Direct evaluation of macroalgal removal by herbivorous coral reef fishes |
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Authors: | C S Mantyka D R Bellwood |
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Institution: | (1) Australian Research Council Centre of Excellence for Coral Reef Studies and School of Marine and Tropical Biology, James Cook University, Townsville, QLD, 4811, Australia |
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Abstract: | Few studies have examined the relative functional impacts of individual herbivorous fish species on coral reef ecosystem processes
in the Indo-Pacific. This study assessed the potential grazing impact of individual species within an inshore herbivorous
reef fish assemblage on the central Great Barrier Reef (GBR), by determining which fish species were able to remove particular
macroalgal species. Transplanted multiple-choice algal assays and remote stationary underwater digital video cameras were
used to quantify the impact of local herbivorous reef fish species on 12 species of macroalgae. Macroalgal removal by the
fishes was rapid. Within 3 h of exposure to herbivorous reef fishes there was significant evidence of intense grazing. After
12 h of exposure, 10 of the 12 macroalgal species had decreased to less than 15% of their original mass. Chlorodesmis fastigiata (Chlorophyta) and Galaxaura sp. (Rhodophyta) showed significantly less susceptibility to herbivorous reef fish grazing than all other macroalgae, even
after 24 h exposure. Six herbivorous and/or nominally herbivorous reef fish species were identified as the dominant grazers
of macroalgae: Siganus doliatus, Siganus canaliculatus, Chlorurus microrhinos, Hipposcarus longiceps, Scarus rivulatus and Pomacanthus sexstriatus. The siganid S. doliatus fed heavily on Hypnea sp., while S. canaliculatus fed intensively on Sargassum sp. Variation in macroalgal susceptibility was not clearly correlated with morphological and/or chemical defenses that have
been previously suggested as deterrents against herbivory. Nevertheless, the results stress the potential importance of individual
herbivorous reef fish species in removing macroalgae from coral reefs. |
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Keywords: | Herbivory Fishes Algal assays Video camera Ecosystem processes |
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