Invasive Tunicates in Washington State
Report your sighting toWDFW: 360-902-2700
Didemnum sp.
Didemnum in Edmonds Underwater Park
- Photo by Gretchen Lambert
Didemnum is a colonial tunicate that grows in sponge-like mats containing thousands of individual tunicates. Colonies have been found on both the east and west coasts of the United States and Canada. The particular species has not yet been formally compared to other known species that have been found in other parts of the world, and are referred to for now as Didemnum sp. The colonies exhibit a wide range of morphology from low mats encrusting the seabed to long stringy colonies hanging from elevated substrates.
(Below: Didemnum on mussel cage, Okeover inlet, BC. Photo by Gordon King)
Colonies
have been found at 64 sites along the N.E. Coast line of the United States,
and the colony off Georges Bank has grown from approximately six square
miles in November, 2003 to an estimated 90 square miles in late 2005.
Anecdotal reports by fishermen in that region of finding an organism resembling
Didemnum mixed in with mud in their nets go back several decades. However,
current observations of Didemnum in both the Atlantic and Pacific are
found attached to hard substrates. There are also Anecdotal reports by
shellfish growers in Washington and British Columbia that species resembling
Didemnum have been growing on shellfish lines and cages for decades. It
is difficult to ascertain whether these reports are of similar species
that are easily confused with Didemnum, or whether the genus has been
present for a long time, and only recently begun growing rapidly enough
to become considered invasive.
There are several colonies around Vancouver Island, B.C. and on mussel cages in Okeover Bay, B.C. They have also been found at Des Moines Marina, Edmonds Marina, EdmondsUnderwater Park, and on mussel lines in Totten Inlet, and Dabob Bay in Hood Canal.
For more information on invasive tunicates, please go to the PNW Scuba website: www.pnwscuba.com/critterwatchers/invasive.htm
Didemnum
on sunken boat at Edmonds Underwater Park
photo by Kirby Johnson
Report your sighting to WDFW: 360-902-2700
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