This study employs closed-circuit respirometry to evaluate the effect of declining ambient oxygen partial pressure (PO2) and temperature on mass specific rates of oxygen uptake (VO2) in Nautilus pompilius. At all temperatures investigated (11, 16, and 21 degrees C), VO2 is relatively constant at high PO2 (oxyregulation) but declines sharply at low PO2 (oxyconformation). The critical PO2 below which oxyconformation begins (Pc) is temperature dependent, higher at 21 degrees C (49 mmHg) than at 11 degrees C or 16 degrees C (21.7 mmHg and 30.8 mmHg respectively). In resting, post-absorptive animals, steady-state resting VO2 increases significantly with temperature resulting in a Q10 value of approximately 2.5. The metabolic strategy of N. pompilius appears well suited to its lifestyle, providing sufficient metabolic scope for its extensive daily vertical migrations, but allowing for metabolic suppression when PO2 falls too low. The combination of low temperatures and low PO2 may suppress metabolic rate 16-fold (assuming negligible contributions from anaerobic metabolism and internal O2 stores), enhancing hypoxia tolerance.
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