Trophic relationships and pelagicbenthic coupling during summer in the Barents Sea Marginal Ice Zone, revealed by stable carbon and nitrogen isotope measurements

Abstract

Food web structure and pathways from primary production were studied in pelagic, sympagic (ice-associated) and benthic communities during summer in a seasonally ice covered region of the northern Barents Sea. Stable isotopes of carbon ( 13 C) and nitrogen ( 15 N) were used as tracers of organic material through marine food webs and trophic levels of organisms, respectively. Measurements of 15 N show that sympagic amphipods occupy the lowest trophic levels (ca. 2), for primary consumers, followed by zooplankton (2.0 to 2.6), benthic suspension and deposit feeders (2.2 to 3.7), benthic carnivores (3.6 to 4.4) and fishes (3.3 to 4.4). The 13 C values indicate that zooplankton mainly graze on suspended particulate organic material (POM). Sympagic amphipods derive most of their energy from ice POM, but some species had 13 C values indicating that phytoplankton also contributes to their energy intake. 13 C values of some components of the benthic community suggest that POM settling out of the water column is efficiently exploited by the benthic fauna. Elevated 13 C values of the benthic fauna relative to zooplankton at some stations indicate that the degree of pelagic-benthic coupling at stations separated by only 90 km is determined by a combination of factors, including water-mass properties and the primary-production regime. These results may qualify findings of previous studies that have sampled from discrete locations or have pooled specimens collected from a broad area to make conclusions about food webs on a regional scale.