Understanding the drivers of variability in the composition of fish assemblages across
the Indo-Pacific region is crucial to support coral reef ecosystem resilience. Whilst
numerous relationships and feedback mechanisms between the functional roles of
coral reef fishes and reef benthic composition have been investigated, certain key
groups, such as the herbivores, are widely suggested to maintain reefs in a coraldominated
state. Examining links between fishes and reef benthos is complicated by
the interactions between natural processes, disturbance events and anthropogenic
impacts, particularly fishing pressure. This study examined fish assemblages and
associated benthic variables across five atolls within the Chagos Archipelago, where
fishing pressure is largely absent, to better understand these relationships. We found
high variability in fish assemblages among atolls and sites across the archipelago,
especially for key groups such as a suite of grazer-detritivore surgeonfish, and the
parrotfishes which varied in density over 40-fold between sites. Differences in fish
assemblages were significantly associated with variable levels of both live and recently
dead coral cover and rugosity. We suggest these results reflect differing coral recovery
trajectories following coral bleaching events and a strong influence of 'bottom-up'
control mechanisms on fish assemblages. Species level analyses revealed that Scarus
niger, Acanthurus nigrofuscus and Chlororus strongylocephalos were key species
driving differences in fish assemblage structure. Clarifying the trophic roles of
herbivorous and detritivorous reef fishes will require species-level studies, which also
examine feeding behaviour, to fully understand their contribution in maintaining reef
resilience to climate change and fishing impacts.