Potential Effects of Altered Salinity Regimes and Copper Pollution on Oyster (Crassostrea virginica) Tissue Copper and Spat Settlement in an Urban Estuary (Naples Bay, Florida, USA)

Copper (Cu) is both an essential micronutrient and a pollutant, with its effects depending on its concentration, environmental context, and the species and life history stages of the organisms exposed. To advance the understanding of copper effects in the context of variation in other environmental conditions, eastern oyster (Crassostrea virginica) spat recruitment and adult tissue copper concentration [Cu] were monitored in conjunction with water column [Cu], salinity, pH, dissolved oxygen, and temperature for a year at five sites in or near Naples Bay, Florida, an urbanized estuary with some of the highest copper pollution levels in the US. Relationships among the environmental variables were explored using principal component analysis, then the effects of key variables on oyster responses were assessed using regression models and multi-model comparison. There were significant differences among sites and dates in terms of salinity, water column and tissue [Cu], and spat recruitment. Tissue [Cu] was high, up to 2868 ppm, and was correlated with high water column [Cu] in parts of the estuary (up to 7.55 mg/L). Oyster tissue [Cu] was best predicted by a linear model incorporating both salinity and water column [Cu], and oyster spat recruitment was best modeled using a polynomial fit to salinity and a negative linear relationship with water column [Cu]. This is consistent with the hypothesis that high [Cu] in conjunction with low salinities reduces spat recruitment in this system, but alternative hypotheses cannot be excluded without further assessment. Given these findings, hydrologic restoration to stabilize salinity regimes and management actions to eliminate copper pollution sources are recommended to protect oysters and improve ecological integrity in the system.