Slimy and spreading fast. Shellfish farms face biofouling 'invasion'

Scientists are monitoring dozens of sites in Nova Scotia and southern New Brunswick to see if the latest warm winter in Atlantic Canada accelerated the spread of slimy marine invertebrates.

Six invasive sea squirt — or tunicate — species have become established in Nova Scotia in the last decade. Two more are believed to have arrived.

The creatures cling to anything they come into contact with and have become a major problem in the shellfish aquaculture sector. They are 95 per cent water and heavy, weighing down ropes and increasing shear stress during storms and the risk of lost gear and product.

"There's no doubt in my mind that most of these species are here because of the warming climate," said Claudio DiBacco, a federal research scientist specializing in aquatic invasive species at the Bedford Institute of Oceanography in Dartmouth, N.S.

Tunicates are a sack full of organs and water that are adept at filtering food, reproducing and "biofouling" — accumulating on everything from boats to underwater pipes. When poked or prodded, they shoot water from a siphon — hence the name, sea squirt.

The invasives arrive primarily on vessel hulls and in ballast water discharge.

Tunicates are now a year-round fact of life for Nolan D'Eon, who produces 1.4 million oysters annually on his farm in Argyle, N.S.

"There's some tunicates on the cages. They're very, very small as of right now. But we don't ever let them grow," D'Eon said as he recently examined an oyster cage pulled on board a service boat at a site in Eel Lake.

His solution is to flip each cage upside down for 48 hours and let sun and heat kill the tunicates — but they always come back.

"We have a spawn of tunicates at a time that we've never had before. And they used to all turn green in the winter. In the spring, they were all dead. Now you lift up your cages and they're all alive. They don't die over the winter, which is a lot more work for us," D'Eon said.

The creatures are also unsightly.

"Scraping tunicates off mussels is my life," joked Peter Darnell, a veteran mussel and scallop farmer in Mahone Bay, N.S. "There's just so many of them. They're prolific. They're unbelievable. They'll spawn twice in a season, so you have two cohorts in one year and there's just billions of the things."

To track the spread and survival of invasive tunicates, Fisheries and Oceans Canada monitors between 50 and 70 locations from northern Cape Breton, along the Atlantic coast of Nova Scotia and southern New Brunswick.

Metal plates are suspended below public wharves, aquaculture sites and even inside the marine protected area in the Musquash Estuary near Saint John.