Ridding Sitka harbor of invasive squirt is a big challenge

September 26, 2012 

Didemnum vexillum

WASHINGTON DEPT. OF FISH AND WILDLIFE

If you want to eradicate an invasive species, first you have to figure out how to tell if you've killed it. That's one of the challenges for scientists trying to rid Sitka's Whiting Harbor of a non-native sea squirt that some locals are calling "sea vomit" because of its offputting nature. KCAW reports that it probably showed up in Sitka as a hitchhiker on a ship from the south.

Marnie Chapman is an associate professor of Marine Biology with the University of Alaska Southeast in Sitka. Chapman got to see how fast [Didemnum vexillum] colonies can grow first hand. She had been using a mesh bag to transport samples when she noticed a few tiny fragments left behind.

"It was amazing," she said. "In two weeks it was much larger, and two weeks after that it was much larger. In about two and a half months it was huge it covered the whole laundry bag it was dripping down from the laundry bag and dripping down to the bottom below out there at Whiting."

This dripping is the main reason why eradicating D. vex is so difficult. Once a fragment breaks off and lands on a new spot, it can actually seed an entire new colony.

People in Sitka are especially worried that the creature will hurt the area's lucrative herring roe harvest. It's a determined foe: So far, D. vex hasn't been eradicated from any harbor that it has invaded, but divers say it doesn't seem to have spread much since its original discovery in Sitka.

Read more about the battle against D. vex in a two-part series at KCAW: Scientists look for ways to kill Sitka tunicate

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