A NEW invader has arrived on Scottish shores and is threatening to smother underwater life.
Carpet sea squirt is believed to have made its way to Scotland by attaching itself to the hulls of boats.
A colony of the alien creatures has been discovered in Largs Yacht Haven in the Firth of Clyde.
Sea squirt, a marine animal originally fro
m Japan, has spread around the world but Scotland has until now been free of the spongy invader.
Dr David Donnan, policy and advice manager at Scottish Natural Heritage, warned the sea squirt has caused economic and environmental problems in other countries, including Canada, New Zealand, continental Europe and Ireland.
"The carpet sea squirt can reproduce and spread rapidly and tends to smother other marine life that grows on the seabed," he said.
"It is especially good at growing over underwater structures such as aquaculture equipment, boat hulls and pontoons."
He added: "The removal of the large, gelatinous growths can be difficult and costly."
The creatures have already been seen in North Wales and the south of England.
Chris Beveridge from the Scottish Association for Marine Science (Sams) noticed the small colony during a routine survey.
She said: "This is one of our target species, so when I spotted a mussel on a pontoon, covered with a fawn coloured growth, I immediately suspected the invasive sea squirt."
She later found a larger colony on the marina's mooring lines. Surveys of west coast marinas are carried out every year to check for a variety of non-native species.
Ms Beveridge believes the sea squirt may have been brought into Largs Yacht Haven on the hulls of leisure craft that have travelled from Wales or Ireland, where it is already established.
"It could be a real menace for all users of the marine environment if it spreads up the coast, with considerable economic impact," she said.
Now marine scientists are to survey marinas in the Firth of Clyde and on the Argyll coast to find out how far the invaders have spread.
The surveys will be carried out from late January by Sams and then decisions will be made about how best to deal with the species.
Meanwhile boat owners are being asked to make extra effort to keep boat hulls clean to help prevent its spread, and to clean fishing gear on a regular basis.
Carpet sea squirt is a distinctive mustard, pale orangey-yellow or beige colour and often appears as pale flat patches.
Larger growths may look like wax dripping from artificial structures just below the water level. Its surface has leaf-like veins with tiny pores and it has a spongy texture and a leathery feel.
A poster alerting the public to the carpet sea squirt is being sent to marinas in Scotland.
