Dikerogammarus villosus

Dikerogammarus villosus, also known as the killer shrimp,[1][2] 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.

Dikerogammarus villosus
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Crustacea
Class:
Malacostraca
Order:
Amphipoda
Family:
Gammaridae
Genus:
Dikerogammarus
Species:
D. villosus
Binomial name
Dikerogammarus villosus
(Sowinsky, 1894)

Description
A diagram showing the typical anatomical features of an amphipod

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.[2]

Distribution

D. villosus was originally found in the lower courses of large rivers in the Black Sea and Caspian Sea drainage basins.[3] It has become an invasive species across central and western Europe, using the Danube river and its tributaries in its expansion.[2][4] 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.[5][6] It is unknown how the species is dispersed but it is probably related to shipping activity.[4] 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 Grand Canal d'Alsace (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.[1][6] In September 2010, it was found in Grafham Water in Cambridgeshire, the first report of the species in the United Kingdom[4] and it was found in Wales in November 2010.[7]

There are fears that it could spread to the Great Lakes in North America in future, carried in the ballast water of ships.[2]

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.[6]

Habitat

D. villosus can colonise many types of habitat 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.[2] 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.[1]

Feeding

D. villosus is omnivorous and feeds on a variety of invertebrates, including other members of the Gammaridae family.[5] It has been found to kill blue-tailed damselfly nymphs, water hoglice, water boatman, fish leeches as well as small fish and the eggs of other vertebrates.[8] Often it only kills prey but does not eat it.[6][9] It kills its prey by biting it with its large mandibles and then shreds it before eating it.[2]

Growth and reproduction

D. villosus breeds all year round so long as the water temperature is above 13 °C (55 °F). When they mate, the female is carried on the ventral side of the male. 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.[2][5]

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.[10] It is thought to have displaced two other species of Dikerogammarus (D. bispinosus and D. haemobaphes) which were previously invasive in the Danube.[11] Its ability to attack and feed on a range of species could cause the local extinction of some species.[9]

gollark: I mostly just stick `print`s in.
gollark: Imagine actually using and/or knowing how to operate a debugger.
gollark: Hmm, this msgpack library MAY be filled with invisible bees.
gollark: ... why are all database accesses now causing apioforms
gollark: `SIGSEGV: Illegal storage access. (Attempt to read from nil?)` in some random internal apiocode.

References
  1. René Gergs; Karl-Otto Rothhaupt (2008). "Effects of zebra mussels on a native amphipod and the invasive Dikerogammarus villosus: the influence of biodeposition and structural complexity" (PDF). Journal of the North American Benthological Society. 27 (3): 541–548. doi:10.1899/07-151.1.
  2. Danielle M. Crosnier; Daniel P. Molloy (October 2006). "Killer Shrimp - Dikerogammarus villosus" (PDF). Aquatic Nuisance Species Research Program. United States Army Corps of Engineers. Archived from the original (PDF) on December 29, 2009. Retrieved September 9, 2010.
  3. Michał Grabowski; Karolina Bącela; Remi Wattier (2007). "Dikerogammarus villosus (Sowinsky, 1894) (Crustacea, Amphipoda) colonizes next alpine lake – Lac du Bourget, France" (PDF). Aquatic Invasions. 2 (3): 268–271. doi:10.3391/ai.2007.2.3.13.
  4. "Alien 'killer' shrimp found in UK". BBC News. September 9, 2010. Retrieved September 9, 2010.
  5. Simon Devin; Jean-Nicolas Beisel (November 16, 2006). "Dikerogammarus villosus" (PDF). Delivering Invasive Alien Species Inventories for Europe. Archived from the original (PDF) on October 1, 2013. Retrieved September 9, 2010.
  6. Sandra Casellato; Giovanni La Piana; Leonardo Latella; Sandro Ruffo (2006). "Dikerogammarus villosus (Sowinsky, 1894) (Crustacea, Amphipoda, Gammaridae) for the first time in Italy" (PDF). Italian Journal of Zoology. 73 (1): 97–104. doi:10.1080/11250000500502293. Archived from the original (PDF) on 2012-03-12. Retrieved 2010-09-09.
  7. "Invasive 'killer' shrimp found at two sites in Wales". BBC Wales. November 29, 2010. Retrieved December 1, 2010.
  8. Taylor, N. G.; Dunn, A. M. (2016-09-08). "Size matters: predation of fish eggs and larvae by native and invasive amphipods". Biological Invasions. 19: 89–107. doi:10.1007/s10530-016-1265-4. ISSN 1387-3547.
  9. Paul Brown (January 3, 2001). "'Killer shrimp' threatens native species in Britain's rivers". The Guardian. Retrieved September 9, 2010.
  10. Jaimie A. T. Dick; Dirk Platvoet (2000). "Invading predatory crustacean Dikerogammarus villosus eliminates both native and exotic species". Proceedings of the Royal Society B. 267 (1447): 977–983. doi:10.1098/rspb.2000.1099. PMC 1690628. PMID 10874746.
  11. Jakob C. Müller; Stephanie Schramm; Alfred Seitz (2002). "Genetic and morphological differentiation of Dikerogammarus invaders and their invasion history in Central Europe". Freshwater Biology. 47 (11): 2039–2048. doi:10.1046/j.1365-2427.2002.00944.x.
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