The Effects of Algal Turf Sediments and Organic Loads on Feeding by Coral Reef Surgeonfishes

Herbivorous and detritivorous fishes interact closely with the epilithic algal matrix (EAM) on coral reefs. While sediment and organic detrital loads within the EAM might influence this interaction, the responses of functionally distinct fishes to changing sediment and organic loads have not been investigated. Aquarium based feeding trials were performed to assess how different sediment and organic loads affected feeding by the highly abundant surgeonfishes, Ctenochaetus striatus, a detritivore, and Acanthurus nigrofuscus, a herbivore. C. striatus were highly sensitive to even small increases in sediment loads (of just 75 g m-2), displaying a significant decline in feeding rates as sediment loads increased. Although C. striatus is a specialised detritivore, changing organic loads had no effect and suggests that selection of feeding surfaces is primarily mediated by total sediment loads rather than organic loads. By contrast, A. nigrofuscus displayed no changes to its feeding behaviour regardless of sediment or organic load. These findings highlight the complex, species-specific way that sediments may mediate key ecological processes on coral reefs.