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

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



Selected Resources:

Council or Task Force

Stop the Invasion: Invasive Tunicate (Jun 2016; PDF | 484 KB)
Washington State Recreation and Conservation Office. Washington Invasive Species Council.
See also: Outreach and Educational Materials - Invasive Species Fact Sheets for more resources


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

NEANS Panel Online Guide - 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.

TISI Inventory - Colonial Tunicate / Sea Squirt
Texas State University System. Texas Invasive Species Institute.

Invasive Species Compendium - Didemnum vexillum
CAB International.

Global Invasive Species Database - Didemnum spp. (tunicate)
IUCN. Species Survival Commission. Invasive Species Specialist Group.

Alien Species Alert: Didemnum vexillum Kott, 2002: Invasion, impact, and control (Feb 2017; PDF | 1.67 MB)
International Council for the Exploration of the Sea.
See also: Alien Species Alert for more information

Federal Government

Marine Nuisance Species - Species Didemnum vexillum
DOI. USGS. Woods Hole Coastal and Marine Science Center.

National Exotic Marine and Estuarine Species Information System (NEMESIS) - Didemnum vexillum
Smithsonian Institution. Smithsonian Environmental Research Center. Marine Invasions Research Lab.

International Government

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

State Government

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

Aquatic Invasive Species: 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.

Invasive Tunicate Identification Card: Colonial Tunicate and Club Tunicate (PDF | 1.6 MB)
University of Washington. Washington Sea Grant Program.



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: Jul 17, 2018
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