Project: Collaborative Research: Revealing the changing trophic niches of large herbivorous fish on modern coral reefs using an interdisciplinary approach

NSF Award Abstract:
Globally, coral reefs are experiencing human-induced disturbances with growing intensity and pace. Coral recovery after a disturbance is shaped, in part, by whether grazing herbivores prevent harmful algae from blooming and taking over the reef. This important grazing activity is carried out by a diverse group of co-existing herbivorous fish species, such as parrotfishes and surgeonfishes, which collectively control algae and thereby facilitate coral recovery. However, the specific types of algae that many of these fish feed on is largely unknown. It is also unknown if the feeding behaviors of these herbivores are constant, or instead depend on reef condition such as loss of coral. More detailed studies of herbivore diets are needed to understand how these species co-exist, as well as which species have unique roles and underpin key ecosystem processes on modern reefs. The aims of this project are thus to (a) define the feeding behaviors and diets of herbivorous fishes on healthy coral reefs - using both traditional and cutting-edge techniques - to better quantify resource partitioning among these herbivores, and (b) determine whether and how the feeding ecology of each herbivore shifts with changing reef conditions. To accomplish these objectives, the research team is focusing on core members of the coral reef herbivorous fish assemblage and quantifying their feeding ecology on reefs that range from minimally impacted to heavily degraded. By revealing hidden aspects of herbivore feeding, as well as which herbivorous fishes serve unique ecological roles, this project stands to reshape our understanding of coral reef ecology. More broadly, this project is: (1) cross-training a diverse group of undergraduate and graduate students in cutting-edge scientific methods, (2) augmenting public data repositories to foster scientific discovery across the wider scientific community, (3) sharing results with resource managers to enhance decision-making processes, and (4) increasing public science literacy and engagement via the co-development of visual art.

On coral reefs, many herbivorous fish species co-exist and exert strong impacts on benthic communities via top-down control of a diverse algal assemblage. However, resource partitioning among these species is not fully understood and the extent of niche overlaps that exist among herbivorous fishes remains unknown. It also remains unknown how the feeding activities and diet (i.e., the 'trophic niche') of each herbivore shifts in response to changing ecosystem context, such as the loss of coral. Broad, higher-resolution studies are thus needed to understand how these species co-exist, as well as which species are functionally unique and underpin key ecosystem processes on modern reefs. The researchers' preliminary work showed that DNA metabarcoding of gut contents, a cutting-edge tool, vastly improves niche descriptions for herbivorous fishes. This technique illuminates fine-scale differences among species, thus complementing previous approaches that, albeit coarser, quantify the niche at larger scales of space and time. The aims of this project are to (a) define the trophic niches of key herbivorous fishes on healthy reefs - using a combination of field observations, traditional diet tracing methods, compound-specific isotopes, and high-resolution DNA metabarcoding of gut contents - to better quantify the types and degree of trophic niche partitioning in such ecosystems, and (b) determine whether and how herbivore niches shift with changing reef condition. To meet these objectives, the researchers are characterizing the trophic niches of key members of the coral reef herbivorous fish guild (via the aforementioned methods) at numerous study sites that span a gradient of reef condition. By quantifying herbivore niche overlaps on healthy reefs, species-level niche expansions or contractions as a function of reef decline, and resultant impacts to total trophic niche breadth, this research is reshaping our understanding of large consumers on coral reefs, with implications for managing fisheries and reef processes simultaneously. More broadly, this study provides new insights into the niche, a fundamental concept in ecology that underlies topics ranging from species coexistence to the relationship between biodiversity and ecosystem function.