Harsh environmental conditions limit how species use the landscape, strongly infuencing the way assemblages are distributed. In the wake of repeated coral bleaching mortalities in Lakshadweep, we examined how wave exposure infuences herbivory in exposed and sheltered reefs. We used a combination of i. feld observations of fsh herbivore composition, abundance and activity across 6 exposed and 6 sheltered reefs; ii. experimental manipulations in a subset of these reefs (herbivore exclosures); and iii. opportunistic observations of fsh recruitment, to determine how exposure infuences herbivore biomass and herbivory. Species richness, biomass, abundance, total bite rates and species-specifc per capita bite rates were lower in exposed compared to sheltered reefs, linked to strong environmental fltering of species composition, abundance and behaviour. For some critical species, this environmental fltering begins with diferential recruitment and post-recruitment processes between exposures. Bite rates at sheltered sites were dominated by just a few species, most being laterally compressed surgeonfsh that may fnd it difcult accessing or surviving in wave-battered shallow reefs. Exclosure experiments confrmed that exposed reefs were less controlled by herbivores than sheltered reefs. In post-disturbed reefs like Lakshadweep, environmental gradients appear to be key mediators of critical functions like herbivory by determining species composition, abundance and behaviour.