Estuarine, Coastal and Shelf Science

Pinctada fucata martensii mantle tissue and gut contents were examined as baseline indicators of carbon and nitrogen isotope composition at six stations in the Uwa Sea, Japan. Substantial variations in d 13 C and d 15 N values of oysters among stations were observed, with d 13 C being consistently lower at Hiburi Island (� 18.1&) than at other stations (� 17.2&). Oysters from fish farm sites were enriched in d 15 N (8.1&) relative to those from unaffected sites (6.8&), suggesting that fish farming tends to increase baseline d 15 N values. The mean Dd 13 C (0.8&) was consistent over space and time, whereas the average Dd 15 N slightly increased in summer. The relatively low d 15 N enrichment compared to the theoretical isotope fractionation factor (3.4&) may be due to oyster-specific physiological attributes. Carbon and nitrogen isotope turnover rates were roughly similar within a tissue, and mantle tissue turnover rate was esti- mated to be 120-180 days. These results indicated that oysters are long-term integrators of d