Stable Isotope Analyses On Clam Shells in Reconstruction of the Life History

Stable isotopic composition of clam shells can be used in reconstruction of marine environmental changes that the animal experienced. In this study, we reported carbon and oxygen isotope ratios of shell carbonate analyzed from geoduck (Panopea abrupta) and Yesso scallop (Patinopecten yessoensis). The two clams were collected from different settings, but the isotopic compositions of the species reflect their life history and behavior respectively. The lifetime d¹⁸O values of the Yesso scallop, for example, showed four peaks and valleys continuously, indicating about 4-year life history in growth. The large differences in d¹⁸O values (2.5-3.0‰) between the first peak and the others suggest that the animal may encounter two significantly different environments in its life history: this scallop was originally in a warmer habitat and transferred to a colder ground (roughly 10-12 ^oC cooler) in one year later, and was continuously growing there for the rest three years. The life-time d¹³C values of the scallop, in contrast, showed a stable decrease from about +1 to -0.5‰ over the 4-year period. These examples suggest that clam shells are good proxies for life history studies, and the isotopic data have the potential to predict clam growth and the environmental conditions.