Bussol Strait Research Articles

A census and properties of mesoscale Kuril eddies in the altimetry era

The ocean-side area of the Kuril Islands is a region with high bioproductivity and rich fishing and a convergence of transformed subtropical and subarctic waters with significant impact on weather and climate. Waters of different origin mix in the region including Kuroshio Extention, Japan Sea, Oyashio, Okhotsk Sea and Alaskan Stream waters. Despite the important role of Kuril eddies (KE) in transporting heat, salt, nutrients and their biological activity, there are still major gaps in our knowledge of the properties and dynamics of these energetic and mesoscale features in the northwestern Pacific Ocean. Using altimetry data during 1993–2021, we conducted the first systematic census of KE with the help of the automatic eddy tracking algorithm AMEDA. We separated KE into four groups according to their places of formation in relation to the Kuril-Kamchatka Trench and found a strong inhomogeneous spatial distribution of the Kuril cyclones (KC) and anticyclones (KAC). Different kinematic properties of KE have been studied and analyzed. The Trench has been found to play a role of an eddy guide for long-lived eddies with a comparatively small number of KE being able to cross the Trench. The highest occurrence frequency of KAC was observed along the Trench, especially in the area east off the Bussol Strait, whereas KC occurred more frequently along the ocean side of the Trench. Among the observed long-lived KE, there were more than 90% of eddies with the nonlinearity parameter exceeding 1 implying that the majority of KE are coherent vortices transporting water with its properties. The relative concentrations of waters of different origin inside KAC and KC cores were computed for each group applying the new Lagrangian algorithm. It allowed us to detect transportation of subtropical water in the KE cores to north and subarctic water to south over the distance of the order of 1000 km and more.

Change of nitrogen chemical tracer N2* between the Okhotsk Sea and the subarctic North Pacific

Using the nitrogen chemical tracer N2* (an anomaly of [N2] in terms of the saturation ratio of dissolved nitrogen gas to dissolved argon gas in seawater), we quantitatively investigated the processes that affect the flux of oceanic nitrogen gas at the air-sea interface in the subarctic region of the Sea of Okhotsk (OK) and the North Pacific Ocean (NP): denitrification, air injection, and rapid cooling, in five regions, (i) the inflow region from NP into OK, (ii) the continental shelf region, (iii) the continental slope region, (iv) the Okhotsk Sea pelagic ocean region and (v) the outflow region from OK to NP following the flow of seawater from upstream to downstream. In the inflow region, half of ∼1 μmol kg−1 of N2* amount was due to the denitrification effect, followed by 40% due to the rapid cooling effect, and the remaining about 10% was due to the air injection effect. On the continental shelf, N2* showed a maximum value of ∼8 μmol kg−1, of which about 56% was the rapid cooling effect, followed by the denitrification effect of 44%, which resulted from the formation of the dense shelf water (DSW) and the active biological production on the continental shelf. On the continental slope, the denitrification effect accounted for three-fourths of N2*, and the remaining one-fourth was due to the rapid cooling effect, which is due to the mixing of DSW with the surrounding seawater and the active denitrification at a wide depth on the continental slope. In the pelagic ocean region, the N2* content was the lowest in OK and the fraction of the three effects are almost the same as on the continental slope, which is related to the process of DSW incorporation into the Okhotsk Sea Intermediate Water. In the outflow region from OK to NP, which is downstream of the above regions, the N2* content steeply decreased by 60% compared to the Okhotsk Sea pelagic ocean region due to tidal mixing in the Bussol Strait. The above quantitative analysis of these five regions showed that the Kruzenshtern Strait, the Bussol’ Strait and the continental shelf and slope of OK play an important role in controlling the three effects affecting the flux of ocean nitrogen gas in OK and NP.

Four new species of Careproctus (Cottoidei: Liparidae) from the deep-water vicinity of the southern Kuril Islands (Western North Pacific).

Four new species of Careproctus (Cottoidei: Liparidae) are described from the Bussol Strait (the deepest channel of the Kuril archipelago) and two neighboring abyssal basins of the Western North Pacific. Careproctus laperousei sp. nov. from the northern slope of the Kuril-Kamchatka Trench (depths of 4796-4803 m) has the following characters: vertebrae 57, pectoral-fin rays 26, principal caudal-fin rays 8 and pore pattern 2-6-7-1; it differs from the most similar congeners from the North Pacific in having a black peritoneum, short head (22.5 % of standard length, SL) and large disk (37.0 % of head length, lc). Careproctus brevipectoralis sp. nov. from the Kuril Basin of the Sea of Okhotsk (depths of 3301 m) has the following characters: vertebrae 55, pectoral-fin rays 26, caudal-fin rays 9, pore pattern 2-6-7-1 and peritoneum black; it differs from congeners by the absence of pleural ribs, deep and compressed leaf-like body (greatest depth 119 % lc, depth above anal-fin origin 113 % lc), small head (18 % SL), short pectoral fin (11 % SL) and cartilaginous-like tissue surrounding the dorsal fin. Careproctus pulcher sp. nov. and Careproctus globulus sp. nov., both having 46 vertebrae, are found on the Pacific side of the Bussol Strait at depths of 2350-2358 m. Careproctus pulcher sp. nov. is characterized by pectoral-fin rays 31-32, caudal-fin rays 10, pore pattern 2-6-7-1 and peritoneum pale; it differs from the most similar congeners in having a shorter head (25.5-26.3 % SL in adults) and gill opening reaching ventrally to 4th pectoral ray. Careproctus globulus sp. nov. has the following characters: pectoral-fin rays about 24, caudal-fin rays 8 and peritoneum black; it differs from other species in having a globular body, deep curve of vertebral column and pore pattern 2-5-6-1. Thus, based on these collections, the underwater sill of the Bussol Strait is inhabited by different species of Careproctus than the neighboring abyssal plains, Kuril-Kamchatka Trench and the Kuril Basin of the Sea of Okhotsk. Careproctus laperousei sp. nov. is the most deep-water Careproctus in the North Pacific.

GMT-based geological mapping and assessment of the bathymetric variations of the Kuril-Kamchatka Trench, Pacific Ocean

This manuscript summarizes the results of the geospatial analysis undertaken by means of Generic Mapping Tools (GMT). The comparative assessment of the bathymetry of the Kuril-Kamchatka hadal trench was performed for southern and northern segments separated by the Bussol Strait. The formation of the hadal trench is affected by the impacts of local geological and geophysical settings varying along the trench. The methodological approach is as follows. The profiling was undertaken using GMT modules ‘grdimage’, ‘grdtrack’ and ‘psxy’. The modelling consists of the collected data of 10706 observation samples from 52 profiles in southern part and 12726 from 62 profiles in the northern segment. The GMT modules ‘psrose’ and ‘pshistograms’ were used to plot histograms and rose diagrams visualizing bathymetric variables of depths. The geology was mapped using GMT modules ‘pscoast’, ‘grdcut’, ‘grdcontour’ and ‘psxy’ to plot lineaments and geological objects (ophiolites, faults, earthquakes, trench, magnetic anomalies, tectonic slabs, fracture zones and volcanoes). The base map is based on the ETOPO Global Relief Model. The comparison of the bathymetry shown variations in the northern and southern segments: southern part reaches -8,200 m maximal depths while northern has -7,800 m. This is influenced by the geological settings: earthquakes magnitude and seismisity are higher in the south-west. The submarine terraces and floodplains were observed at -4000 m depth forming landforms located southwards off the Bussol Strait. This geospatial analysis contributes to the development of the geological mapping with an example of the Kamchatka area, a region with high seismisity and repeated earthquakes.

Interaction of Mesoscale and Submesoscale Eddies in the Sea of Okhotsk Based on Satellite Data

We have investigated the interaction between the mesoscale and submesoscale eddies in the deep Kuril Basin of the Sea of Okhotsk. An analysis of the long-term series of satellite altimetry observations (2000–2011) has demonstrated that the circulation in the Kuril Basin is determined by quasi-stationary mesoscale anticyclonic eddies. Based on the QuikSCAT SeaWind scatterometer satellite data, a negative vorticity wind-stress field exists over the deep part of the Sea of Okhotsk in the warm season, which generates anticyclonic circulation composed of mesoscale eddies. An analysis of the satellite infrared images reveals that submesoscale processes determine the interaction of mesoscale eddies with the waters of the zone of intense tidal mixing on the shelf of the Kuril Islands. Submesoscale cyclonic eddies are formed at the fronts of tidal mixing and near the Bussol Strait located in the central part of the Kuril Islands. Applications of Lagrangian analysis have shown that submesoscale eddies move at the periphery of the northern mesoscale eddy within the advective streamer limited by the transport barriers. The formation and destruction of submesoscale eddies caused by horizontal mixing leads to the injection of cold water rich in nutrients from the zone of intense tidal mixing to the deep Kuril Basin. In the summer period, high concentrations of chlorophyll-a are observed in the upper layer of the northeastern part of the Sea of Okhotsk due to the interaction between submesoscale and mesoscale eddies.

Tanaidacean faunas of the Sea of Okhotsk and northern slope of the Kuril-Kamchatka Trench

The Sea of Okhotsk is one of the world’s largest marginal seas; its benthic fauna, especially from deeper parts, remains virtually unexplored. The material for this study was collected in the Sea of Okhotsk, Bussol Strait, and from the northern slope of the Kuril-Kamchatka Trench, during the Russian-German expedition Sea of Okhotsk Biodiversity Studies (SokhoBio) onboard the RV Akademik M.A. Lavrentyev in 2015. Material was collected using a camera-equipped epibenthic sledge (C-EBS). Forty-six tanaidacean species representing 31 genera and 12 families were found in 19 samples collected at depths from 1696 to 4798 m. All the species were new to science. The highest number of species (44) was recorded in the deepest part of the Sea of Okhotsk (Kuril Basin), followed by the northern slope of the Kuril-Kamchatka Trench (16 species) and the Bussol Strait (3 species). Almost one-third of all tanaidaceans (14 species) were common to both sides of the Kuril Island archipelago. Our results reveal a substantial faunal exchange between those two areas, although the small number of samples makes final conclusions about faunal similarity between the Sea of Okhotsk and the Pacific Ocean not fully possible. The level of rarity and patchiness of the tanaidacean fauna was high. The large number of species and individuals per sample observed in the Sea of Okhotsk might reflect high food availability in this area.

Deep-sea amphipod fauna of the Sea of Okhotsk

During joint Russian-German SokhoBio expedition held in 2015, the deepest area of the Sea of Okhotsk (Kuril Basin), the Bussol Strait and the western abyssal slope of the Kuril-Kamchatka Trench were investigated using camera epibenthic sledge. In total, 19 stations ranged between 1696 and 4798 m depth were sampled. The amphipods constituted 10% of all macroinvertebrates and one fourth of all Peracarida. The identification of families resulted in 32 taxa of which two (Liljeborgiidae and Valettiopsidae) were recorded for the first time from the Sea of Okhotsk. The most abundant group was Corophiida (17.4%), followed by the Oedicerotidae (15.8%), the Phoxocephalidae (12.3%), and the Eusiridae (11.7%). A multivariate analysis carried on the amphipod family abundance data (three stations excluded), discriminated four different assemblages in the studied area: a Bussol Strait assemblage (group A, two stations, 2327–2333 m) dominated by Corophiida group; a Kuril Basin assemblage (group B, 11 stations, 3210–3366 m) characterized by Oedicerotidae and Phoxocephalidae; and two assemblages in the Kuril-Kamchatka Trench area: a single station (group C, 4681 m) dominated by Phoxocephalidae and two grouped stations (group D, 3371–4798 m) characterized by Lysianassoidea. The effect of environmental variables on amphipod taxocenosis was also discussed.

КОМПЛЕКСНЫЕ ГЕОЛОГО-ГЕОФИЗИЧЕСКИЕ ИССЛЕДОВАНИЯ ПОДВОДНОГО ВУЛКАНИЧЕСКОГО МАССИВА АРХАНГЕЛЬСКОГО (КУРИЛЬСКАЯ ОСТРОВНАЯ ДУГА)

The article presents the results of integrated geologic-geophysical investigation of the Arkhangelsky submarine volcanic massif, which is located in the Bussol Strait in the central zone of the Kurile Island Arc. The massif consists of amalgamated and eroded volcanic edifices and is built up of endogenous basalts and exogenous tuffs. Rocks and minerals to the exclusion of quartz are hydrothermally altered; moreover they were altered after the formation of tuff. High values of the natural remnant magnetization of dredged rocks are caused by the high content of single-domain and pseudo-single-domain grains of titanomagnetite and magnetite. The Arkhangelsky massif most likely was formed during periods of global geomagnetic disturbances. The authors have revealed feeders of the near-vertical and southeastern trends and causative magnetic blocks with different geometric and magnetic characteristics in the edifice of the massif. A peripheral magma chamber has been revealed between depths of 1100–1200 m. At the southeast foot of the massif we found large landslide blocks.

Deep-sea spoon worms (Echiura) from the Sea of Okhotsk and the adjacent slope of the Kuril-Kamchatka Trench

During the SokhoBio (Sea of Okhotsk Biodiversity Studies) expedition from July to August 2015, eleven sites across the Kuril Basin of the Sea of Okhotsk and the landward abyssal slope of the Kuril-Kamchatka Trench (KKT) off the Bussol Strait were surveyed and benthic communities were investigated. Samples comprised 260 echiurans from seven species of seven genera belonging to the family Bonelliidae, were collected at eight of the eleven sites of the SokhoBio expedition. The family Bonelliidae is most common in abyssal and hadal environments in the world ocean with high abundances in all investigated regions. The description of deep-water echiurans from the Sea of Okhotsk is the first one based on complete collected specimens with living colouration. The descriptions provide new information on the morphology and taxonomic details of the species, which were previously noted from the northwestern Pacific and described from damaged or incomplete specimens. Two species are identified as representatives of the two genera, Bengalus and Bonelliopsis, which never have been noted before in the northwestern Pacific and the genus Bengalus is reported for the first time in the Pacific. The knowledge of the geographic ranges of these genera are expanded and discussed.

First insights into macrofaunal composition from the SokhoBio expedition (Sea of Okhotsk, Bussol Strait and northern slope of the Kuril-Kamchatka Trench)

Macrofauna (46,343 invertebrates from 41 taxa) were collected by means of a camera-epibenthic sledge (C-EBS) during the expedition SokhoBio (Sea of Okhotsk Biodiversity Studies) on board of the RV Akademik M.A. Lavrentyev in 2015. In total 11 sites and 22 stations were sampled at bathyal and abyssal depths ranging from 1696 m to 4798 m in the Kuril Basin of the Sea of Okhotsk (16 stations), the Bussol Strait (two stations) and western slope of the Kuril-Kamchatka Trench (KKT) (four stations). Polychaetes occurred most frequently in the samples with 17,546 individuals, followed by Peracarida with 14,099 individuals (5625 isopods, 3887 amphipods, 3225 tanaids, 1269 cumaceans, and 90 mysids), Copepoda (4679 ind.) and Bivalvia (3999 ind.).Numbers of individuals ranged between 140 at station 3–10–6383 at station 7–3. The numbers of taxa per station were smallest at station 3–10 (4 taxa) and highest at station 2–7 (31 taxa).Peracarida were the most common malacostracan crustaceans recorded, with Isopoda comprising 40% of all peracarids within this fraction, followed by Amphipoda with 27%, Tanaidacea with 23%, Cumacea with 9% and Mysida with 1%. At station 3–10, not a single peracarid was sampled. Isopoda dominated most of the stations, especially in the abyssal sites of the Kuril Basin. Amphipoda occurred in higher numbers in the Bussol Strait at site 8 as well as at Pacific station 9-7. In the SokhoBio area, studied macrofauna was distributed very patchily.In terms of diversity and composition the abyssal macrofauna of the Kuril Basin shows an intermediate state between the adjacent studied abyssal areas: the semi-isolated Sea of Japan and the open abyssal plain of the Kuril-Kamchatka Trench (KKT) area.

Composition of deep-sea polychaetes from the SokhoBio expedition with a description of a new species of Labioleanira (Annelida: Sigalionidae) from the Sea of Okhotsk

During the SokhoBio expedition in 2015, deep-sea benthic invertebrate fauna of the Kuril Basin of the Sea of Okhotsk and the Pacific Ocean between the Bussol Strait and the Kuril-Kamchatka Trench was sampled on board of the R/V Akademik M.A. Lavrentyev. Over 18,400 polychaetes belonging to 48 families, 139 genera, and 189 species were found in the studied area. The abyssal zone of the Sea of Okhotsk and the Pacific slope of the Kuril-Kamchatka Trench are the areas of high polychaete diversity and species richness. The diversity of the Kuril Basin is higher than that in the deep-sea basin of the Sea of Japan and is comparable to that in the abyssal plain adjacent to Kuril-Kamchatka Trench. A total of 160 polychaete species belonging to 124 genera and 47 families were identified from depths of 1676–3366 m in the Kuril Basin. Over half of these (93 species, 58%) occur on the Pacific slope of the Kuril-Kamchatka Trench. The records of widespread and eurybathic species common to both the Kuril Basin and the Pacific slope confirm the relationship between the abyssal fauna of the Kuril Basin and deep sea North-West Pacific. Nine genera and 18 species have been reported for the North-West Pacific for the first time. One family, 36 genera and 49 species were first records for the Sea of Okhotsk. More than 40% of the collected polychaete species were new to science. Among these, a sigalionid Labioleanira okhotica sp. nov. described herein, is the deepest (3211–4803 m) record for the genus Labioleanira. This species is easily recognized by the lack of eyes, the presence of nodular auricles instead of ear-shaped ones, and the presence of small dorsal tubercles on chaetiger 3. The genus Labioleanira Pettibone, 1992 is newly recorded in the North-West Pacific. An updated key to the species of the genus Labioleanira is provided.

Deep-water Octocorallia (Cnidaria: Anthozoa) of the temperate Northern Pacific: Notes on the distribution and new bathyal-abyssal taxa from the Sea of Okhotsk

The published data about the deep-water octocoral fauna of the cold temperate Northwest Pacific (particularly Far East seas) remains scarce and mostly presented in a few papers published before 1970. This paper gives a list of Octocorallia collected from the Kuril Basin of the Sea of Okhotsk and the Bussol Strait in 2015 during the SokhoBio 2015 expedition. The present paper records seven species, of which three new deep-sea octocoral species and two new genera are described: Ignis rubeus gen. et sp. nov. attributed to the family Haimeidae, Aspera rosea gen. et sp. nov. attributed to the family Nephtheidae, and Radicipes sakhalinensis sp. nov. of the family Chrysogorgiidae. Distinctive characters for each new taxon are provided and depicted with scanning electron microscopy imaging. The present finding of previously undescribed species emphasizes the need for further surveys, particularly in shelf and deeper waters, in order to improve knowledge of this neglected fauna in Far East seas. The diversity and distribution of deep-water Octocorallia in the temperate Northwest Pacific are discussed based on the published literature and own data.

Desmosomatidae (Isopoda: Asellota) from the Kuril Basin of the Sea of Okhotsk: First data on diversity with the description of the dominant species Mirabilicoxa biramosa sp. nov.

During the SokhoBio expedition in 2015, the macrobenthos was sampled by an epibenthic sledge at eleven sites at the abyssal and bathyal depths of the Kuril Basin of the Sea of Okhotsk, in the Bussol Strait, and on the western abyssal slope of the Kuril-Kamchatka Trench (KKT). Desmosomatidae constituted 30% of all isopod specimens (Crustacea: Malacostraca). Twenty-three species in eight genera (Desmosoma, Chelator, Eugerda, Eugerdella, Mirabilicoxa, Momedossa, Prochelator, and Oecidiobranchus) were found in the abyss of the Kuril Basin (at depths of 3210–3366 m) and the KKT slope (3371–4798 m). From these 17 species were found in the Sea of Okhotsk. This is the first record of this family at the abyssal depths of the Sea of Okhotsk. At the bathyal sites, Desmosomatidae were absent. This is the first report of the genus Oecidiobranchus in the North Pacific. Twenty species (86%) are new to science. The abundance and species richness of Desmosomatidae in the abyssal zone of the Kuril Basin varied from 0 to 282 individuals and 14 species per station. No relationships were found between the data on desmosomatid composition and abiotic parameters in the abyssal zone of the sea. In contrast, low oxygen content in the bathyal zone of the Kuril Basin and strong currents in the Bussol Strait can prevent colonization by the Desmosomatidae. The desmosomatid fauna in the abyssal zone of the Sea of Okhotsk is linked to the Pacific abyssal fauna of the KKT area. Among desmosomatids collected in the Sea of Okhotsk, seven genera and 10 species were found previously in the KKT abyssal zone during the KuramBio expedition (2012). The shelf desmosomatid fauna of the Sea of Okhotsk is more similar to the fauna of the bathyal and even abyssal zones of the Sea of Japan than the abyssal zone of the Sea of Okhotsk. These distributional patterns can be explained by taking into account the hydrology of the Sea of Okhotsk. The dominant species in the abyssal zone of the Kuril Basin, which comprises 27% of all specimens of the family, Mirabilicoxa biramosa sp. nov., is described. The new species can be distinguished from all other species of the genus by the presence of biramous uropods. A modified diagnosis of the genus Mirabilicoxa is presented.

Unusually diverse, abundant and endemic deep–sea sponge fauna revealed in the Sea of Okhotsk (NW Pacific Ocean)

The deep–sea sponge fauna of the NW (North–West) Pacific has been re–examined with new and previously collected specimens. In total, 555 new sponge specimens were collected in the under–explored deep Kuril Basin (Sea of Okhotsk), Bussol Strait and adjacent NW Pacific Ocean sites during the Russian–German expedition SokhoBio (Sea of Okhotsk Biodiversity Studies) in 2015. Our knowledge of Sea of Okhotsk deep–sea sponge species has nearly tripled (additional 19 spp.) as a result of this expedition, taking the total of known deep–sea species to 32 for this region. Close to half of species collected were either new to science or new to this region, and two–thirds of species were only found at one site during this study. The Sea of Okhotsk is unlikely to be a sink population, and could be considered a source population for several species due to the large numbers of individuals found. The NE Kuril Basin (Sea of Okhotsk) harboured nearly half of all sponge individuals found during this expedition, and is more species diverse than other Kuril Basin sectors, highlighting the variability in abundance and diversity found in this basin; and is also far richer than the Bussol Strait and NW Pacific sites explored. These differences are potentially due to the presence of productive currents, variable substrates, and niche differences in throughout this region. The semi–enclosed abyssal sector of the Sea of Okhotsk is partially connected with the adjacent NW Pacific abyssal plains through the Bussol and Krusenstern straits, and these straits have enabled faunal connectivity. The long–term partial isolation of the Sea of Okhotsk, low population density of deep–sea sponges, high productivity, and its unusual marine environment, could be key to understanding the exceptional levels of regional deep–sea sponge endemism and diversity.

Description and DNA barcoding of Lycenchelys lenzeni, a new species of eelpout (Perciformes: Zoarcidae) from the deep sea off the Kuril Archipelago.

A new species of eelpout genus Lycenchelys Gill, 1884 is described based on seven specimens caught at a depth of about 2350 m in the Bussol Strait, southwest of the Kuril Island Simushir. The species differs from its congeners in the following combination of characters: vertebrae 26-28 + 100-102 = 126-130; interorbital and occipital pores absent; postorbital pores 3-4; suborbital pores 7 (rarely 6); preoperculomandibular pores 4 + 4; gill rakers 11-16; dorsal fin rays 118-122; anal fin rays 105-108; pelvic fin rays 2; middle and lower ray tips of pectoral fin very slightly exserted; lateral line double with mediolateral and ventral branches; pyloric caeca not developed. The new species is morphologically most similar to Lycenchelys micropora and Lycenchelys jordani, which differ from the new species in having three pelvic-fin rays (vs. two pelvic-fin rays in the new species). L. micropora has the pectoral-fin origin below body midline, whereas the new species has the pectoral-fin origin at body midline. Middle and lower ray tips of pectoral fin are very slightly exserted in L. lenzeni sp. nov., whereas they are well exserted in L. jordani and L. micropora. Mitochondrial COI sequences were analyzed from four paratype specimens and all show the same haplotype sequence. The DNA barcodes allowed discrimination of L. lenzeni sp. nov. from other species of Lycenchelys where sequence data were available. The nearest match with already published sequences was Lycenchelys antarctica, with a sequence similarity of 98.25%, followed by Lycenchelys aratrirostris (sequence similarities 97.95-97.96%) and L. jordani (sequence similarity of 97.81%).

First records of deep-sea Munnopsidae (Isopoda: Asellota) from the Kuril Basin of the Sea of Okhotsk, with description of Gurjanopsis kurilensis sp. nov.

The deep-sea Munnopsidae Lilljeborg, 1864 of the Kuril Basin of the Sea of Okhotsk, the Bussol Strait, as well as the western abyssal slope of the Kuril-Kamchatka Trench (KKT) off the Bussol Strait were studied. The material was collected during the expedition SokhoBio (Sea of Okhotsk Biodiversity Studies) in the summer of 2015. The first data on the composition and distribution of the family Munnopsidae from the SokhoBio samples are presented. In total 2190 individuals of Munnopsidae from 53 species, 26 genera and seven subfamilies have been collected at 19 of 21 C-EBS stations at all 11 sites of the SokhoBio expedition. The most abundant subfamily in the samples was Ilyarachninae Hansen, 1916 (36%), followed by Eurycopinae Hansen, 1916 (29%). In the Kuril Basin 39 species of 20 genera and 5 subfamilies were found, the main portion of munnopsids here was represented by the Ilyarachninae (39%), followed by the group of genera incertae sedis (31%) and Eurycopinae (27%). The abyssal munnopsid fauna of the Kuril Basin is an intermediate in terms of diversity and species richness between the adjacent studied abyssal areas, the Sea of Japan and the open abyssal of the KKT. Half of the collected species, 27 species (51%) are shared with the KKT area, 22 species (41.5%) are common to the Kuril Basin and the Pacific sites. About 80% of the collected species are new to science. One of the new species, Gurjanopsis kurilensis sp. nov. is described herein. GurjanopsisMalyutina and Brandt, 2007 is the only genus within the Munnopsidae having a posteromedial notch in the pleotelson containing tiny uropods and the anus. A similar notch in the pleotelson containing uropods within Janiroideа Kussakin, 1967 is known only in species of Jaera Leach, 1814 (Janiridae G.O. Sars, 1897). The male pleopods of Gurjanopsis which cover the pleopodal cavity of the pleotelson are unusual for the family. This “operculum” is formed by the small pleopods 1 and 2 and the enlarged exopods of pleopods 3. This is similar to the pleopodal structure found in the primitive asellote superfamilies Aselloidea Latreille, 1802 and Stenotrioidea Hansen 1905, while in Janiroideа only pleopods 1 and 2 are operculate. The new species is the third species of the rare genus Gurjanopsis and the first record of the genus, previously only known from the deep-sea of the Arctic and the Antarctic, for the Pacific Ocean. The finding a species of Baeonectes Wilson, 1982 in abyssal depths of the Kuril Basin is the deepest record of the genus.

Deep-sea Entoprocta from the Sea of Okhotsk and the adjacent open Pacific abyssal area: New species and new taxa of host animals

The Entoprocta fauna still remains almost unexplored: many geographical areas have not yet been studied for their diversity, and almost nothing is known about deep-sea species. We described four new species of solitary Entoprocta from the family Loxosomatidae. The material was collected within a depth range between 3206 m and 3580 m during the German-Russian deep-sea expedition SokhoBio aboard R/V Akademik Lavrentyev in July - August 2015 in the Kuril Basin of the Sea of Okhotsk, Bussol Strait, and the adjacent open Pacific abyssal area. We used methods of light and scanning electronic microscopy and also laser confocal microscopy for morphological studies. Maximum likelihood and Bayesian analyses of partial DNA sequences of 18S and 28S rRNA genes were used to reconstruct phylogenetic trees. Loxosomella aeropsis sp. nov. was found on spines of the sea urchin Aeropsis fulva; Loxosomella cyatiformis sp. nov. was found on shells of the propeamussiid bivalve Catillopecten squamiformis; Loxosomella malakhovi sp. nov. was found living as an epibiont of the nephtyid polychaete Aglaophamus sp., and Loxosomella sextentaculata sp. nov., as an epibiont of the spionid polychaete Laonice sp. Echinoidea and Bivalvia have been first recorded as hosts of loxosomatid entoprocts in their symbiotic associations. A molecular phylogenetic analysis of partial 18S rRNA and 28S rRNA of Loxosomella aeropsis sp. nov., L. cyatiformis sp. nov., and L. malakhovi sp. nov. show that these species nest in the clade of solitary entoprocts among other Loxosomella species. Musculature of investigated species, Loxosomella aeropsis sp. nov and L. malakhovi sp. nov., is typical for loxosomatids and includes the longitudinal muscles of a stalk, the musculature of the digestive tract, the atrial muscular ring, and tentacle muscles. Each species has species-specific muscles so details of myoanatomy can be used for identification of species in addition to other morphological features.

Arcturoid isopods (Isopoda: Valvifera) from the SokhoBio expedition: First records from the abyss of the Sea of Okhotsk with description of Neastacilla birsteini sp. nov.

In the samples of the expedition SokhoBio (Sea of Okhotsk Biodiversity Studies) arcturoid isopods were present at eight sites in the Kuril Basin of the Sea of Okhotsk (1685–3366m), the Bussol Strait (2327–2358m), and the western abyssal slope of the Kuril-Kamchatka Trench (KKT) (3371–3377m). They were represented by eight species of three genera and two families, Antarcturus, Chaetarcturus (Antarcturidae), and Neastacilla (Arcturidae). Six species turned out to be new to science. The composition of fauna and distribution of arcturoids in the Kuril Basin and the adjacent regions are discussed. A list of all arcturoid species known from the Sea of Okhotsk and the adjacent waters off the Pacific coast of the Kuril Islands and the Southeastern Kamchatka at depths > 500m is provided. In the abyss of the Sea of Okhotsk two species (Chaetarcturus cf. beddardi (Gurjanova, 1935) and Neastacilla birsteini sp. nov.) were found. Neastacilla birsteini sp. nov., the dominant species in the abyss of the Kuril Basin, is described herewith. The new species differs from all other species of the genus by the 6-articled antennae I. N. birsteini sp. nov. most closely resembles N. anophthalma (Birstein, 1963) comb. nov. nov. Both species can be distinguished from all other species of the genus by the absence of eyes and a long article 5 of antenna I which is longer than articles 1–3 together. N. birsteini sp. nov. differs from N. anophthalma in the following characters: the pleon of the new species is 1.5 times longer than pereonite 4 and has an elongated distal part with a notch at the apex; the pereopod I carpus is 3.2 times as long as wide.

Bivalve molluscs of the abyssal zone of the Sea of Okhotsk: Species composition, taxonomic remarks, and comparison with the abyssal fauna of the Pacific Ocean

SokhoBio expedition Until recently hardly anything was known about the abyssal bivalve fauna of the Sea of Okhotsk, which communicates with the Pacific Ocean via many straits between the Kuril Islands with a maximum depth of 2318m in Bussol Strait, and about its similarity with the deep-water fauna of the Pacific. Investigation of the materials collected by the SokhoBio Russian-German deep-sea expedition (RV “Akademik M.A. Lavrentyev”, 2015), and two Russian expeditions (RV “Toporok”, 1948; RV “Vityaz”, 1949) from the bottom of the Kuril Basin of the Sea of Okhotsk (2850–3366m depth) revealed a rich fauna of bivalves including 25 species belonging to 12 families, of which only 12 species (48.0%) were determined to the species level. Nine species (Poroleda extenuata, Katadesmia vincula, Dacrydium rostriferum, Bathyarca imitata, Catillopecten squamiformis, Channelaxinus excavata, Vesicomya pacifica, Cuspidaria cf. abyssopacifica, Myonera garretti) were first records for the Sea of Okhotsk. The richest families were Thyasiridae (7 species) and Cuspidariidae (6 species). The high diversity and richness of the bivalve fauna on the bottom of the Kuril Basin are probably caused by the favorable trophic conditions. The Kuril Basin is characterized by very high rates of sedimentation and high content of organic matter in the sediments. For estimation of connections between deep-water faunas of the Sea of Okhotsk and the Pacific Ocean, the SokhoBio expedition performed 1 station at the maximum depth of the Bussol Strait and 2 stations (3342–3432 and 4679–5013m) on the Pacific slope of the Kuril Islands opposite to the Bussol Strait, where 24 species belonging to 13 families were found. Among the 25 species found in the deep part of the Kuril Basin more than half of species (17 species, 68%) occur in the Pacific Ocean. Most of them are widespread in the northern Pacific and are eurybathic bathyal-abyssal species. This probably allows them to penetrate into the Sea of Okhotsk through deep straits between the Kuril Islands. Photographs and taxonomic remarks are provided for all identified species (15) that were found in the Sea of Okhotsk and/or the Pacific Ocean. Taxonomic decisions herein: Nuculana aikawai Habe, 1958 and Nuculana sagamiensis Okutani, 1962 are synonymized with Nuculana leonina (Dall, 1896); Arca (Bathyarca) nucleator Dall, 1908 is synonymized with Bathyarca imitata (Smith, 1885); for Leda extenuata Dall, 1897, a new combination is suggested, Poroleda extenuata (Dall, 1897).

Nemerteans from deep-sea expedition SokhoBio with description of Uniporus alisae sp. nov. (Hoplonemertea: Reptantia s.l.) from the Sea of Okhotsk

Approximately 90 nemertean specimens were obtained from the material collected by the SokhoBio expedition 2015 in the Kuril Basin of the Sea of Okhotsk and in the Pacific Ocean between the Bussol Strait and the Kuril-Kamchatka Trench. The collected samples included representatives of five nemertean groups: (1) Palaeonemertea; (2) Heteronemertea; (3) pelagic Hoplonemertea; (4) reptantian Hoplonemertea; (5) eumonostiliferous Hoplonemertea. Tubulanid palaeonemerteans, heteronemerteans, and eumonostiliferous hoplonemerteans dominated the samples. Systematic position of 20 specimens was estimated based on five gene markers (16S, 28S, 18S, COI, and H3). Unknown abyssal and hadal nemerteans from the basal family Carininidae were found near the Bussol Strait, as well as in the Kuril-Kamchatka Trench and the adjacent abyssal plain. Four heteronemertean species without longitudinal cephalic slits were collected from the Kuril Basin. The new records of abyssal Sonnenemertes cantelli in the Sea of Okhotsk and near the Bussol Strait confirm the relationships between the abyssal fauna of the Kuril Basin and parts of the Northwest Pacific fauna. The find of Uniporus alisae sp. nov. in the Sea of Okhotsk, described in the article, is the deepest (3301m) record for the genus Uniporus. The results of a phylogenetic analysis have shown that the new species is referred to Cratenemertea rather than to Polystilifera. A DNA analysis has shown that Nectonemertes major, described from the Sea of Okhotsk, is not a valid species. Gononemertes, obtained from the peribranchial cavity of carnivorous ascidians Culeolus sp. in the Kuril Basin, is closely related to Gononemertes sp. MCZ IZ 45558 from the abyssal plain of the Northwest Pacific, but both do not form a common clade with the shallow-water Gononemertes parasita.