Aerial and aquatic respiration in the ghost crab,Ocypode saratanII respiratory gas exchange and transport in the haemolymph

Abstract

Ocypode saratan breathing humid air has a postpulmonary PO2 of 15.7 kPa and PCO2 of 1.0 kPa with a gas exchange ratio over the lung of 0.42. When in air, however, O. saratan perfuses the lung in parallel with the gills to generate a mixed postbranchial PaO2 of 10.5 kPa and PaCO2 of 1.7 kPa in humid conditions with access to water and a PaO2 of 2.7 kPa and PaCO2 of 1.1 kPa in dry conditions with no access to water. When submerged O. saratan does not perfuse the lungs, to give a postbranchial PO2 of 2.7 kPa and a PCO2 in both post and prebranchial haemolymph of approximately 1 kPa. Submerged crabs accumulate lactate ions after 5–6 h which appears to be buffered by either HCO‐ 3 uptake or H+ excretion during passage of the haemolymph through the branchial circulation. The gas exchange ratio across the gills is approximately 1. These data suggest that the main site for oxygen and CO2 exchange in O. saratan is the lungs and that respiratory gas exchange is impaired during desiccation and during submersion, whe...