Paleoenvironmental implications of carbon stable isotope composition of land snail tissues

Land snail shell δ13C value is often used as a paleovegetation proxy assuming that snails ingest all plants in relation to their abundance, and that plants are the only source of carbon. However, carbonate ingestion and variable metabolic rates complicate these relationships. We evaluate if live-collected snails from Lanzarote (Canary Islands) reflect the abundance of C3 and CAM plants. Snails were collected on either CAM or C3 plants for isotope analysis of shell and body, and shell size. Respective shell and body δ13C values of snails collected on CAM plants averaged − 8.5 ± 1.7‰ and − 22.8 ± 1.6‰, whereas specimens from C3 plants averaged − 10.1 ± 0.7‰ and − 24.9 ± 1.1‰. A flux balance model suggests snails experienced comparable metabolic rates. A two-source mass balance equation implies that snails consumed ~ 10% of CAM, which agrees with their abundance in the landscape. Snails collected on CAM plant were smaller than those on C3 plants. Conclusively: 1) snails consume CAM plants when they are available; 2) migration of snails among C3 and CAM plants is a common phenomenon; and 3) C3 plants may be a more energetic food for growth than CAM plants. This study shows that shell δ13C values offer approximate estimates of plants in C3–CAM mixed environments.