REPORT Phase shifts and the role of herbivory in the resilience of coral reefs M. H. Ledlie Æ N. A. J. Graham Æ J. C. Bythell Æ S. K. Wilson Æ S. Jennings Æ N. V. C. Polunin Æ J. Hardcastle Received: 7 November 2006 / Accepted: 22 March 2007 / Published online: 17 May 2007 Ó Springer-Verlag 2007 Abstract 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 be- came 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. Keywords Recovery  Coral bleaching  Seychelles  Marine protected areas  Coral reef fishes  Feeding observations Introduction The interaction between natural and anthropogenic distur- bance has undermined the resilience of coral reefs and led to their worldwide degradation (Nystro ¨m et al. 2000; Gardner et al. 2003; Hughes et al. 2003). Coral bleaching is one such disturbance which, through potential enhance- ment by anthropogenic global warming (Reaser et al. 2000), poses a great challenge to coral reef management. While the immediate effects of coral bleaching on reef fish assemblages are largely restricted to species which depend on live coral for habitat or food (reviewed by Wilson et al. 2006), there is evidence that reefs can support abundant and diverse fish assemblages after bleaching as long as reef structure is maintained (Lindahl et al. 2001). However, the longer-term loss of structural complexity can affect recruitment, competition and predation (Buchheim and Hixon 1992; Hixon and Beets 1993;O ¨ hman et al. 1998), leading to declines in species richness (Graham et al. 2006) and numerical abundance (Garpe et al. 2006). Communicated by Ecology Editor P.J. Mumby. M. H. Ledlie (&)  N. A. J. Graham  S. K. Wilson  N. V. C. Polunin School of Marine Science and Technology, Newcastle University, Newcastle-upon-Tyne NE1 7RU, UK e-mail: maryledlie@hotmail.com J. C. Bythell School of Biology, Newcastle University, Newcastle-upon-Tyne NE1 7RU, UK S. K. Wilson Australian Institute of Marine Science, Townsville MC, Townsville, QLD 4810, Australia S. Jennings Lowestoft Laboratory, Centre for Environment, Fisheries and Aquaculture Science, Lowestoft NR33 0HT, UK J. Hardcastle Nature Seychelles, The Centre for Environment and Education, P.O. Box 1310, Roche Caiman, Mahe ´, Seychelles 123 Coral Reefs (2007) 26:641–653 DOI 10.1007/s00338-007-0230-1