Food spectrum and trophic position of an Arctic cephalopod, Rossia palpebrosa (Sepiolida), inferred by stomach contents and stable isotope (δ13C and δ15N) analyses

Rossia palpebrosa (Sepiolida) is the most abundant nekto-benthic cephalopod in the Arctic; however, its feeding and trophic ecology are largely unknown. This work aims to assess the role of this species in Arctic ecosystems based on the contents of its stomach and analyses of δ13C and δ15N stable isotopes in its beak. The main taxa identified in the food spectrum were Crustacea (frequency of occurrence: 52.1%), followed by Polychaeta (14.6%) and fishes (6.3%). Sipuncula and Echinoidea were occasionally found and were recorded here as R. palpebrosa prey for the first time, as well as Polychaeta and Euphausiacea. A significant geographic increase in δ13C values (mean ± SE, -19.3 ± 0.2‰) from the Barents Sea to West Greenland was found, but no significant ontogenetic increase, suggesting no migrations occurred among different water masses. Values of δ15N (8.7 ± 0.2‰) and trophic level (TL; 3.6 ± 0.1) revealed significant ontogenetic increases and an absence of geographic patterns, suggesting the trophic role of this species is similar throughout the studied part of the Arctic. Stable isotope values, TL and food spectrum for R. palpebrosa are close to Arctic nekto-benthic predatory fishes and shrimps, especially Pandalus borealis. However, sepiolids prey on organisms exceeding their own size and do not scavenge. A gradual ontogenetic decrease in isotopic niche width, while increasing diversity in the food spectrum of larger specimens, was observed in R. palpebrosa. However, δ13C values, i.e. variation in primary productivity supporting food sources, were more responsible for these ontogenetic differences in niche size than δ15N values

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