Thermoregulation and Evaporative Water Loss of Green Sea Turtles, Chelonia mydas

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Abstract
Twelve green sea turtles, Chelonia mydas (57 g-8.6 kg), were heated and cooled in air and water (15°C → 35°C → 15°C). All live turtles heated faster than they cooled. Thermal time constants (τ) were calculated and combined with time constants from the literature. Regression equations were calculated for 9 turtles from 139 g to 115 kg. Formulas (with mass, M, in kilograms) in water were τ w=12.0M0.54 and τ c=21.8M0.65 for warming and cooling respectively. Values for air (250 cm sec-1) were τ w=34.0M0.33 and τ c=53.4M0.53. Dead turtles heated and cooled at the same rate in water and may be described as τ d=44.2M0.76. Heart rates during warming exceeded heart rates during cooling at the same body temperature in air and water. Heart rates (HR) could be described by linear regression equations of the form Y = mχ + b. Warming and cooling regression equations for turtles in air were HRw = 3.19T - 22.1 and HRc = 0.23T + 5.7, respectively (T is temperature in °C). Similar values in water were HRw = 3.19T - 13.8 and HRc = 0.375T - 0.178. Green sea turtles show a larger heart rate hysteresis than any other reptile thus far tested and are able to warm in a smaller fraction of the time required to cool than any other reptile tested. Evaporative water loss (EWL) was determined for 12 turtles at 35°C (30% Rh). Water loss was correlated with mass as g hr-1=5.01M0.65. Skin resistance to water loss (Rs) was 16.7 sec cm-1 for live turtles and 20.7 sec cm-1 for dead ones.