IT LOOKS like brown slime and has the potential to spread across Scotland's coastal waters, clogging up fishing gear and smothering other species.
Colonial tunicate is one of four non-native marine creatures about to invade Scotland, according to experts.
They warn that if extreme caution is not taken the species could arrive imminently on our shores, and wreak havoc.
Colonial tunicate is
a tiny animal species that is not native to the UK. It has few natural predators, meaning it spreads rampantly, creating mat-like colonies that smother other marine life.
It has already caused severe problems in New Zealand, North America and other parts of Europe.
Dr Fiona Manson, marine advisor at Scottish Natural Heritage, warned: "It can have an economic impact by growing on fish farm equipment.
"It can grow completely over shellfish farms and stop them feeding and eventually kill them."
Another alien species about to cross the border, she warned, was the Chinese mitten crab.
It has already spread from the Thames as far as the Tyne in north-east England, bringing it worryingly close to the Border.
It too can cause serious damage, by burrowing into river banks and clogging up drainage systems. The crab also eats juvenile fish.
And the slipper limpet, originally from North America, may also soon invade. It would compete with native oysters and mussels, and could clog up oyster beds. Groups of individual slipper limpets piggyback on one another, and blanket whole areas of the sea floor.
The Pacific oyster is already farmed in Scotland, but until now the water has been too cold for it to reproduce.
However, in the south of England, it has started to breed, and has started competing with native species of oyster and mussels.
There are fears that climate change could lead to a similar pattern beginning in Scotland.
Experts from SNH have warned that if the species arrive, they will be extremely difficult and costly to remove.
Already Scotland has problems with existing invasive species, such as the grey squirrel, Japanese knotweed and Rhododendron ponticum.
According to Dr Manson, every effort must be taken to keep the creatures out.
The said they were most likely to be spread by people, on boating or fishing gear, and she urged vigilance.
"All four species are already found in England, Wales and Ireland, and the pattern tends to be that when they are found there they spread north.
"We need to try to stop them arriving. Once they have arrived it's very difficult to do anything about them."
She urged fish farmers and boat owners to keep their gear clean and avoid moving equipment from one area to another.
Robin Payne, invasive non-native species co-ordinator at SNH, said: "These things are knocking on our door and we have to do what we can to keep them out."
SPECIES TO FEAR IN THE OCEANSColonial tunicateMat-like organisms that have been invading coastal waters in many countries. They form yellowish colonies that smother stationary objects. Transported in the ballast water of ships, or on the hull.
Chinese mitten crabNative to east Asia but has arrived in Britain, probably in the ballast water of ships. Adults live in freshwater and migrate to coastal regions to breed. A voracious predator that poses a threat to many native species, such as the crayfish. Also damages river banks and fishing nets.
Slipper limpet Native to North America. Probably arrived in England with the oyster trade. Competes with native molluscs and can be a serious pest on oyster beds. Reproduces quickly.
Pacific oysterFarmed in the UK since the 1920s but previously thought unable to breed here. Several populations of escapees from oyster farms are now found on the British coast. Fears it threatens native species, particularly mussels.
