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You are here: Home / Aquatic Species / Species Profiles / Sea Squirt
Aquatic Species
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Sea Squirt

Sea SquirtScientific name: Didemnum vexillum Kott, 2002 (Stefaniak et al. 2009)

Common names: Sea squirt, ascidian, colonial tunicate, compound sea squirt, carpet sea squirt

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Selected Resources

Native To: Unknown, possibly Japan (Lambert 2009)

Date of U.S. Introduction: First confirmed sighting in 1993 (Lambert 2009)

Identification of this species has been problematic. For more information, see:

Means of Introduction: Introductions likely due to shipping (either via hull or sea chest fouling) (Lambert 2009)

Impact: Forms dense colonies that can smother native species (Bullard et al. 2007)

Current U.S. Distribution:

  • Coastal New England, Coastal Pacific Northwest



  • Carpet Sea Squirt (or select Play button below)
    Great Britain Non-Native Species Secretariat. (YouTube).

Selected Resources:


Didemnum Tunicate
Narragansett Bay Research Reserve. Coastal Training Program. Rhode Island Marine & Estuarine Invasive Species Site.

Sea Squirt
Northeast Aquatic Nuisance Species Panel.

The Exotics Guide: Non-native Marine Species of the North American Pacific Coast (Revised Sep 2011) - Didemnum sp. A
San Francisco Estuary Institute; Center for Research on Aquatic Bioinvasions.

Invasive Species Compendium - Didemnum vexillum
CAB International.
Taxonomy; Identification/Description; Impacts; Life Cycle; Habitat; Distribution; Controls

Global Invasive Species Database - Didemnum spp. (tunicate)
World Conservation Union. Invasive Species Specialist Group.


Genus Didemnum - Marine Invasive Species
DOI. USGS. Woods Hole Science Center.

Invasive Species Alert: Colonial Sea Squirt (Apr 2011; PDF | 3.44 MB)
Smithsonian Environmental Research Center. Marine Invasions Research Lab.

Invasive Exotic Colonial Sea Squirt
New South Wales Department of Primary Industries (Australia).


Invasive Species - Didemnum Tunicate (Didemnum vexillum)
Alaska Department of Fish and Game.

Invasive Tunicate Species Management Program
Washington Department of Fish and Wildlife.


Introduced Species Summary Project - Sea Squirt
Columbia University. Center for Environmental Research and Conservation.

Colonial Tunicate / Sea Squirt
Texas State University System. Institute for the Study of Invasive Species.


Invasive Tunicate in Washington State
Reef Environmental Education Foundation.


Bullard, S.G., G. Lambert, M.R. Carman, J. Byrnes, R.B. Whitlatch, G. Ruiz, R.J. Miller, L. Harris, P.C. Valentine, J.S. Collie, J. Pederson, D.C. McNaught, A.N. Cohen, R.G. Asch, J. Dijkstra, and K. Heinonen. 2007. The colonial ascidian Didemnum sp. A: Current distribution, basic biology and potential threat to marine communities of the northeast and west coasts of North America. Journal of Experimental Marine Biology and Ecology 342(1):99-108.

Lambert, G. 2009. Adventures of a sea squirt sleuth: unraveling the identity of Didemnum vexillum, a global ascidian invader. Aquatic Invasions 4(1):5-28.

Stefaniak, L., G. Lambert, A. Gittenberger, H. Zhang, S. Lin, and R.B. Whitlatch. 2009. Genetic conspecificity of the worldwide populations of Didemnum vexillum Kott, 2002. Aquatic Invasions 4(1):29-44.

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Last Modified: Mar 20, 2015
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