Mercury poses both ecosystem and human health concerns that are exacerbated by the production of methylmercury (CH3Hg+; MeHg), which is often associated with sulfate-reducing bacteria (SRB) in marine sediments. We examined the relationship between MeHg concentrations and reduced-sulfur stable isotope δ34S values in four coastal consumer organisms collected from northern and southern regions of Florida’s Big Bend seagrass meadows: pinfish (Lagodon rhomboides), pigfish (Orthopristis chrysoptera), black sea bass (Centropristis striata), and shrimp (Tozeuma carolinense and Tozeuma serratum). We tested the hypothesis that depletion in δ34S, which is an indicator of the extent of sulfate reduction within sediments of seagrass dominated systems, would be related to the concentration of MeHg in fauna within these systems. We found that as δ34S became more depleted, indicating more relative sulfate reduction in sediments, the MeHg concentrations increased significantly (r = 0.52; p < 0.001; total n = 157). Stable δ34S values ranged from 17.4 to 4.8‰ and MeHg concentrations from 37.3 to 832 ng g−1 dry weight (DW). Correlations between tissue MeHg and δ13C were also observed (r = 0.44; p < 0.001; total n = 122), indicating that variations in benthic/water column feeding could also be important in controlling the MeHg distributions in the selected fauna. In addition, we observed spatial differences in δ34S, δ13C, and δ15N isotopic values and MeHg concentrations of consumers. Fauna from the southern region of the study area were 13C enriched, 15N depleted, 34S depleted, and had elevated MeHg concentrations relative to their northern Big Bend counterparts.
Estuaries and Coasts – Springer Journals
Published: Dec 28, 2017
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