Carcinus maenasgreen crab

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Geographic Range

The green crab is native to the Atlantic Ocean off of the coast of Europe. Around the early eighteen hundreds the green crab was first seen on the Atlantic coast of North America. The crab can now be found from ranging from as far north as Nova Scotia and to the southern state of Virginia. In the late eighties, the crab mysteriously showed up in the San Francisco Bay area, and has since been spotted as far north as Oregon. This crab has also been found in such areas as far reaching as the continent of Australia.(Deegan, et al 1999, Holden 1997)

Habitat

The green crab resides among tidal marshes, sandflats, and coasts with a rocky terrain. They tend to stay around these areas for protection from predators, and to be close to a readily available food supply.(Holden 1997, Deegan, et al 1999)

Physical Description

The name, green crab, can be deceiving. The color of this crab depends on the molting cycle the crab is undergoing. These colors can range from green to orange and even red in some cases. Green crabs are also visibly identifiable by the yellowish spots on the abdomen, which are also accompanied by five small spines also located on the front edge of the shell. The adult green crab only grows to about three inches in width and two inches in length. (Washington Dept 1997, Jaquette 1998)

Reproduction

The mating process of the green crab begins with the seeking out of a recently molted female crab by a male green crab. The female lays eggs which she carries in a pouch underneath her abdomen where the male crab fertilizes them. The female green crab can lay as many as a hundred thousand eggs at one time. Following fertilization, the females then travel to deeper water to more stable water conditions where the eggs begin to develop. Once the eggs have developed into a larvae,or the zoea stage, the larvae then return to the surface waters for about two weeks. Once the larvae have entered the final stage of development or the megalopae stage, the young crabs travel to the coastal waters where they begin a molting cycle and life as a juvenile crab. In approximately three years the juvenile crab will become a fully developed crab and be able to mate and reproduce.(Bamber and Naylor 1997, Washington Dept. 1997)

Behavior

Possibly the most noticable behavior pattern of the green crab is their annual movement to deeper water. It is believed that this movement to deeper water is to take advantage of the stable temperatures and salinity of this area of ocean. When the mating process of the green crab occurs it is generally immediately after the molting of the female crab. A male crab will pick a female before molting occurs and will stay with her until fertilization. The is very beneficial for the female crab because she is protected from predators and other males during a vulnerable time in her life cycle. Studies have shown that the green crabs that are red in coloration tend to have a greater chance of mating with female green crabs, this is partly due to the enlarged claw size that the red males possess. The red-colored green crab males also have a thicker exoskeleton. This thicker exoskeleton, while conferring an advantage in male-male interactions, it is thought to reduce their ability to tolerate salinity changes. (Bamber and Naylor 1997,Reid, et al 1997, Washington Dept. 1997)

Food Habits

The green crab enjoys a variety of different foods. These foods include clams, oysters, mussels, and other small crabs. The green crab is very dexterous and has many ways in which to open up the shellfish on which it feeds. The green crab is known as a very vicious carnivore that will consume anything it can get its claws on.(Holden 1997, Washington Dept. 1997)

Economic Importance for Humans: Positive

The green crab serves no basic benefit to humans.

Economic Importance for Humans: Negative

Due to the number of shell fish the green crab eats, and the rate at which it is done, the green crab is seen as a large threat to the many of the nations commercial shellfisheries. It is estimated that millions of dollars could be spent and are spent each year to try and thwart the green crabs from destroying a very important industry, and helping to maintain biodiversity in areas poplutlated by the green crab. The green crab also carries a parasitic worm that can infect birds that prey on the crabs. This can have a potentially devastating effect by throwing off the food chain, and on the ecosystem as a whole in these areas. (Washington Sea 1998, Washington Dept.1997, Jaquette 1998, Holden 1997)

Conservation Status

No conservation of the green crab is currently under way.

Other Comments

The United States government is currently undergoing programs in which to slow the growth of green crab populations fearing a shift in biodiversity in many of the nations coastal regions. Several options are being discussed in which to achieve this. One of which includes introducing a barnacle that can sterilize female green crabs, and the egg predator, Carcinonemertes epialti, to limit the number of green crab offspring being produced.(Washington Dept. 1997)

Contributors

Chris Tutt (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Bamber, S., E. Naylor. Feb,1997. Sites of Release of Putative Sex Pheromone and Sexual Behaviour in Female Carcinus maenas. Estaurine, Coastal and Shelf Science, 44: 195-202.

Deegan, L., R. Garritt, S. Komarow, T. Young. Oct,1999. Population size and summer home range of the green crab, Carcinus maenas, in salt marsh tidal creeks. Biological Bulletin: 297-299.

Gosner, K. 1978. Peterson Field Guide: A Guide to the Atlantic Sea Shore. New York, New York: Houghton Mifflin Co.

Holden, C. April 11,1997. Green crabs advance north. Science: 206.

Jaquette, L. Oct,1998. Invasion of the Green crabs. Trailer Boats: 66-67.

Reid, D., P. Abello, M. Kaiser, C. Warman. Feb, 1997. Carapace Colour, Inter-moult Duration and the Behavioural amd Physiological Ecology of the Shore Crab Carcinus maenus. Estuarine, Coastal and Shelf Science, 44: 203-211.

Washington Dept. of Fish and Wildlife, 2000. "Carcinus maenas (European Green crab)" (On-line). Accessed 10/03/2013 at http://wdfw.wa.gov/ais/species.php?Name=carcinus_maenas.

Washington Sea Grant Program, 1998. "Green Crab" (On-line). Accessed April 11, 2000 at http://www.wsg.washington.edu/outreach/mas/aquaculture/crab.html.