Selenium and Mercury Partitioning and Trophic Transfer at the Base of a Coastal Food Web

Abstract There is persistent interest in the importance of selenium (Se) and mercury (Hg) interactions in aquatic ecosystems; however, the influence of Se on partitioning and trophic transfer of Hg at the base of food webs is largely unexplored. We conducted a two-year field study with monthly field collections (water, phytoplankton, oysters, ancillary water quality variables) at four sites distributed along the coastal Connecticut portion of Long Island Sound, USA, to characterize relationships between Se and Hg partitioning and trophic transfer. Chl a concentrations significantly increased with increasing dissolved Se concentrations, while dissolved Se concentrations did not reliably predict Hg partitioning from the dissolved phase to particulates. Hg and Se partitioning to particulates were significantly positively associated, with particulate Se concentrations explaining 95% of the variation in Hg particulate concentrations compared to other macronutrients. We observed a positive association between Hg and Se trophic transfer from particulates to oysters; however, oyster Hg and Se concentrations were not significantly correlated, indicating that Hg and Se concentrations are decoupled in primary consumers. The results of this study inform and motivate future research on the role of Se in Hg cycling and the mechanisms driving Hg partitioning and trophic transfer in aquatic food webs.