European GreenCrab

What Is The European Green Crab

The European green crab is an invertebrate that is now common around the world. The actual scientific name given to the species is Carcinus maenas, though it is also referred to as the European shore crab. It is a littoral crab widely found in marine habitats throughout various geographical regions such as Northern Europe, North America (Pacific and Atlantic coasts), South Africa, as well as Australia and New Zealand. Its fame is unfortunately down to it being among the worlds one hundred top, and therefore worst, invasive alien species.

The species is relatively small. It grows to around a maximum width of only three and a half inches. Typically it will consume an assortment of marine worms, molluscs, as well as small crustaceans. It is this aspect which impacts negatively on commercial fisheries and local economies that depend upon the ocean for their livelihood.

It has been spread far and wide not without the help of man. In fact the far reaching dispersal can today be put down to such factors as the water used as ships ballast, aquaculture, rafting, and similar modern practices.

The European green crab has five small teeth found along the rims behind each eye and also three slight undulations between its eyes. These undulations are the easiest way to distinguish this species from its close relative Carcinus aestuarii which is also invasive in nature. With the latter the carapace does not have any noticeable bumps and also extends forward past the eyes. You can also learn how to distinguish between these two species by examining the first two pleopods. In the European green crab these curve outwards, whereas with Carcinus aestuarii they are parallel and straight.

The actual color of the European green crab can be varied from brown to green, red, or grey. This is primarily down to genetics though environmental factors are also important. Usually it is found that the individuals that have delayed moulting are more red than green in colour. These are also more aggressive and strong than other colored individuals though are thought of as being far less tolerant when it comes to environmental stress such as low salt content or low oxygen content in the water.

The geographic dispersion of the species in Europe today stretches from the North African coast to the Baltic Sea; it is replaced in the Mediterranean by its cousin Carcinus aestuarii. It was first spotted on the North American east coast in 1817 in Massachusetts but now can be found as far south as Virginia. It is believed that by the year 2007 it had extended its range up into Newfoundland. On the pacific coast the species was first spotted only in 1989, this was in San Francisco bay. Its range did not noticeably increase until the late 1990s when it was spotted along the Oregon and Washington state coasts. By 1999 it had managed to reach the shores of Vancouver Island and further north. Unfortunately this incredibly versatile crab has now found its way down the coast of South America, even as far as Patagonia in Argentina.

The European green crab is able to thrive in a wide variety of estuarine and marine habitats; this includes sand, mud, and rock substrates, as well as emergent marshes and aquatic vegetation.

The species is euryhaline which means it can cope with a wide range of salinities and is able to survive in water temperatures ranging from 32f to 86f (0c to 30c). It is this dynamic that has allowed it to become just so invasive.

A female is able to produce as many as 200,000 eggs. The larvae first develop away from the shore before they become juvenile crabs and move into the inter-tidal zone. You can find the young crabs living amongst seaweeds and sea grasses until they mature.

Because of its potential to cause harm to native ecosystems, various steps have been made to try to control the population of the European shore crab around the world. For example in North America it is believed that the native blue crab can help to protect native local ecosystems from the threat.

Currently the species is fished on a relatively small scale in the north eastern region of the Atlantic Ocean. The latest figures point to more than a thousand tonnes caught on an annual basis, primarily in the UK and France. In the North West Atlantic it is not a species which is widely consumed or fished for though you can often find fishermen using them as bait to catch large fish.

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