High-Resolution Intrashell Oxygen Isotope Studies of Cathaica fasciola and Bradybaena ravida Land Snails and Their Environmental Implications

Intrashell oxygen isotope (δ¹⁸O_s) analyses of terrestrial snails have been carried out over two decades. However, the intraspecies/interspecies differences are not yet well understood. Here, we conducted a high-resolution intrashell δ¹⁸O_s study on 43 shells from Cathaica fasciola and Bradybaena ravida, and 1449 δ¹⁸O_s data were obtained. These large amounts of data demonstrate the reproducibility of intrashell δ¹⁸O_s. Our results suggest that C. fasciola and B. ravida have similar growing seasons mainly from March to October in the studied region. The ecological habits of the two species could explain the distinctive variations in their δ¹⁸O_s sequences. Therefore, our study may interpret the discrepancy between the studies of land snail species and the stable/clumped isotopes of their shells. Moreover, the calculated average growth rate is ∼290 μm/day (from 250 to 330 μm/day) for nonadult C. fasciola. Thus, the use of snail shells for reconstructing high-resolution terrestrial climate changes is promising.