The Assessment of Herbivorous Coral Reef Fish Clearance of Macroalgae

Abstract

Numerous studies have examined the comparative functional effects of herbivorous fish species on ecological functions in Indian coral reefs. This study investigated the potential grazing effect of individual species within an inshore herbivorous reef fish ecosystem in the central Great Barrier Reef (GBR) by determining whether fish species were capable of eradicating specific macroalgal species. Using transplanted multiple-choice algal tests in conjunction with stationary remote digital submerged video cameras, the effects of six varieties of macroalgae on local herbivorous reef fish species were examined. Fishes have been reported to eliminate macroalgae rapidly. Three hours of exposure to herbivorous reef fishes resulted in the observation of extensive grazing. After 12 hours of exposure, the mass of four of the six macroalgal species reduced by less than 15%. Even after 24 hrs of exposure, Chlorodesmisfastigiata (Chlorophyta) & Galaxaura sp. (Rhodophyta) were significantly more resistant to herbivorous reef fish grazing than any other macroalgae. 6 herbivorous or ostensibly herbivorous reef fish species were found as the most important macroalgae grazers: Acanthuruslineatus, Acanthurusnigrofuscus, Zebrasoma scopas, Scaridae (Parrot fishes), Pomacentridae (Damsel fishes) & Siganidae (Rabbit fishes). Scaridae (Parrot fishes) fed voraciously on Hypnea sp., whereas Siganidae (Rabbit fishes) fed heavily on Sargassum sp. Variability in macroalgal susceptibility was uncorrelated with morphological and/or chemical herbivore repellents previously reported. In spite of this, the results highlight the potential importance of particular herbivorous reef fish species in the reduction of macroalgae on coral reefs.