| Summary: | Field and laboratory studies were conducted to determine the metabolic response
to seasonal cold exposure in juvenile green sea turtles (Chelonia mydas). Field studies
were conducted with turtles at Heron Island, Australia during the summer and winter.
Field metabolic rate (FMR) of turtles was determined using the doubly labeled water
technique, and diving patterns were recorded using data loggers. Laboratory experiments
were conducted with captive-reared juvenile green turtles exposed to a thermal regime
which mirnicked seasonal temperature changes at subtropical latitudes. Oxygen
consumption (V0₂), breathing frequency (/B), heart rate (/H), and blood flow distribution
were determined at 26°C and after 4 - 16 weeks exposure to 17°C. Temperature effects
on maximal activity of oxidative and glycolytic enzymes were determined in skeletal
muscle tissue obtained from turtles at Heron Island and from captive turtles. Turtles at
Heron Island showed seasonal differences in diving patterns, but FMRs during the
summer (85.0 kJ-kg⁻¹-day⁻¹) and winter (66.5 kJ-kg⁻¹-day⁻¹) were not significantly
different. Likewise, V02 of captive turtles was not significantly different during
exposure to 26°C (0.44 ml-min⁻¹-kg⁻¹) and 17°C (0.34 ml-mm⁻¹-kg⁻¹). Q10 for metabolic
rate of turtles at Heron Island (1.66) and in captivity (1.33) was lower than Qf 0 observed
in acute studies of temperature effects on metabolism of green turtles (2.1-2.7). There
was no significant difference in /B during exposure to 17°C and 26°C, however / H was
significantly lower at 17°C than at 26°C. The mismatch between V02 and / H at low
temperatures may be offset by adjustments in stroke volume or blood oxygen carrying
capacity to ensure that O₂ supply meets demand. Regional blood flow distribution was
not significantly different at 17°C and 26°C. Activity of oxidative and glycolytic
enzymes showed a low thermal dependence. Compensation in oxidative enzyme activity
did not occur. However, a compensatory increase in glycolytic enzyme activity was
observed for captive turtles during exposure to 17°C. Results suggest that a combination
of low thermal dependence and thermal acclimation of metabolic and physiological
variables allow juvenile green turtles to remain active over the range of temperatures
experienced seasonally at tropical and subtropical latitudes. === Science, Faculty of === Zoology, Department of === Graduate
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