Invertivore fish predation is an overlooked source of carbonate sediment on a turbid coral reef

Abstract The geomorphic stability of coral reef islands depends on a continued supply of biologically derived sediment from reefs. However, the ecological processes that produce detrital sediment remain poorly resolved. The role of fishes as sediment producers has largely focused on coral sand generated by parrotfishes (Labridae: Scarinae) in clear-water settings, while the contribution of other groups, such as durophagous invertivores, remains poorly understood. Here, we quantify the contribution of invertivores to carbonate sediments at an inshore reef in the Exmouth Gulf, Western Australia, by combining fish census data and dietary analysis, coupled with taphonomic and compositional analysis of benthic sediments. Invertivore species were among the most abundant fish groups, contributing nearly two-thirds of total fish biomass (28.51 kg out of 48.29 kg). Tuskfish species ( Choerodon schoenleinii and Choerodon cyanodus ) dominated the invertivore assemblage, with dietary analysis indicating that these species, together with Choerodon cauteroma , Lethrinus laticaudis , and Diagramma pictum labiosum , had stomach contents composed of > 50% carbonate shell material. Benthic sediment analysis revealed that ~ 40% of sediments comprised mollusc and echinoderm fragments, with more than one-third of mollusc fragments displaying edge characteristics consistent with durophagy, providing direct evidence of fish predation. Together, these data suggest that invertivore fishes represent a previously unrecognised pathway of carbonate sediment production through the rapid mechanical breakdown of calcareous benthic invertebrates. Quantifying sediment production by invertivores is, therefore, critical for improving carbonate sediment budget estimates, especially turbid reefs with high benthic invertebrate diversity and biomass.