UC San Diego

Herbivores on coral reefs are instrumental in mitigating the competitive interactions between reef-building corals and fleshy algae; however, not all herbivores provide the same ecological function. Grazers/ detritivores consume turf algae (and associated organic matter), which are the primary spatial competitors to corals in the Main Hawaiian Islands. This study highlights functional diversity among surgeonfishes through observations of foraging behavior, analysis of stomachcontents, and analysis of stable isotopic signatures of muscle tissue (δ13C and δ15N) for three common species (Acanthurus nigrofuscus, Acanthurus olivaceus, and Ctenochaetus strigosus) on the leeward side of Maui. Similar foraging behavior was observed in A. nigrofuscus and C. strigosus, with both biting primarily on turf; A. olivaceus grazed primarily sand in addition to turf. Diet composition based on stomach contents was different among species, and variation in composition was influenced by site. Measured δ15N values indicate similar trophic position in the three species; however, δ13C values varied among species at different sites, indicating consumption of different algal resources. Collectively, these data suggest that surgeonfish grazers exhibit significant within-guild functional diversity; however, the differences and degree of divergence revealed depend on the methods used.