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The Global Spread of the Chinese Mitten Crab
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Professor Matt Bentley
Galil, B.S., Clark, P.F., Carlton, J.T.
In the Wrong Place- Alien Marine Crustaceans: Distribution, Biology and Impacts
Springer Series on Invasion Ecology
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Chinese mitten crabs are one of the World’s most notorious aquatic invasive species. Their catadromous life history, in which they spend most of their lives growing to maturity in freshwater, and their extreme euryhalinity, has made it relatively easy for the species to gain a foothold in the World’s river systems. Ballast water introductions are thought to have brought them to continental Europe in the early twentieth century. These will have probably been as larvae, which will then have settled in the estuaries subsequently moving upstream as juveniles. The capacity of these crabs to move upstream (and over land) is staggering and individuals in their native range in the Far East have been found more than 1,000 km from the sea,where they must return to breed. A number of successful separate introductions of mitten crabs have taken place in Europe, including the UK and America. Europe (Northern Germany) saw initial introductions in 1912, followed by others into both the North Sea coasts and English Channel coasts of France. The extensive network of Northern European waterways facilitated the spread in river systems. After a lag phase, which is typical of many invasive species following introduction, numbers of mitten crabs increased dramatically such that by 1936 attempts at removing the animals from rivers in Germany were abandoned; some 220 metric tonnes were removed from the River Weser alone in that year. Introductions into the UK (River Thames) followed in the mid-1930s but initial introductions appear not to have founded a population. It was not until 1970s that mitten crabs numbers increased and the Thames population became established, and it has subsequently increased and spread. The crab had spread rapidly both around UK coasts and up river systems by the end of the twentieth century and into the 1st decade of the 21st. Evidence suggests that there have been several separate introductions in France; the first in Northern France and then subsequently into western France. Whilst the most likely and common route of introduction is via discharge of ships’ ballast water, it is possible that there may have already been and may also be future deliberate introductions. The mitten crab has considerable economic value and is farmed in the Far East. Introductions into San Francisco Bay area of the USA later in the twentieth century may have been a deliberate attempt to create a fishery for the species. In its native range, the mitten crab carries a lung fluke trematode parasite
that infects humans. The intermediate host for
is a snail of the genus
, which is not present in the USA and Northern Europe. This means that mitten crabs in these areas are likely to remain parasite free. Whatever the route of entry, the crab has become a major problem in the San Francisco Bay area as it interferes with other fishery activities and causes significant habitat modification. The large crab is a burrowing species creating long burrows in soft river banks causing siltation of the waterways, bank erosion and increasing the risk of flooding. These habitat effects are likely to be apparent wherever the crab is well established. The global spread of
continues. In the UK, for example, it has extended its range to the river systems of South-West England, the Welsh River Dee and the River Mersey (North-West England) and has reached as far north as the River Tyne in northeast England. The crab has not yet been reported from further north in England and is so far absent in Scotland. In the USA, it has recently been found along the Atlantic seaboard around Chesapeake Bay, and it appears almost inevitable that many more estuaries and river systems around the globe will become host to the Chinese mitten crab.
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