Respiration in the Land Crab, Gecarcinus Lateralis

The oxygen consumption, ventilation and blood gas transport were investigated in the tropical land crab Gecarcinus lateralis to determine the adaptations of the respiratory system for aerial respiration. The gills of Gecarcinus are reduced in size and specialized, in part, for salt and water uptake. The epibranchial space of the branchial chamber is very much enlarged and lined with what is probably a respiratory epithelium. There is a high ventilatory air-flow, produced by the beating of the scaphognathites, but the percentage extraction of oxygen is extremely low. This may be the result of ventilatory ‘shunts’, whereby a proportion of the air does not come into contact with the respiratory surfaces. The energetic cost of a high ventilation rate need not be high, because of the low inertial mass of air in comparison with water. A high oxygen tension gradient of 103 torr is maintained across the respiratory surfaces. This is interpreted as an adaptation to achieve a high oxygen diffusion rate through the reduced surface area of the gills. The blood has a relatively high oxygen capacity which is again thought to be an adaptation to compensate for the reduced gill surface area. Carbon dioxide tensions and content were high as in other terrestrial animals. Overall, the respiratory adaptations are thought to be related primarily to the reduction in the respiratory surface area which has evolved to deal with the problems of water conservation in these terrestrial animals.