Inhibition of Giant Kelp Recruitment by an Introduced Brown Alga

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Abstract
Following a natural disappearance of the native giant kelp Macrocystis pyrifera, an invasion of the introduced brown alga Sargassum muticum apparently prevented giant kelp recruitment. Experimental removal of adult S. muticum resulted in a significant increase in giant kelp recruitment compared to nonremoval areas. Two requirements for the successful establishment of giant kelp apparently were an absence of S. muticum and the presence of nearby giant kelp adults to supply sufficient spores. Higher densities of giant kelp in removal areas persisted throughout the period when S. muticum dies back to a perennial holdfast. Shading at a critical time in the giant kelp life cycle is suggested as a possible mechanism for the inhibition of giant kelp recruitment.