Damselfish as Keystone Species in Reverse: Intermediate Disturbance and Diversity of Reef Algae

Substrates located within the defended territories of Hawaiian damselfish for 1 year were subjected to intermediate grazing intensity and, as a result, showed greater diversity of algae than substrates either protected within fish-exclusion cages or exposed to intense fish grazing outside territories. Thus, this damselfish enhances local diversity on reefs through "intermediate-disturbance" effects, and is a keystone species that decreases rather than increases overall predation intensity relative to areas where it is absent.