Local News

Looking for solutions to Sitka's sea squirt invasion



Dvex (Didemnum vexillum) was discovered last summer in Sitka during a citizen-science project called “Bioblitz,” a collaboration between the University of Alaska, the Smithsonian Institution, ADF&G, USF&W, the Sitka Tribe, and the Sitka Sound Science Center. This summer, researchers have returned to Sitka to try and learn if Dvex has spread outside of Whiting.

Over the past several days, teams of Bioblitz volunteers placed over 200 test plates in intertidal areas along the road system.

Linda McCann, with the Smithsonian Environmental Research Center, heads the project. KCAW’s Robert Woolsey caught up with her on the Samson barge dock. McCann, UAS biology professor Marnie Chapman, and US Fish & Wildlife invasive species specialist Kimberly Holzer, were patiently setting test plates amid the din of rock-loading operations for Sitka’s airport expansion.

“So we’re out here right now deploying some collecting devices. This is a really high-tech piece of scientific equipment. You can write about it – a piece of plastic attached to a brick. This was designed because we know Dvex and other invasive species commonly settle on artificial, or manmade, substrate. This will fit under a microscope quite easily, we can take it on and off. So it hangs like this at approximately a meter below the surface of the water, and we’ll leave it out for three months. We’re coming back in September and we’ll hopefully find that it’s not at any of these other sites. During the Bioblitz we had volunteers out surveying a lot of the sites that we’re doing today, and they didn’t find it. But, you can only see so far down from a dock. This will allow us to see what’s subtidal.”

KCAW – “What’s the next step for an invasive like this? Is there a strategy for reducing it or eliminating it that anybody is even discussing at this point?”

McCann – “Absolutely. The first step, as we saw it, was to document where it already was, because we can’t effectively manage or eradicate anything if we don’t know the extent of the infestation. So we’ve been focused on that this year. And also drafting potential plans and options for any kind of management that we might pursue. The next step is to figure out what we can do to get rid of it. So this trip we initiated an experiment out in Whiting Harbor where we tested different kinds of eradication methods including acetic acid, or vinegar; bleach, or chlorine; low dissolved oxygen, basically starving the animal of oxygen; drying it out, or dessicating it; and fresh water. So a lot of these things have been tried in different parts of the world to varying degrees of success. We’re trying to find out where the threshold is: Where is the line where you get 100-percent mortality of Dvex? A lot of the literature suggests that you can kill 80-percent of it, but we want to kill all of it. So we want to find where that line is.”

 With over 200 test plates in the water at 11 locations around Sitka, the hanging bricks are not hard to find. Each is also marked with a large, yellow plastic plate identifying it as the property of the Smithsonian. If the test plates are disturbed, scientists could lose valuable information about the spread of Dvex.

Currently, there is no statutory authority for the state to close waters to prevent the spread of invasive marine organisms. The agencies attempting to contain the infestation are asking for the voluntary cooperation of the public to keep vessels out of Whiting Harbor. Dvex easily fragments, and can be spread easily on an anchor, boat hull, or the sole of a boot.
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