Photographer: United States Geological Survey Source: usgs.gov
These small crabs are identified by a square-shaped shell and three spines on each side of the carapace. Their coloration can range from orange-brown to green, or even purple! There is a distinctive banding pattern present on the legs, and the claws are speckled. As adults they only reach 1.5 inches in length. The juvenile stage is very small and hard to identify.
Hemigrapsus sanguineus prey on a variety of animals including algae, snails, barnacles, worms, juvenile fish and clams; making them a threat to several species of animals. They even consume larval lobsters, which has a great economic impact. Due to their ability to reproduce rapidly they quickly overrun local rock crabs, and have the potential to displace them altogether. They are able easily outcompete other native marine invertebrates for food and space. They are also very tolerant of various water salinities and temperatures, suggesting they could invade waters farther south.
Breeding season goes from May to September. A single female can bear 2-4 clutches with approximately 50,000 eggs per clutch, that’s up to 200,000 per female in a breeding season! On average they live 3-5 years.
First reported near Cape May, New Jersey in 1988. It has spread as far north as Maine, and as far south as South Carolina. Due to its small size it was probably a stowaway on a cargo ship’s ballast water.
western North Pacific Ocean
U.S. Habitat: intertidal or shallow subtidal zone, where water depths are a couple of feet at low tide.
U.S. Present: CT, DE, MA, MD, ME, NH, NJ, NY, RI, SC, and VA
For a state and county distribution map provided by the USGS click here
Unfortunately, as is the case with many invasive marine animals, there are no control measures at the time. Studies have shown that rockfish and seagulls due prey upon these crabs. Also, in the crab’s native lands parasites help control populations. Researchers are looking into the affects those parasites could have on the crabs in the Atlantic Ocean.
Brousseau, D. J., Goldberg, R., & Garza, C. 2014. Impact of Predation by the Invasive Crab Hemigrapsus sanguineus on Survival of Juvenile Blue Mussels in Western Long Island Sound. Northeastern Naturalist, 21(1), 119-133.
Epifanio, C. E., Tilburg, C. E., & Dittel, A. I. 2013. Abundance of invasive and native crab larvae in the mouth of Delaware Bay: Hemigrapsus sanguineus and Uca pugnax. Journal of Shellfish Research, 32(2), 543-550.
McDermott, J. J. 1998. The western Pacific brachyuran (Hemigrapsus sanguineus: Grapsidae), in its new habitat along the Atlantic coast of the United States: geographic distribution and ecology. ICES Journal of Marine Science: Journal du Conseil, 55(2), 289-298.
Tiedemann, J. A. 2015. Observations of the Invasive Asian Shore Crab (Hemigrapsus sanguineus) in Upper Barnegat Bay, New Jersey. Bulletin: New Jersey Academy of Science, 60(1).