Physiological Compensation to Short-Term Air Exposure in Red Rock Crabs, Cancer productus Randall, from Littoral and Sublittoral Habitats. II. Acid-Base Balance

Hemolymph acid-base disturbance during 4 h emersion was qualitatively similar in large (>200 g) subtidal and small (<100 g) intertidal size classes of Cancer productus. Combined metabolic and respiratory acidosis, indicated by elevation of hemolymph lactate and CO₂ tension (Pco2), was associated with increased CO₂ content (Cco₂) and a small increase in hemolymph ammonia. Small crabs experienced a less severe acidosis in spite of greater increases in both lactate and Pco₂. It is concluded that compensation occurred largely via Cco₂ elevation with only a small contribution from shell buffering. Restoration of acid-base balance following reimmersion involved a rapid phase, believed to be of respiratory origin, and a slower phase that could involve metabolic processes. Changes in pHa − pHv indicate that branchial CO₂ excretion was reduced during emersion but greatly enhanced following immersion. Small C. productus were able to compensate for disturbances arising during emersion and reimmersion more rapidly and more effectively than large C. productus or other species which have been studied.