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Didemnum vexillum

Tunicates Home | Ciona savignyi | Styela clava | Didemnum vexillum
Report a sighting to WDFW: (360) 902-2700
Don't forget to report it on your survey form too!

Didemnum vexillum on the dock near the boat ramp at
Shilshole Bay in Seattle
- photo by Janna Nichols

What's the latest news about Didemnum vexillum?

  • Until recently, Didemnum vexillum in our area was referred to as Didemnum sp. However, new studies (Lambert, 2009; Stefaniak et al., 2009) have shown that it is Didemnum vexillum, and that it most likely originated in Japan. This website has been updated to reflect that change.
  • REEF members Rhoda Green and Karlista Rickerson found Didemnum vexillum covering many areas on the undersides of Dockton Park marina on Vashon Island in Feb 2008. They organized a volunteer project to remove much of it. WDFW staff divers also experimented with using wraps and vinegar (acetic acid) sprays to kill the Didemnum vexillum under this dock.
  • REEF member Rhoda Green found three patches of Didemnum vexillum at the public boat ramp near Shilshole bay in Seattle Sept 2006. All of these were removed March 2007.
  • REEF member Mary Jo Adams found Didemnum vexillum on rocks at Larabee State Park in Washington. WDFW staff has now gone out and removed this patch.
  • Didemnum vexillum has been successfully managed at Edmonds Underwater Park (eradicated)
  • Didemnum vexillum is growing in Hood Canal near Shellfish farms, Dabob Bay.
  • REEF AAT member Stan Kurowski and diver Frank Poole both sighted Didemnum vexillum on dives in British Columbia
  • Didemnum vexillum dies back when covered with Saran Wrap type plastic and subjected to increased salinity. There are other methods of removal that WDFW is using, including acetic acid.
  • Didemnum vexillum does not grow in the winter, and in fact dies back a bit during that time period.

Didemnum vexillum surrounds a Plumose Anemone. Note the channels and how the
outflow holes for the colony are starting to form 'drips'. - photo by Janna Nichols

What is this critter?
The species we are concerned about is
Didemnum vexillum. It was originally a European species and is now found in New England and California. But most alarmingly has been found in Edmonds Underwater Park as well as Hood Canal.

When was it first found in our area?
The first sightings of these colonial tunicates were at Edmonds underwater park. Spotted back in March 2004 by NOAA employee and marine biologist Kinsey Frick (who had seen this nasty critter in full swing on the East Coast), it grew rapidly by October 2004.

What's the big deal?
Didemnum vexillum is a non-native, colonial tunicate species that is an aggressive invader and a threat to a variety of marine life including our commercial shellfish fisheries. It has no natural predators in our area, since it creates metabolic toxins, and grows rapidly in size, taking over underwater real estate and smothering out other native species. It has also invaded other areas, including the East Coast, New Zealand, and the Prince Edward Islands, where it's a huge problem.

Didemnum vexillum surrounding a Plumose Anemone. I found a small sculpin living
underneath this loosely attached patch. - photo by Janna Nichols

Should I get a sample or touch it?
Touching it can spread it to other dive sites via your dive gear, or by simply breaking off pieces of it that will drift in the current and start new colonies. Try to take a photo if you can! Then report it.

What does this critter look like? Give me the SHORT answer!
Yellowish to tan in color. Darker 'channels' can be seen through the somewhat transparent outer layer. Sometimes many small white dots may be seen on the surface. More mature patches take on a 'drippy' look, with long lobes hanging down off the colony. Look carefully at the following photos...

Closeup showing drips that form on more mature colonies.
- photo by Janna Nichols

Yellowish to tan in color. May have many small white visible dots, and darker 'channels' can be seen through the somewhat transparent outer layer.
- photo by Janna Nichols

OK, I'd like more info than that please!

  • Description: As a colonial tunicate the individual animals are connected by a membrane - the tunic. Unlike other tunicates (or "sea squirts") you will not see a pair of openings on the outer surface.
  • Color: Seems to be a yellowish to tan color in the northwest.
  • Size: Individual animals are small, colonies can get very large. The colony found at Edmonds was about 6 feet by 6 feet. The Shilshole patches were about 3-4 feet across.
  • Habitat: Hard substrates: wood and metal pilings, dock structures, moorings and ropes, chains, boat hulls, tires. It likes artificial reef habitat.
  • Depth: Intertidal to shallow subtidal in our area so far. Usually we see in very shallow water - less than 20 feet.
  • Similar looking species: many of our local sponges
  • Gretchen Lambert, an ascidian biologist who has tracked this species worldwide, provided this description: "Each zooid has 2 siphons but only the incurrent one opens on the surface of the tunic so in this species you won't see paired openings; the excurrent siphon of each zooid opens at the side, into a spacious chamber inside the colony. Here and there at the surface are large round transparent openings which are the common atrial openings from which the waste products and tadpoles are released. By combining the excurrent water of many zooids, a sufficient current is produced to carry these products away. Thus on the surface one will see many randomly spaced tiny incurrent openings, and here and there a large atrial opening."
  • Many small white dots can be seen on the surface - (these are tightly packed bundles of calcium carbonate spicules). These are not always apparent to divers underwater.
  • Channels through which water travels inside the colony can be seen just under the outer layer.
  • May take on a variety of forms: flat mats, structures with projections and beard-like lobes, or long stringy lobes or "ropes"

A Painted Greenling sits atop a mass of Didemnum vexillum - Photo by Frank Poole

On the lighter side - Possible uses for removed Didemnum vexillum....

Janna models Didemnum as a fake beard

Rhoda contemplates taking a bite out of Didemnum

Valerie demonstrates uses for the gag and joke shop market

More photos of invasive tunicates are on this website

For more info on this colonial tunicate see:

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Tunicates Home | Ciona savignyi | Styela clava | Didemnum vexillum
Report a sighting to WDFW: (360) 902-2700
Don't forget to report it on your survey form too!