Thursday, 30. April 2009, 19:09
Text: Oliver Mengedoht, Monika Rademacher
Fotos: Oliver Mengedoht
Translated by Ulli Bauer
Scientific name: Carcinus maenas
Trivial name: Shore crab
Other names: European Shore Crab, Green Crab, European Green Crab, Applejacks, Addlers
Systematics: Domain: Eucaryota, kingdom: Animalia, subkingdom: Metazoa (multiple-celled animals), Eumetazoa (true tissue), grade: Bilateria, branch: Protostomia, infrakingdom: Ecdysozoa (molting animals), phylum: Arthropoda (jointed-leg invertebrates), subphylum: Crustacea, class: Malacostraca (higher crustaceans), superorder: Eucarida, order: Decapoda (ten-legged crayfish), suborder: Pleocyemata, infraorder: Reptantia, section: Brachyura (true crabs), superfamily: Portunoidea, family: Portunidae (swimming crabs), subfamily: Carcininae, genus: Carcinus, species: Carcinus maenas
[attachment=8286]
more pix: www.panzerwelten.de/v/Carcininae/Strandkrabben/
Origin/Range: Carcinus maenas live on all kinds of sea shores down to a depth of 60 meters, but mainly on beaches and in shallow water. These crabs are the most prominent species on the North Sea and are originally found in northwestern Europe (starting in Norway) down to the Mediterranean, the Baltic Sea and the northafrican Atlantic (Mauretania). A natural border for their distribution is the Baltic Sea with its lower salinity; with freshwater continuously diffusing into it, the crab would have to spend too much energy for osmotic regulation and thus would not have enough energy left to live.
However, today this species is found globally.
The European shore crab has also invaded North America as a neozoon (1817: Masachusetts; today found from Nova Scotia to Virginia), as well as Asia and Australia. In the 1890s, this species appeared in Australia (Victoria, 1971: New South Wales, 1976: South Australia, 1993: Tasmania), in 1983 in South Africa, in 1989 on the US Pacific Coast in the Bay of San Francisco (USA), in 1997 in Oregon and in 1998 in Washington (USA) as well as in 1999 in British Columbia (Canada). In 2003, Carcinus maenas also took hold in Argentina, and in the meantime it is also said to be found in Japan (however, it is possible that the crabs found there belong to the Mediterranean species C. aestuarii or a hybrid of both).
Individual specimens so far not leading to stable populations have been found in Brazil, Panama, Hawaii, Madagascar, the Red Sea, Pakistan, Sri Lanka and Burma.
[attachment=8287]
Description: Five prominent teeth on the frontal side edges (behind the eyes), three rounded teeth between the eyes. Their basic color varies from grey over brown to green or red. According to one source, the males are more often green and the females reddish, at the same time the colors are said to vary with age. Another source says that about five percent of the adult animals are green.
Another explanation says that the color has a genetic component but also depends on environmental factors. According to this, specimens delaying a molt become rather reddish than greenish in color, and reddish crabs are said to be stronger and more aggressive, but less tolerant towards environmental variables like lower salinity or oxygen deficiency.
Young crabs show a variety of colors and often have red, black or white dots or even combinations of these colors.
[attachment=8288]
Sex differences: Typical for crabs, the males have a narrow apron (whose 3rd to 5th segments are fused); the females have a wider apron covering nearly the entire abdomen. Moreover, the males' claws are bulkier.
Size: up to 10 cm carapace width (approx. 150 grams), males are larger than females
[attachment=8289]
Example for a small shore aquaterrarium with brackish water for young crabs.
Life span: up to about 6 years (females possibly only 4 years)
Temperature: 0 to 30 degrees Celsius
Tank size/stock: Individual specimen: starting at 60 cm tank length, bigger is better
In nature, up to 200 0.5 centimeter small young crabs can be found on one square meter of tideland. Of course, such a stock would never work in a tank! A 60 cm long tank is too small for an adult specimen with a carapace width of 6 cm. As this species is rather aggressive a lot depends on the size. A group of four adults might work in a 500 liter tank, 4 to 6 young crabs with a carapace of under 2 cm in width can probably be kept in a 60 cm tank...
Tank set-up: North Sea or brackish water tank, if possible with a land part (sandy area, rocks), also possible in a (tropical) seawater tank.
[attachment=8290]
[attachment=8291]
[attachment=8292]
Their natural habitat (here near Cuxhaven, Germany): Shores and tidelands.
Food: Typical for crabs, they are omnivores.
• Leaves (the main staple of many crabs in nature; mostly oak and beech are fed, however, all European broadleaved tree leaves are possible, also Indian almond leaves), muck, water plants
• Vegetables/fruit: nearly all vegetables and fruit are suitable (peas, lettuce, cucumber, apple, zucchini, pear, banana, grapes, tomato, Brussels sprouts, bell peppers) except for parsley and beans or other kinds that contain Prussic acid or copper; carrots (boiled); potato and rice (boiled) or noodles (uncooked? Don't leave these in the tank for too long a time though, they can be the cause of turbid water and finally lead to a bacteria bloom and oxygen depletion); no citrus fruit due to their high acid content
• Dry food: Catfish tabs, fish (flake) food, food pellets, rabbit, guinea pig and chinchilla food pellets (without copper!), Spirulina tabs, crayfish tabs, Gammarus
• Frozen food: Black, glass and blood worms, Cyclops, brine shrimp, clam meat
• Live food: Earthworms (it's best to cut them into pieces though, or else these worms might burrow in the substrate, possibly also under water, die and rot there unnoticed until it's too late)
• Meat (rarely): Chicken bones with meat rests (rinsed well to prevent too much fat from getting into the terrarium)
• Fish: deep-frozen smelts et.al., tuna fish, sardines, herring etc. fresh or from a can (in their own juice, not in oil)
• Calcium: cuttlebone, smashed eggshells or powdered calcium in self-made food sticks
[attachment=8295]
Shore crab digging into the substrate hind legs first.
Behavior: Carcinus maenas is an aggressive species that can be active at all times. Various sources list it as especially active at night, at high tide, at daytime or indeed "around the clock".
[attachment=8296]
Hard to see, awaiting the things to come.
Reproduction: unspecific, goes through several larvae stages. Mating is only possible when the female has just molted - in order not to miss this and to prevent the female from mating with other males the male crabs carry the females around for several days before they molt in spring and summer. After mating, the female carries up to 200,000 eggs, from which finally pelagic (free-swimming) larvae hatch. After the protozoea there are four zoea stages and a megalopa larva before the young crabs return to shore.
The young crabs prefer to live in seaweed and molt every few days (inflating themselves with water in order to grow as long as they are soft); after only a week on tideland they can reach a carapace width of 0.5 cm. According to scientific research, Carcinus maenas in their first year can reach a carapace width of as much as 1.5 cm. The young crabs migrate to deeper water zones for hibernation.
[attachment=8297]
Socialization: Only with species you are ready to run the risk of losses (this applies to other crab species as well as snails, other inverts or fish). All animals smaller or of the same size are considered food.
[attachment=8298]
This crab is very overgrown with barnacles and cannot even move its right eye. If it doesn't molt soon the barnacles are going to cover its mandibles, too, and the crab will starve to death.
Additional information:
• Carcinus maenas is considered to be one of the world's 100 worst invaders.
• The species lives on all sheltered and semi-sheltered marine and estuary habitats, including muddy, sandy and rocky substrates, in underwater vegetation like salt meadows - soft ground is preferred, though. Carcinus maenas is an euryhaline species, i.e. they can live in water with varying salinity, as adults in 4 to 52 per mil. C. maenas cannot cross the deep sea, however.
[attachment=8299]
• C. maenas is the most commonly found species in the North Sea. Even though it belongs to the swimming crabs (Portunidae) it does not have swimming legs. It is the most prominent and striking crustacean in the German tidelands and eats up to 10% of the biomass there (in Tasmania, they are considered the main reason for the dying out of local crabs and molluscs; in California they are assumed to be the cause of the decline of local clams). At the same time, the shore crab is an important bird food (seagulls, ducks) and larger fish (plaice, eel and codfish) as well as the crab Callinectus sapidus. In captivity, C. maenas has been reported to be predated on by great crabs (Cancer pagurus), lobsters (Homarus gammarus) and Callinectes sapidus – however, the first two are not very likely to meet shore crabs in nature.
[attachment=8300]
Various colorations are possible.
• When the tide is low, especially the older crabs often migrate towards the open sea following the water and come back with high tide. When the tidelands fall dry before they can reach their hideaways on gullies, water holes or in mussel beds they dig into the ground. When it is dry they can breathe air and will survive for up to 12 hours given that their gills are moist. Water is first gathered in the gills, then circulated across the carapace back inside the body. During this process the water takes up extra oxygen from the air on which the crab can "breathe again".
In winter, however, the older crabs migrate to deeper waters with the outgoing tide or hibernate dug into the muddy tidelands. You can only find shore crabs in fresh or brackish water during summertime, when the water is colder osmotic regulation is harder for them and the crabs have to retreat to regions with a higher salinity. In summer they like to leave the water and breathe athmospheric oxygen while sitting on rocks.
[attachment=8301]
Three juvies.
• When feeling threatened, these crabs often stand on their hind legs and menacingly wave their claws - the larger of which, btw, serves for breaking open hard things like clams, and the smaller one is for cutting through softer materials. If one of their legs or claws is caught they can discard it (autotomy) and flee - lost limbs will regrow at the next molt, after all.
[attachment=8302]
A juvenile next to its old carapace.
• C. maenas is an invasive species that has populated nearly the entire world by now. The planktonic larvae are mostly spread in the ballast water of ships. As is often the case with invasive species they are more successful in new areas (due to the lack of natural parasites) and thus outpopulate local species, moreover, they often grow larger.
[attachment=8303]
Juvie with black and white spots.
• Moreover, C. maenas is very adaptable regarding temperatures and salinities (see above). This is true even for the larvae. Only the first larval stage (zoea I) needs a salinity of over 17 per mil - all the following stages do well in salinities of 10.2 to 44.3 per mil, young crabs can even live in only 5.3 per mil. When the salinity is only 1 per mil, however, 80 to 100% of the young crabs die within a day.
[attachment=8304]
• During the last years, C. maenas itself is suppressed by invasive species in Europe (France, Spain, the Netherlands, Germany and Portugal): Especially the species Hemigrapsus sanguineus and H. takanoi (Asian shore crab) give the European shore crab a hard time due to their higher rate of reproduction and high aggressivity and have displaced the local species almost totally from several beaches after only a few years now. These species are considered to have the potential of possibly eliminating C. maenas entirely.
[attachment=8305]
• C. maenas are often parasitized by the arthropod Sacculina carcini.
•• http://de.wikipedia.org/wiki/Sacculina
•• http://sabella.mba.ac.uk/1158/01/Notes_o...ompson.pdf
•• http://www.werc.usgs.gov/chis/Goddardetal05.pdf
•• http://discovermagazine.com/2000/aug/cover
•• http://www.sgnis.org/publicat/kurigodd.htm
![[Bild: 878144b3ffd6400883853d4857b8f15d]](http://vg08.met.vgwort.de/na/878144b3ffd6400883853d4857b8f15d)
Fotos: Oliver Mengedoht
Translated by Ulli Bauer
Scientific name: Carcinus maenas
Trivial name: Shore crab
Other names: European Shore Crab, Green Crab, European Green Crab, Applejacks, Addlers
Systematics: Domain: Eucaryota, kingdom: Animalia, subkingdom: Metazoa (multiple-celled animals), Eumetazoa (true tissue), grade: Bilateria, branch: Protostomia, infrakingdom: Ecdysozoa (molting animals), phylum: Arthropoda (jointed-leg invertebrates), subphylum: Crustacea, class: Malacostraca (higher crustaceans), superorder: Eucarida, order: Decapoda (ten-legged crayfish), suborder: Pleocyemata, infraorder: Reptantia, section: Brachyura (true crabs), superfamily: Portunoidea, family: Portunidae (swimming crabs), subfamily: Carcininae, genus: Carcinus, species: Carcinus maenas
[attachment=8286]
more pix: www.panzerwelten.de/v/Carcininae/Strandkrabben/
Origin/Range: Carcinus maenas live on all kinds of sea shores down to a depth of 60 meters, but mainly on beaches and in shallow water. These crabs are the most prominent species on the North Sea and are originally found in northwestern Europe (starting in Norway) down to the Mediterranean, the Baltic Sea and the northafrican Atlantic (Mauretania). A natural border for their distribution is the Baltic Sea with its lower salinity; with freshwater continuously diffusing into it, the crab would have to spend too much energy for osmotic regulation and thus would not have enough energy left to live.
However, today this species is found globally.
The European shore crab has also invaded North America as a neozoon (1817: Masachusetts; today found from Nova Scotia to Virginia), as well as Asia and Australia. In the 1890s, this species appeared in Australia (Victoria, 1971: New South Wales, 1976: South Australia, 1993: Tasmania), in 1983 in South Africa, in 1989 on the US Pacific Coast in the Bay of San Francisco (USA), in 1997 in Oregon and in 1998 in Washington (USA) as well as in 1999 in British Columbia (Canada). In 2003, Carcinus maenas also took hold in Argentina, and in the meantime it is also said to be found in Japan (however, it is possible that the crabs found there belong to the Mediterranean species C. aestuarii or a hybrid of both).
Individual specimens so far not leading to stable populations have been found in Brazil, Panama, Hawaii, Madagascar, the Red Sea, Pakistan, Sri Lanka and Burma.
[attachment=8287]
Description: Five prominent teeth on the frontal side edges (behind the eyes), three rounded teeth between the eyes. Their basic color varies from grey over brown to green or red. According to one source, the males are more often green and the females reddish, at the same time the colors are said to vary with age. Another source says that about five percent of the adult animals are green.
Another explanation says that the color has a genetic component but also depends on environmental factors. According to this, specimens delaying a molt become rather reddish than greenish in color, and reddish crabs are said to be stronger and more aggressive, but less tolerant towards environmental variables like lower salinity or oxygen deficiency.
Young crabs show a variety of colors and often have red, black or white dots or even combinations of these colors.
[attachment=8288]
Sex differences: Typical for crabs, the males have a narrow apron (whose 3rd to 5th segments are fused); the females have a wider apron covering nearly the entire abdomen. Moreover, the males' claws are bulkier.
Size: up to 10 cm carapace width (approx. 150 grams), males are larger than females
[attachment=8289]
Example for a small shore aquaterrarium with brackish water for young crabs.
Life span: up to about 6 years (females possibly only 4 years)
Temperature: 0 to 30 degrees Celsius
Tank size/stock: Individual specimen: starting at 60 cm tank length, bigger is better
In nature, up to 200 0.5 centimeter small young crabs can be found on one square meter of tideland. Of course, such a stock would never work in a tank! A 60 cm long tank is too small for an adult specimen with a carapace width of 6 cm. As this species is rather aggressive a lot depends on the size. A group of four adults might work in a 500 liter tank, 4 to 6 young crabs with a carapace of under 2 cm in width can probably be kept in a 60 cm tank...
Tank set-up: North Sea or brackish water tank, if possible with a land part (sandy area, rocks), also possible in a (tropical) seawater tank.
[attachment=8290]
[attachment=8291]
[attachment=8292]
Their natural habitat (here near Cuxhaven, Germany): Shores and tidelands.
Food: Typical for crabs, they are omnivores.
• Leaves (the main staple of many crabs in nature; mostly oak and beech are fed, however, all European broadleaved tree leaves are possible, also Indian almond leaves), muck, water plants
• Vegetables/fruit: nearly all vegetables and fruit are suitable (peas, lettuce, cucumber, apple, zucchini, pear, banana, grapes, tomato, Brussels sprouts, bell peppers) except for parsley and beans or other kinds that contain Prussic acid or copper; carrots (boiled); potato and rice (boiled) or noodles (uncooked? Don't leave these in the tank for too long a time though, they can be the cause of turbid water and finally lead to a bacteria bloom and oxygen depletion); no citrus fruit due to their high acid content
• Dry food: Catfish tabs, fish (flake) food, food pellets, rabbit, guinea pig and chinchilla food pellets (without copper!), Spirulina tabs, crayfish tabs, Gammarus
• Frozen food: Black, glass and blood worms, Cyclops, brine shrimp, clam meat
• Live food: Earthworms (it's best to cut them into pieces though, or else these worms might burrow in the substrate, possibly also under water, die and rot there unnoticed until it's too late)
• Meat (rarely): Chicken bones with meat rests (rinsed well to prevent too much fat from getting into the terrarium)
• Fish: deep-frozen smelts et.al., tuna fish, sardines, herring etc. fresh or from a can (in their own juice, not in oil)
• Calcium: cuttlebone, smashed eggshells or powdered calcium in self-made food sticks
[attachment=8295]
Shore crab digging into the substrate hind legs first.
Behavior: Carcinus maenas is an aggressive species that can be active at all times. Various sources list it as especially active at night, at high tide, at daytime or indeed "around the clock".
[attachment=8296]
Hard to see, awaiting the things to come.
Reproduction: unspecific, goes through several larvae stages. Mating is only possible when the female has just molted - in order not to miss this and to prevent the female from mating with other males the male crabs carry the females around for several days before they molt in spring and summer. After mating, the female carries up to 200,000 eggs, from which finally pelagic (free-swimming) larvae hatch. After the protozoea there are four zoea stages and a megalopa larva before the young crabs return to shore.
The young crabs prefer to live in seaweed and molt every few days (inflating themselves with water in order to grow as long as they are soft); after only a week on tideland they can reach a carapace width of 0.5 cm. According to scientific research, Carcinus maenas in their first year can reach a carapace width of as much as 1.5 cm. The young crabs migrate to deeper water zones for hibernation.
[attachment=8297]
Socialization: Only with species you are ready to run the risk of losses (this applies to other crab species as well as snails, other inverts or fish). All animals smaller or of the same size are considered food.
[attachment=8298]
This crab is very overgrown with barnacles and cannot even move its right eye. If it doesn't molt soon the barnacles are going to cover its mandibles, too, and the crab will starve to death.
Additional information:
• Carcinus maenas is considered to be one of the world's 100 worst invaders.
• The species lives on all sheltered and semi-sheltered marine and estuary habitats, including muddy, sandy and rocky substrates, in underwater vegetation like salt meadows - soft ground is preferred, though. Carcinus maenas is an euryhaline species, i.e. they can live in water with varying salinity, as adults in 4 to 52 per mil. C. maenas cannot cross the deep sea, however.
[attachment=8299]
• C. maenas is the most commonly found species in the North Sea. Even though it belongs to the swimming crabs (Portunidae) it does not have swimming legs. It is the most prominent and striking crustacean in the German tidelands and eats up to 10% of the biomass there (in Tasmania, they are considered the main reason for the dying out of local crabs and molluscs; in California they are assumed to be the cause of the decline of local clams). At the same time, the shore crab is an important bird food (seagulls, ducks) and larger fish (plaice, eel and codfish) as well as the crab Callinectus sapidus. In captivity, C. maenas has been reported to be predated on by great crabs (Cancer pagurus), lobsters (Homarus gammarus) and Callinectes sapidus – however, the first two are not very likely to meet shore crabs in nature.
[attachment=8300]
Various colorations are possible.
• When the tide is low, especially the older crabs often migrate towards the open sea following the water and come back with high tide. When the tidelands fall dry before they can reach their hideaways on gullies, water holes or in mussel beds they dig into the ground. When it is dry they can breathe air and will survive for up to 12 hours given that their gills are moist. Water is first gathered in the gills, then circulated across the carapace back inside the body. During this process the water takes up extra oxygen from the air on which the crab can "breathe again".
In winter, however, the older crabs migrate to deeper waters with the outgoing tide or hibernate dug into the muddy tidelands. You can only find shore crabs in fresh or brackish water during summertime, when the water is colder osmotic regulation is harder for them and the crabs have to retreat to regions with a higher salinity. In summer they like to leave the water and breathe athmospheric oxygen while sitting on rocks.
[attachment=8301]
Three juvies.
• When feeling threatened, these crabs often stand on their hind legs and menacingly wave their claws - the larger of which, btw, serves for breaking open hard things like clams, and the smaller one is for cutting through softer materials. If one of their legs or claws is caught they can discard it (autotomy) and flee - lost limbs will regrow at the next molt, after all.
[attachment=8302]
A juvenile next to its old carapace.
• C. maenas is an invasive species that has populated nearly the entire world by now. The planktonic larvae are mostly spread in the ballast water of ships. As is often the case with invasive species they are more successful in new areas (due to the lack of natural parasites) and thus outpopulate local species, moreover, they often grow larger.
[attachment=8303]
Juvie with black and white spots.
• Moreover, C. maenas is very adaptable regarding temperatures and salinities (see above). This is true even for the larvae. Only the first larval stage (zoea I) needs a salinity of over 17 per mil - all the following stages do well in salinities of 10.2 to 44.3 per mil, young crabs can even live in only 5.3 per mil. When the salinity is only 1 per mil, however, 80 to 100% of the young crabs die within a day.
[attachment=8304]
• During the last years, C. maenas itself is suppressed by invasive species in Europe (France, Spain, the Netherlands, Germany and Portugal): Especially the species Hemigrapsus sanguineus and H. takanoi (Asian shore crab) give the European shore crab a hard time due to their higher rate of reproduction and high aggressivity and have displaced the local species almost totally from several beaches after only a few years now. These species are considered to have the potential of possibly eliminating C. maenas entirely.
[attachment=8305]
• C. maenas are often parasitized by the arthropod Sacculina carcini.
•• http://de.wikipedia.org/wiki/Sacculina
•• http://sabella.mba.ac.uk/1158/01/Notes_o...ompson.pdf
•• http://www.werc.usgs.gov/chis/Goddardetal05.pdf
•• http://discovermagazine.com/2000/aug/cover
•• http://www.sgnis.org/publicat/kurigodd.htm