STABLE OXYGEN ISOTOPE SCLEROCHRONOLOGY OF OSTREA EDULIS SHELLS FROM THE ADRIATIC SEA

The European flat oyster, Ostrea edulis is commonly found in archaeological deposits and the fossil record throughout much of Europe and the Mediterranean. Few studies have focused on the relationship between seawater temperature, salinity, and the shell oxygen isotope (δ¹⁸O) chemistry of O. edulis. Previous work on related species, Crassostrea virginica and Crassostrea gigas, have established that these oysters record environmental changes in their shell δ¹⁸O values and thus can be used as paleoenvironment and archaeological season of capture indicators. However, this has yet to be addressed using O. edulis as a series of validation tests must be performed to determine whether O. edulis can be used in paleoclimate and seasonality studies. In this study, shells of wild caught and aquaculture grown O. edulis were collected from two locations in the Adriatic Sea along the coast of Croatia. Contemporaneous data on sea water temperature and salinity were obtained from the CTD probe set up at the aquaculture site in Mali Ston Bay. The temperature values ranged from 9°C – 28°C, while salinity values were between 34 – 37. Sequential powdered samples of shell calcite were collected from the hinge of the left valve via micromill to measure δ¹⁸O values. The seawater temperature and salinity were used to create an idealized time series model of oyster shell δ¹⁸O that was then compared to the data from the measured samples. Preliminary data display sinusoidal oscillations in δ¹⁸O values suggesting archaeological season of capture estimates may be possible, but additional analysis is required to assess their potential utility in paleoclimate reconstruction.