Ice Algae-Produced Carbon Is Critical for Overwintering of Antarctic Krill Euphausia superba

Antarctic krill Euphausia superba (“krill”) constitute a fundamental food source for Antarctic seabirds and mammals, and a globally important fisheries resource. The future resilience of krill to climate change depends critically on the winter survival of young krill. To survive periods of extremely low production by pelagic algae during winter, krill are assumed to rely partly on carbon produced by ice algae. The true dependency on ice algae-produced carbon, however, is so far unquantified. This confounds predictions on the future resilience of krill stocks to sea ice decline. Fatty acid (FA) analysis, bulk stable isotope analysis (BSIA), and compound-specific stable isotope analysis (CSIA) of diatom- and dinoflagellate-associated marker FAs were applied to quantify the dependency of overwintering larval, juvenile, and adult krill on ice algae-produced carbon (αIce) during winter 2013 in the Weddell-Scotia Confluence Zone. Our results demonstrate that the majority of the carbon uptake of the overwintering larval and juvenile krill originated from ice algae (up to 88% of the carbon budget), and that the dependency on ice algal carbon decreased with ontogeny, reaching <56% of the carbon budget in adults. Spatio-temporal variability in the utilization of ice algal carbon was more pronounced in larvae and juvenile krill than in adults. Differences between αIce estimates derived from short- vs. long-term FA-specific isotopic compositions suggested that ice algae-produced carbon gained importance as the winter progressed, and might become critical at the late winter-spring transition, before the phytoplankton bloom commences. Where the sea ice season shortens, reduced availability of ice algae might possibly not be compensated by surplus phytoplankton production during wintertime. Hence, sea ice decline could seriously endanger the winter survival of recruits, and subsequently overall biomass of krill

Sea-ice habitat minimizes grazing impact and predation risk for larval Antarctic krill

Survival of larval Antarctic krill (Euphausia superba) during winter is largely dependent upon the presence of sea ice as it provides an important source of food and shelter. We hypothesized that sea ice provides additional benefits because it hosts fewer competitors and provides reduced predation risk for krill larvae than the water column. To test our hypothesis, zooplankton were sampled in the Weddell-Scotia Confluence Zone at the ice-water interface (0–2 m) and in the water column (0–500 m) during August–October 2013. Grazing by mesozooplankton, expressed as a percentage of the phytoplankton standing stock, was higher in the water column (1.97 ± 1.84%) than at the ice-water interface (0.08 ± 0.09%), due to a high abundance of pelagic copepods. Predation risk by carnivorous macrozooplankton, expressed as a percentage of the mesozooplankton standing stock, was significantly lower at the ice-water interface (0.83 ± 0.57%; main predators amphipods, siphonophores and ctenophores) than in the water column (4.72 ± 5.85%; main predators chaetognaths and medusae). These results emphasize the important role of sea ice as a suitable winter habitat for larval krill with fewer competitors and lower predation risk. These benefits should be taken into account when considering the response of Antarctic krill to projected declines in sea ice. Whether reduced sea-ice algal production may be compensated for by increased water column production remains unclear, but the shelter provided by sea ice would be significantly reduced or disappear, thus increasing the predation risk on krill larvae

Zooplankton communities at the sea surface of the eastern Indian sector of the Southern Ocean during the austral summer of 2018/2019

Knowledge on the distribution of zooplankton in the many unique habitats of the Southern Ocean is essential for understanding food web dynamics, assessing the impacts of environmental change and for managing the exploitation of marine living resources. Variation in the distribution of zooplankton may occur in the horizontal as well as the vertical plane, and the latter may show a diel cycle (diel vertical migration or DVM). Conventional sampling methods, including several types of nets and acoustics, often undersample or ignore the top 10 m of the water column. The surface waters may, however, host a specific zooplankton community and therefore be an important foraging ground for higher trophic level predators. In order to investigate the importance of the surface waters for understanding the distribution of species and potentially improving abundance estimates, the upper two meters of the water column were sampled in the eastern Indian sector of the Southern Ocean using a Surface and Under Ice Trawl (SUIT). Findings were compared to the zooplankton community structure in the epipelagic (15–200 m). Results showed that the surface zooplankton community could largely be divided into two regions. The surface community of the western side of the sampling area hosted large numbers of Antarctic krill, Euphausia superba, which were only present in low densities in the epipelagic depth layer. Densities of Limacina helicina were also relatively high in the west. The copepod Calanus propinquus and the amphipod Themisto gaudichaudii were present in relatively large numbers throughout the sampling area. T. gaudichaudii was the dominant species of the surface in the eastern side of the sampling area in the absence of Antarctic krill. Apart from cirripedia nauplii, no species were uniquely found in the surface water compared to the 15–200 m depth layer. Surface water sampling revealed patterns in vertical distribution and DVM, and showed that these patterns changed between the first and second half of the expedition. This could partially be explained by environmental variables but was likely also a result of sampling time and location, and associated variation in the size and ontogeny of species. Results revealed the impact of undersampling the surface layer regarding knowledge on distribution and vertical migration patterns of zooplankton species

Plastic and other anthropogenic debris in Arctic fox (Vulpes lagopus) faeces from Iceland

Anthropogenic debris, including plastic pollution, is a growing concern in the Arctic and negatively impacts both marine and coastal organisms. The aim of this study was to investigate the potential for using Arctic fox (Vulpes lagopus) faeces as a monitoring tool for plastic pollution in the Arctic environment. Arctic fox faeces were collected in different regions of Iceland and analysed for anthropogenic debris presence larger than 300 µm, and diet composition. In total, 235 faecal samples from 1999, 2017, 2018 and 2020 were analysed. The overall frequency of occurrence of plastic and other anthropogenic material was 5.11% and was found in samples across all regions and years. There were no statistical differences in anthropogenic debris ingested, depending on year or region. There were no obvious differences in diet composition between samples that contained anthropogenic debris and samples without. The suitability of Arctic fox faeces as a method to monitor plastic and anthropogenic debris levels in the Arctic environment remains debatable: Whilst the vast distribution range of the Arctic fox and the non-invasive collection methodology of faecal samples could be utilised as a good monitoring tool, the overall low uptake and unclear source of plastic and anthropogenic debris (marine or terrestrial) makes the interpretation of the data difficult. Nevertheless, debris ingestion by Arctic foxes remains a concern and warrants further studie

Video footage of Arnoux's beaked whales (Berardius arnuxii) observed in the Weddell Sea during POLARSTERN expedition PS129

Arnoux's beaked whales (Berardius arnuxii) were observed in the western Weddell Sea during a dedicated top predator helicopter survey from Polarstern. The group of eight whales were observed in the pack-ice on the 21 April 2022 at 14:37h, at -63.7172˚S, -51.2116˚W. This was the third group of Arnoux's beaked whales observed during expedition PS129

Zooplankton and environmental parameters sampled under-ice during POLARSTERN cruise PS81 (ANT-XXIX/7)

Sampling was performed during RV Polarstern expedition PS81 (ANT XXIX/7), between 31 August and 2 October 2013, across the ice-covered Weddell Sea, between 61°S, 42°W and 58°S, 25°W. Horizontal hauls were performed with a Surface and Under Ice Trawl (SUIT). Environmental data were collected with sensors mounted in the SUIT frame. The SUIT consists of a steel frame with a 2 m x 2 m opening and two parallel 15-m long nets attached: PLK (0.3 mm mesh; 0.5 m of opening width) and SUIT (7 mm mesh, 1.5 m of opening width). Zooplankton data contains mezo- and macrozooplankton species with numbers of specimens at each event (station). Trawled distances to derive areal abundance can be found in the environmental data table

Under-ice fauna abundance of Arctic pack ice north of Svalbard during the Polarstern expedition PS92 in 2015

We investigated the taxonomic composition and abundance of under-ice fauna (metazoans >300 µm) at fourteen stations in the Arctic Ocean, north of Svalbard. Sampling was conducted during spring in 2015 with the Surface and Under Ice Trawl (SUIT) and the catch of the plankton net (300 µm mesh size) was investigated for under-ice fauna. Abundances of individuals/m² were calculated from counting numbers

Sympagic Fauna in and Under Arctic Pack Ice in the Annual Sea-Ice System of the New Arctic

A strong decline and thinning of the Arctic sea-ice cover over the past five decades has been documented. The former multiyear sea-ice system has largely changed to an annual system and with it the dynamics of sea-ice transport across the Arctic Ocean. Less sea ice is reaching the Fram Strait and more ice and ice-transported material is released in the northern Laptev Sea and the central Arctic Ocean. This trend is expected to have a decisive impact on ice associated (“sympagic”) communities. As sympagic fauna plays an important role in transmitting carbon from the ice-water interface to the pelagic and benthic food webs, it is important to monitor its community composition under the changing environmental conditions. We investigated the taxonomic composition, abundance and distribution of sea-ice meiofauna (here heterotrophs >10 μm; eight stations) and under-ice fauna (here metazoans >300 μm; fourteen stations) in Arctic 1.5 year-old pack ice north of Svalbard. Sampling was conducted during spring 2015 by sea-ice coring and trawling with a Surface and Under-Ice Trawl. We identified 42 taxa associated with the sea ice. The total abundance of sea-ice meiofauna ranged between 580 and 17,156 ind.m–2 and was dominated by Ciliophora (46%), Copepoda nauplii (29%), and Harpacticoida (20%). In contrast to earlier studies in this region, we found no Nematoda and few flatworms in our sea-ice samples. Under-ice fauna abundance ranged between 15 and 6,785 ind.m–2 and was dominated by Appendicularia (58%), caused by exceptionally high abundance at one station. Copepoda nauplii (23%), Calanus finmarchicus (9%), and Calanus glacialis (6%) were also very abundant while sympagic Amphipoda were comparatively rare (0.35%). Both sympagic communities showed regional differences in community composition and abundance between shelf and offshore stations, but only for the under-ice fauna those differences were statistically significant. Selected environmental variables moderately explained variations in abundances of both faunas. The results of this study are consistent with predictions of diversity shifts in the new Arctic