Temperature effects on ventilation and acid-base balance of the green turtle

Ventilation (VE), pulmonary gas exchange (MO2 and MCO2), and arterial acid-base status (pH and PaCO2) were measured in immature green turtles. Chelonia mydas, equilibrated at 15, 25, and 35 degrees C. From 25 to 35 degrees C, pH decreased by 0.0134 U/degrees C and PaCO2 increased from 30.1 +/- 1.1 to 46.0 +/- 2.4 Torr (mean +/- SE, n = 8) in conformity with results from other ectotherms. From 15 to 25 degrees C, however, pH fell on the average by 0.06 U/degrees C but the change was not significant. PaCO2 rose over this range from 25.3 +/- 1.6 to 30.1 +/- 1.1 Torr. Calculated plasma [HCO3-], 27-28 meq/l, did not change over the entire temperature range. Both VE and MO2 increased with temperature, but the ratio, VE/MO2 (the air convection requirement), fell with temperature (1.01 +/- 0.10 l/mmol at 35 degrees C, 0.64 +/- 0.03 l/mmol at 25 degrees C, and 0.45 +/- 0.04 l/mmol at 15 degrees C). We conclude that the green turtle adheres to the typical ectotherm blood acid-base pattern over their usual temperature range (25-35 degrees C), but that pH control deviates from this pattern at temperatures below this range.