Didemnum vexillum can grow into colonies resembling soft coral. Photo by Vallorie Hodges, Oregon Coast Aquarium.
One of the state’s most feared invasive species has arrived.
The most immediate threat is to our coastal shellfish. The species, known as Didemnum vexillum, can form huge colonies that cover shellfish beds and literally smother them to death.
It competes with shellfish for plankton and eats the larvae of mussels and oysters.
Researchers with Oregon State University say Didemnum vexillum was discovered in Winchester Bay and Coos Bay earlier this year. But they think the organisms may have been established about two years ago.
“It appears that the infestation is growing rapidly,” says Lorne Curran, one of the people who discovered the colony at Winchester Bay in February. Curran does marine life surveys for the diving organization REEF and made a follow up dive this spring.
A colony in Winchester Bay. Photo by Lorne Curran of REEF.
“Where in February I saw mostly one-foot-square colonies, this time I encountered more colonies that were two-foot to three-foot square.” The tunicates were found on both jetty rocks and on some of the mooring lines and “stringers” of an oyster-growing facility in the triangle.”
ODFW is doing a risk assessment and wants to have a plan to combat the invader soon. In a couple of months the coastal waters will be warm enough to allow Didemnum vexillum to begin reproducing and spreading.
“We’re reviewing the literature for successful eradication projects on rocky outcrops or jetties, but we’re not finding a lot,” says Rick Boatner, ODFW’s aquatic invasive species coordinator. “This is new ground for Oregon, and we’ll have to be creative with our solutions.”
Some methods used in other areas include applying a solution of vinegar and bleach to the colonies or smothering them in clear plastic wrap. While that may sound low tech, it can be expensive. Washington State has spent about $850,000 over the past couple of years trying to control the organism in Puget Sound.
It’s believed Didemnum vexillum is from Japan and may have arrived here through the ballast water of ocean going cargo ships.
For more information:
Pacific Northwest Scuba: Didemnum vexillum
Oregon: 100 Most Dangerous Invaders
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