Invasive Seaweed on the San Diego Coast

Researching the geographic extent and ecological impacts of invasive marine algae in San Diego

Niko Kaplanis (UCSD) and Jill Harris (SIO)

Map of survey sites along the San Diego coast

San Diego’s coastlines are home to a diverse community of seaweed, including at least three invasive species: Undaria pinnatifida, Sargassum muticum and S. horneri (formerly S. filicinum). Invasive species can dramatically damage ecosystems, for example by taking resources from native species or changing the diet and behavior of animals. It is usually very difficult to eradicate or even control the spread of invasive species, so it is important to monitor invasive species and understand how they may be affecting native ecosystems.

Sargassum agardhianum     Sargassum muticum     Sargassum horneri

         Sargassum agardhianum*    Sargassum muticum*      Sargassum horneri*        .

S. agardhianum is a native species, while S. muticum and S. horneri are invasive.


The brown seaweed S. muticum has existed in southern California since the 1970’s, but U. pinnatifida and S. horneri are newer invaders and less is known about their extent and ecological impact. The goal of this project is to document the geographic extent, habitat distribution, and interaction with native San Diego ecosystems for these two species of seaweed.

If you want to know more, contact the Smith Lab manager at



*Seaweed pictures are courtesy of Rory Driskell