Gonionemus vertens

Phylum: Cnidaria
Class: Hydrozoa
Order: Limnomedusae
Species name: Gonionemus vertens A. Agassiz 1862
Synonyms: None
Common name: None
Date of introduction and origin
Gonionemus vertens was first reported from north-east England in 1913 and probably originates from the western Pacific (China, Korea or Japan) via Portugal (Edwards 1976).
Method of introduction
Transport on ships' hulls in the polyp stage (Carlton 1985) from the western Pacific Ocean in the 19th century may be the mechanism of introduction. Edwards (1976) suggested that it may have arrived much earlier from Japan with importations of Japanese oysters Crassostrea gigas 500 or more years ago; he also discusses other shipping- and seaplane-associated methods of transport.
Reasons for success
This species seems to thrive in temperate to warm-temperate regions.
Rate of spread and methods involved
This species shows a variable, generally moderate rate of spread. It is thought to have been initially introduced to Europe in Portugal where the population was localised due to currents, temperatures and salinities. It was exported from 1867 onwards from Portugal to France, again with oysters in the polyp stage. This has probably allowed the spread to other European countries including the British Isles since France was a major oyster exporter (Edwards 1976). It can also disperse in the hydromedusae stage in water currents and ballast water.
It has a patchy distribution around British coasts and, in a new area, is usually first noted in aquaria; it is also found on other western European coasts.
Factors likely to influence spread and distribution
Its spread is likely to have been influenced by movements of oysters, shipping and marginal spread of established populations.
Effects on the environment
Effects on commercial interests
Control methods used and effectiveness
None used.
Beneficial effects
None known.
It is unlikely that the venom of Gonionemus vertens is as harmful to humans as in much studied Gonionemus populations of Far-Eastern Russian waters (see Cornelius (1995) and references therein).
Agassiz, A. 1865. North American Acalephae. Illustrated Catalogue of the Museum of Comparative Zoology at Harvard College, 2: 1-234.
Carlton, J.T. 1985. Transoceanic and interoceanic dispersal of coastal marine organisms: the biology of ballast water. Oceanography and Marine Biology. An Annual Review, 23: 313-371.
Cornelius, P.F.S. 1995. North-west European thecate hydroids and their medusae, Laodiceidea to haleciidae: keys and notes for the identification of the species. Linnean Society of London, Estuarine and Coastal Sciences Association and Field Studies Council. (Synopses of the British Fauna (new series), No. 50.)
Edwards, C. 1976. A study in erratic Distribution the occurrence of the medusa Gonionemus in relation to the distribution of oysters. Advances in Marine Biology, 14: 251-284.
Acknowledgements (contributions from questionnaire)
Dr P.F.S. Cornelius, The Natural History Museum, London.