Hugh Sweatman's research while affiliated with Australian Institute of Marine Science and other places

Publications (62)

Research on the coral-eating crown-of-thorns starfish (CoTS) has waxed and waned over the last few decades, mostly in response to population outbreaks at specific locations. This review considers advances in our understanding of the biology and ecology of CoTS based on the resurgence of research interest, which culminated in this current special issue on the Biology, Ecology and Management of Crown-of-Thorns Starfish. More specifically, this review considers progress in addressing 41 specific research questions posed in a seminal review by P. Moran 30 years ago, as well as exploring new directions for CoTS research. Despite the plethora of research on CoTS (>1200 research articles), there are persistent knowledge gaps that constrain effective management of outbreaks. Although directly addressing some of these questions will be extremely difficult, there have been considerable advances in understanding the biology of CoTS, if not the proximate and ultimate cause(s) of outbreaks. Moving forward, researchers need to embrace new technologies and opportunities to advance our understanding of CoTS biology and behavior, focusing on key questions that will improve effectiveness of management in reducing the frequency and likelihood of outbreaks, if not preventing them altogether.
Reporting progress against targets for international biodiversity agreements is hindered by a shortage of suitable biodiversity data. We describe a cost-effective system involving Reef Life Survey citizen scientists in the systematic collection of quantitative data covering multiple phyla that can underpin numerous marine biodiversity indicators at high spatial and temporal resolution. We then summarize the findings of a continental-and decadal-scale State of the Environment assessment for rocky and coral reefs based on indicators of ecosystem state relating to fishing, ocean warming, and invasive species and describing the distribution of threatened species. Fishing impacts are widespread, whereas substantial warming-related change affected some regions between 2005 and 2015. Invasive species are concentrated near harbors in southeastern Australia, and the threatened-species index is highest for the Great Australian Bight and Tasman Sea. Our approach can be applied globally to improve reporting against biodiversity targets and enhance public and policymakers' understanding of marine biodiversity trends.
Monitoring provides important feedback on how social and environmental systems are tracking and whether or not human activities, including management activities, are having an impact. This paper describes an approach applied to develop an integrated monitoring framework to inform adaptive management of the Great Barrier Reef World Heritage Area, a complex, multi-jurisdictional, multi-sectoral marine system of international importance. It identifies the gaps and opportunities to integrate the existing long-term, short-term and compliance-related monitoring and reporting initiatives to provide the information for more effective and efficient (adaptive) management of the Great Barrier Reef World Heritage Area. And as importantly it aligns expectations among different agencies about how monitoring will inform management. Fifty two high priority values, processes and pressures for management were identified along with 65 existing monitoring programs. Developing the monitoring framework was useful in several ways. First it brought together scientists, policy-makers, managers, and other interested stakeholders with different agendas, philosophies and incentives and established a common purpose, lexicon and language for an integrated monitoring program. Second, it highlighted the importance and usefulness of qualitative conceptual models as a framework for focused discussion around a set of hypotheses with relevance for management. Third, the process started an important conversation about defining and setting a realistic number of monitoring priorities for management. Finally, it has provided direction for how to build on existing initiatives to develop an integrated monitoring program for a globally significant world heritage area.
Ocean warming under climate change threatens coral reefs directly, through fatal heat stress to corals and indirectly, by boosting the energy of cyclones that cause coral destruction and loss of associated organisms. Although cyclone frequency is unlikely to rise, cyclone intensity is predicted to increase globally, causing more frequent occurrences of the most destructive cyclones with potentially severe consequences for coral reef ecosystems. While increasing heat stress is considered a pervasive risk to coral reefs, quantitative estimates of threats from cyclone intensification are lacking due to limited data on cyclone impacts to inform projections. Here, using extensive data from Australia's Great Barrier Reef (GBR), we show that increases in cyclone intensity predicted for this century are sufficient to greatly accelerate coral reef degradation. Coral losses on the outer GBR were small, localized and offset by gains on undisturbed reefs for more than a decade, despite numerous cyclones and periods of record heat stress, until three unusually intense cyclones over 5 years drove coral cover to record lows over >1500 km. Ecological damage was particularly severe in the central-southern region where 68% of coral cover was destroyed over >1000 km, forcing record declines in the species richness and abundance of associated fish communities, with many local extirpations. Four years later, recovery of average coral cover was relatively slow and there were further declines in fish species richness and abundance. Slow recovery of community diversity appears likely from such a degraded starting point. Highly unusual characteristics of two of the cyclones, aside from high intensity, inflated the extent of severe ecological damage that would more typically have occurred over 100s of km. Modelling published predictions of future cyclone activity, the likelihood of more intense cyclones within time frames of coral recovery by mid-century poses a global threat to coral reefs and dependent societies.
Crown-of-thorns starfish (CoTS; Acanthaster spp. ) are an outbreaking pest among many Indo-Pacific coral reefs that cause substantial ecological and economic damage. Despite ongoing CoTS research, there remain critical gaps in observing CoTS populations and accurately estimating their numbers, greatly limiting understanding of the causes and sources of CoTS outbreaks. Here we address two of these gaps by (1) estimating the detectability of adult CoTS on typical underwater visual count (UVC) surveys using covariates and (2) inter-calibrating multiple data sources to estimate CoTS densities within the Cairns sector of the Great Barrier Reef (GBR). We find that, on average, CoTS detectability is high at 0.82 [0.77, 0.87] (median highest posterior density (HPD) and [95% uncertainty intervals]), with CoTS disc width having the greatest influence on detection. Integrating this information with coincident surveys from alternative sampling programs, we estimate CoTS densities in the Cairns sector of the GBR averaged 44 [41, 48] adults per hectare in 2014.
1. Cyclical outbreaks of pests can impact the functioning of entire ecosystems. An eminent example is outbreaks of crown-of-thorns starfish (COTS; Acanthaster planci) that cause substantial coral mortality on the Great Barrier Reef (GBR). 2. We analyse COTS abundance and outbreaks with a Bayesian spatiotemporal model applied to a long-term survey of the GBR (1985–2014). We assess the relative increase in COTS abundance beyond that explained by a reef’s location and explanatory covariates, and thereby incorporate local reef characteristics into the identification of outbreaks, while allowing for both randomness and predictable patterns in the development of outbreaks. 3. The model results confirm that waves of COTS outbreaks originate near Lizard Island (14.67⁰S) and progress in a northwesterly or southeasterly direction, with the southward wave progressing about 60 km/year. 4. The model reveals several previously unidentified hotspots with high average COTS abundance. The abundance of COTS may also have decreased on reefs protected from fishing after an expansion of protected areas within the GBR Marine Park in 2004, which suggests that closing reefs to fishing may help control COTS. 5. Synthesis and applications. In this study, we use 30 years of data from the Great Barrier Reef to show that the timing and geographic location of crown-of-thorns starfish (COTS) outbreaks can be modelled by incorporating covariates, spatial and spatiotemporal dependence within a single coherent framework. The model can be used to identify areas of high average COTS abundance, to assess the impact of fishery management actions such as notake areas and to identify areas where waves of outbreaks may originate. The identification of outbreaks from noisy long-term spatially extensive data may help managers choose appropriate control strategies. This modelling approach is applicable to other ecosystems where outbreaks of damaging pests occur.
of sublethal injuries varied greatly among taxa, but was generally similar between locations; on the Great Barrier Reef, 99.4 % Porites colonies, 66 % of A. hyacinthus, and 64 % of Pocillopora had conspicuous injuries, compared to 92.4 % of Porites, 47.5 % of A. hyacinthus, and 44 % of Pocillopora colonies in Lhaviyani Atoll. These results suggest that background rates of mortality and injury, and associated resilience of coral populations and communities to large-scale disturbances, are conserved at large geographic scales, though adjacent colonies can have markedly different injury regimes, likely to lead to strong intraspe-cific variation in colony fitness and resilience.
The crown-of-thorns starfish (COTS) is a major predator of hard corals. Repeated COTS outbreaks in the Cairns and Central sections of the Great Barrier Reef (GBR) have been responsible for greater declines in coral cover than any other type of disturbance, including cyclones, disease, and coral bleaching. Knowledge of the precise timing and location of primary outbreaks could reveal the initial drivers of outbreaks and so could indicate possible management measures. In the central GBR, COTS outbreaks appear to follow major flooding events, but despite many years of observations, no primary outbreak has ever been unequivocally identified in the central and northern GBR. Here we locate a primary outbreak of COTS on the southern GBR which is not correlated with flooding. Instead it appears to have been the result of a combination of life history traits of COTS and prevailing oceanographic conditions. The hydrodynamic setting implies that the outbreak could disperse larvae to other reefs in the region.
Australian researchers in marine biodiversity and ecosystem science have a disproportionally high impact on global research as measured by their number of publications and their high profile leadership of international initiatives. At least 170 researchers from over 32 institutions contributed to this research which has a high uptake in government agencies and industries as this topic area is the basis from which the impact of human development is measured. Despite this, we know surprisingly little of our marine environment – only 5.2% of the seafloor in Australia's Commonwealth Marine Reserve network has been mapped to acceptable precision, and only about 10% of marine species has been identified. In order to improve and assess marine management initiatives in light of funding accountability, marine biodiversity and ecosystem research needs to be prioritized to fill the knowledge gaps that would have most impact on the diverse set of marine stakeholders. For example, monitoring, evaluation and reporting of ecosystem health and management performance of marine reserves is a clear need that has made some initial progress. Discovery targeted at identifying conservation values, including key ecological features, is another. Improved species inventories, environmental baselines and maps for all habitats ranging from the coasts to the deep sea and from tropical to polar, including nationally consistent approaches are essential to monitoring, evaluating attributing and managing increasing human impact (including cumulative impacts), and ensuring that Australia has a productive and clean marine environment. The difficulty of research in often extreme environments requires a substantial increase in Australia's marine infrastructure for seabed characterisation and biological sampling.
Ecological thresholds, associated with abrupt changes in the state and organisation of ecosystems, challenge both scientists and managers. Adaptive response to such changes, and planning for their occurrence, requires an understanding of the underlying drivers and system responses as well as appropriate monitoring. In addition to field studies, modelling can advance our ability to anticipate or deal with such major ecosystem shifts. Here, we used an existing multi - species model with smooth continuous functions that were modified to include thresholds representing 3 alternative scenarios of predator responses when prey numbers drop below a critical threshold: (I) no threshold-like response; (II) an abrupt decrease in breeding success by 90%, and (III) an abrupt halving of adult survival. Second, we analysed field observations from 3 independent marine case studies (abalone, starfish, penguins) for evidence of abrupt non-linear responses of predators to changes in abundance of principal prey. Third, we compared the model output with empirical results and tested (using both a statistical method and by fitting multispecies models) the 3 alternative response scenarios. With this approach, we found evidence for nonlinear changes in population parameters (such as survival rate) of predators as prey numbers declined below critical thresholds. As an example of the potential for this approach to inform management, we found that abundances of a range of marine predators become more variable as prey numbers decline, which may be a useful indicator that a system is approaching a tipping point.
The crown-of-thorns starfish (COTS) Acanthaster planci is one of the largest causes of coral cover loss on Australia's Great Barrier Reef. Numerous trophic-mediated and anthropogenic- related hypotheses, singly or in combination, have been proposed to explain COTS outbreaks, but the evidence remains inconclusive. There is, however, an urgent need for effective control and mitigation strategies. We develop a model of intermediate complexity for ecosystem assessments to describe the trophic interactions between juvenile and adult COTS and 2 groups of coral (fast-and slow-growing corals). By fitting to available data, the impact of prey-switching behaviour by COTS and its effects on the system are quantified. Simulations are used to evaluate the effects of (1) predation by large fish on adult COTS, (2) predation by benthic invertebrates on juvenile COTS, and (3) manual removal of adult COTS. The results highlight the effectiveness of invertebrate predation at reducing juvenile COTS numbers and suggest that manual removal is unlikely to be an effective control method except on a small scale. Our model focuses on the importance of trophic interactions in COTS control and provides an initial platform for future work which foresees the estimation of the effects of key predators, no-take areas, anthropogenic nutrient enhancement, and reef connectivity in mediating the spatio-temporal heterogeneity of COTS outbreaks.
The reduction in coral cover on many contemporary tropical reefs suggests a different set of coral community assemblages will dominate future reefs. To evaluate the capacity of reef corals to persist over various time scales, we examined coral community dynamics in contemporary, fossil, and simulated future coral reef ecosystems. Based on studies between 1987 and 2012 at two locations in the Caribbean, and between 1981 and 2013 at five locations in the Indo-Pacific, we show that many coral genera declined in abundance, some showed no change in abundance, and a few coral genera increased in abundance. Whether the abundance of a genus declined, increased, or was conserved, was independent of coral family. An analysis of fossil-reef communities in the Caribbean revealed changes in numerical dominance and relative abundances of coral genera, and demonstrated that neither dominance nor taxon was associated with persistence. As coral family was a poor predictor of performance on contemporary reefs, a trait-based, dynamic, multi-patch model was developed to explore the phenotypic basis of ecological performance in a warmer future. Sensitivity analyses revealed that upon exposure to thermal stress, thermal tolerance, growth rate, and longevity were the most important predictors of coral persistence. Together, our results underscore the high variation in the rates and direction of change in coral abundances on contemporary and fossil reefs. Given this variation, it remains possible that coral reefs will be populated by a subset of the present coral fauna in a future that is warmer than the recent past.
Many ecosystems face degradation unless factors that underpin their resilience can be effectively managed. In tropical reef ecosystems, grazing by herbivorous fishes can prevent coral–macroalgal phase shifts that commonly signal loss of resilience. However, knowledge of grazing characteristics that most promote resilience is typically experimental, localized, and sparse, which limits broad management applications. Applying sound ecological theory to broad-scale data may provide an alternative basis for ecosystem management. We explore the idea that resilience is positively related to the diversity within and among functional groups of organisms. Specifically, we infer the relative vulnerability of different subregions of the Great Barrier Reef (GBR) to phase shifts based on functional characteristics of the local herbivorous fish communities. Reef slopes on 92 reefs set in three zones of the continental shelf in eight latitudinal sectors of the GBR were surveyed on multiple occasions between 1995 and 2009. Spatial variation in fish community structure was high and driven primarily by shelf position. Measures of functional diversity, functional redundancy, and abundance were generally higher offshore and lower inshore. Two turbid inshore subregions were considered most vulnerable based on very low measures of herbivore function, and this was supported by the occurrence of phase shifts within one of three subregions. Eleven reefs that resisted phase shifts after major coral mortality included some with very low measures of herbivore function. The fact that phase shifts did not necessarily occur when large herbivores were scarce indicates that other environmental factors compensated to preserve resilience. Estimates of vulnerability based solely on herbivore function may thus prove conservative, but caution is appropriate, since compensatory factors are largely unknown and could be eroded unwittingly by anthropogenic stresses. Our data suggest that managing the threat of phase shifts in coral reef ecosystems successfully will require spatially explicit strategies that consider both the functional characteristics of local herbivore communities and environmental factors that may raise or lower resilience thresholds. A strong positive correlation between water clarity and the species richness and abundance of herbivorous fishes suggests that management of water quality is of generic importance to ensure the ecosystem services of this important group of herbivores.
The world's coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized. This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef. Based on the world's most extensive time series data on reef condition (2,258 surveys of 214 reefs over 1985-2012), we show a major decline in coral cover from 28.0% to 13.8% (0.53% y(-1)), a loss of 50.7% of initial coral cover. Tropical cyclones, coral predation by crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%, and 10% of the respective estimated losses, amounting to 3.38% y(-1) mortality rate. Importantly, the relatively pristine northern region showed no overall decline. The estimated rate of increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85% y(-1), demonstrating substantial capacity for recovery of reefs. In the absence of COTS, coral cover would increase at 0.89% y(-1), despite ongoing losses due to cyclones and bleaching. Thus, reducing COTS populations, by improving water quality and developing alternative control measures, could prevent further coral decline and improve the outlook for the Great Barrier Reef. Such strategies can, however, only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase.
Networks of no-take marine reserves (NTMRs) are widely used for managing marine resources. Because they restrict fishing, managers need to monitor reserves to reassure stakeholders that they are achieving the intended results. In 2004, the Great Barrier Reef (GBR) Marine Park was rezoned and the area of NTMRs was greatly increased. Using manta tow we assessed the effectiveness of the new NTMRs in conserving coral trout (Plectropomus and Variola spp.), the principle targets of the GBR reef line fishery. Over a six year period, we sampled regional groups of matched pairs of similar reefs, ones closed to fishing under the rezoning and ones that remained open. Coral trout populations were significantly higher in NTMRs. While coral trout populations declined on reefs open to fishing, stocks were maintained in NTMRs, highlighting the ongoing benefits of marine reserves.
The composition and functionality of ecologically important herbivorous fish assemblages were examined throughout much of Australia’s Great Barrier Reef (GBR). Diversity and abundance of surgeonfishes (Acanthuridae), parrotfishes (Labridae) and rabbitfishes (Siganidae) were strongly associated with position on the continental shelf, whilst effects of latitude were weaker and inconsistent. Species distributions varied considerably amongst taxonomic groups; parrotfishes were mostly widespread whilst distributions of surgeonfishes were often restricted. Most inshore environments supported depauperate herbivore assemblages dominated by different taxa and functional groups compared with assemblages in offshore environments. There were also strong cross-shelf transitions in the main taxa performing each functional role. Overall, this study show that the functional contributions of herbivorous fish assemblages to important ecosystem processes and the contributing taxa vary considerably amongst different GBR environments. Additionally, the two most numerically dominant herbivores actively select detritus, not algae, supporting increasing evidence for the importance of detritus in coral reef ecology.
Hughes et al. (Coral Reefs, 2011, in press) challenge our interpretations of the changes in coral cover observed on the Great Barrier Reef (GBR) between 1986 and 2004 (Sweatman et al. in Coral Reefs 30:521–531, 2011). They question whether we can accurately assign all causes of coral loss; we contend that this makes no difference to the observed changes. They defend the validity of historical data on coral cover from before the start of systematic large-scale monitoring and conclude that coral cover has been declining since at least 1960, but we find no trend in the early data. We remain convinced that combining data collected at different spatial scales (quadrats and transects in the past mixed with more recent whole-reef averages from manta tows) are likely to overestimate decline, because whole-reef averages will very rarely reach the high cover values that can occur at the quadrat scale. Hughes et al. (Coral Reefs, 2011, in press) state that we dismiss runoff as a cause of ecosystem degradation; we defend our interpretations and dispute some of their examples. In summary, we stand by our conclusion that coral cover on the GBR declined in the period 1986–2004 but through localised and unsynchronised changes that included recovery. KeywordsCoral cover–Meta-analyses–Great Barrier Reef–Degradation
Links between anomalously high sea temperatures and outbreaks of coral diseases known as White Syndromes (WS) represent a threat to Indo-Pacific reefs that is expected to escalate in a changing climate. Further advances in understanding disease aetiologies, determining the relative importance of potential risk factors for outbreaks and in trialing management actions are hampered by not knowing where or when outbreaks will occur. Here, we develop a tool to target research and monitoring of WS outbreaks in the Great Barrier Reef (GBR). The tool is based on an empirical regression model and takes the form of user-friendly interactive ~1.5-km resolution maps. The maps denote locations where long-term monitoring suggests that coral cover exceeds 26% and summer temperature stress (measured by a temperature metric termed the mean positive summer anomaly) is equal to or exceeds that experienced at sites in 2002 where the only severe WS outbreaks documented on the GBR to date were observed. No WS outbreaks were subsequently documented at 45 routinely surveyed sites from 2003 to 2008, and model hindcasts for this period indicate that outbreak likelihood was never high. In 2009, the model indicated that outbreak likelihood was high at north-central GBR sites. The results of the regression model and targeted surveys in 2009 revealed that the threshold host density for an outbreak decreases as thermal stress increases, suggesting that bleaching could be a more important precursor to WS outbreaks than previously anticipated, given that bleaching was severe at outbreak sites in 2002 but not at any of the surveyed sites in 2009. The iterative approach used here has led to an improved understanding of disease causation, will facilitate management responses and can be applied to other coral diseases and/or other regions. KeywordsClimate change–Coral disease–Great Barrier Reef–Environmental management–Outbreaks–White Syndromes
Changes from coral to macroalgal dominance following disturbances to corals symbolize the global degradation of coral reefs. The development of effective conservation measures depends on understanding the causes of such phase shifts. The prevailing view that coral–macroalgal phase shifts commonly occur due to insufficient grazing by fishes is based on correlation with overfishing and inferences from models and small-scale experiments rather than on long-term quantitative field studies of fish communities at affected and resilient sites. Consequently, the specific characteristics of herbivorous fish communities that most promote reef resilience under natural conditions are not known, though this information is critical for identifying vulnerable ecosystems. In this study, 11years of field surveys recorded the development of the most persistent coral–macroalgal phase shift (>7years) yet observed on Australia’s Great Barrier Reef (GBR). This shift followed extensive coral mortality caused by thermal stress (coral bleaching) and damaging storms. Comparisons with two similar reefs that suffered similar disturbances but recovered relatively rapidly demonstrated that the phase shift occurred despite high abundances of one herbivore functional group (scraping/excavating parrotfishes: Labridae). However, the shift was strongly associated with low fish herbivore diversity and low abundances of algal browsers (predominantly Siganidae) and grazers/detritivores (Acanthuridae), suggesting that one or more of these factors underpin reef resilience and so deserve particular protection. Herbivorous fishes are not harvested on the GBR, and the phase shift was not enhanced by unusually high nutrient levels. This shows that unexploited populations of herbivorous fishes cannot ensure reef resilience even under benign conditions and suggests that reefs could lose resilience under relatively low fishing pressure. Predictions of more severe and widespread coral mortality due to global climate change emphasize the need for more effective identification and protection of ecosystem components that are critical for the prevention of coral reef phase shifts. KeywordsCoral reef-Herbivorous fishes-Macroalgae-Phase shift-Diversity-Resilience
The Great Barrier Reef (GBR) provides a globally significant demonstration of the effectiveness of large-scale networks of marine reserves in contributing to integrated, adaptive management. Comprehensive review of available evidence shows major, rapid benefits of no-take areas for targeted fish and sharks, in both reef and nonreef habitats, with potential benefits for fisheries as well as biodiversity conservation. Large, mobile species like sharks benefit less than smaller, site-attached fish. Critically, reserves also appear to benefit overall ecosystem health and resilience: outbreaks of coral-eating, crown-of-thorns starfish appear less frequent on no-take reefs, which consequently have higher abundance of coral, the very foundation of reef ecosystems. Effective marine reserves require regular review of compliance: fish abundances in no-entry zones suggest that even no-take zones may be significantly depleted due to poaching. Spatial analyses comparing zoning with seabed biodiversity or dugong distributions illustrate significant benefits from application of best-practice conservation principles in data-poor situations. Increases in the marine reserve network in 2004 affected fishers, but preliminary economic analysis suggests considerable net benefits, in terms of protecting environmental and tourism values. Relative to the revenue generated by reef tourism, current expenditure on protection is minor. Recent implementation of an Outlook Report provides regular, formal review of environmental condition and management and links to policy responses, key aspects of adaptive management. Given the major threat posed by climate change, the expanded network of marine reserves provides a critical and cost-effective contribution to enhancing the resilience of the Great Barrier Reef.
The widespread decline of coral reefs requires integrated management measures across whole regions. Knowledge of demographic processes of reef organisms is important for informed management, yet current techniques for assessing such processes are time consuming, making it impractical to gather relevant information over large scales. We tested the usefulness of digital still photography as a rapid assessment technique to estimate coral recruitment--an important process in coral reef recovery. Estimates of the density and diversity of juvenile hard corals from digital images were compared with direct visual estimates from the same plots made in the field. Multiple plots were sampled on four reefs from a range of locations on Australia's Great Barrier Reef. On average, estimates of juvenile densities from photographic images were lower, in both absolute and relative terms, than that estimated from images. This was the case whether colonies <20 mm or <50 mm in diameter were considered. Overall differences between methods were generally greater at reefs where recruitment was higher, though proportional differences (density from images/density from direct visual census) still varied among reefs. Although the ranking of taxa, in terms of their densities, from the two methods were similar, the density of common genera was generally underestimated in images, and the occurrence of 'unknown' taxa was higher. We conclude that photographic images do not constitute a reliable rapid assessment method for estimating the spatial patterns in the density or diversity of juvenile hard corals.
Many marine scientists have concluded that coral reefs are moving toward or are locked into a seaweed-dominated state. However, because there have been no regional- or global-scale analyses of such coral reef "phase shifts," the magnitude of this phenomenon was unknown. We analyzed 3581 quantitative surveys of 1851 reefs performed between 1996 and 2006 to determine the frequency, geographical extent, and degree of macroalgal dominance of coral reefs and of coral to macroalgal phase shifts around the world. Our results indicate that the replacement of corals by macroalgae as the dominant benthic functional group is less common and less geographically extensive than assumed. Although we found evidence of moderate local increases in macroalgal cover, particularly in the Caribbean, only 4% of reefs were dominated by macroalgae (i.e., > 50% cover). Across the Indo-Pacific, where regional averages of macroalgal cover were 9-12%, macroalgae only dominated 1% of the surveyed reefs. Between 1996 and 2006, phase shift severity decreased in the Caribbean, did not change in the Florida Keys and Indo-Pacific, and increased slightly on the Great Barrier Reef due to moderate coral loss. Coral reef ecosystems appear to be more resistant to macroalgal blooms than assumed, which has important implications for reef management.
The functional roles of certain reef fishes are considered to facilitate recovery of reef ecosystems following coral mortality. Maintenance of high fish species diversity and associated functional diversity are thought to represent an ‘ecological insurance’ against ecosystem degradation. We examined responses of reef fish communities to varied levels of coral decline on 22 individual reefs of the Great Barrier Reef over an 11 yr period. Using 7 measures of species diversity, we found that fish diversity rarely decreased due to coral declines, even on 7 reefs that suffered massive coral losses (cover decreased by >75%). However, maintenance of fish diversity on those 7 reefs belied major changes in fish communities that involved increases in abundance of large herbivores and decreases in abundance of both coral-dependent fishes and species with no obvious dependence on coral. The magnitude of change in species abundances increased linearly with the magnitude of coral decline. While the proportion of species that increased or decreased in abundance varied considerably among reefs, 45 to 71% of fish species decreased in abundance on some reefs. Ecological function is related to abundance, so such decreases are likely to indicate reduced ecosystem function. Our results suggest that: (1) reef fish diversity may not be a reliable indicator of reef resilience and (2) predicted declines in coral cover due to global warming are likely to cause changes in the structure of reef fish communities, but the nature of these changes and associated capacity of reef fishes to assist ecosystem recovery will vary among reefs.
Coral reefs are consistently and increasingly subject to acute disturbance events that often lead to a reduction in live coral cover with concomitant effects on the diversity and abundance of coral reef fishes. Here we examine changes in both hard coral and reef-fish assemblages over 15 yr following major losses of coral from exposed reefs in 2 widely separated sectors of the Great Barrier Reef (GBR), Australia. While the rate and extent of increase in coral cover (from <15 to >60%) was similar in the 2 sectors, differences in the rugosity of the underlying reef framework influenced the structure of fish communities. Soon after disturbance, when coral cover was very low and the limestone reef framework constituted most of the surface relief, the relatively featureless substrate on reefs of the southern sector supported fewer fish species than reefs of the northern sector, which had a more rugose substrate. At first, northern reefs also had a higher proportion of herbivorous fish species, presumably because the more complex reef surface provided shelter and allowed them to exploit the abundant algal turf. With increasing coral cover, coral colonies came to provide most of the surface relief in both sectors, and species richness and the trophic structure of the fish communities converged. Variation in the cover of branching corals explained significant variation in the fish communities in both sectors over time, reflecting the importance of this growth form to small coralassociated fishes. These results show that the recovery of the coral community and the complexity of underlying reef framework interact to determine the functional structure of associated fish communities despite differences in regional settings.
The crown-of-thorns starfish, Acanthaster planci, is a predator of corals that is a major management issue on coral reefs [1]. It occurs throughout the Indo-Pacific and shows boom-bust population dynamics with low background densities and intermittent outbreaks. Three waves of population outbreaks have affected Australia's Great Barrier Reef (GBR) since the 1960s. The waves of outbreaks appear to start ∼15°S [2] and progress southward through the central GBR (Figure 1A), causing major losses of living coral on many reefs across a large area and dwarfing losses from other disturbances such as storms or coral bleaching over the same period [3]. Humans can potentially influence starfish population dynamics by exploiting predators, though evidence to date is circumstantial. Extensive surveys in the GBR Marine Park (GBRMP) show that protection from fishing affects the frequency of outbreaks: the relative frequency of outbreaks on reefs that were open to fishing was 3.75 times higher than that on no-take reefs in the mid-shelf region of the GBR, where most outbreaks occur, and seven times greater on open reefs if all reefs were included. Although exploited fishes are unlikely to prey on starfish directly, trophic cascades could favour invertebrates that prey on juvenile starfish.
No-take marine reserves (NTMRs) are much advocated as a solution to managing marine ecosystems, protecting exploited species and restoring natural states of biodiversity [1,2]. Increasingly, it is becoming clear that effective marine conservation and management at ecosystem and regional scales requires extensive networks of NTMRs [1,2]. The world's largest network of such reserves was established on Australia's Great Barrier Reef (GBR) in 2004. Closing such a large area to all fishing has been socially and politically controversial, making it imperative that the effectiveness of this new reserve network be assessed. Here we report evidence, first, that the densities of the major target species of the GBR reef line fisheries were significantly higher in the new NTMRs, compared with fished sites, in just two years; and second, that the positive differences were consistent for multiple marine reserves over an unprecedented spatial scale (>1,000 km).
Inshore reefs A team from James Cook University surveyed reef biota using underwater visual census (UVC) (S1) from 3, 9 and 4 no-take and open reef sites around three inshore island groups: Palm, Whitsunday, and Keppel Islands respectively. Sites were surveyed once before and once 1.5 - 2 years after the July 2004 rezoning of the GBRMP. Proportional changes in counts of coral trout were evaluated for open and no-take sites using a generalized linear mixed effects model (GLMM) with a Poisson error distribution and log link- function. Fixed effects were time (pre- vs post-rezoning), reserve status (open or no-take) and island group, with random intercepts for reef sites nested in island group. The change in coral trout density on no-take reef sites relative to changes on open reef sites was assessed using a separate GLMM with a fixed term for the interaction between reserve status and time (pre- vs post- rezoning). Parameters estimating the geometric mean counts of trout in fished and no-take areas (pre- and post-rezoning) were converted to densities and shown in Figure 1A.
Author Summary Coral reefs have been decimated over the last several decades. The global decline of reef-building corals is of particular concern. Infectious diseases are thought to be key to this mass coral mortality, and many reef ecologists suspect that anomalously high ocean temperatures contribute to the increased incidence and severity of disease outbreaks. This hypothesis is supported by local observations—for example, that some coral diseases become more prevalent in the summertime—but it has never been tested at large spatial scales or over relatively long periods. We tested the temperature–disease hypothesis by combining 6 years of survey data from reefs across 1,500 kilometers of Australia's Great Barrier Reef with a new ocean temperature database derived from satellite measurements. Our results indicate that major outbreaks of the coral disease white syndrome only occurred on reefs with high coral cover after especially warm years. The disease was usually absent on cooler, low-cover reefs. Our results suggest that climate change could be increasing the severity of disease in the ocean, leading to a decline in the health of marine ecosystems and the loss of the resources and services humans derive from them.
We investigated spatial patterns of synchrony among coral reef fish populations and environmental variables over an eight-year period on the Great Barrier Reef, Australia. Our aims were to determine the spatial scale of intra- and interspecific synchrony of fluctuations in abundance of nine damselfish species (genus Pomacentrus) and assess whether environmental factors could have influenced population synchrony. All species showed intraspecific synchrony among populations on reefs separated by < or =100 km, and interspecific synchrony was also common at this scale. At greater spatial scales, only four species showed intraspecific synchrony, over distances ranging from 100-300 km to 500-800 km, and no cases of interspecific synchrony were recorded. The two mechanisms most likely to cause population synchrony are dispersal and environmental forcing through regionally correlated climate (the Moran effect). Dispersal may have influenced population synchrony over distances up to 100 km as this is the expected spatial range for ecologically significant reef fish dispersal. Environmental factors are also likely to have synchronized population fluctuations via the Moran effect for three reasons: (1) dispersal could not have caused interspecific synchrony that was common over distances < or =100 km because dispersal cannot link populations of different species, (2) variations in both sea surface temperature and wind speed were synchronized over greater spatial scales (>800 km) than fluctuations in damselfish abundance (< or =800 km) and were correlated with an index of global climate variability, the El Niño-Southern Oscillation (ENSO), and (3) synchronous population fluctuations of most damselfish species were correlated with ENSO; large population increases often followed ENSO events. We recorded regional variations in the strength of population synchrony that we suspect are due to spatial differences in geophysical, oceanographic, and population characteristics, which act to dilute or enhance the effects of synchronizing mechanisms. We conclude that synchrony is common among Pomacentrus populations separated by tens of kilometers but less prevalent at greater spatial scales, and that environmental variation linked to global climate is likely to be a driving force behind damselfish population synchrony at all spatial scales on the Great Barrier Reef.
Ocean warming due to climate change could increase the frequency and severity of infectious coral disease outbreaks by increasing pathogen virulence or host susceptibility. However, little is known about how temperature anomalies may affect disease severity over broad spatial scales. We hypothesized that the frequency of warm temperature anomalies increased the frequency of white syndrome, a common scleractinian disease in the Indo-Pacific. We created a novel 4 km satellite temperature anomaly dataset using data from NOAA's Pathfinder program and developed four different temperature anomaly metrics, which we correlated with white syndrome frequency at 47 reefs spread across 1500 km of the Great Barrier Reef. This cross-sectional epidemiological analysis used data from disease field surveys conducted by the Australian Institute of Marine Science six to twelve months after the summer of 2002, a year of extensive coral bleaching. We found a highly significant positive relationship between the frequency of warm temperature anomalies and the frequency of white syndrome. There was also a highly significant, nearly exponential relationship between total coral cover and the number of disease cases. Further, coral cover modified the effect of temperature on disease frequency. Both high coral cover (>50%) and anomalously warm water appear to be necessary for white syndrome outbreaks to occur and these two risk factors explained nearly 75% of the variance in disease cases. These results suggest that rising ocean temperatures could exacerbate the effects of infectious diseases on coral reef ecosystems.
The territorial waters of Australia and Papua New Guinea (PNG) are similar in that they contain extensive, biodiverse coral reef systems that remain in relatively good condition, despite some recent setbacks. However there are stark contrasts in the socio-economic environments of the two countries; Australia is a modern developed economy with a high level of affluence, while PNG is still in transition from a basic subsistence economy. The different socio-economic circumstances have lead to a marked difference between the two countries in the way reef resources are used, and consequently, how they are managed. Approaches to reef management have continued to diverge during the past decade. Australia is setting an example to the rest of the world for the conservation of coral reefs through a system of central planning, legislation and enforcement. Conversely in PNG, there is minimal central management, although there is recognition by government of the importance of state controls and legislation. An alternative model is developing in PNG for a decentralised, community-based system for reef resource management driven largely by NGOs, because there are limited resources for national control. Results from established or planned monitoring programs will determine the effectiveness of these differing approaches in the long-term.
Using trained observers and video images of reef transects from many parts of the Great Barrier Reef, we investigated (1) accuracy of classification of benthos and (2) variability contributed by observers to the precision of estimates of benthic cover obtained from video tapes. In order to estimate accuracy of identification, benthic organisms were identified twice, first in the field and later from video images. These identifications were then compared. The effect of observer error on precision of benthic cover estimates was examined by having 2 observers sample the same video images on 3 separate occasions. These estimates were then compared at the level of different benthic groups (hard coral, soft coral and algae) and for different hierarchical levels of classification of hard corals (life form, family, genus and species). 'Benthic groups' (mean accuracy of 90 +/- 8%) and 'families of hard coral' (91 +/- 7%) were identified most accurately and least variably from video images, although many genera and some distinctive species were also identified reliably. Life forms of hard corals proved to be the least accurate and most variable level of classification, with a mean accuracy rating of 74 +/- 16%. There was little additional variation in estimates of cover when 2 trained observers sampled images, compared with variation in estimates of cover from repeated samples of images by a single observer. At 10% cover, variability in estimates made by a single observer resulted in mean CIs of 7.9 to 12.1%. Inclusion of variation between observers expanded CIs by only +/-0.22%. Furthermore, total observer error was small relative to estimates of cover. For example, at 30% cover, the mean Cl due to both between- and within-observer variability was 27.2 to 32.8%.
Changes in reef assemblages of corals and fishes following a tropical cyclone were assessed using data sets from (1) manta tow surveys of entire reef perimeters and (2) intensive surveys of specific sites, across 11 reefs lying close to the cyclone's track. Only one of the reefs experienced an obvious and immediate decline in mean coral cover (from 24 to 8%) due to the cyclone. The abundance and species richness of adult damselfish assemblages on intensive survey sites at this reef were not affected in the short term (6-8 weeks), despite the removal of 48% of living hard coral. Assemblages of adult fishes showed a similar lack of response at three other reefs where no significant habitat changes had occurred. Eleven to twelve months later, the total abundance of damselfishes had decreased substantially at eight of the sampled reefs, while the abundance of larger mobile fishes remained stable. We infer that the effects on coral assemblages reflect the short duration and orientation of the cyclone, the history of exposure to wave energy (influencing life-form structure and therefore degree of fragility), and the degree of consolidation of the reef matrix. The lack of short-term effects of the cyclone on adult fishes shows that these fishes can endure periods of intense underwater turbulence. The lack of change in damselfish assemblages weeks after loss of coral cover implies that this resource was not limiting adult fish densities. The reasons for widespread decreases in damselfish numbers 11-12 months after the cyclone are unknown.
While a relatively small proportion of coral reefs in the Great Barrier Reef (GBR) World Heritage Area lie within 20 km of the shore, those that do are the most accessible to coastal communities and most vulnerable to pollution and increased sediment loads caused by changes in coastal land use. There is little information on the status of inshore reefs in the southern GBR and very little ongoing monitoring of reef status. This four-day survey aimed to assess the status of major reef biota around the perimeter of nine islands within the Northumberland Islands group. Manta tows and spot observations on snorkel were used to assess reef development around the perimeter of all islands. SCUBA surveys provided more detailed information on benthos and fish assemblages on three island fringing reefs.
Competition for space among scleractinians by overgrowth, overtopping, extracoelenteric digestion and the use of sweeper tentacles is well recognized, but another potential mode of competitive interaction, allelopathy, is largely uninvestigated. In this study, chemical extracts from Tubastraea faulkneri Wells were tested for deleterious effects on competent larvae of 11 other species of coral belonging to seven genera of four scleractinian families. Larvae exposed to extract concentrations from 10 to 500 μg ml−1 consistently suffered higher mortality than larvae in solvent controls. Larvae of Platygyra daedalea (Ellis and Solander) and Oxypora lacera (Verrill) were the most sensitive, experiencing high mortality even at the lowest extract concentration. The toxic compounds from T. faulkneri did not kill any conspecific larvae. The estimated concentrations of active compounds within T. faulkneri tissues were 100–5000 times higher than the experimental concentrations. Pure compounds isolated from bioactive fractions of the extract were indole alkaloids identified as aplysinopsin, 6-bromoaplysinopsin, 6-bromo-2′-de-N-methylaplysinopsin and its dimer. The first three occur in other non-zooxanthellate corals in the same family as T. faulkneri, whereas the dimer is novel. These compounds could act as allelochemicals that prevent potential competitors from recruiting in the vicinity of T. faulkneri colonies and help to pre-empt interactions with competitively dominant species.
From 1992 to 1997 changes in cover of hard and soft corals and macro-algae were monitored using annual video transect surveys on the northeast flank of up to 52 reefs along most of the Great Barrier Reef (GBR). Trends in cover of hard corals, algae and soft corals were usually consistent among clusters of adjacent or nearby reefs. This consistency probably reflected the spatial scales of the effect of episodic disturbances caused by cyclones or crown-of-thorns starfish Acanthaster planci. Hence, our comprehensive monitoring of a single habitat provided an effective indicator of the status and trends on adjacent reefs. Moreover, we observed broad-scale patterns of increase and decline in coral cover that suggest that a 'patchwork mosaic' null model is a useful concept at scales of whole reefs and regions. At a large spatial scale (up to 10 degrees of latitude), cover of hard corals within the NE slope habitat averaged 29% (+/-12.4 standard deviation) and increased by 1.7% (+/-6.5) over 5 yr of surveys. Cover of soft corals and algae remained constant and averaged 14% (+/-12.4) and 41% (+/-16.6) respectively. Inner shelf, mid-shelf and outer shelf reefs in a 'recovery' phase increased their cover of hard coral at average annual rates of 2.6% (+/-3.0), 3.9% (+/-4.1) and 4.3% (+/-4.5) respectively. Year-to-year changes in cover of soft corals were typically smaller and less variable than changes in cover of hard corals or algae. There was no evidence of any shift to alternative stable states of assemblage composition.
Coral reefs are complex, biologically diverse, and highly valued ecosystems that are declining worldwide due to climate change and ocean acidification, overfishing, land-based sources of pollution, and other anthropogenic threats. To assist policymakers and resource managers at international, national, and local levels in effectively implementing ecosystem approaches to sustainable management and conservation of coral reefs and their biodiversity, it is necessary to have timely, unbiased integrated ecosystem observations about the conditions of coral reefs and the complex physical and biogeochemical processes supporting them. To provide these interdisciplinary ecosystem observations, an International network of Coral Reef Ecosystem Observing Systems (I-CREOS) is proposed that will organize and build upon existing coral reef observation systems being developed around the globe. This paper uses examples of some developing observation systems to demonstrate some of the approaches and technologies available for acquiring biological, physical, and geochemical observations using combinations of visual surveys, moored instrument arrays, spatial-hydrographic and water-quality surveys, satellite remote sensing, and hydrodynamic and ecosystem modeling. This fledgling, and hopefully expanding, network of observing systems represents the early stages of an integrated ecosystem observing system for coral reefs capable of providing policymakers, resource managers, researchers, and other stakeholders with essential information products needed to assess various responses of coral reef ecosystems to natural variability and anthropogenic perturbations. While significant challenges and gaps in the I-CREOS network remain, it demonstrably fulfills the requirements of an operational, integrated, inter-disciplinary, coastal component of GOOS. Continued support, further development, and open expansion of this emerging network are encouraged and needed to ensure the continually increasing value of the network's observational and predictive capacity. With common goals to maximize versatility, accessibility, and robustness, the existing infrastructure and capacity provide a foundation by which increased global cooperation and coordination could naturally lead to a globally comprehensive I-CREOS.
Summary This project has several components divided between the Australian Institute of Marine Science (AIMS) and Reef Check Australia (RCA). The AIMS monitoring program makes surveys of different sets of reefs in alternating years. Surveys of the long-term monitoring sites in the current years are on track though surveys of reefs in the Cairns sector were limited by unfavourable weather. Two more survey cruises are scheduled. Initial results of surveys completed so far found an increase in the number of reefs where crown-of-thorns starfish (COTS) were sighted north of Cairns, but to the north of the putative 'initiation zone' for the waves of outbreaks. Only single starfish were sighted on the majority of the reefs and no reef had outbreak densities, but similar surveys next year may be necessary. Secondly, some reefs in the Capricorn-Bunker group have lost coral cover, most probably due to storm events. The forthcoming surveys may provide some assessment of the effects of Tropical Cyclone Hamish. Analysis of results from the second set of surveys to assess the effects of rezoning the Great Barrier Reef (GBR) in 2004 found that the early increase in coral trout numbers and biomass in no-take zones compared with zones that were open to fishing has been maintained, but the differences have not increased significantly over the ensuing two years. There is no evidence of trophic cascades where the higher numbers of predatory fishes affect the numbers of prey after three to four years.
Climate change will affect populations and communities of marine fishes in many ways, ranging from indirect effects associated with habitat degradation and altered resource availability to direct effects of rapidly changing environmental conditions. In the short-term (up to 2030), the impact of climate change on Australia's tropical coastal and demersal fishes is largely tied to the fate of critical benthic habitats, especially for coral reef environments, which are highly vulnerable to elevated temperature and ocean acidification. There is good evidence and high consensus that climate-induced coral bleaching affects the community structure and abundance of reef-associated fishes, especially when it leads to the structural collapse of reef habitat. In the longer-term (after 2030), sea level rise and altered rainfall patterns will also significantly alter coastal wetlands that are important nursery areas for estuarine and nearshore species. In addition to the effects of habitat degradation, warmer ocean temperatures will cause distributional shifts in some tropical fishes, increasing the geographic ranges of some species and decreasing the ranges of others, including some commercially important species. Life history traits and population dynamics will be affected by warmer temperatures, with potential implications for fisheries yields. Altered oceanic circulation and ocean acidification could have very significant effects on populations and communities of coastal fishes. However, these impacts are still poorly understood and are likely to become most apparent in the longer term. There are a many critical knowledge gaps in our understanding of the effect of climate change on tropical marine fish, including the impact of warmer temperatures on adult reproduction, and the development, survival and behaviour of larvae; the effect of ocean acidification on the development, survival and behaviour; and the degree to which fish will acclimate or adapt to the expected rapid climate change.Non-reefal environments and commercially important species are especially understudied in relation to climate change impacts. Key strategies in mitigating effects of climate change on coastal marine Munday et al. 2009 fishes are to maintain and restore habitat quality, incorporate climate uncertainty into fisheries management plans, and limit impacts of other human activities in coastal regions.
oral reefs are the most diverse of all marine ecosystems, and they are rivaled in biodiversity by few ter- restrial ecosystems. They support peo- ple directly and indirectly by building islands and atolls. They protect shore- lines from coastal erosion, support fish- eries of economic and cultural value, provide diving-related tourism and serve as habitats for organisms that produce natural products of biomed- ical interest. They are also museums of the planet's natural wealth and places of incredible natural beauty. Despite their recognized biological, economic and aesthetic value, coral reefs are being destroyed at an alarm- ing rate throughout the world. Some countries have seen 50 percent of their coral reefs destroyed by human activi- ties in the past 15 years. Some human influences are acute—for example, mining reefs for limestone, dumping mine tailings on them, fishing with ex- plosives and cyanide, and land recla- mation. Reefs that experience such in- sults often die; those that deteriorate but survive cannot recover to their original health as long as the distur- bances continue. In other countries the disturbances are more chronic than acute. Reefs are assaulted by muddy runoff, nutrients and pesticides from adjacent river catchments, overfishing and global-warming effects. These dis- turbances affect the key parameters permitting reef resilience: water and substratum quality. As a result, corals fail to reproduce successfully, and the coral larvae arriving from more pris- tine reefs are unable to settle and thrive on substrata covered by mud, cyano- bacteria or fleshy algae. Coral popula- tions thus fail to recover or reestablish themselves. Can science help save coral reefs? Despite much talk about managing coral reefs, the potential role of science is limited. But it is important: Scientists can demonstrate the key processes con- trolling the health of coral reefs and how human activities damage them. Then, we can hope, land-use managers and marine-resources managers will be able to modify human behavior to re- duce or reverse damage to coral reefs. Toward this end we have developed a large-scale model for illuminating reef degradation and predicting the impact of future human activity.
This paper synthesises information from the Australian Institute of Marine Science (AIMS) Long Term Monitoring Project (LTMP), which involves making annual visits to about 50 reefs from north of Cooktown to the Capricorn-Bunker Group. Visual censuses of fish assemblages on reef fronts show clear cross-shelf differences at the family level and some north-south differences. Taxa showing cross-shelf differences include lutjanids and siganids being more common inshore and acanthurids, scarids and zanclids increasing in number offshore. Acanthurids, scat-ids, lutjanids and zanclids decline in abundance from north to south. As a family, pomacentrids show different cross-shelf distribution patterns at different latitudes. This is also true of most of the constituent genera. Building on this, inshore, and offshore fish assemblages were identified, as well as a group with a general distribution. The existence of these groups should be reflected in conservation initiatives. Reef fish assemblages have been shown to recover from major.habitat losses due to storms or Acanthaster planci outbreaks, presumably through larval recruitment from unaffected areas. Recent research suggests that larval dispersal is more localised that has previously been accepted.

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Top co-authors (50)

Ian Miller
  • Australian Institute of Marine Science
Michael J. Emslie
  • Australian Institute of Marine Science
David H Williamson
  • James Cook University
Angus A. Thompson
  • Australian Institute of Marine Science
Richard Evans
  • Marine Science Program
Michelle Jonker
  • Australian Institute of Marine Science
Aaron Macneil
  • Dalhousie University
Steven Delean
  • University of Adelaide

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