An alien species of seaweed, known as wireweed, has been spreading along Scotland’s west coast and has been noted in Argyll waters. Scottish Natural Heritage (SNH) is investigating how far it has reached.
The first reports of wireweed (Sargassum muticum) in Scotland were in Loch Ryan in Galloway in 2004. Since then it has been seen growing abundantly in a number of places in the Firth of Clyde. Last summer, detached pieces of the seaweed were seen floating in the Firth of Lorn and near to Oban.
Although it’s harmless in its native western Pacific, wireweed is a nuisance species in the UK. It grows very rapidly in the summer and where it becomes established on the lower shore it can reduce the diversity of native seaweeds by effectively smothering them. It can foul boat hulls, propellers and water intakes, and it
can get entangled in shellfish farming equipment.
Dr Fiona Manson, SNH’s Marine Advisory Officer says that wireweed can spread into new areas by natural means. Fronds can break off and float for long distances before releasing seedlings. These can then attach themselves to the seabed and grow rapidly, establishing new colonies in the right conditions.
Wireweed can also be spread unintentionally by transportation, perhaps in connection with the movement of shellfish, like oysters and mussels, for cultivation, or attached to recreational or commercial boats. SNH is appealing to boat users to take care not to spread the seaweed – for instance by clearing anchors of weed before moving to another area.
SNH is asking coastal walkers, boat users and recreational divers tin Argyll to keep a look out for wireweed. It can be seen either washed up on beaches, out on the water, or entangled on anchors. Anyone spotting the speciesis asked to report the sighting, if possible with an exact location or grid reference, by emailing wireweed@snh.gov.uk or by calling Dr Fiona Manson on 01738 458641.
Information about wireweed, and what to look for, can be found opn the SNH website. Leaflets to help identify the species are available from Dr Fiona Manson at SNH. Advice on cleaning boats and equipment is available from The Green Blue, an environmental awareness initiative by the British Marine Federation and the Royal Yachting Association.