Dynamics of parrotfish grazing scars
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ORIGINAL PAPER
Dynamics of parrotWsh grazing scars Roberta Martini Bonaldo · David R. Bellwood
Received: 25 September 2008 / Accepted: 8 January 2009 / Published online: 31 January 2009 © Springer-Verlag 2009
Abstract ParrotWshes 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 parrotWshes in reef resilience is well documented, the basis of this role and the eVect 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 parrotWsh 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 diVerent 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 diVerences between scraping and excavating parrotWshes and, in a system with just one
Communicated by S.D. Connell. R. M. Bonaldo (&) · D. R. Bellwood Australian Research Council Centre of Excellence for Coral Reef Studies and School of Marine and Tropical Biology, James Cook University, Townsville, QLD 4811, Australia e-mail: [email protected]
abundant large excavating species, emphasizes the potential for low functional redundancy in high diversity coral reef systems.
Introduction ParrotWshes (Labridae) are conspicuous inhabitants of tropical reefs and are well known for their critical functional roles in the maintenance of the diversity and structure of coral reef ecosystems (Lewis and Wainwright 1985; Choat 1991; Bellwood et al. 2003; Mumby et al. 2006; Hughes et al. 2007). These Wshes play a number of functional roles on coral reefs, including algal grazing, coral predation, sediment removal, and bioerosion (Choat 1991; Bruggemann et al. 1996; Rotjan and Lewis 2005, 2008; Hoey and Bellwood 2008). Despite the importance of the group for coral reefs, parrotWshes are among the most threatened reef species, as they are one of the main targets of artisanal and commercial Wsheries (Ferreira and Gonçalves 1999; Nyström et al. 2000; Aswani and Hamilton 2004; Floeter et al. 2006). As a result, many reefs around the world have severely depleted parrotWsh popul
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