The effects of temperature on acid—base balance and ventilation of the marine iguana

Marine iguanas, Amblyrhynchus cristatus, held for 12–18 h at 16, 24 and 35°C exhibited an arterial pH change of −0.011 ΔpH/Δ°C. The arterial pH changed by −0.004 ΔpH/Δ°C between 16 and 24°C and by −0.015 ΔpH/Δ°C between 24 and 35°C. When the animals were allowed to cool to 16°C and rewarm to 35°C after 12–18 h at 35°C, the pH change was −0.015 ΔpH/Δ°C. Arterial pH measured during warming to 35°C after 12–18 h at 16°C was relatively constant at around pH ≅ 7.60 returning slowly toward the 35°C equilibrium pH ≅ 7.44. An increase in V dot e M dot CO 2 (L·mmol −1) is seen with decline in equilibrium body temperature from 0.79 at 35°C to 1.66 at 16°C. The ventilatory response is associated with a fall in Pa CO 2 (24 Torr, 35°C; 14 Torr, 16°C). Arterial CO 2 content and [HCO 3 −1] remain relatively constant. The observed arterial pH-body temperature relationship is similar to other reptiles; however, thermal history appears to influence the relationship. Marine iguanas probably experience only brief periods of time at body temperature as low as 18°C.