California Aquatic Invasive Species (AIS)
University of California
California Aquatic Invasive Species (AIS)

Invasive Seaweeds and Hull Fouling Species

Colonial Sea Squirt or Tunicate

Scientific Name

Diplosoma listerianum - Visit ITIS for full scientific classification. 

Description

 

  • Colonial tunicate ("sea squirt") with small, cylindrical-shaped individuals immersed in a communal structure.
  • The colony forms flat, thin, mucous-covered sheets, up to 2 inches wide that grow on a variety of surfaces.  
  • Translucent appearance.
  • Can be milky yellow, or greenish, with white or grey colored spots.
  • Feed through incurrent siphons (tubular openings) that bring food particles in with the water current.
Habitat
  • Subtidal marine environments.
  • Attach to a variety of surfaces including rocks, shells, other marine animals, seaweeds, buoys, lines, woody debris, vessel hulls, etc. 
Invasion Pathways and Distribution
  • Spread by attaching to vessel hulls, from which larvae swim to settle on surfaces in marinas.
  • Originally described from the English Channel.
  • However, there are many similar species and it has a very broad global distribution, therefore the exact native origin is difficult to determine.
  • It appears to be introduced along much of the North American coast, including California.
  • See NEMESIS for distribution maps. 
Life History
  • Filter-feeder. 
  • Reproduces asexually by budding or sexually by releasing sperm and eggs into the water, where they unite to form swimming larvae.
Impacts
  • Colony forms a dense aggregation on boat hulls.
  • This fouling growth roughens the hull’s surface, creating friction or “drag” that slows sailboats and increases fuel consumption for powerboats.
  • Tolerant of copper in antifouling paint.
References and Useful Links

For references by category and links to other useful AIS sites see our LEARN MORE page.

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