Respiratory, cardiovascular, and hemolymph acid‐base changes in the amphibious crab, Cardisoma guanhumi, during immersion and emersion

Abstract

The cardiorespiratory and hemolymph acid base status of bimodal breathing crabs, Cardisoma guanhumi, was monitored during the transition from breathing air to breathing water. Upon immersion, oxygen uptake (MO2) decreased by half. Ventilatory frequency (fsc) increased more than 5 fold, causing a decrease in hemolymph carbon dioxide partial pressure (PCO2). This was nearly fully compensated for by a gradual decrease in hemolymph bicarbonate concentration ([HCO3 ‐]) over 96 hours post‐immersion. After one to two weeks of immersion, when crabs were removed from the water, oxygen uptake initially increased, but eventually returned to the initial immersed value. Heart rate was unchanged but fsc slowed dramatically. The decreased ventilation resulted in a buildup of hemolymph PCO2, causing a respiratory acidosis that was slowly compensated for by increased hemolymph [HCO3 ‐]. C. guanhumi appears to be a truly amphibious crab with respiratory and acid‐base adaptations found in both fully aquatic and fully terrestrial species.