Bottom-pelagic links of hydrobionts in the Kara Sea according to data on δ15N and δ13C and feeding of fish

To compare trophic properties in pelagic and benthic communities of the Kara Sea, isotopic composition of carbon and nitrogen (δ13C and δ15N) was examined in tissues of zooplankton, zoobenthos, and fish. The organisms exhibited rather low δ13C values in the surveyed area. Because of stable difference in isotopic composition of carbon for zooplankton and zoobenthos, the pelagic and benthic communities could be separated by the level δ13C = –21.5 ‰, on average. The δ15N values for these communities varied within their 3 trophic levels in the range from 6.4 ‰ (for bivalve Serripes groenlandicus) to 16.3 ‰ (for lycod Lycodes seminudus), reflecting the input of predation. The bottom and pelagic communities in the Kara Sea demonstrated trophic interdependence. Both pelagic and bottom fish species, more or less, consumed both pelagic and benthic prey. Taking into account the content of 13C isotope in tissues of zooplankton and zoobenthos, about 40 % of the bottom nekton species were linked mainly with the pelagic food web and bypassed the benthic one. Pelagic fish fed mainly on pelagic prey, though the portion of zoobenthos in food of the dominant species — arctic cod had increased with the fish size increasing. On the contrary, the portion of zoobenthos in food of ruffed flounder had decreases with their size.