Regional benthic food web structure on the Alaska Beaufort Sea shelf

Trophic structure and resilience of regional benthic food webs were studied on the Alaska Beaufort Sea shelf across 3 geographic regions (east, central, and west) and 2 depth ranges (14 to 90 m [shallow] and 100 to 220 m [deep]). Carbon (delta C-13) and nitrogen (delta N-15) isotope ratios were measured from water column and sediment particulate organic matter (POM) as markers of primary food sources and from common benthic invertebrate taxa. Isotopic niche space (delta C-13-delta N-15) occupied by benthic taxa provided measures of community-wide trophic redundancy and separation. delta C-13 values of the water column and sediment POM were patchy but generally indicative of terrestrial input across the shelf, especially near the mouth of the Colville River (< -25.5%). Food web structures in the shallow and deep western Beaufort regions, however, reflected marine carbon inputs, with most consumers occupying intermediate trophic levels (TLs) and food webs of intermediate trophic redundancy and separation relative to the other regions. In the central shallow and east regions, the terrestrial carbon found in sediments was mirrored in consumer tissues. The central deep region contained the highest proportions of higher TL taxa, particularly within the predator feeding guild, possibly reflecting resource partitioning of a limited prey spectrum. The comparatively large isotopic niche space in the central deep region, with high trophic niche separation but low trophic redundancy, suggests that this region may be most vulnerable to perturbations. This study provides a valuable new understanding of benthic food web dynamics in the understudied Alaska Beaufort Sea region and represents a baseline for future comparison.