Fig. 5. Percentage hemocyanin-oxygen saturation as a function of oxygen partial pressure P_O2 (mmHg; 1 mmHg=133.3 Pa) at pH 7.61 and 7.36 for Benthoctopus sp. (B. A. Seibel, unpublished data). Ambient P_O2 at capture depth (51 mmHg) is indicated by an arrow. At ambient P_O2, a drop in blood pH of 0.3 units results in a 40% decrease in hemocyanin saturation. All measurements were on dialyzed hemolymph at 5°C. Changes in pH were achieved by varying CO₂ concentrations, thus we cannot distinguish between pH and CO₂ effects on oxygen binding.