Description: The Arctic marine food web is based on organic matter produced by both phytoplankton and sea-ice algae. With the decline of Arctic sea ice, the sustained availability of organic carbon of sea-ice origin is unclear. Recently, the detection of the sea-ice diatom biomarker IP25 in a range of Arctic benthic macrofauna indicated that this is a highly suitable biomarker for the identification of organic carbon derived from sea-ice primary production in Arctic food webs. However, the data presented previously were restricted to a single geographical region in the Canadian Arctic. Here, we show that IP25 is present in sea urchins of the genus Strongylocentrotus collected from ten locations with seasonal sea-ice cover from the Canadian Archipelago, Greenland and Spitsbergen. In contrast, IP25 was not found in specimens of Echinus esculentus collected from the southwest UK, where sea ice is absent. Our findings provide evidence that the presence of IP25 in macrobenthic organisms can be used across different Arctic regions as a versatile indicator of a diet containing carbon of sea-ice origin.

Description: Increased public awareness of the global significance of polar regions and opening of the Russian Arctic to foreign researchers have led to a pronounced intensification of benthic research in Arctic seas. The wealth of information gathered in these efforts has markedly enhanced our knowledge on the Arctic benthos. While some scientific concepts have been corroborated by the novel findings (e.g., low endemism and high faunistic affinity to northern Atlantic assemblages), other common notions need to be revised, particularly with regard to the often-cited differences between Arctic seas and the Southern Ocean. It has been demonstrated that benthos assemblages vary broadly in diversity between Arctic regions and that, hence, the idea of a consistently poor Arctic benthos—being in stark contrast to the rich Antarctic bottom fauna—is an undue overgeneralization. In terms of biogeographic diversity, both Arctic and Antarctic waters seem to be characterized by intermediate species richness. Levels of disturbance—a major ecological agent known to heavily affect benthic diversity and community structure—have been assumed to be relatively high in the Arctic but exceptionally low in the Southern Ocean. The discovery of the great role of iceberg scouring in Antarctic shelf ecosystems, which has largely been overlooked in the past, calls for a reconsideration of this notion. The novel data clearly demonstrate that there are marked differences in geographical and environmental setting, impact of fluvial run-off, pelagic production regime, strength of pelago–benthic coupling and, hence, food supply to the benthos among the various Arctic seas, impeding the large-scale generalization of local and regional findings. Field evidence points to the great significance of meso-scale features in hydrography and ice cover (marginal ice zones, polynyas, and gyres) as ‘hot spots’ of tight pelago–benthic coupling and, hence, high benthic biomass. In contrast, the importance of terrigenic organic matter discharged to the Arctic seas through fluvial run-off as an additional food source for the benthos is still under debate. Studies on the partitioning of energy flow through benthic communities strongly suggest that megafauna has to be adequately considered in overall benthic energy budgets and models of carbon cycling, particularly in Arctic shelf systems dominated by abundant echinoderm populations. Much progress has been made in the scientific exploration of the deep ice-covered Arctic Ocean. There is now evidence that it is one order of magnitude more productive than previously thought. Therefore, the significance of shelf–basin interactions, i.e., the importance of excess organic carbon exported from productive shelves to the deep ocean, is still debated and, hence, a major topic of on-going research. Another high-priority theme of current/future projects are the ecological consequences of the rapid warming in the Arctic. Higher water temperatures, increased fluvial run-off and reduced ice cover will give rise to severe ecosystem changes, propagating through all trophic levels. It is hypothesized that there would be a shift in the relative importance of marine biota in the overall carbon and energy flux, ultimately resulting in a switch from a ‘sea-ice algae–benthos’ to a ‘phytoplankton–zooplankton’ dominance.

Description: Coralline algae (Corallinales, Rhodophyta) that form rhodoliths are important ecosystem engineers and carbonate producers in many polar coastal habitats. This study deals with rhodolith communities from Floskjeret (78°18′N), Krossfjorden (79°08′N), and Mosselbukta (79°53′N), off Spitsbergen Island, Svalbard Archipelago, Norway. Strong seasonal variations in temperature, salinity, light regime, sea-ice coverage, and turbidity characterize these localities. The coralline algal flora consists of Lithothamnion glaciale and Phymatolithon tenue. Well-developed rhodoliths were recorded between 27 and 47 m water depth, while coralline algal encrustations on lithoclastic cobbles were detected down to 77 m water depth. At all sites, ambient waters were saturated with respect to both aragonite and calcite, and the rhodolith beds were located predominately at dysphotic water depths. The rhodolith-associated macrobenthic fauna included grazing organisms such as chitons and echinoids. With decreasing water depth, the rhodolith pavements were regularly overgrown by non-calcareous Polysiphonia-like red algae. The corallines are thriving and are highly specialized in their adaptations to the physical environment as well as in their interaction with the associated benthic fauna, which is similar to other polar rhodolith communities. The marine environment of Spitsbergen is already affected by a climate-driven ecological regime shift and will lead to an increased borealization in the near future, with presently unpredictable consequences for coralline red algal communities.

Description: The Laptev Sea still ranks among the less known regions of the world’s ocean. Here, we describe the distribution and composition of macrobenthic communities of the eastern shelf and identify key environmental control factors. Samples were collected from dredge catches carried out at 11 stations at depths between 17 and 44 m in August/September 1993 during the TRANSDRIFT I cruise of the Russian R/V “Ivan Kireev.” A total of 265 species were identified from the samples, mostly crustaceans (94). Species numbers per station ranged from 30 to 104. Macrobenthic community distribution clearly showed a depth zonation, consisting of a “Shallow” zone (〈20 m), dominated by the crustaceans Mysis oculata (Mysidacea) and Saduria entomon (Isopoda) as well as molluscs, an “Intermediate” zone (20–30 m), characterised by a clear dominance of the bivalve Portlandia arctica, and a “Deep” zone (〉30 m) with bivalves P. arctica and Nuculoma bellotii as well as brittle stars Ophiocten sericeum and Ophiura sarsi being most abundant. According to a correlation analysis between faunal and environmental data a combination of duration of ice cover and water depth, respectively, showed the highest affinity to macrobenthic distribution. We conclude that the food input to the benthos, which is largely related to ice-cover regime, and the stress due to the pronounced seasonal salinity variability, which is primarily related to water depth, are prime determinants of macrobenthic community distribution and major causes of the prominent depth zonation in the Laptev Sea. Within the depth zones, sediment composition seems to be most significant in controlling the patterns in the distribution of the benthic fauna.

Description: Benthic communities north of Svalbard are less investigated than in other Arctic shelf regions, as this area was covered by sea-ice during most of the year. Improving our knowledge on this region is timely, however, since climate change is strongly evident there, particularly with regard to the extent of sea-ice decline and its huge ecological impact on all marine biota, including the benthos. Moreover, longer ice-free periods will certainly lead to an increase in human activity levels in the area, including bottom trawling. In two adjacent shelf and slope regions off northern Svalbard, we studied the composition of epibenthic megafauna and seafloor habitat structures by analyzing seabed images taken with both still and video cameras. In addition, we also used an Agassiz trawl to catch epibenthic organisms for ground-truthing seabed-image information. A wide variety of mostly sessile organisms 141 epibenthic taxa were identified in the images. The brittle star Ophiura sarsii and the soft coral Gersemia rubiformis were the most common species. At all stations 〉300 m in depth, evidence of trawling activities was detected at the seabed. The distribution of the benthic fauna in the study area exhibited a clear depth zonation, mainly reflecting depth-related differences in seabed composition. We conclude that natural factors determining the composition of the seafloor mostly affect the distribution and composition of epibenthic assemblages. Anthropogenic impact indicated by the trawl scours found is likely also important at smaller spatial scales.