Document: KEV-3-84-13

Effects of the invasive seaweed Sargassum muticum in a native algal community.

BRITTON-SIMMONS, K.H.*

The University of Chicago, Chicago, IL 60637 USA ¹

Abstract:
Exotic species impact native ecosystems at all levels and are a leading threat to biodiversity. The Japanese seaweed, Sargassum muticum, was introduced to the northwest coast of North America in the 1940's and subsequently expanded its range south as far as Baja California. Many of the reports of its impacts on native flora and fauna in the northeast Pacific are anecdotal or based on indirect evidence. In an ongoing study, I am exploring the impacts of Sargassum on native, subtidal seaweed communities in the San Juan Islands of Washington State. The subtidal algal community in this region is diverse and structurally complex, consisting of a canopy of brown algal species and an understory of red algal species. Field experiments suggest that Sargassum reduces the density and species richness of native canopy seaweeds and reduces the density, but not richness, of understory seaweeds. These effects are variable in space and time and may be influenced by physical characteristics of the habitat. Furthermore, Sargassum grows taller than all but one native canopy species and experiments suggest that light attenuation by Sargassum is an important mechanism underlying the observed impacts.

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This abstract is being presented at: 9:15 AM in session:
Oral Session #37: Phytoplankton.