Institute of Marine Research in Norway

In areas with high densities of salmon farming, spillover of the ectoparasitic salmon louse Lepeophtheirus salmonis poses a major threat to wild anadromous salmonids. By combining experimentally salmon louse infestation (mean ± standard deviation = 0.25 ± 0.25 lice g⁻¹ fish) with acoustic telemetry, we studied the behavior of wild first‐time migrating sea trout Salmo trutta (n = 58, fork length = 138–204 mm) from late June to September in a marine area with naturally low infestation pressure. We observed that a similar proportion of sea trout from the control and exposed groups returned to fresh water both temporarily and permanently. However, sea trout from the control group spent nearly twice the amount of time in the fjord before first freshwater detection compared to exposed individuals (32 vs. 17 days), and statistical models indicated a dose–response of louse burden on the timing of freshwater return. This effect was combined with evidence of negative impacts of salmon louse burden on overall marine residency. Sea trout predominantly utilized waters within their natal fjord during the marine migration, with exposed fish spending significantly more time close to their home river than sea trout from the control group. In summary, the behavioral modifications caused by salmon lice could reduce individual marine growth, increase long‐term mortality, and ultimately harm recruitment at the population level.

Atlantic salmon is an important aquaculture species that has fascinated naturalists for centuries, resulting in its biology being widely characterized. Certain details about the early development and the inheritance of meristic variation in the post‐cranial axial skeleton are, however, largely unexplored. The present study gives a detailed description of the sequence of formation of the post‐cranial axial skeleton based on whole‐mount staining and used radiology to investigate the inheritance of meristic variation in isogenic hybrid all‐male families of Atlantic salmon (~4 kg). Eight different families were created by crossing two homozygous double haploid XX females (dam A, B) with four different double haploid homozygous YY super males (sires a to d). In the caudal fin complex, the first bone to form is hypural 1 and its associated lepidotrichia followed by a bidirectional formation of new bones. In the dorsal and anal fins, development starts in the cranial part, and new bones form bidirectionally towards the head and tail fin. The neural and haemal arches start to form at segment 43, and further development is bidirectional. The first parapophysis form in the caudal part of the abdomen followed by a unidirectional completion cranially. The first ribs form at segment 3 and new ribs develop unidirectional caudally. Chordacentra formation starts at segment 24 followed by formation of chordacentrum number 58 (caudal‐most vertebra). New chordacentrae form bidirectionally from segment 24 in parallel with the formation of chordacentrum number 57. The first epineuralia form at segment 1 followed by a unidirectional completion caudally until segment 30. The first supraneuralia to develop is number 10 closely followed by number 1, then new supraneurals form bidirectionally from number 10. Analysis of the inheritance on the post‐cranial axial skeletal bones showed a strong maternal effect on total vertebrae centra and tail fin lepidotrichia counts. For these skeletal counts, dam A produced offspring with modes of 58 and 45 respectively, while dam B produced offspring with modes of 59 and 42. The higher number of total vertebrae centra produced by dam B was associated with additional abdominal and/or transitional vertebrae. The completion of formation in different post‐cranial axial skeletal parts are either bi‐ or unidirectional, and the initiation of formation is site specific for each skeletal part with some inter‐part similarities. Further, the present results may suggest that there has been a maternally driven selection for more abdominal vertebrae associated with a higher number of total vertebrae, and more tail fin lepidotrichia associated with a lower number of total vertebrae. These changing meristic counts may impact on important fitness‐related traits, such as fecundity and swimming ability, making the present findings relevant for both ecological and aquaculture sciences.

Aim Salmonids are some of the best studied species with respect to their pathobiome, and at the northern range limit, there is potential for pathogens to expand with both climate change and increased fish farming in the north. Location We sampled sea‐run brown trout from throughout Norway for gill tissue and conducted both pooled and individual screenings for a total of 47 pathogens. Time Period Samples were collected during spring in 2020 and 2021. Major Taxa Bacteria, viruses and parasites of sea‐run brown trout. Methods Brown trout were gill biopsied as part of the national sea lice monitoring programme and samples were sent for laboratory analysis using the Fluidigm system, which screened for a broad panel of different pathogenic species. Results Permutated multivariate analysis of variance revealed that the pathobiome richness of trout was more related to latitude than to fish farming biomass in the region where samples were taken. However, non‐metric multidimensional scaling revealed a significant association between the individual pathobiome and the number of copepodid‐stage Lepeophtheirus salmonis lice, which did reveal a south/central versus northern Norway segregation in pathogen distributions. Importantly, many pathogens positively associated with sea lice in southern/central Norway are known to be carried, and potentially transmitted by sea lice. Main conclusions In northern Norway, pathogens normally associated with infection and disease in trout were more commonly observed. However, given that most pathogens were detected from southern to northern Norway, it appears that further expansion of farms in the north are not likely to lead to further introductions of pathogens into northern areas of Norway, although it could amplify the prevalence of these pathogens on wild salmon.

Decapod crustaceans, commonly utilised for pure or applied scientific research and commercial food production, have generally remained outside ethical debate. However, in the last decade many parts of the world have seen an increase in public interest in the welfare of decapod crustaceans and statutory legal protection has been introduced in several countries. Although still limited to a small number of countries and remaining relatively unharmonised, relevant legislation could be increasingly broadened to include decapods in further jurisdictions. Much existing legislation, originally intended for protecting terrestrial vertebrates during scientific study, might be unsuitable for aquatic invertebrates such as decapods. Indeed, precedence with many fish species and cephalopods suggests detail is lacking with respect to fundamental guidance. Therefore, similar inclusion of decapods into such legislation could make welfare or scientific goals more challenging to achieve unless relevant guidance is available, particularly to animal care practitioners. This horizon paper aims to summarise existing decapod legislation, and the considerations required should decapods be included in current conceptual frameworks and scientific legislation.

On the deep and dark seafloor, a cryptic and yet untapped microbial diversity flourishes around hydrothermal vent systems. This remote environment of difficult accessibility exhibits extreme conditions, including high pressure, steep temperature- and redox gradients, limited availability of oxygen and complete darkness. In this study, we analysed the genomes of three aerobic strains belonging to the phylum Planctomycetota that were isolated from two deep-sea iron- rich hydroxide deposits with low temperature diffusive vents. The vents are located in the Arctic and Pacific Ocean at a depth of 600 and 1,734 m below sea level, respectively. The isolated strains Pr1dT, K2D and TBK1r were analyzed with a focus on genome-encoded features that allow phenotypical adaptations to the low temperature iron-rich deep-sea environment. The comparison with genomes of closely related surface-inhabiting counterparts indicates that the deep-sea isolates do not differ significantly from members of the phylum Planctomycetota inhabiting other habitats, such as macroalgae biofilms and the ocean surface waters. Despite inhabiting extreme environments, our “deep and dark”-strains revealed a mostly non-extreme genome biology.

Norway employs an environmental management system to assess benthic organic loading from aquaculture activities. Monitoring surveys, mostly performed through grab sampling, scrutinise responses to enrichment within soft-sediment macrofaunal communities. However, new methods and indicators of organic enrichment (IOE) need to be identified for mixed- and hard-bottom substrates. We used image characterisation to examine temporal changes in the abundance and coverage of benthic IOE on mixed- and hard-bottom substrates (organic pellets, sulphur-oxidising bacterial mats, opportunistic polychaete complexes [OPC], polychaete tube aggregations [PTA]) in relation to changes in organic deposition pressure through 1 yr of production at a rainbow trout farm on the western coast of Norway. Rates of organic deposition on the seafloor around the farm increased towards the end of the survey period as fish biomass increased. PTA were significantly associated with low levels of organic deposition and their abundance declined in 2 of the 3 study cages as the production cycle progressed. OPC coverage significantly increased with organic deposition and was greatest, 4 mo before the end of the production cycle. Organic pellet coverage closely followed the patterns of organic deposition on the seafloor, whereas bacterial mat coverage showed no relationship with deposition. Our findings provide new knowledge on the annual impact of organic enrichment on IOE beneath fish farms over mixed- and hard-bottom substrates, highlighting image characterisation methods as a means to improve benthic monitoring. This knowledge can contribute to the development of an environmental proxy to assess the enrichment stage around aquaculture farms placed over mixed- and hard-bottom areas.

Ostrea edulis, the European flat oyster, was once a widespread economically and ecologically important marine species, but has suffered dramatic declines over the past two centuries. Consequently, there has been a surge in European restoration efforts, many of which focus on restocking as a conservation measure. In this study, we used whole-genome sequencing (WGS) data to investigate the population structure, demographic history, and patterns of local adaptation of O. edulis across its natural distribution with increased sampling densities at Scandinavian localities. Results revealed seven distinct genetic clusters, including previously undescribed complex population structure in Norway, and evidence for introgression between genetic clusters in Scandinavia. We detected large structural variants (SVs) on three pseudo-chromosomes. These megabase long regions were characterised by strong linkage disequilibrium and clear geographical differentiation, suggestive of chromosomal inversions potentially associated with local adaptation. The results indicated that genomic traces of past translocations of non-native O. edulis were still present in some individuals, but overall, we found limited evidence of major impacts of translocations on the scale of contemporary population structure. Our findings highlight the importance of considering population structure and signatures of selection in the design of effective conservation strategies to preserve and restore wild native European flat oyster populations, and we provide direct knowledge safeguarding sustainable mitigation actions in this important species. 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.

The mesopelagic zone represents one of the few habitats that remains relatively untouched from anthropogenic activities. Among the many species inhabiting the north Atlantic mesopelagic zone, glacier lanternfish (Benthosema glaciale) is the most abundant and widely distributed. This species has been regarded as a potential target for a dedicated fishery despite the scarce knowledge of its population genetic structure. Here, we investigated its genetic structure across the North Atlantic and into the Mediterranean Sea using 121 SNPs, which revealed strong differentiation among three main groups: the Mediterranean Sea, oceanic samples, and Norwegian fjords. The Mediterranean samples displayed less than half the genetic variation of the remaining ones. Very weak or nearly absent genetic structure was detected among geographically distinct oceanic samples across the North Atlantic, which contrasts with the low motility of the species. In contrast, a longitudinal gradient of differentiation was observed in the Mediterranean Sea, where genetic connectivity is known to be strongly shaped by oceanographic processes such as current patterns and oceanographic discontinuities. In addition, 12 of the SNPs, in linkage disequilibrium, drove a three clusters' pattern detectable through Principal Component Analysis biplot matching the genetic signatures generally associated with large chromosomal rearrangements, such as inversions. The arrangement of this putative inversion showed frequency differences between open‐ocean and more confined water bodies such as the fjords and the Mediterranean, as it was fixed in the latter for the second most common arrangement of the fjord's samples. However, whether genetic differentiation was driven by local adaptation, secondary contact, or a combination of both factors remains undetermined. The major finding of this study is that B. glaciale in the North Atlantic‐Mediterranean is divided into three major genetic units, information that should be combined with demographic properties to outline the management of this species prior to any eventual fishery attempt.

Fishes inhabiting the mesopelagic zone of the world's oceans are estimated to account for the majority of the world's fish biomass. They have recently attracted new attention because they are part of the biological carbon pump and have been reconsidered as a contribution to food security. Hence, there is an urgent need to understand how environmental conditions and species interactions shape their assemblages, and how they contribute to the functioning of marine ecosystems. Trait‐based approaches are valuable for addressing these types of questions. However, the biology and ecology of mesopelagic fishes are understudied compared to fishes in shallow and epipelagic waters. Here, we synthesise existing knowledge of traits of mesopelagic fishes and relate them to their role in survival, feeding and growth and reproduction, the key functions that contribute to fitness. Vertical migrations, specialised vision and the use of bioluminescence are among the most striking adaptations to the conditions in the mesopelagic realm. Many traits are interrelated as a result of trade‐offs, which may help to understand selection pressures. While morphological traits are straightforward to observe, major knowledge gaps exist for traits that require frequent sampling, assessment under experimental conditions or age determination. The unique adaptations of mesopelagic fishes need to be included in management strategies as well as fundamental research of the habitat.

Sensing limitations have impeded knowledge about how individual predator-prey interactions build to organized multi-species group behaviour across an ecosystem. Population densities of overlapping interacting oceanic fish predator and prey species, however, can be instantaneously distinguished and quantified from roughly the elemental individual to spatial scales spanning thousands of square kilometres by wide-area multispectral underwater-acoustic sensing, as shown here. This enables fundamental mechanisms behind large-scale ordered predator-prey interactions to be investigated. Critical population densities that transition random individual behaviour to ordered group behaviour are found to rapidly propagate to form vast adversarial prey and predator shoals of capelin and surrounding cod in the Barents Sea Arctic ecosystem for these keystone species. This leads to a sudden major shift in predator-prey balance. Only a small change in local behaviour triggers the shift due to an unstable equilibrium. Such unstable equilibria and associated balance shifts at predation hotspots are often overlooked as blind spots in present ocean ecosystem monitoring and assessment due to use of highly undersampled spatio-temporal sampling methods.

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66–2034 MPs/cm2 (size range 10–5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze–thaw cycling alongside contact with water, which were 15–453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321–1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27–46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

To inform the performance of ecological engineering designs for artificial structures at sea, it is essential to characterise their impacts on the epibenthic communities colonising them. In this context, the present study aims to compare the community structure among natural and four different artificial hard habitats with different ages and features installed in the Bay of Cherbourg (English Channel): i) cinder blocks and ii) boulders, both installed six years prior to the study, and iii) smooth and iv) rugous concrete dykes, both installed one year prior to this study. Results showed that artificial habitats installed six years ago harboured communities with functional and taxonomic diversity characteristic of mature communities but were still different from those of natural habitat. Conversely, the two dyke habitats installed one year prior to this study presented a poorly diversified community dominated by opportunistic taxa. Furthermore, while the concrete used for the two dyke habitats presented different rugosity properties, both habitats supported similar communities, suggesting that such eco-engineering measures did not affect the settlement of early colonisers. Overall, this study highlights the need for long-term monitoring to comprehensively evaluate epibenthic colonisation of artificial structures.

Seagrass meadows are well-known for their capacity to capture and store blue carbon in sediments. However carbon stocks vary significantly between meadows, spanning more than three orders of magnitude on both local and global scales. Understanding the drivers of seagrass carbon stocks could help improve strategies for incorporating blue carbon into management plans. Here, we measured sediment carbon stocks in eelgrass (Zostera marina) meadows and unvegetated areas along the Norwegian coast, spanning wide gradients in temperature, wave exposure, water depth, salinity, and eelgrass biomass. Carbon stocks were generally higher in eelgrass meadows than in adjacent unvegetated areas, yet they displayed considerable variation (400 − 30 000 g C m⁻² at 50 cm sediment depth) even among nearby sites. Overall, the highest carbon stocks were found in deeper, muddier, sheltered meadows near river mouths. These sites likely have the highest input and retention of carbon from different sources. Consequently, they should be prioritized as conservation targets for preserving coastal blue carbon stocks. Despite ever-increasing efforts to quantify seagrass blue carbon globally, high uncertainties still persist, partly due to differing methodologies, processes, and environmental context. Blue carbon stock estimates could be improved through the coordination of standardised mapping and sampling methods.

Sustainable fisheries management is important for the continued harvest of the world's marine resources, especially as they are increasingly challenged by a range of climatic and anthropogenic factors. One of the pillars of sustainable fisheries management is the accurate identification of the biological units, i.e., populations. Here, we developed and implemented a genetic baseline for Atlantic herring harvested in the Norwegian offshore fisheries to investigate the validity of the current management boundaries. This was achieved by genotyping > 15,000 herring from the northern European seas, including samples of all the known populations in the region, with a panel of population‐informative SNPs mined from existing genomic resources. The final genetic baseline consisted of ~1000 herring from 12 genetically distinct populations. We thereafter used the baseline to investigate mixed catches from the North and Norwegian Seas, revealing that each management area consisted of multiple populations, as previously suspected. However, substantial numbers (up to 50% or more within a sample) of herring were found outside of their expected management areas, e.g., North Sea autumn‐spawning herring north of 62° N (average = 19.2%), Norwegian spring‐spawning herring south of 62° N (average = 13.5%), and western Baltic spring‐spawning herring outside their assumed distribution area in the North Sea (average = 20.0%). Based upon these extensive observations, we conclude that the assessment and management areas currently in place for herring in this region need adjustments to reflect the populations present. Furthermore, we suggest that for migratory species, such as herring, a paradigm shift from using static geographic stock boundaries towards spatial dynamic boundaries is needed to meet the requirements of future sustainable management regimes.

Marine heatwaves (MHWs) are becoming more frequent and intense. At the same time, diverse human activities are causing coastal darkening: increased turbidity and reduced light at the seafloor. Since both temperature and light are critical to the physiological and ecological performance of seaweeds—important habitat-formers and primary producers—these co-occurring stressors could have knock-on effects in coastal ecosystems. We tested the effects of MHWs under different irradiance levels on 3 brown seaweeds: the kelp Ecklonia radiata and 2 common understorey species, Zonaria turneriana and Lobophora variegata. The seaweeds were subjected to 15 d MHWs of different maximum intensities (25° and 28°C) at 2 reduced light levels (~40 and ~10 µmol m ⁻² s ⁻¹ ). Effects on cover of bleached tissue, biomass, maximum quantum yield and pigment concentrations were assessed. Temperature was the main cause of observed changes in seaweed condition, with strong negative effects of the most intense MHW (28°C) especially for tissue bleaching and maximum quantum yield. Low light had a minor effect at 19°C (background temperature) and in the moderate MHW treatment (25°C). However, at extreme temperatures (28°C), low light enhanced the negative effects on virtually all seaweed condition metrics. For all species, the negative effects of the most severe MHW persisted during the recovery period, during which temperatures were returned to background conditions. The compounding effect of high temperature and reduced light highlights the need to assess the interactive nature of multiple stressors with respect to the emerging threat of MHWs to reef ecosystems.

Aim Ocean warming and marine heatwaves are rapidly reconfiguring the composition of seaweed forests—the world's largest coastal vegetated biome. Seaweed forest responses to climate change in remote locations, which constitute the majority of the forest biome, remain however poorly quantified. Here, we examine the temporal stability of the seaweed forests across a global seaweed biodiversity hotspot where several species are predicted to undergo severe range contractions in this century. Location Western south coast of Australia. Methods Seaweed forest canopies were censused at 18 shallow (< 10 m) sheltered reefs between 1997 and 2006 and again between 2021 and 2024 (six sites per location). We also surveyed 24 sites to examine whether temporal changes differed over gradients of wave exposure and depth. Results Seaweed forest canopies across all locations showed surprisingly little change in biomass, cover, stand density and species composition over two decades, with strong spatial structuring across depth and exposure gradients persisting over time. The average thermal affinity of forest canopies (i.e., the community temperature index, CTI) did not track warming, suggesting that factors other than temperature (e.g., wave exposure and depth) are more important drivers of forest stand structure and/or that key thermal thresholds have not yet been crossed. Forests in the location with the most pronounced warming exhibited increased thermal bias over time (total bias of 0.8°C–2.2°C), indicating they were dominated by species with cooler affinities than their local temperatures. Main Conclusions The greater thermal bias in forests at the warmer edge of southern Australia suggests these will be more susceptible to future warming‐related compositional changes than forests in cooler locations. The relative stability we found contrasts with a current context of rapidly changing seaweed forests nationally and globally, highlighting the need to deepen our ecological understanding of the region so that future changes to its unique biodiversity and ecosystem services can be predicted and mitigated.

The hearts of salmonids display remarkable plasticity, adapting to various environmental factors that influence cardiac function and demand. For instance, in response to cold temperature, the salmonid heart undergoes growth and remodeling to counterbalance the reduced contractile function associated with dropping temperatures. Alongside heart size, the distinct pyramidal shape of the wild salmonid heart is essential for optimal cardiac performance, yet the environmental drivers behind this optimal cardiac morphology remain to be fully understood. Intriguingly, farmed salmonids often have rounded, asymmetrical ventricles and misaligned bulbi from an early age. These deformities are noteworthy given that farmed salmon are often not exposed to natural cues, such as a gradual temperature increase and changing day lengths, during critical developmental stages. In this study, we investigated whether natural environmental conditions during early life stages are pivotal for proper cardiac morphology. Atlantic salmon were raised under simulated natural conditions (low temperature with a natural photoperiod; SIMNAT) and compared with those reared under simulated farming conditions (SIMFARM). Our findings reveal that the ventricle shape and bulbus alignment in SIMNAT fish closely resemble those of wild salmon, while functional analyses indicate significant differences between SIMNAT and SIMFARM hearts, suggesting diastolic dysfunction and higher cardiac workload in SIMFARM hearts. These findings highlight the profound influence of environmental factors such as water temperature and photoperiod on the structural development of the salmonid heart, underscoring the importance of early environmental conditions for cardiac health.

The rapid growth of marine industries has emphasized the focus on environmental impacts for all industries, as well as the influence of key environmental parameters on, for instance, offshore wind or aquaculture performance, animal welfare and structural integrity of different constructions. Development of automatized sensors together with efficient communication and information systems will enhance surveillance and monitoring of environmental processes and impact. We have developed a modular Smart Ocean observatory, in this case connected to a large-scale marine aquaculture research facility. The first sensor rigs have been operational since May 2022, transmitting environmental data in near real-time. Key components are Acoustic Doppler Current Profilers (ADCPs) for measuring directional wave and current parameters, and CTDs for redundant measurement of depth, temperature, conductivity and oxygen. Communication is through 4G network or cable. However, a key purpose of the observatory is also to facilitate experiments with acoustic wireless underwater communication, which are ongoing. The aim is to expand the system(s) with demersal independent sensor nodes communicating through an “Internet of Underwater Things (IoUT)”, covering larger areas in the coastal zone, as well as open waters, of benefit to all ocean industries. The observatory also hosts experiments for sensor development, biofouling control and strategies for sensor self-validation and diagnostics. The close interactions between the experiments and the infrastructure development allow a holistic approach towards environmental monitoring across sectors and industries, plus to reduce the carbon footprint of ocean observation. This work is intended to lay a basis for sophisticated use of smart sensors with communication systems in long-term autonomous operation in remote as well as nearshore locations.

Atlantic bluefin tuna (ABFT; Thunnus thynnus) is a highly migratory species. To investigate the migrations and vertical behaviours of ABFT migrating to Nordic waters, we deployed pop-up satellite archival transmitting tags on 25 ABFT off Norway (curved fork length: 228–292 cm). We obtained 16 full-year migrations, which differed between individuals, and physically recovered 13 tags, which provided 4699 days of archival depth and temperature data. ABFT occupied waters from the Arctic Circle to as far south as Cabo Verde, Africa, and occupied depths down to 1190 m and temperatures from 0.5 to 27.8°C. During their annual migrations, ABFT spent, on average, 68 days in Norwegian waters, 65 days in the Newfoundland Basin, 35 days around the Canary Islands and 33 days in the West European Basin. Most ABFT entered the Mediterranean Sea with a mean entry date of 13 May and visited known spawning grounds, staying, on average, 44 days. All ABFT with full-year deployments returned to Norwegian waters. ABFT displayed high site-fidelity and dynamic vertical diving behaviours that varied between hotspots and seasons. These spatiotemporal data provide important ecological knowledge for sustainable management and the conservation of the recently recovered eastern ABFT stock.