Erosion is a key process in shaping the physical structure of coral reefs, yet due to erosion occurring beneath the reef surface it is difficult to quantify, and information remains limited. We measured erosion at Ningaloo Reef using a combination of direct and indirect approaches within reef slope and sheltered lagoonal habitats. Direct measurements of erosion on coral blocks were among the highest found globally, with erosion three times higher on the reef slope than in the lagoon. Intense grazing by parrotfish accounted for 62% of block erosion, with rates strongly influenced by the species and size of parrotfish. In contrast, grazing urchins contributed to 17% of total erosion. Scanning electron microscopy and computed tomography show that micro and macroborer erosion rates on blocks were low, most likely due to heavy grazing by parrotfish and the short deployment period of blocks. A substantial portion (35%) of external erosion on blocks could not be attributed to bioeroders, suggesting processes not quantified contribute to this unaccounted erosion. Our results confirm that bioerosion by parrotfish is especially significant at Ningaloo Reef, and large-bodied individuals of C. microrhinos are key in conserving this key ecological process.