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Coral Reefs

, Volume 28, Issue 4, pp 949–957 | Cite as

Connectivity, regime shifts and the resilience of coral reefs

  • Toby ElmhirstEmail author
  • Sean R. Connolly
  • Terry P. Hughes
Report

Abstract

Connectivity of larvae among metapopulations in open marine systems can be a double-edged sword, allowing for the colonization and replenishment of both desirable and undesirable elements of interacting species-rich assemblages. This article studies the effect of recruitment by coral and macroalgae on the resilience of grazed reef ecosystems. In particular, we focus on how larval connectivity affects regime shifts between alternative assemblages that are dominated either by corals or by macroalgae. Using a model with bistability dynamics, we show that recruitment of coral larvae erodes the resilience of a macroalgae-dominated ecosystem when grazing is high, but has negligible effect when grazing is low. Conversely, recruitment by macroalgae erodes the resilience of a coral-dominated ecosystem when grazing is low, leading to a regime shift to macroalgae. Thus, spillover of coral recruits from highly protected areas will not restore coral cover or prevent flips to macroalgae in the surrounding seascape if grazing levels in these areas are depleted, but may be pivotal for re-building coral populations if grazing is high. Fishing restrictions and the re-introduction of herbivores should therefore be a prime conservation objective for preventing undesirable regime shifts. Connectivity by some components of coral reef assemblages (e.g., macroalgae, pathogens, crown-of-thorns starfish) may be detrimental to sustaining reefs, especially where overfishing and other drivers have eroded their resilience, making them more vulnerable to a regime shift.

Keywords

Regime shifts Resilience Recruitment Larval connectivity Herbivory Threshold dynamics 

Notes

Acknowledgments

We thank Matthew Spencer and an anonymous reviewer for their helpful comments and suggestions on the manuscript. This work was supported by the Australian Research Council and a grant from the Packard Foundation to the Resilience Alliance.

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Toby Elmhirst
    • 1
    Email author
  • Sean R. Connolly
    • 1
    • 2
  • Terry P. Hughes
    • 1
  1. 1.ARC Centre of Excellence for Coral Reef StudiesJames Cook UniversityTownsvilleAustralia
  2. 2.School of Marine and Tropical BiologyJames Cook UniversityTownsvilleAustralia

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