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Phase shifts and the role of herbivory in the resilience of coral reefs


Cousin Island marine reserve (Seychelles) has been an effectively protected no-take marine protected area (MPA) since 1968 and was shown in 1994 to support a healthy herbivorous fish assemblage. In 1998 Cousin Island reefs suffered extensive coral mortality following a coral bleaching event, and a phase shift from coral to algal dominance ensued. By 2005 mean coral cover was <1%, structural complexity had fallen and there had been a substantial increase in macroalgal cover, up to 40% in some areas. No clear trends were apparent in the overall numerical abundance and biomass of herbivorous fishes between 1994 and 2005, although smaller individuals became relatively scarce, most likely due to the loss of reef structure. Analysis of the feeding habits of six abundant and representative herbivorous fish species around Cousin Island in 2006 demonstrated that epilithic algae were the preferred food resource of all species and that macroalgae were avoided. Given the current dominance of macroalgae and the apparent absence of macroalgal consumers, it is suggested that the increasing abundance of macroalgae is reducing the probability of the system reverting to a coral dominated state.

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Funding for this work was provided by Nature Seychelles under the Global Environment Facility project ‘Improving management of NGO and privately-owned islands of high biodiversity value in Seychelles’, Newcastle University, the British Overseas Development Administration (now Department for International Development), the Leverhulme Trust, the Western Indian Ocean Marine Science Association (WIOMSA) and the Fisheries Society of the British Isles. We thank Nature Seychelles for logistical support and V.R. Johnson and the wardens of Cousin Island for assistance in the field.

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Correspondence to M. H. Ledlie.

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Communicated by Ecology Editor P.J. Mumby.

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Ledlie, M.H., Graham, N.A.J., Bythell, J.C. et al. Phase shifts and the role of herbivory in the resilience of coral reefs. Coral Reefs 26, 641–653 (2007).

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  • Recovery
  • Coral bleaching
  • Seychelles
  • Marine protected areas
  • Coral reef fishes
  • Feeding observations