The thermal dependence of metabolism in three sea turtle species and the effects of activity.

Temperature is of central importance to life and structures biological processes across levels of organization. For ectothermic marine turtles, temperature profoundly affects their metabolism, overall physiology, behaviour and distribution. Marine turtles are globally threatened and a detailed understanding of their energy requirements is essential to comprehend their role in marine ecosystems and to guide conservation efforts. We used flow-through respirometry to study the effects of seasonal changes in water temperature (Tw) on the resting oxygen consumption rates (V̇O2) of three sea turtle species (green, loggerhead and hawksbill turtles). Tw changes between winter and summer (maximum range: 20.3-31.9°C) had a clear effect on mass-specific V̇O2 (sV̇O2) that increased on average by ∼50% across species in summer. Hence, the thermal sensitivity of metabolism was similar in all species with Q10 values ranging between 2.1 and 2.7, typical for reptiles. Changes in sV̇O2 were paralleled by changes in respiratory frequency (fR) in all species. In separate trials with loggerhead turtles resting and swimming in a tank, we recorded body acceleration (PDBA) together with V̇O2 to investigate the effects of activity on metabolism and to establish a predictive equation that can be used to estimate turtle energy expenditure at sea from the recording of body acceleration. Moderate swimming activity increased sV̇O2 up to 3.2 times over resting. We found a significant positive relationship between sV̇O2 and PDBA (r2=0.63, P<0.0001) with small associated error estimates, indicating that body acceleration is a good predictor of V̇O2 in loggerhead turtles, similar to what has previously been reported for green turtles.