Asian Shore Crab (Hemigrapsus sanguineus) — identification, habitat & look-alikes

The Asian shore crab is a small crab from East Asia that has become an abundant invasive species on rocky shores along much of the U.S. Atlantic coast. It was first found in the U.S. in 1988, probably carried over in ships' . Look for its square shell, three spines on each side, and banded legs. It's also called the Japanese shore crab.

Appearance

Appearance: A square shell typically about 1–1.6 in (2.5–4 cm) wide, with three spines along each side. Color ranges from green to purple, orange-brown, or red. The legs have light and dark bands, and the claws have red spots. Males have a fleshy bulb at the base of the movable claw finger.

Look-alikes

European green crabCarcinus maenas

Green crabs have five curved spines on each side of the eyes, a fan-shaped shell, claws of different sizes, and grow much bigger, up to about 4 in (10 cm). Asian shore crabs have three spines, a square shell, and banded legs.

Why they get mixed upBoth are invasive crabs that share the same rocky New England shores.

Harris mud crabRhithropanopeus harrisii

This tiny native crab tops out around 3/4 in (2 cm), has a fan-shaped shell, cream-colored claw tips, and a right claw larger than the left. Asian shore crabs are bigger, square-shelled, and have banded legs.

Why they get mixed upBoth are small crabs of shallow coastal water.

Say mud crabDyspanopeus sayi

Say mud crabs have a domed, six-sided shell, black claw tips, and a thinner left claw, without banded legs.

Why they get mixed upIt hides under rocks in the same small-crab size range.

Where it lives

Typical habitats: Rocky shores
Cobble and boulder beaches
Jetties and seawalls
Range: Native to the northwestern Pacific from Russia's Far East through Korea, eastern China, and Japan to Hong Kong. In the U.S. it is established and very abundant along the Atlantic coast from Maine to North Carolina; it has also spread to northwestern Europe.
Preferred conditions: Lives between the tides on rocky shores, hiding among boulders. It also turns up on oyster reefs and in salt marshes.
Seasons: In the US
Breeding May–Sep

Behavior

Diet: An opportunistic that prefers animal food: mussels and other shellfish, snails, small crustaceans, barnacles, and worms, plus seaweed, marsh grass, and young fish.

Life cycle

Breeding season: In U.S. waters it breeds from May to September, about twice as long as native crabs.
Clutch size: Up to 50,000 eggs per clutch, with 3–4 clutches a season
Larva: Larvae drift in the water for about a month, which helps the species spread long distances.

Conservation

IUCN Red List: NENot EvaluatedNot yet assessed
Threats: It may displace native mud crabs from rocky hiding spots and may also compete with blue crabs, rock crabs, and lobsters. The parasites that help keep it in check in Asia are absent on the U.S. coast.