Respiration of the emersed shore crab at variable ambient oxygenation

Summary In the intertidal shore crab,Carcinus maenas, pH and values of the prebranchial venous hemolymph, and, the PO₂ values of the arterialized cardiac hemolymph,, were measured, and the ventilatory activity was assessed by measuring the hydrostatic pressures at the exits of the epibranchial cavities, under four environmental conditions: normoxic water, normoxic air, hypoxic gas, hyperoxic gas.In the crab breathing normoxic air, was lower and higher than in animals breathing normoxic water. With the switch to hypoxic gas, ventilation increased and and decreased. With the switch to hyperoxic gas, ventilation decreased, and increased and decreased.Thus these crabs breathing air were not as well oxygenated as when breathing air-equilibrated water, and because of their low, they were relatively hypervetilating and hypocapnic compared to air-breathing vertebrates. Hyperoxic breathing, increasing and reducing ventilatory drive, led to increased. Conversely, was reduced by hypoxic breathing. These observations suggest that the gas exchanger of intertidal crabs is not as successfully designed for air breathing as that of land-colonizing insects and air-breathing vertebrates.