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?
No! 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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