Stable carbon isotopic profiles of sea turtle humeri: implications for ecology and physiology

Analyses of sequential growth layers of marine turtle humeri indicate that diet is the primary influence on the carbon isotopic composition of sea turtle bone carbonate. However, secondary physiological and geographical factors, such as foraging locality, migratory range, physiological interactions with ocean water, and especially respiratory physiology, also influence carbon isotope values of biogenic structural carbonate. The difference in carbon isotope compositions between diet and bone structural carbonate is consistently smaller in the deep-diving leatherback (Dermochelys coriacea) and olive ridley (Lepidochelys olivacea) turtles than in the shallow-diving green turtle (Chelonia mydas). Although diet has considerable influence on sea turtle bone carbonate δ13C, respiration appears to be an additional influence, because of the accumulation of respired CO2 in blood during extended breath-hold diving and the concomitant incorporation of blood-CO2 into bone carbonate. Preliminary analyses of collagen and muscle tissue do not show evidence of respiratory effects on their carbon isotope compositions.