Community-wide ramifications of an associational refuge on shallow rocky reefs.

Little attention has been given to associational refuges in ecology, despite their potential for maintaining species diversity and supporting higher trophic levels. Here I show how the colonial anemone, Corynactis californica, creates a refuge for benthic macroalgae and invertebrate fish prey on intensively grazed shallow rocky reefs in the Santa Barbara Channel off southern California, U.S.A. On reefs heavily grazed by sea urchins, benthic macroalgae and invertebrate fish prey were relatively more abundant among Corynactis colonies than adjacent areas lacking the anemone. Results from field experiments showed that Corynactis facilitated the recruitment of macroalgae and tubicolous amphipods in "urchin-barren" areas subjected to intensive grazing. In areas forested by giant kelp (Macrocystis pyrifera), where grazing intensity from urchins was low, Corynactis suppressed algal recruitment but facilitated tubicolous amphipods. A manipulation of fish and sea urchins suggested that grazing by urchins, as opposed to predation from fish (primarily surfperch Embiotocidae), suppressed tubicolous amphipods, and this activity was hindered by the presence of Corynactis. In systems where human activity has intensified herbivory, associational refuges may maintain species diversity and support higher trophic levels.