Seasonal variation of copper and zinc concentrations in the oyster Saccostrea cuccullata from the Dampier Archipelago, Western Australia: implications for pollution monitoring.

The intertidal rock oyster Saccostrea cuccullata, sampled at eight sites on eight occasions over a 1-year period, contained mean Cu and Zn concentrations ranging between 34 and 267 and 206 and 4078 mg kg-1 dry weight, respectively. In the study area, Cu and Zn emanate from sewage and boat slips (antifouling paints), while Zn probably also originates from coolant water from an electricity power generating station and iron ore exporting facilities. Highest oyster wet weight, Cu and Zn concentrations and loads occurred in January (spawning period), indicating that metal variation was not reciprocating wet weight. Lowest metal concentrations and loads occurred in October (period of onset of gametogenesis), while lowest wet weight occurred in April (post-spawning period). No significant (P less than 0.001) variation in the wet to dry weight ratio was noted temporally. However, significant, though slight, variation was noted between polluted and unpolluted oysters. Results of this study indicate that pollution control monitoring programs should consider: seasonal variation of metal concentrations; portion of the year during which standards are exceeded; oyster size and availability for human consumption; suitability of standards where shellfish are not consumed as a staple diet; appropriate size indicies which can be used for selecting specimens for intersite comparisons; wet to dry weight calculations: techniques, spatial and temporal variations; and the physical dynamics of sites used.