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

The cardiorespiratory and hemolymph acid base status of bimodal breathing c rabs, Cardisoma guanhumi, was monitored during the transition from breathin g air to breathing water. Upon immersion, oxygen uptake (MO2) decreased by half. Ventilatory frequency (f(SC)) increased more than 5 fold, causing a d ecrease in hemolymph carbon dioxide partial pressure (PCO2). This was nearl y fully compensated for by a gradual decrease in hemolymph bicarbonate conc entration ([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 ra te was unchanged but f(SC) slowed dramatically. The decreased ventilation r esulted in a buildup of hemolymph PCO2, causing a respiratory acidosis that was slowly compensated for by increased hemolymph [HCO3-]. C. guanhumi app ears to be a truly amphibious crab with respiratory and acid-base adaptatio ns found in both fully aquatic and fully terrestrial species.