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International audience; Invasive alien species are a major worldwide driver of biodiversity change. The current study lists verified records of non-indigenous species (NIS) in European marine waters until 2020, with the purpose of establishing a baseline, assessing trends, and discussing appropriate threshold values for good environmental status (GES) according to the relevant European legislation. All NIS records were verified by national experts and trends are presented in six-year assessment periods from 1970 to 2020 according to the European Union Marine Strategy Framework Directive. Altogether, 874 NIS have been introduced to European marine waters until 2020 with the Mediterranean Sea and NorthEast Atlantic Ocean hosting most of the introductions. Overall, the number of new introductions has steadily increased since 2000. The annual rate of new introductions reached 21 new NIS in European seas within the last six-year assessment period (2012-2017). This increase is likely due to increased human activities and research efforts that have intensified during the early 21st century within European Seas. As Europe seas are not environmentally, nor geographically homogenous, the setting of threshold values for assessing GES requires regional expertise. Further, once management measures are operational, pathway-specific threshold values would enable assessing the effectiveness of such measures.

1. Due to globalisation, trade and transport, the spread of alien species is increasing dramatically. Some alien species become ecologically harmful by threatening native biota. This can lead to irreversible changes in local biodiversity and ecosystem functioning, and, ultimately, to biotic homogenisation. 2. We risk-assessed all alien plants, animals, fungi and algae, within certain delimitations, that are known to reproduce in Norway. Mainland Norway and the Arctic archipelago of Svalbard plus Jan Mayen were treated as separate assessment areas. Assessments followed the Generic Ecological Impact Assessment of Alien Species (GEIAA) protocol, which uses a fully quantitative set of criteria. 3. A total of 1519 species were risk-assessed, of which 1183 were species reproducing in mainland Norway. Among these, 9% were assessed to have a severe impact, 7% high impact, 7% potentially high impact, and 49% low impact, whereas 29% had no known impact. In Svalbard, 16 alien species were reproducing, one of which with a severe impact. 4. The impact assessments also covered 319 so-called door-knockers, i.e. species that are likely to establish in Norway within 50 years, and 12 regionally alien species. Of the door-knockers, 8% and 10% were assessed to have a severe and high impact, respectively. 5. The impact category of most species was driven by negative interactions with native species, transformation of threatened ecosystems, or genetic contamination. The proportion of alien species with high or severe impact varied significantly across the different pathways of introduction, taxonomic groups, time of introduction, and the environments colonised, but not across continents of origin. 6. Given the large number of alien species reproducing in Norway and the preponderance of species with low impact, it is neither realistic nor necessary to eradicate all of them. Our results can guide management authorities in two ways. First, the use of quantitative assessment criteria facilitates the prioritisation of management resources across species. Second, the background information collected for each species, such as introduction pathways, area of occupancy and ecosystems affected, helps designing appropriate management measures. 1. Globalisering, handel og transport fører til en dramatisk økning i spredningen av fremmede arter. Noen fremmede arter er skadelige og truer det stedegne naturmangfoldet. Lokalt kan dette medføre irreversible endringer i det lokale biologiske mangfoldet og økosystemenes funksjon; globalt en homogenisering av artssammensetningen. 2. Vi har gjennomført risikovurderinger av alle fremmede planter, dyr, sopper og alger som reproduserer i Norge og oppfyller visse avgrensninger. Svalbard og Jan Mayen ble behandla som et eget vurderingsområde, adskilt fra Fastlands‐Norge. Risikovurderingene ble gjort i tråd med GEIAA (Generic Ecological Impact Assessment of Alien Species), som benytter et rent kvantitativt kriteriesett. 3. Totalt ble 1519 arter risikovurdert, hvorav 1183 reproduserte i Fastlands‐Norge. Av disse ble 9 % vurdert til å utgjøre en svært høy risiko, 7 % en høy risiko, 7 % en potensielt høy risiko, 49 % en lav risiko og 29 % ingen kjent risiko. På Svalbard forekom 16 reproduserende fremmede arter, hvorav én med svært høy risiko. 4. Risikovurderingene omfatta også 319 såkalte dørstokkarter, dvs. fremmede arter som antas å kunne etablere seg i Norge innen 50 år, samt 12 regionalt fremmede arter. Blant dørstokkartene ble 8 % og 10 % vurdert til å utgjøre en svært høy respektive høy risiko. 5. For de fleste arter ble risikokategorien bestemt av artenes interaksjoner med stedegne arter, tilstandsendringer i trua naturtyper eller genetisk forurensning. Andelen av fremmede arter med høy eller svært høy risiko varierte signifikant på tvers av ulike introduksjonsveier, artsgrupper, tidspunkt for introduksjon og koloniserte naturtyper, men ikke på tvers av opphavsområder. 6. Gitt det store antallet av fremmede arter som reproduserer i Norge, og overvekten av arter som har lav risiko, er det verken realistisk eller nødvendig å utrydde alle. Resultatene våre kan hjelpe forvaltningsmyndighetene på to måter. For det første gjør bruken av kvantitative kriterier det lettere å prioritere ressurser på tvers av arter. For det andre kan passende forvaltningstiltak utarbeides på grunnlag av den innsamla bakgrunnsinformasjonen om artene, f.eks. deres spredningsveier, forekomstareal og berørte naturtyper. This is an open access article under the terms of the Creative Commons Attribution License, which permits use,distribution and reproduction in any medium, provided the original work is properly cited.c 2020 The Authors. Ecological Solutions and Evidence published by John Wiley & Sons Ltd on behalf of British Ecological Society

Climate change and increased anthropogenic activities are expected to elevate the potential of introducing nonindigenous species (NIS) into the Arctic. Yet, the knowledge base needed to identify gaps and priorities for NIS research and management is limited. Here, we reviewed primary introduction events to each ecoregion of the marine Arctic realm to identify temporal and spatial patterns, likely source regions of NIS, and the putative introduction pathways. We included 54 introduction events representing 34 unique NIS. The rate of NIS discovery ranged from zero to four species per year between 1960 and 2015. The Iceland Shelf had the greatest number of introduction events (n = 14), followed by the Barents Sea (n = 11), and the Norwegian Sea (n = 11). Sixteen of the 54 introduction records had no known origins. The majority of those with known source regions were attributed to the Northeast Atlantic and the Northwest Pacific, 19 and 14 records, respectively. Some introduction events were attributed to multiple possible pathways. For these introductions, vessels transferred the greatest number of aquatic NIS (39%) to the Arctic, followed by natural spread (30%) and aquaculture activities (25%). Similar trends were found for introductions attributed to a single pathway. The phyla Arthropoda and Ochrophyta had the highest number of recorded introduction events, with 19 and 12 records, respectively. Recommendations including vector management, horizon scanning, early detection, rapid response, and a pan‐Arctic biodiversity inventory are considered in this paper. Our study provides a comprehensive record of primary introductions of NIS for marine environments in the circumpolar Arctic and identifies knowledge gaps and opportunities for NIS research and management. Ecosystems worldwide will face dramatic changes in the coming decades due to global change. Our findings contribute to the knowledge base needed to address two aspects of global change—invasive species and climate change., This paper examines the current status and future risks of biological invasions in the marine environments of the Arctic, within the context of climate change, natural resource development, and expanded Arctic shipping. The number of nonindigenous species introductions varied across the region with the greatest number of introductions recorded in the Iceland Shelf, followed by the Barents Sea and the Norwegian Sea. Most introductions were attributed to vessels, natural spread, and aquaculture activities. Vector management, horizon scanning, early detection, rapid response, and a pan‐Arctic biodiversity inventory are recommended to address future invasion risks.

The threat posed by invasive non-native species worldwide requires a global approach to identify which introduced species are likely to pose an elevated risk of impact to native species and ecosystems. To inform policy, stakeholders and management decisions on global threats to aquatic ecosystems, 195 assessors representing 120 risk assessment areas across all six inhabited continents screened 819 non-native species from 15 groups of aquatic organisms (freshwater, brackish, marine plants and animals) using the Aquatic Species Invasiveness Screening Kit. This multi-lingual decision-support tool for the risk screening of aquatic organisms provides assessors with risk scores for a species under current and future climate change conditions that, following a statistically based calibration, permits the accurate classification of species into high-, medium-and low-risk categories under current and predicted climate conditions. The 1730 screenings undertaken encompassed wide geographical areas (regions, political entities, parts thereof, water bodies, river basins, lake drainage basins, and marine regions), which permitted thresholds to be identified for almost all aquatic organismal groups screened as well as for tropical, temperate and continental climate classes, and for tropical and temperate marine ecoregions. In total, 33 species were identified as posing a 'very high risk' of being or becoming invasive, and the scores of several of these species under current climate increased under future climate conditions, primarily due to their wide thermal tolerances. The risk thresholds determined for taxonomic groups and climate zones provide a basis against which area-specific or climate-based calibrated thresholds may be interpreted. In turn, the risk rankings help decision-makers identify which species require an immediate 'rapid' management action (e.g. eradication, control) to avoid or mitigate adverse impacts, which require a full risk assessment, and which are to be restricted or banned with regard to importation and/or sale as ornamental or aquarium/fishery enhancement. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/)., Cefas Science Excellence fund; [TKP2020-NKA-16], This study is dedicated to our co-author, the late Prof. Olaf Weyl, whose sudden passing during field work in November 2020 was received by us with great sadness. This study represents a contribution to the term of reference 'd' (Advance knowledge base to further develop indicators to evaluate the status and impact of non-indigenous species in marine environments) of the ICES working group on Introductions and Transfers of Marine Organisms. The participation of GHC was supported by the Cefas Science Excellence fund. AW and AF were supported by TKP2020-NKA-16 project.

The calyptraeid gastropod Crepidula fornicata is native to the eastern coast of the United States but has now become an extremely successful invader along much of the European coastline. As the northern limit of its spread is thought to be determined by an inability of adults to tolerate prolonged exposure to low winter temperatures, this study sought to compare the fecundity of females collected from two sites along the Norwegian coastline with that of females collected from Rhode Island, USA. Few other studies have compared the fecundities of marine invertebrates from invasive populations with those found in native populations. For both populations studied, fecundities increased with increasing shell length. However, contrary to expectations, size-related fecundities were significantly higher for Norwegian females than for Rhode Island females, with Norwegian females producing larger egg capsules and a greater number of embryos per capsule, but not a greater number of egg capsules per brood. Current evidence suggests that at the northern extreme of its invaded range, the fecundity of C. fornicata is increased rather than compromised.

This is a post-peer-review, pre-copyedit version of an article published in Biological Invasions. The final authenticated version is available online at: https://doi.org/10.1007/s10530-019-02058-x. We present the results of an inventory and status assessment of alien species in Norway. The inventory covered all known multicellular neobiota, 2496 in total, 1039 of which were classified as naturalised. The latter constitute c. 3% of all species known to be stably reproducing in Norway. These figures are higher than expected from Norway’s latitude, which may be due a combination of climatic and historical factors, as well as sampling effort. Most of the naturalised neobiota were plants (71%),followed by animals (21%) and fungi (8%). The main habitat types colonised were open lowlands (79%), urban environments (52%) and woodlands (42%). The main areas of origin were Europe (67%), North America (15%) and Asia (13%). For most taxa, the rate of novel introductions seems to have been increasing during recent decades. Within Norway, the number of alien species recorded per county was negatively correlated with latitude and positively correlated with human population density. In the high-Arctic territories under Norwegian sovereignty, i.e. Svalbard and Jan Mayen, 104 alien species were recorded, of which 5 were naturalised.

Aim: Anticipated changes in the global ocean climate will affect the vulnerability of marine ecosystems to the negative effects of non-indigenous species (NIS). In the Arctic, there is a need to better characterize present and future marine biological introduction patterns and processes. We use a vector-based assessment to estimate changes in the vulnerability of a high-Arctic archipelago to marine NIS introduction and establishment. Location: Global, with a case study of Svalbard, Norway. Methods: We base our assessment on the level of connectedness to global NIS pools through the regional shipping network and predicted changes in ocean climates. Environmental match of ports connected to Svalbard was evaluated under present and future environmental conditions (2050 and 2100 predicted under the RCP8.5 emissions scenario). Risk of NIS introduction was then estimated based on the potential for known NIS to be transported (in ballast water or as biofouling), environmental match, and a qualitative estimate of propagule pressure. Results: We show that Svalbard will become increasingly vulnerable to marine NIS introduction and establishment. Over the coming century, sea surface warming at high latitudes is estimated to increase the level of environmental match to nearly one-third of ports previously visited by vessels travelling to Svalbard in 2011 (n = 136). The shipping network will then likely connect Svalbard to a much greater pool of known NIS, under conditions more favourable for their establishment. Research and fishing vessels were estimated to pose the highest risk of NIS introduction through biofouling, while ballast water discharge is estimated to pose an increased risk by the end of the century. Main conclusions: In the absence of focused preventative management, the risk of NIS introduction and establishment in Svalbard, and the wider Arctic, will increase over coming decades, prompting a need to respond in policy and action.

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Several decades of research on invasive marine species have yielded a broad understanding of the nature of species invasion mechanisms and associated threats globally. However, this is not true of the Arctic, a region where ongoing climatic changes may promote species invasion. Here, we evaluated risks associated with non-indigenous propagule loads discharged with ships' ballast water to the high-Arctic archipelago, Svalbard, as a case study for the wider Arctic. We sampled and identified transferred propagules using traditional and DNA barcoding techniques. We then assessed the suitability of the Svalbard coast for non-indigenous species under contemporary and future climate scenarios using ecophysiological models based on critical temperature and salinity reproductive thresholds. Ships discharging ballast water in Svalbard carried high densities of zooplankton (mean 1522335 SE individuals m(-3)), predominately comprised of indigenous species. Ballast water exchange did not prevent non-indigenous species introduction. Non-indigenous coastal species were present in all except one of 16 ballast water samples (mean 14467 SE individuals m(-3)), despite five of the eight ships exchanging ballast water en route. Of a total of 73 taxa, 36 species including 23 non-indigenous species were identified. Of those 23, sufficient data permitted evaluation of the current and future colonization potential for eight widely known invaders. With the exception of one of these species, modelled suitability indicated that the coast of Svalbard is unsuitable presently; under the 2100 Representative Concentration Pathway (RCP) 85 climate scenario, however, modelled suitability will favour colonization for six species.Synthesis and applications. We show that current ballast water management practices do not prevent non-indigenous species from being transferred to the Arctic. Consequences of these shortcomings will be shipping-route dependent, but will likely magnify over time: our models indicate future conditions will favour the colonization of non-indigenous species Arctic-wide. Invasion threats will be greatest where shipping transfers organisms across biogeographic realms, and for these shipping routes ballast water treatment technologies may be required to prevent impacts. Our results also highlight critical gaps in our understanding of ballast water management efficacy and prioritization. Thereby, our study provides an agenda for research and policy development. We show that current ballast water management practices do not prevent non-indigenous species from being transferred to the Arctic. Consequences of these shortcomings will be shipping-route dependent, but will likely magnify over time: our models indicate future conditions will favour the colonization of non-indigenous species Arctic-wide. Invasion threats will be greatest where shipping transfers organisms across biogeographic realms, and for these shipping routes ballast water treatment technologies may be required to prevent impacts. Our results also highlight critical gaps in our understanding of ballast water management efficacy and prioritization. Thereby, our study provides an agenda for research and policy development.

Journal homepage: http://www.esajournals.org/loi/ecol Until the last decade it was assumed that most marine species have pronounced gene flow over vast areas, largely because of their potential for dispersal during early life stages. However, recent genetic, modeling, and field studies have shown that marine populations may be structured at scales that are inconsistent with extensive dispersal of eggs and larvae. Such findings have stimulated the birth of new studies explaining the mechanisms that promote population structure and isolation in the oceans, in the face of high potential for dispersal. Here we study the vertical and horizontal distribution of cod (Gadus morhua) eggs in relation to small-scale circulation and water column hydrography in a coastal location of southern Norway. Previous studies conducted in this region have shown that cod populations inhabiting fjord locations, which are on average 30 km apart, are genetically differentiated, a remarkable outcome considering that Atlantic cod have pelagic egg stages and long pelagic larval duration. We document that cod eggs are found in greater abundance in shallow water layers, which on average are flowing up the fjord (away from the open ocean), and in the inner portion of the fjord, which is subject to lower current speeds compared to the outer or mouth of the fjord. Eggs were found to be neutrally buoyant at shallow depths, a trait that also favors local retention, given the local circulation. The same patterns held during two environmentally contrasting years. These results strongly suggest that population structure of Atlantic cod is favored and maintained by a balance between water circulation and egg characteristics.

The abundance and diversity of species in ballast water, a recognised vector for the accidental introduction of nonindigenous organisms, has been examined through many studies around the world over the last 25 years. The results of European research activities are summarised in this contribution by outlining the objectives of some of these studies, and by focusing on the diversity of taxa determined from ballast water and tank sediment samples. In total 1508 samples (1219 ballast water, 289 tank sediment) were collected on 550 ships. A total of 990 taxa were identified during the 14 European shipping studies. The diversity of species found included bacteria, fungi, protozoans, algae, invertebrates of different life stages including resting stages, and fishes with a body length up to 15 cm. Crustacean, molluscan and polychaete invertebrates and algae form the majority of species found.