Methylmercury dietary pathways and bioaccumulation in Arctic benthic invertebrates of the Beaufort Sea

This study investigated methylmercury (MeHg) concentrations in Arctic benthic invertebrates from two shelf sites in the Canadian Beaufort Sea. Carbon, nitrogen, and sulfur stable isotopes and fatty acids were measured to examine diet influences on MeHg concentrations in 476 individuals from 53 taxa of benthic invertebrates representing three different feeding guilds. Taxonomic identifications were based on DNA-barcoding and traditional taxonomy. MeHg concentrations ranged from 3 to 421 ng/g dry weight and increased over three trophic levels (δ15N range = 4.4–14.2‰). Organic matter sources had small but significant influences on MeHg bioaccumulation in the benthic food web. Carbon stable isotope ratios (δ13C, range = −25.5 to −19.8‰) were positively correlated with MeHg concentrations, suggesting greater reliance on benthic carbon contributed to higher concentrations. Sulfur stable isotopes were unrelated to MeHg concentrations. Fatty acids suggested feeding on diatoms versus dinoflagellates, and reliance on benthic resources influenced MeHg concentrations. Higher MeHg concentrations were observed at the site closer to the Mackenzie River mouth than the Cape Bathurst site. This study generated the most taxonomically rich dataset of MeHg concentrations in invertebrates from the Arctic marine benthos to date and provides a basis for future research on food web MeHg dynamics in the Canadian Beaufort Sea.