Locomotory fatigue in the Atlantic blue crab, Callinectes sapidus
Burnett, Louis E
MetadataShow full item record
The Atlantic blue crab, <italic>Callinectes sapidus</italic> (Rathbun), is an important commercial and recreational fishing species that resides in the estuarine waters of the Atlantic Ocean and Gulf of Mexico. These highly mobile crustaceans must locomote to find food, evade predators, find mates and avoid adverse conditions such as hypoxia. In effect, maintaining continuous activity and resisting fatigue for extended periods of time may be necessary for the daily survival of blue crabs. In this study we investigated: 1) the impact of locomotion on the ability of a blue crab to produce a force with their walking legs to hold onto and guard a mate, and 2) the effects of two levels of hypoxia (10.4 kPa, 50% air saturation; 4 kPa, 20% air saturation) on fatigue during sustained continuous exercise. Fatigue was induced by an exercise trial that entailed continuous sideways hexapedal walking on an underwater treadmill. A repeated pull force test is described here that mimicked the way a male holds a female during mate guarding, by measuring the force crabs used to hold onto a mesh grid. The pull force decreased during walking in normoxia by 7.88% h<super>−1</super>. The results indicate that the more time a male crab spends searching for a mate, the less ability he will have to hold and, therefore, guard his mate. Fatigue, defined as a 33% decrease in pull force, was reached after a mean 6.19 h walking for crabs in normoxic seawater, 4 h in 50% air saturation and 2 h in 20% air saturation. Fatigue-resisting behaviors (180° turns, stopping and riding to the end) increased from the initial time point by 0.9 behaviors h<super>−1</super> in normoxia, 4.1 in 50% air saturation, and 13.8 in 20% air saturation. The force and behavioral results indicate that performance is decreased and fatigue is reached more quickly as the level of hypoxia intensifies.