Didemnum Tunicates / Sea Squirts (Didemnum vexillum)



Didemnum Tunicates/Sea Squirts
Didemnum vexillum

 Photo courtesy of Rohan Holt-CCW

No  NBN location data available



  • Marine habitat changes through overgrowth of sedentary benthic organisms such seaweed, scallops, mussels, and oysters.
  • Produces chemicals that deter most fish and other animals.
  • Increases fouling of underwater structures such as docks, moorings, and boat hulls.
  • Increased fouling also interferes with fishing, aquaculture, and other coastal and offshore activities including underwater archaeological sites such as ship wrecks.
  • Vectors for introduction are uncertain but fouling of ocean going vessels and/or contamination of aquaculture produce are possibilities.
  • Once established, it can spread rapidly by both sexual reproduction and asexually by fragmentation of the colonies.
  • Known growth on sedentary and mobile organisms such as crabs means it can become established through movement of shellfish for the aquaculture industry.
  • Fouling on sea going vessels



Do not introduce into the wild. Take measures to ensure there is not transport of bilgewater between waterbodies and inspect boat hulls, trailers, outboard engines, I/O drive legs, water intakes, exhausts and trailers for infestation before moving between waterbodies.

Physical Control


Chemical Control


Biological Control



Non Native Species Secretariat identification guide

Non Native Species Secretariat Fact Sheet

Invasive Species Ireland Fact Sheet

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