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Some biological parameters of the local group of rеd king сrаb in the Dalnezelenetskaya Bay (Barents Sea) are determined in summer 2013. The large-sized mature сrаbs with the carapace width > 100 mm prevailed in scuba diving catches, with equal proportion of females and males. The females with violet eggs dominated among the egg-bearing females. Barren females were not caught. Percentage of the limbs injuries was 62 % that was lower than in the previous year. Total stock of red king crab in the bay was assessed as 4750 individuals. Significant increasing of the large-sized males abundance is noted that corresponds with general growth of their stock in the Barents Sea after the ban on the species fishery within the 12-mile coastal zone in 2011.

Novaya Zemlya Archipelago is the eastern boundary of the Barents Sea. Theplankton of this region have been less intensively studied than thoseof other Arctic areas. This study of the mesozooplankton assemblage of Moller Bay was conducted in August2010. The total mesozooplankton abundance and biomass ranged from 962to 2980 individuals m-3 (mean ± SD: 2263 ± 921 indiv.m-3) and from 12.3 to 456.6 mg dry mass m-3 (mean ± SD:192 ± 170 DM m-3) respectively. Copepods and appendicularians werethe most numerous groups with Oithona similis, Pseudocalanusspp.,Acartiaspp., Calanus glacialis and Oikopleura vanhoeffennibeing the most abundant and frequent. Mesozooplankton abundance tendedto decrease with depth, whereas an inverse pattern was observed for the totalbiomass. Total mesozooplankton biomass was negatively correlated with watertemperature and positively correlated with salinity and chlorophyll aconcentration. Comparison with previous data showed significant interannualvariations in the total zooplankton stock in this region that may be due todifferences in sampling seasons, climatic conditions and the distribution ofpotential food sources (phytoplankton and seabird colonies).

The Barents Sea region is influenced by an increased inflow of warm Atlantic water, which impacts all components of the local ecosystem. Information on the state of benthic communities is required to predict alterations in the food web’s structure and functioning. The spatial distribution of polychaete communities was investigated in relation to environmental conditions at nine stations along the Kola Transect (70°00′–74°00′ N, 33°30′ E) in April 2019. A taxonomically diverse fauna containing 114 taxa was found, with 95 identified at the species level. The fauna was composed predominantly of boreo-Arctic species (63%), followed by boreal (22%) and Arctic species (13%). The polychaete abundance and biomass exhibited considerable variability, ranging from 910 to 3546 ind. m−2 and from 3.4 to 72.7 g m−2, with average values of 1900 ind. m−2 and 18.7 g m−2, respectively. Cluster analysis revealed three distinct polychaete communities differing in dominant species composition, abundance, and biomass. The southern region featured the most abundant community, the middle part exhibited the highest diversity, and the northern area presented the community with the highest biomass. These spatial variations in community structure corresponded closely to the distribution and properties of water masses within the study area. Multivariate analysis identified depth as the primary driver of diversity indices, with higher values observed at shallow water sites. Salinity and water temperature together explained 46% of the variation in abundance, reflecting warming effects and showing positive or negative effects, depending on the taxa. Furthermore, an increase in water temperature had a positive impact on the contribution of boreal species to the total material, while exerting a strong negative effect on the overall community biomass, underscoring the potential of polychaetes in biological indication.

The Iceland scallop from the Barents Sea is a commercially important species with promising aquaculture potential, but information on the biochemical properties of its tissues is limited. Our analysis of the adductor muscle, gonad, and mantle of this bivalve mollusk from coastal waters provided insight into its amino acid composition. Biochemical analysis revealed predominant levels of glycine (11.8, 11.5, and 9.6 mg g−1, respectively) and arginine (11.2, 8.3, and 5.8 mg g−1, respectively). While multivariate comparisons did not reveal significant differences in amino acid composition between the tissues, single comparisons showed significantly higher levels of arginine and leucine in the adductor muscle compared to those of the mantle. The abundant presence of glycine and arginine underscores their importance in maintaining basic physiological processes, consistent with other scallop species. Redundancy analysis identified water depth and scallop gonad index as influential factors shaping the amino acid profile in the adductor muscle. In the case of the mantle, water temperature emerged as the main driver of amino acid content. Our results confirm the richness of essential amino acids in scallop by-products and highlight their potential for human consumption, production of feed ingredients for farmed animals, and nutraceuticals.

The red king crab, Paralithodes camtschaticus, was introduced into the Barents Sea where, after a period of 30 years of adaptation, it has established a new population. This population has been commercially exploited over the past two decades, supporting profitable fisheries in both Russia and Norway. Biochemical studies aimed at assessing fatty acid profiles have been conducted, focusing primarily on the edible parts of red king crabs. Only recently have by-products been included in this research. Capture of female red king crabs is prohibited in Russia but is allowed in Norway. The fatty acids of the egg masses carried by these females have not yet been studied. To fill this knowledge gap, we assayed the fatty acid composition of eggs using gas–liquid chromatography. Our results showed a predominance of polyunsaturated fatty acids, while the concentrations of saturated and monounsaturated fatty acids were similar. Multivariate comparisons showed no significant differences in fatty acid profiles in terms of egg developmental stage (nauplius vs. metanauplius), habitat conditions (soft vs. hard bottoms), female size class, or number of autotomized limbs. However, individual comparisons showed some differences in fatty acids, the most important being the lower content of docosahexaenoic acid in eggs at the metanauplius stage compared to eggs at the nauplius stage, which is likely due to its essential role in the development of red king crab embryos. The total fatty acid content (53.94 mg g−1) was 2–87 times higher in eggs than in other red king crab tissues, confirming the critical role that fatty acids play in maintaining physiological processes during vitellogenesis. The high content of essential fatty acids and an optimal omega-3-to-omega-6 ratio (4.9) suggest that red king crab eggs are a good product for a healthy diet and a valuable source for extracting essential fatty acids.

Sarsia tubulosa (M. Sars, 1835), a colonial hydrozoan of the family Corynidae, is common in the Barents Sea. This study provides new evidence that the species acts as an epibiont of the red king crab Paralithodes camtschaticus, a non-indigenous but remarkably abundant decapod crustacean of immense commercial value in the coastal regions of the sea. This finding adds to the current collection of identified epibionts on the red king crab and highlights the prospect of ongoing symbiotic relationships between the crab and the regional fauna. We also provide photographic evidence of S. tubulosa colonies and a comparative morphological evaluation with another closely related corynid, Coryne hincksi Bonnevie, 1898, previously found on the red king crab. The main differences between these two species are the location of the gonophores (reproductive organs) on the hydranths and the final stage of their development: in the form of free-floating medusae (S. tubulosa) or remaining sessile as sporosacs (C. hincksi). Other distinguishing features include variations in hydranth morphology, number and arrangement of tentacles, and structural development of gonophores.

The species composition of epibiotic communities on red king crab was investigated in Sayda Bay, Russia, during November of 2015 and 2016. The community consisted of 12 species in total. Among epibionts, the barnacle Balanus crenatus was most prevalent (67.0%), while the amphipod Ischyrocerus commensalis was the most frequent symbiont (77.3%). Infestation levels in May–June 2005 and September 2004 were higher, as a larger proportion of small crabs without fouling species were present during those seasons. The lower infestation intensities recorded for other common associated organisms during winter can be attributed to their increased mortality due to unfavorable temperature conditions. The localization of epibionts and symbionts were related to larval settlement patterns of attached species and feeding behavior of mobile species. Monthly growth increments for I. commensalis and B. crenatus were estimated at 2 mm in body length and 1.35 mm in basal diameter, respectively. Size-at-age data for epibionts can aid in the age determination of large male crabs that may skip an annual molt.

The continental shelf of the northeastern Barents Sea is presently experiencing a weak influx of Atlantic water from the west. In recent times, warming in Arctic regions has led to an increase in extended ice-free periods in this area, instead of significantly elevating water temperatures. The implications of this phenomenon on the structure and functioning of benthic communities were investigated during the autumn of 2019 within the Makarov Strait, located in the southwestern part of the St. Anna Trough. The macrozoobenthic communities exhibited a clear connection with the duration of ice-free periods. This variable influenced a vertical carbon flux, which subsequently served as the primary predictor for faunal abundance and diversity, as demonstrated by redundancy and correlation analyses. Two faunal groups were identified, corresponding to short and long open-water periods. Both groups had similar alpha diversity (65 ± 6 and 61 ± 9 species per station) and biomasses (39 ± 13 and 47 ± 13 g m−2) but displayed differing abundances (1140 ± 100 vs. 4070 ± 790 ind. m−2) and other diversity indices. We observed a decline in the proportion of polychaetes, accompanied by an increase in the proportion and diversity of bivalves, as well as a rise in the abundance of infaunal species, sub-surface deposit feeders, and mobile suspension feeders, in response to the increasing vertical carbon flux. The potential increase in anthropogenic pressures related to oil development in the northeastern Barents Sea highlights the importance of our study for conservation and monitoring efforts in the region.

The use of biological objects in monitoring the state of the environment and the changes caused by the impact of environmental pollution on marine and fresh waters is a promising tool due to a lower cost in comparison to traditional monitoring and the ability to receive immediate information about the ecosystem status. In this review, we summarize the biological information about shellfish biomonitors and the results of studies focused on the development and use of the bioindicator species in early warning systems in Russia. Since the mid-1980s, Russian specialists have developed online biomonitoring systems; as in the rest of world, there are two main approaches that are currently applied to study the physiological status of potential biosensor shellfish species and to monitor freshwater and marine systems: valvometry (registration of gaping activity in bivalve mollusks) and photoplethysmography (registration of cardiac activity in mollusks and crustaceans). Valve movement responses to stressors such as abnormal conditions and pollutants include the closure of shell valves for a long period, decrease in the average distance between valves, rapid shell opening, and higher closing frequency. Cardiac activity reactions of shellfish to stress factors include rapid increases in heart rate and stress index, higher variability in heart rate than under normal conditions, and longer periods required for heart rate recovery after stress. The most common bioindicators used to monitor environmental disturbances in marine ecosystems are blue mussels, Iceland scallops, and red king crabs in cold-water habitats and Black Sea mussels in warmer waters as well as freshwater mussels and crayfish in fresh waters.

We assayed the fatty acid composition of muscles of the northern pike Esox lucius Linnaeus, 1758 inhabiting the Gyda River, Siberia, Russia using gas-liquid chromatography. Of 43 fatty acids identified in the pike samples, 23 fatty acids accounted for 99.3% of the total content. The most abundant saturated fatty acids (SFA, 31.6%) were palmitic (C16:0, 20.0%) and stearic (C18:0, 7.3%) acids. Among monounsaturated fatty acids (MUFA, 15.1%), oleic acid (C18:1n9, 10.2%) and palmitoleic acid (C16:1, 4.1%) demonstrated the highest levels. The most represented polyunsaturated fatty acids (PUFA, 53.3%) were arachidonic acid (C20:4n-6, 7.6%), eicosapentaenoic acid (EPA, C20:5n-3, 7.3%), and docosahexaenoic acid (DHA, C22:6n-3, 26.3%). The fatty acid profile of specimens from the Gyda River was different in comparison to profiles found in other pike populations, most likely due to different diets. Pike flesh has good nutrition quality in terms of a low n-6/n-3 ratio (0.36), low atherogenic (0.39), and thrombogenic (0.22) indices, and a high ratio of hypocholesterolemic to hypercholesterolemic fatty acids (2.83), and this species can be recommended as a replacement or alternative to other fish sources in traditional diets.

Red king crab (Paralithodes camtschaticus) is a large shelf species native to the Pacific Ocean. Due to its high commercial value, this species was introduced into the Barents Sea, where it has formed a new population that now supports a stable commercial fishery. Information on fatty acid profiles in different tissues of the Barents Sea P. camtschaticus is scarce. For this reason, the gonads of red king crabs collected at a coastal site in the Barents Sea during the summer were analyzed for fatty acid composition by gas-liquid chromatography. The proportions of total saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids in the ovaries of P. camtschaticus were 25.9 ± 2.0%, 22.5 ± 2.3%, and 51.6 ± 2.5%, respectively; in the testes, these levels accounted for 35.1 ± 5.7%, 19.1 ± 2.0%, and 45.8 ± 4.5%, respectively. Fatty acid profiles were similar in larger and smaller red king crabs and crabs with old and new shells. Concentrations of fatty acids were higher in ovaries compared to testes, reflecting higher reproductive efforts in female red king crabs. High levels of docosahexaenoic and eicosapentaenoic fatty acids detected in the ovaries of red king crabs from the Barents Sea indicate that these gonads can be a good alternative source for these fatty acids in the human diet and/or for extracting important fatty acids for use in the medical and pharmaceutical industries.

To provide a baseline description of copepod assemblages in the Pechora Sea, an estuarine area with great economical and ecological importance, we conducted a survey during the summer season. A total of 24 copepod taxa were identified in the study, with Acartia longiremis, Calanus finmarchicus, Centropages hamatus, Copepoda nauplii, Eurytemora affinis, Oithona similis, Pseudocalanus spp., and Temora longicornis being the most numerous. The high diversity (Shannon index = 2.51 ± 0.06), density (18,720 ± 3376 individuals m−3) and biomass (89 ± 18 mg dry mass m−3) of copepods were revealed. Populations of common small copepod taxa were dominated by the young stages, indicating spawning, while older copepodites prevailed among medium- and large-sized species, showing that their reproduction occurred before our survey. Cluster analysis indicated three groups of stations that mainly differed in the abundance of particular species. There were clear associations between copepod assemblages and environmental variables. Statistical analyses showed significant correlations between copepod abundance and water temperature or sampling depth, while other factors had a lesser influence. Our results suggest a strong effect of local circulation and currents on the spatial pattern of the copepod assemblages in the study area. This study may be useful for future biomonitoring in the south-eastern Barents Sea.

Coryne hincksi Bonnevie, 1898 (Cnidaria, Hydrozoa) is a rare corynid hydrozoan that was first found in the coastal Barents Sea on the surface of other hydrozoan species and on the body of spider crabs in 1913. After the introduction of red king crabs into the Barents Sea in the 1960s and their range expansion and population growth, colonies of C. hincksi were registered on this host as well. In this paper, we update a list of C. hincksi records on red king crabs and present a detailed description. Also, for the first time, we provide quality photographs of a living colony of this species. Despite relatively low prevalence rates (1.4–3.2% in certain years), currently in the Barents Sea, C. hincksi occurs on crustaceans thus exhibiting a predominantly symbiotic lifestyle.

The biodiversity, infestation patterns, and spatial distribution of organisms living in association with the introduced red king crab Paralithodes camtschaticus were studied in Dalnezelenetskaya Bay, southern Barents Sea, in 2009–20013 to update a list of species, reveal long-term changes in this epibiotic community, and identify key factors affecting the prevalence and intensity of infestation. A total of 90 associated species were found throughout the study period, or twice as many as in 2004–2008, reflecting relatively low similarity between these periods. Half of the species were found on one to three crabs only. Copepods had the maximum diversity (23 species). For the first time, macroalgae were found as epibionts of red king crabs. Overall, the highest prevalences were found for the amphipod Ischyrocerus commensalis (74.2%), the copepods Tisbe furcata (57.7%) and Harpacticus uniremis (29.4%), the amphipod Ischyrocerus anguipes (27.3%), and the fish leech Johanssonia arctica (16.2%). Redundancy analysis showed that host size was the most important driver of species abundance, followed by shell condition, water temperatures in the coastal Barents Sea in May and June, and sex. These factors, coupled with the range expansion of red king crabs and climate changes in the Barents Sea, provide good explanations for the differences between the 2004–2008 and 2009–2013 fouling communities. Distribution patterns for common taxa on the host reflect larval settlement patterns and/or relationships between the host and associated species. These results expand our knowledge of infestation patterns for the invasive red king crab and provide a reference point for further monitoring.

In this study, nematodes were first reported in the amphipods, Ischyrocerus commensalis, collected from the introduced and commercially important red king crabs, Paralithodes camtschaticus, in the coastal Barents Sea in July 2022. Commensal amphipods were registered on all red king crabs captured (n = 70, prevalence 100%). Further laboratory analysis revealed that 11 out of 467 amphipod individuals (prevalence 2.4%) harbored single third-stage larvae of Hysterothylacium sp. l. (Nematoda: Anisakidae). The nematode larvae ranged from 0.63 to 6.10 mm in body length. Due to the low prevalence of nematodes and lower vulnerability of the host amphipods to fish predators, negative effects on the Barents Sea ecosystem through the range expansion of crab-associated amphipods and their parasites are unlikely.

Sea cucumbers are a popular luxury and delicacy food items in Asian markets. These echinoderms possess a wide range of bioactive substances that can be used to produce pharmaceutical products. Recent depletion of natural populations of sea cucumbers requires involving new objects both in commercial harvesting and aquaculture. The northern sea cucumber Cucumaria frondosa is the most abundant sea cucumber in the Barents Sea. In this paper, we summarized literature data on the biology of this polar species to evaluate its fishery and aquaculture potential in the area. This eurythermic sea cucumber is typically occurs at 20–100 m depth. Cucumaria mainly colonize rocky or pebbly bottoms. Their main food items are detritus, pellets, phytoplankton, and small planktonic crustaceans. Spawning is registered in February–May. The age of commercial specimens (body length 25–30 cm, wet weight 300–350 g) is 10 years. The most abundant stocks of C. frondosa are registered in the central and south-eastern parts of the sea. Due to the low growth rate of Cucumaria the most appropriate cultivation method for these holothurians is a combination of larval culture and sea ranching. Coastal sites of the Barents Sea merit all the criteria for sea ranching of Cucumaria, but the development of their extensive aquaculture requires significant investments with long pay-back periods.

In this paper, we analyzed the diversity and structure of helminth communities of 12 common fish species from the coastal zone of Crimea. A total of 53 helminth species were found. The total number of parasite species per host fish ranged from 3 to 18. Species richness at the infracommunity and component community levels were from 1.4–4.2 to 1.7–7, respectively. The Brillouin index for the infracommunites was 0.1–1, while the Shannon index for the component communities was 0.3–1.2. Component communities demonstrated a bi- or tri-modal distribution of the parasite prevalence and positive correlations between the prevalence and log-transformed abundance indices, thus following the “core–satellite” conception. Overall, the prevalence and abundance index of the dominant parasite in the component communities ranged from 18 to 80% and from 0.6 to 61.5 ind. per fish, respectively. The structure of the helminth component communities demonstrated good accordance with the nestedness mode where the rarest species occurred in the most diverse infracommunities, while the poorest infracommunities were composed of a few dominating species. More than two-thirds of the studied helminth species had an aggregated distribution indicating well-structured and developed communities. Our data provide a basis for further research and may be used for fish resource monitoring and management.

We studied the spatial patterns of the planktonic ecosystems at two Arctic sites strongly affected by Atlantic Inflow (FS, the Fram Strait; and BS, the Barents Sea). A high degree of similarity in the bacterial abundance (mean: 3.1 × 105 cells mL−1 in FS vs. 3.5 × 105 cells mL−1 in BS) was found, while other plankton characteristics were different. Bacterial biomass reached a maximum in BS (3.2–7.9 mg C m−3), while viral abundances tended to be higher in FS (2.0–5.7 × 106 particles mL−1). Larger bacterial cells were found in BS, suggesting the presence of different bacterial populations at both locations. The virus-to-bacteria ratio was significantly higher in FS than in BS (13.5 vs. 4.7). Chlorophyll a concentration was extremely low (−3). The highest zooplankton abundance was in the surface layer (919 individuals m−3 in FS vs. 602 ind. m−3 in BS). Zooplankton biomass strongly varied (1–39 mg C m−3), with the maximum in BS. High proportions of boreal taxa in the total zooplankton abundance indicate the Atlantification of pelagic ecosystems in the Arctic. Plankton indicators are correlated with temperature, salinity, and sampling depth. Strong intercorrelations were found between major plankton groups, suggesting tight links in the studied plankton ecosystems.

Despite significant research efforts focused on benthic assemblages in West Spitsbergen, there is a lack of knowledge regarding the shallow water bryozoan communities in Grønfjorden, a glacier fjord belonging to the Isfjorden system, Norway. Here, we studied species composition, richness, distribution, and biomass of bryozoans in the intertidal and upper subtidal zones of Grønfjorden in summer. We found 62 bryozoan species, among which Celleporella hyalina (Linnaeus, 1767), Harmeria scutulata (Busk, 1855), and Tegella arctica (d’Orbigny, 1853) were most prevalent while the highest contributions to the total biomass were registered for Eucratea loricata (d’Orbigny, 1853), Tricellaria gracilis (Van Beneden, 1848), Turbicellepora incrassata (Lamarck, 1816), and Tricellaria ternata (Ellis and Solander, 1786). Alpha-diversity varied from 1 to 50 averaging 15.1 ± 2.6 species. Bryozoan biomass ranged from 0.008 to 10.758 g m−2 with a mean value of 2.67 g m−2 being lower than in the central and northern parts of the Barents Sea. For the first time, we registered the presence of the circumpolar bryozoan Amathia arctica in Svalbard waters probably as a result of stronger advection of Atlantic water into the fjord. Cluster analysis revealed two groups, mainly composed of stations in colder and warmer waters. A relatively high proportion of outlying stations reflected habitat heterogeneity in Grønfjorden. Redundancy analysis indicated that bryozoan diversity and biomass were strongly negatively associated with temperature. A positive relationship was found between bryozoan biomass and the proportional contribution of macrophytes to a pool of substrates. Our study provides a reference point for further monitoring of changing marine ecosystems at high latitudes.

The Arctic climate strongly affects phytoplankton production and biomass through several mechanisms, including warming, sea ice retreat, and global atmospheric processes. In order to detect the climatic changes in phytoplankton biomass, long-term variability of chlorophyll a (Chl-a) was estimated in situ with the changes in the surface sea temperature (SST) and salinity (SSS) in the Barents Sea and adjacent waters during the period of 1984–2021. Spatial differences were detected in SST, SSS, and Chl-a. Chl-a increased parallel to SST in the summer-autumn and spring periods, respectively. Chl-a peaks were found near the ice edge and frontal zones in the spring season, while the highest measures were observed in the coastal regions during the summer seasons. SST and Chl-a demonstrated increasing trends with greater values during 2010–2020. Generalized additive models (GAMs) revealed that SST and Chl-a were positively related with year. Climatic and oceanographic variables explained significant proportions of the Chl-a fluctuations, with six predictors (SST, annual North Atlantic Oscillation index, temperature/salinity anomalies at the Kola Section, and sea ice extent in April and September) being the most important. GAMs showed close associations between increasing Chl-a and a decline in sea ice extent and rising water temperature. Our data may be useful for monitoring the Arctic regions during the era of global changes and provide a basis for future research on factors driving phytoplankton assemblages and primary productivity in the Barents Sea.

Kola Bay is the most developed coastal area in the Russian part of the Barents Sea, but despite a long history of research, information about the local shallow-water benthic communities is lacking. For this reason, in this fjord area, we investigated the soft-bottom zoobenthos to determine its distribution and the factors influencing its abundance, biomass, and diversity. An analysis of 24 samples collected by divers at eight stations located at 7–8 and 10–15 m depths revealed 127 benthic taxa with an average abundance and biomass of 12,190 ± 4740 ind. m−2 and 30 ± 8 g m−2, respectively. The most severe abiotic conditions (high rates of sedimentation and eutrophication) were found at the head of the bay while the highest densities of predator red king crabs were registered in the middle part. The total benthic abundance and biomass, as well as the abundances of infauna, mobile taxa, subsurface deposit feeders, and surface deposit feeders, decreased towards the central part of the bay, reflecting gradients in the environmental conditions. In the inner part of the bay, we registered two communities: Cossura pygodactylata + Ciliatocardium ciliatum and Arctica islandica + Laonice cirrata, while the benthos of the middle part was less structured. Redundancy analysis indicated that the faunal abundances were influenced mainly by predator density (negative association) and the organic matter content (positive association). The total benthic biomass was negatively linked to water temperature due to the predominance of cold-water species in the area and a close positive association of this factor with crab abundance. In contrast, the highest diversity was registered at the warmer sites, which may have been a reflection of the borealization process in the Arctic. Our results contribute towards the proper management and conservation of the local benthic ecosystem and provide reference data for future monitoring programs and coastal management guidelines.

We examined the effects of environmental factors (water temperature, the North Atlantic Oscillation winter index – NAOw, and cod biomass) on the abundance (population number), biomass and mean individual weight of juvenile red king crab (Paralithodes camtschaticus) at a typical coastal site of the Barents Sea, Dalnezelenetskaya Bay, a place of red king crab introduction. Current-year abundance and stock data for 3–5-year-old crabs were positively related to water temperature in September and October. The biomass of crabs at age 0–2 year was positively correlated with lag 1 water temperature in August, while the abundance of age 0–5 year was positively correlated to the NAOw indicating more favorable habitat conditions in warmer periods. The abundance of crabs at age 3–5 year was negatively correlated to December temperature and mean water temperature and temperature anomaly with a 1-year lag. These temperature relationships, together with negative correlations between stock indices of crabs and cod (Gadus morhua) and positive relationships between mean crab weight and cod biomass, suggests that the fish predation, which is higher in warmer years, has a more important role in mortality of 3–5 year crabs than 0–2 year crabs. Our findings may be useful for modeling recruitment processes and management of red king crab in the Barents Sea.

Only a few studies have reported the presence and levels of thyroid hormones in invertebrates. At the same time, the administration of these hormones has been shown to be a profitable method for inducing growth in crustaceans. Knowledge of thyroid hormone concentrations is required to involve this approach in crustacean aquaculture. For this reason, we examined hemolymph samples of the invasive red king crab Paralithodes camtschaticus from the Barents Sea population for the levels of triiodothyronine (T3) and thyroxine (T4). Radioimmunoassays indicated that T3 ranged from 0.26 to 1.55 μg dL–1, whereas T4 varied from 52 to 203 μg dL–1. Adult crabs demonstrated higher levels of T3 than juveniles, while juvenile crabs had higher levels of T4 in comparison to larger conspecifics. The thyroxine levels were consistent throughout the study period. In contrast, significant seasonal variations were found for T3. In immature crabs, the maximum concentration was found in October, whereas in adult crabs, the highest level of T3 was registered in August. Most likely, these results are explained by changes in physiological conditions of the crabs associated with their molting calendar and migration activity. Our data may have important implications for aquaculture of Paralithodes camtschaticus in the Barents Sea.

Mesozooplankton play an important role in Arctic shelf ecosystems as a trophic link and a key food source for many larval fish species. The distribution of mesozooplankton in the eastern Barents Sea was studied along a 500 nautical mile-long transect in May 2016 during the spring bloom. Mesozooplankton were sampled using a Juday net hauled from the surface to the bottom at 12 stations. We found good correspondence between the distribution of water masses and mesozooplankton assemblages. Mesozooplankton abundance (mean 73·103 individuals m−2) in Novaya Zemlya coastal water was dominated by Copepoda ova and nauplii, Thyssanoessa spp. nauplii and Oithona similis. Parasagitta elegans and Calanus finmarchicus comprised most of the total mesozooplankton biomass (mean 0.9 g dry mass m−2) in that water mass. A second assemblage (mean abundance 171·103 individuals m−2) was associated with the colder Barents Sea water, with Oithona similis, Copepoda nauplii, Fritillaria borealis and Cirripedia nauplii being the most numerous. In that water mass, C. finmarchicus, Metridia longa, Cirripedia nauplii and Calanus glacialis contributed most to the total biomass (mean 3 g dry mass m−2). The dominance of young stages of Copepoda and a high proportion of meroplankton were typical of spring mesozooplankton assemblages. The spatial distribution of mesozooplankton abundance and biomass was strongly correlated with latitude, longitude and chlorophyll a concentration, which together explained 10% of the total variance in mesozooplankton density. The present investigation is a baseline study for the assessment of the spring mesozooplankton assemblage in the eastern Barents Sea, and for an evaluation of the possible impact of future environmental changes on the Arctic shelf marine ecosystem.

In the marine environment, bacteria and viruses play a significant role in carbon fluxes, remineralization processes, and the infection of various organisms. We performed a survey in the northeastern Barents Sea, a region adjacent to the Arctic Ocean, to investigate spatial patterns of microbial plankton, after the main productive period, in October 2020. Two main water masses occurred in the study region—colder Arctic Water and warmer Barents Sea Water, representing transformed Atlantic Water. Multivariate analyses detected patchiness in the horizontal distribution of bacteria and viruses, and their abundances showed no clear association with the water masses. There was an obvious vertical pattern in microbial concentration, with the highest estimates in the upper layers. Surface viral and bacterial abundance varied in a wide range (2.20 × 105–10.7 × 105 cells·mL−1 and 0.86 × 106–14.98 × 106 particles·mL−1, respectively) and were correlated with each other. Bacterioplankton was dominated by small-sized cells (3), and the average volume of bacterial cells tended to increase toward the seafloor. The ratio of viral to bacterial abundance (VBR) was 11 ± 1 and did not differ between water masses and depth layers. VBR were higher, compared to summer values, suggesting a strong impact of viruses on bacterioplankton, after the main productive season. Redundancy and correlation analyses showed that inorganic nutrients (nitrate and phosphate) and organic carbon from zooplankton were most responsible for the total variability in the microbial parameters. Water temperature and salinity, also, had a measurable impact, but their influence was lower. Bacterial abundance was lower than in other seasons and regions of the Barents Sea, while viral abundance was comparable, suggesting a stronger viral impact on Arctic marine bacteria in the autumn season.

The presence of vertebrate-related steroid sex hormones has been reported in both freshwater and marine crustaceans. However, despite the commercial importance of king crabs, many aspects of their endocrinology are still unknown. For this reason, we examined hemolymph samples of the red king crab Paralithodes camtschaticus from the Barents Sea population for the presence of testosterone and 17β-estradiol using radioimmunoassay. The mean testosterone concentration was 0.46 ± 0.04 (range 0.08–1.39) ng mL–1, whereas the mean 17β-estradiol concentration was 1248.9 ± 91.4 (range 217.7–4100.1) pg mL–1. In general, the levels of 17β-estradiol and testosterone in red king crabs were higher than reported for the hemolymph of amphipods, crabs, and shrimps from warm and temperate waters, probably because the king crabs analyzed were larger and heavier than the other crustaceans. The concentrations of sex steroids did not differ significantly between males and females and between immature and mature red king crabs. Seasonal variations in the level of testosterone with the maximum value in the spawning period (May) indicate a potential role of the sex hormones in the maturation and reproduction processes of red king crab. Taking into account the slow growth rate in P. camtschaticus, our data could be useful not only for further physiological studies but also for the development of reliable techniques for red king crab aquaculture.

There is a lack of knowledge regarding the modern status of intertidal bryozoan communities in the coastal Barents Sea. Here, we studied species composition, richness, and biomass of bryozoans in Yarnyshnaya and Dalnezelenetskaya Bays, both located in the eastern part of the Kola Peninsula (Barents Sea), in summer. Species composition and biodiversity were consistent with previous research but the record of the ctenostome bryozoan Walkeriauva is the first for the region indicating eastward range expansion of this species associated with climate forcing in the Arctic. Mean biomass was relatively low accounting for 2.25 ± 0.95 g·m−2. The most common species were Eucratea loricata, Harmeria scutulata, Crisia eburnea, and Cribrilina cryptooecium averaging 96% of the total biomass. Cluster analysis delineated two distinct groups of stations, one with true marine conditions and another with brackish water conditions. Redundancy analysis revealed that bryozoan diversity was strongly associated with salinity fluctuations being extremely low at brackish water sites. In contrast, water temperature was found to be a significant contributor to biomass with the lowest values found at warmer waters probably owing to the predominance of Boreo-Arctic species which prefer lower-temperatures. Other hydrological variables (dissolved organic matter, silicates, and oxygen) were consistent with usual summer values and had no significant effects on the bryozoan assemblages. Our study provides a reference point for further biodiversity studies in changing marine ecosystems of the Arctic region.

During diving surveys for a Russian research project that monitored introduced species, red king crabs (Paralithodes camtschaticus) were collected at a coastal site of the Barents Sea to study the structure and dynamics of this species. Sampling of the organisms colonizing the crabs was part of this research project. For the first time, the presence of relatively large specimens of the common starfish Asterias rubens as epibionts of P. camtschaticus was observed in July 2010, 2018, and 2019. In 2010 and 2019, we also found three other echinoderm species (the Atlantic sea cucumber Cucumaria frondosa, the green sea urchin Strongylocentrotus droebachiensis, and the brittle star Ophiura sarsii). These findings add to the current list of associated species on king crabs not only in the Barents Sea but also in native areas of this host. Red king crabs have been documented as predators for these echinoderm species, and our records show additional possible interactions between king crabs and echinoderms in this region. More likely, the epibiotic lifestyle allows these echinoderms to avoid predation from red king crabs. There are no potential disadvantages derived by red king crabs through their relationships with the echinoderm epibionts due to low occurrences of these associations. We suggest no negative effects for the local red king crab population and populations of other commercial species in the Barents Sea.