Seasonal and spatial variations of biomarker responses of rock oysters in a coastal environment influenced by large estuary input

The present study assessed the spatial and temporal variations and the potential influences of the Pearl River discharge on trace metal bioaccumulation and biomarker responses in Hong Kong coastal waters. A suite of biomarkers including antioxidant defense, oxidative stress, metal detoxification, cellular response, neurotoxicity, and energy reserve were quantified in the rock oyster Saccostrea cucullata over spatial scale across the east and west of Hong Kong. We documented the elevated Cd, Cu and Zn concentrations in all western stations in the fall season, as a result of time-integrated accumulation during the peak discharge of the Pearl River Estuary (PRE) in summer. Lipid peroxidation and total glutathione corresponded well with the overall metal gradient and showed significant correlation with the tissue Cu bioaccumulation. The eastern station (Clear Water Bay) also exhibited high Cd and Cu concentrations with increased oxidative stress responses. In the spring, metal bioaccumulation in the oysters was reduced due to the weakened influence of PRE, with correspondingly less obvious biomarker responses. Our coupling measurements of biomarkers and tissue metal concentrations for the first time revealed that the large PRE could have latent and seasonal biological effects on the Hong Kong coastal biota. Sensitive biomarkers such as lipid peroxidation and glutathione responses might be good candidates for detecting the early biological responses in such sub-lethal contaminated environments. Pearl River Estuary discharge could significantly affect the biochemical biomarker responses of rock oysters in Hong Kong coastal environments.