Latin name: Sargassum muticum
Global Distribution: Originally from Japan – now worldwide distribution
UK Distribution: Along the south coast to the Isles of Scilly and along the north Cornish coast to Lundy. Populations have also been recorded in Strangford Lough, Northern Ireland and Loch Ryan and the Firth of Clyde, Scotland
Diet: photosynthesis
Size: More than 1m long
Habitat: Grows on hard substrata in shallow waters and can also tolerate estuarine conditions

Wireweed is a non-indigenous invasive species and was first spotted on the Isle of Wight in 1973. The species’ introduction into European waters is thought to have unintentionally occurred through commercial oysters that were transported from British Columbia, Canada or Japan into France. Following this event, the introduction into British water is thought to have occurred by natural dispersal or as a fouling organism on boats or shellfish. The species has a very efficient dispersal due to its reproduction method which involves floating fragments that can continue to shed germlings as they drift in the ocean. The successful worldwide establishment of the Wireweed was possible because of its high tolerance for salinity and temperature variations. This invasive species has a rapid growth rate and easily out competes the native seaweed species, causing biodiversity changes. Its dense stands also reduce light necessary for other species survival and catch nutrients in disfavor of other species. The Wireweed also causes economical problems for shellfish farms as it attaches itself on the shells of oysters and it has to be eliminated manually which is very costly and time consuming. Wireweed is also considered a nuisance in harbours, beaches and shallow waters and can impair recreational activities such as swimming, diving, sailing and kayaking through entanglement. There are some potential benefits of the algae, such as the use in agriculture as fertiliser and the use as an anti-fouling agent.

Fun facts

  • This seaweed could have various anti-pollution properties, able to catch both heavy metals and the organic matter in sewage.
  • They also contain high concentrations of chemicals that could be used in medicines, including the anti-cancer compound, fucoxanthin.
  • In spring the species can grow up to 10 cm a day!
Photo credit: By Graça Gaspar – uploaded with the author’s permission, CC BY-SA 3.0,

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