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Wireweed external site (Sargassum muticum) is an invasive non-native seaweed that has recently arrived in Scotland. Please help us to track its spread by reporting any sightings.

Reporting your sightings

If you think you have found wireweed, please email us at and tell us:

  • where and when you found it,
  • whether it was floating or attached,
  • an estimate of the length of the branches,
  • a grid reference or geographical co-ordinates for the location of your sighting would be useful, but otherwise please provide the name of the beach or shoreline or sea area where you found it,
  • if possible, take a digital photograph of the plant and attach this to your email.

How to recognise wireweed

Wireweed is a large, olive-brown seaweed that can grow more than a metre long. The plants have long main branches with side branches that, when held out of the water, hang like washing from a line. The side branches support distinctive, grape-like air bladders. These branches can break off from the base and can be found floating individually or in large clumps. The base remains attached to the rock and will regenerate new branches in spring. See more details and photographs of wireweed diagnostic features, plus comparisons with similar species.  PDF document

Distribution of wireweed

Wireweed is originally a native of the western Pacific but has become established in many other regions around the world as an invasive, non-native species. It was first recorded in the UK in 1973 on the Isle of Wight, and has since spread along the south coast of England and into Wales and Ireland. The first reports of wireweed in Scotland were in Loch Ryan in 2004 and, since then, established populations have also been found throughout the Firth of Clyde, in a number of west coast sea lochs and around Inner Hebridean islands. Floating strands of wireweed have been reported from the Outer Hebrides.

Why is wireweed a problem?

Wireweed is undesirable for a number of reasons. It is a fast-growing species and has an impact on our nature and landscapes by competing with native seaweeds and seagrasses. Wireweed can form a distinct band along the lower shore which alters the ecology and visual character of the shore. Where wireweed becomes established in large quantities, it has the potential to be a nuisance. For example, in harbours and shallow waters, floating clumps may become a hazard to commercial and recreational boating through the entanglement of propellers or blocked engine cooling systems.

Last updated on Wednesday 31st August 2016 at 10:00 AM. Click here to comment on this page