Large-scale patterns in community structure of benthos and fish in the Barents Sea

Biogeographical patterns have an ecological basis, but few empirical studies possess the necessary scale and resolution relevant for investigation. The Barents Sea shelf provides an ideal study area, as it is a transition area between Atlantic and Arctic regions, and is sampled by a comprehensive survey of all major functional groups. We studied spatial variation in species composition of demersal fish and benthos to elucidate how fish and benthos communities co-varied in relation to environmental variables. We applied co-correspondence analysis on presence–absence data of 64 fishes and 302 benthos taxa from 329 bottom trawl hauls taken at the Barents Sea ecosystem survey in August–September 2011. We found highly significant similarities in the spatial pattern of distribution of benthos and fishes, despite their differences in motility and other ecological traits. The first common ordination axis separated boreal species in the south-west (Atlantic temperate water) from Arctic species in the north-east (Arctic cold water, ice-covered in winter). The second common axis separated shallow bank species from species found in deep basins and trenches. Our results show that fish and benthos communities had a similar relationship to the environmental gradients at the scale of hundreds to thousands of kilometres. We further discussed how fish–benthos interactions vary between sub-regions in the Barents Sea based on species traits and a food web topology for the Barents Sea. This study forms a basis for further investigations on links between fish and benthos communities in the Barents Sea

Variation of interspecific interactions at different ecological levels within an assemblage of Arctic marine predators

International audienceHow interspecific interactions change across scales is poorly known. Such knowledge might help us understand how species interact within communities and highlight scale-dependent ecological processes in play among species. Here, I propose to analyze the inter-annual variation of a species assemblage at different ecological levels. For this, I joined a two-stage modeling approach and a spatially explicit multivariate model to analyze the interspecies relationships among six species of pelagic seabirds from 2004 to 2015 in the Barents Sea. The large-scale (~400 km) pattern of interactions revealed by the analyses suggests a change in the composition of the seabird community along the climatic gradient from south to north. At medium-scale (~300 km), the community was split into two areas (i.e., Arctic and sub-Arctic areas) suggesting niche differentiation of Arctic and sub-Arctic species driven by resource partitioning and interference competition. At a small-scale (~40 km), species with different body sizes were positively associated suggesting facilitation for accessing food although the species with the smallest body size was negatively associated with the species involved in the facilitation process suggesting interspecific interference competition. Over the years, the large-scale patterns were persistent, suggesting niche establishment, while small-scale patterns were highly variable suggesting only ephemeral interactions among species. My study demonstrates that interspecific relationships are scale-dependent and play major roles in structuring community. Untangling how species are associated with different ecological levels over time is indispensable to better understand how community structure contributes to ecological system dynamics