AN ALIEN seaweed which can foul boat hulls, propellers, water intakes and become entangled in shellfish farming equipment is spreading along the west coast of Scotland.
Its increasing prevalence has prompted Scottish Natural Heritage (SNH) to investigate and call for vigilance among sea-goers.
The first reports of wireweed or 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 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 outgrowing and shading them.
Last year SNH launched a public appeal to help track the spread of the seaweed, resulting in a number of new records for the Firth of Clyde. This year, SNH has commissioned researchers to investigate its spread in detail.
The researchers have developed models to predict where the seaweed is likely to turn up next, using wind and tide data combined with information on local habitats.
Most of the immediately vulnerable areas lie in the Firth of Clyde and along the Argyll coast. Over the summer surveys will be carried out in these areas to look for the seaweed. The species is included in SNH's Species Action Framework which promotes action to protect Scotland's biodiversity.
Dr Fiona Manson, marine advisory officer at SNH said: “Wireweed can spread into new areas by natural means, as fronds can break off and float for long distances before releasing young germlings (seedlings). These can then attach themselves to the seabed and grow rapidly, establishing new colonies if conditions are right.
“Wireweed can also be spread by accidental or intentional human transportation.
“This may be in connection with the movement of shellfish for cultivation, or attached to recreational or commercial boats. We are appealing to boat users to take care not to spread the seaweed. Anchors should always be cleared of weed before moving to another area, to reduce the likelihood of spreading this species.”
SNH is keen for coastal walkers, boat users and recreational divers to keep a look out for wireweed. Anyone seeing it can report the sighting, with an exact location or grid reference, by e-mailing wireweed@snh.gov.uk or by calling Fiona Manson on 01738 458641.
Information about wireweed can be found at www.snh.org.uk/wireweed