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The German waters of the North and Baltic Sea contain over 1.6 million tons of dumped munition, mostly left after the first and second World Wars. Some of the dumpsites consist of old mines and shells containing TNT, which is known to have toxic effect on marine organisms. The objective of this study was to investigate whether the structure and composition of benthic macrofauna is influenced by the munition.Two munition sites were chosen in the western Baltic Sea – Kolberger Heide (=‘KH’, Kiel Bay) and Haffkrug (=‘H’, Lübeck Bay). Samples were taken with 0.1 m2 van-Veen grab (two replicates per station), sieved through 1 mm sieve and fixed with formalin. Stations were taken at several areas near the munition dumpsites, each time arranged in two short parallel transects with ~100 m step (6-10 station per area). In addition, samples in the background areas away from munition were taken. A total of 19 stations (37 samples) were taken in ‘KH’ and 25 stations (50 samples) were taken in ‘H’. Environmental values used in this study included depth, TNT-content in bottom water layer, distance from the maximum concentration of the munition objects, latitude and longitude.A total of 118 taxa were found in ‘KH’ and 121 taxa in ‘H’. Abundance and biomass values varied among the samples greatly in both areas (from 10 to 1730 ind. 0.1 m-2 and from 0.09 to 155.37 g wet weight 0.1 m-2 respectively), although the dominant taxa were similar in all samples, including polychaetes Scoloplos armiger, Pygospio elegans, Dipolydora quadrilobate and Lagis koreni and gastropods Peringia ulvae.In ‘KH’ notably higher abundance and biomass values were observed in the control sites, while the diversity expressed in different indices (Shannon index, Rarefaction curves, Pielou’s evenness etc.) was relatively higher in the munition sites. According to the canonical correspondence analysis, species and samples were grouped along two axes, roughly corresponding to the larger TNT content and shallower depths. Linear mixed-effect model showed statistically significant values for TNT content vs. Shannon diversity index with negative linear relation.In ‘H’ the results were different with no clear abundance biomass or diversity relations to the environmental factors. However, this can be connected to a different munition distribution within the Lübeck Bay, which is more dispersed through the area, without such clear concentration area as in ‘KH’. Further possible conclusions will be discussed.

Only seven frenulate species are currently known along the Eurasian coast of the Arctic Ocean. We describe a new genus and a new species of frenulates Crispabrachia yenisey, gen. nov. et sp. nov. The morphological analysis involved standard anatomical techniques, semithin sections and scanning electron microscopy (SEM). The molecular study included four markers (partial COI, 16S, 18S and 28S) and implemented Bayesian and Maximum likelihood phylogenetic approaches. The description of Crispabrachia gen. nov. is the first documented finding of frenulates in the Kara Sea at the estuary of the Yenisey River in rather shallow water (28 m). The establishment of a new genus is warranted based on the composition of morphological characters and several specific features including free, comparatively short curly tentacles, a triangular cephalic lobe with amplate base, the valvate extension of the posterior part of the forepart and prominent papillae on the nonmetameric region. The tube structure with prominent frills and the worm’s numerous tentacles, metameric papillae with cuticular plaques and segmental furrow on the forepart indicate that the new genus belongs to the polybrachiid group. Although the type locality in the Yenisey River estuary is unusual for siboglinids in general, the physical conditions here are common for other frenulates habitats, i.e. salinity ~30–33, bottom water temperature –1.5°C. This finding was made in the Yenisey Gulf in the region with the highest methane concentrations in the southern part of the Kara Sea that reflects permafrost degradation under the influence of river flow. Further study of the region would help to understand the factors influencing frenulate distributions and improve our knowledge of their biodiversity.

The benthic fauna of Sedova Bay (Kara Sea, Novaya Zemlya Archipelago) was studied during two cruises of the R/V Academik Mstislav Keldysh in 2015–2016. Three macrobenthic communities were described. The species composition of the benthic communities is formed by two orthogonal environmental gradients: vertical (depth) and horizontal (the distance from the apex of the bay). Horizontal changes are mainly determined by terrigenous runoff, despite the generally low content of suspended particles in the water column of the bay. This factor determines the trophic conditions for benthic invertebrates and affects the changes in the share of dominant species within one assemblage. An increased effect of this factor results in significant reorganization of bottom communities (disappearance of a number of species, separation of the marginal communities, and fauna depletion) as were described for the neighboring bays on the eastern coast of Novaya Zemlya.

Diel and seasonal vertical migrations of zooplankton represent a widespread phenomenon occurring in marine and freshwater environments. Diel migrations are panoceanic, while seasonal migrations usually occur in temperate and polar areas. This paper describes differences in the diel and seasonal vertical migrations in the Drake Passage north and south of the Polar Front (PF). We analyzed material of 85 stations collected in spring of 2008 and 2010 (October–November) and in summer of 2010 and 2011 (January) within the 0–300 m depth range during various time of a day. At each station we sampled the upper mixed (UL), the middle (ML), and the deeper layers (DL) bounded by hydrological gradients. Diel migrations were significantly different south and north of the PF in terms of total abundance, biomass, diversity and individual taxa density. In both seasons, mesoplankton dielly migrated between the ML/DL and the UL north of the PF and between layers below 300 m and the DL and ML south of the PF. Deeper range of diel migrations south of the PF was coupled with a general mesoplankton descent in summer period compared to spring. Conversely, north of the PF, mesoplankton ascended to upper layers in summer, which was mirrored in lesser depths of diel migrations. The differences in the plankton distribution on both sides of the PF are likely associated with variations of vertical distribution of phytoplankton. Some abundant taxa such as Aetideus sp. and Oithona plumifera showed both common (nighttime ascend) and inverted (nighttime descend) vertical migrations depending on season and position related to the PF.

Two areas with cold methane seeps on the outer shelf of the Laptev Sea were studied by two interdisciplinary expeditions onboard the RV Akademik Mstislav Keldysh in August–September of 2017 and 2018. These fields lie in water between depths of 63 and 73 m, and in a region of growing interest to the international community. Characteristic features of the methane seeps were obtained, which include their distribution and appearance on the seabed based on acoustic anomalies and seafloor observations. The cold seeps are part of a domain striking in a SW–NE direction along the Laptev Sea Rift System, Khatanga–Lomonosov Fracture Zone, and the Gakkel Ridge junction, and its structure was determined by shallow faults on the outer shelf. These faults are related to subsidence of the outer shelf cutting the caprock formed by permafrost and gas hydrates. Faults serve as conduits for an intense bubble methane discharge at the seabed. Shallow-water methane seep fauna were described for the first time in the Siberian Arctic. The frenulate siboglinid tubeworm Oligobrachia haakonmosbiensis was among the dominant species of the methane seep communities. A newly discovered gastropod species Frigidalvania sp. was also found in abundance at the seeps as well as an ophiuroid Ophiocten sericeum. Significant differences were observed between benthic communities of the two seep fields and background fauna including integral community parameters and the presence/absence of certain species. Development of shallow methane seep communities in the Laptev Sea apparently is related to extremely oligotrophic conditions in this area.

Despite a large number of studies, a detailed overall picture of benthic communities zonation in the Arctic fjords is currently lacking. Our study aimed to find out whether there is a universal model for the distribution of benthic communities based on the structural features of the fjords. We examined benthic macrofaunal communities in fjords with various environmental settings on the eastern coast of Novaya Zemlya Archipelago, Kara Sea. The material was collected during five cruises undertaken from 2013 to 2016. A total of 50 stations located in the five fjords were taken. In all five fjords, macrofauna had a similar composition assembled from a regional species pool, with a predominance of species tolerant to glacial sedimentation and fluctuations in temperature and salinity. Benthic communities changed consistently along the axis of the bay from the outer slope to the inner parts. Biodiversity and quantitative characteristics of the macrofauna decreased along the environmental gradient related to terrigenous and glacial runoff, consistent with patterns reported in other studies of Arctic glacial fjords. The most impoverished communities were dominated by bivalvePortlandia arcticaand isopodSaduria sabini. At the same time, fjord walls and sills, characterized by low sedimentation rates, strong currents and the presence of ice-rafted debris, were inhabited by patchy distributed benthic communities dominated by species confined to hard substrates. In general, the distribution of communities corresponded to five zones: depleted inner periglacial areas, the upper subtidal belt with stony substrates, deep inner semi-isolated basin, outer non-isolated basins and upper slope transitioning to lower slope. Our study can provide a reference point for monitoring changes in fjord ecosystems in response to climate change and the potential impact of human activities.

An annotated species list of all macrobenthic invertebrates inhabiting the Siberian sector of the Arctic Ocean is presented. The area considered includes the Kara, Laptev and East Siberian seas and the adjacent region of the deep-sea Central Arctic. Entries on species occurrences in the database are supported by corresponding references. Species of Polychaeta, Crustacea and Echinodermata in addition contain information on bathymetric distribution. Apart from published data, 12 taxa were identified in the area for the first time. In total 1574 macrobenthic species were recorded within the considered area. The most species rich was the Kara Sea with 1184 species. The Laptev and East Siberian seas and the Central Arctic showed lower species richness with correspondingly 1105, 780 and 268 species. The much smaller numbers of species in the East Siberian Sea and in the deep-sea Central Arctic can be related to taxonomic impoverishment or/and much smaller study effort in those regions.

The ability of bivalve mollusks to accumulate chemical elements from the environment makes them an important object for environmental monitoring and assessments of anthropogenic impact on marine ecosystems. The paper presents the data on the content of 65 chemical elements in soft tissues and shells of five species of bivalve mollusks (Astarte crenata, Ciliatocardium ciliatum, Portlandia arctica, Chlamys islandica, Hiatella arctica), as well as in the upper layer (0-5 cm) of bottom sediments of the Kara Sea, the Arctic Ocean. The content of major-, trace and rare-earth elements was determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). The age, size, and weight of mollusks were measured. There were differences in the content of chemical elements accumulated in soft tissues and shells of mollusks, as well as the significant interspecific difference in the chemical composition of the studied mollusks. The soft tissues of mollusks were accumulated with toxic metals (Hg, Ag, and Cd) in comparison with the content of these elements in bottom sediments. In Chlamys islandica and Hiatella arctica, the shell was accumulated in Cd in contrast to other species. The data obtained may be used for a comprehensive assessment of the state of ecosystems in the seas of the Siberian sector of the Arctic Ocean under changing environment and for studying the fundamental base of the accumulation of chemical elements by marine organisms.

The benthic fauna of Oga Bay (Kara Sea, Novaya Zemlya archipelago) was studied in 2015–2016 during the R/V Akademik Mstislav Keldysh expeditions. Five grab stations at depths of 70–140 m were sampled (three grabs per station). Three macrobenthic communities consecutively replacing each other from the inner near-glacier part of the bay toward the outer slope were revealed. Concentration of suspended matter in the water column and in the near-bottom layer, caused by powerful sedimentation from the Goluboi (Oga) glacier was the main factor determining the macrobenthic communities distribution. An overall decrease in abundance, biomass and diversity of macrofauna was found in the area of glacier discharge. The community dominated by bivalve Portlandia arctica inhabits the main part of the bay. The peculiarities of the benthic communities of the Arctic glacial bays and fjords are discussed.

There are numerous studies measuring the rate and extent of bioturbation worldwide, however, information on mixing rates in the deep ocean, especially in the polar regions , are extremely scarce. The present study presents mixing rates and mixed layer depths for the deep seafloor at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean . Two stations at similar water depths (HG-IV at 2492 m, and S3 at 2391 m) but different distances to the ice edge (approx. 65 km and 115 km, respectively) were chosen to carry out long-term in situ bioturbation experiments (2 and 4 years, respectively), using luminophores as a tracer. Enhanced bioturbation at the northern site, located closer to the high productive Marginal Ice Zone (MIZ) and thus expected to receive higher amounts of settling organic matter thereby supporting a richer benthic community , could not be confirmed. Instead, biodiffusion-like mixing rates ( Db) at the experimental sites showed no significant differences (0.26 ± 0.27 SD cm−2 y−1 at station HG-IV; 0.28 ± 0.40 SD cm−2 y−1 at station S3). Moreover, mixed layer depths (L) at the two sites were almost identical; mixing of surface sediments occurred down to approx. 6–7 cm sediment depth. Indications for a non-local transport of sediment particles from the surface to deeper parts of the sediment, resulting in higher values for the Non-Local Index (NLI), could only be found for the central HAUSGARTEN site HG-IV. Differences in macro- and megafauna communities at the two experimental sites might be responsible for subsurface maxima in luminophore distribution and slightly (non-significantly) higher NLI values at this site (5.37 ± 3.35 SD at station HG-IV; 3.26 ± 1.82 SD at station S3). Temporal variations in benthic activities should have been levelled out in the multi-year experiments, thus providing reliable baseline data for the deep Fram Strait.

Regular biological observations of the deep sea bottom fauna are very important for understanding the role benthic biota plays in ocean ecosystems. Temporal variability in macrobenthos structure is usually studied in terms of general community characteristics including density, biomass and diversity. In this investigation, we also focused on the species composition and their individual characteristics in terms of temporal dynamics. The deep-sea macrofauna was studied based on the material collected in the Eastern Fram Strait during two expeditions in July–August 2003 and July 2012. Stations were taken at depths of about 2500 m at the deep-sea observatory using the USNEL box corer (0.25 m2). Three stations at varying distances were sampled in 2003 (three cores per station). In 2012, the same stations were resampled with an additional station taken close to the central HAUSGARTEN permanent sampling site (one core per station). No significant changes in the total density and biomass were found between the two sampling events. However, the density of several common species has changed significantly (e.g. densities of Mendicula ockelmanni and Chaetozone cf. jubata have increased). Four species out of total 64 were unique for the 2003 samples, while six species out of 52 were unique for 2012 samples. The absence of several particular species in the samples from the different years is estimated to be not random: the number of samples required to find these species was less than the number of samples collected. The differences in time between the very same stations exceeded the inner spatial heterogeneity of each of the three stations. However, the spatial heterogeneity within the scale of 20–25 km exceeded the temporal differences.

Deep-sea regions provide vast ecosystem services such as biological habitat and nutrient cycling. Even though being threatened by climate change and facing possible biodiversity loss, these deep-sea ecosystems are poorly understood. So are macrobenthic communities and their functions within these ecosystems. Biodiversity and ecosystem function relationships as well as their link to environmental drivers can be assessed with the biological trait analysis. We used this approach for the first time for macrofauna assemblages across the deep Fram Strait between Greenland and Svalbard (1000–5500 m water depth) to evaluate their community-specific function from the upper continental slope down to the deepest known Arctic depression, the Molloy Deep. We aimed to investigate whether there are changes in benthic functioning along the bathymetric gradient and if so, which environmental stressors may drive these changes. In total, 16 stations were sampled with a giant box corer (0.25 m2) in 2016 and 2018. Sediments were sieved through a 0.5 mm mesh size sieve and fauna was identified to lowest possible taxonomic entity. Functions of species were characterized by using six traits split in 24 modalities gathered in a fuzzy coded species × traits array. Environmental parameters shaping the benthic habitat and reflecting food availability were gathered from remote sensing, mooring deployments, and sediment sampling. A distance-based redundancy analysis indicated near-bottom water temperature, seabed inclination, water depth as well as phytodetritial matter at the sea surface and seafloor (indicating food availability) to be the best variables explaining the trait and station distribution. Stations clustered into three groups based on their trait composition. Shallower stations characterized by high chlorophyll a concentration with large organisms, living within the sediment as well as predating specimens clustered in one group. A second group was characterized by stations with low chlorophyll a concentration and medium-sized, suspension feeding, epifaunal living macrofauna. A third group comprised stations with water depths ≥ 3000 m and was dominated by medium sized, surface deposit feeding and infaunal living specimens. Overall, the functional structure of macrofauna communities in the Fram Strait followed a food availability-driven gradient. Based on the relationship between sea ice, surface water primary production and food availability at the seafloor, these results point to macrobenthos being sensible to predicted anthropogenically generated environmental variations in polar regions. Alterations in benthic ecosystem functions might be expected when environmental conditions change.

BackgroundMethane seeps support unique benthic ecosystems in the deep sea existing due to chemosynthetic organic matter. In contrast, in shallow waters there is little or no effect of methane seeps on macrofauna. In the present study we focused on the recently described methane discharge area at the northern Laptev Sea shelf. The aim of this work was to describe the shallow-water methane seep macrofauna and to understand whether there are differences in macrobenthic community structure between the methane seep and background areas.MethodsSamples of macrofauna were taken during three expeditions of RVAkademik Mstislav Keldyshin 2015, 2017 and 2018 using 0.1 m2grabs and the Sigsbee trawl. 21 grabs and two trawls in total were taken at two methane seep sites namedOdenandC15, located at depths of 60–70 m. For control, three 0.1 m2grabs were taken in area without methane seepage.ResultsThe abundance of macrofauna was higher at methane seep stations compared to non-seep sites. Cluster analysis revealed five station groups corresponding to control area,Odensite andC15site (the latter represented by three groups). Taxa responsible for differences among the station groups were mostly widespread Arctic species that were more abundant in samples from methane seep sites. However, high densities of symbiotrophic siboglinidsOligobrachiasp. were found exclusively at methane seep stations. In addition, several species possibly new to science were found at several methane seep stations, including the gastropodFrigidalvaniasp. and the polychaeteOphryotrochasp. The fauna at control stations was represented only by well-known and widespread Arctic taxa. Higher habitat heterogeneity of theC15site compared toOdenwas indicated by the higher number of station groups revealed by cluster analysis and higher species richness inC15trawl sample. The development of the described communities at the shallow-water methane seeps can be related to pronounced oligotrophic environment on the northern Siberian shelf.

Benthic fauna in Stepovoi Bay (Kara Sea, Novaya Zemlya) was studied during expeditions of the R/V Professor Shtokman in 2013–2014. Sampling was carried out at ten grab stations from the head of the bay to a depth of 180 m on the slope of the Novaya Zemlya Trough. The quantitative characteristics of the bottom fauna were obtained, and the main macrozoobenthic communities were specified. An important part of the fauna is represented by species associated with rocky substrates, attached forms in particular. There was a notable absence of a number of Arctic deep-sea species (e.g., Ophiopleura borealis) and deposit-feeding bivalve mollusks (Portlandia arctica, Ennucula tenuis, Yoldiella solidula, and Yoldiella lenticula), which play the leading role in the communities of the inner parts of bays with intense fine-grained mineral sedimentation. The main trends in the distribution patterns of benthic communities–bathymetric and horizontal (related to the position along the gradient from the head to the outer slope)–were revealed. The benthic communities of Stepovoi Bay were compared to communities of other Arctic bays and fjords.

With current climate trends, longer ice-free periods and increased human activity are observed in the previously hard to access Arctic Siberian seas. This provides for a rare opportunity to observe the progress of species invasion in pristine areas. The snow crab, Chionoecetes opilio, is a unique example of an alien Brachyura crab in the Arctic. Its distribution, population size structure, as well as biotic and abiotic conditions affecting its survival in the Kara Sea are discussed. Crabs were collected using trawl sampling in 2014. It has been estimated that the invasion took place in the late 2000s through the northern and eastern borders with the Barents Sea. Presently, snow crabs are found throughout the western part of the sea, from Kara Gates to St. Anna Trough; the entire area between Yamal Peninsula and Novaya Zemlya; and the northeastern shelf of the sea. Benthic abiotic conditions of the Kara Sea are unlikely to limit survival and further progress of snow crab population. However, the length of the ice-free period could limit its reproduction potential. The collected data do not allow us to presume the existence of a reproducing population, yet the presence of a settler-size group in the central part of the western Kara shelf could indicate local recruitment. Food availability in the Kara Sea is unlikely to limit growth of early benthic stages of snow crabs such as those collected in 2014. However, the question remains open whether benthic productivity is sufficient to allow these crabs to reach commercial sizes.

The studies of functional structure of high-Arctic Ecosystems are scarce. We used data on benthic macrofauna from 500-km latitudinal transect in the eastern Laptev Sea, from the Lena delta to the continental shelf break, to describe spatial patterns in species composition, taxonomic and functional structure in relation to environmental factors. Both taxonomy-based approach and Biological Trait analysis yielded similar results and showed general depth-related gradient in benthic diversity and composition. This congruence between taxonomical and functional dimensions of community organization suggests that the same environmental factors (primarily riverine input and regime of sedimentation) have similar effect on both community structure and functioning. BTA also revealed a distinct functional structure of stations situated at the Eastern Lena valley, with dominance of motile, burrowing sub-surface deposit-feeders and absence of sedentary tube-dwelling forms. The overall spatial distribution of benthic assemblages corresponds well to that described there in preceding decades, evidencing the long-term stability of bottom ecosystem. Strong linear relationship between species and traits diversity, however, indicates low functional redundancy, which potentially makes the ecosystem susceptible to a species loss or structural shifts.

The first ecological survey in the tropical part of the northern Mid-Atlantic Ridge (MAR) was conducted between 17°14′N and 16°40′N in February–March 2015 during the 37th cruise of the RV Professor Logachev. Significant effort of the survey was aimed at studies of benthic non-vent soft sediment fauna at depths from 2270 m to 3900 m. Samples of this fauna at seven stations revealed ~780 specimens and at least 136 species. The most common species was the hermit crab Parapagurus cf. nudus. Also common were the ophiuroids Ophiotypa simplex and Ophiomusium cf. lymani. Most benthic organisms were

Background Spatial distribution of zooplankton communities influenced by various environmental factors is always important for understanding pelagic ecosystems. The area of the Drake Passage (Southern Ocean) is of particular interest owing to the high spatial and temporal variability of hydrological parameters affecting marine fauna. This study provides a survey of zooplankton composition and spatial distribution along a transect in the Drake Passage sampled during the 31th Cruise of RV “Akademik Sergey Vavilov” in November, 2010. The main aim was to trace the main regularities in spatial zooplankton structure and its relationships with the environmental parameters. Methodology A total of 43 vertical hauls from the surface to 1,000 m depth were made at 13 stations using the Juday plankton net. 60 taxa were recorded, abundance and biomass of each were assessed. Environmental parameters including temperature, salinity, depth, horizontal distance between stations and surface chlorophyll concentration were tested as environmental factors possibly explaining plankton distribution. Results Higher zooplankton abundance and biomass with lower diversity were observed near the Polar Front. Cluster analysis revealed five different groups of zooplankton samples, four of which were arranged mostly by depth. Along the transect within the 1,000 m depth range, the qualitative taxonomical composition differed significantly with depth and to some extent differed also among horizontal hydrological regimes, while the quantitative structure of the communities (abundance of taxa) was mainly determined by depth. Plankton assemblages within the upper 300-m layer depended on hydrological fronts. Abundance of dominant taxa as well as total zooplankton abundance showed a clear correlation with depth, salinity and surface chlorophyll concentration. Some taxa also showed correlations with temperature and latitude. Between the stations the similarity in zooplankton structure was clearly dependent on the distance among them which indicates an importance of latitudinal gradient. Surface chlorophyll concentration was not correlated with zooplankton biomass, which can be explained by the uncompleted seasonal migrations of zooplankton from deeper waters in early spring.

Quantitative camera surveys of benthic megafauna were carried out during the expedition ARK-XXVII/3 to the Eastern Central Arctic basins with the research icebreaker Polarstern in summer 2012 (2 August-29 September). Nine transects were performed for the first time in deep-sea areas previously fully covered by ice, four of them in the Nansen Basin (3571-4066m) and five in the Amundsen Basin (4041-4384m). At seven of these stations benthic Agassiz trawls were taken near the camera tracks for species identification. The observed Arctic deep-sea megafauna was largely endemic. Several taxa showed a substantially greater depth or geographical range than previously assumed. Variations in the composition and structure of megabenthic communities were analysed and linked to several environmental variables, including state of the sea ice and phytodetritus supply to the seafloor. Three different types of communities were identified based on species dominating the biomass. Among these species were the actiniarian Bathyphellia margaritacea and the holothurians Elpidia heckeri and Kolga hyalina. Variations in megafaunal abundance were first of all related to the proximity to the marginal ice zone. Stations located closer to this zone were characterized by relatively high densities and biomass of B. margaritacea (mean 0.2-1.7 ind m-2; 0.2-1.5 g ww.m-2). The food supply was higher at these stations, as suggested by enhanced concentrations of pigments, organic carbon, bacterial cell abundances and porewater nutrients in the sediments. The fully ice-covered stations closer to the North Pole and partially under multi-year ice were characterized by lower concentrations of the same biogeochemical indicators for food supply. These stations nevertheless hosted relatively high density and biomass of the holothurians E. heckeri (mean 0.9-1.5 ind m-2; 0.3-0.4 g ww.m-2) or K. hyalina (mean 0.004-1.7 ind m-2; 0.01-3.5 g ww.m-2), which were observed to feed on large food falls of the sea-ice colonial diatom Melosira arctica. The link between the community structure of megafauna and the extent and condition of the Central Arctic sea-ice cover suggests that future climate changes may substantially affect deep ocean biodiversity.

This study compares the macrofaunal communities along two bathymetric transects (1000 – 2500 m water depth) in predominantly ice-covered western (offshore Greenland) and generally ice-free eastern (offshore Svalbard) regions of the Fram Strait. Material was collected using an USNEL 0.25 m2 box corer and all sediment samples were processed through a 500-μm sieve. A total of 1671 organisms from 169 species were found. Densities off Greenland were generally lower than those observed off Svalbard. On both sides of the Fram Strait, density, biomass and biodiversity generally decreased with increasing water depth. An exception was observed at the deepest station off Greenland (2500 m water depth), which was located within the Marginal Ice Zone. At this station, macrofaunal density was elevated (992 ± 281 ind. m−2) compared to the adjacent shallower sampling areas off Greenland (272 ± 208 ind. m−2 to 787 ± 172 ind. m−2) and the deeper stations (2000 and 2500 m water depth) off Svalbard (552 ± 155 ind. m−2 and 756 ± 182 ind. m−2). The most abundant species along both transects was the polychaete Galathowenia fragilis (off Greenland: 288 ind. m−2, off Svalbard: 740 ind. m−2). Sea ice coverage and water depth, as well as the associated food availability at the seafloor, seem to be crucial factors driving the macrofaunal community patterns. A strong pelago-benthic coupling is observed to be typical in Arctic deep-sea ecosystems, and is also confirmed by our study.

This study was carried out in the Yenisei estuary and in the adjacent part of the Kara Sea shelf. We analyzed and compared the distribution patterns of the different benthic taxa and size classes (micro-, meio-, macro- and megabenthos) along a pronounced gradient of environmental factors. Four ecological zones were distinguished based on certain environmental parameters, from the upper riverine area to the mouth of the estuary and the Kara Sea slope, which had normal marine conditions. The distribution of the metazoan assemblages generally corresponded to the divisions of these zones and represented a series of species assemblages with coincident boundaries that changed successively along the estuarine gradient. For all three size classes of metazoan benthos, we detected three main species assemblages: brackish-water, transitional and marine. Each taxon showed, however, its own particular spatial pattern and, therefore, has a set of environmental variables that is responsible for its fine-scale distribution. The distribution of unicellular organisms showed a worse match with the division of the estuary into environmental zones. Foraminifers established a single association in most of the estuary but were absent in the upper desalinated part. Diatom algae were patchily distributed, with a number of local communities and many rare species. We conclude that the estuarine habitat appears to drive the distribution of the various benthic taxa in taxa-specific ways. The distribution of size classes (i.e., mega-, macro-, or meiofauna) that combine several high-level taxa demonstrates a better match with the multivariate environmental zonation than the distribution of the separate taxa. The role of different benthic taxa and size classes in biomonitoring studies is discussed.

The benthic fauna was studied in the Blagopoluchiya Bay (Kara Sea, Novaya Zemlya Archipelago) during an expedition of the R/V Professor Shtokman in autumn 2013. The inner basin of the bay, with depths of around 150 m, is separated from the outer slope of Novaya Zemlya by a shoal 30 m in depth. Six macrobenthic communities were described at nine stations (25 bottom grab samples) taken along a transect from the inner part of the bay to the outer part of the slope. The depths, position on the transect axis and sediment types were the major factors influencing the distribution of the communities. The benthic abundance and biomass in the inner and outer parts of the bay did not differ significantly. The diversity of macrobenthic organisms (α-diversity as the number of species in the sample and β-diversity as the rate of increase in species number in the area) was lower in the inner part of the bay. The intertidal zone (littoral) has been described. The littoral fauna was very poor; it comprised only the amphipods Gammarus setosus inhabiting the near-surface area.

Spatial distribution patterns in macrobenthos were studied based on the material collected during the R.V. Polarstern expedition ARK-XXVII/2 in July 2012. Eleven stations along the latitudinal transect at the deep-sea observatory HAUSGARTEN in the Fram Strait were taken at depths of about 2500 m. Macrofauna was obtained using the USNEL box corer. A single core (0.25 m2) was taken at each station and four subcores (0.03 m2) were taken from each core and used for the quantitative analysis. The results suggest that the single highly variable macrobenthic community with the dominance of polychaetes Galathowenia fragilis and Myriochele heeri inhabits the studied area. The prevalence of a mosaic in the community structure with the grain size at least more than the size of a core was detected. However, several abundant species (e.g. the polychaetes Prionospio sp. and Galathowenia fragilis) tend to form patches at the scale less than a core (0.25 m2). Despite the lack of significant differences in species distribution patterns along the latitudinal transect, there is a slight difference in community structure between the northernmost and southernmost stations (~170 km apart), which can be explained by variations in environmental factors (e.g. higher food availability in the northern part of the transect).

Permanent ice coverage and the low primary production in the mostly ice-covered Central Arctic ocean basins result in significantly lower biomass and density of macrobenthos in the abyssal plains compared to the continental slopes. However, little is known on bathymetric and regional effects on macrobenthos diversity. This study synthesizes new and available macrobenthos data to provide a baseline for future studies of the effects of Arctic change on macrofauna community composition in the Arctic basins. Samples taken during three expeditions (in 1993, 2012 and 2015) at 37 stations on the slope of the Barents and Laptev Seas and in the abyssal of the Nansen and Amundsen Basins in the depth range from 38 m to 4381 m were used for a quantitative analysis of species composition, abundance and biomass. Benthic communities clustered in five depth ranges across the slope and basin. A parabolic pattern of species diversity change with depth was found, with the diversity maximum for macrofauna at the shelf edge at depths of 100-300 m. This deviates from the typical species richness peak at mid-slope depths of 1500-3000 m in temperate oceans. Due to the limited availability of standardized benthos data, it remains difficult to assess the massive sea ice retreat observed in the past decade has affected benthic community composition. The polychaeteYmerana pteropodaand the bryozoanNolellasp. were found for the first time in the deep Nansen and Amundsen Basins, as a potential first sign of increasing productivity and carbon flux with the thinning ice.

Trawl samples were collected in the northern region of Yenisei Bay and adjacent parts of the Kara Sea shelf. A total of eight stations were taken. We found more than 200 species of benthic organisms. A consecutive replacement of benthic communities is observed when going to the north from the Ob and Yenisei estuaries to the open parts of the sea. We could distinguish four different species complexes in the investigated area: a brackish-water complex where Saduria entomon is dominant; an intermediate complex where S. sibirica, S. sabini and Portlandia aestuariorum are dominant; a transitional complex with P. arctica as a dominant species and with a small amount of Ophiocten sericeum; a marine complex where O. sericeum is dominant. When salinity increased, some brackish-water species were replaced by related euryhaline species. One such example was the replacement of brackish-water Saduria entomon isopods by two euryhaline species: S. sibirica and S. sabini. The consecutive replacement of benthic communities showed a break near Sverdrup Island. In this area the marine complex was replaced by a transitional complex with P. arctica.

Taxonomic composition and ecological structure of benthic communities of the southern part of St. Anna Trough were investigated during the 54th and 59th cruises of RV Akademik Mstislav Keldysh. Material was collected using Sigsbee trawl at 10 stations arranged in two transects (depth range 57–554 m). It was shown that benthic communities of the western arm of the St. Anna Trough differ considerably from the communities of the eastern arm. The western arm communities develop under the influence of active near-bottom hydrodynamics in conditions of rugged topography and a coarse-grained sediment or hard substrate. The wastern arm of the trough is characterized by the predomination of the soft sediment, smooth topography, and weak currents. In the western arm of the trough the influence of the Barents Sea fauna is traced down to the edge of the internal shelf (about 150 m depth). The community of the eastern arm of the trough situated out from the direct influence of the Barents Sea waters represents a continuation of the Ophiocten sericeum community, typical for external Kara Sea shelf. With increasing depth, Ophiopleura borealis becomes the dominant species of the community. In the greatest explored depths some deep-water High-Arctic species, such as echinoids Pourtalesia jeffreysi, were observed. The major factors determining the distribution of benthic communities in the investigated area are the microrelief pattern, the sediment structure, and near-bottom hydrodynamics.

The southeastern part of Kara Sea is a highly dynamic area influenced by freshwater masses of Ob and Yenisei rivers. It is possible to estimate the annual changes of bottom communities in such areas by studying the temporal and spatial distribution of benthic organisms. In the previous studies of the same areas, the communities differing essentially in the composition and abundance were described mainly due to the different sampling methods employed and possible temporal changes in the macrobenthos. The aims of this study were to redescribe the benthic communities in the area of the Ob Bay and the adjacent Kara Sea shelf by using trawl and grabs, to compare the results obtained with these gears with each other and to reveal the environmental factors influencing the macrobenthos. Samples were taken along the transect from the northern half of the Ob Bay to the central part of the Kara Sea. Total biodiversity generally increased toward the open shelf regions. The data obtained only partly confirmed the previously recorded trend of gradual substitution of crustacean communities by communities dominated by bivalves and echinoderms. Three community complexes were distinguished in the studied area—the freshwater, the brackish-water and the marine. The contact area of the brackish-water and the marine complexes demonstrated the gradual transition. Salinity, correlated with the temperature, was the most important environmental factor influencing the benthic communities along the Ob Bay. The other factors were the sediment structure and depth.