Climate change is radically altering the frequency, intensity and spatial scale of severe weather... more Climate change is radically altering the frequency, intensity and spatial scale of severe weather events, such as heatwaves , droughts, floods and fires 1. As the time interval shrinks between recurrent shocks 2-5 , the responses of ecosystems to each new disturbance are increasingly likely to be contingent on the history of other recent extreme events. Ecological memory defined as the ability of the past to influence the present trajectory of ecosystems 6,7-is also critically important for understanding how species assemblages are responding to rapid changes in disturbance regimes due to anthropogenic climate change 2,3,6-8. Here, we show the emergence of ecological memory during unprecedented back-to-back mass bleaching of corals along the 2,300 km length of the Great Barrier Reef in 2016, and again in 2017, whereby the impacts of the second severe heatwave, and its geographic footprint, were contingent on the first. Our results underscore the need to understand the strengthening interactions among sequences of climate-driven events, and highlight the accelerating and cumulative impacts of novel disturbance regimes on vulnerable ecosystems. Changes through time are fundamental to the study of ecology and evolution, yet our understanding of the contemporary condition of ecosystems often discounts the role of non-equilibrial dynamics and history 6,9. Emerging theoretical frameworks and models point to the important effects of time lags and memory, as the enduring influences of past experiences and changing conditions unfold over time 7. For example, the responses of ecosystems during ecological succession, and the evolution of life history traits, are key legacy effects of the history of recurrent disturbances 2. On most coral reefs, for instance, where recurrent tropical cyclones have historically been the most significant external disturbance 10 , regional-and global-scale bleaching of corals has become a major additional agent of mortality of reef-building corals in recent decades 5,11. Here, we document how ecological memory of severe coral bleaching on the Great Barrier Reef in 2016 12 subsequently transformed the response of corals to heat stress during a second marine heatwave in 2017. We show further that the geographic pattern of heat exposure in 2016 had a lingering impact on the spatial footprint of bleaching along the 2,300 km length of the world's largest reef system during the subsequent heatwave one year later-history has a geographic signal. Our results demonstrate the need to understand the combined , interactive effects of sequences of recurrent climate-related disturbances at a hierarchy of spatial scales, and the critical role of recent history for predicting ecological outcomes in an era of rapid global change. The response of corals to heat stress during the second of two unprecedented back-to-back bleaching events on the Great Barrier Reef was markedly different from the first. Heat stress-measured from satellites as degree heating weeks (DHW; °C-weeks)-was greater in 2017 on 79.9% of individual reefs (n = 3,863 reefs; Fig. 1a and Supplementary Fig. 1), yet despite the higher and/ or longer-lasting summer sea surface temperatures, the surviving corals were more resistant in 2017 to a recurrence of bleaching compared with the previous year (Fig. 1b and Supplementary Fig. 2). Specifically, in 2016, an exposure of 4-5 °C-weeks elicited a 50% probability of severe bleaching (affecting > 30% of corals), but in 2017 the same 50% response occurred at a much higher level of heat exposure of 8-9 °C-weeks. In comparison, an exposure of 8-9 °C-weeks in 2016 was associated with a >
The U.S. National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch (CRW) operates... more The U.S. National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch (CRW) operates a global 4-Month Coral Bleaching Outlook system for shallow-water coral reefs in collaboration with NOAA's National Centers for Environmental Prediction (NCEP). The Outlooks are generated by applying the algorithm used in CRW's operational satellite coral bleaching heat stress monitoring, with slight modifications, to the sea surface temperature (SST) predictions from NCEP's operational Climate Forecast System Version 2 (CFSv2). Once a week, the probability of heat stress capable of causing mass coral bleaching is predicted for 4- months in advance. Each day, CFSv2 generates an ensemble of 16 forecasts, with nine runs out to 45-days, three runs out to 3-months, and four runs out to 9-months. This results in 28-112 ensemble members produced each week. A composite for each predicted week is derived from daily predictions within each ensemble member. The probability of each of four heat stress ranges (Watch and higher, Warning and higher, Alert Level 1 and higher, and Alert Level 2) is determined from all the available ensemble members for the week to form the weekly probabilistic Outlook. The probabilistic 4-Month Outlook is the highest weekly probability predicted among all the weekly Outlooks during a 4-month period for each of the stress ranges. An initial qualitative skill analysis of the Outlooks for 2011-2015, compared with CRW's satellite-based coral bleaching heat stress products, indicated the Outlook has performed well with high hit rates and low miss rates for most coral reef areas. Regions identified with high false alarm rates will guide future improvements. This Outlook system, as the first and only freely available global coral bleaching prediction system, has been providing critical early warning to marine resource managers, scientists, and decision makers around the world to guide management, protection, and monitoring of coral reefs since 2012. This has been especially valuable during the third global coral bleaching event that started in mid-2014 and extended into mid-2017. The Outlook system is an integrated component of CRW's global decision support system for coral bleaching. Recent management actions taken in light of this system are discussed.
Coral disease events are emerging as a significant threat to coral reefs in a changing climate. O... more Coral disease events are emerging as a significant threat to coral reefs in a changing climate. Over the past few years, several modelling studies have derived empirical relationships linking white syndrome (WS) disease outbreaks on Pacific coral reefs with unusual temperatures in summer and winter, and host density. These relationships have informed development of a series of predictive tools -maps of outbreak likelihood for Australia's Great Barrier Reef and the Hawaiian archipelago. These tools are key to strategic regional frameworks to respond to coral disease outbreaks. They inform both the targeted monitoring that can improve our understanding of coral disease dynamics and trials of experimental management actions that may mitigate disease impacts. Early research suggests that water quality could be another key driver of coral disease prevalence on reefs, as poor water quality has been correlated with increased susceptibility of corals to diseases and bleaching. Therefore we plan to test the inclusion of water quality measurements as a means of increasing the predictive capacity of these management-directed tools. By reducing the number of false positives and negatives, we aim to refine and improve the accuracy of tools developed to assess disease outbreak likelihood. Ongoing and future work also includes testing for links between environmental parameters and other coral diseases; expanding this work spatially, including a specific focus on coral disease dynamics in the Caribbean; and combining the learned relationships with climate predictions to examine potential future disease scenarios.
The Hawaiʻi Coral Disease database (HICORDIS) houses data on colony-level coral health condition ... more The Hawaiʻi Coral Disease database (HICORDIS) houses data on colony-level coral health condition observed across the Hawaiian archipelago, providing information to conduct future analyses on coral reef health in an era of changing environmental conditions. Colonies were identified to the lowest taxonomic classification possible (species or genera), measured and assessed for visual signs of health condition. Data were recorded for 286,071 coral colonies surveyed on 1819 transects at 660 sites between 2005 and 2015. The database contains observations for 60 species from 22 genera with 21 different health conditions. The goals of the HICORDIS database are to: i) provide open access, quality controlled and validated coral health data assembled from disparate
Coral bleaching events threaten the sustainability of the Great Barrier Reef (GBR). Here we show ... more Coral bleaching events threaten the sustainability of the Great Barrier Reef (GBR). Here we show that bleaching events of the past three decades have been mitigated by induced thermal tolerance of reef-building corals, and this protective mechanism is likely to be lost under near-future climate change scenarios. We show that 75% of past thermal stress events have been characterized by a temperature trajectory that subjects corals to a protective, sub-bleaching stress, before reaching temperatures that cause bleaching. Such conditions confer thermal tolerance, decreasing coral cell mortality and symbiont loss during bleaching by over 50%. We find that near-future increases in local temperature of as little as 0.5°C result in this protective mechanism being lost, which may increase the rate of degradation of the GBR.
To forecast marine disease outbreaks as oceans warm requires new environmental surveillance tools... more To forecast marine disease outbreaks as oceans warm requires new environmental surveillance tools. We describe an iterative process for developing these tools that combines research, development and deployment for suitable systems. The first step is to identify candidate host–pathogen systems. The 24 candidate systems we identified include sponges, corals, oysters, crustaceans, sea stars, fishes and sea grasses (among others). To illustrate the other steps, we present a case study of epizootic shell disease (ESD) in the American lobster. Increasing prevalence of ESD is a contributing factor to lobster fishery collapse in southern New England (SNE), raising concerns that disease prevalence will increase in the northern Gulf of Maine under climate change. The lowest maximum bottom temperature associated with ESD prevalence in SNE is 128C. Our seasonal outlook for 2015 and long-term projections show bottom temperatures greater than or equal to 128C may occur in this and coming years in the coastal bays of Maine. The tools presented will allow managers to target efforts to monitor the effects of ESD on fishery sustainability and will be iteratively refined. The approach and case example highlight that temperature-based surveillance tools can inform research, monitoring and management of emerging and continuing marine disease threats.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2016
Infectious marine diseases can decimate populations and are increasing among some taxa due to glo... more Infectious marine diseases can decimate populations and are increasing among some taxa due to global change and our increasing reliance on marine environments. Marine diseases become emergencies when significant ecological, economic or social impacts occur. We can prepare for and manage these emergencies through improved surveillance, and the development and iterative refinement of approaches to mitigate disease and its impacts. Improving surveillance requires fast, accurate diagnoses, forecasting disease risk and real-time monitoring of disease-promoting environmental conditions. Diversifying impact mitigation involves increasing host resilience to disease, reducing pathogen abundance and managing environmental factors that facilitate disease. Disease surveillance and mitigation can be adaptive if informed by research advances and catalysed by communication among observers, researchers and decision-makers using information-sharing platforms. Recent increases in the awareness of the threats posed by marine diseases may lead to policy frameworks that facilitate the responses and management that marine disease emergencies require.
Incorporating warming disturbances into the design of marine protected areas (MPAs) is fundamenta... more Incorporating warming disturbances into the design of marine protected areas (MPAs) is fundamental to developing appropriate conservation actions that confer coral reef resilience. We propose an MPA design approach that includes spatially- and temporally-varying sea-surface temperature (SST) data, integrating both observed (1985-2009) and projected (2010-2099) time-series. We derived indices of acute (time under reduced ecosystem function following short-term events) and chronic thermal stress (rate of warming) and combined them to delineate thermal-stress regimes. Coral reefs located on the Brazilian coast were used as a case study because they are considered a conservation priority in the southwestern Atlantic Ocean. We show that all coral reef areas in Brazil have experienced and are projected to continue to experience chronic warming, while acute events are expected to increase in frequency and intensity. We formulated quantitative conservation objectives for regimes of thermal stress. Based on these objectives, we then evaluated if/how they are achieved in existing Brazilian MPAs and identified priority areas where additional protection would reinforce resilience. Our results show that, although the current system of MPAs incorporates locations within some of our thermal-stress regimes, historical and future thermal refugia along the central coast are completely unprotected. Our approach is applicable to other marine ecosystems and adds to previous marine planning for climate change in two ways: (i) by demonstrating how to spatially configure MPAs that meet conservation objectives for warming disturbance using spatially- and temporally-explicit data; and (ii) by strategically allocating different forms of spatial management (MPA types) intended to mitigate warming impacts and also enhance future resistance to climate warming.
Exposure to disturbance is rarely considered in marine protected area planning. Typically, repres... more Exposure to disturbance is rarely considered in marine protected area planning. Typically, representing and replicating the habitat types present within protected areas is used to spread the risk of protecting frequently disturbed sites. This was the approach used during the 2004 re-zoning of the Great Barrier Reef Marine Park (GBRMP) via the Representative Areas Program. Over 10 years later, we examine whether the risk was spread by mapping exposure of coral reefs in the GBRMP to four disturbances that cause coral mortality: bleaching, tropical cyclones, crown-of-thorns starfish outbreaks, and freshwater inundation. Our objectives were to: (1) assess whether no-take areas include a range of disturbance regimes, and (2) identify coral reef areas with lower relative exposure. At least 13% and an average of 31% of reef locations in each of 11 exposure classes are included within no-take areas. A greater proportion of low-exposure areas are within no-take areas than high-exposure areas (34.2% vs. 28.3%). The results demonstrate the value of risk spreading when exposure data are not available while also showing that regularly assessing exposure increases capacity for adaptive, resilience-based reef management.
Maynard et al. . List of IPCC CMIP5 models used for the ensemble of GCMs for RCP8.5 (33 models) a... more Maynard et al. . List of IPCC CMIP5 models used for the ensemble of GCMs for RCP8.5 (33 models) and RCP4.5 (35 models). Models used only in RCP8.5 have a single asterisk, and models used only in RCP4.5 have a double asterisk.
Rising sea temperatures are likely to increase the frequency of disease outbreaks a ecting reef-b... more Rising sea temperatures are likely to increase the frequency of disease outbreaks a ecting reef-building corals through impacts on coral hosts and pathogens. We present and compare climate model projections of temperature conditions that will increase coral susceptibility to disease, pathogen abundance and pathogen virulence. Both moderate (RCP 4.5) and fossil fuel aggressive (RCP 8.5) emissions scenarios are examined. We also compare projections for the onset of disease-conducive conditions and severe annual coral bleaching, and produce a disease risk summary that combines climate stress with stress caused by local human activities. There is great spatial variation in the projections, both among and within the major ocean basins, in conditions favouring disease development. Our results indicate that disease is as likely to cause coral mortality as bleaching in the coming decades. These projections identify priority locations to reduce stress caused by local human activities and test management interventions to reduce disease impacts.
HF ocean surface radar provides a valuable multiparameter monitoring technique for the investigat... more HF ocean surface radar provides a valuable multiparameter monitoring technique for the investigation and management of coral bleaching. The physical parameters normally associated with bleaching are temperature and light, which are primarily controlled by insolation, wind, waves and currents. The radar provides a useful monitoring of wind and waves, and is the leading technology for monitoring surface currents. The deployment of an HF radar in the Great Barrier Reef at the Heron Island study area provides ideal infrastructure for the study of the physical processes which affect coral bleaching and the spread of coral disease .
Coral reefs across the world's oceans are in the midst of the longest bleaching event on record (... more Coral reefs across the world's oceans are in the midst of the longest bleaching event on record (from 2014 to at least 2016). As many of the world's reefs are remote, there is limited information on how past thermal conditions have influenced reef composition and current stress responses. Using satellite temperature data for 1985–2012, the analysis we present is the first to quantify, for global reef locations, spatial variations in warming trends, thermal stress events and temperature variability at reef-scale (~4 km). Among over 60,000 reef pixels globally, 97% show positive SST trends during the study period with 60% warming significantly. Annual trends exceeded summertime trends at most locations. This indicates that the period of summer-like temperatures has become longer through the record, with a corresponding shortening of the 'winter' reprieve from warm temperatures. The frequency of bleaching-level thermal stress increased threefold between 1985–91 and 2006–12 – a trend climate model projections suggest will continue. The thermal history data products developed enable needed studies relating thermal history to bleaching resistance and community composition. Such analyses can help identify reefs more resilient to thermal stress.
• Despite covering less than 0.1% of the sea floor area, coral reefs provide nearly US$9.8 trilli... more • Despite covering less than 0.1% of the sea floor area, coral reefs provide nearly US$9.8 trillion globally of social, economic and cultural services each year and provide habitat for over 25% of marine fish species. • The rate of warming in coral reef areas has increased from ~0.04°C/decade over the past century to 0.2°C/ decade over recent decades (1985-2012). Across this period, reefs were exposed to prolonged, high temperatures that caused bleaching once every six years. However, within the last three decades, as the planet has warmed the frequency of bleaching stress has increased threefold. • The latest climate models predict that ocean warming will cause annual coral bleaching for almost all reefs by 2050. They also predict that disease is as likely to be a future cause of coral mortality as coral bleaching. Unabated temperature increases will produce serious consequences for coral reef ecosystems and dependent communities. • The proportion of reefs in which ocean chemistry will allow coral reefs to grow has decreased from 98% (ca. 1780) to 38% (ca. 2006) due to ocean acidification and continues to drop. • Tropical cyclones can reduce thermal stress but can physically damage reefs. Ocean warming may increase the severity of cyclones. Warming-related coral bleaching has likely reduced the ability of reefs to recover from cyclone damage. • Sea-level rise is predicted to accelerate. Historically reefs have not been able to keep up with rapid sea-level rise, and this is even less likely in the future if ocean warming and acidification slow reef growth. • Loss of coral reefs would diminish the services these ecosystems provide, such as coastal protection from storm waves, habitat for reef fauna, and tourism. Predictions of ecosystem service losses from ocean warming and acidification globally reach US$1 trillion/year by 2100. • Reducing atmospheric CO 2 is critical for coral reefs to continue. While reduced emissions will slow ocean warming and acidification, current CO 2 levels already exceed the 320-350 ppm needed for healthy coral reefs. While this is pursued, enhancing reef resilience through targeted management actions will help reefs to resist and recover from disturbance. Local actions to mitigate climate change impacts may be necessary to preserve reef resources.
Coral reefs live within a fairly narrow envelope of environmental conditions constrained by water... more Coral reefs live within a fairly narrow envelope of environmental conditions constrained by water temperatures, light, salinity, nutrients, bathymetry and the aragonite saturation state of seawater. While the natural environment can be highly variable and potentially stressful to corals, humans are now placing the world’s coral reefs in crisis as a result of direct local- to regional-scale insults combined with accelerating global changes. The global-scale insults result from increased concentrations of atmospheric greenhouse gases that are rapidly acidifying and warming ocean waters. This chapter focuses on the changing physical environment surrounding coral reef ecosystems and especially the rising SSTs that are responsible for most mass coral bleaching events. We make use of improved long-term records of surface ocean climate to document SST changes in the vicinity of coral reefs and how the risk of SST conditions conducive to coral bleaching varies with climate variability such as El Niño--Southern Oscillation events. We describe the application of satellite-based SSTs and related products that have been developed to detect and monitor environmental conditions leading to coral bleaching around the globe.
Climate change is radically altering the frequency, intensity and spatial scale of severe weather... more Climate change is radically altering the frequency, intensity and spatial scale of severe weather events, such as heatwaves , droughts, floods and fires 1. As the time interval shrinks between recurrent shocks 2-5 , the responses of ecosystems to each new disturbance are increasingly likely to be contingent on the history of other recent extreme events. Ecological memory defined as the ability of the past to influence the present trajectory of ecosystems 6,7-is also critically important for understanding how species assemblages are responding to rapid changes in disturbance regimes due to anthropogenic climate change 2,3,6-8. Here, we show the emergence of ecological memory during unprecedented back-to-back mass bleaching of corals along the 2,300 km length of the Great Barrier Reef in 2016, and again in 2017, whereby the impacts of the second severe heatwave, and its geographic footprint, were contingent on the first. Our results underscore the need to understand the strengthening interactions among sequences of climate-driven events, and highlight the accelerating and cumulative impacts of novel disturbance regimes on vulnerable ecosystems. Changes through time are fundamental to the study of ecology and evolution, yet our understanding of the contemporary condition of ecosystems often discounts the role of non-equilibrial dynamics and history 6,9. Emerging theoretical frameworks and models point to the important effects of time lags and memory, as the enduring influences of past experiences and changing conditions unfold over time 7. For example, the responses of ecosystems during ecological succession, and the evolution of life history traits, are key legacy effects of the history of recurrent disturbances 2. On most coral reefs, for instance, where recurrent tropical cyclones have historically been the most significant external disturbance 10 , regional-and global-scale bleaching of corals has become a major additional agent of mortality of reef-building corals in recent decades 5,11. Here, we document how ecological memory of severe coral bleaching on the Great Barrier Reef in 2016 12 subsequently transformed the response of corals to heat stress during a second marine heatwave in 2017. We show further that the geographic pattern of heat exposure in 2016 had a lingering impact on the spatial footprint of bleaching along the 2,300 km length of the world's largest reef system during the subsequent heatwave one year later-history has a geographic signal. Our results demonstrate the need to understand the combined , interactive effects of sequences of recurrent climate-related disturbances at a hierarchy of spatial scales, and the critical role of recent history for predicting ecological outcomes in an era of rapid global change. The response of corals to heat stress during the second of two unprecedented back-to-back bleaching events on the Great Barrier Reef was markedly different from the first. Heat stress-measured from satellites as degree heating weeks (DHW; °C-weeks)-was greater in 2017 on 79.9% of individual reefs (n = 3,863 reefs; Fig. 1a and Supplementary Fig. 1), yet despite the higher and/ or longer-lasting summer sea surface temperatures, the surviving corals were more resistant in 2017 to a recurrence of bleaching compared with the previous year (Fig. 1b and Supplementary Fig. 2). Specifically, in 2016, an exposure of 4-5 °C-weeks elicited a 50% probability of severe bleaching (affecting > 30% of corals), but in 2017 the same 50% response occurred at a much higher level of heat exposure of 8-9 °C-weeks. In comparison, an exposure of 8-9 °C-weeks in 2016 was associated with a >
The U.S. National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch (CRW) operates... more The U.S. National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch (CRW) operates a global 4-Month Coral Bleaching Outlook system for shallow-water coral reefs in collaboration with NOAA's National Centers for Environmental Prediction (NCEP). The Outlooks are generated by applying the algorithm used in CRW's operational satellite coral bleaching heat stress monitoring, with slight modifications, to the sea surface temperature (SST) predictions from NCEP's operational Climate Forecast System Version 2 (CFSv2). Once a week, the probability of heat stress capable of causing mass coral bleaching is predicted for 4- months in advance. Each day, CFSv2 generates an ensemble of 16 forecasts, with nine runs out to 45-days, three runs out to 3-months, and four runs out to 9-months. This results in 28-112 ensemble members produced each week. A composite for each predicted week is derived from daily predictions within each ensemble member. The probability of each of four heat stress ranges (Watch and higher, Warning and higher, Alert Level 1 and higher, and Alert Level 2) is determined from all the available ensemble members for the week to form the weekly probabilistic Outlook. The probabilistic 4-Month Outlook is the highest weekly probability predicted among all the weekly Outlooks during a 4-month period for each of the stress ranges. An initial qualitative skill analysis of the Outlooks for 2011-2015, compared with CRW's satellite-based coral bleaching heat stress products, indicated the Outlook has performed well with high hit rates and low miss rates for most coral reef areas. Regions identified with high false alarm rates will guide future improvements. This Outlook system, as the first and only freely available global coral bleaching prediction system, has been providing critical early warning to marine resource managers, scientists, and decision makers around the world to guide management, protection, and monitoring of coral reefs since 2012. This has been especially valuable during the third global coral bleaching event that started in mid-2014 and extended into mid-2017. The Outlook system is an integrated component of CRW's global decision support system for coral bleaching. Recent management actions taken in light of this system are discussed.
Coral disease events are emerging as a significant threat to coral reefs in a changing climate. O... more Coral disease events are emerging as a significant threat to coral reefs in a changing climate. Over the past few years, several modelling studies have derived empirical relationships linking white syndrome (WS) disease outbreaks on Pacific coral reefs with unusual temperatures in summer and winter, and host density. These relationships have informed development of a series of predictive tools -maps of outbreak likelihood for Australia's Great Barrier Reef and the Hawaiian archipelago. These tools are key to strategic regional frameworks to respond to coral disease outbreaks. They inform both the targeted monitoring that can improve our understanding of coral disease dynamics and trials of experimental management actions that may mitigate disease impacts. Early research suggests that water quality could be another key driver of coral disease prevalence on reefs, as poor water quality has been correlated with increased susceptibility of corals to diseases and bleaching. Therefore we plan to test the inclusion of water quality measurements as a means of increasing the predictive capacity of these management-directed tools. By reducing the number of false positives and negatives, we aim to refine and improve the accuracy of tools developed to assess disease outbreak likelihood. Ongoing and future work also includes testing for links between environmental parameters and other coral diseases; expanding this work spatially, including a specific focus on coral disease dynamics in the Caribbean; and combining the learned relationships with climate predictions to examine potential future disease scenarios.
The Hawaiʻi Coral Disease database (HICORDIS) houses data on colony-level coral health condition ... more The Hawaiʻi Coral Disease database (HICORDIS) houses data on colony-level coral health condition observed across the Hawaiian archipelago, providing information to conduct future analyses on coral reef health in an era of changing environmental conditions. Colonies were identified to the lowest taxonomic classification possible (species or genera), measured and assessed for visual signs of health condition. Data were recorded for 286,071 coral colonies surveyed on 1819 transects at 660 sites between 2005 and 2015. The database contains observations for 60 species from 22 genera with 21 different health conditions. The goals of the HICORDIS database are to: i) provide open access, quality controlled and validated coral health data assembled from disparate
Coral bleaching events threaten the sustainability of the Great Barrier Reef (GBR). Here we show ... more Coral bleaching events threaten the sustainability of the Great Barrier Reef (GBR). Here we show that bleaching events of the past three decades have been mitigated by induced thermal tolerance of reef-building corals, and this protective mechanism is likely to be lost under near-future climate change scenarios. We show that 75% of past thermal stress events have been characterized by a temperature trajectory that subjects corals to a protective, sub-bleaching stress, before reaching temperatures that cause bleaching. Such conditions confer thermal tolerance, decreasing coral cell mortality and symbiont loss during bleaching by over 50%. We find that near-future increases in local temperature of as little as 0.5°C result in this protective mechanism being lost, which may increase the rate of degradation of the GBR.
To forecast marine disease outbreaks as oceans warm requires new environmental surveillance tools... more To forecast marine disease outbreaks as oceans warm requires new environmental surveillance tools. We describe an iterative process for developing these tools that combines research, development and deployment for suitable systems. The first step is to identify candidate host–pathogen systems. The 24 candidate systems we identified include sponges, corals, oysters, crustaceans, sea stars, fishes and sea grasses (among others). To illustrate the other steps, we present a case study of epizootic shell disease (ESD) in the American lobster. Increasing prevalence of ESD is a contributing factor to lobster fishery collapse in southern New England (SNE), raising concerns that disease prevalence will increase in the northern Gulf of Maine under climate change. The lowest maximum bottom temperature associated with ESD prevalence in SNE is 128C. Our seasonal outlook for 2015 and long-term projections show bottom temperatures greater than or equal to 128C may occur in this and coming years in the coastal bays of Maine. The tools presented will allow managers to target efforts to monitor the effects of ESD on fishery sustainability and will be iteratively refined. The approach and case example highlight that temperature-based surveillance tools can inform research, monitoring and management of emerging and continuing marine disease threats.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2016
Infectious marine diseases can decimate populations and are increasing among some taxa due to glo... more Infectious marine diseases can decimate populations and are increasing among some taxa due to global change and our increasing reliance on marine environments. Marine diseases become emergencies when significant ecological, economic or social impacts occur. We can prepare for and manage these emergencies through improved surveillance, and the development and iterative refinement of approaches to mitigate disease and its impacts. Improving surveillance requires fast, accurate diagnoses, forecasting disease risk and real-time monitoring of disease-promoting environmental conditions. Diversifying impact mitigation involves increasing host resilience to disease, reducing pathogen abundance and managing environmental factors that facilitate disease. Disease surveillance and mitigation can be adaptive if informed by research advances and catalysed by communication among observers, researchers and decision-makers using information-sharing platforms. Recent increases in the awareness of the threats posed by marine diseases may lead to policy frameworks that facilitate the responses and management that marine disease emergencies require.
Incorporating warming disturbances into the design of marine protected areas (MPAs) is fundamenta... more Incorporating warming disturbances into the design of marine protected areas (MPAs) is fundamental to developing appropriate conservation actions that confer coral reef resilience. We propose an MPA design approach that includes spatially- and temporally-varying sea-surface temperature (SST) data, integrating both observed (1985-2009) and projected (2010-2099) time-series. We derived indices of acute (time under reduced ecosystem function following short-term events) and chronic thermal stress (rate of warming) and combined them to delineate thermal-stress regimes. Coral reefs located on the Brazilian coast were used as a case study because they are considered a conservation priority in the southwestern Atlantic Ocean. We show that all coral reef areas in Brazil have experienced and are projected to continue to experience chronic warming, while acute events are expected to increase in frequency and intensity. We formulated quantitative conservation objectives for regimes of thermal stress. Based on these objectives, we then evaluated if/how they are achieved in existing Brazilian MPAs and identified priority areas where additional protection would reinforce resilience. Our results show that, although the current system of MPAs incorporates locations within some of our thermal-stress regimes, historical and future thermal refugia along the central coast are completely unprotected. Our approach is applicable to other marine ecosystems and adds to previous marine planning for climate change in two ways: (i) by demonstrating how to spatially configure MPAs that meet conservation objectives for warming disturbance using spatially- and temporally-explicit data; and (ii) by strategically allocating different forms of spatial management (MPA types) intended to mitigate warming impacts and also enhance future resistance to climate warming.
Exposure to disturbance is rarely considered in marine protected area planning. Typically, repres... more Exposure to disturbance is rarely considered in marine protected area planning. Typically, representing and replicating the habitat types present within protected areas is used to spread the risk of protecting frequently disturbed sites. This was the approach used during the 2004 re-zoning of the Great Barrier Reef Marine Park (GBRMP) via the Representative Areas Program. Over 10 years later, we examine whether the risk was spread by mapping exposure of coral reefs in the GBRMP to four disturbances that cause coral mortality: bleaching, tropical cyclones, crown-of-thorns starfish outbreaks, and freshwater inundation. Our objectives were to: (1) assess whether no-take areas include a range of disturbance regimes, and (2) identify coral reef areas with lower relative exposure. At least 13% and an average of 31% of reef locations in each of 11 exposure classes are included within no-take areas. A greater proportion of low-exposure areas are within no-take areas than high-exposure areas (34.2% vs. 28.3%). The results demonstrate the value of risk spreading when exposure data are not available while also showing that regularly assessing exposure increases capacity for adaptive, resilience-based reef management.
Maynard et al. . List of IPCC CMIP5 models used for the ensemble of GCMs for RCP8.5 (33 models) a... more Maynard et al. . List of IPCC CMIP5 models used for the ensemble of GCMs for RCP8.5 (33 models) and RCP4.5 (35 models). Models used only in RCP8.5 have a single asterisk, and models used only in RCP4.5 have a double asterisk.
Rising sea temperatures are likely to increase the frequency of disease outbreaks a ecting reef-b... more Rising sea temperatures are likely to increase the frequency of disease outbreaks a ecting reef-building corals through impacts on coral hosts and pathogens. We present and compare climate model projections of temperature conditions that will increase coral susceptibility to disease, pathogen abundance and pathogen virulence. Both moderate (RCP 4.5) and fossil fuel aggressive (RCP 8.5) emissions scenarios are examined. We also compare projections for the onset of disease-conducive conditions and severe annual coral bleaching, and produce a disease risk summary that combines climate stress with stress caused by local human activities. There is great spatial variation in the projections, both among and within the major ocean basins, in conditions favouring disease development. Our results indicate that disease is as likely to cause coral mortality as bleaching in the coming decades. These projections identify priority locations to reduce stress caused by local human activities and test management interventions to reduce disease impacts.
HF ocean surface radar provides a valuable multiparameter monitoring technique for the investigat... more HF ocean surface radar provides a valuable multiparameter monitoring technique for the investigation and management of coral bleaching. The physical parameters normally associated with bleaching are temperature and light, which are primarily controlled by insolation, wind, waves and currents. The radar provides a useful monitoring of wind and waves, and is the leading technology for monitoring surface currents. The deployment of an HF radar in the Great Barrier Reef at the Heron Island study area provides ideal infrastructure for the study of the physical processes which affect coral bleaching and the spread of coral disease .
Coral reefs across the world's oceans are in the midst of the longest bleaching event on record (... more Coral reefs across the world's oceans are in the midst of the longest bleaching event on record (from 2014 to at least 2016). As many of the world's reefs are remote, there is limited information on how past thermal conditions have influenced reef composition and current stress responses. Using satellite temperature data for 1985–2012, the analysis we present is the first to quantify, for global reef locations, spatial variations in warming trends, thermal stress events and temperature variability at reef-scale (~4 km). Among over 60,000 reef pixels globally, 97% show positive SST trends during the study period with 60% warming significantly. Annual trends exceeded summertime trends at most locations. This indicates that the period of summer-like temperatures has become longer through the record, with a corresponding shortening of the 'winter' reprieve from warm temperatures. The frequency of bleaching-level thermal stress increased threefold between 1985–91 and 2006–12 – a trend climate model projections suggest will continue. The thermal history data products developed enable needed studies relating thermal history to bleaching resistance and community composition. Such analyses can help identify reefs more resilient to thermal stress.
• Despite covering less than 0.1% of the sea floor area, coral reefs provide nearly US$9.8 trilli... more • Despite covering less than 0.1% of the sea floor area, coral reefs provide nearly US$9.8 trillion globally of social, economic and cultural services each year and provide habitat for over 25% of marine fish species. • The rate of warming in coral reef areas has increased from ~0.04°C/decade over the past century to 0.2°C/ decade over recent decades (1985-2012). Across this period, reefs were exposed to prolonged, high temperatures that caused bleaching once every six years. However, within the last three decades, as the planet has warmed the frequency of bleaching stress has increased threefold. • The latest climate models predict that ocean warming will cause annual coral bleaching for almost all reefs by 2050. They also predict that disease is as likely to be a future cause of coral mortality as coral bleaching. Unabated temperature increases will produce serious consequences for coral reef ecosystems and dependent communities. • The proportion of reefs in which ocean chemistry will allow coral reefs to grow has decreased from 98% (ca. 1780) to 38% (ca. 2006) due to ocean acidification and continues to drop. • Tropical cyclones can reduce thermal stress but can physically damage reefs. Ocean warming may increase the severity of cyclones. Warming-related coral bleaching has likely reduced the ability of reefs to recover from cyclone damage. • Sea-level rise is predicted to accelerate. Historically reefs have not been able to keep up with rapid sea-level rise, and this is even less likely in the future if ocean warming and acidification slow reef growth. • Loss of coral reefs would diminish the services these ecosystems provide, such as coastal protection from storm waves, habitat for reef fauna, and tourism. Predictions of ecosystem service losses from ocean warming and acidification globally reach US$1 trillion/year by 2100. • Reducing atmospheric CO 2 is critical for coral reefs to continue. While reduced emissions will slow ocean warming and acidification, current CO 2 levels already exceed the 320-350 ppm needed for healthy coral reefs. While this is pursued, enhancing reef resilience through targeted management actions will help reefs to resist and recover from disturbance. Local actions to mitigate climate change impacts may be necessary to preserve reef resources.
Coral reefs live within a fairly narrow envelope of environmental conditions constrained by water... more Coral reefs live within a fairly narrow envelope of environmental conditions constrained by water temperatures, light, salinity, nutrients, bathymetry and the aragonite saturation state of seawater. While the natural environment can be highly variable and potentially stressful to corals, humans are now placing the world’s coral reefs in crisis as a result of direct local- to regional-scale insults combined with accelerating global changes. The global-scale insults result from increased concentrations of atmospheric greenhouse gases that are rapidly acidifying and warming ocean waters. This chapter focuses on the changing physical environment surrounding coral reef ecosystems and especially the rising SSTs that are responsible for most mass coral bleaching events. We make use of improved long-term records of surface ocean climate to document SST changes in the vicinity of coral reefs and how the risk of SST conditions conducive to coral bleaching varies with climate variability such as El Niño--Southern Oscillation events. We describe the application of satellite-based SSTs and related products that have been developed to detect and monitor environmental conditions leading to coral bleaching around the globe.
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Papers by Scott F. Heron