Spatial and Temporal Patterns of Mercury in Annual Forage Fish, the Atlantic Silverside (menidia Menidia)

In fish methylmercury (MeHg) can reach concentrations that pose health risks to their predators, including people who consume fish in high quantities. Pathways and mechanisms of MeHg accumulation in forage fish are among the areas that require more research attention to enable proper management of human and wildlife health, especially given the ongoing environmental changes, including climate. On the east coast of the Atlantic Ocean predatory fish such as bluefish and juvenile striped bass rely heavily on Atlantic silversides for diet. During warm months, silversides thrive in shallow ( 2-5 m in depth) embayments, where concentrations of MeHg dissolved in seawater are an order of magnitude higher than in deeper offshore waters. The dietary significance of this species, and elevated MeHg in its habitat make M. menidiaan important food web vector of MeHg transfer in which to study: 1. ontogenetic changes in MeHg bioaccumulation in the wild, 2. spatial differences in MeHg concentrations in these fish within a single estuary i.e. Long Island Sound (LIS; 41°N), and 3. differences in estuaries across latitude. MeHg concentrations of mature silversides in Long Island Sound vary by as much as 30%, depending on month, location and sex, and could double in a time frame of 2-3 months. Along a section of the North Atlantic coast ( 38.5°N - 45.5°N) MeHg concentrations in M. menidiaincreased northward in both juvenile as well as adult fish. The increase of MeHg in adults was steeper than in juveniles, achieving an order of magnitude difference in the scope of 7 degrees in latitude. Whether this spatial and temporal variation is transferred to predators of M. menidiais not known, warranting further research. Findings from this research can be used to validate MeHg bioaccumulation models for coastal forage fish. Future research could focus on effects of climate and other environmental changes on MeHg bioaccumulation in coastal food webs.