Positive and Negative Effects of a Threatened Parrotfish on Reef Ecosystems |
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| Authors: | DOUGLAS J MCCAULEY HILLARY S YOUNG ROGER GUEVARA GARETH J WILLIAMS ELEANOR A POWER ROBERT B DUNBAR DOUGLAS W BIRD WILLIAM H DURHAM FIORENZA MICHELI |
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| Institution: | 1. University of California Santa Barbara, Ecology, Evolution and Marine Biology, Santa Barbara, , CA 93106, U.S.A.;2. Red de Biología Evolutiva, Instituto de Ecología AC, , Xalapa, Veracruz, Mexico;3. Center for Marine Biodiversity & Conservation, Scripps Institution of Oceanography, , La Jolla, CA 92083, U.S.A.;4. Department of Anthropology, Stanford University, 450 Serra Mall, Building 50, , Stanford, CA 94305, U.S.A.;5. Department of Environmental Earth Systems Science, Stanford University, , Stanford, CA 94305, U.S.A.;6. Hopkins Marine Station, Stanford University, , Pacific Grove, CA 93950, U.S.A. |
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| Abstract: | Species that are strong interactors play disproportionately important roles in the dynamics of natural ecosystems. It has been proposed that their presence is necessary for positively shaping the structure and functioning of ecosystems. We evaluated this hypothesis using the case of the world's largest parrotfish (Bolbometopon muricatum), a globally imperiled species. We used direct observation, animal tracking, and computer simulations to examine the diverse routes through which B. muricatum affects the diversity, dispersal, relative abundance, and survival of the corals that comprise the foundation of reef ecosystems. Our results suggest that this species can influence reef building corals in both positive and negative ways. Field observation and simulation outputs indicated that B. muricatum reduced the abundance of macroalgae that can outcompete corals, but they also feed directly on corals, decreasing coral abundance, diversity, and colony size. B. muricatum appeared to facilitate coral advancement by mechanically dispersing coral fragments and opening up bare space for coral settlement, but they also damaged adult corals and remobilized a large volume of potentially stressful carbonate sediment. The impacts this species has on reefs appears to be regulated in part by its abundance—the effects of B. muricatum were more intense in simulation scenarios populated with high densities of these fish. Observations conducted in regions with high and low predator (e.g., sharks) abundance generated results that are consistent with the hypothesis that these predators of B. muricatum may play a role in governing their abundance; thus, predation may modulate the intensity of the effects they have on reef dynamics. Overall our results illustrate that functionally unique and threatened species may not have universally positive impacts on ecosystems and that it may be necessary for environmental managers to consider the diverse effects of such species and the forces that mediate the strength of their influence. Efectos Positivos y Negativos de un Pez Loro Amenazado Sobre Ecosistemas Arrecifales |
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| Keywords: | benthic Bolbometopon coral function diversity management simulation threatened species Bé ntico Bolbometopon coral diversidad especie amenazada funció n manejo simulació n |
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