Invasive Seaweeds and Hull Fouling Species

Spirorbis spp. - Visit ITIS for full scientific classification. 

Spirorbis spp. (small round coils). Photo by Carrie Culver © 2008 Regents, University of California.

• Small, tube-dwelling, marine worms.
• Forms white calcareous (chalk-like) small spiral-shaped tubes, up to 1/8 of an inch wide. 
• When viewed under a microscope, body segments and feather-like tentacles can be seen.

• Common in lower intertidal, and shallow subtidal areas.
• Spiral tubes encrust submerged vegetation including the blades of giant kelp (Macrocystis pyrifera) along the California coast.
• Also found settled on rocks, pier pilings, vessel hulls, shells of other animals, etc. 

• Spread by attaching to vessel hulls, from which larvae swim to settle on surfaces in marinas
• Found worldwide, including throughout California.
• Native range is unknown. 

• Filter-feeder, uses feather-like gill tentacles to capture particles in the water.
• Reproduce sexually by releasing sperm and eggs into the water, where they unite to form swimming larvae.

• The chalky tubes form crusts 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, and very difficult to remove. 

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