Controlling the violet tunicate

By Clayton Hunt

FOR THE SOU’WESTER

It seems like something out of a science fiction movie.

It's not very pretty, it's creepy, it's crawly and it's slimy. It arrives from a foreign environment but can adapt very quickly and expand its population quite rapidly in its new habitat. It is aggressive and can displace local native species, and it can definitely be a costly nuisance to human activities in its new area.

However, the Botrylloides Violaceus, or violet tunicate, is not something from a movie. It is an all too real invasive species that was discovered in Belleoram in September 2007 and it can be costly to aquaculture projects in the area, especially mussel operations.

Although the violet tunicate population has grown since its discovery, the species is localized to a very small section of the harbour. Officials from the federal Department of Fisheries and Oceans (DFO) and officials with the Ocean Sciences Centre (OSC) at Memorial University were in Belleoram in mid-March to try and control the spread of the species’ population.

"We will be trying to stamp out the violet tunicate before it spreads around the harbour and to other areas of Fortune Bay,” said OSC employee Philip Sargent.

He noted that the species is located on the hulls of vessels, on wharf pilings and on rocks on the bottom of the harbour. The MUN crew will be using techniques similar to those used in New Zealand and other countries to help eradicate the violet tunicate.

"We will wrap the hulls of infected vessels with a type of wrap and pump in fresh water. The water should turn to slush and kill what's growing on the boats,” said Sargent. "We will place pallet wrap around the wharf pilings to choke out the organisms and we will physically remove smaller rocks from the harbour."

He noted that the work crew is aiming at a success rate of 90 per cent and that officials will come back in the summer to check the situation again.

Dr. Don Deibel, a scientist with OSC at MUN, said that it is very important to all stakeholders in government and industry to control the violet tunicate population.

"The main reason why DFO and OSC officials are in Belleoram…is because the violet tunicate is a quite aggressive invasive species,” he said. “We have to be aggressive in our attempt to remove it from the Belleoram harbour.”

The violet tunicate can be a costly nuisance to mussel growers as the species can grow on mussel shells and on ropes used in mussel operations. According to Deibel, the violet tunicate can cover the shells and ropes so densely that when you haul out of the water, all you would see is a solid mass of the invasive species.

The species would cause a lower meat yield and, because of the extra production cost in removing the tunicate from the lines and mussels, it would add an extra large cost to the operation.

"The violet tunicate can be a real problem,” Deibel said. “Any man-made structure that is in the ocean could potentially be colonized and grown on, and overgrown, by the kind of aggressive space occupying species such as the violet tunicate."

According to the scientist, the violet tunicate discovered in Belleoram may have originated in the Eastern Mediterranean Sea. The species has been found in other areas of the Eastern Atlantic Seaboard such as the Cape Hatteras area, Chesapeake Bay, North Carolina and may be moving up the eastern seaboard due to a slight drop in water temperatures. Belleoram is the only area in Newfoundland and Labrador know to have a population of the violet tunicate.

(Clayton Hunt is a journalist with Transcontinental Media’s Coaster newspaper and a contributor to the Sou’Wester.)