King Abdullah University of Science & Technology, Saudi Arabia
Abstract: Herbivorous fishes contribute to the resilience of coral reefs by removing algae, leading to positive feedbacks for coral reef health. The resiliency of herbivore fish functions is often attributed to high levels of trophic redundancy between species. This is especially true for browsing herbivorous fishes, well-known for their role in removing macroalgae. However, most of these findings are based on algal transplant assays, confounding natural estimates of resource use and redundancy, which could vary substantially across reefscapes. Here, we combine stomach contents and stable isotope analyses to yield insight into natural browsing fish trophic redundancy. We collected browsers from offshore reefs largely devoid of macroalgae and nearshore reefs with greater macroalgae biomass to understand how resource availability drives trophic redundancy through both space and time. We documented that trophic redundancy of browsing fishes appears to be largely habitat dependent. Higher levels of trophic redundancy existed on nearshore reefs with more abundant macroalgae, with greater complementarity on offshore reefs. These findings were consistent between methods, highlighting temporal stability in trophic partitioning among browsers. We also documented yet undescribed species-specific variation in trophic ecology between reefs, including substantial omnivory in some species, highlighting species’ flexibility in trophic ecology. These findings underscore dynamic variability in the delivery of key herbivore functions to reef resiliency across habitats. We highlight greater susceptibility of browsing herbivory to anthropogenic disturbances on reefs with low algae cover, supporting the inclusion benthic assessments alongside standard fish assessments when considering function-focused conservation efforts.