Latitudinal Variation of Claw Attributes in East Coast Cancrid Crabs

Abstract

Mechanical advantage and relative chela size of Jonah (Cancer borealis) and rock (Cancer irroratus) crabs were compared from locations along the east coast of North America, from Nova Scotia to Florida, to determine whether attributes of the chelae varied by sex, size class, or latitude. There was no relationship between mechanical advantage and sex. However, males of both crab species had larger chelae than females of comparable body size. There were no differences in mechanical advantage among size classes in the Jonah crab, nor was there a relationship between mechanical advantage and latitude, although mechanical advantage varied among the populations sampled. Relative chela size increased with the size of the crab and differed by site among populations sampled. The mechanical advantage of rock crab claws differed among size classes, varied according to site, and increased with latitude. The relative chela size of rock crabs also increased with size class and differed among sites. Differences may be attributed to pressures related to prey choice and availability, substrate preference, and habitat choice and availability, as well as competition and predation.