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AN EXPERIMENTAL APPROACH TO ASSESSING TIPPING POINTS ON CORAL REEFS

Coral reefs can switch abruptly from a coral community to one where seaweeds are a major space holder. Effective means to prevent such a shift or restore the coral state can benefit by knowledge of three issues: (1) how much herbivory is needed to prevent the widespread establishment of macroalgae; (2) where ambient herbivory lies in relation to the minimum needed to retain control; and (3) whether there is hysteresis in the herbivory – macroalgae relationship that would hinder reversibility of the state shift. We developed an experimental approach to answer those questions and applied it to reefs surrounding Moorea, French Polynesia. Our design created a gradient in herbivory, which broadly mimicked the effect of variation in fishing intensity on herbivorous fishes. We found that the shape of the herbivory – macroalgae relationship was highly non-linear, with a sharp herbivory threshold below which seaweeds escaped control. Further, the intensity of ambient herbivory in relation to the tipping point varied among reefs; herbivory at some reefs was far above the threshold while at others it was not. Hysteresis also was evident in the relationship, indicating that it took more herbivory to remove seaweeds than to prevent them from becoming established. We also found that reversibility of the state shift, as indicated by the range of herbivory over which hysteresis was detected, varied among reefs. Our experimental approach can be applied to other reef systems, and as such, it can provide a powerful tool to inform resilience-based management strategies.

Authors

Schmitt, R. J., UC Santa Barbara, USA, schmitt@lifesci.ucsb.edu

Holbrook, S. J., UC Santa Barbara, USA, holbrook@lifesci.ucsb.edu

Brooks, A. J., UC Santa Barbara, USA, ajbrooks@ucsb.edu

Adam, T. C., UC Santa Barbara, USA, adam@lifesci.ucsb.edu

Davis, S. L., UC Santa Barbara, USA, samantha.davis@lifesci.ucsb.edu

Details

Oral presentation

Session #:067
Date: 03/02/2017
Time: 14:45
Location: 323 A

Presentation is given by student: No