Invasive Species in USA Waterways - Part 47
European Green Crab
The European Green Crab is an invasive species of littoral crab. Native to the north east Atlantic Ocean and Baltic Sea. Other names include Shore Crab, Green Shore Crab and European Shore Crab.
Invasive Species Definition
The definition of an invasive species is any species that is not native to our ecosystems and cause harm when introduced to the ecosystems. Furthermore, these may include amphibians, plants, insects, fish, fungus, bacteria and more. Impacts on the environment may cause economic loss or affect human health.
While, Invasive species tend to grow and reproduce quickly and spread aggressively with the potential to cause harm on the environment, economy or even human health. Therefore, given the label “invasive”.
Description of the European Green Crab
The hexagonal shaped carapace is 90mm long and 210mm wide. However, can reach up to 713mm wide. Generally, the carapace has five short teeth along the rim behind each eye with three undulations between the eyes.
While, these undulations are the simplest means of distinguishing this crab from the closely related Carcinum aestuarii. The color varies greatly from green to brown, grey or even red. Largely due to environmental factors.
Individuals who delay molting will become red in color. While, red crabs are generally stronger and more aggressive but less tolerant of environmental stresses such as salinity or hypoxia.
Generally, juvenile crabs display greater patterning than adults. Furthermore, the carapace has a granular texture and is usually mottled dark green or brown with white to yellowish spots. While, the underside various from green to yellow, orange or red depending on the molt status.
Meanwhile, the second and third pairs of walking legs are the longest and are almost twice the length of the carapace length. However, the fourth pair is the shortest and are flat in comparison and bear hairs.
Differences between Carcinum maenas and Carcinum aestuarii
Biology of the European Green Crab
Primarily diurnal but depending on tide the crabs can be active at any time of the day.
Inhabits all types of protected and semi-protected marine and estuarine habitats, including those with mud, sand or rock substrates. With submerged aquatic vegetation and emergent marshes.
However, it can tolerate a wide range of salinities and survive in temperatures between 32°F to 86°F. Therefore, allowing Green Crabs to inhabit extremely cold temperatures beneath the ice in winter.
Distribution of the European Green Crab
Native to the north east Atlantic Ocean and Baltic Sea. But has colonized similar habitats in Australia, South Africa, South America and the Atlantic and Pacific Coasts of North America.
First observed in Massachusetts in 1817 but by 2007 the species had extended its range to include South Carolina, Newfoundland, San Francisco Bay, California, Oregon, Washington, British Columbia.
Australia first reported the species in the 1850s in Victoria. But since has spread along the south eastern and south western seaboards reaching New South Wales, South Australia and Tasmania. As well as, Western Australia.
While, reaching South Africa in 1983 in the Table Docks Area near Cape Town. Meanwhile, now spread as far as Saldanha Bay in the north and Camps Bay in the south. Furthermore, this invasive species has been found in Brazil, Panama, Hawaii, Madagascar, the Red Sea, Pakistan, Sri Lanka, Japan and Myanmar.
Effect on the Ecosystem
Feeding habitats and tolerance of a wide variety of environmental conditions has enabled the green crab to spread far outside its native range. Another reason the crab is dangerous is that is preys on bivalves and other crustaceans like soft shell clams, scallops and is great in clearing out populations of mussels.
Introduction to the USA
Successfully dispersed by a variety of mechanisms including ballasts, ships’ hulls, sea planes, packing materials and bivalves moved from aquaculture. As well as rafting, migration of crab larvae on the ocean currents and movement of submerged aquatic vegetation. Currently, the Green Crab is found in Massachusetts, New Jersey, Virginia, Maine, Nova Scotia, California, San Francisco Bay, Washington, Oregon, and New England.
Management of the European Green Crab
Due to the harmful effects it has on the ecosystem, various efforts have been made to control the introduced populations around the world. While, native blue crabs in Eastern North America can control populations, numbers of these two species are negatively correlated.
Furthermore, the species has been used as food source. While, with the development of value-added green crab products, driving business interest, stimulating a commercial green crab fishery and alleviating predation effects.
Fencing, trapping, poisoning, prohibiting possession and transportation of the green crab are a few methods of management that have been introduced in various states.