Publication Abstract

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

M.H. Ledlie, N.A.J. Graham, J.C. Bythell, S.K. Wilson, S. Jennings, N.V.C. Polunin and J. Hardcastle

Cousin Island marine reserve, Seychelles has been an effectively protected No-Take Zone (NTZ) 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 from 1994 to 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 dominance of macroalgae following the phase shift, 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.

Reference

M.H. Ledlie, N.A.J. Graham, J.C. Bythell, S.K. Wilson, S. Jennings, N.V.C. Polunin and J. Hardcastle (2007) Phase shifts and the role of herbivory in the resilience of coral reefs. Coral Reefs, 26: 641-653