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X‐ray micro‐computed tomography scans were used to examine the caudal‐fin structure of an unusual double‐tailed deformity in an adult brown surgeonfish Acanthurus nigrofuscus from the Great Barrier Reef. In both this case and in a similar double‐tailed deformity in a juvenile Tomini surgeonfish Ctenochaetus tominiensis from the Philippines, the caudal fin was duplicated along the dorsoventral axis. Detailed examination of the A. nigrofuscus specimen revealed that the deformity was associated with duplication and reflection of the hypural plates and the posterior vertebrae, yet the fish survived to adulthood, indicating that the effects of duplication on survival may be limited. [ABSTRACT FROM AUTHOR]

This study investigated the basis of pair formation in the abundant herbivorous rabbitfish Siganus doliatus on Orpheus Island, Great Barrier Reef. Pair formation was the most common social system in S. doliatus, with 67·4% of all individuals occurring in pairs. Pairs were stable ( i.e. individuals remained with the same partner throughout the study) and pair members were found within 5 m of each other 82·9% of the time. Of the examined pairs, 25% were homosexual resulting in a proportion of heterosexual pairs (75%) that was significantly lower than expected if pairs were formed solely for reproductive reasons. Therefore, although reproduction appears to be the main driver of pair formation in S. doliatus, other factors are likely to influence this behaviour. The high density of individuals on the reef crest (5·7 ± 0·9 individuals 200 m−2; mean ± s.e.) and extensively overlapping home ranges of pairs indicated that the defence of territories plays no role in pair formation. Instead, it appears that pair formation in S. doliatus is driven, in part, by other, non-reproductive, ecological factors. It is suggested that pair formation allows for increased vigilance against predation and enables S. doliatus to execute a novel feeding behaviour. [ABSTRACT FROM AUTHOR]

Understanding diel patterns in sea urchin activity is important when assessing sea urchin populations and when interpreting their interactions with predators. Here we employ a combination of surveys and a non-invasive tethering technique to examine these patterns in an intact coral reef system on the Great Barrier Reef (GBR). We also assess local scale variation in relative diurnal predation pressure. Surveys revealed that sea urchins were active and exposed at night. Echinometra mathaei and Echinothrix calamaris were the most abundant species with significantly higher night densities (0.21 and 0.03 ind. m, respectively), than daytime densities (0.05 and 0.001, respectively). Bioassays revealed that exposed adult E. mathaei (the most abundant sea urchin species) were 30.8 times more likely to be eaten during the day than at night when controlling for sites. This observation concurs with widely held assumptions that nocturnal activity is a risk-related adaptive response to diurnal predation pressure. Despite relatively intact predator communities on the GBR, potential predation pressure on diurnally exposed E. mathaei assays was variable at a local scale and the biomass of potential fish predators at each site was a poor predictive measure of this variation. Patterns in predation appear to be more complex and variable than we may have assumed. [ABSTRACT FROM AUTHOR]

Formal monitoring of the Great Barrier Reef was initiated in 1986 in response to the clear scientific evidence (and growing public concern) over the loss of corals caused by two protracted outbreaks of crown-of thorns starfish, which began in 1962 and 1979. Using monitoring data from manta tows along and across the Great Barrier Reef, Sweatman et al. (Coral Reefs 30:521-531, ) show that coral cover after these outbreaks declined further from 28 to 22% between 1986 and 2004. Pointing to the current levels of protection of the Great Barrier Reef, they state that earlier estimates of losses of coral cover since the early 1960s have been exaggerated. However, the loss of close to one-quarter of the coral cover over the past two decades represents an average loss of 0.34% cover per year across the whole GBR after 1986, which is very similar to previously reported rates of annual loss measured over a longer timeframe. The heaviest recent losses have occurred on inshore and mid-shelf reefs, which Sweatman et al. (Coral Reefs 30:521-531, ) attribute to a natural cycle of disturbance and recovery. But there has been very limited recovery. While coral cover has increased for short periods on some individual reefs, it has declined sharply on many more to produce the observed system-wide trend of declining cover. Close to 40% of coral cover on inner reefs has been lost since 1986. Of particular significance is the new evidence that coral cover has remained unchanged or declined further from a low 1986 baseline in 28 out of 29 sub-regions of the Great Barrier Reef, indicating a gradual erosion of resilience that is impeding the capacity of this huge reef system to return towards its earlier condition. This result, and other clear evidence of widespread incremental degradation from overfishing, pollution, and climate change, calls for action rather than complacency or denial. [ABSTRACT FROM AUTHOR]

The humphead parrotfish, Bolbometopon muricatum, the largest of all parrotfish species, is heavily fished throughout most of its range. In remote and heavily protected locations, such as the Great Barrier Reef (GBR), it is a major component of parrotfish biomass and plays a critical role in ecosystem processes. However, extensive surveys of GBR populations have revealed a striking lack of juveniles. Of 633 individuals censused, just four were juveniles. This represents 0.6% juveniles and contrasts markedly with the 20.2-40.2% juveniles recorded in eight other medium to large parrotfish species. These low values in Bolbometopon are corroborated by over 5,000 h of independent observations and extensive museum collections. Whilst there is no evidence to suggest that this is an extraordinary new condition for GBR Bolbometopon, it may nevertheless expose them to special risks in a changing and unpredictable world. Despite excellent management on the GBR, Bolbometopon populations may be more vulnerable than previously thought. [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]

The article focuses on a study about latitudinal variation in the consumption of the brown macroalgae Sargassum by fishes found in the Great Barrier Reef (GBR) in Australia. The study aims to explore herbivory on fleshy macroalgae as well as determine the rates of removal across regional scales. Results of the study are also presented including the high Sargassum tissue loss rates in the northern and central regions of GBR and the low rates in the southern region. Several factors behind the variation in the feeding propensity of herbivorous fishes across the regions are cited which include temperature, decrease in preference for the transplanted algae and topographic complexity.

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.

Marginal coral reef systems may provide valuable insights into the nature of ecosystem processes in systems on the trajectory towards a phase shift to an alternate ecosystem state. This study investigates the process of herbivory in a marginal coral reef system in the Keppel Islands at the southern end of the Great Barrier Reef. Branching Acropora coral and the brown macroalga Lobophora variegata occupied up to 95% of the reef crest substratum at the three surveyed reefs. Feeding rates of herbivorous fishes and removal rates of Lobophora were directly quantified within areas of branching Acropora and on planar surfaces. Feeding rates by herbivorous fishes were habitat dependent with the highest bite rates being found in planar habitats for both Lobophora and the epilithic algal matrix (EAM) by 1–2 orders of magnitude, respectively. Feeding rates on Lobophora were, however, much lower than rates on the EAM. The low rates of Lobophora removal and significantly lower rates of herbivory in branching habitats were consistent with the high biomass of this brown alga throughout the Keppel Islands and with its distribution on reef crests, where Lobophora biomass was 20 times greater in branching than in planar habitats. This lack of feeding by herbivorous fishes within branching coral habitats in the Keppel Islands contrasts with the typical role of coral and topographic complexity on herbivores on coral reefs and highlights the potential for complex interactions between algae, corals and fishes on coral reefs. On marginal systems, herbivory may modify algal distributions but may be unable to contain the proliferation of algae such as Lobophora. [ABSTRACT FROM AUTHOR]

Herbivory is widely accepted as a key process determining the structure and resilience of coral reefs, with regional reductions in herbivores often being related to shifts from dominance by coral to leathery macroalgae. The removal of leathery macroalgae may therefore be viewed as a critical process on coral reefs. However, few studies have examined this process beyond a within-reef scale. Here, browsing activity was examined across the entire Great Barrier Reef shelf using bioassays of the leathery macroalga Sargassum to directly quantify algal removal. The assays revealed marked cross-shelf variation in browsing intensity, with the highest rates recorded on mid-shelf reefs (55.2–79.9% day−1) and decreasing significantly on inner- (10.8–17.0% day−1) and outer-shelf (10.1–10.4% day−1) reefs. Surprisingly, the variation in browsing intensity was not directly related to estimates of macroalgal browser biomass; rather, it appears to be shaped primarily by the local environment and behaviour of the component species. Removal rates across the inner- and mid-shelf reefs appear to be related to the attractiveness of the assays relative to the resident algal communities. Controlling for the influence of the resident algal communities revealed a positive relationship between removal rates and the biomass of a single macroalgal browsing species, Naso unicornis. In contrast, the low removal rates on the outer-shelf reefs displayed no relationship to algal or herbivore communities and appeared to reflect a negative behavioural response by the resident fishes to a novel, or unfamiliar, alga. These findings not only highlight the complexities of the relationship between fish presence and ecological function, but also the value of examining ecological processes across broader spatial scales. [ABSTRACT FROM AUTHOR]

Herbivory is widely accepted as a key process determining the benthic community structure and resilience of coral reefs. Recent studies have mostly focused on the importance of roving herbivorous fishes in ecosystem processes. Here, we examine the role of territorial damselfish in shaping patterns of macroalgal distribution based on benthic surveys and macroalgal bioassays. The territory composition and effect of resident damselfish on the removal of Sargassum bioassays were quantified for six species of damselfish on Lizard Island, a mid-shelf reef in the northern Great Barrier Reef (GBR). The functional composition of algal communities within territories varied markedly among species. The territories of four species ( Dischistodus perspicillatus, Dischistodus pseudochrysopoecilus, Plectroglyphidodon lacrymatus, and Stegastes nigricans) were characterized by algal turfs, while the territories of two species ( Dischistodus prosopotaenia and Hemiglyphidodon plagiometopon) were characterized by foliose and leathery brown macroalgae. Sargassum, a generally rare alga on mid-shelf reefs, was a particularly common alga within D. prosopotaenia territories on the leeward side of the island but absent within their territories on the windward side of the island. D. prosopotaenia was the only species to retain the transplanted Sargassum, with only a minimal reduction in Sargassum biomass (1.1%) being recorded within their territories at both leeward and windward sites over a 24-h period. In contrast, reductions in Sargassum biomass were high in areas adjacent to D. prosopotaenia territories (83.8%), and within and adjacent to the territories of the five remaining damselfish species (76.2–92.5%). Overall, only one of the six damselfish species provided a refuge for leathery brown macroalgae and may facilitate the development of this macroalgae on mid-shelf reefs of the GBR. [ABSTRACT FROM AUTHOR]

Threats to coral reefs may be manifested through an increase in macroalgae. Across the globe, phase-shifts from coral to macroalgal dominance have been reported from the Caribbean, Indian and Pacific Oceans. While the Great Barrier Reef (GBR) is in relatively good condition, inshore reefs may exhibit over 50% macroalgal cover. However, our understanding of the processes preventing the macroalgal expansion remains uncertain. Using a remote video bioassay approach, this study quantified herbivory in three bays along the leeward margin of Orpheus Island. Despite significant within bay variation in herbivory there was no detectable statistical difference in the rates of herbivory among bays. Furthermore, of the 45 herbivore species recorded from the island, only three played a significant role in bioassay removal, Siganus canaliculatus, Siganus javus and Kyphosus vaigiensis, with only one species predominating in each bay. Reefs of the GBR may therefore be more vulnerable than previously thought, with the removal of macroalgae depending on just a few species, which exhibit considerable spatial variability in their feeding behaviour. [ABSTRACT FROM AUTHOR]

Herbivorous fishes are a key functional group on coral reefs. These fishes are central to the capacity of reefs to resist phase shifts and regenerate after disturbance. Despite this importance few studies have quantified the direct impact of these fishes on coral reefs. In this study the roles of parrotfishes, a ubiquitous group of herbivorous fishes, were examined on reefs in the northern Great Barrier Reef. The distribution of 24 species of parrotfish was quantified on three reefs in each of three cross-shelf regions. Functional roles (grazing, erosion, coral predation and sediment reworking) were calculated as the product of fish density, bite area or volume, bite rate, and the proportion of bites taken from various substrata. Inner-shelf reefs supported high densities but low biomass of parrotfishes, with high rates of grazing and sediment reworking. In contrast, outer-shelf reefs were characterised by low densities and high biomass of parrotfish, with high rates of erosion and coral predation. Mid-shelf reefs displayed moderate levels of all roles examined. The majority of this variation in functional roles was attributable to just two species. Despite being rare, Bolbometopon muricatum, the largest parrotfish species, accounted for 87.5% of the erosion and 99.5% of the coral predation on outer-shelf reefs. B. muricatum displayed little evidence of selectivity of feeding, with most ubstrata being consumed in proportion to their availability. In contrast, the high density of Scarus rivulatus accounted for over 70% of the total grazing and sediment reworking on inner-shelf reefs. This marked variation in the roles of parrotfishes across the continental shelf suggests that each shelf system is shaped by fundamentally different processes. [ABSTRACT FROM AUTHOR]

Few studies have examined the relative functional impacts of individual herbivorous fish species on coral reef ecosystem processes in the Indo-Pacific. This study assessed the potential grazing impact of individual species within an inshore herbivorous reef fish assemblage on the central Great Barrier Reef (GBR), by determining which fish species were able to remove particular macroalgal species. Transplanted multiple-choice algal assays and remote stationary underwater digital video cameras were used to quantify the impact of local herbivorous reef fish species on 12 species of macroalgae. Macroalgal removal by the fishes was rapid. Within 3 h of exposure to herbivorous reef fishes there was significant evidence of intense grazing. After 12 h of exposure, 10 of the 12 macroalgal species had decreased to less than 15% of their original mass. Chlorodesmis fastigiata (Chlorophyta) and Galaxaura sp. (Rhodophyta) showed significantly less susceptibility to herbivorous reef fish grazing than all other macroalgae, even after 24 h exposure. Six herbivorous and/or nominally herbivorous reef fish species were identified as the dominant grazers of macroalgae: Siganus doliatus, Siganus canaliculatus, Chlorurus microrhinos, Hipposcarus longiceps, Scarus rivulatus and Pomacanthus sexstriatus. The siganid S. doliatus fed heavily on Hypnea sp., while S. canaliculatus fed intensively on Sargassum sp. Variation in macroalgal susceptibility was not clearly correlated with morphological and/or chemical defenses that have been previously suggested as deterrents against herbivory. Nevertheless, the results stress the potential importance of individual herbivorous reef fish species in removing macroalgae from coral reefs. [ABSTRACT FROM AUTHOR]

The evolution of ecological processes on coral reefs was examined based on Eocene fossil fishes from Monte Bolca, Italy and extant species from the Great Barrier Reef, Australia. Using ecologically relevant morphological metrics, we investigated the evolution of herbivory in surgeonfishes (Acanthuridae) and rabbitfishes (Siganidae). Eocene and Recent surgeonfishes showed remarkable similarities, with grazers, browsers and even specialized, long-snouted forms having Eocene analogues. These long-snouted Eocene species were probably pair-forming, crevice-feeding forms like their Recent counterparts. Although Eocene surgeonfishes likely played a critical role as herbivores during the origins of modern coral reefs, they lacked the novel morphologies seen in modern Acanthurus and Siganus (including eyes positioned high above their low-set mouths). Today, these forms dominate coral reefs in both abundance and species richness and are associated with feeding on shallow, exposed algal turfs. The radiation of these new forms, and their expansion into new habitats in the Oligocene–Miocene, reflects the second phase in the development of fish herbivory on coral reefs that is closely associated with the exploitation of highly productive short algal turfs. [ABSTRACT FROM AUTHOR]