Sargassum muticum Research

Over half a century ago, a non-native seaweed called Sargassum muticum was accidentally introduced into Washington’s inland waters with oysters imported from Asia. The seaweed invaded the entire region, and can be found in lower intertidal and shallow subtidal rocky habitats throughout Puget Sound, the Strait of Juan de Fuca and the San Juan Islands.

Despite its abundance, not much was known about Sargassum muticum. Because introduced species can radically change the structure and function of native ecosystems and are a leading threat to marine biodiversity in our region, the SeaDoc Society took the initiative to support critical research by Drs. Timothy Wootton and Kevin Britton-Simmons on the seaweed invader. Britton-Simmons and Wootton conducted three years of cutting-edge field and laboratory experiments to better understand the impacts of Sargassum muticum and to discover ways in which we might prevent or slow its spread.

Their research showed that Sargassum muticum out-competes native kelp for light and indirectly harms green urchins. This was an important finding and a big concern because native kelps are an important source of food and provide critical habitat for a huge number of species in the nearshore ecosystem. Also, green urchins have an influential role in structuring shallow subtidal communities in this region and are a commercially important species that is harvested for its eggs (“uni”).

Once they had elucidated the negative impacts of Sargassum, Britton-Simmons and Woottton conducted experiments showing that after manual removal of the seaweed, the native community recovered within about a year, which suggests that Sargassum-induced changes are reversible. While completely eradicating Sargassum muticum is extremely labor-intensive, small-scale removal is possible and can be successful, particularly if focused on target areas such as marine reserves.

Britton-Simmons and Wootton also demonstrated that physical disturbance of kelp beds can help spread the seaweed, so now we know that minimizing disturbance of nearshore kelp forests from human activities can help reduce the spread and consequent damage of Sargassum muticum to native kelps and green urchins. These results are being published in peer-reviewed journals and are being shared with people who manage kelp and other algae.

This project is just one of many ways in which the SeaDoc Society is improving the health of marine wildlife populations.

Thank you for your support,

Kirsten Gilardi & Joe Gaydos