COASTAL URBAN WATERSHED SIGNATURE IN OYSTERS

Rapid increase of urbanization along coastal areas of the United States is resulting in a substantial increase of anthropogenic pollution in urban watershed runoff, which can have a detrimental effect on marine organism populations. Oysters offer both economic and ecological services, and it is crucial to understand the impact that water quality has on the filtration capabilities of bivalves in order to predict how these services will be impacted in the future as urbanization increases. In this study, we tested trace heavy metal content, filtration effectiveness, and condition index of oysters from a highly urbanized watershed and a relatively less impacted control watershed. The influence of water acclimation on filtration ability of oysters was also investigated. Mass of feces produced, turbidity reduction, and percent of total nitrogen and phosphorous removed within a set filtration period were used as proxies of filtration effectiveness. Soft tissue and shell samples from the highly urbanized and the control watershed were digested and analyzed for heavy metals. Oysters from highly urbanized watershed showed higher concentrations in the soft tissue of specimens of the polluted site samples than in the control site. Condition indices, defined as the ratio of soft tissue mass to shell mass, of the control oysters were higher than those of urbanized sites by an average of 8.4%. Results for filtration effectiveness varied between sites and were dependent on oyster acclimation to water temperature and water from the watersheds. Based on these results, it can be concluded that oysters which develop in polluted waters are able to reduce nitrogen and phosphorus levels but have higher concentrations of heavy metals and lower soft tissue to shell ratio than those in less contaminated waters.