Practical information to identify and manage non-native, invasive plants and animals
The Quiet Invasion:
A Guide to Invasive Species of the Galveston Bay Area
European green crab, Mediterranean green crab
Carcinus maenas, C. aestuarii

ITIS TSN:98734
Presence:Species of Concern
Habitat:Aquatic
Native Range:C. maenas is native to Atlantic Europe and Northwest Africa. C. aestuarii is native to the Mediterranean Sea and possibly the Canary Islands
Human Health
These species pose no known human health impacts.
Prohibited Lists
As of 2010, these species are not prohibited in Texas.
Introduction Pathways
C. maenus was first reported in the U.S along the Atlantic Coast in 1817  and along the Pacific Coast in 1989-90 (Carlton and Cohen 2003). Means of introduction include ships, ballast and hulls, packing materials (seaweeds) used to ship live marine organisms, bivalves moved for aquaculture, rafting, and migration on surface currents (Perry 2010a). C. aestuarii is not reported in the U.S.
Geographic Distribution
As of 2010, these species are not reported in Texas. C. maenus is reported in 13 states including: California, Connecticut, Delaware, Hawaii, Massachusetts, Maryland, Maine, New Hampshire, New Jersey, New York, Oregon, Rhode Island, and Washington (Perry 2010a).
Specific Primary Habitats
These species are found in protected and semi-protected marine and estuarine habitats, including those with mud, sand, or rock substrates, submerged aquatic vegetation, and emergent marsh (including marsh dominated by smooth cordgrass, S. alterniflora) (Cohen et al. 1995; Perry 2010a). C. maenus can tolerate salinities from 4 to 54 ppt and temperatures from near freezing to about 33° C (Cohen 2005).
Ecological, Economic, or Social Impact
These predatory crabs are able to crush bivalves (e.g. softshell clams and mussels). By entering and filling traps, the European green crab has been a pest of trap fisheries in eastern Canada and California. The green crab can dig 15 centimeters down in sand or mud when searching for prey; affecting the populations of benthic organisms living in the sediment. C. maenus can also cause trophic cascades, increasing the populations of some species by eating their predators or competitors (Cohen 2005).
Physical Description
The carapace (outer shell) of the green crab is fan-shaped with five notches/blunt spines on each side of the carapace behind the eyes. There are 3 rounded notches on the edge of the carapace between the eyes. Freshly molted crabs tend to be bright green in color on top of the carapace and yellow on the underside (Cohen 2005). Adults are variable in color; mottled orange-green, green-brown or green-grey. Large crabs can measures up to 90 mm wide. C. maenas can be differentiated from C. aestuarii in 3 ways: 1) the male pleopods (two appendages found under the male's abdominal flap) in C. maenas curve outward, touching each other in the central part of the curve, while in C. aestuarii, the pleopods are straight and parallel and do not touch; 2) C. maenas is slightly wider than C. aestuarii; and 3) the front of the carapace between the eyes protrudes more in C. aestuarii (Cohen 2005).
Reproduction Characteristics
Green crabs can reproduce in salinities of 13 to 53 ppt and temperatures near 18-26° Celsius. Mating takes place between spring and fall though timing may vary depending on location and temperatures. Males carry the female until the female molts and mating takes place. In favorable conditions, females can spawn up to 200,000 eggs at a time. Fertilized eggs are carried on the abdomen of the female. The eggs hatch and larvae drift with the currents. Juvenile crabs eventually settle to the bottom (Cohen 2005).
Feeding
This species is documented to consume a wide variety of prey items including organisms from 104 families and 158 genera from 5 plant and protist phyla and 14 animal phyla. Prey have been found to include mussels, clams, snails, polychaetes, crabs, isopods, barnacles and algae (Cohen 2005).
Control
Since early detection is key to preventing the spread and establishment of this species, regional/local monitoring or surveillance is essential. Green crabs should not be imported or released in local waterways. If found in local waters, note the capture location, kill and freeze the animal, and notify the TPWD.

This species belongs to the following lists:
Images
To view a larger version of an image, click on the thumbnail.
European green crab (<i>C. maenas</i>). Photo courtesy USGS NAS Database, http://nas.er.usgs.gov.
European green crab (C. maenas). Photo courtesy USGS NAS Database, http://nas.er.usgs.gov.
Mediterranean green crab (<i>C. aestuarii</i>). Photo courtesy George Chernilevsky.
Mediterranean green crab (C. aestuarii). Photo courtesy George Chernilevsky.
Page Updated/Reviewed: 07/14/2010 11:09 AM
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