Dynamics of parrotfish grazing scars
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Parrotfishes exhibit a range of feeding modes. These species vary in both feeding morphology and behaviour, but the vast majority of species leave distinctive scars on the substratum when feeding. Although the role of parrotfishes in reef resilience is well documented, the basis of this role and the effect of their grazing scars on the benthic community structure remain unclear. This study evaluated the dynamics of grazing scars of large adult Scarus rivulatus and Chlorurus microrhinos on an inshore reef in the Great Barrier Reef (GBR). These species represent the most abundant scraping and excavating parrotfish species on inshore reefs. Grazing scars of each species were marked, measured and observed for seven consecutive days. S. rivulatus grazing scars were smaller in area and volume and more rapidly reoccupied by algae than those of C. microrhinos. However, because of the higher abundance and feeding frequency of S. rivulatus at the study site, this species had higher algal removal rates than C. microrhinos. These species appear to play distinctly different functional roles in shaping the benthic community of inshore GBRs. S. rivulatus is primarily responsible for algal dynamics dominated by vegetative regrowth. In contrast, C. microrhinos opens relatively large areas which remain clear for several days. These scars may represent settlement sites which are relatively free from algae and sediment. This study provides new information on the differences between scraping and excavating parrotfishes and, in a system with just one abundant large excavating species, emphasizes the potential for low functional redundancy in high diversity coral reef systems.
KeywordsCoral Reef Great Barrier Reef Algal Turf Reef Crest Scar Area
We thank J.H. Choat and J.P. Krajewski for helpful suggestions; C. Cvitanovic, J.P. Krajewski and C. Ryen for assistance in the field; J.P. Krajewski for comments and photographs; L. Castell for reviewing the manuscript; S.R. Conolly for statistical advice; Orpheus Island Research Station staff for logistical support; and the Australian Research Council, Great Barrier Reef Marine Park Authority and CAPES-Brazil for financial support.
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