A non-native seaweed Wireweed, Sargassum muticum, was initially introduced to France on oysters either from Canada or Japan, and it was first found on the Isle of Wight in 1973. It is a fast-growing species producing large numbers of spores and can spread at the rate of approximately 30 km per year. It prefers warmer waters, but will tolerate a wide range of temperatures and salinity including estuarine conditions.
Wireweed can be a pest in harbours, shallow waters and on beaches, interfering with recreational use of waterways with detached plants forming large floating masses which can block propellers and intakes. It can also foul oyster beds and fishermens nets and competes with native plants such as sea grasses.
It was first recorded in south-west Scotland in 2005 and subsequently found in surveys conducted from 2010-2012. It was found on North Uist in August 2013. This was the first record for the islands and for Scotland beyond the Firth of Clyde and Loch Fyne.