A multiaxial growth analysis of stable isotopes in the modern shell of Saxidomus gigantea : implications for sclerochronology studies.

Abstract

Stable-isotope ratios of two modern Saxidomus gigantea specimens from Namu, British Columbia, are presented to show intraspecimen and interspecimen isotopic variation. Isotopic profiles (δ 13Cshell, δ 18Oshell) were generated along the axis of maximum growth. The profiles show that analogous seasonal variation is recorded in δ 18Oshell; however, significant variability is recorded in δ 13Cshell. We suggest this is caused by differences in metabolic activity between individuals. Intrashell variability along a growth horizon shows good reproducibility in δ 13Cshell but significant variability in δ 18Oshell, especially at the sinistral margin. A multiaxial growth analysis generated several profiles from a single valve. Similar seasonal variations are recorded in δ 18Oshell along all axes. δ 13Cshell show significantly less covariation, possibly related to internal metabolic activity. This study highlights that δ 18Oshell profiles generated from any portion of the shell can be used to evaluate seasonal fluctuations and may be excellent to evaluate types and rates of shell growth