Dikerogammarus villosus
Encyclopedia
Dikerogammarus villosus, also known as the killer shrimp, is a species of amphipod
crustacean
native to the Ponto-Caspian region of eastern Europe, but which has become invasive
across the western part of the continent. In the areas it has invaded, it lives in a wide range of habitats and will kill many other animals, often not eating them. It is fast growing, reaching sexual maturity in 4–8 weeks. As it has moved through Europe it threatens other species and has already displaced native amphipods as well as other amphipods which had invaded areas previously.
D. villosus can grow up to 30 millimetres (1.2 in) in length, relatively large for a freshwater amphipod. It varies in appearance, with some specimens being striped, and some not. It has relatively large mandibles
which allow it to be an effective predator.
and Caspian Sea
drainage basin
s. It has become an invasive species
across central and western Europe, using the Danube
river and its tributaries in its expansion. It is thought to have first escaped from the Danube in 1992 when the Rhine–Main–Danube Canal was opened and has since spread to nearly all the major rivers in western Europe, including the Rhône
, Loire
, Seine
, Moselle
, Meuse
, Rhine and Main, as well as the Baltic Sea
. It is unknown how the species is dispersed but it is probably related to shipping activity. It spread quickly through western Europe; found in the Rhine at the German–Dutch border (1995), the canals and rivers of northern Germany (1998), the Baltic Szczecin Lagoon (2001), the Moselle (2001), the Netherlands (2002), Lake Constance
(2003), Lake Leman, the Rhine in France (2003), the (2003) and Lake Garda
(2003). Its spread is thought to be related to the previous introduction of the zebra mussel
, Dreissena polymorpha which it has evolved alongside
. In September 2010, it was found in Grafham Water
in Cambridgeshire
, the first report of the species in the United Kingdom
and it was found in Wales in November 2010.
There are fears that it could spread to the Great Lakes
in North America
in future, carried in the ballast water of ships.
as it is able to tolerate a wide range of temperatures (0–30 °C or 32–86 F), low oxygen concentrations
, and salinity
up to 20‰. It is found in lakes, canals and rivers living in a range of substrates. It is thought that zebra mussels change habitats by increasing the amount of benthic organic matter, which benefits D. villosus helping them to outcompete other species. When given a choice, D. villosus spend more time feeding around zebra mussel shells than a bare substrate.
and feeds on a variety of invertebrate
s, including other members of the Gammaridae
family. It has been found to kill blue-tailed damselfly
nymphs, water hoglice
, water boatman
, fish leech
es as well as small fish and the eggs of other vertebrate
s. Often it only kills prey but does not eat it. It kills its prey by biting it with its large mandibles and then shreds it before eating it.
. Each pair produces an average of 27 eggs, but up to 50 eggs can be laid. The young animals become sexually mature in 4 to 8 weeks, once they are 6 mm in length and after moulting
several times. They are fast growing, during winter increasing by 1.3–2.9 mm in length per month and by 2.0–2.6 mm every two weeks in spring. Populations are predominantly female.
(D. bispinosus and D. haemobaphes) which were previously invasive in the Danube. Its ability to attack and feed on a range of species could cause the local extinction
of some species.
Amphipoda
Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...
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...
native to the Ponto-Caspian region of eastern Europe, but which has become invasive
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....
across the western part of the continent. In the areas it has invaded, it lives in a wide range of habitats and will kill many other animals, often not eating them. It is fast growing, reaching sexual maturity in 4–8 weeks. As it has moved through Europe it threatens other species and has already displaced native amphipods as well as other amphipods which had invaded areas previously.
Description
Mandible (arthropod)
thumb|250px|The mandibles of a [[Bull ant]]The mandible of an arthropod is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda , Crustacea and Hexapoda...
which allow it to be an effective predator.
Distribution
D. villosus was originally found in the lower courses of large rivers in the Black SeaBlack Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
and Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
s. It has become an 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....
across central and western Europe, using the Danube
Danube
The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....
river and its tributaries in its expansion. It is thought to have first escaped from the Danube in 1992 when the Rhine–Main–Danube Canal was opened and has since spread to nearly all the major rivers in western Europe, including the Rhône
Rhône
Rhone can refer to:* Rhone, one of the major rivers of Europe, running through Switzerland and France* Rhône Glacier, the source of the Rhone River and one of the primary contributors to Lake Geneva in the far eastern end of the canton of Valais in Switzerland...
, Loire
Loire
Loire is an administrative department in the east-central part of France occupying the River Loire's upper reaches.-History:Loire was created in 1793 when after just 3½ years the young Rhône-et-Loire department was split into two. This was a response to counter-Revolutionary activities in Lyon...
, Seine
Seine
The Seine is a -long river and an important commercial waterway within the Paris Basin in the north of France. It rises at Saint-Seine near Dijon in northeastern France in the Langres plateau, flowing through Paris and into the English Channel at Le Havre . It is navigable by ocean-going vessels...
, Moselle
Moselle
Moselle is a department in the east of France named after the river Moselle.- History :Moselle is one of the original 83 departments created during the French Revolution on March 4, 1790...
, Meuse
Meuse
Meuse is a department in northeast France, named after the River Meuse.-History:Meuse is one of the original 83 departments created during the French Revolution on March 4, 1790...
, Rhine and Main, as well as the 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...
. It is unknown how the species is dispersed but it is probably related to shipping activity. It spread quickly through western Europe; found in the Rhine at the German–Dutch border (1995), the canals and rivers of northern Germany (1998), the Baltic Szczecin Lagoon (2001), the Moselle (2001), the Netherlands (2002), Lake Constance
Lake Constance
Lake Constance is a lake on the Rhine at the northern foot of the Alps, and consists of three bodies of water: the Obersee , the Untersee , and a connecting stretch of the Rhine, called the Seerhein.The lake is situated in Germany, Switzerland and Austria near the Alps...
(2003), Lake Leman, the Rhine in France (2003), the (2003) and Lake Garda
Lake Garda
Lake Garda is the largest lake in Italy. It is located in Northern Italy, about half-way between Brescia and Verona, and between Venice and Milan. Glaciers formed this alpine region at the end of the last ice age...
(2003). Its spread is thought to be related to the previous introduction of the zebra mussel
Zebra mussel
The zebra mussel, Dreissena polymorpha, is a small freshwater mussel. This species was originally native to the lakes of southeast Russia being first described in 1769 by a German zoologist Peter Simon Pallas in the Ural, Volga and Dnieper rivers. They are still found nearby, as Pontic and Caspian...
, Dreissena polymorpha which it has evolved alongside
Co-evolution
In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...
. In September 2010, it was found in Grafham Water
Grafham Water
Grafham Water is a reservoir with a circumference of about . It is located between the villages of Grafham and Perry in the English county of Cambridgeshire ....
in Cambridgeshire
Cambridgeshire
Cambridgeshire is a county in England, bordering Lincolnshire to the north, Norfolk to the northeast, Suffolk to the east, Essex and Hertfordshire to the south, and Bedfordshire and Northamptonshire to the west...
, the first report of the species in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and it was found in Wales in November 2010.
There are fears that it could spread to the Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
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...
in future, carried in the ballast water of ships.
Ecology
In its natural range, D. villosus is not the most abundant species of amphipod and it does not behave as aggressively as it does in areas it has invaded.Habitat
D. villosus can colonise many types of habitatHabitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
as it is able to tolerate a wide range of temperatures (0–30 °C or 32–86 F), low oxygen concentrations
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...
, and 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...
up to 20‰. It is found in lakes, canals and rivers living in a range of substrates. It is thought that zebra mussels change habitats by increasing the amount of benthic organic matter, which benefits D. villosus helping them to outcompete other species. When given a choice, D. villosus spend more time feeding around zebra mussel shells than a bare substrate.
Feeding
D. villosus is omnivorousOmnivore
Omnivores are species that eat both plants and animals as their primary food source...
and feeds on a variety of invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, including other members of the Gammaridae
Gammaridae
Gammaridae is a family of amphipods. In North America they are included among the folk taxonomic category of "scuds", and otherwise gammarids is usually used as a common name....
family. It has been found to kill blue-tailed damselfly
Blue-tailed Damselfly
The Blue-tailed Damselfly, Ischnura elegans, is a European damselfly.Adult male Blue-tailed Damselflies have a head and thorax patterned with blue and black. They have a largely black abdomen with very narrow pale markings where each segment joins the next...
nymphs, water hoglice
Water hoglouse
Asellus aquaticus is a freshwater crustacean resembling a woodlouse. It is known by many common names including "waterlouse", "aquatic sowbug" and "water hoglouse".-Ecology:...
, water boatman
Water boatman
Corixidae is a family of aquatic insects in the order Hemiptera that inhabit ponds and slow moving streams, where they swim near the bottom. There are about 500 known species worldwide, in 33 genera, including the genus Sigara....
, fish leech
Leech
Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...
es as well as small fish and the eggs of other vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s. Often it only kills prey but does not eat it. It kills its prey by biting it with its large mandibles and then shreds it before eating it.
Growth and reproduction
D. villosus breeds all year round so long as the water temperature is above 13 °C (55.4 °F). When they mate the female is carried on the back of the maleAmplexus
Amplexus is a form of pseudocopulation in which a male amphibian grasps a female with his front legs as part of the mating process...
. Each pair produces an average of 27 eggs, but up to 50 eggs can be laid. The young animals become sexually mature in 4 to 8 weeks, once they are 6 mm in length and after 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...
several times. They are fast growing, during winter increasing by 1.3–2.9 mm in length per month and by 2.0–2.6 mm every two weeks in spring. Populations are predominantly female.
Effects on other species
In the Netherlands, D. villosus is threatening the native amphipod species Gammarus duebeni, as well as Gammarus tigrinus which had previously become invasive after previously being introduced from North America. It is thought to have displaced two other species of DikerogammarusDikerogammarus
Dikerogammarus is a genus of amphipod crustaceans, containing the following species:*Dikerogammarus aralychensis *Dikerogammarus batalonicus Ponyi, 1955*Dikerogammarus bispinosus Martynov, 1925...
(D. bispinosus and D. haemobaphes) which were previously invasive in the Danube. Its ability to attack and feed on a range of species could cause the local extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
of some species.