Integrating spatial patterns of herbivorous fish functional diversity to inform coral reef management

Stuart, C.E. and Benkwitt, C.E. and Stamoulis, K.A. and Pittman, S.J. and Green, S.J. and Young, M.A. and Purkis, S.J. and Graham, N.A.J. and Wedding, L.M. (2026) Integrating spatial patterns of herbivorous fish functional diversity to inform coral reef management. Marine Ecology Progress Series, 780: 15071. ISSN 0171-8630

Abstract

Herbivory is a key ecological process on coral reefs, regulating algal-coral competition, facilitating coral recruitment, and supporting reef resilience. Herbivorous fishes provide most of this function and can be categorised into 5 functional groups based on diet, foraging behaviour, and ecological impact. Here, we assess drivers of herbivorous fish functional diversity, abundance, and richness across Tetiaroa Atoll, Te Ao Mā’ohi (French Polynesia), using data from 89 underwater visual transects. Spatial-environmental variables derived from in situ and remotely sensed data were incorporated alongside transect data in generalised linear mixed models. Water depth, area of grazeable coral and hardbottom habitats, seabird-driven nutrient enrichment, and proximity to spearfishing were among the strongest predictors of herbivorous fish abundance and richness, although their effects varied in magnitude and direction across functional groups. Herbivory in Tetiaroa’s lagoon appeared relatively robust, with ~75% of transects containing representatives from 3 of the 5 distinct herbivorous fish functional feeding groups. Consistent co-occurrence of functional groups suggests strong spatial complementarity in the removal of macroalgal germlings, grazing of algal turfs, and clearing of reef substrate. However, the near absence of browsers and excavators indicates a potential vulnerability in controlling mature macroalgae and sustaining the natural erosion and renewal of the reef’s calcium carbonate structure. Our spatially explicit, process-oriented generalised linear mixed modelling approach provides a scalable framework for assessing reef herbivory—moving beyond biomass or presence-absence metrics to identify functional gaps and guide targeted, scale-sensitive strategies that maintain critical ecological processes in tropical reefs facing mounting anthropogenic and climate pressures.