Spatial and temporal patterns of epibenthic community and food web structures in the Chukchi sea between 2004-2012

Abstract

The Chukchi Sea shelf, an area undergoing rapid environmental change and concurrently increasing human activity, supports communities of epibenthic organisms and food webs that are sustained by high primary productivity in the overlying water column and are influenced by physical environmental conditions. The goal of this study was to characterize these epibenthic communities (using trawl hauls) and benthic food webs (using carbon and nitrogen stables isotopes) in 2009 and 2012 and to identify persisting or changing patterns between 2004, 2009 and 2012 as part of NOAA's Russian-American long-term Census of the Arctic (RUSALCA) program. Fifteen stations each were sampled in August to September of 2009 and 2012 in the Chukchi Sea, of which eight repeat stations in the southern Chukchi were sampled in 2004, 2009 and 2012 for temporal comparisons. Epibenthic communities differed in structure between the northern and the southern study regions, with somewhat variable subgroupings within each of those larger regions between years. Overall biomass (mean 49680 ± 45510 g wet weight 1000 m⁻²) was dominated by echinoderms in particular at northern stations, followed by crustaceans. Repeat stations retained relatively consistent epibenthic community composition across sampling years, despite the at times drastic temporal variability in abundance and biomass. Point in time measurements of water column environmental variables (e.g., salinity, oxygen, temperature) were less strongly correlated to the epifaunal community structure than comparatively stable environmental measures (e.g., substrate type, depth, latitude). Benthic food web structure in the southern Chukchi Sea varied significantly and consistently between water masses in all study years, while δ¹⁵N and δ¹³C of pelagic particulate organic matter (PPOM) did not. This indicates that benthic consumers integrate the highly variable POM isotopic signatures and reflect long-term conditions. A persistent gap in δ¹⁵N values between PPOM and epibenthic consumers in nutrient-poor Alaska Coastal Water indicated that the majority of consumers in that water mass did not directly consume POM, which may undergo an additional trophic step of microbial processing before entering the benthic food web. In contrast, shorter food webs without this gap in the nutrient-rich Bering Sea Anadyr Water reflected tight pelagicbenthic coupling. The mostly consistent temporal patterns in epibenthic and food web structure compared to variable standing stock stress the importance of selecting multiple metrics for ecosystem monitoring. The data from this study may serve as a benchmark by which to measure a biological response to climate change and human impacts.