Differences in diet and foraging behaviour of commercially important rabbitfish species on coral reefs in the Indian Ocean

Abstract

Herbivorous fishes consume algae on coral reefs, and this ecological function is pivotal in helping reefs to resist and recover from disturbance. Although numerous studies have differentiated between those fishes that graze on low-profile algae and those that browse on larger fleshy macroalgae, little is known about the feeding behaviours of some herbivorous fishes (e.g. rabbitfishes, Siganidae), limiting our understanding of whether, and how, these species contribute to ecological functions on coral reefs. Here, we examine how the feeding ecology of four species of rabbitfishes that dominate the artisanal fishery in the Seychelles changed spatially and temporally. Siganus argenteus and S. sutor were generalist herbivores feeding on a range of substrata (e.g. turf algae, macroalgae, seagrass and epiphytic algae), whereas S. corallinus and S. stellatus were specialist herbivores feeding primarily on substrata covered in turf algae. Bite rates of S. argenteus and S. sutor were positively correlated with the cover of macroalgae, seagrass and epiphytic algae. By contrast, bite rates of S. corallinus and S. stellatus were not correlated with changes in the cover of turf algae. These findings illustrate possible differences in the ecological contributions among rabbitfish species on coral reefs, and emphasize the need for caution when assigning species to functional groups and assuming within-group functional equivalence. The results also support the classic niche theory that species within a community must use resources differently in order to coexist over evolutionary timescales. These results further provide valuable insights for the management of rabbitfishes in tropical fisheries because it implies that the conservation of different species might result in distinct shifts in the competitive dominance of coral and algae.