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

Invasive Seaweeds and Hull Fouling Species

Asian Kelp

Scientific Name

Undaria pinnatifida - Visit algaeBASE for full scientific classification. 



  • 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.
Invasion Pathways and Distribution
  • 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.
Life History
  • 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.
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: