Habitat-related phenotypic variation in adult Western Atlantic stone crabs (Menippe mercenaria Say, 1818) (Decapoda: Brachyura)

Abstract

Habitat partitioning by different life stages or phenotypes in a heterogeneous marine environment could confer fitness advantages. Two distinct phenotypes of the Western Atlantic stone crab ( Menippe mercenaria Say, 1818), spotted and brown, are easily distinguishable and occupy different habitats in allopatry. Intermediate phenotypes occur in two geographic zones, the northeastern Gulf of Mexico and the southern Atlantic coast of the USA from South Carolina to northern Florida. We examined stone crab phenotypic variation and demography in two adjacent rivers near Charleston, SC, USA, the Kiawah and Stono rivers. The intertidal oyster habitat (quantified as reef per meter shoreline) in the Kiawah River is more than twice as dense as the oyster habitat in the Stono River. Significantly more brown than spotted crabs, a higher proportion of males, and larger individuals were collected in the Kiawah River in a year-long trapping study. Brown coloration for stone crabs on oyster reefs could confer a fitness advantage if these crabs are more cryptic than spotted crabs. The timing of ovigery and egg development did not differ between crabs in the Kiawah and Stono rivers or between brown and spotted stone crabs regardless of capture location. Males exhibited greater cheliped wear than females, but wear was unrelated to proximity to an oyster-reef habitat. Demographic patterns related to habitat use presented here are consistent with habitat use in the northeastern Gulf of Mexico zone of phenotypic variation. The differences in stone crab demographics in these two coastal rivers in South Carolina indicate that further studies are needed to determine whether this habitat-related phenotypic variation is representative of stone crab distributions throughout the South Atlantic Bight.