Cross-habitat patterns of sediment transport and release by surgeonfishes

Sterling Tebbett, David Bellwood, James Gahan, Isabelle Ng & Alexandre Siqueira

Abstract:

Building a comprehensive understanding of geo-ecological functions is viewed as a critical step in the quantification of carbonate and sediment budgets on coral reefs. Although parrotfishes are known to play key roles in such functions, the roles of surgeonfishes are less well understood. This is despite surgeonfishes being some of the largest and most abundant, nominally herbivorous fishes on reefs, with the potential to play a major role in sediment dynamics. Here, we quantified the role of four focal surgeonfish species across two functional groups (sediment suckers and brushers) in cross-habitat sediment dynamics by combining data on behavioural observations, fish abundance, gut content analysis, and published gut throughput rates. On average, these surgeonfish species together were estimated to rework and/or transport 71.4 ± 12.7 kg 100 m−2 year−1 of sediment. A single 30–35 cm surgeonfish was estimated to rework ~ 36 kg individual−1 year−1, a value equivalent to that of large parrotfishes. However, the two functional groups of surgeonfishes contributed to sediment dynamics in fundamentally different ways. The brusher, Ctenochaetus striatus, was primarily involved in on-reef sediment reworking. In contrast, the three sediment suckers were primarily involved in off-reef sediment reworking and in driving a potential net flux of sediment onto the reef. These results highlight the importance of off-reef shallow sand habitats as key feeding grounds for some surgeonfishes, as well as the role of these surgeonfishes in connecting off-reef habitats to reefs via biological sediment fluxes.