Variation in the stable isotopes of land-snail shells potentially provides useful information for reconstructing the terrestrial paleoenvironment. In this study, we investigated the relationship between vegetation and variation in the shell carbon (13C/12C) isotope ratios in the land snail Mandarina chichijimana on Chichijima of the Ogasawara Islands. In modern samples, the mean δ13C value of the adult shell (range -13.8∼-9.6) was higher at sites that contain a greater proportion of C4 plants, especially near the coast (regression equation, mean δ13C=6.594×[C4 plant proportion]-12.43). The shell δ13C of the living snails was also significantly positively correlated with the δ13C of the body tissues. As no differences were found in the δ13C values of shells collected in carbonate-rich areas and volcanic rock settings, we conclude that δ13C in M. chichijimana is almost exclusively influenced by the plants that they consume. Also, in fossil shells from limestone outcrops, the mean δ13C value (-11.6∼-11.4) was significantly lower than in modern shells from the same limestone outcrops (-11.0∼-9.6). This is therefore preliminary evidence that C4 vegetation declined in line with a decrease in sea level around the time of the Last Glacial Maxima. Together, the findings may form a basis for the future use of land snail shells to estimate the paleoenvironment of the Pacific Islands in this region.
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