RESPIRATORY AND CARDIOVASCULAR RESPONSES OF TWO SPECIES OF DEEP-SEA CRABS, CHACEON FENNERI AND C. QUINQUEDENS, IN NORMOXIA AND HYPOXIA

ABSTRACT The respiratory and cardiovascular variables in Chaceon fenneri and C. quinquedens were examined in animals during normoxia, animals exposed to hypoxia, and animals allowed to recover in normoxia. Chaceon fenneri was characterized by a relatively low metabolic rate (low oxygen uptake), and low ventilatory frequency. This species displayed a pattern of oxy-independent O2 uptake when exposed to hypoxia: MO2 was maintained primarily through hyperventilation. At an environmental PO2 of about 25 torr, respiratory and cardiovascular functions shut down, and the animal appeared to make the transition to exclusively anaerobic energy production. Lactate accumulated in the hemolymph during hypoxia and during recovery. Recovery was also characterized by elevated O2 uptake, and prolonged hyperventilation, indicating the repayment of an oxygen debt. Oxygen uptake in resting C. quinquedens was roughly double that in C. fenneri, and ventilatory frequency was 3-fold higher. MO2 declined in hypoxia, and hyperventilation was absent, a more typical oxy-dependent pattern of respiration. The ambient PO2 at which ventilatory and cardiovascular shutdown occurred was about 17 torr, but oxygen uptake continued at very low levels even in severe hypoxia. Lactate buildup in the hemolymph was not observed. During recovery, normal levels of O2 uptake were quickly restored, and hyperventilation was absent. Chaceon quinquedens appeared not to utilize anaerobic metabolism during hypoxia or to incur an oxygen debt. The differences in respiratory and cardiovascular responses to hypoxia in these two species appear to be due to a combination of differences in metabolic rate and body morphology.