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The combined effects of dispersal and herbivores on stable states in coral reefs


Theory and empirical work suggest that coral reefs may exhibit alternative stable states of coral versus macroalgal dominance. However, it is unclear how dispersal of coral and macroalgae among reefs might impact this bistability and the resilience of the coral-dominated state. We develop a mathematical model to investigate how reef cover dynamics are affected by (1) coral and macroalgal dispersal between two reefs and (2) heterogeneous grazer abundances. We find that at low coral and macroalgal dispersal levels, a new type of stable state emerges with both coral and macroalgae present. Furthermore, we show that a reef abundant with coral and grazers can support a coral-dominated stable state in a second reef depauperate of grazers by dispersal of coral larvae. These results help explain previous empirical findings on reefs once thought to be incongruent with traditional coral-macroalgal alternative stable states theory—such as intermediate coral and macroalgal cover stable states and high coral-low grazing scenarios. Our findings indicate that changing dispersal levels (e.g., due to climate change, reef degradation) between reefs changes the possible stable states and the grazing rate at which the coral-dominated state is predicted to be stable. This work demonstrates the relevance of accounting for the level of dispersal among coral reefs or other bistable ecosystems when designing conservation management plans.

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We wish to thank Compute Canada for providing computational resources and Z. Ahmed for his guidance in this process. We wish to thank A. McLeod and E. Tekwa for helpful comments on the project.


This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Canada Graduate Scholarship to A.G. and NSERC Discovery Grants (no. 4922 to M.K. and no. 5134 to M.-J. F.) and Canada Research Chairs to M.K and M.-J.F.

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All authors contributed to the study conception and design. A.G. led the design of the study, ran the model and wrote the first draft of the manuscript. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Ariel Greiner.

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The authors declare no competing interests.

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Greiner, A., S. Darling, E., Fortin, MJ. et al. The combined effects of dispersal and herbivores on stable states in coral reefs. Theor Ecol 15, 321–335 (2022).

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