Timing of Ice Algal Grazing by the Arctic Nearshore Benthic Amphipod Onisimus litoralis

Sea ice algae have been widely discussed as a potential food source for pelagic and benthic animals in ice-covered waters, specifically in the light of current substantial changes in the Arctic ice regime. Stomach and gut contents of the Arctic nearshore lysianassid amphipod Onisimus litoralissampled from February to May 2003 indicate that Arctic ice algae were dominant food no earlier than the onset of ice melt. Crustaceans, common prey in a previous study, were absent in stomachs and guts during the survey period. Our data support the concept that sea ice-derived organic carbon is of specific relevance for Arctic plankton and benthos during the period of ice melt.On a souvent discuté du fait que les algues de glace de mer pourraient être une source d'alimentation pour les animaux pélagiques et benthiques des eaux recouvertes de glace, surtout à la lumière des changements considérables qui caractérisent le régime de glaciation de l'Arctique. Le contenu de l'estomac et des intestins des amphipodes lysianassides Onisimus litoralisen proximité des rives de l'Arctique qui a été échantillonné de février à mai 2003 indique que les algues de glace de l'Arctique étaient dominantes pas plus tôt qu'au moment de la fonte des glaces. Les crustacés, qui étaient une proie courante dans le cadre d'une étude antérieure, ne se retrouvaient pas dans les estomacs et les intestins des animaux au cours de la période d'échantillonnage. Nos données viennent soutenir le concept selon lequel le carbone organique dérivé de la glace de mer revêt une importance particulière pour le plancton de l'Arctique et le benthos pendant la période de la fonte des glaces

First trait-based characterization of Arctic ice meiofauna taxa

Trait-based approaches connect the traits of species to ecosystem functions to estimate the functional diversity of communities and how they may respond to environmental change. For the first time, we compiled a traits matrix across 11 traits for 28 species of Arctic ice meiofauna, including Copepoda (Subclass), Nematoda (Phylum), Acoela (Order), Rotifera (Phylum), and Cnidaria (Phylum). Over 50 years of pan-Arctic literature were manually reviewed, and trait categories were assigned to enable future trait–function connections within the threatened ice-associated ecosystem. Approximately two-thirds of the traits data were found at the genus or species level, ranging from 44% for Nematoda to 100% for Cnidaria. Ice meiofauna were shown to possess advantageous adaptations to the brine channel network within sea ice, including a majority with small body widths < 200 μm, high body flexibility, and high temperature and salinity tolerance. Diets were found to be diverse outside of the algal bloom season, with most organisms transitioning to ciliate-, omnivore-, or detritus-based diets. Eight species of the studied taxa have only been recorded within sea ice, while the rest are found in a mixture of sympagic–pelagic–benthic habitats. Twelve of the ice meiofauna species have been found with all life stages present in sea ice. Body width, temperature tolerance, and salinity tolerance were identified as traits with the largest research gaps and suffered from low-resolution taxonomic data. Overall, the compiled data show the degree to which ice meiofauna are adapted to spending all or portions of their lives within the ice

Isotopic turnover of polar cod (Boreogadus saida) muscle determined through a controlled feeding experiment

Polar cod (Boreogadus saida) is an important trophic link within Arctic marine food webs and is likely to experience diet shifts in response to climate change. One important tool for assessing organism diet is bulk stable isotope analysis. However, key parameters necessary for interpreting the temporal context of stable isotope values are lacking, especially for Arctic species. This study provides the first experimental determination of isotopic turnover (as half-life) and trophic discrimination factors (TDFs) of both δ13C and δ15N in adult polar cod muscle. Using a diet enriched in both 13C and 15N, we measured isotopic turnover times of 61 and 49 days for δ13C and δ15N, respectively, with metabolism accounting for >94% of the total turnover. These half-life estimates are valid for adult polar cod (>3 years) experiencing little somatic growth. We measured TDFs in our control of 2.6‰ and 3.9‰ for δ13C and δ15N, respectively, and we conclude that applying the commonly used TDF of ~1‰ for δ13C for adult polar cod may lead to misrepresentation of dietary carbon source, while the use of 3.8‰ for δ15N is appropriate. Based on these results, we recommend that studies investigating seasonal shifts in the diet of adult polar cod sample at temporal intervals of at least 60 days to account for isotopic turnover in polar cod muscle. Although isotopic equilibrium was reached by the fish in this study, it was at substantially lower isotope values than the diet. Additionally, the use of highly enriched algae in the experimental feed caused very high variability in diet isotope values which precluded accurate calculation of TDFs from the enriched fish. As a result of the challenges faced in this study, we discourage the use of highly enriched diets for similar experiments and provide recommendations to guide the design of future isotopic turnover experiments.publishedVersio

Weak seasonality in benthic food web structure within an Arctic inflow shelf region

The Arctic Ocean is characterized by pronounced seasonality in the quantity and quality of organic matter exported from the surface ocean. While it is well established that changes in food availability can alter the abundance, biomass and function of benthic organisms, the impact on food web structure is not well studied. We used bulk carbon and nitrogen stable isotope analysis to assess the quantity and quality of sediment organic matter and structure of the benthic food web in four seasons within the Northern Barents Sea (76°N − 82 °C). Despite a highly seasonal vertical flux, we found that the organic carbon and chlorophyll-a content of surface sediments was seasonally stable, suggesting a lack of seasonality in food availability at the seafloor. However, organic biomarkers indicate that the quality of sediment organic matter increased to a maximum in August and December, up to 6 months after the spring bloom. The seasonal stability of food quantity was mirrored in food-web structure (e.g., total isotopic range, number of trophic levels) which did not change significantly across sampling periods. We expected that suspension and deposit feeders would respond more readily to seasonal changes in food quality compared to predators. However, we observed no significant seasonal changes in the trophic levels or isotopic niche areas of benthic functional groups. The centroids of isotopic niches of all benthic functional groups shifted seasonally by <2 ‰ along the δ13C-axis, suggesting minimal shifts in carbon resource use. Because the northern Barents Sea experiences significant changes in seasonal sea ice cover, we expected that stable-isotope ratios of benthic organisms would show an increased consumption of sympagic-derived organic matter through less negative δ13C values in early spring and summer. However, only two taxa (the soft coral Gersemia spp. and bivalves in the family Yoldiidae) showed 13C-enrichment in spring or summer consistent with the assimilation of sympagic-derived organic matter, despite previous evidence suggesting widespread use of this carbon source. Overall, our results show that there is an apparent de-coupling in time between pelagic processes and benthic food-webs in which the accumulation and assimilation of high-quality organic matter occurs for benthos during the fall and early winter months when there is little to no fresh organic matter generated at the surface. This temporal mismatch highlights the importance of considering the timescales over which components of the marine ecosystem respond to short-term environmental changes and the methods employed to assess seasonality.Weak seasonality in benthic food web structure within an Arctic inflow shelf regionpublishedVersio

What we do in the dark: Prevalence of omnivorous feeding activity in Arctic zooplankton during polar night

During the productive polar day, zooplankton and sea-ice amphipods fulfill a critical role in energy transfer from primary producers to higher trophic-level species in Arctic marine ecosystems. Recent polar night studies on zooplankton and sea-ice amphipods suggest higher levels of biological activity than previously assumed. However, it is unknown if these invertebrates maintain polar night activity on stored lipids, opportunistic feeding, or a combination of both. To assess how zooplankton (copepods, amphipods, and krill) and sea-ice amphipods support themselves on seasonally varying resources, we studied their lipid classes, fatty acid compositions, and compound-specific stable isotopes of trophic biomarker fatty acids during polar day (June/July) and polar night (January). Lipid storage and fatty acid results confirm previously described dietary sources in all species during polar day. We found evidence of polar night feeding in all species, including shifts from herbivory to omnivory. Sympagic-, pelagic-, and Calanus spp.-derived carbon sources supported zooplankton and sea-ice amphipods in both seasons. We provide a first indication of polar night feeding of sea-ice amphipods in the pelagic realm

Ice-Associated Amphipods in a Pan-Arctic Scenario of Declining Sea Ice

Sea-ice macrofauna includes ice amphipods and benthic amphipods, as well as mysids. Amphipods are important components of the sympagic food web, which is fuelled by the production of ice algae. Data on the diversity of sea-ice biota have been collected as a part of scientific expeditions over decades, and here we present a pan-Arctic analysis of data on ice-associated amphipods and mysids assimilated over 35 years (1977–2012). The composition of species differed among the 13 locations around the Arctic, with main differences between basins and shelves and also between communities in drift ice and landfast sea ice. The sea ice has been dramatically reduced in extent and thickness during the recorded period, which has resulted in reduced abundance of ice amphipods as well as benthic amphipods in sea ice from the 1980’s to the 2010’s. The decline mainly involved Gammarus wilkitzkii coinciding with the disappearance of much of the multiyear sea ice, which is an important habitat for this long-lived species. Benthic amphipods were most diverse, and also showed a decline over the time-span. They had higher abundance closer to land where they are associated with landfast ice. However, they also occurred in the Central Arctic Ocean, which is likely related to the origin of sea ice over shallow water and subsequent transport in the transpolar ice drift. Recent sampling in the waters east and north of Svalbard has found continued presence of Apherusa glacialis, but almost no G. wilkitzkii. Monitoring by standardized methods is needed to detect further changes in community composition of ice amphipods related to reductions in sea-ice cover and ice type

Editorial: Towards a Unifying Pan-Arctic Perspective of the Contemporary and Future Arctic Ocean

An international symposium addressing pan-Arctic perspectives of the marine ecosystems of the Arctic Ocean took place in October 2017 and this editorial introduces the publications that derived from the conference. The symposium focused in particular upon physical forcing and biogeochemical cycling in surface waters of the Arctic Ocean, connectivity between surface and deep waters in the central basins and adjacent slopes and the ecology of the lesser-known shelf ecosystems. The symposium was the fourth in a sequence that has pan-Arctic integrations of Arctic Ocean ecosystems at its core. The series started in 2002 and its first volume was published under the title Structure and function of contemporary food webs on Arctic shelves (Wassmann, 2006). At the 2002-meeting, a suite of marine Arctic researchers from the main nations that work in the Arctic Ocean started applying the now-ubiquitous term pan-Arctic. The term underlined that the applied research goals and directions were more than a circumarctic perspective, but distinctly considered the entire expanse of the Arctic Ocean. Based upon this exercise, increased interest in the Arctic and some of the scientific endeavors of the 4th International Polar Year central projects and key oceanographers operating in the pan-Arctic region convened at the 2nd pan-Arctic integration symposium, entitled Arctic Marine Ecosystems in an Era of Rapid Climate Change in 2009 (Wassmann, 2011). After a decade of pan-Arctic research and building upon the foundation presented in Wassmann (2006, 2011) a 3rd conference was initiated in 2012, entitled Overarching perspectives of contemporary and future ecosystems in the Arctic Ocean (Wassmann, 2015). This Research Topic brings together 13 publications from the 4th pan-arctic integration symposium held in 2017, entitled Toward a Unifying Pan-Arctic Perspective of the Contemporary and Future Arctic Ocean. We, the editors of the Research Topic, are delighted with the breadth, quality and diversity of the papers. We introduce the essence of the publications under three, summarizing headlines • Physical connectivity, yet regionality • What shapes pan-Arctic primary production • The fate of production. Toward the end we incorporate the knowledge presented in this volume into the overall progress. and status of pan-Arctic marine ecosystem integration that has been achieved, so far, through the four pan-Arctic integration symposia

Uniform bathymetric zonation of marine benthos on a Pan-Arctic scale

While numerous regional studies of bathymetric zonation of benthic fauna globally have been done, few large-scale analyses exist, and no ocean-scale studies have focused on the Arctic Ocean to date. In the present work we, hence, examined bathymetric zonation of macro- and megabenthos over a depth range spanning from the shelf to the abyssal plain (14 – 5416 m) and regionally extending from the Fram Strait to the Beaufort Sea (as a whole hereafter called the Central Arctic). Based on 104 quantitative (box-corers and grabs) and 37 semi- quantitative (trawls) samples compiled from different studies we evaluated bathymetric zonation patterns in abundance, biomass and diversity, and also compared species composition among samples. Abundance and biomass decreased with depth from > 3000 ind. m−2 and > 40 g ww m−2 to ∼ 130 ind. m−2 and −2 corroborating previous studies. Diversity showed a parabolic pattern, peaking at ∼ 100–600 m. Cluster analysis revealed four (macrofauna) and five (megafauna) groups of benthic assemblages, including three that covered the upper and lower continental slope and the abyssal plains with relatively little overlap (named the Lower Shelf – Upper Slope 1, the Lower Slope and the Abyss). Substantial changes in benthic community composition were observed at depths 650–950 m (between the Lower Shelf – Upper Slope 1 and the Lower Slope) and 2600–3000 m (between the Lower Slope and the Abyss), so we interpreted these two depth horizons as major bathymetric boundaries. The first boundary (650–950 m) corresponds to the transition from sublittoral to bathyal fauna consistent with previous studies. The second boundary (2600–3000 m) reflects a decrease in benthic abundance, biomass and diversity within the Central Arctic abyssal plain. Bathymetric patterns and species overturn of benthos were relatively uniform throughout the entire Central Arctic continental slope and abyssal plain. For some regions of the Arctic Ocean, foremost for the area north from Greenland and Canadian Archipelago, benthic data are still unavailable and further research is needed

Developing an observational design for epibenthos and fish assemblages in the Chukchi Sea

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Published version available at https://doi.org/10.1016/j.dsr2.2018.11.005.In light of ongoing, and accelerating, environmental changes in the Pacific sector of the Arctic Ocean, the ability to track subsequent changes over time in various marine ecosystem components has become a major research goal. The high logistical efforts and costs associated with arctic work demand the prudent use of existing resources for the most comprehensive information gain. Here, we compare the information that can be gained for epibenthic invertebrate and for demersal fish assemblages reflecting coverage on two different spatial scales: a broader spatial coverage from the Arctic Marine Biodiversity Observing Network (AMBON, 67 stations total), and the spatial coverage from a subset of these stations (14 stations) that reflect two standard transect lines of the Distributed Biological Observatory (DBO). Multivariate cluster analysis was used to discern community similarity patterns in epibenthic invertebrate and fish communities. The 14 stations reflecting the two DBO lines captured about 57% of the epibenthic species richness that was observed through the larger-scale AMBON coverage, with a higher percentage on the more southern DBO3 than the northern DBO4 line. For demersal fishes, both DBO lines captured 88% of the richness from the larger AMBON spatial coverage. The epifaunal assemblage clustered along the south-north and the inshore-offshore axes of the overall study region. Of these, the southern DBO3 line well represented the regional (southern) epifaunal assemblage structure, while the northern DBO4 line only captured a small number of the distinct assemblage clusters. The demersal fish assemblage displayed little spatial structure with only one coastal and one offshore cluster. Again, this structure was well represented by the southern DBO3 line but less by the northern DBO4 line. We propose that extending the coverage of the DBO4 line in the northern Chukchi Sea farther inshore and offshore would result in better representation of the overall northern Chukchi epifaunal and fish assemblages. In addition, the multi-annual stability of epifaunal and, to a lesser extent also fish assemblages, suggests that these components may not need to be sampled on an annual basis and sampling every 2–3 years could still provide sufficient understanding of long-term changes. Sampling these assemblages every few years from a larger region such as covered by the AMBON project would create the larger-scale context that is important in spatial planning of long-term observing

Meroplankton Diversity, Seasonality and Life-History Traits Across the Barents Sea Polar Front Revealed by High-Throughput DNA Barcoding

In many species of marine benthic invertebrates, a planktonic larval phase plays a critical role in dispersal. Very little is known about the larval biology of most species, however, in part because species identification has historically been hindered by the microscopic size and morphological similarity among related taxa. This study aimed to determine the taxonomic composition and seasonal distribution of meroplankton in the Barents Sea, across the Polar Front. We collected meroplankton during five time points seasonally and used high-throughput DNA barcoding of individual larvae to obtain species-level information on larval seasonality. We found that meroplankton was highly diverse (72 taxa from eight phyla) and present in the Barents Sea year-round with a peak in abundance in August and November, defying the conventional wisdom that peak abundance would coincide with the spring phytoplankton bloom. Ophiuroids, bivalves, and polychaetes dominated larval abundance while gastropods and polychaetes accounted for the bulk of the taxon diversity. Community structure varied seasonally and total abundance was generally higher south of the Polar Front while taxon richness was overall greater to the north. Of the species identified, most were known inhabitants of the Barents Sea. However, the nemertean Cephalothrix iwatai and the brittle star Ophiocten gracilis were abundant in the meroplankton despite never having been previously recorded in the northern Barents Sea. The new knowledge on seasonal patterns of individual meroplanktonic species has implications for understanding environment-biotic interactions in a changing Arctic and provides a framework for early detection of potential newcomers to the system