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 $(T_{a})$. Increasing $T_{a}$ from 24°C to 30°C (40%-50% relative humidity) increased the rate of water loss from 2.3% h⁻¹ ± 0.2% h⁻¹ to 3.6% h⁻¹ ± 0.6% h⁻¹. 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⁻¹. Finally, rapidly dehydrated crabs were dehydrated by 3.6% of their initial body mass at a rate of 3.6% h⁻¹. The maximal rate of oxygen consumption $\dot{V}o_{max}$ determined during treadmill exercise was decreased by ...