Response of fishes to algae reduction on Glovers Reef, Belize

Many Caribbean coral reefs have experienced an increase in erect brown alga e (species of Sargassum, Turbinaria and Lobophora) over the past 18 yr. We explored the effects of fleshy algal overgrowth on coral reef fishes by red ucing erect algae by similar to2.5 kg(wet) m(-2) on 8 patch reefs (average size similar to 1000 m(2)) whereby half were in a new no-fishing zone and h alf in an unrestricted fishing zone. Another 8 reefs were left as unmanipul ated controls in the respective zones. Multivariate ordination indicated th at the algal removal had marginal effect on whole-fish assemblages but that effect was highly significant on the biomass of common herbivores. The red uction of erect algae resulted in a rapid increase in the abundance of the blue-headed wrasse Thalassoma bifasciatum (Labridae), in the biomass of the blue tang Acanthurus coeruleus (Acanthuridae), and in both the abundance a nd biomass of the spotlight parrotfish Sparisoma viride (Scaridae). Bite ra tes and intra- and inter-specific aggressive encounters were used as measur es of resource quality, and we found that these measures increased for surg eonfishes and damselfishes after the algal reduction, particularly in the c enter of the patch reefs, where most erect algae was originally located. In creased accessibility, net production and palatability of the early success ional turf algae on the manipulated reefs are likely to account for the inc reased numbers, biomass and feeding rates of the dominant herbivorous fishe s.