Locomotory Fatigue and Size in the Atlantic Blue Crab, Callinectes sapidus

Size is an important factor for the Atlantic blue crab, Callinectes sapidus (Rathbun), with large male crabs often having an advantage over small crabs in mating, molting, and locomoting. The ability of larger crabs to resist fatigue may be another benefit of being big. We describe a novel pull force test that measures the force crabs use to hold onto a mesh grid, mimicking the way a male holds a female during mate guarding. In this study, we used this pull force test to determine whether larger male crabs have an advantage over smaller crabs by being able to sustain a greater pull force even after fatigue from sustained walking. Fatigue was induced by a 6-h exercise trial that entailed continuous sideways hexapedal walking on an underwater treadmill. Larger crabs maintained an advantage over smaller crabs even after fatigue. In crabs, including the Atlantic blue crab, increased size seems to have advantages. These include reproduction