Food web structure in the high Arctic Canada Basin:: evidence from δ13C and δ15N analysis

The food-web structure of the Arctic deep Canada Basin was investigated in summer 2002 using carbon and nitrogen stable isotope tracers. Overall food-web length of the range of organisms sampled occupied four trophic levels, based on 3.8parts per thousand trophic level enrichment ( delta(15)N range: 5.3-17.parts per thousand). It was, thus, 0.5-1 trophic levels longer than food webs in both Arctic shelf and temperate deep-sea systems. The food sources, pelagic particulate organic matter (POM) (delta(13)C= -25.8parts per thousand, delta(15)N= 5.3parts per thousand) and ice POM (delta(13)C= -26.9parts per thousand, delta(15)N= 4.1parts per thousand), were not significantly different. Organisms of all habitats, ice-associated, pelagic and benthic, covered a large range of delta(15)N values. In general, ice-associated crustaceans (delta(15)N range 4.6-12.4parts per thousand, mean 6.9parts per thousand) and pelagic species (delta(15)N range 5.9-16.5, mean 11.5parts per thousand) were depleted relative to benthic invertebrates (delta(15)N range 4.6-17.7parts per thousand, mean 13.2parts per thousand). The predominantly herbivorous and predatory sympagic and pelagic species constitute a shorter food chain that is based on fresh material produced in the water column. Many benthic invertebrates were deposit feeders, relying on largely refractory material. However, sufficient fresh phytodetritus appeared to arrive at the seafloor to support some benthic suspension and surface deposit feeders on a low trophic level ( e. g., crinoids, cumaceans). The enriched signatures of benthic deposit feeders and predators may be a consequence of low primary production in the high Arctic and the subsequent high degree of reworking of organic material.