Trophic and benthic responses to no-take marine reserve protection in the Philippines

Abstract

No-take marine reserves are expected to enhance coral reef resilience indirectly through suppression of algal growth and thus maintenance of coral dominance. The mechanism of such enhancement is protection of functionally important herbivorous fishes from harvest. We provide indirect (inferred) evidence of reserves performing this role. We used data on herbivorous fishes, macroalgae and corals collected at one point in time in 15 reserves (range of duration of protection: 0.5 to 11 yr) and at 15 fished sites in the Philippines. Results inferred a 9- and 15-fold increase in density and biomass, respectively, of herbivorous fishes, which coincided with a 13-fold decrease in macroalgal cover inside reserves after 11 yr of protection. The inferred decline in macroalgal cover was more rapid during the first 5 yr of protection. No significant trends in fish abundance or macroalgal cover were detected among fished sites. Bio-mass of herbivorous fishes was 8 times higher, and cover of macroalgae 25 times lower, on average, inside older (8 to 11 yr) reserves than at fished sites. Parrotfishes (Scaridae) and surgeonfishes (Acanthuridae) had markedly different inferred trajectories of population recovery. Recovery of parrotfish was more rapid than that of surgeonfish in the first 5 yr of protection, suggesting that the functional role of parrotfish was important in reducing macroalgal cover. The inferred relationships of hard coral cover with duration of reserve protection and with herbivore biomass were non-significant. Even at fished sites, coral cover (mostly <25 %) was much higher than macrolgal cover (mostly >15%). Thus, there was no evidence that the current levels of fishing of herbivores on these reefs have led to 'benthic phase shifts'. © Inter-Research 2009.