Abstract: Herbivorous fish plays an important role in controlling macroalgal overgrowth on coral reefs. Here, we used 18S rRNA high-throughput sequencing to investigate the diet composition and macroalgae consumption of two herbivorous fish (Acanthurus triostegus and Siganus punctatissimus), the common herbivores species on reefs of Jinqing Island, Xisha, China. The two species differed in food composition pattern. A. triostegus fed more on Rhodophyta, Ochrophyta, and Bacillariophyta, whereas S. punctatissimus preferred Porifera, Ochrophyta, and Streptophyta. The dominant operational taxonomic unit (OTU) in the intestines also varied between the two species. Moreover, the two species showed different feeding preferences for macroalgae. The grazer A. triostegus consumed eight species of macroalgae and fed mostly on turf algae, whereas S. punctatissimus consumed 16 macroalgae species and preferred fleshy macroalgae. Our findings indicated that both A. triostegus and S. punctatissimus are important for preserving the health of coral reefs, by removing macroalgae and consuming predators of corals, namely sponges.

Key words: coral reef, herbivorous fish, diet composition, macroalgae, 18S rRNA gene.