Excluding consumers leads to divergent coral reef benthic communities during succession

Jamie M. McDevitt-Irwin, Hopkins Marine Station, Stanford University, Pacific Grove, CA, Douglas J. McCauley, Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, CA and Fiorenza Micheli, Center for Ocean Solutions, Stanford University, Pacific Grove, CA

Background/Question/Methods
As communities form and undergo succession after a disturbance, they can converge to a single state (i.e. exhibit low beta diversity across space and time) or diverge to multiple states (i.e. exhibit high beta diversity across space and time), even while experiencing the same environment. Consumers can influence convergence or divergence during succession, but previous research on consumers’ influences yielded conflicting results. On coral reefs, benthic feeding fishes (e.g. corallivores, herbivores) play vital roles in structuring benthic communities, especially after disturbances (e.g. bleaching events, hurricanes). However, little is known about how these consumers influence multi-year community state and beta diversity through space and time after a disturbance. Our study evaluates how consumers influence successional divergence or convergence of coral reef benthic communities. We deployed 180 paired tiles, caged (excluding large fish) and uncaged, at three sites within Palmyra Atoll, a remote marine wildlife refuge, and compared species composition one and three years after deployment. We ask the question: how does the exclusion of benthic feeding fishes influence beta diversity across space and over time during community succession?
Results/Conclusions
Consumer exclusion leads to greater divergence in coral reef benthic communities over three years during succession, with increased beta diversity across space and over time. Our results indicate that benthic feeding fishes play a deterministic role in coral reef benthic community development following a disturbance, with their feeding resulting in more predictable community states, dominated by crustose coralline algae and green encrusting algae. Thus, the loss of benthic feeding fishes, through their overexploitation or from cascading effects of predator removals, may lead to divergent benthic communities during succession that are more stochastically assembled. These results demonstrate that impacts of fishing or other pressures on coral reef fish communities can have cascading consequences for the spatial heterogeneity and temporal variability of entire benthic communities. As coral reefs continue to undergo reassembly after natural and human induced disturbances, we must consider that consumer overexploitation may lead to greater variability of benthic communities and multiple unstable states during succession.