Low-quality sediments deter grazing by the parrotfish Scarus rivulatus on inner-shelf reefs
- 575 Downloads
Elevated sediment loads in the epilithic algal matrix (EAM) deter grazing by herbivorous fishes and may compromise their critical roles on coral reefs. However, the properties of sediments that drive herbivore deterrence are unknown. Binary choice trials in aquaria were used to examine the effects of three sediment attributes—sediment source, grain size and organic load—on grazing by the abundant inner-shelf parrotfish, Scarus rivulatus. Fish were presented with a choice between EAM-covered rocks treated with (a) terrigenous or reefal sediments, (b) fine or coarse sediments or (c) sediments with high or low organic loads. Scarus rivulatus did not show a preference for sediments from different sources (terrigenous vs. reefal); however, a clear preference was evident for fine-grained sediments over coarse (109 % more bites) and sediments with high organic loads over low (147 % more bites). The avoidance of coarse sediments is likely to be a key factor driving the inhibition of grazing on mid-shelf reefs, which are dominated by coarse sediments. In contrast, on inner-shelf reefs, grazing by parrotfishes may be deterred primarily by high sediment loads, which reduce the proportional organic content in EAM sediments. Our study highlights the potential impact of sediments on critical ecological processes and the threats posed by changing sediment loads on inner-shelf reefs.
KeywordsHerbivory Algae Inner-shelf reef Parrotfish Resilience Terrestrial sediments
We thank P. Smallhorn-West, T. Healy, R. McAndrews, J. Khan, C. Buelow, T. Stephens, G. Molinaro, A. Cabrera-Garcia, W. Haydon and the staff of Orpheus Island Research Station for field assistance, C. Grant and R. Warburton for laboratory assistance and R. Baker, N. Gardiner, P. Munday, M. Kramer and three anonymous reviewers for helpful comments on earlier drafts. Research was funded by the Australian Research Council (DRB).
- Birrell CL, McCook LJ, Willis BL, Diaz-Pulido GA (2008) Effects of benthic algae on the replenishment of corals and the implications for the resilience of coral reefs. Oceanogr Mar Biol Annu Rev 46:25–63Google Scholar
- Burke L, Reytar K, Spalding M, Perry A (2011) Reefs at risk revisited. World Resources Institute, Washington, DC, pp 21–65Google Scholar
- Furnas MJ (2003) Catchment and corals: terrestrial run-off to the GBR. Australian Institute of Marine Science and CRC Reef Research Centre, TownsvilleGoogle Scholar
- Horn MH (1997) Feeding and digestion. In: Evans DH (ed) The physiology of fishes, 2nd edn. CRC Press, Boca Raton, pp 43–65Google Scholar
- Lutgens FK, Tarbuck EJ (2006) Essentials of geology, 9th edn. Pearson Prentice Hall, New JerseyGoogle Scholar
- Purcell SW (2000) Association of epilithic algae with sediment distribution on a windward reef in the northern Great Barrier Reef, Australia. Bull Mar Sci 66:199–214Google Scholar
- Torres JL (2001) Impacts of sedimentation on the growth rates of Montastraea annularis in southwest Puerto Rico. Bull Mar Sci 69:631–637Google Scholar
- Wilson SK, Bellwood DR, Choat JH, Furnas MJ (2003) Detritus in the epilithic algal matrix and its use by coral reef fishes. Oceanogr Mar Biol Annu Rev 41:279–309Google Scholar
- Zar JH (1974) Biostatistical analysis. Prentice-Hall, New JerseyGoogle Scholar