Solitary and Colonial Tunicate Species | Region 10 | US EPA

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Solitary and Colonial Tunicate Species

Tunicates are simple filter feeding organisms that often resemble sponges. They may be either large solitary individuals, or colonial individuals that spread like a dense mat over large areas, encrusting everything it their path. Like many other invasive organisms, tunicates reproduce in large numbers, and their settling larvae will blanket all available surfaces. As they grow, they smother or push out the other native species. No other species is known to eat or overgrow them. Likely introduction pathways include ballast water, ship hulls, and aquaculture.

Status in the Pacific Northwest. Several marine species of both types are of concern in the Northwest. The solitary tunicates Steyla clava and Ciona savignyi and a colonial tunicate, Didemnum sp., have been discovered in various sized patches in a number of areas within Puget Sound. Steyla Clava heavily infests several marinas; Pleasant Harbor marina alone supported thousands of pounds of them. Didemnum and Ciona are located in scattered patches around the Sound. These must be controlled; Didemnum now covers over 80 square miles of the Georges Bank, one of the most important New England fishing grounds, and it is still expanding there. We don’t want this situation in Puget Sound! Other tunicate species not yet observed here, but that would be of concern if they are discovered, include colonial tunicates Botryllus schlosseri and Botrylloides violaceus and the solitary tunicate Molgula manhattensis .

The Washington Department of Fish and wildlife (WDFW) has established a Tunicate Response Advisory Committee to study and recommend actions to deal with tunicate invasions, and the Puget Sound Partnership has entered into a $300,000 contract with WDFW for tunicate management that includes surveying Puget Sound for infestations, developing a tunicate management plan, and researching eradication methods. The management plan, when completed, will be available on the WDFW website. The WDFW 2007 Tunicate Report to the Legislature summarizes actions taken and recommends future actions. WDFW is also formally listing the three species as Prohibited Species, which makes it illegal to buy, sell, or otherwise possess or introduce them, and therefore allows the department to employ enforcement action if needed to control them.

Chemical control in aquatic habitats is regulated under the NPDES permit program, which EPA has delegated to the Department of Ecology. To allow use of chemicals in rapid response situations, Ecology has begun developing a general permit to cover non-native invasive aquatic animal and marine algae control activities that result in the discharge of chemicals and other control products into WA fresh, brackish, marine, and estuarine waters. For permit information, go to

What can you do? Learn to recognize these tunicates, and report any sightings to the appropriate office.
In Washington: 1-360-902-2700 (ANS Coordinator)
In Oregon: 1-866 INVADER (hotline)
In Alaska: 1-877 INVASIVE (hotline)

The links provided may be outside the domain.

Solitary Tunicates

Puget Sound Tunicate Report to legislature

WDFW Tunicate Management Plan
(Contact WDFW)

Tunicates in WA State

Tunicates of the West Coast- Photos

Steyla Clava Fact Sheets

Ciona savignyi Fact Sheets

Molgula manhattensis Fact Sheets

Colonial Tunicates

Didemnum sp. Fact Sheets

Botryllus schlosseri Fact sheets

Botrylloides violaceus Fact sheet

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