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

Invasive Seaweeds and Hull Fouling Species

Solitary Sea Squirts or Tunicate

Scientific Name

Ciona spp. (C. intestinalis, & C. savignyi) - Visit ITIS for full scientific classification. 



  • Solitary tunicates ("sea squirts") with cylindrical-shaped bodies that can grow to about 6 inches long.
  • Soft, gelatinous bodies attach to surfaces.
  • Translucent and creamy yellowish-green in color.
  • Their sac-like body is filled with water being brought in through an incurrent siphon (or tubular opening).
  • They filter-feed on particles brought in with the water current, and push waste water back outside the body through the excurrent siphon.
  • Marine environments.
  • Occurring in low intertidal to subtidal areas.
  • Found attached to a variety of surfaces including rocks, woody debris, and vessel hulls in marinas. 
Invasion Pathways and Distribution
  • Spread by attaching to vessel hulls, from which larvae swim to settle on surfaces in marinas.
  • Very broad global distribution, and native ranges are difficult to determine.
  • C. intestinalis appears to be native to the North Atlantic, and C. savignyi to Japan and possibly Alaska.
  • Non-natives in California.
  • See NEMESIS for distribution maps. 
Life History
  • Pumps water through its siphons and filters food particles from the water.
  • Reproduce sexually by releasing sperm and eggs into the water, where they unite to form swimming larvae.
  • 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.
  • Filter large amounts of water, thus reducing amount of food available for native species. 
References and Useful Links

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

Top of page

Webmaster Email: