Polar cod (Boreogadus saida) and capelin (Mallotus villosus) as key species in marine food webs of the Arctic and the Barents Sea

Abstract Polar cod and capelin are key species in Arctic and sub-Arctic marine food webs, respectively, and the objective of this study is to compare and contrast the two species. Their distributions are dependent on water masses, with polar cod being associated with cold, sub-zero Arctic water, whereas capelin is distributed further south into Atlantic water masses. The distribution of polar cod is more static than that of capelin, whose distribution extends further north in warm years and fluctuates greatly based on predator–prey relationships. The species occur sympatrically in the Barents Sea, with large standing biomasses (0.5–1.5×106 t polar cod versus 3–4×106 t capelin). They overlap in distribution in the southern and eastern Barents Sea, whereas polar cod are most abundant in the icy waters of the Arctic. Both species aggregate in large schools and utilize zooplankton food sources, such as calanoid copepods. Polar cod also feed to a larger extent on amphipods, whereas capelin feed predominately on krill. Both species represent high-energy prey (lipids) for upper trophic levels. Global warming, with reduction in sea ice and increase in temperature, is expected to affect these two species differently. Polar cod will likely lose the sympagic (ice-associated) part of its life cycle and become more restricted in pelagic distribution during summer, whereas the capelin stock may expand to the north and east, although with considerable interannual fluctuations.