Search

Between 3rd February and 30th March 2021 the research icebreaker RV Polarstern conducted an extensive multidisciplinary research expedition across the southern Weddell Sea, Antarctica. During the Continental Shelf Multidisciplinary Flux Study (COSMUS) expedition (designated research expedition PS124) the Ocean Floor Observation and Bathymetry System (OFOBS) was deployed 20 times to collect high resolution seafloor image and acoustic data with a 26-megapixel resolution camera, HD (high definition) video camera, forward facing acoustic camera and multibeam side-scan system from heights of between 1.5 and 4.5 m above seafloor. To localise the collected data the OFOBS was equipped with a Posidonia transponder for ultra- short baseline position triangulation, an Inertial Navigation System (INS) and a seafloor tracking Dynamic Velocity Logger (DVL). The 20 deployments were made across contrasting areas of the Weddell Sea, Filchner Trough, Filchner Sill and Filchner Shelf. Here, we present the full image data set collected from across the various deployments, as well as raw side-scan data, and derived high resolution bathymetric maps produced from this acoustic data after the cruise. All images are available from: https://doi.pangaea.de/10.1594/PANGAEA.936205 (Purser et al., 2021b) and https://doi.pangaea.de/10.1594/PANGAEA.932827 (Purser et al., 2021c). Acoustic data for all deployments is also available from PANGAEA, with the raw side scan data available at: https://doi.pangaea.de/10.1594/PANGAEA.939322 (Hehemann et al., 2021b), forward facing acoustic camera data at: https://doi.pangaea.de/10.1594/PANGAEA.939341 (Purser et al., 2021a). Seafloor topographic maps derived from the side scan data are available at: https://doi.pangaea.de/10.1594/PANGAEA.939087 (Hehemann et al., 2021a).

Parental care is a rather common reproductive strategy in fishes, particularly in species with low fecundity and large eggs as the Antarctic icefish (Channichthyidae). The infrequent use of underwater devices to record fish behaviour and the logistic limitations of operating in the Antarctic marine environment have prevented, so far, the collection of data about rare species. Integrating results from benthic trawling and underwater photographic images, we provide the first demographic and reproductive behavioural data for the channichthyid Neopagetopsis ionah, describing the nesting and parental care behaviour of a spawning population in the south-eastern Weddell Sea. The population sampled by the Agassiz trawl was dominated by females, and consisted of several post-spawning as well as a few mature females spread over a narrow size range. Based on otolith reading, the population included two cohorts estimated as four- and five-year-old fish. Following common trade-off between fecundity and egg size, females of N. ionah spawned few large eggs (733-1810 eggs/female, 4.9-6.5 mm in diameter). The nesting site was characterized by fine sediments with sparse gravel and the accompanying benthic invertebrate community showed low densities and was relatively poor. A total of 93 nests were counted along the video transect, most of them with a single guarding male or left unattended. Fish remains or whole dead specimens were frequently observed in the proximity of the nest. This observation represents the first record of post-spawning mortality associated with parental care which has never been documented before in Antarctic fishes.

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

Knowledge of seasonal dynamics and composition of meroplankton (larvae of benthic invertebrates) is rather limited for sub-Antarctic regions. We studied the seasonal dynamics of meroplankton in a sub-Antarctic proglacial basin (Gallegos Sound, Chile), by examining changes in the meroplankton community in relation to hydrographic variables along four sampling cruises between early winter 2010 and late winter 2011. The local meroplankton community was composed of 39 larval morphotypes distributed among 11 major taxa, being polychaetes the best represented (15 larvae morphotypes), and bivalve the most abundant. We found distinct seasonal differences in terms of meroplanktonic composition and abundance, with higher abundance and larval morphotype number during austral spring and late winter, and lower in summer and early winter. The pattern observed for meroplankton was directly related to seasonal variations of fluorescence of chlorophyll a and temperature. We found meroplankton abundances lower than those of other sub- and Polar environments. However, meroplanktonic temporal dynamics showed a common pattern for sub- and Polar fjords, suggesting a strong link between benthic spawning and the occurrence of phytoplankton blooms. Supplementary Information The online version contains supplementary material available at 10.1007/s00300-021-02823-6.

Ice retreat in West Antarctica and Antarctic Peninsula has led to important changes in seafloor communities and gains in benthic blue carbon. In most of the Antarctic, however, sea ice increased between the 1970s and 2014, but its effects on the benthos remain largely unexplored. Here, we provide a 1988–2014 record of macro- and megafauna from the north-eastern Weddell Sea shelf, where benthic biomass decreased by two thirds and composition shifted from suspension feeders to deposit feeders. Concomitant increases in sea-ice cover suggest a reduced flux of primary production to the benthos. As benthic communities are major repositories for Antarctic biodiversity and play an important role in biogeochemical cycling, the observed changes have far-reaching consequences for the Antarctic ecosystem and its feedback to the climate system. The findings underscore the importance of long-term ecological monitoring in a region vulnerable to warming and ice-shelf collapse. Sea-ice cover in Antarctica has increased over the last decades and reached a maximum in 2014. Here, the authors report strong declines in zoobenthic biomass and abundance and changes in community composition on the NE Weddell Sea shelf over 26 years, with implications for blue carbon and biochemistry in a globally important marine region.

This review focuses on studies dealing with the coupling between the benthic and pelagic realms on Antarctic shelves and on factors that regulate these processes. Such studies in Antarctic waters are scarce, especially on the shelves, where flux studies via moorings are highly endangered by drifting icebergs. Nevertheless, such studies are essential to understand these processes and functioning of the cold water ecosystem and how energy is transported through its different compartments. Different abiotic (e.g., currents, sea ice, water depth, topography of the seafloor, seasonality) and biotic (e.g., composition and structure of the benthic and pelagic flora and fauna, primary production, vertical migrations) factors are presented as parameters regulating the coupling between benthos and pelagos, here defined as benthos-pelagos interconnectivity. Regional variability in these parameters may result in delayed or even different coupling and/or decoupling of these realms. This is exemplarily discussed comparing the West Antarctic Peninsula (WAP) and Eastern Weddell Sea Shelf (EWSS). While in the WAP both compartments appear decoupled, on the EWSS both compartments appear tightly connected. The development of the benthos in the Larsen embayments after the shelf ice disintegration is described as an example of how changes in the pelagic realm affect and modify also the benthic realm.

Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m2, which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose fam- ily, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dol- loidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepi- dorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni).

18 pages, 6 figures, 5 tables, Due to extreme pack ice, the Filchner Region in the southern Weddell Sea is one of the least studied regions on the planet. Here, we provide a detailed description of the benthic communities of this high-Antarctic ecosystem, and assess the relationship between environmental factors and benthic distribution patterns. Fieldwork was performed in the austral summers of 2013-14 and 2015-16 during the R/V ‘Polarstern’ cruises PS82 and PS96. Using a combination of multibox corer (MBC) and seabed image data from 37 stations (water depths 243-1217 m), we differentiated 6 station groups. While 1 of these groups was comprised of a single station, the other 5 groups represented distinct benthic communities. Three of these correspond to the previously described Eastern Shelf, Southern Shelf, and Southern Trench communities. However, we found distribution shifts and MBC abundance and biomass reductions when comparing our results with earlier studies. The other 2 groups have novel characteristics and are presented here as an Ice/Ice Shelf Water-related community and a Continental slope community. Water depth in combination with 2 or 3 other environmental variables (out of 7 available) explained

Corer sampling and seabed imaging are two quantitative approaches used to investigate benthic fauna. Despite the complementary nature of these methods, very few studies have been done using both in parallel. Here, we compare benthic composition and abundance data derived from the quantitative faunistic analysis of both multibox corer samples (MBC) and seabed images (SBI) taken concomitantly at 16 stations in the Filchner–Ronne region of the southern Weddell Sea (Southern Ocean) during R/V Polarstern cruise PS82 (ANT-XXIX/9) in 2013/14. A total of 43 benthic taxa were found, 34 in MBC and 29 in SBI samples. Mean benthic abundance derived from MBC was 20 times higher than the SBI abundance (1708 vs. 71 ind m−2)—best explained by SBI being a method focusing on the epifauna alone, whereas MBC also captures the more abundant infauna. Differences in taxa caught by both gears demonstrated that MBC alone were not sufficient for a comprehensive representation of the entire benthic fauna. The among-station similarity patterns derived from both methods correlated significantly; a different combination of taxa best explained the specific distribution patterns. Overall, our results demonstrate similar and comparable spatial distribution patterns in the benthic communities by both methods. We therefore highly recommend the use of both, MBC and SBI in combination.