Stable Carbon Isotopic Evidence for Carbon Limitation in Hydrothermal Vent Vestimentiferans

Abstract

Stable carbon isotope composition (δ¹³C values) can be used to evaluate an animal's source of nutritional carbon. Most animals with chemoautotrophic endosymbionts have quite negative tissue δ¹³C values due to discrimination against ¹³C associated with chemoautotrophic assimilation of inorganic carbon. However, the δ¹³C values of hydrothermal vent (HTV) vestimentiferans are significantly higher than the values reported for non-HTV vestimentiferans or other invertebrates with chemoautotrophic endosymbionts. Tissue δ¹³C values of two species of HTV vestimentiferans increase with increasing size of the animals. This relation supports the hypothesis that the relatively high δ¹³C values are the result of inorganic carbon limitation during carbon fixation. A more favorable relation between gas exchange and carbon fixation in the smaller individuals is expected, due to differences in the geometric scaling of gas-exchange surfaces and trophosome volume.