Recovery from exhausting exercise in a bimodally breathing crab, Leptograpsus variegatus (Decapoda: Grapsidae)

Abstract

The acid-base status of the postbranchial haemolymph of adult purple rock crabs Leptograpsus variegatus Fabricius, 1793, was examined at 15°C after running in air on a motorized treadmill at 8.2 cm·s −1 (≈0.5 body lengths·s −1) for a mean time of 4.8 min. Serial haemolymph samples were taken from resting crabs maintained under conditions which allowed a free choice between air and seawater, in the same animals immediately after exercising to exhaustion and after 1, 4, and 24 h of recovery in either air or completely submerged in seawater. Activity produced a marked haemolymph acidosis (0.4 pH units) which had both respiratory and metabolic components. Haemolymph [lactate −] increased by ≈8 mmol·1 −1 immediately post-exercise and had risen slightly more after 1 h's recovery in water and in air. Excess lactate was cleared with a half-time of ≈6.5 h. Despite the slow lactate clearance, restoration of pH commenced within 1 h in both groups and was nearly completed at this time in the water-recovery group. After 24 h recovery in air, the acid-base status of the haemolymph was essentially similar to the pre-exercise state with respect to pH, [lactate −], total CO 2, P co 2 (calc), [Ca 2+],and osmolarity. However, after 24 h recovery in seawater, total CO 2 and P co 2 (calc) were lower than pre-exercise values and a small respiratory alkalosis appeared. This indicates that, when given a choice of media, adults of this crab adopt an essentially aerial respiratory and acid-base status. Compared with Cyclograpsus lavauxi, another New Zealand high-shore grapsid, L. variegatus appears better able to deal with disturbances of acid-base state associated with aerial activity and can restore haemolymph pH without return to water.