Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)


Moss Landing Marine Laboratories


The Japanese brown alga, Sargassum muticum, was first introduced to the Pacific Northwest coast in the early 1940's, and now occupies intertidal and shallow subtidal areas ranging from southern Alaska to southern Baja California. While several studies have shown that S. muticum can impact communities on a very local scale, broader-scale changes to the communities it invades are largely unknown. I combined a broad-scale survey of tidepools in rocky intertidal areas that have been invaded by S. muticum with a smaller scale experiment that manipulated S. muticum abundance to assess the potential effects of the invader on native tidepool communities. Percent cover of sessile species, counts of mobile species, and species richness estimates were compared between areas with high cover of S. muticum and those where the invasive alga was absent (either naturally absent or experimentally removed). There was general agreement between the survey and experiment: S. muticum had little or no effect on the communities studied. This was surprising since S. muticum is a visibly conspicuous alga. The results contrast with findings of previous work and indicate that species invasions may have different consequences for different habitats.


Thesis (M.S.) Earth Systems Science & Policy Institute. Moss Landing Marine Laboratories