Morphometrics and estimates of force generation by the chelae of a North American population of the invasive green crab, Carcinus maenas (L.)

The European green crab, Carcinus maenas, is an invasive species in eastern North America and has the potential to significantly impact wild and aquaculture shellfish in the southern Gulf of St. Lawrence, Canada. To examine potential predation effects on local shellfish and assess the appropriateness of extrapolating results from studies conducted elsewhere, the morphometry of chelae from a recently established population of C. maenas in Nova Scotia was examined for comparison with the presumed founding (European) population, and forces generated by the chelae over a range of crab sizes were estimated. The Nova Scotia population was found to be morphologically very similar to European populations with respect to chela structure. Force generation by the chelae was found to scale with isometry in the female crab and with positive allometry in the male. Estimated forces compare well with previously reported forces, and force generation is calculated to increase in a nonlinear manner proceeding from the chela tips proximally toward the fulcrum. The calculated forces generated by the chelae are clearly sufficient for outright crush - ing of some shells (e.g., Mya arenaria), even for small crabs, but appear to be too low for crushing those of other molluscs. There is a complex interplay between gape and maximum force along the length of the dactyl that allows great variability in force application, and thus also in the size of prey consumed and prey-handling behaviour. We suggest that for such a lever system, the gape angle of the chelae, which does not change with crab size, is optimal with respect to the resultant force generated.