Mercury content of blue crabs (Callinectes sapidus) from southern New England coastal habitats: Contamination in an emergent fishery and risks to human consumers

Total mercury (Hg; ppm dry weight) was measured in blue crabs, Callinectes sapidus, collected from Narraganset Bay and adjacent coastal lagoons and tidal rivers (Rhode Island/Massachusetts, USA) from May to August 2006-2016. For juvenile crabs (21-79 mm carapace width, CW), total Hg was significantly greater in chelae muscle tissue (mean ± 1 SD = 0.32 ± 0.21 ppm; n = 65) relative to whole bodies (0.21 ± 0.16 ppm; n = 19), and irrespective of tissue-type, crab Hg was positively related to CW indicating bioaccumulation of the toxicant. Across a broader range of crab sizes (43-185 mm CW; n = 465), muscle Hg concentrations were significantly higher in crabs from the Taunton River relative to other locations (0.71 ± 0.35 ppm and 0.20 ± 0.10 ppm, respectively). Spatial variations in crab Hg dynamics were attributed to habitat-specific Hg burdens of their prey, including bivalves, gastropods, polychaetes, and shrimp. Prey Hg, in turn, was directly related to localized sediment Hg and methylmercury conditions. Biota-sediment accumulation factors for crabs and prey were negatively correlated with sediment organic content, verifying that organically-enriched substrates reduce Hg bioavailability. From a human health perspective, frequent consumption of crabs from the Taunton River may pose a human health risk (23% of legal-size crabs exceeded US EPA threshold level); thus justifying spatially-explicit Hg advisories for this species.