Using food web structure based on stable nitrogen and carbon isotopes to investigate pelagic-benthic coupling in different areas of the Barents Sea

Abstract

Pelagic-benthic coupling is generally assumed to be tighter on Arctic shelves than in lower latitudes, due to for example pronounced seasonal cycles of sunlight and primary production and a potential mismatch between the bloom and its pelagic consumers. Pelagic-benthic coupling is also often stronger in shallower areas compared to deeper areas, due to the shorter distance between the productive, euphotic zone and the benthic realm. Recent studies have investigated this relationship between the pelagic and benthic communities and found stable isotope ratios to be depleted in areas where the coupling is tight and enriched where coupling is weaker. This study compares the pelagic-benthic coupling in the NE Fram Strait and SW Barents Sea and on the continental shelf relative to the continental slope, via the use of stable nitrogen and carbon isotopes. The approach was to study those contrasting regimes, both at the level of select species and at that of feeding guilds. Niche metrics were calculated to describe and compare trophic structure between the different areas. Contrary to the expectations, however, no differences in isotopic enrichment between the NE Fram Strait and the SW Barents Sea or between the continental shelf and the continental slope were observed. Pelagic feeding guilds were depleted in $^1^5$N and $^1^3$C compared to benthopelagic and benthic feeding guilds. The similarities observed between the NE Fram Strait and SW Barents sea may be attributed to substantial advection of Atlantic Water, with its associated biota, in the West Spitsbergen Current, which would cause the two areas to have the same water mass characteristics. The similarities observed between the continental shelf and to the continental slope sea may be attributed to deep vertical mixing in the study area.