Methane gas Seeps Along the Oxic/Anoxic Gradient in the Black Sea: Manifestations, Biogenic Sediment Compounds and Preliminary Results on Benthic Ecology

Abstract. Sediment parameters (grain size, organic content, chloroplastic pigments, Adenylates, Potential hydrolytic activity and electron transport system activity) and benthic biota were studied in methane seep area south-west of the Crimean Peninsula in the Black Sea over a depth range from 60 to 260m. A control transect with similar depths was performed in an adjacent nonseep area. Methane seepage in this region occurs from 35 to ˜ 85m depth, passing the oxic anoxic interface zone at 130 to 180m. The methane seep areas were characterized by abundant carbonate precipitates which occurred in various shapes from small, flat structures to tall chimneys with increasing anoxia. The carbonates were associated with distinct bacterial mats. Most of the measured biochemical parameters in the sediment were quite similar in the seep and nonseep areas. The content of organic matter was higher and grain size was more uniform in the nonseep areas. However, the seep areas were charaterized by highter proportions of the larger fauna (size classes 0.5–1 mm and ≥ 1mm) as well as increased total numbers of benthic fauna in the suboxic and upper anoxic zone. The animals did not show any seep-specific adaptations. In addition to methane seepage, highly variable hydrochemical and sedimentary conditions on the lower shelf and upper slope may also play an important role in structuring the composition and distribution of the benthic fauna.     

Influence of Sedimentation on the Geomorphology of the Northwestern Continental Margin of India

Based upon the analysis of about 10,000 line km of echosounding and bathymetric data and variations in mass accumulation rate along the NW continental margin of India (between Kori creek and Mumbai), we have deduced that in the northern region (in the vicinity of the River Indus) the shelf-break occurs at a shallower depth and the slope is shallower, has the steepest gradient (<1:20), is smoother with no major features, and has reduced width (slope edge at 1450 m; width 19 km than off Mumbai). The width and depth of the slope edge gradually increases southwards, and is at maximum off DamanMumbai (slope edge depth 2900 m; width 84 km). The intensity of the occurrence of physiographic features also increases southwards. The shelf edge off Saurashtra is undulating and on the slope, regional notches and benches (the most prominent at 560 m) are observed. Further southwards off Khambhat-Mumbai, the slope is characterized by the presence of bathymetric highs and lows. We have also observed numerous features on the shelf, with a variable depth of the shelf-break. The gradient of the continental slope is also reduced from the northern region to the southern region. The variations in the gradient of the slope and the presence of distinct physiographic features in this area are examined vis-a-vis fluvial supply of the sediments into the region.     

Community structure of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean)

Community structure and faunal composition of bathyal decapod crustaceans off South-Eastern Sardinian deep-waters (Central-Western Mediterranean) were investigated. Samples were collected during 32 hauls between 793 and 1598 m in depth over the 2003–2007 period. A total of 1900 decapod specimens belonging to 23 species were collected. Multivariate analysis revealed the occurrence of three faunistic assemblages related to depth: (i) an upper slope community at depths of 793–1002 m; (ii) a middle slope community at depths of 1007–1212 m and (iii) a lower slope community at depths greater 1420 m. In the upper and middle slopes the benthic ( Polycheles typhlops ) and epibenthic–endobenthic feeders (mainly Aristeus antennatus and Geryon longipes ), which eat infaunal prey, were dominant, followed by the macroplankton–epibenthic feeders such as Acanthephyra eximia and Plesionika acanthonotus . In the deepest stratum, the most remarkable feature was the prevalence of macroplankton–epibenthic feeders ( A. eximia and P. acanthonotus ). A small percentage of the benthic deep-sea lobster Polycheles sculptus was also present. The biomass presented higher values in the middle slope and declined strongly in the lower slope. There was no general pattern of mean individual weight/size versus depth among decapods, and the changes seemed to be species-specific with different trends.     

A Wandering Population of the HexactinelIid Sponge Pheronema carpenteri on the Continental Slope off Morocco, Northwest Africa

Abstract. A photo transect along the continental slope off Morocco, Northwest Africa revealed an extensive population of the hexactinellid sponge Pheronema carpenteri ( thomson , 1869). The population forms a distinct band parallel to the depth contours between 740 and 820 m. Because of the long persistence of dead hexactinellid skeletons, living and dead individuals of P. carpenteri were recorded, together with the spicular remains of disintegrated individuals. Furthermore, the presence of small individuals and that of other epifaunal elements were recorded. The peaks of abundance of dead and living sponges, respectively. are not at the same depth, the maximum abundance of living individuals being above that of the dead ones; small, i.e ., probably young P. carpenteri individuals were observed only in the upper zone. This can be interpreted as a successional phenomenon, i.e ., the population of P. carpenteri has apparently 'moved' slowly up the slope. The fauna associated with the P. carpenteri population along the Moroccan coast seems to be much poorer than that associated with another band-shaped population in the Porcupine Seabight investigated by B ett & R ice (1992). indicating that the presence of dense hexactinellid populations does not invariably lead to conspicuous benthic faunal enrichment.     

Benthic fauna of Blagopoluchiya Bay (Novaya Zemlya Archipelago,Kara Sea)

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.     

Small benthic size classes along the N.W. European Continental Margin: spatial and temporal variability in activity and biomass

In the context of the European OMEX Programme this investigation focused on gradients in the biomass and activity of the small benthic size spectrum along a transect across the Goban Spur from the outer Celtic Sea into Porcupine Abyssal Plain. The effects of food pulses (seasonal, episodic) on this part of the benthic size spectrum were investigated. Sediments sampled during eight expeditions at different seasons covering a range from 200 m to 4800 m water depth were assayed with biochemical bulk measurements: determinations of chloroplastic pigment equivalents (CPE), the sum of chlorophyll a and its breakdown products, provide information concerning the input of phytodetrital matter to the seafloor; phospholipids were analyzed to estimate the total biomass of small benthic organisms (including bacteria, fungi, flagellata, protozoa and small metazoan meiofauna). A new term ‘small size class biomass' (SSCB) is introduced for the biomass of the smallest size classes of sediment-inhabiting organisms; the reduction of fluorescein-di-acetate (FDA) was determined to evaluate the potential activity of ester-cleaving bacterial exoenzymes in the sediment samples.At all stations benthic biomass was predominantly composed of the small size spectrum (90% on the shelf; 97–98% in the bathyal and abyssal parts of the transect). Small size class biomass (integrated over a 10 cm sediment column) ranged from 8 g C m⁻² on the shelf to 2.1 g C m⁻² on the adjacent Porcupine Abyssal Plain, exponentially decreasing with increasing water depth. However, a correlation between water depth and SSCB, macrofauna biomass as well as metazoan meiofauna biomass exhibited a significantly flatter slope for the small size classes in comparison to the larger organisms.CPE values indicated a pronounced seasonal cycle on the shelf and upper slope with twin peaks of phytodetrital deposition in mid spring and late summer. The deeper stations seem to receive a single annual flux maximum in late summer. SSCB and heterotrophic activity are significantly correlated to the amount of sediment-bound pigments. Seasonality in pigment concentrations is clearly followed by SSCB and activity. In contrast to macro- and megafauna which integrate over larger periods (months/years), the small benthic size classes, namely bacteria and foraminifera, proved to be the most reactive potential of the benthic communities to any perturbations on short time scales (days/weeks). The small size classes, therefore, occupy a key role in early diagenetic processes.     

Dense infaunal assemblages on the continental slope off Cape Hatteras, North Carolina

Unusually dense assemblages of benthic infaunal invertebrates have been discovered in continental slope sediments off Cape Hatteras, North Carolina. Densities were highest on the upper slope, ranging from 24,055 to 61,244 (X¯=46,255) individuals m⁻² in nine samples taken at a 600-m site in 1984 and 1985, and from 15,522 to 89,566 (X¯=37,282) individuals m⁻² in single samples at 15 stations over a wider depth range of 530 to 1535 m in 1992. A lower slope station at 2000 m sampled six times in 1984–1985 and again in 1992, had densities consistently higher than 8500 individuals m⁻². Species richness and diversity are consistently lower on the Cape Hatteras slope than at other locations off North Carolina and elsewhere in the western North Atlantic. The 1992 studies indicated that the upper slope infaunal assemblages (600m) were dominated by oligochaetes, while the middle slope assemblages (800–1400 m) were dominated by the polychaeteScalibregma inflatum. This latter depth range could be defined into two assemblages based upon suites of less abundant species. At depths of 1500–2000 m, a lower slope assemblage dominated by various deposit feeding polychaetes and oligochaetes was found. Results from the 1984–1985 studies suggest seasonal or year-to-year patterns in the dominance ofS. inflatum andCossura longocirrata. Unusually high sedimentation rates and organic carbon flux have been recorded from the slope off Cape Hatteras and may account for the high infaunal productivity in the area. Most of the dominant infaunal organisms are species more typical of shallow, coastal habitats rather than deep-sea species that dominate other areas of the U.S. Atlantic continental slope. Parallel investigations regarding the nature of organic matter in the Cape Hatteras sediments have revealed a mixture of both marine and terrestrially derived carbon, only a small percentage of which is composed of the smaller molecular weight polyunsaturated fatty acids more typical of continental slope sediments. It is likely that the high percentage of refractory organic matter would favor the survival of preadapted shelf species over those from adjacent slope environments.     

2016年夏季舟山近岸海域底栖生物调查与研究

底栖生物是海洋环境质量的重要指标。2016年夏季对舟山近岸海域37个站位的底栖生物进行调查,此次调查共鉴定出底栖生物45种,平均栖息密度为41 ind/m2,平均生物量为3.92 g/m2,底栖生物的栖息密度和生物量基本上由西向东逐渐升高。底栖生物的种类、密度、生物量、多样性指数与水深及水质中的盐度、pH、悬浮物、总磷、总氮呈弱或中等程度相关,与沉积物中重金属（铜、锌、铅、镉、铬、总汞）、砷、有机碳呈弱或中等程度的相关性,尤其与镉含量的相关性最为明显。由ABC曲线分析可知,该调查海域底栖生物受到一定程度的扰动。与2005年该海域调查结果比较表明,该海域底栖生物的多样性指数平均值较2005年略有降低,平均生物量较2005年降低,但平均密度较2005年升高。此次调查出现无底栖生物站位所占的比例较2005年上升。研究表明,2016年舟山海域海洋环境质量状况劣于2005年,应加强海洋环境监测与治理。     

Foraminifera from the continental slope off Cape Hatteras, North Carolina

The recent benthic meiofaunal foraminiferal assemblage from the continental slope (590-2 003 m) off Cape Hatteras, North Carolina exhibits high species richness and evenness, moderate diversity values, and lacks numerically dominant species. The preserved planktic assemblage has relatively low species richness, high evenness, low diversity, and a few numerically dominant species. Approximately 9% of the benthic species are those that typically live within continental shelf depth ranges. The benthic assemblage abundances and diversities do not follow depth patterns or geophysical characteristics. No biogeographic boundary can be described within the study area for meiofaunal foraminifera. Oxygen limitation does not appear to be a factor affecting the benthos of the North Carolina continental slope based upon the community structure of the benthic foraminifera, if total assemblage is assumed to reflect the recently living community. The high carbonate content of sediments in the area may be explained by foraminiferal tests. Within the study area, the foraminiferal assemblages are uniform, and probably reflect relative consistency of primary environmental variables as well as dynamic downslope transport and high influx of material from the water column in the vicinity where the Gulf Stream and the Western Boundary Undercurrent cross.     

Cold seeps of the deep Gulf of Mexico: Community structure and biogeographic comparisons to Atlantic equatorial belt seep communities

Quantitative collections of tubeworm- and mussel-associated communities were obtained from 3 cold seep sites in the deep Gulf of Mexico: in Atwater Valley at 1890 m depth, in Alaminos Canyon at 2200 m depth, and from the Florida Escarpment at 3300 m depth. A total of 50 taxa of macro- and megafauna were collected including 2 species of siboglinid tubeworms and 3 species of bathymodiolin mussels. In general, the highest degree of similarity was between communities collected from the same site. Most of the dominant families at the well-characterized upper Louisiana slope seep sites of the Gulf of Mexico were present at the deep sites as well; however, there was little overlap at the species level between the upper and lower slope communities. One major difference in community structure between the upper and lower slope seeps was the dominance of the ophiuroid Ophioctenella acies in the deeper communities. The transition between upper and lower slope communities appears to occur between 1300 and 1700 m based on the number of shared species with the Barbados seeps at either end of this depth range. Seep communities of the deep Gulf of Mexico were more similar to the Barbados Accretionary Prism seep communities than they were to either the upper slope Gulf of Mexico or Blake Ridge communities based on numbers of shared species and Bray–Curtis similarity values among sites. The presence of shared species among these sites suggests that there is ongoing or recent exchange among these areas. An analysis of bathymodioline mussel phylogeography that includes new collections from the west coast of Africa is presented. This analysis also suggests recent exchange across the Atlantic equatorial belt from the Gulf of Mexico to the seeps of the West Nigerian margin.     

Bathymetric distribution patterns of Southern Ocean macrofaunal taxa: Bivalvia, Gastropoda, Isopoda and Polychaeta

The aim of this study is to compare the depth distributions of four major Southern Ocean macrobenthic epi- and infaunal taxa, the Bivalvia, Gastropoda, Isopoda, and Polychaeta, from subtidal to abyssal depth. All literature data up to summer 2008, as well as the unpublished data from the most recent ANDEEP I–III (Antarctic benthic deep-sea biodiversity: colonisation history and recent community patterns) expeditions to the Southern Ocean deep sea are included in the analysis. Benthic invertebrates in the Southern Ocean are known for their wide bathymetric ranges. We analysed the distributions of four of the most abundant and species-rich taxa from intertidal to abyssal (5200 m) depths in depth zones of 100 m. The depth distributions of three macrofaunal classes (Bivalvia, Gastropoda, Polychaeta) and one order (Isopoda) showed distinct differences. In the case of bivalves, gastropods and polychaetes, the number of species per depth zone decreased from the shelf to the slope at around 1000 m depth and then showed stable low numbers. The isopods showed the opposite trend; they were less species rich in the upper 1000 m but increased in species numbers from the slope to bathyal and abyssal depths. Depth ranges of families of the studied taxa (Bivalvia: 31 families, Gastropoda: 60, Isopoda: 32, and Polychaeta: 46 families) were compiled and illustrated. At present vast areas of the deep sea in the Southern Ocean remain unexplored and species accumulation curves showed that only a fraction of the species have been discovered to date. We anticipate that further investigations will greatly increase the number of species known in the Southern Ocean deep sea.     

Spatial and temporal variability of particulate matter in the benthic boundary layer at the N.W. European Continental Margin (Goban Spur)

Near bottom water samples and sediments were taken during five cruises to 6 stations forming a transect across the N.W. European Continental Margin at Goban Spur. Flow velocity spot measurements in the benthic boundary layer (BBL) always increased from the shelf to the upper slope (1470 m) from 5 to 9 cm s⁻¹ in spring/summer and from 15 to 37 cm s⁻¹ in autumn/winter. Decreasing values were detected at the lower slope (2000 m) and the lowest values of ca. 2 cm s⁻¹ at the continental rise at 4500 m water depth. Long term measurements with a benthic lander at 1470 m show that currents have a tidal component and reach maximum velocities up to 20 cm s⁻¹, sufficiently high periodically to resuspend and transport phytodetritus. During these long-term observations, currents were always weaker in spring/summer than in autumn/winter. Critical shear velocities of shelf/slope sediments increased with depth from 0.5 to 1.7 cm s⁻¹ and major resuspension events and Intermediate Nepheloid Layers (INLs) should occur around 1000 m. Chloroplastic Pigment Equivalents (CPE) ranged from 0.0 to 0.21 μg dm⁻³, Particulate Organic Carbon (POC) from 12 to 141 μg dm⁻³ and Total Particulate Matter (TPM) from 0.2 to 10.0 mg dm⁻³. Aggregates in the BBL occurred with a median diameter of 152 to 468 μm. Data on suspended particulate matter in the near-bottom waters showed that hydrodynamic sorting within the particulate organic fraction occurred. Phytodetritus was packaged in relatively large aggregates and contributed little to the total organic carbon pool in nearbottom waters (CPE/POC ca.0.2%). The main organic fraction has low settling velocities and high residence times within the benthic boundary layer. As POC was not concentrated in the near bed region the degree to which carbon is accessible to the benthic community depends on aggregate formation, subsequent settling and/or biodeposition of the POC. Close to the sea bed downslope transport may dominate. Under flow conditions high enough to resuspend fresh phythodetritus from sediments at the productive shelf edge, this could be transported to 1500 m (Goban Spur) or abyssal depth (Canyon site between Meriadzek and Goban Spur) within 21 days.     

Biological characterization of a whale-fall near Vancouver Island,British Columbia,Canada

Video analysis of a whale-fall discovered in the northeast Pacific Ocean, off Vancouver Island at a depth of 1288 m during ROV diving operations has identified 26 taxa of deep-sea benthic organisms inhabiting the seafloor immediately surrounding remnants of the whale skeleton. A photo-mosaic derived from high-definition video provides a quantitative visual record of the present condition of the site, the species richness, and substrate preference. Only the skull and caudal vertebrae remains of this large whale skeleton are estimated to have been approximately 16.5 m in length. Most organisms identified near the whale-fall are common benthic deep-sea fauna, typical of this water depth and seafloor composition. Much of this species richness comes from sessile suspension feeding cnidarians attached to the numerous glacial dropstones found throughout the area rather than the presence of the whale skeleton. Seep and bone specialists are rare (4 taxa) and may be, in part, a remnant population from a sulphophilic stage of whale-fall decomposition. Evidence of past colonization by Osedax sp. is visible on the remaining bones and we conclude that rapid degradation of the missing bones has occurred at this site as has been observed at whale-falls off central California in Monterey Canyon.     

The distribution and abundance of cephalopods on the continental slope of the eastern South Atlantic

During a cruise in March 1988 dedicated to investigation of the marine resources of South Africa's continental slope, 62 species in 22 families of Cephalopoda were collected from the Cape Canyon and Cape Point Valley. Multivariate analysis revealed a clear distinction between cephalopods of the upper and lower continental slope in both benthic and epibenthic habitats. Todaropsis eblanae and Todarodes angolensis were indicator species for the upper slope benthic, from 300 to 500 m, but on the lower slope, in 700–900 m of water, they were replaced by Histioteuthis miranda and Opisthoteuthis agassizii. In the epibenthic, both upper and lower slopes were dominated by Abraliopsis gilchristi and Lycoteuthis ?diadema, but other species characteristic of the lower slope were the oceanic species Mastigoteuthis hjorti, Ctenopteryx sicula and Taonius sp. A. Cranchia scabra indicated the presence of oceanic water at stations 700–900 m deep. Other species of significance in the catches were Todarodes filippovae, Histioteuthis macrohista, Rossia enigmatica and Bathypolypus valdiviae. Species affinities indicate that the cephalopod fauna of the southern African continental slope includes the following zoogeographic components: southern African endemic, circum-Subantarctic species associated with Antarctic Intermediate Water, circum-global southern tropical/subtropical, tropical Indo-Pacific and cosmopolitan tropical/subtropical.     

白令海和楚科奇海表层沉积中的有孔虫及其沉积环境

通过对白令海和北冰洋楚科奇海39个表层沉积样品中有孔虫的定量分析,发现表层沉积中浮游有孔虫稀少可能与该区表层生产力低、碳酸盐溶解作用较强有关,而底栖有孔虫的分布则主要受表层初级生产力以及与水深相关的碳酸盐溶解作用和水团性质所控制,其中北冰洋楚科奇海陆架区有孔虫以Elphidium spp.组合和Nonionella robusta组合为主,丰度和分异度低,受北冰洋沿岸水团控制;白令海陆坡区有孔虫以Uvigerina peregrina-Globobulimina affinis组合为主,含N.robusta较多,丰度和分异度相对高,受太平洋中层和深层水团控制,但该区碳酸盐溶跃层和补偿深度(CCD)相对浅,约分别位于2000和3800m处.此外,白令海陆坡上部表层沉积中含有北冰洋陆坡区典型深水底栖有孔虫种Stetsonia arctica,说明白令海峡两侧的海区曾有深部水交流.     

Response of infaunal macrobenthos to the sediment granulometry in a tropical continental margin–southwest coast of India

Surficial sediment samples, collected from the continental margin of the southwest coast of India in July 2004, were examined for the grain size and soft-bottom macrobenthic fauna, to understand the sediment granulometry and its effect on the faunal distribution. Samples were collected using Smith-McIntyre Grab, from 20 to 200 m depth range, consisting of mid-shelf, outer shelf and slope. Fine-grained sediment located in the mid shelf and supported low faunal abundance. Polychaetes constituted the bulk of the fauna. Feeding guild changed with depth and sediment granulometry. Coexistence of deposit feeders and carnivores in outer shelf and deposit feeders and filter feeders in the slope region indicated the effective utilization of different food resources. In general, richness and diversity were high in the southern region. Depth wise, the diversity and abundance were relatively high in the 50–75 m depth range. Correlation and BIO-ENV analysis showed that combination of different factors such as sediment texture, sediment sorting and depth were found to influence the distribution of macrobenthos. Hence, spatial variations observed in benthic community were presumably linked to the variations in sediment granulometry and the energy level conditions prevailing in the area.     

Depth-related distribution and abundance of seastars (Echinodermata: Asteroidea) in the Porcupine Seabight and Porcupine Abyssal Plain,N.E. Atlantic

The depth-related distribution of seastar (Echinodermata: Asteroidea) species between 150 and 4950 m in the Porcupine Seabight and Porcupine Abyssal Plain is described. 47 species of asteroid were identified from ∼14,000 individuals collected. The bathymetric range of each species is recorded. What are considered quantitative data, from an acoustically monitored epibenthic sledge and supplementary data from otter trawls, are used to display the relative abundance of individuals within their bathymetric range. Asteroid species are found to have very narrow centres of distribution in which they are abundant, despite much wider total adult depth ranges. Centres of distribution may be skewed. This might result from competition for resources or be related to the occurrence of favourable habitats at particular depths. The bathymetric distributions of the juveniles of some species extend outside the adult depth ranges. There is a distinct pattern of zonation with two major regions of faunal change and six distinct zones. An upper slope zone ranges from 150 to ∼700 m depth, an upper bathyal zone between 700 and 1100 m, a mid-bathyal zone from 1100 to1700 m and a lower bathyal zone between 1700 and 2500 m. Below 2500 m the lower continental slope and continental rise have a characteristic asteroid fauna. The abyssal zone starts at about 2800 m. Regions of major faunal change are identified at the boundaries of both upper and mid-bathyal zones and at the transition of bathyal to abyssal fauna. Diversity is greatest at ∼1800 m, decreasing with depth to ∼2600 m before increasing again to high levels at ∼4700 m.     

Colonization and Disappearance ofMytilus galloprovincialisLam. on an Artificial Habitat in the Mediterranean Sea

AMytilus galloprovincialispopulation, settled on a new artificial habitat at 12 m depth in the Central Tyrrhenian Sea, was investigated for 10 years. The new substratum, located at a depth lower than the preferential range of the species, was colonized temporarily by mussels which reached very high densities and dominated the benthic community from their colonization until the third year. The length-frequency distribution analysis showed a progressively complex population structure with up to three cohorts. The yearly recruitments were observed once a year in spring. The growth curve provided a maximum length higher than that reported for shallow waters. Nevertheless, the gregarious habits of mussels and the reduced water movement caused edaphic modifications of the substratum, which was covered progressively by sediments and biodeposits (pseudofaeces). Consequently, the population structure was affected by a reduction of the newly recruited cohorts, and mussels disappeared after 5 years of colonization. This may be explained by the reduction in the substratum available for the first settlement (hydroid covering), as well as by the modification of the surface required for final settlement.     

Foraminifera in surface sediments of the Bering and Chukchi Seas and their sedimentary environment

Based on a quantitative analysis of foraminifera in 39 surface samples of the Bering andChukchi Seas, the nearly absence of planktonic foraminifera in the surface sediments can be related to the low surface primary productivity and strong carbonate dissolution in the study area. It has been revealed that the surface primary productivity, and carbonate dissolution and properties of water masses related to the water depth mainly control the distribution of benthic foraminifera. The shelf of the Chukchi Sea is dominated by the Elphidium spp. assemblage and Nonionella robusta assemblage with low foraminiferal abundance and diversity, which is controlled by the coastal water mass of the Arctic Ocean. The slope of the Bering Sea is dominated by the Uvigerina peregrina - Globobulimina affinis assemblage with abundant N. robusta, and relatively high foraminiferal abundance and diversity, which is controlled by the intermediate and deep water masses of the Pacific Ocean. However, the Bering Sea has relatively sha     

Patterns and drivers of asteroid abundances and assemblages on the continental margin of Atlantic Canada

Although continental shelf and slope environments typically exhibit high epifaunal biomass and have been subjected to increasing fishing pressure, ecological information on assemblages of non‐commercial invertebrate species from subtidal and bathyal areas remains limited. Sea stars (Echinodermata: Asteroidea), which are known to influence communities through their feeding habits, have received less attention than structural taxa such as corals and sponges. To better understand the ecological roles of asteroids on continental shelves, we investigated ~30 species and assessed their distributions and co‐occurrence with other benthic invertebrates on the shelf and slope of Eastern Canada. Using fisheries data and in situ video footage, we compiled a large dataset covering ~600,000 km² that included over 350,000 individual asteroid records (37–2243 m depth). Multivariate analyses revealed geographically distinct asteroid assemblages, with a maximal overall density at 400–500 m and the highest diversity at 500–700 m. The most abundant and densely occurring species was Ctenodiscus crispatus. We found that asteroids associate with corals, sponges, bivalves, and other echinoderms, and that depth and substrate influence these assemblages. We identified species likely to affect coexisting organisms by their burrowing behavior that can disrupt epi‐ and infauna (C. crispatus) and through predation on ecologically important corals (Hippasteria phrygiana). In addition to providing baseline distribution and ecological information for many bathyal asteroid species in the Northwest Atlantic, this work highlights the abundance and diversified roles of asteroids within continental shelf and slope ecosystems.