Population dynamics of the non-native crab Petrolisthes armatus invading the South Atlantic Bight at densities of thousands m(-2)

The green porcelain crab Petrolisthes armatus recently invaded oyster reefs of the South Atlantic Bight. In 2 estuaries of coastal Georgia, USA, crab densities reached peak densities of 4000 to 11000 crabs m(-2) in some periods and locations. Densities generally were higher in the low versus the high intertidal and in the lower versus upper regions of the estuaries. In warmer months, 20 to 90 % of adult females were gravid, recruits were dense, and population levels were high. In colder months, densities dropped by 64 to > 99 %. Male:female ratios were near 1: 1 across times and locations. Maximum mean densities of P. armatus in Georgia were 37 times the highest densities recorded in the presumptive native range. Crabs in the new range reproduced at a smaller size, and the percentage of gravid females was similar between the old and new range. Thus, population fecundity in Georgia exceeds that of the native range by more than 1 order of magnitude. Densities of native mud crabs in the genera Panopeus and Eurypanopeus were unrelated to, or positively correlated with, densities of the exotic crabs; correlations were never significantly negative. The impact of Petrolisthes armatus on native communities is unclear, but could be considerable if this filter-feeding crab impacts oysters, which are the foundation species of inshore reefs.