Growth histories of strombid snails from Bermuda recorded in their O-18 and C-13 profiles

The isotopic ratios ¹⁸O/¹⁶O and ¹³C/¹²C show an annal periodicity in the strombid snails Strombus gigas and S. costatus from Bermuda. S. gigas appears to have a constant displacement of 0.5 from oxygen isotopic equilibrium, whereas S. costatus fractionates the oxygen istopes in accordance with established fractionation relationships. With this tool, the growth in strombid snails during different stage can readily be determined on one and the same snail. A 24.8 cm long S. gigas showed an age of 7, a 19.3 cm long S. costatus of 5, and a 7.8 cm long S. costatus of 2 years. From the annual range in oxygen isotopes, growth restricted to warmer periods of the year is assumed. The abundances of ¹⁸O and ¹³C tend to be positively correlated in adult S. gigas and S. costatus speciments, but were inversely related in a juvenile S. costatus.