (London) collections, to improve future taxonomic and biodiversity studies of this region. Five taxa in this study had no morphological or genetic matches within the literature and therefore are possibly new to science, but their suboptimal morphological preservation prevented the formalisation of new species. The most abundant taxon Lumbrinerides cf. laubieri (NHM_0020) was compared with the holotype of Lumbrinerides laubieri Miura, 1980 from the deep Northeast Atlantic. Currently no reliable morphological characters separating the Pacific and Atlantic specimens have been found and molecular data from the Atlantic specimens was not available.

In this study, we collected water eDNA from sampling stations at the first full scale floating offshore wind farm (OWF), the Hywind Pilot Park, east of Peterhead, UK, and a nearby reference area. We combined targeted droplet digital PCR (ddPCR) quantification of two commercially important species, Atlantic mackerel (Scombrus scombrus) and Atlantic herring (Clupea harengus), with metabarcoding of fish and plankton communities. The goal of this study was to assess the performance of eDNA data to characterize pelagic communities and its use for environmental monitoring. The metabarcoding recovered 26 fish species including both pelagic and demersal taxa. The plankton data were dominated by dinoflagellates (Karenia) and calanoid copepods. We found that both specific quantification of eDNA from mackerel and herring and eDNA metabarcoding of fish communities were able to reveal spatial patterns: Mackerel was most abundant in the surface across both OWF and reference sites; herring was present at a wider depth range. While ddPCR and metabarcoding data for these two species were broadly congruent, we observed detection/non‐detection mismatches for both methods, highlighting the need for robust sampling design. There was no consistent OWF versus reference area pattern in the demersal fraction of fish assemblages. We interpret our findings as representing a snapshot of fish school location around the time of sampling, and do not consider the single timepoint data from this pilot study to be sufficient to attribute any effects to the OWF itself. As a non‐invasive tool, we conclude that eDNA has a high potential in future environmental monitoring of OWFs. We recommend further ground‐truthing and biomass correlation of eDNA data with catch data and establishing eDNA time series as next steps towards implementation of eDNA in OWF environmental monitoring.