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There have been few studies of coral predation by fishes on the Great Barrier Reef (GBR). However, these studies have indicated that it is an important factor that may shape coral demographics. Here, for the first time, we document the spatial and temporal variation in coral predation by parrotfishes on an inshore reef on the GBR. The densities of parrotfish feeding scars on massive Porites spp. were compared within core and non-core areas of three Chlorurus microrhinos home ranges. The density of parrotfish feeding scars on massive Porites is among the highest recorded on the GBR and elsewhere with a higher abundance of excavating feeding scars within core areas, reflecting the higher occupancy of these areas by C. microrhinos. Furthermore, excavating scars were more abundant in October than in April. This may be related to the higher nutritional quality of coral colonies in October, as coral spawning usually occurs in November at this study location. No spatial or temporal variation was noted in the abundance of feeding scars from scraping parrotfishes. The lack of temporal differences may be a result of the shallow scraping scars which would not be able to reach the gonads within coral polyps. The frequency of parrotfish predation on Porites and the spatial and temporal variation recorded herein highlight the potential importance of parrotfish corallivory on the GBR. [ABSTRACT FROM AUTHOR]

Of all benthic components on tropical reefs, algal turfs are the most widespread and the main source of primary productivity. We compared the importance of grazing by herbivores on algal turfs on two zones with marked differences in terms of benthic composition, herbivore biomass and grazing pressure, the inner flat and crest, of an inshore reef on the Great Barrier Reef, Australia. A combination of herbivore exclusion cages and transplants of coral rubble covered by algal turfs between reef zones was used to examine changes in algal turfs over a 4-day experimental period. In situ crest turfs had lower algal height, sediment loads and particulate content than reef flat turfs. Caged samples on the crest exhibited an increase in all three variables. In contrast, in situ and caged treatments on the flat presented algal turfs with similar values for the three analysed variables, with high algal height and heavy particulate and sediment loads. In the absence of cages, reef flat turfs transplanted to the crest had decreased algal height, total particulate material and particulate inorganic content, while the opposite was found in crest turf samples transplanted to the flat. Our results highlight the dynamic nature of algal turfs and the clear differences in the relative importance of herbivory in shaping turf length and sediment load between the reef crest and inner flat. [ABSTRACT FROM AUTHOR]

Parrotfish grazing scars on coral colonies were quantified across four reef zones at Lizard Island, Northern Great Barrier Reef (GBR). The abundance of parrotfish grazing scars was highest on reef flat and crest, with massive Porites spp . colonies having more parrotfish grazing scars than all other coral species combined. Massive Porites was the only coral type positively selected for grazing by parrotfishes in all four reef zones. The density of parrotfish grazing scars on massive Porites spp., and the rate of new scar formation, was highest on the reef crest and flat, reflecting the lower massive Porites cover and higher parrotfish abundance in these habitats. Overall, it appears that parrotfish predation pressure on corals could affect the abundance of preferred coral species, especially massive Porites spp , across the reef gradient. Parrotfish predation on corals may have a more important role on the GBR reefs than previously thought. [ABSTRACT FROM AUTHOR]

The article presents a study on the relative effects of parrotfish groups on reef corals at Lizard Island on the Great Barrier Reef in Queensland. The researches used the presence of the distinctive grazing scars caused by the parrotfishes on live coral as an indicator of parrotfish feeding on corals. They surveyed seven 20-meter transects within every study location to determine the relative abundance of scraping against excavating and solitary against grouped parrotfish bite marks on coral. They found that slope, crest and reef flat presented higher abundance of scraping than of excavating grazing scars.

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. [ABSTRACT FROM AUTHOR]