Moderate Dehydration Decreases Locomotor Performance of the Ghost Crab, Ocypode quadrata

The effect of dehydration on the aerobic metabolism and endurance of sustained, terrestrial locomotion was determined for the ghost crab, Ocypode quadrata. The rate of evaporative water loss, measured as the percentage of decrease in body mass per hour, was influenced by ambient temperature (Ta). Increasing Ta from 240 C to 300 C (40%-50% relative humidity) increased the rate of water loss from 2.3% h-' + 0.2% h-' to 3.6% h' + 0.6% h-'. Crabs were divided into three treatment groups to determine the effect of dehydration on aerobic metabolism: hydrated control crabs, slowly dehydrated crabs, and rapidly dehydrated crabs. Hydrated control crabs lost only 1.2% of their initial body mass. Slowly dehydrated crabs were dehydrated by 3.6% of their initial body mass at a rate of 2.3% h-. Finally, rapidly dehydrated crabs were dehydrated by 3.6% of their initial body mass at a rate of 3.6% h-'. The maximal rate of oxygen consumption (17o2max) determined during treadmill exercise was decreased by 30% for slowly dehydrated crabs and by 70% for rapidly dehydrated crabs, as compared to hydrated controls. The minimum cost of locomotion was independent of the dehydration state for hydrated and slowly dehydrated crabs but was 62% lower for rapidly dehydrated crabs. Endurance was correlated with the speed at which Vo2 max was attained (the maximum aerobic speed [MAS]). The MAS was highest for hydrated control crabs and was decreased by 32% for slowly dehydrated crabs and by 68% for rapidly dehydrated crabs. We conclude that moderate dehydration can substantially decrease the ghost crab 's capacity for sustained, terrestrial locomotion.