Ventilation and gas exchange during rest and exercise in adult green sea turtles

Summary

Ventilation and metabolic rate were measured during exercise in adult female green turtles at Tortuguero, Costa Rica. Six turtles were studied at night on the beach while actively covering their nests. Five turtles, captured after nesting, were studied at rest, during 20 min of spontaneous activity, and during recovery from the activity. Arterial blood samples were obtained from the latter animals and analyzed for pH,$P_{CO_2 } , P_{O_2 }$, O₂ concentration and lactate concentration. Blood was obtained by heart puncture from 8 turtles immediately after nesting and analyzed for blood lactate. Active metabolism ($\dot V_{O_2 }$) in both groups was almost 10 times the standard resting value (0.024 l/kg·h). The increase in ventilation during exercise, due exclusively to higher breathing frequency, exceeded the increase in$\dot V_{O_2 }$, so that the ratio$\dot V_{E_2 } /\dot V_{O_2 }$ (the air convection requirement), more than doubled. The respiratory exchange ratio,$\dot V_{CO_2 } /\dot V_{O_2 }$, that averaged 0.56 in the resting turtles, increased to 1.08 during exercise in the captured turtles and was 0.90 in the nesting animals. Arterial$P_{O_2 }$ and O₂ saturation remained unchanged during exercise, indicating efficient gas exchange in the lungs. Pre-exercise values of all variables were restored 1 h after the end of exercise. Blood acid-base changes associated with activity in the captive turtles were variable and not statistically significant, but suggested partially compensated metabolic acidosis. Lactate concentrations were significantly elevated in the nesting turtles.