Effects of Temperature on Gas Exchange and Acid-Base Balance in the Sea Turtle Caretta Caretta at Rest and During Routine Activity

Oxygen consumption, lung ventilation, plasma ion concentrations and osmolality, venous blood acid-base status and gas tensions were measured in unrestrained loggerhead sea turtles in sea water at 10, 15, 20 and 30 °C at rest and during routine activity. Moderate activity caused a threefold increase in oxygen consumption, accommodated by a twofold increase in ventilation (the result of increases in breathing frequency) and a 60% increase in lung oxygen extraction. There was an increase in oxygen consumption with temperature (Q₁₀ = 2·4) also due primarily to an increase in oxygen extraction (decline in air convection requirement, ACR) since neither the tidal volume nor the breathing frequency changed.

Over the temperature range 15–30°C venous blood pH decreased by 0·017 units °C⁻¹, indicating that the maintenance of constant relative alkalinity is not confined to species of low aerobic scope. Venous blood and increased with temperature. However, [HCO₃⁻] decreased, suggesting that ventilatory adjustments alone are insufficient for regulating the thermally dependent shifts in blood pH. Plasma [K⁺] increased with temperature, which may be related to cellular-mediated adjustments in blood pH.

Temperature-related adjustments of blood pH in the loggerhead appear to be managed both at the lung (ACR-driven changes in blood ⁠) and tissue (ion exchange) levels. This mixed regulation is associated with the unique mode of respiration of the sea turtle.