Green crab (Carcinus maenas)

Green Crab

Photo credit: Hans Hillewaert, https://flic.kr/p/eKkonM

(Carcinus maenas)

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If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

One of the world’s most successful invaders, the green crab is a voracious predator from Europe that feeds on shellfish, causing declines of other crabs and bivalve species. It is capable of learning, and can improve its prey-handling skills while foraging.

Identification

Despite its name, the green crab is not always green, but can be mottled dark brown to dark green on the top shell (carapace) with small yellow patches. The underside of the shell may change from green to orange and then red during the molting cycle. It has an array of five spines on either side of the eyes on the front end of the carapace. It also has three rounded lobes or bumps present between its eyes. Adult crabs are typically 6 cm (2.5 in) long, but can range up to 10 cm (4 in). The last pair of hind walking legs are relatively flat, similar to those of a Dungeness crab.

Similar Species

While it may be confused with other native crab species, the green crab can be distinguished by the array of five spines on either side of the eyes, as well as the three lobes between the eyes.

Habitat

Found in a variety of habitats, the green crab can tolerate a wide range of environmental conditions including salinity and temperature fluctuations. It is also found to inhabit protected rocky shores, cobble beaches, sand flats, and tidal marshes.

Spread

The green crab was most likely introduced through ballast water and shipping; however, it may have also arrived hidden in kelp packing material used in live lobster and bait worm shipments. Once established, the green crab has a floating larval stage that allows it to expand its distribution to new locations on water currents.

Distribution

Native to the Atlantic coast of Europe and northern Africa, the green crab first arrived in the Cape Cod region of the United States in the mid-1800's via sailing ships. It began its northward expansion along the Atlantic coast in the early 1900's and was discovered on the West Coast in 1989. Today, the green crab is found throughout the coast of the Mid-Atlantic region from North Carolina northward.

 

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.

Environmental Impacts

The green crab threatens populations of crabs, clams, mussels and oysters through competition, predation, and its burrowing activities. It has contributed to the decline of many valuable economic commercial species, such as soft shell crabs on the East Coast and Dungeness crabs on the West Coast. This voracious predator can consume 40 half-inch clams per day, as well as crabs its own size.

Videos
Note

Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).