Variation in strong interactions in the intertidal zone along a geographical gradient: a Washington-Alaska comparison

Abstract

Identical and simultaneous experiments involving the removal of an abundant herbivore, the chiton Katharina tunicata, were performed in the low intertidal zone in Washington and southeast Alaska. While in Washington this manipulation resulted in dramatic changes in community structure, in Alaska there was little coupling between K. tunicata and other community components over the same 3 yr interval. A persistent intertidal kelp bed developed in Washington in the absence of K. tunicata, whereas in Alaska kelp abundance was highly variable, and unrelated to chiton abundance. This difference was probably attributable to the predominance of a perennial kelp in Washington and an annual kelp at the Alaskan site. Limpets declined in abundance following chiton removal in both regions, but the increase in abundance and diversity of other algae that occurred in Washington did not take place in Alaska. Our experiments show that the presence of a strong interaction in one region does not guarantee its existence in another, even if community composition is very similar in the 2 locales.