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European Sea Squirt

Ascidiella aspersa

Report it

If you think you have found an aquatic invasive species:

  1. take photos
  2. note:
    • the exact location (GPS coordinates)
    • the observation date
    • identifying features
  3. contact us to report it

Identifying features

  • Body egg shaped, semi-translucent. Firm, slightly bumpy surface;
  • May reach 5 cm in length;
  • Color grayish with pinkish hue;
  • Solitary but can develop dense aggregations.
European sea squirt is a tall solitary tunicate that is often found in dense unfused aggregations.

European sea squirt is a tall solitary tunicate that is often found in dense unfused aggregations.

Similar species

Sea grapes, sea potatoes and sea peaches are native solitary tunicates, but they are shaped differently and may be found individually or in small clumps. For example, sea grapes are spherical with two siphons close together at the top.

Among invasive species, European sea squirts may be mistaken for vase or clubbed tunicates but their shape, tunic surface and color are different. In addition, the European sea squirt has one siphon on top and one on the side (at approximately one third of its body length).

Where it has been found

This European Sea Squirt was first introduced in New England in the 1980’s and can now be found in most of the Gulf of Maine. It was first detected on the south shore of Nova Scotia in 2012.

Ecological and economic impacts

Potential impacts of a European sea squirt invasion are widespread. The species grows rapidly and can tolerate a wide variety of conditions, making it a major biofouling pest. This species may outcompete other organisms for food and space, thereby altering the natural community dynamics. Moreover, it threatens aquaculture, fishing and other coastal and offshore activities. The European Sea Squirt leads to an increase in the weight of the aquaculture cultivation gear, causing work to be more demanding. Which result in an increase of the operating costs for shellfish producers and processors.

Origins and mode of arrival

Native to the Mediterranean Sea and occurs throughout Europe.

European sea squirt was most likely introduced to North America through hull fouling and/or ballast water.

Government action

Scientific research

Fisheries and Oceans Canada is studying the green crab population to improve its understanding of how it reacts and adapts to Canadian conditions.

For further information


  • Mackenzie, A.B. 2011. Biological synopsis of the compound sea squirt (Diplosoma listerianum). Can. Manuscr. Rep. Fish. Aquat. Sci. 2966: v + 18 p.
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