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