Haemolymph gases, acid-base status, and metabolite levels were studied in Cardisoma carnifex a t rest and after 10 minutes of mild (0.2 body lengthdsecond) or severe (exhausting, 0.5 BL/second) exercise. 0, transport is very similar to that in aquatic crabs. At rest, arterial haemocyanin saturation is = 8796, venous saturation is =45%, and tissue utilization is -57%. During exercise, &loz rises 2-3-fold. Po2s fall so that O2 transport is shifted onto the steep part of the dissociation curve, venous saturation decreases markedly while arterial saturation remains high, and cardiac output rises. These adjustments raise the Po, gradient a t the respiratory surface, tap the haemolymph O2 store, and maintain or increase the a-v 0, difference so that utilization reaches 4 2 % .Postexercise acidosis augments these effects via the Bohr shift. Resting Pco?)s are low (=15 torr) for an air-breather, and PacOz changes minimally despite 2.5-5-fold evaluations in &Icoz. All haemolymph gas levels return to normal within 0.5-1.0 hours. Postexercise acidosis is largely metabolic, and smaller than in aquatic crabs. Lactate anions and protons enter the haemolymph in equivalent amounts and totally account for the metabolic acidosis. Elevated NH3 and pyruvic acid levels have negligible influence. During recovery, the metabolic acid load is reduced faster than the lactate load, resulting in alkalosis, possibly because of CaC03 mobilization from the carapace. Exercise metabolism appears largely anaerobic, but changes in haemolymph lactate levels do not correlate with the O2 debt. However, the "excess lactate" concept which compensates for pyruvate elevation gives a good index of the debt. All changes are more marked after severe than after mild exercise, but the patterns are similar.In the previous paper (Wood and Randall, %l), we have shown that the land crab Cardisoma carnifex has considerable running ability. Exercise is facilitated by marked increases in ventilation, 0, consumption, CO, production, and the acquisition of a substantial O2 debt. Basically similar effects were seen in Cardisoma guanhami (Herreid et a1.,'79). Very little is known about the role of haemolymph gas transport in these events, about the nature of the O2 debt, or about the influence of the increased CO, flux and anaerobic metabolism on acid-base regulation in land crabs, though these areas have been extensively studied in marine brachyurans (Johansen et al., '70; Mangum and Weiland, '75 Increased 0, delivery to the tissues during exercise in aquatic crabs is facilitated by reductions in both p,,, and p,,*. This taps the haemolymph 0, store, increases the diffusion gradient for O2 loading a t the gills, and a t the same time takes maximum advantage of the O2 transport properties of the respiratory pigment, haemocyanin. The extremely low in vivo Poz)s, arterial saturations, and in vitro Ps0's reported for Cardisoma guanhami a t rest (Redmond, '62, '68a; Young, '73) make it questionable whether this strategy can be implemented by the exercising land cra...
