Dietary reliance on benthic primary production as a predictor of mercury accumulation in freshwater fish and turtles

Abstract

The feeding ecology of a species can affect the transfer and accumulation of contaminants such as mercury (Hg). Modeling the accumulation of Hg through food webs can help identify which animals are likely to be burdened by elevated Hg concentrations. In lakes, most of the Hg is sequestered in the sediments. Therefore, species ultimately relying on benthic primary production may experience a greater trophic transfer of Hg relative to species that rely on pelagic primary production. This hypothesis was tested in a simple food web using muscle tissue collected from three species of fish (Lepomis gibbosus, Notropis heterodon, and Labidesthes sicculus) and blood from two species of turtles (Sternotherus odoratus and Chrysemys picta) that differ in reliance on benthic primary production. Averaged multiple linear regression models were used to predict Hg concentrations in the five consumers with respect to reliance on benthic primary production, while controlling for other factors known to influence Hg accumulation (sex, size, lake, species identity, and trophic level). A positive and significant relationship was found between Hg burden and dietary reliance on benthic primary production, animal length, trophic level, and species identity in fish. In turtles, the relationship between Hg burden and dietary reliance on benthic primary production was not significant, but trophic level, animal length, and species identity significantly influenced Hg burden. Overall, reliance on benthic primary production was an important predictor of Hg burden for fish, but not for turtles. Future attempts to model Hg accumulation in similar study systems and/or fish species should include dietary reliance on benthic primary production as a predictor variable.