POPULATIONS OF THE GREEN PORCELAIN CRAB, <i>Petrolisthes armatus</i>, VARY IN COLD TOLERANCE WITHIN THE SPECIES’ NORTHERNMOST INVADED RANGE
The green porcelain crab, <i>Petrolisthes armatus</i>, is a highly abundant invader of intertidal oyster reef habitats in Atlantic waters of the southeastern US. Cold water temperatures likely limit the species’ poleward range, which is predicted to shift as water temperatures rise. I established five study locations along the species’ poleward expansion front from Savannah, GA (Skidaway Island) to Wilmington, NC. Trends in <i>P. armatus</i> populations and resident crab assemblages were assessed seasonally at each location, and live crabs were collected for cold tolerance incubation trials. The taxonomic composition of crab assemblages differed between locations within each season, with obvious dissimilarities between northern and southern locations in the summer and fall, primarily driven by differences in <i>P. armatus</i> abundance. Abundances were highest in the summer and decreased from southern to northern locations. Sex ratios varied seasonally; becoming male biased in the fall. Adult-sized crabs were collected in the spring, indicating that overwintering of adults does occur. Chronic cold temperature trials were conducted seasonally to expose crabs from each location to decreasing water temperatures and assess sublethal and lethal effects. Crabs from northern locations were more tolerant of cold water temperatures in the fall, possibly due to increased acclimatization plasticity present in individuals from northern populations in response to a comparatively colder environment. Females were more tolerant than males in the summer and spring, possibly due to differences in male and female reproductive stressors. Smaller crabs were more tolerant than larger crabs regardless of season indicating molt cycle may play a role in cold tolerance. Given the trend of warming ocean waters, which may move thermal barriers to <i>P. armatus</i> range expansion to higher latitudes, and apparent higher cold tolerance in poleward populations, there is potential that this species will continue its poleward range expansion.