TRENDS IN EASTERN OYSTER (CRASSOSTREA VIRGINICA) TISSUE METALS IN LONG ISLAND SOUND

Eastern oysters (Crassostrea virginica) are known to accumulate contaminants in their tissues in proportion to their surrounding environment and are used to assess the overall health of coastal estuaries. NOAA Status &Trends monitoring in Long Island Sound has primarily focused on blue mussels and oysters have not been included in the monitoring program in over 20 years. This study examined variations in oyster tissue metal contents collected from shellfish beds along the Connecticut coastline. Oysters and sediment were sampled from fifteen shellfish beds along the Connecticut shoreline representing a variety of sediment environments and salinity regimes and include commercial beds (Norwalk harbor, New Haven harbor, Bridgeport harbor, New London), local shellfish beds (Branford, Westbrook), and restricted shellfish areas in the Housatonic River estuary and Norwalk harbor. Oysters were collected from select oyster beds in the fall and spring (October 2007, June 2008, November 2008, June 2009, October 2009, and June 2011). Shell length (80-100 mm), tissue dry weight, and oyster condition index were determined prior to tissue metal analyses. Replicate oyster tissue (n=12) and sediment (n=3) samples from each site were analyzed for copper (Cu), zinc (Zn), cadmium (Cd), mercury (Hg), and iron (Fe). Mean oyster tissue metal concentrations (dry weight) ranged from 122 – 2,240 mg/kg for Cu, 105- 999 mg/kg for Fe, 1,275 – 18,300 mg/kg for Zn, 1.58 – 9.48 mg/kg for Cd and 0.103 – 0.313 mg/kg for Hg. Results of this study did not show a direct correlation between sediment metal concentrations and corresponding oyster tissue metal concentrations. An inverse relationship between oyster tissue metals (Cu, Zn, and Cd) and salinity was observed for oysters sampled from three sites in the lower Housatonic river estuary. Regardless of mode of uptake, or other controls on metals regulation, Cu and Zn are accumulated/regulated in oysters in direct proportion to each other. Compared to recent (2004-2005) NS&T analyses of oyster tissue metals from the mid-Atlantic to the Gulf States, results showed that the vast majority of Connecticut oyster tissue Cu, Zn, Cd and Hg concentrations fell within the medium to high concentration ranges.