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Many Caribbean coral reefs have experienced an increase in erect brown algae (species of Sargassum, Turbinaria and Lobophora) over the past 18 yr. We explored the effects of fleshy algal overgrowth on coral reef fishes by reducing erect algae by ~2.5 kg(wet) m -2 on 8 patch reefs (average size ~1000 m 2 ) whereby half were in a new no-fishing zone and half in an unrestricted fishing zone. Another 8 reefs were left as unmanipulated controls in the respective zones. Multivariate ordination indicated that the algal removal had marginal effect on whole-fish assemblages but that effect was highly significant on the biomass of common herbivores. The reduction 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 and biomass of the spotlight parrotfish Sparisoma viride (Scaridae). Bite rates and intra-and inter-specific aggressive encounters were used as measures of resource quality, and we found that these measures increased for surgeonfishes and damselfishes after the algal reduction, particularly in the center of the patch reefs, where most erect algae was originally located. Increased accessibility, net production and palatability of the early successional turf algae on the manipulated reefs are likely to account for the increased numbers, biomass and feeding rates of the dominant herbivorous fishes.KEY WORDS: Acanthuridae · Algal-fish interactions · Brown algae · Herbivory · Labridae · Management interactions · Sargassum · Scaridae · Turbinaria Resale or republication not permitted without written consent of the publisher

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The aim of this field study was to investigate effects of estimated fish-and sea urchin herbivory on the reproductive potential of four species of macroalgae; Halimeda macroloba (Decasine), H. renschii (Hauck), Turbinaria ornata (Turner) and Padina boergesenii (Allender et Kraft). Fish and sea urchin herbivory were calculated based on reported consumption rates for their biomass estimates. We hypothesized that reduced herbivory would increase algal size and the reproductive potential, which may promote algal recruitment and be one of the driving mechanisms behind algal shifts and persistent algae-dominated reefs. Algae were investigated in field sites where the estimated fish-and or sea urchin herbivory differed. Our results suggest that algal fecundity of T. ornata and P. boergesenii are positively correlated to their size. Fecundity of T. ornata was higher and individuals grew larger in areas where estimated fish herbivory was lower. The two species of Halimeda grew larger and had higher fecundity in areas where estimated sea urchin herbivory was lower. P. boergesenii responded ambiguously to patterns in herbivory. Due to species-specific responses to different herbivores, it is difficult to generalize about effects of overfishing on algal fecundity.