77.4 Friday, Jan. 6 A consumer one-two punch: facilitation and functional diversity prevent reversals in community state ELAHI, R.*; SEBENS, K.P.; Friday Harbor Labs, University of Washington; Friday Harbor Labs, University of Washington email@example.com
Declines in global biodiversity have prompted ecologists to question the relative importance of diversity and identity in the context of species loss. We tested the effects of consumer functional diversity and identity on subtidal rock wall epifauna using two field experiments in the San Juan Islands, WA. In the first, we added urchins to walls every two weeks for three months and demonstrated that urchins control the structure of this community by grazing on sessile taxa, exposing algal crusts and bare rock (together considered ‘space’), and facilitating chitons and other consumers. In the context of diet analyses, we conclude that urchins create space by consuming macroalgae and invertebrate colonies, while chitons maintain available space by grazing primarily on microalgae and diatoms. In the second experiment, we conducted a factorial removal of urchins and chitons from walls every two weeks for the duration of a year. The removal of each functional group in isolation had no effect on the epifaunal community, but the removal of both consumers caused a decrease in space and an increase in clonal ascidians. Together, these experiments suggest that urchins and chitons can be considered functionally redundant in the maintenance of space, but not the creation of space. Facilitation and redundancy among consumers may contribute to the resiliency of urchin-mediated ‘barrens’, even if urchins do not persist.