Invasive Seaweeds and Hull Fouling Species

Hydroides spp. (H. elegans, & H. gracilis) - Visit ITIS for full scientific classification. 

Hydroides spp. Photo by Carrie Culver © 2008 Regents, University of California.

• Small, tube-dwelling, marine worms.
• Attach to hard surfaces by forming long, thick, irregularly coiled, white calcareous (chalk-like) tubes.
• When viewed under a microscope, body segments and feather-like tentacles can be seen.

• Occur in subtidal and low intertidal areas.
• Abundant in marinas, docks, and rocky environments with many hard surfaces.
• Found on a variety of natural and man-made surfaces including: woody debris, shells of other animals, oyster reefs, rocky reefs, pier pilings, vessel hulls, intake lines, canals, etc. 

• Spread by attaching to vessel hulls, from which larvae swim to settle on surfaces in marinas.
• One species, Hydroides elegans, is originally described from Sydney, Australia.
• The exact native origin is assumed to be somewhere in the Indo-Pacific.
• The origin of a close relative, H. gracilis, is Pacific Grove, California.
• Both are found worldwide, including all along the California coast.
• See NEMESIS for a distribution map. 

• Filter-feeders; use 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

• Hydroides elegans is a well-known, dominant fouling species with the potential to outcompete native species for space and food.
• The chalky tubes form heavy 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 are very difficult to remove.

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