An alien species of seaweed is spreading on the west coast, Scottish Natural Heritage confirmed yesterday.

Wireweed (Sargassum muticum), has spread further and much faster than was thought. It can cause commercial and environmental damage and has been found in Ardnamurchan and on Skye, and in the Solway Firth.

It is the second alien species found to be threatening our seas in recent months. The Japanese seaweed Heterosiphonia japonica, was found in May by a marine biologist diving off Oronsay at the mouth of Loch Sunart.

SNH is asking the public to report sightings of wireweed. It originates from the western Pacific, where it is harmless, but in the UK it is a nuisance.

A survey this summer found it is well-established around Cumbrae and Arran and on the Ayrshire coast. It has also become established on the Kintyre peninsula.

Dr Fiona Manson, marine advisory officer at SNH, explained: "Wireweed spreads easily and grows very fast. Where it becomes established it grows so densely that it blocks out light to the seabed and stops our native seaweeds growing.

" This has a knock-on effect on other marine plants and animals. It also has an economic impact, entangling boat propellers and clogging water intakes and fish farming equipment."

The Japanese seaweed is new to Scotland but in Norway it has densely coated seabeds. The worry is it might take over and out-compete all the other plants.

Information on wireweed, and what to look for, is at www.snh.org.uk/wireweed.