Effects of ambient PO2 and temperature on oxygen uptake in Nautilus pompilius

This study employs closed-circuit respirometry to evaluate the effect of de clining ambient oxygen partial pressure (PO2) and temperature on mass speci fic rates of oxygen uptake ((V) over dot O-2) in Nautilus pompilius. At all temperatures investigated (11, 16, and 21 degrees C), (V) over dot O-2 is relatively constant at high PO2 (oxyregulation) but declines sharply at low PO2 (oxyconformation). The critical PO2 below which oxyconformation begins (P-c) is temperature dependent, higher at 21 degrees C (49 mmHg) than at 1 1 degrees C or 16 degrees C (21.7 mmHg and 30.8 mmHg respectively). In rest ing, post-absorptive animals, steady-state resting (V) over dot O-2 increas es significantly with temperature resulting in a Q(10) value of approximate ly 2.5. The metabolic strategy of N. pompilius appears well suited to its l ifestyle, providing sufficient metabolic scope for its extensive daily vert ical 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 O-2 stores), enhancing hypoxia tolerance.