On coral reefs, diverse assemblages of herbivorous fishes co-exist and exert strong impacts on benthic communities. However, food resource partitioning among herbivorous reef fishes is not fully understood. We do not know the extent of feeding redundancies (niche overlaps) among herbivorous fishes, nor do we know how herbivore niches shift with changing reef conditions. This information is especially needed now – a time when habitat perturbations are increasing, and the ecological roles of herbivores on modern reefs are hotly debated. Our preliminary work revealed that DNA metabarcoding of gut contents, an emerging molecular technique, vastly improves niche descriptions for Caribbean herbivorous fishes. This technique illuminates fine-scale differences among species, thus complementing approaches that, albeit coarser, quantify the niche at larger scales of space and time. The aims of this project are thus to (1) define the trophic niches of key herbivore species on minimally impacted Caribbean coral reefs – using traditional diet tracing methods, compound-specific isotopes, and high-resolution gut content DNA metabarcoding – to better quantify the extent of trophic niche partitioning in such systems, and (2) determine how the trophic niche of each species shifts with changing reef conditions. To accomplish our objectives, we will focus on core members of the Caribbean herbivorous fish guild and quantify their niches on nine reefs in the Dominican Republic that range from minimally impacted to heavily degraded.