Asian Shore Crab
Photo credit: Northeast Coast & Barrier Network,
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Species at a Glance
The Asian shore crab, also called the Japanese shore crab, is a small species of crab from the Asia-Pacific region. It has a very broad diet and has the potential to affect populations of native species, such as crabs, fish, and shellfish in its introduced range. It may also compete with larger species, like the blue crab, rock crab, and even invasive green crabs.
The Asian shore crab is small, with adults ranging from 35 mm (1.5 in) to 42 mm (1.65 in) in carapace width. It has a square-shaped shell with three spines on each side of the carapace. Carapace color can be green, purple, orange, brown, or red. It has light and dark bands along its legs and red spots on its claws. Male crabs have a distinctive, fleshy, bulb-like structure at the base of the moveable finger on the claws.
The Asian shore crab may be confused with other species of crab, such as the green crab (Carcinus maenas); however, the green crab is larger and has five points on the carapace instead of three.
A very versatile crab, the Asian shore crab can tolerate a wide range of temperature and salinity ranges, inhabiting any shallow hard-bottom intertidal or sometimes subtidal habitat. It can live on artificial structures and on mussel beds and oyster reefs. It also tends to aggregate at high densities under rocks where its habitat can overlap with native crab species.
It is unknown how this species was introduced to the United States, although many speculate that both adults and larvae were introduced through ballast water discharges from transoceanic ships. It is highly prolific, with females producing 50,000 eggs per clutch, and 3-4 clutches per breeding season. The larvae are suspended in the water for approximately one month before developing into juvenile crabs, allowing them to be transported over great distances to new locations.
Native to the coasts of China, Hong Kong, Korea, Russia, and Japan, the Asian shore crab was first reported in the United States at Townsend Inlet in New Jersey in 1988. It is now well established along the Atlantic intertidal coastline of the United States from Maine to North Carolina. Because it is tolerant of a wide range of environmental conditions, it is likely that its spread will continue along the U.S. coastline.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Because it has a very broad diet, the Asian shore crab has the potential to affect native populations by disrupting the food web. It has also been known to feed on commercially important species, such as larval lobsters, crabs, fish, and shellfish. Trends are showing the numbers of shore crabs are steadily increasing, while native crab populations are decreasing because they occupy habitats very similar to the native crabs. The Asian shore crab may also pose a threat to coastline ecosystems and aquaculture operations.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).