Watch out for these invaders!

If you see one of these potential invasive species, contact Save The Bay at 401-315-2709 or email us photos at

Chinese Mitten Crab,
Eriocheir sinensis

Physical Description: Light brown to olive green shell up to 4 inches wide. Claws equally-sized, white-tipped with dense fuzzy patches. Four spines on each side of carapace; notch between eyes.

Habitat: Estuaries and freshwater streams.
Threat: Chinese mitten crabs have been found on the East Coast, but the existence of an established population has not been confirmed. There are NO native freshwater crabs in New England, and mitten crabs are highly adaptable to new food sources, so this invasion could seriously change our freshwater ecosystems.


Shore Crab

Hemigrapsus takanoi

Physical Description: Square-shaped shell up to 1 inch wide with 3 spines on each side. Color ranges from orange-brown to green and maroon. Light brown-yellow fuzzy growth at base of pincers (males only). Light and dark banded legs. Small dark spots on claws.

Habitat: Rocky intertidal zone.


Threat: Originally from Asia, the brush-clawed shore crab appeared in Europe in 1993, likely transported in ballast water. This species reproduces much more quickly than our native crabs. If the shore crab does make it to the North American coast, it will wreak havoc on native ecosystems.

Photo: Hans Hillewaert

Asian Isopod,
Synidotea laevidorsalis

Physical Description: Small, flat crustacean up to 1.2 inches long. Mottled tan to brown color. Blunt, concave tail with two points (similar-looking species have slightly different tails).

Habitat: Shallow, protected brackish or salt water attached to docks and pilings.

Threat: Originating from the western Pacific, this isopod is already present in Europe, South America, Australia and both the Southeast and West Coast of the United States. It outcompetes native invertebrates for available food resources.

Photo: The Southern Regional Taxonomic Center, South Carolina Department of Natural Resources.

Wakame Seaweed,
Undaria pinnatifida

Physical Description: Wide, flat, brown kelp with finger-like blades when mature. Can be confused for several native species – look for a folded, ruffle-like structure at the base of the leaf.

Habitat: Shallow water up to 15 feet deep. Grows on rocks, docks and moorings and can form dense “kelp forests.”

Threat: Wakame is widely cultivated in Asia for human consumption, but it can starve ecosystems that are unaccustomed to its rapid reproduction and wide leaves blocking sunlight to deeper water.

Photo: Chela Zabin


Veined Rapa Whelk, Rapana venosa

Physical Description: Rounded, heavily ribbed shell, up to 7 inches long and nearly as wide. Gray to reddish brown with black veins throughout shell. Inside of shell is a distinctive deep orange. Egg cases look like small mats of yellow shag carpet.

Habitat: Young rapa whelks live on rocky surfaces until about 2.7 inches long, then burrow into sand and mud to feed on clams and oysters.

Threat: Rapa whelks are already present in the lower Chesapeake Bay. If their population here continues to grow, they may pose a serious threat to native ecosystems and shellfish harvests.

Photo: George Chernilevsky

Corella eumyota

Physical Description: Grayish, semi-translucent egg-shaped organism commonly found clumped together. Body up to 1.5 inches long. Two prominent siphon tubes, one at the top and one a third of the way down the body. Very similar to native “sea grapes” – pay special attention to siphon position to tell them apart.

Habitat: Shallow, calm water. Attaches to docks, pilings and other submerged structures.

Threat: This tunicate is widely distributed throughout the southern hemisphere and has been sighted in France leading to concerns that it is continuing to spread. It grows in clumps over just about anything and can destroy shellfish beds by completely covering them.

Photo: David Fenwick, A-P-H-0-T-O Wildlife Image Libraries.

Japanese Seaweed, Sargassum muticum

Physical Description: Golden-brown seaweed growing up to 3 feet long. Leafy branches alternate sides off central stem. Pea-sized, air-filled floats on branches. Similar native species has dark spots on leaves – S. muticum does not.

Habitat: Attaches to rocks in shallow, calm water. Commonly found in disturbed areas.

Threat: Japanese seaweed is already present on the West Coast and in Europe. It grows quickly in the spring, reproduces quickly and blocks sunlight from reaching other plants and algae. This limits the survival of native species such as eelgrass. Furthermore, it is not a suitable food for native species, such as sea urchins, which normally keep seaweed populations in check.

Photo: Graca Gaspar

Invasive species already present in New England:

Dead man’s fingers,
Codium fragile

Physical Description: Green, spongy seaweed with round, finger-like branches. Grows up to 3 feet long.

Habitat: Shallow waters and permanent tidepools. Attaches to rocks, shells or other hard surfaces.

Threat: Originally from Japan, this seaweed was introduced to New York in 1957 and is now abundant from North Carolina to Canada. It can regrow from broken pieces and spreads quickly, outcompeting native species such as eelgrass and thus harming the populations of all the native organisms which rely on eelgrass.

Photo: David Prescott, Save The Bay.


European Green Crab,
Carcinus maenas

Physical Description: Color ranges from green to brown or orange. Five spines on either side of shell, which grows up to 3.6 inches wide.

Habitat: Sheltered mud, sand or rocky shorelines and salt marshes

Threat: The green crab likely made it from Europe to America in the early 1800’s, and has since become well established from Delaware to Nova Scotia. It eats just about anything, harms shellfish populations and competes with native crabs for limited resources.

Photo: Hans Hillewaert

Asian Shore Crab,
Hemigrapsus sanguineus

Physical Description: Color ranges from orange-brown to green and maroon. Light and dark banded legs with red spots on claws. Square shell up to 2 inches wide with 3 spines on either side.

Habitat: Intertidal zone, prefers rocky shore but also found in sand and mud.

Threat: Asian shore crabs reproduce 3-4 times per summer,  producing twice as many eggs as native species which only spawn twice a summer. Coupled with an ability to eat a very wide range of both plants and animals and an aggressive disposition, Asian shore crabs have been displacing native species at an alarming rate since their arrival in New Jersey in the 1980s.

Photo: GFDL


Club Tunicate (sea squirt),
Styela clava

Physical Description: Club-shaped body up to 8 inches long; attaches to hard surface by a stalk. Tough, leathery, bumpy exterior often covered by other organisms. Two siphon tubes extend from top end.

Habitat: Sheltered waters on hard surfaces, especially docks and pilings.

Threat: The club tunicate first appeared on the West Coast in the 1920s, and reached the East Coast in 1973. It spread rapidly from New Jersey to Canada and competes with native species for food and space.

Photo: N. Balcom, CT Sea Grant.