Functional Distinctions in Feeding Behavior of Two Herbivorous Reef Fish Lineages

Understanding the mechanisms and variation of how herbivorous fishes feed is key to understanding the dynamics of herbivory on coral reefs. In our comparative study of closely related nominally herbivorous fishes, we investigate the use of 10 distinct behaviors used to support feeding on algae. We found that species within Siganidae share 5 out of the 10 behaviors with Acanthuridae while also exhibiting two additional family-specific behaviors: presence of nibbling and extra jaw closure. Siganids predominantly use movements of the jaws whereas acanthurids also employ body and head movements while detaching algae from the substrate. A comparison among siganid species revealed an axis of diversity in the frequency and extent of their feeding behaviors, with the main axis of variation being strongly associated with sociality (schooling vs. pairing) and morphology (short-snouted vs. long-snouted). Overall, we show that siganids and acanthurids display distinct behaviors during feeding. Thus, our results suggest potential niche differences between 2 major groups of herbivorous reef fishes.