THE INFLUENCE OF AERIAL EXPOSURE ON GAS-EXCHANGE AND CARDIAC ACTIVITY IN THE SHORE CRAB, CARCINUS-MAENAS (L)

The cardiovascular physiology of adult C. maenas (L.) emerging into air has been investigated at 3 different air temperatures. Transition from seawater to air or vice versa triggered transient increases in cardiac and locomotor activity. However, crabs became inactive 5-10 min after emerging from seawater (15.degree. C) into air at the same temperature (15.degree. C) or at lower temperatures (12.degree.-13.degree. C) and heart rate fell. At higher air temperatures (18.degree.-20.degree. C) heart rate rose but to a lesser extent than predicted from aquatic Q10 heart-rate values. Crabs were again quiescent in aerial conditions. Mean arterial oxygen tension (PaO2) was .apprx. 74 mm Hg in submerged crabs but fell to .apprx. 38 mm Hg in air while mean arterial carbon dioxide tension (PaCO2) increased from 1 to 4 mm Hg resulting in respiratory acidosis. A model of gill function is proposed to explain the development of internal hypoxia in air. The results are discussed in relation to the distribution of adult and juvenile C. maenas in situ.