Carcinus maenas (Linnaeus, 1758) Common name(s): European green crab, Green crab, European shore crab
Synonyms: Cancer granarius, Cancer granulatus, Cancer maenas, Cancer pygmaeus, Cancer rhomboidalis, Cancer viridis, Megalopa montagui, Monoculus taurus, Portunis carcinoides, Portunis menoides
Phylum Arthropoda  Subphylum Crustacea  Class Malacostraca  Subclass Eumalacostraca  Superorder Eucarida  Order Decapoda  Suborder Pleocyemata  Infraorder Brachyura Superfamily Portunoidea  Family Portunidae
	Carcinus maenas found in the intertidal at Cape Alava, WA. Note that this crab is missing legs 2-4.
	(Photo by:  Dave Cowles)

Description:  Neither this crab species nor its family (Portunidae) are native to the Pacific Northwest coast. Members of Family Portunidae have a carapace described as "round, oval, or square" and without a rostrum. The fifth pair of legs is flattened and usually used for swimming. In some species (apparently such as this one) it is used for digging. Portunis maenas has an approximately oval carapace with three points between the eyes and five anterolateral teeth, making it look approximately like a cancer crab. Its color is variable--green, reddish, or brown. In my experience the molted carapaces are often but not always orange-brown (photos). The dactyl of the claws is mostly black. Maximum carapace length 6 cm, width = 9 to 10 cm.

How to Distinguish from Similar Species:  Local cancer crabs (members of family Cancridae) have similar-shaped oval carapaces with no rostrum but their carapace has 5 points between the eyes and none of them has 5 anterolateral teeth on the carapace. The underside of Carcinus maenas also seems to have a distinctive dark-and-white pattern on the abdomen and maxillipeds as seen in the photo above. A closely-related species C. aestuarii, not currently found in the Pacific Northwest, has a smooth projection without the three points between the eyes.

Geographical Range:  Native to the European coast of the Atlantic Ocean and Baltic Sea including Iceland, but introduced into Australia, South Africa, eastern and western North America, central America, Brazil, and Patagonia. 

Depth Range:  Mostly intertidal

Habitat:  Wide variety of habitats but most common on soft bottoms. Can be found in rocky, muddy, or sandy substrates including in seagrass. Tolerates a wide range of salinity from 4 ppt at least to full seawater. Common in estuaries. 

Biology/Natural History:  This is an infamous "invasive species" which was found in San Francisco Bay in 1989 but reached the Pacific Northwest by 1997 or 1998. It was first discovered in Lummi Bay in the Salish Sea in 2019 and is spreading south into Padilla Bay. It has also appeared at Mukkaw Bay and Cape Alava on the Washington coast and in Willapa bay. Its diet includes bivalves such as clams such as Mya arenaria, scallops, mussels, and oysters; worms, and crustaceans, including small crabs (up to their own size, including young Metacarcinus magister) native to the Pacific Northwest. Large red rock crab Cancer productus is an important predator. Carcinus maenas digs burrows, and may compete for burrows with the Oregon shore crab Hemigrapsus oregonensis. Its color variations seem to be influenced by both genetics and the environment, with delayed molting associated with red colors instead of green. After a pelagic larval stage the juveniles settle in seaweed or seagrass. 

References:

General References:
 

Scientific Articles:
Ruiz, Gregory M., James T. Carlton, Edwin D. Grosholz,  and Anson H. Hines, 1997. Global invasions of marine and estuarine habitats by non-indiginous species: mechanisms, extent, and consequences. American Zoologist 37:6 pp. 621-632

Web sites:

General Notes and Observations: Locations, abundances, unusual behaviors:

Dorsal view of the crab shown at the top of the page. Captured live at Capa Alava, WA. Photo by Dave Cowles (via GoPro camera, which can be difficult to focus)
 

Dorsal and ventral views of a frozen male Carcinus maenas collected in Padilla Bay, WA courtesy of Roger Fuller from the Padilla Bay National Estuarine Research Reserve. Photos by Dave Cowles, July 2022

Dorsal and ventral views of a frozen female Carcinus maenas collected in Padilla Bay, WA courtesy of Roger Fuller from the Padilla Bay National Estuarine Research Reserve. Photos by Dave Cowles, July 2022

Another live Carcinus maenas found at Cape Flattery July 2022. Photos by Dave Cowles via GoPro

Views of several carapace molts from Carcinus maenas we found on the Capa Alava beach intertidal, July 2022. Photos by Dave Cowles, via GoPro

Authors and Editors of Page:
Dave Cowles (2022):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University