Paleoenvironmental implications of carbon stable isotope composition of land snail tissues

Land snail shell delta C-13 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 C-3 and CAM plants. Snails were collected on either CAM or C-3 plants for isotope analysis of shell and body, and shell size. Respective shell and body delta C-13 values of snails collected on CAM plants averaged -85 +/- 1.7 parts per thousand. and -22.8 +/- 1.6 parts per thousand, whereas specimens from C-3 plants averaged -10.1 +/- 0.7 parts per thousand. and -24.9 +/- 1.1 parts per thousand. A flux balance model suggests snails experienced comparable metabolic rates. A two-source mass balance equation implies that snails consumed similar to 10% of CAM, which agrees with their abundance in the landscape. Snails collected on CAM plant were smaller than those on C-3 plants. Conclusively: 1) snails consume CAM plants when they are available; 2) migration of snails among C-3 and CAM plants is a common phenomenon; and 3) C-3 plants may be a more energetic food for growth than CAM plants. This study shows that shell delta C-13 values offer approximate estimates of plants in C-3-CAM mixed environments. (C) 2013 University of Washington. Published by Elsevier Inc All rights reserved.