Body temperature stability achieved by the large body mass of sea turtles.

Katsufumi Sato

doi:10.1242/jeb.109470

Abstract

To investigate the thermal characteristics of large reptiles living in water, temperature data were continuously recorded from 16 free-ranging loggerhead turtles, Caretta caretta, during internesting periods using data loggers. Core body temperatures were 0.7-1.7°C higher than ambient water temperatures and were kept relatively constant. Unsteady numerical simulations using a spherical thermodynamic model provided mechanistic explanations for these phenomena, and the body temperature responses to fluctuating water temperature can be simply explained by a large body mass with a constant thermal diffusivity and a heat production rate rather than physiological thermoregulation. By contrast, body temperatures increased 2.6-5.1°C in 107-152 min during their emergences to nest on land. The estimated heat production rates on land were 7.4-10.5 times the calculated values in the sea. The theoretical prediction that temperature difference between body and water temperatures would increase according to the body size was confirmed by empirical data recorded from several species of sea turtles. Comparing previously reported data, the internesting intervals of leatherback, green and loggerhead turtles were shorter when the body temperatures were higher. Sea turtles seem to benefit from a passive thermoregulatory strategy, which depends primarily on the physical attributes of their large body masses.

Highlights

Large reptiles, including giant dinosaurs, might have had relatively constant body temperatures (Colbert et al, 1946; Bakker, 1972; McNab and Auffenberg, 1976; Barrick and Showers, 1994)
Short-term relationship in the sea Vertical movements of turtles led to them being exposed to sudden changes in ambient water temperature; the measured body temperature did not follow such short-term (
The calculated core body temperature for a spherical model (69 kg, rR=0.25 m) fitted with the measured body temperature, which remained constant despite rapid changes in water temperature

Summary

Introduction

Large reptiles, including giant dinosaurs, might have had relatively constant body temperatures (Colbert et al, 1946; Bakker, 1972; McNab and Auffenberg, 1976; Barrick and Showers, 1994). Theoretical simulation has raised the interesting idea that large reptiles might maintain a high body temperature as a result of large size alone (Spotila et al, 1973; Stevenson, 1985). Sea turtles spend almost all their time under water, and their range of both vertical and horizontal movements are large. To substantiate their thermal characteristics under natural conditions, long and Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan

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Results

Conclusion