Carcinus maenas
Encyclopedia
Carcinus maenas is a common littoral
crab
, and an important invasive species
, listed among the 100 "world's worst alien invasive species". It is native to the north-east Atlantic Ocean
and Baltic Sea
, but has colonised similar habitats in Australia, South Africa, South America and both Atlantic and Pacific
coasts of North America. It grows to a carapace
width of 90 millimetres (3.5 in), and feeds on a variety of molluscs
, worms and small crustaceans, potentially impacting a number of fisheries. Its successful dispersion has occurred via a variety of mechanisms, such as on ships' hulls, packing materials, bivalves moved for aquaculture
, and rafting.
C. maenas is known by different names around the world. In the British Isles
, it is generally referred to simply as the shore crab. In North America
and South Africa
, it bears the name green crab or European green crab. In Australia
and New Zealand
, it is referred to as either the European green crab or European shore crab.
C. maenas has a carapace
up to 60 millimetres (2.4 in) long and 90 mm (3.5 in) wide, with five short teeth along the rim behind each eye, and three undulations between the eyes. The undulations, which protrude beyond the eyes, are the simplest means of distinguishing C. maenas from the closely related C. aestuarii
, which can also be an invasive species. In C. aestuarii, the carapace lacks any bumps and extends forward beyond the eyes. Another characteristic for distinguishing the two species is the form of the first and second pleopods (collectively the gonopods), which are straight and parallel in C. aestuarii, but curve outwards in C. maenas.
The colour of C. maenas varies greatly, from green to brown, grey or red. This variation has a genetic component, but is largely due to local environmental factors. In particular, individuals which delay moulting
become red–coloured rather than green. Red individuals are stronger and more aggressive, but are less tolerant of environmental stresses, such as low salinity
or hypoxia
.
C. maenas is native to European and North African coasts as far as the Baltic Sea in the east, and Iceland and central Norway in the north, and is one of the most common crabs throughout much of its range. In the Mediterranean Sea, it is replaced by the closely related species Carcinus aestuarii.
C. maenas was first observed on the east coast of North America in Massachusetts
in 1817, and may now be found from southern Virginia
northwards; by 2007, this species had extended its range northwards to Placentia Bay
, Newfoundland
. In 1989, the species was found in San Francisco Bay
, California
, on the Pacific coast of the United States. Until 1993, it was not able to extend its range, but reached Oregon
in 1997, the state of Washington in 1998 and British Columbia
in 1999, thus extending its range by 750 kilometres (466 mi) in ten years. By 2003, C. maenas had extended to South America with specimens discovered in Patagonia
.
In Australia, C. maenas was first reported "in the late 1800s", in Port Phillip Bay, Victoria. It has since spread along the south-eastern and south-western seaboards, reaching New South Wales in 1971, South Australia in 1976 and Tasmania in 1993. One specimen was found in Western Australia
in 1965, but there have been no further discoveries in the area since.
C. maenas first reached South Africa in 1983, in the Table Docks area near Cape Town
. Since then, it has spread at least as far as Saldanha Bay
in the north and Camps Bay
in the south, over 100 kilometres (62.1 mi) apart.
There have been appearances of C. maenas recorded in Brazil, Panama, Hawaii, Madagascar
, the Red Sea
, Pakistan
, Sri Lanka
and Myanmar
; however, these have not resulted in invasions, but remain isolated findings. Japan has been invaded by a related crab, either C. aestuarii
or a hybrid of C. aestuarii and C. maenas.
It is believed, based on the ecological conditions, that C. maenas could eventually extend its range to colonise the Pacific coast of North America from Baja California
to Alaska
. Similar ecological conditions are to be found on many of the world's coasts, with the only large potential area not to have been invaded yet being New Zealand
; the New Zealand government has taken action, including the release of a Marine Pest Guide in an effort to prevent colonisation by C. maenas.
, although soft bottoms are preferred. C. maenas is euryhaline
, meaning that it can tolerate a wide range of salinities
(from 4 to 52 ‰
), and survive in temperatures of 0 to 30 °C (32 to 86 F). The wide salinity range allows C. maenas to survive in the lower salinities found in estuaries
. A molecular biological
study using the COI gene
found genetic differentiation between the North Sea and the Bay of Biscay
, and even more strongly between the populations in Iceland and the Faroe Islands
and those elsewhere. This suggests that C. maenas is unable to cross deeper water.
Females can produce up to 185,000 eggs, and larva
e develop offshore in several stages before their final moult to juvenile crabs in the intertidal zone. Young crabs live among seaweeds and seagrasses, such as Posidonia oceanica
, until they reach adulthood.
C. maenas has the ability to disperse by a variety of mechanisms, including ballast water
, ships' hulls, packing materials (seaweed
s) used to ship live marine organisms, bivalves moved for aquaculture
, rafting, migration of crab larva
e on ocean currents, and the movement of submerged aquatic vegetation for coastal zone management initiatives. Thresher et al. found C. maenas dispersed in Australia mainly by rare long-distance events, possibly caused by human actions.
C. maenas is a predator, feeding on many organisms, particularly bivalve molluscs
(such as clam
s, oyster
s, and mussel
s), polychaete
s and small crustacean
s. They are primarily nocturnal, although activity also depends on the tide, and crabs can be active at any time of day. In California
, preferential predation
of C. maenas on native clams (Nutricola spp.) resulted in the decline of the native clams and an increase of a previously introduced clam (the amethyst gem clam, Gemma gemma
). C. maenas has been implicated in the destruction of the soft-shell clam (Mya arenaria) fisheries on the east coast of the United States and Canada, and the reduction of populations of other commercially important bivalves (such as scallops, Argopecten irradians
, and northern quahogs, Mercenaria mercenaria). The prey of C. maenas includes the young of bivalves and fish, although the effect of its predation on winter flounder
, Pseudopleuronectes americanus is minimal. C. maenas can, however, have substantial negative impacts on local commercial and recreational fisheries
, by preying on the young of species, such as oyster
s and the Dungeness crab
, or competing with them for resources.
, and 10 ton
s were caught.
There is evidence that the native blue crab in eastern North America, Callinectes sapidus, is able to control populations of C. maenas; numbers of the two species are negatively correlated
, and C. maenas is not found in the Chesapeake Bay
, where Callinectes sapidus is most frequent. On the west coast of North America, C. maenas appears to be limited to upper estuarine habitats, in part because of predation by native rock crabs (Romaleon antennarium and Cancer productus
) and competition for shelter with a native shore crab, Hemigrapsus oregonensis
. Host specificity testing has recently been conducted on Sacculina carcini
, a parasitic barnacle
, as a potential biological control agent of C. maenas. In the laboratory, Sacculina settled on, infected, and killed native California crabs, including the Dungeness crab
, Metacarcinus magister (formerly Cancer magister), and the shore crabs Hemigrapsus nudus
, Hemigrapsus oregonensis and Pachygrapsus crassipes. Dungeness crabs were the most vulnerable of the tested native species to settlement and infection by the parasite. Although Sacculina did not mature in any of the native crabs, developing reproductive sacs were observed inside a few Metacarcinus magister and Hemigrapsus oregonensis. Any potential benefits of using Sacculina to control C. maenas on the west coast of North America would need to be weighed against these potential non-target impacts.
, with approximately 1200 tonne
s being caught annually, mostly in France and the United Kingdom. In the northwest Atlantic, C. maenas was the subject of fishery in the 1960s, and again since 1996, with up to 86 tonnes being caught annually.
, Cancer maenas, by Carl Linnaeus in his 1758 tenth edition of Systema Naturae
. An earlier description was published by Georg Eberhard Rumphius
in his 1705 work De Amboinsche Rariteitkamer, calling the species Cancer marinus sulcatus, but this predates the starting point for zoological nomenclature. A number of later synonyms
have also been published:
The lectotype
chosen for the species came from Marstrand
, Sweden
, but it is assumed to have been lost. In 1814, writing for The Edinburgh Encyclopaedia, William Elford Leach
erected a new genus, Carcinus
to hold this species alone (making it the type species
of the genus, by monotypy). In 1847, Nardo described a distinct subspecies
occurring in the Mediterranean Sea
, which is now recognised as a distinct species, Carcinus aestuarii
.
Littoral
The littoral zone is that part of a sea, lake or river that is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes this intertidal zone and is often used to...
crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
, and an important invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
, listed among the 100 "world's worst alien invasive species". It is native to the north-east Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, but has colonised similar habitats in Australia, South Africa, South America and both Atlantic and Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
coasts of North America. It grows to a carapace
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
width of 90 millimetres (3.5 in), and feeds on a variety of molluscs
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
, worms and small crustaceans, potentially impacting a number of fisheries. Its successful dispersion has occurred via a variety of mechanisms, such as on ships' hulls, packing materials, bivalves moved for aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
, and rafting.
C. maenas is known by different names around the world. In the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
, it is generally referred to simply as the shore crab. In North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, it bears the name green crab or European green crab. In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, it is referred to as either the European green crab or European shore crab.
Description
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
up to 60 millimetres (2.4 in) long and 90 mm (3.5 in) wide, with five short teeth along the rim behind each eye, and three undulations between the eyes. The undulations, which protrude beyond the eyes, are the simplest means of distinguishing C. maenas from the closely related C. aestuarii
Carcinus aestuarii
Carcinus aestuarii is a littoral crab, native to the Mediterranean Sea. It bears some similarities to Carcinus maenas and was sometimes considered to be a subspecies thereof, rather than a species in its own right, but a molecular biological study using the COI gene found the difference between the...
, which can also be an invasive species. In C. aestuarii, the carapace lacks any bumps and extends forward beyond the eyes. Another characteristic for distinguishing the two species is the form of the first and second pleopods (collectively the gonopods), which are straight and parallel in C. aestuarii, but curve outwards in C. maenas.
The colour of C. maenas varies greatly, from green to brown, grey or red. This variation has a genetic component, but is largely due to local environmental factors. In particular, individuals which delay moulting
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
become red–coloured rather than green. Red individuals are stronger and more aggressive, but are less tolerant of environmental stresses, such as low salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
or hypoxia
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
.
Native and introduced range
C. maenas was first observed on the east coast of North America in Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
in 1817, and may now be found from southern Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
northwards; by 2007, this species had extended its range northwards to Placentia Bay
Placentia Bay
Placentia Bay is a body of water on the southeast coast of Newfoundland, Canada. It is formed by Burin Peninsula on the west and Avalon Peninsula on the east. Fishing grounds in the bay were used by native people long before the first European fishermen arrived in the 16th century. For a time, the...
, Newfoundland
Newfoundland and Labrador
Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...
. In 1989, the species was found in San Francisco Bay
San Francisco Bay
San Francisco Bay is a shallow, productive estuary through which water draining from approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, on the Pacific coast of the United States. Until 1993, it was not able to extend its range, but reached Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
in 1997, the state of Washington in 1998 and British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
in 1999, thus extending its range by 750 kilometres (466 mi) in ten years. By 2003, C. maenas had extended to South America with specimens discovered in Patagonia
Patagonia
Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
.
In Australia, C. maenas was first reported "in the late 1800s", in Port Phillip Bay, Victoria. It has since spread along the south-eastern and south-western seaboards, reaching New South Wales in 1971, South Australia in 1976 and Tasmania in 1993. One specimen was found in Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
in 1965, but there have been no further discoveries in the area since.
C. maenas first reached South Africa in 1983, in the Table Docks area near Cape Town
Cape Town
Cape Town is the second-most populous city in South Africa, and the provincial capital and primate city of the Western Cape. As the seat of the National Parliament, it is also the legislative capital of the country. It forms part of the City of Cape Town metropolitan municipality...
. Since then, it has spread at least as far as Saldanha Bay
Saldanha Bay
Saldanha Bay is a natural harbour on the south-western coast of South Africa, north west of Cape Town. The town that developed on the northern shore of the bay, also called Saldanha, was incorporated with five other towns into the Saldanha Bay Local Municipality in 2000. The current population of...
in the north and Camps Bay
Camps Bay
Camps Bay is an affluent suburb of Cape Town, South Africa. In summer it attracts a large number of foreign visitors as well as South Africans looking for a beach holiday. It is renowned for its white sandy beaches fringed by palm trees and has a trendy nightlife.-History:The first residents of...
in the south, over 100 kilometres (62.1 mi) apart.
There have been appearances of C. maenas recorded in Brazil, Panama, Hawaii, Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
, the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
and Myanmar
Myanmar
Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
; however, these have not resulted in invasions, but remain isolated findings. Japan has been invaded by a related crab, either C. aestuarii
Carcinus aestuarii
Carcinus aestuarii is a littoral crab, native to the Mediterranean Sea. It bears some similarities to Carcinus maenas and was sometimes considered to be a subspecies thereof, rather than a species in its own right, but a molecular biological study using the COI gene found the difference between the...
or a hybrid of C. aestuarii and C. maenas.
It is believed, based on the ecological conditions, that C. maenas could eventually extend its range to colonise the Pacific coast of North America from Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
to Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
. Similar ecological conditions are to be found on many of the world's coasts, with the only large potential area not to have been invaded yet being New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
; the New Zealand government has taken action, including the release of a Marine Pest Guide in an effort to prevent colonisation by C. maenas.
Ecology
C. maenas can live in all types of protected and semi-protected marine and estuarine habitats, including habitats with mud, sand, or rock substrates, submerged aquatic vegetation, and emergent marshMarsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
, although soft bottoms are preferred. C. maenas is euryhaline
Euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh, brackish, or salt water. The European shore crab is an example of a euryhaline invertebrate that can live in salt and brackish water...
, meaning that it can tolerate a wide range of salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
(from 4 to 52 ‰
Permille
A per mil or per mille is a tenth of a percent or one part per thousand. It is written with the sign ‰ , which looks like a percent sign with an extra zero at the end...
), and survive in temperatures of 0 to 30 °C (32 to 86 F). The wide salinity range allows C. maenas to survive in the lower salinities found in estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
. A molecular biological
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
study using the COI gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
found genetic differentiation between the North Sea and the Bay of Biscay
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
, and even more strongly between the populations in Iceland and the Faroe Islands
Faroe Islands
The Faroe Islands are an island group situated between the Norwegian Sea and the North Atlantic Ocean, approximately halfway between Scotland and Iceland. The Faroe Islands are a self-governing territory within the Kingdom of Denmark, along with Denmark proper and Greenland...
and those elsewhere. This suggests that C. maenas is unable to cross deeper water.
Females can produce up to 185,000 eggs, and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e develop offshore in several stages before their final moult to juvenile crabs in the intertidal zone. Young crabs live among seaweeds and seagrasses, such as Posidonia oceanica
Posidonia oceanica
Posidonia oceanica is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The fruit is free floating and known in Italy as 'the olive of the sea'...
, until they reach adulthood.
C. maenas has the ability to disperse by a variety of mechanisms, including ballast water
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
, ships' hulls, packing materials (seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
s) used to ship live marine organisms, bivalves moved for aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
, rafting, migration of crab larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e on ocean currents, and the movement of submerged aquatic vegetation for coastal zone management initiatives. Thresher et al. found C. maenas dispersed in Australia mainly by rare long-distance events, possibly caused by human actions.
C. maenas is a predator, feeding on many organisms, particularly bivalve molluscs
Bivalvia
Bivalvia is a taxonomic class of marine and freshwater molluscs. This class includes clams, oysters, mussels, scallops, and many other families of molluscs that have two hinged shells...
(such as clam
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...
s, oyster
Oyster
The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
s, and mussel
Mussel
The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval.The...
s), polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
s and small crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. They are primarily nocturnal, although activity also depends on the tide, and crabs can be active at any time of day. In California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, preferential predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
of C. maenas on native clams (Nutricola spp.) resulted in the decline of the native clams and an increase of a previously introduced clam (the amethyst gem clam, Gemma gemma
Amethyst gem clam
The amethyst gem clam, Gemma gemma, is a small species of marine bivalve mollusk. It is a member of the family Veneridae, the Venus clams.It is one of the smaller species of marine clam, reaching a length of only 5 mm...
). C. maenas has been implicated in the destruction of the soft-shell clam (Mya arenaria) fisheries on the east coast of the United States and Canada, and the reduction of populations of other commercially important bivalves (such as scallops, Argopecten irradians
Argopecten irradians
Argopecten irradians, formerly classified as Aequipecten irradians, common names the "Atlantic bay scallop" or "bay scallop", is an edible species of saltwater clam, a scallop, a marine bivalve mollusk in the family Pectinidae, the scallops....
, and northern quahogs, Mercenaria mercenaria). The prey of C. maenas includes the young of bivalves and fish, although the effect of its predation on winter flounder
Winter flounder
The winter flounder, Pseudopleuronectes americanus, is a right-eyed flatfish of the family Pleuronectidae. It is native to coastal waters of the western north Atlantic coast, from Labrador, Canada to Georgia, United States...
, Pseudopleuronectes americanus is minimal. C. maenas can, however, have substantial negative impacts on local commercial and recreational fisheries
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
, by preying on the young of species, such as oyster
Oyster
The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. The valves are highly calcified....
s and the Dungeness crab
Dungeness crab
The Dungeness crab, Metacarcinus magister , is a species of crab that inhabits eelgrass beds and water bottoms on the west coast of North America. It typically grows to across the carapace and is a popular seafood...
, or competing with them for resources.
Control
Due to its potentially harmful effects on ecosystems, various efforts have been made to control introduced populations of C. maenas around the world. In Edgartown, Massachusetts, a bounty was levied in 1995 for catching C. maenas, to protect local shellfishShellfish
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater...
, and 10 ton
Ton
The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.It is derived from...
s were caught.
There is evidence that the native blue crab in eastern North America, Callinectes sapidus, is able to control populations of C. maenas; numbers of the two species are negatively correlated
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
, and C. maenas is not found in the Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...
, where Callinectes sapidus is most frequent. On the west coast of North America, C. maenas appears to be limited to upper estuarine habitats, in part because of predation by native rock crabs (Romaleon antennarium and Cancer productus
Cancer productus
Cancer productus, one of several species known as the red rock crab, is a crab of the genus Cancer found on the western coast of North America.- Description :...
) and competition for shelter with a native shore crab, Hemigrapsus oregonensis
Yellow shore crab
Hemigrapsus oregonensis is a small shore crab of the family Varunidae; it was formerly classified under the family Grapsidae. It is known under several common names, including yellow shore crab, hairy shore crab, green shore crab, mud-flat crab, and Oregon shore crab.Despite its name, the body...
. Host specificity testing has recently been conducted on Sacculina carcini
Sacculina
Sacculina is a genus of barnacles that is a parasitic castrator of crabs. The adults bear no resemblance to the barnacles that cover ships and piers; they are recognised as barnacles because their larval forms are like other members of the barnacle class Cirripedia...
, a parasitic barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
, as a potential biological control agent of C. maenas. In the laboratory, Sacculina settled on, infected, and killed native California crabs, including the Dungeness crab
Dungeness crab
The Dungeness crab, Metacarcinus magister , is a species of crab that inhabits eelgrass beds and water bottoms on the west coast of North America. It typically grows to across the carapace and is a popular seafood...
, Metacarcinus magister (formerly Cancer magister), and the shore crabs Hemigrapsus nudus
Purple shore crab
The purple shore crab, Hemigrapsus nudus, is a common crab of the family Varunidae. It can be found sheltering under rocks in inter-tidal areas along the west coast of North America, from Alaska to Baja California in Mexico. This crab primarily eats sea lettuce and other green algae, and...
, Hemigrapsus oregonensis and Pachygrapsus crassipes. Dungeness crabs were the most vulnerable of the tested native species to settlement and infection by the parasite. Although Sacculina did not mature in any of the native crabs, developing reproductive sacs were observed inside a few Metacarcinus magister and Hemigrapsus oregonensis. Any potential benefits of using Sacculina to control C. maenas on the west coast of North America would need to be weighed against these potential non-target impacts.
Fishery
C. maenas is fished on a small scale in the north-east Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, with approximately 1200 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s being caught annually, mostly in France and the United Kingdom. In the northwest Atlantic, C. maenas was the subject of fishery in the 1960s, and again since 1996, with up to 86 tonnes being caught annually.
Taxonomic history
Carcinus maenas was first given a binomial nameBinomial nomenclature
Binomial nomenclature is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages...
, Cancer maenas, by Carl Linnaeus in his 1758 tenth edition of Systema Naturae
Systema Naturae
The book was one of the major works of the Swedish botanist, zoologist and physician Carolus Linnaeus. The first edition was published in 1735...
. An earlier description was published by Georg Eberhard Rumphius
Georg Eberhard Rumphius
Georg Eberhard Rumphius or originally Rumpf was a German-born botanist employed by the Dutch East India Company in what is now eastern Indonesia, and is best known for his work, Herbarium Amboinense....
in his 1705 work De Amboinsche Rariteitkamer, calling the species Cancer marinus sulcatus, but this predates the starting point for zoological nomenclature. A number of later synonyms
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
have also been published:
- Monoculus taurus Slabber, 1778
- Cancer granarius Herbst, 1783
- Cancer viridis Herbst, 1783
- Cancer pygmaeus Fabricius, 1787
- Cancer rhomboidalis Montagu, 1804
- Cancer granulatus Nicholls, 1943
- Megalopa montagui Leach, 1817
- Portunus menoides Rafinesque-Schmaltz, 1817
- Portunus carcinoides Kinahan, 1857
The lectotype
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
chosen for the species came from Marstrand
Marstrand
Marstrand is a seaside locality situated in Kungälv Municipality, Västra Götaland County, Sweden. It had 1,432 inhabitants in 2005. It has held city privileges since 1200. The most striking feature about Marstrand is the 17th century fortress Carlsten, named after King Carl X Gustav of Sweden. The...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, but it is assumed to have been lost. In 1814, writing for The Edinburgh Encyclopaedia, William Elford Leach
William Elford Leach
William Elford Leach FRS was an English zoologist and marine biologist.Leach was born at Hoe Gate, Plymouth, the son of a solicitor. At the age of twelve he went to school in Exeter, studying anatomy and chemistry. By this time he was already collecting marine samples from Plymouth Sound and along...
erected a new genus, Carcinus
Carcinus
Carcinus is a genus of crabs, which includes Carcinus maenas, an important invasive species, and C. aestuarii, a species endemic to the Mediterranean Sea.-Carcinus maenas:...
to hold this species alone (making it the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of the genus, by monotypy). In 1847, Nardo described a distinct subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
occurring in the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, which is now recognised as a distinct species, Carcinus aestuarii
Carcinus aestuarii
Carcinus aestuarii is a littoral crab, native to the Mediterranean Sea. It bears some similarities to Carcinus maenas and was sometimes considered to be a subspecies thereof, rather than a species in its own right, but a molecular biological study using the COI gene found the difference between the...
.
External links
- Species Profile- European Green Crab (Carcinus maenas), National Invasive Species Information Center, United States National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for European Green Crab.