Photographer:David Knott Source: www.bugwood.org Copyright: CC BY-NC 3.0
Petrolisthes armatus is a very small (around 1cm in width), flat crab that is dark-brown to orange-brown in color. The Green coloration in its name refers to the olive green or dark green color Petrolisthes armatus has as juveniles. The chelae (pinchers) are quite long and have a conspicuous orange spot which is visible when they are open. Also, the Green Porcelain Crab has distinctive blue mouth parts and finally, unique to all porcelain crabs, the antennae insert external to the eyes and not between them like most other crabs.
Not much is presently known about the ecological impact of this recently established filter-feeding crustacean in its newly exploited habitat; however, it is thought that the small Petrolisthes armatus would provide an alternative for larger xanthid crabs. The xanthid crabs are predators of newly settled oysters and the increase of alternative food sources could help oyster population’s succeed but increase the xanthid crab population, which would be a negative impact on the ecosystem balance. Alas, there is always a threat with so little being known about the invasive Petrolisthes armatus.
Petrolisthes armatus eggs hatch and enter into three free-floating larval stages before it is ready to settle in the sediment and enter the juvenile stage. The Green Porcelain Crab is primarily a filter feeder that extends and waves its mouthparts back and forth straining plankton from the water. Northward expansion of Petrolisthes armatus up the Atlantic coast is highly unlikely because it is not cold-tolerate, however their salinity tolerance is somewhat broad.
Introduction has been a result of both natural and from human activity; including transport in ballast water from foreign and domestic ports and among cultured mollusks transported from localities within its previously established range. As early as the 1930s, this species was collected from the Florida Atlantic coast at Biscayne Bay and Miami Beach, but the fall of 1994, when faunal surveys at St. Catherines Island, GA revealed its presence there. Petrolisthes armatus increased dramatically in abundance there, becoming the dominant decapod crustacean on rocky substrates and tidal creek oyster bars by the following spring. In South Carolina, it was first observed in low densities in the spring of 1995 at various locations, becoming quite abundant by the fall. By 1999 it has been well established along the coast of Mississippi.
U.S. Present: FL, GA, MS and SC
U.S. Habitat: Shallow subtidal habitats like ruck rubble and oyster reefs.
The invasion of Petrolisthes armatus may be too recent to fully understand the impact that it will have on oyster reefs in the Atlantic Ocean, Mississippi Sound and Gulf of Mexicoand therefore, not known on how to manage this filter-feeding crab. What could be done for now is to understand the full established range of this small crab and remove (without chemicals) any small populations found in marine environments.
Boudreaux M.L., Stiner J.L., and L.J. Walters. 2006. Biodiversity of sessile and motile macrofauna on intertidal oyster reefs in Mosquito Lagoon, Florida. Journal of Shellfisheries Research 25:1079-1089.
Knott D.M., Boyko C., and A. Harvey. 1999. Introduction of the green porcelain crab, Petrolisthes armatus (Gibbes, 1850) into the South Atlantic Bight. In: J. Pederson (Ed.). Marine Bioinvasions: the Proceedings of the First National Conference. Massachusetts Institute of Technology, Cambridge, Massachusetts. pp. 404.
Lohrer A.M. 2001. The threat of invasion in South Carolina estuaries: A focus of exotic decapod crabs. Paper presented at the 16th Biennial Conference of the Estuarine Research Federation, November 4-8, 2001. St. Petersburg Beach, FL.