Energetics of the Exercising Wharf Crab Sesarma cinereum

Crabs (1.9 g) were exercised for up to 60 min on a miniature treadmill respirometer. O2 consumption (V̇o2) at all velocities was low, a maximum of only 1.5 times the resting rate. V̇o2 was not related to the velocity of running. Five weeks of treadmill training produced a minor rise in V̇o2 at the maximum sustainable velocity, but the highest V̇o2 was still only two times the resting V̇o2. Crabs exercising in 100% O2 significantly increased their endurance capacity, indicating that this crab's O2 conductance system is severely limited. Anaerobic metabolism with lactate as an end product supplemented aerobic energy production to a minor extent. Wholebody lactate (WBL) increased at a constant but small rate (0.10 mg·g⁻¹·min⁻¹) when the crab ran at the highest velocity (0.14 km·h⁻¹). Wharf crabs fatigued rapidly when run in a 100% N2 atmosphere, indicating they do not have unusual anaerobic capacities or unusually high levels of O2 stores or phosphagen reserves to compensate for the very low V̇o2. Hence, all data suggest that Sesarma cinereum has a uniquely reduced metabolic rate during exercise.