Description: In the Arctic Ocean, increased sea surface temperature and sea ice retreat have triggered shifts in phytoplankton communities. In Fram Strait, coccolithophorids have been occasionally observed to replace diatoms as the dominating taxon of spring blooms. Deep-sea benthic communities depend strongly on such blooms, but with a change in quality and quantity of primarily produced organic matter (OM) input, this may likely have implications for deep-sea life. We compared the in situ responses of Arctic deep-sea benthos to input of phytodetritus from a diatom (Thalassiosira sp.) and a coccolithophorid (Emiliania huxleyi) species. We traced the fate of 13C- and 15N-labelled phytodetritus into respiration, assimilation by bacteria and infauna in a 4-day and 14-day experiment. Bacteria were key assimilators in the Thalassiosira OM degradation, whereas Foraminifera and other infauna were at least as important as bacteria in the Emiliania OM assimilation. After 14 days, 5 times less carbon and 3.8 times less nitrogen of the Emiliania detritus was recycled compared to Thalassiosira detritus. This implies that the utilization of Emiliania OM may be less efficient than for Thalassiosira OM. Our results indicate that a shift from diatom-dominated input to a coccolithophorid-dominated pulse could entail a delay in OM cycling, which may affect benthopelagic coupling.

Description: Arctic Ocean surface sea-ice conditions are linked with the deep sea benthic oxygen fluxes via a cascade of interdependencies across ecosystem components such as primary production, food supply, activity of the benthic community, and their functions. Additionally, each ecosystem component is influenced by abiotic factors such as light availability, temperature, water depth, and grain size structure. In this study, we investigated the coupling between surface sea-ice conditions and deep-sea benthic remineralization processes through a cascade of interdependencies in the Fram Strait. We measured sea-ice concentrations, a variety of different sediment characteristics, benthic community parameters, and oxygen fluxes at 12 stations of the LTER HAUSGARTEN observatory, Fram Strait, at water depths of 275–2500 m. Our investigations reveal that the Fram Strait is bisected into two long-lasting and stable regions: (i) a permanently and highly sea-ice-covered area and (ii) a seasonally and low sea-icecovered area. Within the Fram Strait ecosystem, sea-ice concentration and water depth are two independent abiotic factors, controlling the deep-sea benthos. Sea-ice concentration correlated with the available food and water depth with the oxygen flux. In addition, both abiotic factors sea-ice concentration and water depth correlate with the macrofauna biomass. However, at water depths 〉 1500m the influence of the surface sea-ice cover is minimal with water depth becoming more dominant. Benthic remineralization across the Fram Strait on average is � 1 mmol Cm

Description: Bioturbation is one of the key mediators of biogeochemical processes in benthic habitats that can have a high contribution to seafloor functioning and benthic pelagic coupling in coastal waters. Previous studies on bioturbation were limited to point locations and extrapolations in single regions, but have not accounted for regional differences under changing environmental conditions, though there are indications that species contributions will differ across regions or with biotic and abiotic context. To capture those differences and assess global patterns and commonalities, multi-regional analyses are imperative. Here for the first time, bioturbation potential (BPc), a functional indicator of benthic community bioturbation, was estimated based on macrofauna data from four regions (i.e. German Baltic Sea, German North Sea, Belgian part of the North Sea and the Eastern English Channel). For each region and sediment type we identified key species contributing to BPc. Comparison within and across regions demonstrated regional differences, and both overlap and mismatch between species that are functionally important and those that are dominant in biomass. Knowledge on the functionally important species is crucial when management objectives include the protection of certain ecosystem functions. Available environmental layers were used as predictors to model the spatial distribution of BPc for each area and to explore the underlying drivers of differences. Random forest models were trained using as response variables either i) BPc initially calculated per station; or ii) BPp – the species-specific contribution to BPc – for key species (with subsequent summation of their predicted full-coverage distributions to BPc). Maps of BPc distribution predicted by random forest were compared with those generated using natural neighbour interpolation. Overall, derived BPc values increased towards the German parts of the North and Baltic Seas. The relevance of BPc for ecosystem processes and functions, however, vary with biotic and abiotic settings. Results revealed a strong association of BPc with species diversity and region, but less with sediment grain size. A large range of BPc occurred when species richness was low. This suggests that the provisioning of high bioturbation activity is possible also under low diversity, where it is vulnerable due to reduced resilience. The executed multi-regional analysis allowed identifying regional differences in performance of macrofauna, suggesting the need for regionspecific conservation and management strategies. https://doi.org/10.1016/j.ecolind.2019.105945 Received 26 July 2019; Received in revised form 12 November 2019; Accepted 14 November 2019 ⁎ Corresponding author. E-mail address: mayya.gogina@io-warnemuende.de (M. Gogina). Ecological Indicators 110 (2020) 105945 1470-160X/ Crown Copyright © 2019 Published by Elsevier Ltd. All rights reserved. T

Description: The western Antarctic Peninsula is one of the fastest warming regions on Earth, leading inter alia to glacier retreat, increasing glacial discharge and ice-scouring. While glacier retreat lays bare new settling ground, glacial discharge and ice-scouring are known factors modifying the structure of coastal benthic communities. However, effects on benthic biogeochemical processes like benthic carbon cycling remain largely unknown. To assess this question, diver-operated in situ measurements and sampling were performed at Potter Cove (King George Island, Antarctic Peninsula) at three sites, which differ in intensity of glacial discharge, frequency of ice-scouring and time since the Fourcade glacier retreated. Total and diffusive oxygen uptake (TOU and DOU), inorganic nitrogen fluxes and phosphate fluxes were determined and sediment characteristics and abundances of the dominant bivalve Laternula elliptica analysed. At the glacier front (recently glacier-free, high glacial discharge, high ice-scouring frequency) TOU, inorganic nitrogen and phosphate fluxes were lowest, while the highest fluxes were determined at the oldest glacier-free site (intermediate glacial discharge, intermediate ice-scouring frequency). In contrast, DOU revealed the opposite trend. At all sites TOU exceeded DOU at least five-fold, indicating that biogeochemical fluxes in Potter Cove were primarily mediated by macrofauna. This was partly supported by the trend of abundances of Laternula elliptica. Furthermore, sediment characteristics changed from silt-dominated at the glacier front to sand-dominated at the other sites. Our results reveal that high glacial discharge and high ice-scouring frequency influences benthic community structure, resulting in suppressed mineralization rates at glacier fronts. In contrast, intermediate disturbance seem to structure benthic communities in a way that causes higher mineralization rates compared to sites with low disturbances. In conclusion, ongoing warming will cause increasing remineralization rates in Antarctic coastal waters due to warming related increasing disturbance by glacial discharge and ice-scouring and their modifying effect on benthic community structures.

Description: Thinning sea ice and shrinking sea-ice coverage is currently changing production regimes in the pelagic and sympagic Arctic Ocean. It usually remains unknown, how these changes affect export fluxes and hence, benthic communities and remineralization rates in the Arctic deep sea. To tackle this question, we took sediment samples from two bathymetric transects in the Arctic Fram Strait - East Greenland continental slope and West Spitsbergen continental slope (i.e. HAUSGARTEN observatory) – characterized by annual high and low sea-ice coverage, respectively. We measured benthic oxygen consumption rates along with various biogenic parameters and characterized macro- and meiofauna communities. A comparison of the two bathymetric transects suggest that low sea-ice coverage may lead to increased food availability for deep-sea benthic communities and enhanced remineralization rates down to a depth of 2000 m. Below 2000 m depth, food availability and remineralization rates are less or even not affected by sea-ice coverage. Furthermore, our data indicate that from high to low sea-ice covered areas macrofauna abundances shifts from polychaete-dominated to nematode-dominated. Such a shift has not been found for macrofauna biomass and meiofauna abundance. This comparative study provides insights into deep-sea benthic activities and community structure in a region strongly influenced by global change. It could help to assess the fate of Arctic benthic ecosystems under future climate scenarios.

Description: Marine renewable energy (MRE) projects are increasingly occupying the European North-Atlantic coasts and this is clearly observed in the North Sea. Given the expected impacts on the marine environment, each individual project is accompanied by a legally mandatory, environmental monitoring programme. These programmes are focused on the resultant effects on ecosystem component structure (e.g. species composition, numbers and densities) of single industrial projects. To date, there is a tendency to further narrow down to only a selection of ecosystem components (e.g. marine mammals and birds). While a wide knowledge-based understanding of structural impacts on (a selection of) ecosystem components exists, this evidence is largely lacking when undertaking impact assessments at the ecosystem functioning level (e.g. trophic interactions, dispersal and nutrient cycling). This critical knowledge gap compromises a scientifically-underpinned answer to the “so what” question of environmental impacts, i.e. whether the observed impacts are considered to be good or bad, or acceptable or unacceptable. The importance of ecosystem functioning is further acknowledged in the descriptors 4 and 6 of the Marine Strategy Framework Directive (EU MSFD) and is at the heart of a sustainable use and management of our marine resources. There hence is a fundamental need to focus on ecosystem functioning at the spatial scales at which marine ecosystems function when assessing MRE impacts. Here, we make a plea for an increased investment in a large (spatial) scale impact assessment of MRE projects focused on ecosystem functioning. This presentation will cover a selection of examples from North Sea MRE monitoring programmes, where the current knowledge has limited conclusions on the “so what” question. We will demonstrate how an ecosystem functioning-focused approach at an appropriate spatial scale could advance our current understanding, whilst assessing these issues. These examples will cover biogeochemical cycling, food webs and connectivity in a cumulative MRE impact assessment context. This presentation will highlight both the available knowledge base and further elaborate on the knowledge gaps. We will offer guidance on how these knowledge gaps could be further investigated, based on examples taken from the recently started projects FaCE-It, Functional biodiversity in a changing sedimentary environment: implications for biogeochemistry and food webs in a managerial setting (financed by the Belgian Science Policy) and UNDINE, Understanding the influence of man-made structures on the ecosystem functions of the North Sea (financed by Oil & Gas UK). This presentation will set the scene and offer further thinking on the current issues associated to MRE monitoring, particularly beyond the level of ecological structure and individual industrial projects. The overall message will aid advancing and strengthening a collaborative MRE monitoring, helping scientists, managers and regulators to answer the much needed “so what” question to support environmental assessments.