Gas Exchange, Hemolymph Acid-Base Status, and the Role of Branchial Water Stores during Air Exposure in Three Littoral Crab Species

Abstract

O₂ uptake and hemolymph acid-base status, together with branchial water volume, CO₂ content, and titratable alkalinity, were measured in three species of intertidal crabs. In Pachygrapsus crassipes, a grapsid crab that actively moves between air and water, O₂ uptake increased on emersion. In Eurytium albidigitum, a mud-burrowing xanthid crab that is air exposed by tidal action, O₂ uptake declines dramatically on emersion. There is no significant lactate production by either crab following emersion. An emersion-induced respiratory acidosis was fully compensated in P. crassipes and another grapsid, Hemigrapsus nudus, but uncompensated in E. albidigitum. Branchial water volume 10 min after emersion was 0.013 ml/g crab weight in P. crassipes and 0.072 ml/g in E. albidigitum. The CO₂ content of branchial water in P. crassipes increased rapidly during air exposure and was accompanied by an increase in titratable alkalinity (TA). The CO₂ content of branchial water in E. albidigitum remained constant for at least...