MIT Sea Grant Center for Coastal Resources

Hemigrapsus sanguineus

Most UnWanted: Hemigrapsus Sanguineus

A new species of crab, Hemigrapsus sanguineus, which is native to the shores of the western North Pacific Ocean, has recently colonized the east coast of the United States. The crab was first reported near Cape May, New Jersey in 1988, where it was probably introduced via ballast water. Since that time, the crab's range has spread as far north as Cape Cod, Massachusetts and as far south as Chesapeake Bay.

We are trying to track the crab's spread; would you like to help us?

Hemigrapsus sanguineus typically lives in the intertidal or shallow subtidal zone, where water depth is only a couple of feet at low tide. The crab can often be found under rocks in the intertidal zone during low tide.

Hemigrapsus sanguineus can be identified by the following characteristics:

It has three spines on each side of the carapace, the exoskeleton covering the main part of the body. The carapace is more square than triangular in shape. The color of the carapace is mottled, and ranges from green to purple to orange-brown. The legs have a distinct banding pattern of alternating light and dark colors. The claws have a speckled pigmentation pattern. Male crabs have a fleshy, bulb-like structure at the base of the moveable finger of the claws. Juvenile crabs can be very small and difficult to identify. Adult crabs can reach over 35 mm (1 1/2 inches) in body size, measured as the width of the carapace.

Hemigrapsus sanguineus will have ecological impacts in its new home by competing for food and habitat space. It eats different types of algae and animals, including juvenile clams. It appears to occupy habitats very similar to crabs that are native to the region. It also may act as a food source for larger animals. Many of these changes to the coastal ecosystem may be subtle and not apparent to many observers. Scientists are now studying potential impacts of this new species.

If you would like to join the search for this crab in new areas and help us track its geographic spread, visit a shoreline at low tide and turn over rocks. Examine the crabs you find closely; you may want to bring a notebook to make sketches and record observations. Be sure to gently replace the rocks to minimize disturbance to other organisms. Please do not move the crab to a new location -- you shouldn't contribute to its spread!

Click Here to view a map of the distribution of H. sanguineus

If you are successful in your search, you will soon be able to fill out our questionnaire , and send, email, or fax it to:

Dr. Nancy J. O'Connor
Department of Biology
University of Massachusetts Dartmouth
285 Old Westport Road
N. Dartmouth, MA 02747-2300
Fax: 508-999-8196

Please understand that we anticipate many responses and may be unable to respond to you personally. Thanks for your help!

Go to the Questionnaire!


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  this page last updated on: 4 December, 2002