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Here, we utilise a unique, 70-year-long (1949–2017), high-resolution historical aerial imagery dataset to track changes to coral reef structures in Bill’s Bay on the Ningaloo coast. Reef habitat was distinguished from sand and rubble substrates based on imagery greyscale values and autoclassified using unsupervised image analysis in ArcMap. This approach was validated through comparison of reef structure (defined by bathymetric LiDAR imagery), greyscale values of aerial photography taken during the same survey, and in-water ground-truthed photographs. Long-term (1990–2015) live coral cover data were then compared with changes in reef structure. Reef structure increased from 11 to 38% within Bill’s Bay between 1949 and 1990. A coral spawn-induced hypoxia event in 1989 caused a loss of live coral cover from 50 to 7%, a 25% reduction in reef structure by 2002, and a switch from branching to massive coral-dominated reef. From 2002, reef structure recovered and continued to expand, peaking at 41% of total area (2017). Live coral cover in 2015 (46%) matches this measured increase in reef structure, despite a drop in coral cover in 2008. Discrepancies observed between live coral cover and reef structure during the 2002–2010 period reflect the persistence of the massive dominated coral community and in situ dead reef framework. Across the entire study period, reef growth was most prominent along the south-western edge of the bay, possibly due to an increase in the availability of hard substrate for coral recruitment. This study provides new insights into reef health over decadal timescales by capturing changes in reef geomorphology that go beyond the spatial scale and scope of traditional in-water assessments. These data further highlight that coral reef structure in Bill’s Bay has expanded even with frequent natural disturbances affecting the region over the last 70 years.

Este artículo contiene 17 páginas, 8 figuras, 5 tablas., Complex histories of chronic and acute sea surface temperature (SST) stresses are expected to trigger taxon- and location-specific responses that will ultimately lead to novel coral communities. The 2016 El Niño-Southern Oscillation provided an opportunity to examine largescale and recent environmental histories on emerging patterns in 226 coral communities distributed across 12 countries from East Africa to Fiji. Six main coral communities were identified that largely varied across a gradient of Acropora to massive Porites dominance. Bleaching intensity was taxon-specific and was associated with complex interactions among the 20 environmental variables that we examined. Coral community structure was better aligned with the historical temperature patterns between 1985 and 2015 than the 2016 extreme temperature event. Additionally, bleaching responses observed during 2016 differed from historical reports during past warm years. Consequently, coral communities present in 2016 are likely to have been reorganized by both long-term community change and acclimation mechanisms. For example, less disturbed sites with cooler baseline temperatures, higher mean historical SST background variability, and infrequent extreme warm temperature stresses were associated with Acropora-dominated communities, while more disturbed sites with lower historical SST background variability and frequent acute warm stress were dominated by stress-resistant massive Porites corals. Overall, the combination of taxon-specific responses, community-level reorganization over time, geographic variation, and multiple environmental stressors suggest complex responses and a diversity of future coral communities that can help contextualize management priorities and activities., T.R.M. and N.A.M. received support from the John D. and Catherine T. MacArthur Foundation, and the Sustainable Poverty Alleviation from Coastal Ecosystem Services (SPACES) project, number NE-K010484-1. E.S.D. was supported by an NSERC Banting Postdoctoral Fellowship and the John D. and Catherine T. MacArthur Foundation. Data collection in the Solomon Islands was supported by the Wallace Research Foundation, and the Waitt Foundation supported data collection in Fiji. Maldives data collection was supported by IUCN and USAID. M.M.M.G. received support from the French National Research Agency under the STORISK project (no. ANR-15-CE03- 0003). Data collection in Zanzibar was partly supported by the NORHED project coordinated by the State University of Zanzibar (SUZA). The Tiffany & Co. Foundation and the John D. and Catherine T. MacArthur Foundation supported data collection at sites in the western Indian Ocean. V.J.P. received support from the DST-INSPIRE Faculty Programme, and Z. Tyabji and S. Chandrasekhar assisted V.J.P. with data collection in the Andaman Islands. R.A. received funding support from the Pew Marine Fellowship and an Intramural Project from the Spanish National Research Council (CSIC-201330E062). S.A.K. was funded by the VILLUM Foundation (grant no. 10114). A.T.H. received funding from the Carnegie Corporation of New York. Indonesia data collection was supported by John D. and Catherine T. MacArthur Foundation and Margaret A. Cargill Philanthropies. The following people assisted with data collection: A. Baird, A. Halford, S. Keith, C. Miternique, E. Montocchio, C. Muhando, J. Ndagala, and N. Summers.

Western Australia’s coral reefs have largely escaped the chronic pressures affecting other reefs around the world, but are regularly affected by seasonal storms and cyclones, and increasingly by heat stress and coral bleaching. Reef systems north of 18°S have been impacted by heat stress and coral bleaching during strong El Nino phases and those further south during strong La Nina phases. Cumulative heat stress and the extent of bleaching throughout the northern reefs in 2016 were higher than at any other time on record. To assess the changing regime of disturbance to reef systems across Western Australia (WA), we linked their site-specific exposure to damaging waves and heat stress since 1990 with mean changes in coral cover. Since 2010, there has been a noticeable increase in heat stress and coral bleaching across WA. Over half the reef systems have been severely impacted by coral bleaching since 2010, which was further compounded by cyclones at some reefs. For most (75%) reef systems with long-term data (5–26 yrs), mean coral cover is currently at (or near) the lowest on record and a full recovery is unlikely if disturbances continue to intensify with climate change. However, some reefs have not yet experienced severe bleaching and their coral cover has remained relatively stable or increased in recent years. Additionally, within all reef systems the condition of communities and their exposure to disturbances varied spatially. Identifying the communities least susceptible to future disturbances and linking them through networks of protected areas, based on patterns of larval connectivity, are important research and management priorities in coming years while the causes of climate change are addressed.

Aim To describe, model and assess the relative importance of environmental and climatic factors likely influencing the regional distribution of coral cover and assemblages with contrasting life histories and susceptibilities to bleaching. Location We compiled the first comprehensive empirical dataset for coral communities in the south-eastern Indian Ocean (SEIO), incorporating information from 392 sites along the western coast of Australia and offshore atolls/islands across ~19° of latitude. Methods We assessed hard coral cover and community composition to genus using point-intercept transects or point-count analysis of digital images taken along transects. We explored spatial variation in environmental conditions and in composition of corals with contrasting life histories. After de-trending the temporal patterns, we assessed the relative importance of environmental metrics to coral cover, life histories and bleaching susceptibility using a full subsets model-selection approach with generalized additive mixed models, accounting for both temporal and among site variation. Results The distribution of temperature, light, the frequency of temperature anomalies and tropical cyclones appear to be drivers of coral community structure. Functional diversity of low- to mid-latitude coral communities may convey some resilience to thermal stress, while higher latitude communities dominated by Competitive and Bleaching-Susceptible taxa may lack this functional resilience. These patterns likely reflect varying historical exposure to cyclones and temperature anomalies. Main conclusions As evident in recent years, changing background conditions and regimes of disturbance in coming decades will shift the distribution, functional diversity and resilience of coral reefs throughout the SEIO. The rate and magnitude of environmental change will ultimately determine the future of the tropical reefs and whether the higher latitude reefs provide some refuge from climate change. Our study highlights the need to quantify the distributional properties of key environmental metrics to better understand and predict reef condition through coming decades.

The movement of water can have a significant influence on the vulnerability of hermatypic corals to environmental disturbances such as cyclone damage, heat stress and anoxia. Here, we explore the relationship between small reef-scale water circulation patterns and measured differences in the abundance, composition and vulnerability of coral assemblages over decades. Changes in coral cover and community structure within Bill’s Bay (Ningaloo Reef, Western Australia) over a 22-yr period, during which multiple disturbance events (including mass bleaching, anoxia, and tropical cyclones) have impacted the area, were compared with spatial variation in water residence times (WRT). We found that reef sites associated with longer water residence times (WRT >15 h) experienced higher rates of coral mortality during acute environmental disturbances compared to reef sites with shorter WRT. Shifts in coral community composition from acroporid to faviid-dominated assemblages were also more prominent at sites with long WRT compared to reef sites with shorter WRT, although shifts in community composition were also observed at sites close to shore. Interestingly, these same long-WRT sites also tended to have the fastest recovery rates so that coral cover was returned to original levels of approximately 20% over two decades. This study provides empirical evidence that spatial patterns in water circulation and flushing can influence the resilience of coral communities, thus identifying areas sensitive to emerging threats associated with global climate change.

Este artículo contiene 10 páginas, 5 figuras., Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy. Strategic conservation and management requires identification of the environmental and socioeconomic factors driving the persistence of scleractinian coral assemblages—the foundation species of coral reef ecosystems. Here, we compiled coral abundance data from 2,584 Indo-Pacific reefs to evaluate the influence of 21 climate, social and environmental drivers on the ecology of reef coral assemblages. Higher abundances of framework-building corals were typically associated with: weaker thermal disturbances and longer intervals for potential recovery; slower human population growth; reduced access by human settlements and markets; and less nearby agriculture. We therefore propose a framework of three management strategies (protect, recover or transform) by considering: (1) if reefs were above or below a proposed threshold of >10% cover of the coral taxa important for structural complexity and carbonate production; and (2) reef exposure to severe thermal stress during the 2014–2017 global coral bleaching event. Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse.

High densities of the corallivorous crown-of-thorns starfish (CoTS; Acanthaster sp.) have occurred throughout the Indo-Pacific often resulting in widespread coral loss. Whilst CoTS have previously been recorded at Barrow and the Montebello Islands, in the Pilbara offshore bioregion of northwestern Australia, their densities were relatively low. Outbreak densities of CoTS have been described as the level at which the rate of coral consumption by the starfish is equal to or greater than rate at which the coral grows. In 2014, we recorded densities as high as 320 ± 58 CoTS ha−1 in the region which is well above recognised outbreak densities. Whilst there is little terrestrial runoff and agriculture in the Pilbara region, both temperature and chlorophyll-α levels appear to be sufficient to allow a high degree of CoTS larval success in most years. The region was subjected to anomalously high water temperatures during the summers of 2010–2011 and particularly 2012–2013 which resulted in the mortality of almost 70% of live coral. We hypothesise that the high densities of CoTS observed are a result of CoTS responding to a reduced food supply and aggregating around the remaining live coral resulting in outbreak densities rather than a significant increase in the number of CoTS in the area. The small amount of remaining live coral is concentrated in a few areas and this, combined with high densities of CoTS in these areas, suggest that CoTS represent a significant threat to the recovery of the coral communities of the region.

Information for monitoring marine communities is increasingly collected using digital imagery and there is a need to understand how data collected using different methods compare. This study investigated the comparability of benthic data collected by downward facing diver operated stereo-video (DOV) with a forward facing stereo-DOV typically used in fish surveys. Data sets were collected by both methods from the same transect along which the benthos visible in each method was identified by taxonomy, growth form or substratum class. Analyses indicated that 77% of taxa were identified by both methods however, forward facing-DOV recorded 35 genera and downward-DOV 43 genera and there were significant (p

Coral reefs have been heavily affected by elevated sea-surface temperature (SST) and coral bleaching since the late 1980s; however, until recently coastal reefs of north-western Australia have been relatively unaffected compared to Timor Sea and eastern Australian reefs. We compare SST time series with changes in coral cover spanning a period of up to 36 years to describe temporal and spatial variability in bleaching and associated coral mortality throughout the Pilbara–Ningaloo region. Declines in coral cover ranged from 12.5 to 51.3%, with relative declines ranging from 38 to 92%. Since 2013, coral cover throughout the region has declined to historically low levels at four of five subregions, with impaired recovery occurring at two subregions. Observations are consistent with global trends of repeated severe heat waves, coral bleaching and acute declines in coral cover. Locations within this study region have already experienced multiple coral-bleaching events within a period of less than 5 years. There is a high likelihood that reefs in the western Pilbara and northern Ningaloo regions will experience more frequent marine heatwaves, coral bleaching and mortality events in the future. Action, therefore, needs to be taken now to support the resilience of coral reef ecosystems in the region, which is arguably the most important coral-reef province on Australia’s western coast.

Este artículo contiene 7 páginas, 2 tablas, 2 figuras., Under extreme heat stress, corals expel their symbiotic algae and colour (that is, ‘bleaching’), which often leads to widespread mortality. Predicting the large-scale environmental conditions that reinforce or mitigate coral bleaching remains unresolved and limits strategic conservation actions1,2. Here we assessed coral bleaching at 226 sites and 26 environmental variables that represent different mechanisms of stress responses from East Africa to Fiji through a coordinated effort to evaluate the coral response to the 2014–2016 El Niño/ Southern Oscillation thermal anomaly. We applied common time-series methods to study the temporal patterning of acute thermal stress and evaluated the effectiveness of conventional and new sea surface temperature metrics and mechanisms in predicting bleaching severity. The best models indicated the importance of peak hot temperatures, the duration of cool temperatures and temperature bimodality, which explained ~50% of the variance, compared to the common degree-heating week temperature index that explained only 9%. Our findings suggest that the threshold concept as a mechanism to explain bleaching alone was not as powerful as the multidimensional interactions of stresses, which include the duration and temporal patterning of hot and cold temperature extremes relative to average local conditions., T.R.M. and N.A.M. received support from the John D. and Catherine T. MacArthur Foundation and the Sustainable Poverty Alleviation from Coastal Ecosystem Services (SPACES) NE-K010484-1 project. E.S.D. was supported by a Banting Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada and the John D. and Catherine T. MacArthur Foundation. Data collection in the Solomon Islands was supported by the Wallace Research Foundation, and the Waitt Foundation supported data collection in Fiji. Maldives data collection was supported by IUCN and USAID. M.M.M.G. received support from the French National Research Agency under the STORISK project (no. ANR-15-CE03-0003). Data collection in Zanzibar was partly supported by the NORHED project coordinated by the State University of Zanzibar (SUZA). The Tiffany & Co. Foundation and the John D. and Catherine T. MacArthur Foundation supported data collection in some Western Indian Ocean reefs. V.J.P. received support from the DST-INSPIRE Faculty Programme, and Z. Tyabji and S. Chandrasekhar assisted V.J.P. with data collection in the Andaman Islands. R.A. received funding support from the Pew Marine Fellowship and an Intramural Project from the Spanish National Research Council (CSIC-201330E062). S.A.K. was funded by the VILLUM Foundation (no. 10114). A.T.H. received funding from the Carnegie Corporation of New York. Indonesia data collection was supported by the John D. and Catherine T. MacArthur Foundation and Margaret A. Cargill Philanthropies. We thank the following people for assistance with data collection: A. Baird, A. Halford, R. J.-L. Komeno, C. Miternique, A. dan Muhidin, E. Muttaqin, E. Montocchio, C. Muhando, S. Pardede, N. Summers and S. Yadav.

Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy. Strategic conservation and management requires identification of the environmental and socioeconomic factors driving the persistence of scleractinian coral assemblages-the foundation species of coral reef ecosystems. Here, we compiled coral abundance data from 2,584 Indo-Pacific reefs to evaluate the influence of 21 climate, social and environmental drivers on the ecology of reef coral assemblages. Higher abundances of framework-building corals were typically associated with: weaker thermal disturbances and longer intervals for potential recovery; slower human population growth; reduced access by human settlements and markets; and less nearby agriculture. We therefore propose a framework of three management strategies (protect, recover or transform) by considering: (1) if reefs were above or below a proposed threshold of >10% cover of the coral taxa important for structural complexity and carbonate production; and (2) reef exposure to severe thermal stress during the 2014-2017 global coral bleaching event. Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse.

The effective management of a coral reef system relies on a detailed understanding of the population structure of dominant habitat-forming species. For some corals, however, high levels of phenotypic plasticity have made species delineation based on morphological character- istics alone unreliable, suggesting that previous studies of population genetic structure may have been influenced by the inclusion of multiple genetic lineages in the analyses. We examined the population structure of the Pocillopora damicornis morphospecies along the World Heritage Ningaloo Coast, Western Australia, and recovered 2 mitochondrial haplotypes from sympatrically occurring colonies possessing morphological characteristics consistent with taxonomic classifica- tion of P. damicornis. Despite a high degree of genetic differentiation between these lineages, we detected low levels of unidirectional admixture between them, suggesting that reproductive bar- riers are not fully developed. We found dual modes of reproduction for both lineages with consid- erable variation in the contribution of sexual reproduction among sample sites. Lastly, we identi- fied a high dispersal potential of sexually produced propagules in the most common lineage with positive spatial autocorrelation detected over distances up to 60 km. Based on these results, it appears that populations of P. damicornis have a high capacity to recover from environmental per- turbations as long as the effects of disturbances are patchy across Ningaloo Reef.

Near real-time observation of sea temperature is an important management tool for monitoring the impacts associated with a changing climate on a range of marine communities particularly within marine protected areas. However, limitations exist when using data derived from satellite remote sensing as virtual stations are usually distant from areas of interest for management. Modelled sea surface temperature will, in most cases, provide a general over a large spatial scale rather than a specific prediction. Understanding the relationship between remotely sensed sea temperature and in situ temperature enables real-time management responses to sea temperature, in relation to both long-term changes and short-term anomalies, and their biological implications. Historically, the effects of most thermal stress events on marine communities have been observed opportunistically or realised well after the event, due to the use of in situ loggers and the associated time-lag between the event, logger retrieval and data interpretation. Understanding the susceptibility of marine communities to, and recovery from, thermal stress events requires reliable estimation of the events in real time at local spatial scales. To further understand the relationship between in situ and satellite derived sea temperatures, and develop a real-time monitoring tool, a simple linear interpolation was undertaken to estimate local in situ temperature, at depth, using near real-time satellite derived sea surface temperatures. The US National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch 50 km sea surface temperature (SST) data was selected because of its readily available and continual near real-time update of sea surface temperatures worldwide. In situ temperature logger data from four Western Australian marine protected areas (MPAs) were used to develop and test the linear interpolation. Utilising the model, we were able to successfully estimate the in situ temperature to within ±1 °C, at least 78% of the time, including temperature anomalies experienced in February 2011, at sites of interest across the four MPAs. This simple linear interpolation model will be used to improve near real-time estimates of temperature for broadscale monitoring of MPAs throughout Western Australia, allowing greater understanding and informed management response to long-term changes and short-term temperature anomalies. Future expansion of the sites monitored, improved satellites resolution and an annual review of data sources will ensure that the data used for management of this threat to water quality remains at the highest level of accuracy possible with the available data.

Areas closed to fishing are advocated as both fisheries management and biodiversity conservation tools. However, few studies investigate the responses of suites of both target and non-target fish species within an assemblage, which is an important consideration for ecosystem-based fisheries management approaches. Diver-operated stereo-video was used to assess the abundance and length of coral reef fish across multiple areas both open and closed to fishing at the Houtman Abrolhos Islands, Western Australia. After taking into consideration spatial differences in benthic habitat, the composition of fish assemblages was found to differ between open and closed areas. The target species, Plectropomus leopardus, was approximately two times more abundant in closed areas. Furthermore, 51 % of P. leopardus were larger than the minimum legal length (MLL) for retention in closed areas compared with only 1.8 % in areas open to fishing. Another target species, Choerodon rubescens was surveyed in greater abundance at sizes larger than the MLL in closed areas (64 % >400 mm) in comparison with areas open to fishing (36 %). A number of non-target species were also larger in closed areas (e.g., Kyphosus cornelii, Scarus schlegeli). In contrast, several non-targeted prey species were more abundant in open areas (e.g., Pomacentrus milleri was six times more abundant in open areas). Our results document complex responses of target and non-target species in closed areas at the Houtman Abrolhos Islands.

Methods for monitoring the status of marine communities are increasingly adopting the use of images captured in the field. However, it is not always clear how data collected from photographic images relate to historic data collected using traditional underwater visual census methods. Here, we compare coral health and disease data collected in situ by scuba divers with photographic images collected simultaneously at 12 coral reef sites. Five globally relevant coral diseases were detected on 194 colonies from in situ surveys and 79 colonies from photos, whilst 698 colonies from in situ surveys and 535 colonies from photos exhibited signs of compromised health other than disease. Comparisons of in situ surveys with photographic analyses indicated that the number of disease cases occurring in the examined coral populations (prevalence) was six times higher (4.5 vs. 0.8% of colonies), whilst compromised health was three times higher (14 vs. 4% of colonies) from in situ surveys. Skeletal eroding band disease, sponge overgrowth and presence of Waminoa flatworms were not detected in photographs, though they were identified in situ. Estimates of black band disease and abnormally pigmented coral tissues were similar between the two methods. Estimates of the bleached and healthy colonies were also similar between methods and photographic analyses were a strong predictor of bleached (r 2 = 0.8) and healthy (r 2 = 0.5) colony prevalence from in situ surveys. Moreover, when data on disease and compromised health states resulting in white or pale coral colony appearance were pooled, the prevalence of ‘white’ colonies from in situ (14%) and photographic analyses (11%) were statistically similar. Our results indicate that information on coral disease and health collected by in situ surveys and photographic analyses are not directly comparable, with in situ surveys generally providing higher estimates of prevalence and greater ability to identify some diseases and compromised states. Careful sampling of photographs can however identify signs of coral stress, including some coral diseases, which may be used to trigger early-warning management interventions.

Baited remote underwater stereo-video (stereo-BRUV) stations and diver operated stereo-video (stereo-DOV) transects are increasingly used to sample both tropical and temperate fish assemblages. Compared to in situ visual census methods, the use of stereo-video reduces inter- observer variability, improves definition of the sample unit area, increases accuracy of fish length estimates and provides a permanent record of the assemblage that can be validated where required or independently reanalysed. Previous studies have suggested that stereo-BRUV collects representa- tive data on both carnivorous and herbivorous species and can be more cost-efficient than diver- based survey methods. This study compares estimates of common fish assemblage metrics obtained with stereo-BRUV stations and stereo-DOV transects across 3 biogeographic regions, and uses a cost- optimization procedure to compare the efficiency of these 2 methods. Stereo-BRUV stations were found to sample greater species richness and obtain greater estimates of relative biomass of general- ist carnivores, but no differences occurred in the biomass of herbivores sampled by the 2 techniques. Stereo-BRUV stations generally obtained estimates of assemblage metrics with less variance, result- ing in greater power to detect spatial and temporal changes in the fish assemblage metrics. Cost-benefit analyses found that stereo-BRUV was generally more time efficient than stereo-DOV transects in terms of smaller standard error around the mean of the various metrics considered. How- ever, across the 3 biogeographic regions sampled there was considerable variation in the magnitude of these differences. Results suggest that stereo-BRUV stations are, in general, a more cost-effective method for monitoring fish assemblages than stereo-DOV transects.

Measures of fish abundance, assemblage composition and length were compared when sampled by baited remote underwater stereo-video (stereo BRUV) and diver-operated stereo-video transects (stereo DOV) at the Houtman Abrolhos Islands and Ningaloo Reef. Species richness counts were 40% higher on stereo BRUV than stereo DOV. Stereo BRUVs also recorded a greater number of large-bodied targeted species in higher abundance than stereo DOV (e.g. Lethrinus nebulosus, Plectropomus leopardus) at the Houtman Abrolhos and at Ningaloo Reef. Many non-targeted species were also recorded in greater abundances on stereo BRUV than stereo DOV (e.g. Coris auricularis, Gymnothorax spp). Stereo DOV transects recorded a greater abundance of some small-bodied Pomacentridae, Labridae and Scaridae species than did stereo BRUV, particularly at Ningaloo Reef. This study demonstrates that choice of sampling technique for surveys of reef fish can lead to very different biological interpretations of fish assemblage structure.

In recent decades, coral reef ecosystems have declined to the extent that reefs are now threatened globally. While many water quality parameters have been proposed to contribute to reef declines, little evidence exists conclusively linking specific water quality parameters with increased disease prevalence in situ. Here we report evidence from in situ coral health surveys confirming that chronic exposure to dredging-associated sediment plumes significantly increase the prevalence of white syndromes, a devastating group of globally important coral diseases. Coral health surveys were conducted along a dredging-associated sediment plume gradient to assess the relationship between sedimentation, turbidity and coral health. Reefs exposed to the highest number of days under the sediment plume (296 to 347 days) had two-fold higher levels of disease, largely driven by a 2.5-fold increase in white syndromes, and a six-fold increase in other signs of compromised coral health relative to reefs with little or no plume exposure (0 to 9 days). Multivariate modeling and ordination incorporating sediment exposure level, coral community composition and cover, predation and multiple thermal stress indices provided further confirmation that sediment plume exposure level was the main driver of elevated disease and other compromised coral health indicators. This study provides the first evidence linking dredging-associated sedimentation and turbidity with elevated coral disease prevalence in situ. Our results may help to explain observed increases in global coral disease prevalence in recent decades and suggest that minimizing sedimentation and turbidity associated with coastal development will provide an important management tool for controlling coral disease epizootics.

Technological advancements in remote sensing and GIS have improved natural resource managers' abilities to monitor large-scale disturbances. In a time where many processes are heading towards automation, this study has regressed to simple techniques to bridge a gap found in the advancement of technology. The near-daily monitoring of dredge plume extent is common practice using Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and associated algorithms to predict the total suspended solids (TSS) concentration in the surface waters originating from floods and dredge plumes. Unfortunately, these methods cannot determine the difference between dredge plume and benthic features in shallow, clear water. This case study at Barrow Island, Western Australia, uses hand digitising to demonstrate the ability of human interpretation to determine this difference with a level of confidence and compares the method to contemporary TSS methods. Hand digitising was quick, cheap and required very little training of staff to complete. Results of ANOSIM R statistics show remote sensing derived TSS provided similar spatial results if they were thresholded to at least 3 mg L(-1). However, remote sensing derived TSS consistently provided false-positive readings of shallow benthic features as Plume with a threshold up to TSS of 6 mg L(-1), and began providing false-negatives (excluding actual plume) at a threshold as low as 4 mg L(-1). Semi-automated processes that estimate plume concentration and distinguish between plumes and shallow benthic features without the arbitrary nature of human interpretation would be preferred as a plume monitoring method. However, at this stage, the hand digitising method is very useful and is more accurate at determining plume boundaries over shallow benthic features and is accessible to all levels of management with basic training.