Feeding complementarity versus redundancy among herbivorous fishes on a Caribbean reef

Abstract

Herbivory is an important driver of community structure on coral reefs. Adequate understanding of herbivory will mandate better knowledge of how specific herbivores impact reef communities and the redundancy versus complementarity of their ecological roles. We used algal communities generated by herbivore manipulations to assess such roles among Caribbean herbivorous fishes. We created large enclosures on a 16- to 18-m-deep reef to create treatments grazed for 10 months by: (1) only Sparisoma aurofrenatum, (2) only Acanthurus bahianus, (3) no large herbivorous fishes, or (4) natural densities of all reef fishes. After 10 months, we removed cages and filmed how free-ranging reef fishes fed among these treatments that differed in algal community structure. In general, Acanthurus spp. and Scarus spp. rapidly grazed exclosure and Sparisoma-only treatments, while Sparisoma spp. preferentially grazed exclosure and Acanthurus-only treatments. These patterns suggest complementarity between Sparisoma spp. and both Acanthurus spp. and Scarus spp. but redundancy between Acanthurus spp. and Scarus spp. Despite these generalities, there was also within-genera variance in response to the different treatments. For example, large Scarus spp., such as Scarus guacamaia, fed more similarly to Sparisoma spp., particularly Sparisoma viride, than to other Scarus spp. Moreover, the three common Sparisoma species differed considerably in the macroalgae to which they exhibited positive or negative relationships. Thus, herbivorous reef fishes vary considerably in their response to different algal communities and exhibit complex patterns of compensatory feeding and functional redundancy that are poorly predicted by taxonomy alone.