Invasive Seaweeds and Hull Fouling Species

Sargassum horneri - Visit algaeBASE for full scientific classification. 

Sargassum horneri. © 2009 Jessie Altstatt.

• Annual brown algae, up to about 15 feet long.
• Small, fern-like leaf blades on wiry "stems" with many small air bladders.
• Forms very dense groves.

• Occurs in the intertidal zone and down to depths of 100 feet.

• Native to warm seas in Japan and Korea.
• Extensive natural dispersal capabilities via drifting fragments.
• Can spread by attaching to vessel hulls or by drifting.
• Invasive in Baja California, Mexico, southern California, and the California Channel Islands.
• First reported in California in 2003.

• Capable of self-fertilization.
• Young plants grow from embryos released from numerous, conspicuous, chili pepper-shaped reproductive structures.
• Completes its life cycle in approximately one year.

• Spreads quickly.
• Areas in southern California currently dominated by this species that thrives in warm water conditions.
• Competes with natives for space and light.

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