Macrobenthic mollusc assemblages and diversity in the West Antarctica from the South Shetland Islands to the Bellingshausen Sea

Although frequent studies have been made on the benthos assemblages living in the Southern Ocean, few studies have dealt with molluscan assemblages and ecology. During the research programmes BENTART carried out in austral summers of 2003 and 2006 in a study area including Low Island, West Antarctic Peninsula, Bellingshausen Sea and Peter I Island, 45 stations were sampled using quantitative box-corer, Agassiz trawl, epibenthic sledge and rock dredge, at depths of 53–3,304 m. These data were used to search and analyse the malacological assemblages. A total of 2,889 living specimens of molluscs belonging to 139 species of shelled Gastropoda, Bivalvia and Scaphopoda were recoded. Gastropods were the best-represented in species richness, but the bivalves accounted the major abundance and Cyamiocardium denticulatum (460 individuals) was the most abundant species. Species richness varied from 1 to 37 species and diversity showed great variations at different stations. Four groups of stations of low similarities and some differences in faunistic composition were observed: one that gathers the Antarctic Peninsula and Peter I Island, one that also includes the Low Island, and two composed by stations of Bellingshausen Sea.     

Hydroid assemblages from the Bellingshausen Sea (Antarctica): environmental factors behind their spatial distribution

Although scientific knowledge about the biodiversity of Antarctic benthic hydrozoans has considerably increased in recent years, little is known about their spatial distribution and underpinning factors. Trying to contribute to filling this gap, benthic hydroid spatial distribution in the Bellingshausen Sea (Southern Ocean) was studied. Samples were collected at 32 stations at depths between 86 and 3,304 m during Spanish Antarctic expeditions in 2003 and 2006. Sediments and bottom water properties were analyzed using an USNEL-type box corer and a Neil Brown Instrument System Mark III CTD, respectively. Forty species were reported (Acryptolaria sp., Stegopoma plicatile, Staurotheca dichotoma having the highest percentages of occurrence), representing ca. 19 % of the species richness of the known benthic hydroid fauna of the Southern Ocean. Three well-defined assemblages (shallow, deep and transitional) were established based on significant differences in species occurrence. Benthic hydroid spatial distribution in the Bellingshausen Sea seems to be controlled mainly by depth and substrate (most hydrozoan species are epibiotic), by species dispersal abilities and by species resilience to changing hydrodynamic conditions. The level of species richness found in the present study, compared with other Antarctic areas, gives support to arguments stated by authors against the idea that the Bellingshausen Sea is “a benthos desert” controlled by oligotrophic conditions and intense iceberg traffic.     

Quantitative analysis of soft-bottom polychaetes of the Bellingshausen Sea and Gerlache Strait (Antarctica)

The basin off the Bellingshausen Sea, in contrast to other better known areas such as the Antarctic Peninsula and the Ross and Weddell Seas, has been little investigated due to remoteness and the prevalence of ice for most of the year. The present study focuses on an analysis of polychaetes collected from soft bottoms of this sea and off the west coast of the Antarctic Peninsula (Gerlache Strait) by means of a box-corer (25 × 25 cm) in two intensive surveys carried out during austral summers of 2002–2003 and 2005–2006 (BENTART-03 and BENTART-06). Three different polychaete assemblages were determined from the classification and ordination analyses of sampling stations based on the Bray-Curtis similarity index. One group of stations encompassed the deep stations from the shelf of the Bellingshausen Sea, the second one the shallower stations from the same area and the third one those stations located near the coast of Peter I Island and Gerlache Strait, off the Antarctic Peninsula. The environmental variables involved in segregating these groups were several sedimentary features (redox potential, gravel content) and depth. The present study provides further support to previous ones that considered the shelf of the Bellingshausen Sea as a differentiated region within the Southern Ocean, clearly distinct to the adjacent Weddell and Scott Seas and the Antarctic Peninsula.     

Polychaete diversity in the Scotia Arc benthic realm: Are polychaetes tracers for faunal exchange?

The Scotia Arc is the only shallow-water and island bridge linking nowadays Patagonia and the Antarctic. The Antarctic Circumpolar Current as an oceanographic peculiarity makes this region an interesting biogeographic transition zone, because this frontal system traditionally is said to isolate the Antarctic fauna from that of the adjacent northern ecosystems. Based on benthos samples from three expeditions onboard R/V Polarstern, we studied distribution patterns of 200 polychaete species and 34 major benthic taxa in order to evaluate the role of polychaetes in the benthic realm of this part of the Southern Ocean. ANOSIM test distinguished three station groups: the central eastern Scotia Sea, the continental shelf off South America and stations at the tip of the Antarctic Peninsula. These station groups differed in organism densities and diversities with stations at the tip of the Antarctic Peninsula hosting the most diverse and dense community. The polychaete diversity patterns in the three assemblages evidenced closer connectivity between the tip of the Antarctic Peninsula and the central eastern Scotia Sea than between the continental shelf off South America with either the stations off the tip of the Peninsula or the central eastern Scotia Sea. This is probably supported by the Polar Front, which divides the island chain into two branches. Species distribution and community patterns of polychaetes appear to be associated with oceanographic and sediment conditions in this region. Most of the shared species showed the capability to tolerate differences in hydrostatic pressure. We suggest that the islands of the Scotia Sea may constitute a bridge for exchange of benthic species, particularly for polychaetes with eurybathic distribution and high dispersal capabilities.     

Genetic homogeneity of krill (Euphausia superba Dana) in the Southern Ocean

Summary Development of a comprehensive picture of the genetic population structure of the Antarctic krill (Euphausia superba) has been hampered by a lack of genetic data from two major areas of the species' distribution, the Bellingshausen Sea and the Ross Sea. Evidence from earlier studies of a discrete Bellingshausen Sea population was based on anomalous allele frequencies in two sample sets that were collected near the west coast of the Antarctic Peninsula rather than in the Bellingshausen Sea proper. In this paper we describe the first biochemical genetic data obtained on krill from the central Bellingshausen Sea and from the Ross Sea. Analyses of eight polymorphic loci in samples from these two areas have failed to provide any evidence of population structuring within the Pacific sector of the Southern Ocean, and have indicated that Pacific sector krill cannot be genetically discriminated from Atlantic sector krill or Indian Ocean sector krill. These findings further support the hypothesis of a single circumpolar breeding population of Antarctic krill.     

How well do we know the Antarctic marine fauna? A preliminary study of macroecological and biogeographical patterns in Southern Ocean gastropod and bivalve molluscs

The aim of this study was to use data for gastropod and bivalve molluscs to determine whether the fauna of the Southern Ocean is sufficiently well known to establish robust biogeographical and macroecological patterns. We chose molluscs for this work because they have been collected by almost every biological expedition to Antarctica, and are relatively well known taxonomically. Sampling of the continental shelf fauna is reasonably full and extensive, although new species are still being described and there are significant gaps in sampling off Wilkes Land and in the Bellingshausen and Amundsen Seas. Species richness was highest in those areas that have been subject to the most intense research activity and this pattern remained even after correction for sampling intensity. The low species richness of the Southern Ocean molluscan fauna compared with many tropical sites is confirmed, and is related principally to the absence of the large number of rare taxa that characterize some tropical assemblages. There is as yet no convincing evidence for a latitudinal cline in molluscan diversity within the Southern Ocean. Multivariate analyses defined biogeographical provinces very similar to those established previously, though they also identified a number of finer-scale sub-provinces including a small area of high diversity off Enderby Land. Most Southern Ocean gastropods and bivalves are rare, with limited distributions; relatively few taxa have circumpolar distributions.     

Abundance and distribution of invertebrate larvae in the Bellingshausen Sea (West Antarctica)

The central part of the Bellingshausen Sea has been poorly studied, partly because of the presence of ice during most of the year. The main aim of this study was to analyse the abundance and distribution of meroplankton, and the influence of oceanographic properties were investigated in the Bellingshausen Sea (West Antarctica) during the BENTART-06 cruise carried out in January–February 2006. Zooplankton samples were collected with a 80-μm mesh plankton net hauled vertically from a depth of 200?m to the surface at fifteen stations across the Bellingshausen Sea. Fifteen types of larval benthic invertebrates were found, with echinospira and nudibranch veligers being the most abundant. Hierarchical analysis and non-metric multidimensional scaling revealed a high degree of spatial variability in both larval abundance and larval types across the Bellingshausen Sea. The variability was significantly correlated with total chlorophyll-a and the contribution of large (>5?μm) phytoplankton to total chlorophyll, indicating the availability of food as an important factor determining the larval distribution observed. Nudibranch veligers, nemertean pilidia, echinoderm and planula larvae were more abundant at stations in the central Bellingshausen Sea, which was characterized by low phytoplankton biomass and production. Higher abundances of echinospira veligers and polychaete larvae were found at the more productive stations close to Peter I Island and the Antarctic Peninsula. The abundance and diversity of larval types found in the Bellingshausen Sea during the BENTART-06 cruise support the hypothesis that indirect development through larval swimming stages plays a key role in benthic recruitment in polar areas.     

Parmales species (siliceous marine nanoplankton) in surface sediments of the Weddell Sea, Southern Ocean: indicators for sea ice environment?

The distribution pattern of the Parmales, a recently described order of siliceous marine nanophytoplankton, is described and quantified in surface sediments of the Atlantic sector of the Southern Ocean. Additional samples were investigated from the Bransfield Strait and the eastern Bellingshausen Sea. Highest abundances occurred in nearshore areas of the southern and southeastern Weddell Sea. Due to the distribution of Parmales species, which is strictly linked to these neritic areas, influenced most of the year by sea ice, it is suggested that the presence of Parmales species may be an indicator of sea ice influence probably useful in later down core studies.     

Hansenomysis anaramosae n. sp., a new suprabenthic mysid (Crustacea: Mysidacea: Petalophthalmidae) from the Bellingshausen Sea (Southern Ocean)

A new petalophthalmid mysid, Hansenomysis anaramosae n. sp., is described from specimens sampled with a suprabenthic sled in the Bellingshausen Sea (Southern Ocean). Hansenomysis anaramosae is clearly distinguishable from its closest congener, H. angusticauda Tattersall, by the carapace sculpturing, the rostrum produced into a spine-like process, the shape and armature of the antennal scale, eyeplate, and telson. This new species is the fourth Hansenomysis species described from the Southern Ocean. A key to these Antarctic species is presented.     

Assemblages of sea stars (Echinodermata: Asteroidea) and brittle stars (Echinodermata: Ophiuroidea) in the Weddell Sea (Antarctica) and off Northeast Greenland (Arctic): a comparison of diversity and abundance

Composition and distribution of asteroid and ophiuroid assemblages were investigated by means of Agassiz trawl catches at 34 stations in 220- to 1,200-m depth in the Weddell Sea and at 17 stations in 90- and 830-m depth off Northeast Greenland. A total of 86 species (48 sea stars, 38 brittle stars) were identified in the Weddell Sea whereas off Northeast Greenland a total of 26 species (16 sea stars, 10 brittle stars) were recorded. In both study areas, brittle stars were numerically more important than sea stars, and abundances generally decreased with water depths. Multivariate analyses revealed a conspicuous depth zonation of sea and brittle stars off Greenland. Very high abundances of Ophiocten sericeum and Ophiura robusta characterized the assemblages on shallow shelf banks whereas in greater depths Ophiopleura borealis, Ophioscolex glacialis and Ophiacantha bidentata became dominant, albeit at significantly lower densities. Mass occurrences of brittle stars, such as those recorded on Greenlandic shelf banks, have not been discovered in the Weddell Sea, where distinct assemblages were discriminated in deep shelf trenches as well as on the eastern and southern shelf. Ophioplocus incipiens, Ophiurolepis martensi and Ophiurolepis brevirima were the most prominent species on the eastern shelf. Ophiacantha antarctica, Ophiurolepis gelida and Ophionotus victoriae on the southern shelf, and Ophiosparte gigas as well as the asteriod Hymenaster sp., in the shelf trenches. Overall, the Weddell Sea housed conspicuously more asterozoan species than the waters off Greenland. Higher species diversity was also evident at both a regional and local scale, especially for the eastern Weddell Sea shelf. However, because many species from the Weddell Sea are closely related, the Weddell Sea assemblages were not significantly different from the Greenland ones in terms of taxonomic diversity and distinctness. Received: 29 April 1996/Accepted: 10 June 1996     

Ophiuroid biodiversity patterns along the Antarctic Peninsula

Benthic ecological surveys using standardized methods are crucial for assessing changes associated with several threats in the Southern Ocean. The acquisition of data on assemblage structure over a variety of spatial scales is important to understand the variation of biodiversity patterns. During the ANT XXIX/3 (PS81) expedition of RV Polarstern, three different regions at the tip of the Antarctic Peninsula were sampled: the northwestern Weddell Sea, the Bransfield Strait, and the northern boundary of the South Shetland Archipelago in the Drake Passage. The aim of this study was to characterize the distribution and biodiversity patterns of ophiuroid assemblages in these regions and depths. We quantified different community parameters in terms of the number of species, abundance, and biomass. Additionally, we calculated various components of species diversity (alpha, beta, and gamma diversity) over the three regions. Based on the benthic surveys, we collected 3331 individuals that were identified to species level (17 species). Overall, species diversity, as measured based on rarefaction, species richness and evenness estimators, was higher in the Bransfield Strait compared to the Weddell Sea and Drake Passage. Two deep stations in the Weddell Sea showed high dominance only of Ophionotus victoriae. Significant differences in the patterns of alpha diversity were found among the regions but not between depth zones, whereas beta diversity showed no differences. Regarding the resemblance among the ophiuroid assemblages of each region, there was a significant gradient from east to west with a maximum distance between the stations in the Drake Passage and the Weddell Sea. This study provides a baseline for detecting potential effects related to climate change, and it furnishes a basis for the implementation of monitoring schemes of Antarctic assemblages.     

Asteroids,ophiuroids and holothurians from the southeastern Weddell Sea (Southern Ocean)

Until the early 1980s, the composition and distribution of the asteroid (starfish), ophiuroid (brittle star) and holothurian (sea cucumber) bottom fauna of the southeastern Weddell Sea was virtually unknown. This southernmost part of the Atlantic sector of the Southern Ocean is a typical high-latitude Antarctic region located in the circumpolar permanent pack-ice zone. It became accessible for large-scale scientific surveys only through the availability of modern ice-breaking research vessels, such as the German RV “Polarstern”. Here, we describe a dataset of the faunal composition and abundance of starfish, brittle star and sea cucumber assemblages in this area, based on collections from trawl catches carried out during three “Polarstern” cruises in 1983, 1984 and 1985. The set comprises a total of 4,509 records of abundances of 35 asteroid species (with a total of 2,089 specimens) and 38 ophiuroid species (with a total of 18,484 specimens) from 34 stations, as well as of 66 holothurian species (with a total of 20,918 specimens) from 59 stations including zero-abundances (absences). A synthesizing zoogeographical community analysis confirms the presence of three distinct assemblages of asteroids, ophiuroids, and holothurians with highest species richness on the eastern shelf. Overall, starfishes, brittle stars and sea cucumbers were present at all sites investigated in the study area but composition and abundance of asterozoan (asteroids and ophiuroids together) and holothurian fauna varied considerably. A synthesizing zoogeographical community analysis confirms the presence of three distinct assemblages of asteroids, ophiuroids, and holothurians with highest species richness on the eastern shelf. In the case of asterozoans, water depth and latitude seemed to be the most important drivers of assemblage distribution and composition. One of the holothurian assemblages was part of the rich macrozoobenthic community dominated by a diverse and abundant epifauna, mainly sponges and gorgonians. Another one was mainly composed of vagrant deposit-feeding species inhabiting a predominantly non-colonised substratum. In addition, a mixed holothurian assemblage was identified.     

Spatial distribution patterns of ascidians (Ascidiacea: Tunicata) on the continental shelves off the northern Antarctic Peninsula

Ascidians (Ascidiacea: Tunicata) are sessile suspension feeders that represent dominant epifaunal components of the Southern Ocean shelf benthos and play a significant role in the pelagic–benthic coupling. Here, we report the results of a first study on the relationship between the distribution patterns of eight common and/or abundant (putative) ascidian species, and environmental drivers in the waters off the northern Antarctic Peninsula. During RV Polarstern cruise XXIX/3 (PS81) in January–March 2013, we used seabed imaging surveys along 28 photographic transects of 2 km length each at water depths from 70 to 770 m in three regions (northwestern Weddell Sea, southern Bransfield Strait and southern Drake Passage), differing in their general environmental setting, primarily oceanographic characteristics and sea-ice dynamics, to comparatively analyze the spatial patterns in the abundance of the selected ascidians, reliably to be identified in the photographs, at three nested spatial scales. At a regional (100-km) scale, the ascidian assemblages of the Weddell Sea differed significantly from those of the other two regions, whereas at an intermediate 10-km scale no such differences were detected among habitat types (bank, upper slope, slope, deep/canyon) on the shelf and at the shelf break within each region. These spatial patterns were superimposed by a marked small-scale (10-m) patchiness of ascidian distribution within the 2-km-long transects. Among the environmental variables considered in our study, a combination of water-mass characteristics, sea-ice dynamics (approximated by 5-year averages in sea-ice cover in the region of or surrounding the photographic stations), as well as the seabed ruggedness, was identified as explaining best the distribution patterns of the ascidians.     

A most isolated benthos: coastal bryozoans of Bouvet Island

Bouvet Island is, uniquely, thousands of km from the next nearest land, even other islands. Its Southern Ocean location, isolation and the exposure of its surrounding cliffs have resulted in only rare visits by ship and its coastal marine fauna is little known. For animal taxa with non-pelagic larvae, such as cheilostome bryozoans, the shelf environment of Bouvet is a rare example of isolated oceanic communities. Agassiz trawl samples of the 2003 ANT XXI-2 cruise of the PFS Polarstern collected a total of 18 species of cheilostomes at four sites around Bouvet Island. Of these only four had been reported before amongst the 20 species of cheilostome previously known from this locality. Furthermore eight of the genera are reported for the first time from Bouvet Island. The assemblages were dominated by Austroflustra vulgaris, and in one case Nematoflustra flagellata. The bryozoan fauna seems to be depauperate and bears only low (32% at species and 46% at genus level) similarity to any location within 3,000 km. Its species composition is typically Southern Ocean, with most affinity to the Scotia Arc and Weddell Sea whereas at generic level it is most similar to the Subantarctic Prince Edward Archipelago.     

Characterization of the bacterial communities associated with the bald sea urchin disease of the echinoid Paracentrotus lividus

The microbial communities involved in the bald sea urchin disease of the echinoid Paracentrotus lividus are investigated using culture-independent techniques. Lesions of diseased specimens from two locations in France, La Ciotat (Mediterranean Sea) and Morgat (Atlantic Ocean), are examined by Scanning Electron Microscopy (SEM) and the diversity of their microbiota is analysed by Denaturing Gradient Gel Electrophoresis (DGGE) and 16S rRNA gene clones libraries construction. Microscopic observations demonstrated that only the central area of the lesions is invaded by bacteria but not the peripheral zone and the surrounding healthy tissues. Molecular analysis identified at least 24 bacterial genomospecies in bald sea urchin lesions: 5 are Alphaproteobacteria, 10 are Gammaproteobacteria, 8 are CFB bacteria and 1 is a Fusobacteria. Out of them, 4 are observed in both locations while 10 occur only in the Atlantic Ocean and 10 only in the Mediterranean Sea. Gammaproteobacteria are the most represented in clones libraries from both locations, with respectively 65% and 43% of the total clones. CFB and Alphaproteobacteria accounted for the majority of the remaining clones and were detected by DGGE in virtually all samples from both stations. Our results demonstrate that bacterial communities observed on diseased individuals of the same echinoid species but originating from distinct locations are not similar and thus support the hypothesis that bacteria involved in the worldwide echinoid disease commonly called the bald sea urchin disease are opportunistic and not specific.     

Possible spreading of toxic Alexandrium tamarense blooms on the Chukchi Sea shelf with the inflow of Pacific summer water due to climatic warming

A high abundance of resting cysts of the toxic dinoflagellate Alexandrium tamarense was recently reported in the vast continental shelf of the Chukchi Sea in the Arctic Ocean, suggesting that the species is widespread in the shelf. Nevertheless, little is known about the occurrence of A. tamarense vegetative cells in the water column of the arctic. Sea ice reduction and the inflow of Pacific summer water (PSW) through the Bering Strait have recently increased owing to warming in the shelf. To determine the spatial and temporal distributions of A. tamarense in the Chukchi Sea shelf and their relationship to the inflow of PSW, field samplings were conducted in the Chukchi Sea and north Bering Sea shelves three times during the summer of 2013 from July to October. Vegetative cells of A. tamarense was detected in both shelves at all sampling periods with a maximum density of 3.55 × 10³ cells L⁻¹. This species was also observed at the station at 73°N, indicating the northernmost record of this species to date. The center of the A. tamarense distribution was between the north Bering and south Chukchi Sea shelf during the first collection period, and spread to the north Chukchi Sea shelf during the second and third collection periods. The species occurrences were mainly observed at stations affected by the PSW, especially Bering shelf water. Water structure of PSW was characterized by warmer surface and bottom water temperatures, and increased temperatures may have promoted the cell growth and cyst germination of A. tamarense. Therefore, it is suggested that an increase in the PSW inflow owing to warming promotes toxic A. tamarense occurrences on the Chukchi Sea shelf.     

Distribution patterns of diatom surface sediment assemblages in the Laptev Sea (Arctic Ocean)

The modern diatom distribution in the Laptev Sea, Arctic Ocean, was investigated in 89 surface sediment samples. Diatom concentrations are relatively low showing values between 0.01×10⁶ and 6.7×10⁶ valves per gram dry sediment. Based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined: the ice diatom assemblage of the central region of the Laptev Sea, the Chaetoceros assemblage of the eastern and southeastern shelf, the Thalassiosira antarctica assemblage of the continental slope and deep sea, the freshwater diatom assemblage in the vicinity of river mouths and deltas, and the Thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central Laptev Sea shelf. The distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses. The main factors controlling the distribution of diatoms in the Laptev Sea are the riverine freshwater input during the summer which strongly affects the salinity conditions, and the sea-ice extent. Furthermore, the composition of the Thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes.     

Description of a new genus and species of zoarcid fish, <Emphasis Type="Italic">Bellingshausenia olasoi</Emphasis>, from the Bellingshausen Sea (Southern Ocean)

A new genus and species of zoarcid fish, Bellingshausenia olasoi, is described on the basis of five specimens collected from the Bellingshausen Sea, Southern Ocean, at depths of 602–615 m. Bellingshausenia is a lycodine that can be distinguished from all other zoarcid genera by the following combination of characters: seven branchiostegal rays, scapular foramen open, cranium narrowed, smooth ceratohyal-epihyal articulation, palatal arch well developed, supratemporal commissure and occipital pores absent, intercalar reduced and displaced backward and parasphenoid wing high. The relationships of the new genus are discussed.     

Filling biodiversity gaps: benthic hydroids from the Bellingshausen Sea (Antarctica)

The Bellingshausen Sea constitutes the third largest sea in the Southern Ocean, though it is widely recognized as one of the less-studied Antarctic areas. To reduce this lack of knowledge, a survey to study the biodiversity of its marine benthic communities was carried out during the Bentart 2003 and Bentart 2006 Spanish Antarctic expeditions. The study of the hydroid collection has provided 27 species, belonging to ten families and 15 genera. Twenty-one out of the 27 species constitute new records for the Bellingshausen Sea, raising the total number of known species to 37, as also do nine out of the 15 genera. Candelabrum penola, Lafoea annulata, and Staurotheca juncea are recorded for the second time. Most species belong to Leptothecata. Sertulariidae with 13 species (48%) is by far the most speciose family, and Symplectoscyphus with seven species (26%), including S. bellingshauseni sp. nov. and S. hesperides sp. nov., the most diverse genus. Considering the whole benthic hydroid fauna of the Bellingshausen Sea, 18 species (69%) are endemic to Antarctic waters, either with a circum-Antarctic (12 species, 46%) or West Antarctic (6 species, 23%) distribution, 23 (88%) are restricted to Antarctic or Antarctic/sub-Antarctic waters, and only three species have a wider distribution. Bellingshausen Sea hydroid fauna is composed of a relatively high diversity of typical representatives of the Antarctic benthic hydroid fauna, though with a surprisingly low representation of some of the most diverse and widespread Antarctic genera (Oswaldella and Schizotricha), what could be related to the fact that its shelf-inhabiting hydroid fauna remains practically unknown.