Invasive Seaweeds and Hull Fouling Species

Undaria pinnatifida - Visit algaeBASE for full scientific classification. 

Undaria pinnatifida. Photo by Carrie Culver © 2008 Regents, University of California.

Undaria pinnatifida. © 2007 Jessie Altstatt

• Large golden-brown seaweed, 3 to 9 feet long.
• A root-like structure, the holdfast, attaches the plant to hard surfaces.
• Mature blades have finger-like marginal lobes.
• A spiral, ruffled reproductive structure, the sporophyll, grows between the holdfast and the blade.

• Found in temperate coastal waters in low intertidal and subtidal areas.
• Grows on a wide range of natural and man-made structures, often forming dense stands.

• Grown for human consumption in its native range in Japan, China and Korea.
• Transported accidentally through oyster aquaculture and attached to vessel hulls.
• Now found in Australia, New Zealand, southern Atlantic and Mediterranean Europe, Argentina, Baja California, Mexico and California, where it occurs in ports and harbors from San Diego to San Francisco; one offshore population at Santa Catalina Island.
• First reported in California in 2000.

• Annual, with two independent life stages.
• The sporophyte stage (the large kelp), present in the spring and summer months, releases spores that settle and develop into a microscopic gametophyte stage that produces sperm and eggs.
• Fertilization results in a new sporophyte, with holdfast and blade.

• Grows quickly to a large size, and may compete with native seaweeds.
• May become a pest, fouling harbors and damaging infrastructure.

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