The role of branchial ventilation in hemolymph acid-base changes in the shore crabCarcinus maenas during hypoxia

Summary

• 1. When exposed to hypoxia in the ambient medium, the crabCarcinus maenas increased and sustained high levels of branchial ventilation for up to 70 h (Fig. 1).

• 2. The role of hyperventilation in establishing changes in hemolymph acid-base status during hypoxia was investigated. Hemolymph pH and$P_{CO_2 }$ changes in hypoxic crabs (Figs. 2 and 4) were compared with crabs whose branchial chambers were artificially hyperventilated in normoxia by siphoning water through a mask attached to the carapace (Fig. 3).

• 3. Hyperventilation alone does not account for the observed alkalosis during hypoxia. It is suggested that changes in both CO₂ production and ventilation may be responsible for altering hemolymph acid-base status.

• 4. Artificial hyperventilation in normoxic crabs resulted in a respiratory alkalosis which is fully compensated after 16 hours by a metabolic acidosis (Fig. 3).

• 5. Reduction of the hemolymph bicarbonate pool during hypoxia did not interfere with the ability of crabs acclimated to low salinity to regulate hemolymph chloride ion concentration (Fig. 5).