Trophic relationships and isotopic gradients among arctic and subarctic marine fauna

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Abstract
Stable carbon and nitrogen isotope measurements of benthic fauna were used to identify an isotopic gradient in plankton along the subarctic and arctic coast of Alaska, and to study food web relationships in 3 geographically distinct arctic environments: the southeast Bering, the Chukchi and the eastern Beaufort Seas. Isotope measurements were also made of selected fauna from the western Beaufort Sea and from the East Siberian Sea. Results show a pronounced difference in the carbon isotope composition of suspension feeders collected in the southeastern Bering, Chukchi and western Beaufort Seas (.delta.13C = -19 to -20.permill.) compared to the eastern Alaskan Beaufort and East Siberian Seas (-25 to -26.permill.). This geographic difference is greatest at lower trophic levels but is observed throughout the food web as a progressive decrease in 13C content of fauna from the southeast Bering to the eastern Beaufort Sea. Predatory and omnivorous gastropods were 13C-enriched relative to most organisms at most geographic locations, occupying a trophic level equivalent to that of demersal fishes. Trophic relationships among fauna from the different geographical areas were similar. In the Chukchi Sea, .delta.13C and .delta.15N values fell in a narrow range compared to other regions studied. The 13C enrichment of secondary consumers in the Chukchi relative to that of zooplankton was also small. This may reflect shorter food chains, which in the Chukchi Sea is related to a more direct coupling of benthic consumers to the very high pelagic primary production, little of which is grazed before reaching the sea bed.