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In this study, 110 male and female blue crabs Callinectes sapidus Rathbun, 1896 were collected from the coastal waters of Morocco, Africa using baited traps between February and December 2021. Here, we report the first occurrence of the species in the ports of Tangier and Tangier Med (the Strait of Gibraltar). These additional records support recent work by others of hundreds of blue crabs (mostly females) collected from different locations along the Moroccan coastline. Combined, these records represent the distribution of the species throughout northwestern Africa. These new locations may be indicative of natural expansion from a previously introduced population in the Tangier Med, which is the largest port in Africa. Additional population genetics are needed to further elucidate questions surrounding the continued spread of C. sapidus along the northwestern African coast. [ABSTRACT FROM AUTHOR]

The study aims to evaluate the shares of primary waters (Atlantic, river, meltwater, and sea water withdrawn for ice formation) in the resulting water masses in the eastern part of the Barents Sea at the end of the hydrological winter. Moreover, the study compares the outcomes achieved by using salinity-δ18O and salinity-δ2H values. The study was based on the data on water temperature and salinity and δ18O and δ2Н stable isotopes values. We implemented field studies in March and April 2021 at the Dalnie Zelentsy research vessel, providing the only known and available source of data on δ18O and δ2Н for the eastern part of the Barents Sea between 70⁰ N and 79⁰ N at the end of the hydrological winter. The results allow for estimating the shares of the primary waters, namely Atlantic, river, meltwater, and sea water, withdrawn for ice formation in the sea water during this period of the year in various water masses meltwater. Moreover, they allow for estimating the influence of each of the primary waters on the salinity of the resulting water masses. However, when we calculate the average Atlantic and ice water shares using the δ2H isotopic parameter, they are somewhat higher than those calculated using δ18O. Conversely, the river water share is somewhat lower. A 0.36 psμ (0.34–0.51 psμ) change (decrease) in salinity in the Atlantic water mass is due to mixing with river waters and 0.04 psμ (−0.05 to 0.10 psμ) with mixing with meltwater. In the Barents Sea winter water mass these values are 0.63 (0.53–0.71 psμ) and 0.31 (0.27–0.42 psμ), respectively. In the water mass called 'Surface waters of the Arctic seas, winter', the processes of ice formation prevail over the processes of ice melting. The average decrease in salinity due to the content of river waters alone could be 0.66 psμ (0.59–0.74 psμ). However, it is only 0.46 psμ (0.41–0.57 psμ) due to salinisation during ice formation. The quantities of meltwater volumes and volumes of water withdrawn for ice formation serve as specific characteristics of «memory», describing the ice formation/ice melting processes. • The study aims to evaluate the shares of primary waters in the sea water in the eastern part of the Barents Sea. • The study was based on the data on water temperature and salinity and δ18O and δ2Н stable isotopes values. • Results enabled us to trace the genesis of the three water masses in this part of the Barents Sea. • The results demonstrate that primary waters calculation based on δ18O–salinity and δ2H–salinity not substantial. [ABSTRACT FROM AUTHOR]

The present study reports the occurrence of several specimens of the African caridean shrimp Lysmata uncicornis Holthuis & Maurin, 1952 in the NE Atlantic coast (Gulf of Cadiz, Spain and the Algarve, Portugal). Lysmata uncicornis is a poorly studied species that has been originally described from the Atlantic waters of Morocco, where it was first collected inside the port of Casablanca in a rocky bottom at 4–5-m depth. While no scientific publication has previously reported this species outside the waters of Morocco, several specimens have been collected in the coastal waters of the Gulf of Cadiz and the Algarve. This species may be able to expand successfully northward along European waters, probably favoured by global warming. It is possible that this expansion may also be enhanced through the marine aquarium trade. Recently, Lysmata arvoredensis Giraldes, Macedo, Brandão, Baeza & Freire, 2018 a new species of shrimp from the south coast of Brazil was described. However, morphological and genetic comparisons revealed no differences between L. uncicornis and L. arvoredensis. Therefore, L. arvoredensis should be considered as a junior synonym of L. uncicornis. While L. uncicornis may well be an amphi-Atlantic species, such as L. grabhami (Gordon, 1935), for now, the introduction of L. uncicornis in Brazilian waters cannot be ruled out. [ABSTRACT FROM AUTHOR]

• Drivers of blue, fin and sei whales' habitat use were determined in NW Spain. • Whale distribution was linked to upwelling events influenced by coastal orientation. • Fisheries pressure rises susceptibility of endangered rorquals to climate change. • This study provides crucial information to devise future adaptation measures. Recent studies show that human impacts on marine ecosystems are threatening marine biodiversity. A greater emphasis on predicting how predators might respond to changes in the marine environment is needed because the effects of human activities are spatially heterogeneous. Here we analyse rorqual whales distribution data in a highly impacted upwelling region (North-western Iberian coast, Spain). Using a multi-model inference approach this study assesses the habitat drivers of the fine-scale distribution of three endangered whale species (blue, fin and sei whales) as a way to better understand how rorqual whales might respond to human-induced changes in the coastal ecosystem. The unequal use of available habitat, concentrated at the edge of the continental slope (200 m depth and strong bottom slope gradient) in areas with a south-easterly coastal orientation, showed that rorqual whales presented a fine-scale pattern of habitat selection in response to prey availability. Rorqual whales' distribution is affected by the coastal upwelling regime of the Iberian Peninsula, which is known to be under impact of climate change. Therefore, responses of rorqual whales to upwelling changes might be manifested at the population level such as shifts in abundance and distribution. This information contributes to extend the scant information available about the presence of these species in the North-east Atlantic. Our findings provide management agencies with an opportunity to devise and implement adequate adaptation measures which may ameliorate adverse effects critical for the conservation of rorquals in a changing climate. [ABSTRACT FROM AUTHOR]

In this study 129I and 236U concentrations in seawater samples collected onboard R/V Polarstern during the PS100 expedition in the Fram Strait in 2016 are presented. The overall aim of the study was to investigate the distribution of these long‐lived radionuclides along the transect located at 79°N. The combination of both radionuclides was used for the first time in the Fram Strait to trace ocean circulation pathways of Atlantic waters. Results show that both 129I and 236U concentrations as well as 236U/238U ratios are about two times higher (> 600 × 107 at kg(−1), > 20 × 106 at kg(−1), and 2.8 × 10−9, respectively) in the cold and fresh outflowing surface waters from the Arctic Ocean (Polar Surface Water, PSW) compared to inflowing Atlantic origin waters (300 × 107 at kg(−1)129I, 12 × 106 at kg(−1)236U, and 1.4 × 10−9 236U/238U). A comparison with the different 129I and 236U input functions for the Atlantic branches entering the Arctic Ocean reveals that the middepth Atlantic origin waters outflowing the Arctic Ocean show more influence of the Barents Sea Branch Water than the Fram Strait Branch Water. The high radionuclide concentrations observed in the PSW indicate substantial influence of the Norwegian Coastal Current. This current carries a significantly larger proportion of 129I and 236U releases from European reprocessing plants than the aforementioned Atlantic branches. We estimate surface water transit times from the northern Norwegian Coast through the Arctic to the PSW of 12–19 years, less than for the middepth Barents Sea Branch Water (16–23 years). Plain Language Summary: In this work we reconstructed the circulation of Atlantic waters in‐ and outflowing the Arctic Ocean through one of the main gates connecting these two oceans: the Fram Strait, located between Greenland and Svalbard. We measured the long‐lived artificial radionuclides 129I and 236U to track the different water masses. These two radionuclides are present in the marine environment after the nuclear weapon tests (1950s‐1960s) and from two European nuclear reprocessing plants (from 1960's until today). In particular the input of 129I from these two reprocessing plants changed over time and can therefore also be used to estimate travel times of water masses. We collected 140 seawater samples at various depths from the Fram Strait in summer 2016. Our results depict higher concentrations of 129I and 236U in the waters outflowing the Arctic Ocean compared to those entering the polar region through the Fram Strait. The combination of 129I and 236U allowed us to distinguish between three main branches of Atlantic origin waters outflowing the Arctic Ocean having different travel times through the Arctic Ocean. We proved that 129I and 236U have a great potential as tracers to understand ocean circulation and travel times in the Arctic and North Atlantic oceans. Key Points: In 2016, inflowing Atlantic waters to the Arctic Ocean have lower 129I and 236U concentrations than outflowing Arctic watersHigh 129I and 236U in outflowing surface Arctic waters indicate substantial influence from the Norwegian Coastal CurrentCombination of 129I and 236U allowed for an estimation of transit times for Atlantic branches through the Arctic Ocean to the Fram Strait [ABSTRACT FROM AUTHOR]

The paper presents results of numerical simulation of variability of the sea ice area and water circulation in the Arctic Ocean performed with use of the atmosphere reanalysis data for the period from middle of the last century to the present time. The model results reflect the ocean responses to changes of the atmosphere circulation regimes that manifests in changes of trajectories of waters coming into the Arctic Ocean from the Pacific and Atlantic oceans. The model results show influence of the Pacific and Atlantic waters on distribution and thickness of the Arctic ice.

This study presents the data on 129I and 236U concentrations in seawater samples and sea ice cores obtained during two expeditions to the Arctic Ocean that took place onboard R/V Polarstern (PS94) and R/V Lance (N‐ICE2015) in summer 2015. Carbon‐14 was also measured in the deep water samples from the Nansen, Amundsen, and Makarov Basins. The main goal was to investigate the distribution of 129I and 236U in a transect from the Norwegian Coast to the Makarov Basin to fully exploit the potential of combining 129I and 236U as a dual tracer to track Atlantic waters throughout the Arctic Ocean. The use of the 129I/236U and 236U/238U atom ratios allowed identifying a third Atlantic branch that enters the Arctic Ocean (the Arctic Shelf Break Branch) following the Norwegian Coastal Current that carries a larger proportion of the European reprocessing plants signal compared to Fram Strait Branch Water and Barents Sea Branch Water. The combination of 129I and 236U also allowed quantifying the different proportions of the La Hague stream, the Scottish stream, and Atlantic waters forming the three Atlantic branches of the Arctic Ocean Boundary Current. The results show that the 129I/236U atom ratio can now be used to identify the different Atlantic branches entering the Arctic Ocean. New input functions for 129I, 236U, and 129I/236U have also been described for each branch, which can be further used for calculation of transit time distributions of Atlantic waters. Plain Language Summary: In this work we present results of artificial radionuclides that were measured in seawater samples collected in the Arctic Ocean. We measured the long‐lived artificial radionuclides 129I and 236U to track the different water masses. These two radionuclides are present in the marine environment after the nuclear weapon tests (1950s–1960s) and from two European nuclear reprocessing plants (from 1960s until today) located in France and United Kingdom. In particular, the input of 129I from these two reprocessing plants changed over time and can therefore also be used to estimate travel times of water masses. In this study, we collected about 150 seawater samples from 20 different stations in the Arctic Ocean in summer 2015, onboard the R/V Polarstern. Our results reveal that the mixing ratios of the two reprocessing plant effluents are different for the Fram Strait Branch and the Barents Sea Branch, contrasting with previous studies. The 129I/236U was used as a new tool to identify the characteristics of these two Atlantic branches entering the Arctic Ocean and even prove the existance of a more surface branch (Arctic Shelf Break Branch) carrying a significant proportion of reprocessing plant‐derived radionuclides. Key Points: The 129I/236U ratio can be used to identify Fram Strait Branch Waters (FSBW) from Barents Sea Branch Waters (BSBW) in the central Arctic OceanThe high 129I/236U atom ratio (> 400) allowed identifying a third branch of Atlantic Waters entering the Arctic OceanNew input functions of 129I, 236U, and 129I/236U for the three Atlantic branches entering into the Arctic Ocean are defined [ABSTRACT FROM AUTHOR]

Relationships between the zooplankton community and various environmental factors (salinity, temperature, sampling depth and bottom depth) were established in the European Arctic Marginal Ice Zone (MIZ) using multivariate statistics. Three main zooplankton communities were identified: an Atlantic Shallow Community (AtSC), an Arctic Shallow Community (ArSC) and a Deep Water Community (DWC). All species belonging to AtSC and ArSC were pooled and their relative abundances in the total zooplankton calculated with respect to a particular layer (surface, mid and deep strata), regions (the Barents Sea, Fram Strait and the waters off northern Svalbard), years (1999 or 2003) and seasons (spring or autumn). Mapping of the proportions of Arctic and Atlantic species led to the conclusion that zooplankton from the MIZs do not exactly follow complementary water masses, although the general pattern of AtSC and ArSC dominance accords with the physical oceanography of the study area (AtW and ArW respectively). The mid layer proved to be a better predictor of mesozooplankton distribution than the unstable conditions near the surface.

Although, pelagic Ostracoda are locally abundant component of the mesozooplankton in the waters around Svalbard, the group remains poorly characterised both taxonomically and ecologically. Herein, the spatial and vertical variations in abundances and species composition of the pelagic Ostracoda assemblages are examined and related to the water masses. The study is based on a series of zooplankton samples collected with a multinet plankton sampler (MPS; HydroBios, Kiel), consisting of five nets fitted with a 180-μm mesh net. Samples were collected from deep stations (i.e., with bottom depths >300 m) around Svalbard and included localities influenced by the West Spitsbergen Current and the East Spitsbergen Current and to the north of Svalbard, between years 2001 and 2006. Throughout all the samples studied Discoconchoecia elegans was the numerically dominant species. The other species found were Boroecia maxima, Boroecia borealis, Obtusoecia obtusata, and a rare novel Boroecia species. Analyses of the pelagic Ostracoda assemblages showed that their variability was predominantly influenced by four factors: water temperature, geographical position, bottom depth and season. The highest densities of D. elegans were correlated with salinities >35 PSU whereas B. maxima distribution was dependent on latitude. Highest concentrations of B. borealis were determined by longitude. Abundances of O. obtusata were positively correlated with warmer water temperatures. Thus this work suggests that halocyprids have the potential to be good indicators of environmental changes associated with shifts in climate at high latitudes in the North Atlantic. [ABSTRACT FROM AUTHOR]

Biological invasions are a present and growing environmental problem because non-indigenous organisms may affect the structure and functioning of native communities. In the marine environment there are records of invasive species in almost all phyla, including crustaceans, and the portunid crabs of the genus Charybdis are among the most widespread invasive groups. We report the first record of Charybdis variegata (Fabricius, 1798) from the western Atlantic coast. This species was collected on an intertidal rocky shore near Santos Harbor, São Paulo state, Brazil. Of 311 portunid crabs sampled, 309 individuals belonged to the non-indigenous Charybdis hellerü (A. Milne Edwards, 1867), one was a native Cronius ruber (Lamarck, 1818), and one was identified as the non-indigenous Charybdis variegata. This individual was a juvenile female measuring 27.5 mm in carapace width. The taxonomic traits used for species identification, as well as a morphological comparison between C. hellerü and C. variegata are presented. The introduction route and establishment status of this species are also discussed. [ABSTRACT FROM AUTHOR]

This paper considers the formation of the thermohaline structure of the Arctic Ocean: the formation of the salinity field and a freshwater reservoir in the Beaufort Sea and the transport of warm Atlantic water into the central part of the Arctic Ocean. A new version of the Finite Element Model of the Arctic Ocean (FEMAO) with a low spatial resolution is used. The main distinctions of this version are the following features: a new equation of state, a more sophisticated parameterization of vertical turbulence, modified formulations for the boundary conditions on open boundaries (using satellite data on the sea level) and at the upper boundary of the ocean, and the use of a variable eddy diffusivity in the parameterization of the eddy transport of a scalar. Our experiments indicated that the use of the parameterization of the eddy transport of a scalar enhances the transport of warm Atlantic waters to the central part of the Arctic Ocean through the Fram Strait; the results are most realistic when a variable coefficient is used. The Neptune effect has a contradictory role and, in the future, a higher spatial resolution should be used instead of this parameterization. We revealed that a key factor in the thermohaline fields on a large time scale is the interaction with the Atlantic Ocean, which is the source of heat and saline water. [ABSTRACT FROM AUTHOR]

• Equations for water mixing in the Arctic are applicable only for ice melting. • A modified system of equations that eliminates these limitations is presented. • The maximum difference in base water content for these systems is 25–30% • Ice water content value is the "memory" of ice events that occurred in these waters. When researching the mixing of two or more water masses and their subsequent transformation, ideally, the most conservative parameters are used. Since the 1970s, the isotopic parameter δ18O has been used in various oceanological research works for example: Ostlund and Hut (1984) [J. Geophys. Res., 89, 6373–6381] and many others. The use of the salinity value and δ18O allowed the construction of a three-component system ("classic") of equations (TSC). Nevertheless, in the work: Dubinina et al. (2019) [Okeanologiya, No. 1, 57. 38–48] it was demonstrated that "the application of the three-component mixing to modified waters causes an overestimation of river water input". A model of 'mixing-modification', which eliminated this drawback, was presented in the work and the difference of estimation with the three-component system may be up to 20%. In the present study are also shown that the classic three-component system is fully applicable only under the conditions of ice melting, and under the conditions of ice formation estimates based on the three-component system give overestimated results of basic waters content in the final water mass. However, the methodology of sea water component composition estimation in this work differs slightly from the methodology presented in the above publication. A modified three-component system (TSM) presented in this work allows elimination of such inaccuracies. The difference between average values for the available series of observations according to TSC and TSM increases in the following order: Kara Sea > Laptev Sea > Barents Sea and the maximum difference for Atlantic waters and river waters (30.5% and 25.2%, respectively) was observed for Laptev Sea; 17.6% and 9.5%, respectively, for the Barents Sea and 16.3% for both components of the Kara Sea. To reveal newly formed water masses, a method of cluster analysis was applied. The composition of basic waters in the final water masses of the seas in question was obtained, as well as the values of these waters modification during ice formation or ice melting. General regularities of water masses formations in the discussed seas are delineated. An illustration of the average values of these magnitudes in water masses (clusters) in the system of coordinates content of: Atlantic Waters – river water– ice water for each sea had similar character, but their magnitudes differed depending on the different magnitude of the river runoff and different extent of these waters' modification during ice formation and ice melting. It is noteworthy that the value of "ice water" has an important scientific and practical significance, because it is used to summarise singular cycle values, and possibly, several observation cycles of ice formation while also being unique, maintaining the "memory" of the ice formation process values, which occurred in these waters. [ABSTRACT FROM AUTHOR]

Prokaryotic abundance, activity and community composition were studied in the euphotic, intermediate and deep waters off the Galician coast (NW Iberian margin) in relation to the optical characterization of dissolved organic matter (DOM). Microbial (archaeal and bacterial) community structure was vertically stratified. Among the Archaea, Euryarchaeota, especially Thermoplasmata, was dominant in the intermediate waters and decreased with depth, whereas marine Thaumarchaeota, especially Marine Group I, was the most abundant archaeal phylum in the deeper layers. The bacterial community was dominated by Proteobacteria through the whole water column. However, Cyanobacteria and Bacteroidetes occurrence was considerable in the upper layer and SAR202 was dominant in deep waters. Microbial composition and abundance were not shaped by the quantity of dissolved organic carbon, but instead they revealed a strong connection with the DOM quality. Archaeal communities were mainly related to the fluorescence of DOM (which indicates respiration of labile DOM and generation of refractory subproducts), while bacterial communities were mainly linked to the aromaticity/age of the DOM produced along the water column. Taken together, our results indicate that the microbial community composition is associated with the DOM composition of the water masses, suggesting that distinct microbial taxa have the potential to use and/or produce specific DOM compounds., (© FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)