HALIFAX — A slew of goopy and gross sea creatures is making its way into or near Canadian waters, leaving a slimy trail that is menacing mussels and threatening rich fishing grounds.

Known as the tunicate, the unappealing sea life has slithered into waters around several provinces, including Prince Edward Island, Nova Scotia and British Columbia, fouling mussel farms and raising anxiety over future invasions. One in particular - didemnum - is alarming marine biologists, who fear the species could get into Canadian waters and smother lucrative scallop beds under a pancake-like batter that chokes off life.

"It's a pretty big problem," Judy Pederson, a marine biologist at the Massachusetts Institute of Technology, said from Cambridge, Mass.

"Where it's found, it can be very, very abundant because once it appears, it tends to spread pretty quickly."

A team of scientists scanned waters on the Canadian portion of the Georges Bank off southern Nova Scotia this past summer to see if the didemnum had spread from the U.S. section of the bank.

Page Valentine, who led the mission, said the tunicate infestation on the northern edge of the bank was limited to an area in American waters near the U.S.-Canada boundary, totalling 228 square kilometres.

But he warned that the Canadian portion could be next if the creature heads north into valuable fishing grounds and scallop beds.

"We expect areas in Canada near the boundary will be the most vulnerable if the tunicate spreads," said Valentine, a scientist with the U.S. Geological Survey in Woods Hole, Mass., who is analyzing the data to see if the tunicate could alter seabeds by forming a barrier between fish and their prey.

If it does, it could be a major problem for fishermen, since the creature, which measures one to two millimetres individually and attaches itself to rocky bottoms, spreads quickly.

The tunicates have recently shown up in two locations in British Columbia and in shallow waters in Cobscook Bay, Maine, just outside the New Brunswick border, alarming fishermen who fear it might move into their fishing grounds.

Larry Harris, a professor at the Center for Marine Biology at the University of New Hampshire, dove at the site in the summer, spotting scattered groupings of the icky blob within minutes.

"Most of the colonies were the size of a dessert dish - about 10 to 15 cm across, but some were up to 30 centimetres in diameter," he said.

Harris said the blob isn't yet in Canadian waters likely because water temperatures are usually colder than it likes.

"It is probably only a matter of time until some ship or pleasure craft brings it to the outer coast of Nova Scotia or Prince Edward Island where summer water temperatures are very favourable for its success."

Another danger, Harris warned, is that didemnum reproduces very easily and could spread far and wide if draggers rake over it and disperse it.

Fishermen on the Atlantic coast have been dealing with different kinds of tunicates for years in mussel, oyster and scallop operations.

Dale Cook had to dispose of more than $140,000 worth of mussels several years ago when he hauled up his catch to find it dripping in the so-called vase tunicate.

It was one of the first recorded cases in the area and little was known about the creature, but Cook said most mussel farmers are now dealing with the nuisance species.

"All of us got it now," he said from his boat off Lunenburg, N.S., describing the life form as a gelatinous, cigar-like tube that weighs down the mussel growing structures.

"You never know from one year to the next what's going to happen."

Cook said he almost got out of the business when the tunicates hit, but instead he downsized and now has to continuously monitor his stocks to keep the creatures in check.

The spread of these species has led to heightened interest in scientific and fishing communities, with marine institutes and government departments in Canada and the U.S. paying more attention to them.

In addition to B.C., didemnum has been found in New Zealand, the Netherlands, France, California and the eastern U.S. seaboard, but scientists haven't determined if they are all the same species.

In Canada, the federal Fisheries Department is monitoring the different species.

"There are a fair number of people trying to figure out if there are ways to identify ways of controlling the species," said Pederson.