Associations between stable carbon isotope ratio and vegetation in modern and fossil land snails Mandarina chichijimana on Chichijima of the Ogasawara Islands

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 (C-13/C-12) isotope ratios in the land snail Mandarina chichijimana on Chichijima of the Ogasawara Islands. In modern samples, the mean delta C-13 value of the adult shell (range - 13.8 similar to-9.6) was higher at sites that contain a greater proportion of C-4 plants, especially near the coast (regression equation, mean delta C-13=6.594x[C-4 plant proportion]-12.43). The shell delta C-13 of the living snails was also significantly positively correlated with the delta C-13 of the body tissues. As no differences were found in tile delta C-13 values of shells collected in carbonate-rich areas and volcanic rock settings, we conclude that delta C-13 in M. chichijintana is almost exclusively influenced by the plants that they consume. Also, in fossil shells from limestone outcrops, the mean delta C-13 value (-11.6 similar to-11.4) was significantly lower than in modern shells from the same limestone outcrops (-11.0 similar to-9.6). This is therefore preliminary evidence that C-4 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.