ENVIRONMENTAL VARIATIONS PRESERVED IN SHELLS OF THE SOUTHERN QUAHOG CLAM (MERCENARIA CAMPECHIENSIS), SW FLORIDA

Previous studies have examined the environmental controls on the stable isotopic composition of shells from the northern quahog clam, Mercenaria mercenaria, and determined that the δ¹⁸O values in this species accurately record seasonal variation in water temperature and salinity (i.e., mixing between fresh- and saltwater end members). In this study, high-resolution (fortnightly to sub-daily) sampling was performed on a M. campechiensis shell from Pine Island Sound in southwest Florida. Measured δ¹⁸O of shell carbonate was compared to a predicted shell calculated using measured water δ¹⁸O values, water temperature, and the equilibrium fractionation equation for aragonite and water. Our findings indicate that M. campechiensis precipitates its shell in oxygen isotope equilibrium with ambient water. Additionally, because Hurricane Charley made landfall directly over the collection site, the isotopic record in this study was also used as a case study to determine that large, local storm occurrences are recorded in shells when sampling is taken at sub-daily resolution.