Coral-reef ecosystems are experiencing frequent and severe disturbance events that
are reducing g... more Coral-reef ecosystems are experiencing frequent and severe disturbance events that are reducing global coral abundance and potentially overwhelming the natural capacity for reefs to recover. While mitigation strategies for climate warming and other anthropogenic disturbances are implemented, coral restoration programmes are being established worldwide as an additional conservation measure to minimise coral loss and enhance coral recovery. Current restoration efforts predominantly rely on asexually produced coral fragments — a process with inherent practical constraints on the genetic diversity conserved and the spatial scale achieved. Because the resilience of coral communities has hitherto relied on regular renewal with natural recruits, the scaling-up of restoration programmes would benefit from greater use of sexually produced corals, which is an approach that is gaining momentum. Here we review the present state of knowledge of scleractinian coral sexual reproduction in the context of reef restoration, with a focus on broadcast-spawning corals. We identify key knowledge gaps and bottlenecks that currently constrain the sexual production of corals and consider the feasibility of using sexually produced corals for scaling-up restoration to the reef- and reef-system scales.
Corals of the eastern tropical Pacific live in a marginal and oceanographically dynamic environme... more Corals of the eastern tropical Pacific live in a marginal and oceanographically dynamic environment. Along the Pacific coast of Panamá, stronger seasonal upwelling in the Gulf of Panamá in the east transitions to weaker upwelling in the Gulf of Chiriquí in the west, resulting in complex regional oceanographic conditions that drive differential coral‐reef growth. Over millennial timescales, reefs in the Gulf of Chiriquí recovered more quickly from climatic disturbances compared with reefs in the Gulf of Panamá. In recent decades, corals in the Gulf of Chiriquí have also had higher growth rates than in the Gulf of Panamá. As the ocean continues to warm, however, conditions could shift to favor the growth of corals in the Gulf of Panamá, where upwelling may confer protection from high‐temperature anomalies. Here we describe the recent spatial and temporal variability in surface oceanography of nearshore environments in Pacific Panamá and compare those conditions with the dynamics of contemporary coral‐reef communities, during and after the 2016 coral‐bleaching event. Although both gulfs have warmed significantly over the last 150 years, thermal maxima in the Gulf of Chiriquí are increasing faster, and ocean temperatures there are becoming more variable than in the recent past. In contrast to historical trends, we found that coral cover, coral survival, and coral growth‐rates were all significantly higher in the Gulf of Panamá. Corals bleached extensively in the Gulf of Chiriquí following the 2015–2016 El Niño event, whereas upwelling in the Gulf of Panamá moderated the high temperatures caused by El Niño, allowing the corals largely to escape thermal stress. As the climate continues to warm, upwelling zones may offer a temporary and localized refuge from the thermal impacts of climate change, while reef growth in the rest of the eastern tropical Pacific continues to decline.
Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determinin... more Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determining the rates of coral recovery and their long-term responses to increasing sea-surface temperatures is challenging. To do so, we first estimated coral recovery rates following past disturbances on reefs in southern Japan and Western Australia. Recovery rates varied between regions, with the reefs in southern Japan showing more rapid recovery rates (intrinsic rate of increase, r = 0.38 year −1) than reefs in Western Australia (r = 0.17 year −1). Second, we input these recovery rates into a novel, nonlinear hybrid-stochastic-dynamical system to predict the responses of Indo-Pacific coral populations to complex inter-annual temperature cycles into the year 2100. The coral recovery rates were overlaid on background increases in global sea-surface temperatures, under three different climate-change scenarios. The models predicted rapid recovery at both localities with the infrequent and low-magnitude temperature anomalies expected under a conservative climate-change scenario, Representative Concentration Pathway (RCP) 4.5. With moderate increases in ocean temperatures (RCP 6.0) the coral populations showed a bimodal response, with model runs showing either recovery or collapse. Under a business-as-usual climate-change scenario (RCP 8.5), with frequent and intense temperature anomalies, coral recovery was unlikely. The rapid rate of contemporary climate change is seriously affecting terrestrial and marine populations 1,2 , particularly on tropical coral reefs where corals have been living close to their upper thermal limits for millennia 3-5. Although corals on tropical reefs are adapted to warm waters, they rarely experience an annual temperature range greater than a few degrees Celsius. Warmer than average temperatures combined with high seasonal irradiance can cause a dysfunction in the coral-dinoflagellate symbiosis that leads to coral bleaching, and under extreme conditions leads to mortality 6-10. There is, however, considerable variability in the range of thermal tolerances among the eight hundred or more extant coral species 11-13 , and there are substantial differences in the rates of population and community recovery from thermal disturbances 14,15. The rate of recovery from a disturbance is a function of a system's stability and resilience 16,17. Stable, resilient systems recover rapidly; whereas unstable, non-resilient systems recover slowly, or even collapse after disturbances 18. Moreover, the slowing of recovery usually indicates that a system is deteriorating and may be approaching a critical threshold, beyond which the system switches to an alternate and often undesirable state 19,20. Indeed, understanding the rates of change and the resilience of systems has become central to our understanding of modern ecology 21,22. On modern coral reefs, we frequently ask the question: how quickly will a reef recover from a given distur-bance? It is challenging to answer this question, particularly given the complexity of coral reefs and the multitude of nuances that influence recovery 23,24. Recovery depends on many interacting factors, including species composition and environmental and geographic vicissitudes. Understanding these factors and accurately predicting the recovery rates of coral populations is critical in a rapidly changing climate 25 , which is characterized by ocean warming and an increase in the frequency of acute thermal-stress events 5. There is, therefore, a need for models that accurately predict the dynamics of coral populations and determine the likelihood of recovery under future climate-change scenarios RCP 4.5, 6.0, and 8.5 26. Many models explore the dynamics of coral populations 25-28 , although most models are built on the traditional foundation of Leslie and Lefkovitch matrices 29-31. The matrix approach is convenient, but does not capture the instantaneous dynamics of a population. A system of differential equations captures the dynamics of
Expert and intelligent systems based on computer-vision algorithms are becoming a common part of ... more Expert and intelligent systems based on computer-vision algorithms are becoming a common part of our daily lives, as they help us solve problems in areas such as medicine, agriculture, transportation, and ecology. In this paper, we focus on the application of computer vision in marine ecology. Here, we propose a new algorithm for mosaicing images of coral reefs captured by scuba divers using hand-held cameras during reef surveys. Such images often capture partial views of the surveyed area that are then collated into mosaics of the reef assemblages. Accurate mosaics will help coral-reef researchers rapidly assess not only the status of coral reefs, but also determine rates of recovery or rates of decline using longitudinal data. Most standard mosaicing algorithms distort the images, however, and moving objects and paral-lax errors, which usually happen in underwater images, hinder mosaic construction. To overcome these issues, our new algorithm uses a two-step approach that first detects and then removes loops and low-quality regions from an estimated camera trajectory. The algorithm then stitches the remaining images by warping parallax-affected image regions with a geometric transformation different from the one used for parallax-unaffected regions. We tested our method on images captured during a large spatial survey of coral reef sites throughout the Caribbean region. Our method obtained better-quality mosaics than other state-of-the-art algorithms.
Outbreaks of coral diseases continue to reduce global coral populations. In the Caribbean, yellow... more Outbreaks of coral diseases continue to reduce global coral populations. In the Caribbean, yellow band is a severe and widespread disease that commonly affects corals of the Orbicella spp. complex, significantly impeding coral reproduction, and hindering the natural recovery of Orbicella spp. populations. Caribbean yellow-band disease (CYBD) lesions may be severe, and often result in the complete loss of coral tissue. The slow spread of CYBD, however, provides an opportunity to test methods to mitigate the disease. Here we report the results of in situ experiments, conducted within Buck Island Reef National Monument in St. Croix, USVI, to test the effectiveness of three techniques to minimize disease impact on Orbicella faveolata: (1) shading, (2) aspirating, and (3) chiseling a " firebreak " to isolate the lesion. Neither shading nor aspirating the diseased tissue significantly reduced CYBD tissue loss. However, chiseling reduced the rate and amount of tissue lost by 31%. While 30–40% of the chiseled lesions appeared to be free of disease signs 12–16 months after treatment, success significantly and steadily declined over 23 months, indicating a possible lack of long-term viability of the technique. The results of this study demonstrate that creating a " firebreak " between diseased and healthy-appearing tissue slows the spread of the disease and may prolong the life of O. faveolata colonies. The firebreak method yielded the best results of all the techniques tested, and also required the least amount of effort and resources. However, we do not recommend that this treatment alone be used for long-term disease mitigation. Rather, we propose that modifications of this and other treatment options be sought. The results also highlight the need for extended monitoring of CYBD after any treatment, due to the slow but variable rate and pattern of tissue loss in this disease.
Recent outbreaks of coral diseases in the Caribbean have been linked to increasingly stressful se... more Recent outbreaks of coral diseases in the Caribbean have been linked to increasingly stressful sea-surface temperatures (SSTs). Yet, ocean warming is spatially heterogeneous and therefore has the potential to lead to hotspots of disease activity. Here, we take an epidemiological approach to examine spatial differences in the risk of white-band disease on Acropora spp. and yellow-band disease on Orbicella spp. in the Caribbean. Our analysis involved examining the spatial patterns of disease prevalence, and creating a Bayesian-risk model that tested for regional differences in disease risk. The spatial examination of disease prevalence showed several clusters of white-band disease, including high prevalence in the Turks and Caicos, Jamaica, Puerto Rico, the Virgin Islands, and Belize, whereas yellow-band disease seemed most prevalent along the Yucatan Peninsula. The Bayesian-risk model showed regional clusters of white-band disease near the southern Dominican Republic, Puerto Rico, the Virgin Islands, and the Lesser Antilles, whereas the risk of yellow-band disease was highest in the southern Caribbean. The relative risk of both diseases increased with warmer SSTs. The Bayesian-risk model allowed us to predict where we should expect future outbreaks of coral diseases at a regional scale, and suggests regions where the implementation of disease mitigation plans may be most urgent.
With the current rapid rate of climate change, coral communities are being repeatedly subjected t... more With the current rapid rate of climate change, coral communities are being repeatedly subjected to anomalously high thermal-stress events. Most global models predict that within the next 100 years, few reef corals will survive in tropical oceans. Yet thermal stresses have long been spatially and temporally variable across the oceans, and coral communities in different geographic regions are likely to be inherently different in their capacity to tolerate thermal stress. Using a spatially explicit Bayesian approach, we examined the response of coral communities to the hazards of climate-change associated thermal stress. We used the rates of change in sea-surface temperatures and the maximum sea-surface temperatures from 1980 to 2012 as predictive covariates of global records of coral bleaching over the same time period. There were negative relationships between the rates of change in sea-surface temperatures and coral bleaching, although the results were misleading because the highest rates of change in sea-surface temperatures were recorded at high latitudes, where average sea-surface temperatures are characteristically cooler than at low latitudes. Also, the results suggested that the most hazardous localities for corals, which experienced the highest maximum sea-surface temperatures, were in the northern hemisphere, particularly in the northern and western Indian Ocean, and along the rim of the eastern and western Pacific Ocean. Coral populations in these localities have suffered the greatest mortality. When a capacity to adapt to thermal stress was considered in the model, several localities responded positively, particularly corals in the Hawaiian Islands, the northern Marshall Islands, Micronesia, the Line Islands, the Cook Islands, the southern Great Barrier Reef, and along the coast of Brazil.
The putative increase in coral diseases in the Caribbean has led to extensive declines in coral p... more The putative increase in coral diseases in the Caribbean has led to extensive declines in coral populations. Coral diseases are a consequence of the complex interactions among the coral hosts, the pathogens, and the environment. Yet, the relative influence that each of these components has on the prevalence of coral diseases is unclear. Also unknown is the extent to which historical thermal-stress events have influenced the prevalence of contemporary coral diseases and the potential adjustment of coral populations to thermal stress. We used a Bayesian approach to test the hypothesis that in 2012 the relative risk of four signs of coral disease (white signs, dark spots, black bands, and yellow signs) differed at reef locations with different thermal histories. We undertook an extensive spatial study of coral diseases at four locations in the Caribbean region (10 3 km), two with and two without a history of frequent thermal anomalies (;4–6 years) over the last 143 years (1870–2012). Locations that historically experienced frequent thermal anomalies had a significantly higher risk of corals displaying white signs, and had a lower risk of corals displaying dark spots, than locations that did not historically experience frequent thermal anomalies. By contrast, there was no relationship between the history of thermal stress and the relative risk of corals displaying black bands and yellow signs, at least at the spatial scale of our observations.
Elevated seawater temperatures during the late summer have the potential to negatively affect the... more Elevated seawater temperatures during the late summer have the potential to negatively affect the development and survivorship of the larvae of reef corals that are reproductive during that time of year. Acropora palmata, a major Caribbean hermatype, reproduces annually during August and September. A. palmata populations have severely declined over the past three decades, and recovery will require high recruitment rates. Such recruitment will be limited if larval supply is reduced by elevated temperatures. The effects of elevated temperatures on development, survival, and larval settlement of A. palmata were investigated by culturing newly fertilized eggs at temperatures ranging from 27.5 to 31.5 degrees C. Development was accelerated and the percentage of developmental abnormalities increased at higher temperatures. Embryo mortality peaked during gastrulation, indicating that this complex developmental process is particularly sensitive to elevated temperatures. Larvae cultured at 3...
Elevated seawater temperatures during the late summer have the potential to negatively affect the... more Elevated seawater temperatures during the late summer have the potential to negatively affect the development and survivorship of the larvae of reef corals that are reproductive during that time of year. Acropora palmata, a major Caribbean hermatype, reproduces annually during August and September. A. palmata populations have severely declined over the past three decades, and recovery will require high recruitment rates. Such recruitment will be limited if larval supply is reduced by elevated temperatures. The effects of elevated temperatures on development, survival, and larval settlement of A. palmata were investigated by culturing newly fertilized eggs at temperatures ranging from 27.5 to 31.5 degrees C. Development was accelerated and the percentage of developmental abnormalities increased at higher temperatures. Embryo mortality peaked during gastrulation, indicating that this complex developmental process is particularly sensitive to elevated temperatures. Larvae cultured at 3...
Over the last half-century, coral diseases have contributed to the rapid decline of coral populat... more Over the last half-century, coral diseases have contributed to the rapid decline of coral populations throughout the Caribbean region. Some coral diseases appear to be potentially infectious, yet little is known about their modes of transmission. This study experimentally tested whether dark-spot syndrome on Siderastrea siderea was directly or indirectly transmissible to neighboring coral colonies. We also tested whether open wounds were necessary to facilitate disease transmission. At the completion of the experiments, we sampled bacterial communities on diseased, exposed, and healthy coral colonies to determine whether bacterial pathogens had transmitted to the susceptible colonies. We saw no evidence of either direct or waterborne transmission of dark-spot syndrome, and corals that received lesions by direct contact with diseased tissue, healed and showed no signs of infection. There were no significant differences among bacterial communities on healthy, exposed, and diseased colonies, although nine individual ribotypes were significantly higher in diseased corals compared with healthy and exposed corals, indicating a lack of transmission. Although our experiments do not fully refute the possibility that dark-spot syndrome is infectious and transmissible, our results suggest that in situ macroscopic signs of dark-spot syndrome are not always contagious.
Over the past 40 years, two of the dominant reef-building corals in the Caribbean, Acropora palma... more Over the past 40 years, two of the dominant reef-building corals in the Caribbean, Acropora palmata and Acropora cervicornis, have experienced unprecedented declines1, 2. That loss has been largely attributed to a syndrome commonly referred to as white-band disease1, 3. Climate change-driven increases in sea surface temperature (SST) have been linked to several coral diseases4, 5, yet, despite decades of research, the attribution of white-band disease to climate change remains unknown. Here we hindcasted the potential relationship between recent ocean warming and outbreaks of white-band disease on acroporid corals. We quantified eight SST metrics, including rates of change in SST and contemporary thermal anomalies, and compared them with records of white-band disease on A. palmata and A. cervicornis from 473 sites across the Caribbean, surveyed from 1997 to 2004. The results of our models suggest that decades-long climate-driven changes in SST, increases in thermal minima, and the breach of thermal maxima have all played significant roles in the spread of white-band disease. We conclude that white-band disease has been strongly coupled with thermal stresses associated with climate change, which has contributed to the regional decline of these once-dominant reef-building corals.
Coral diseases have contributed significantly to the decline in coral cover in the Caribbean. As ... more Coral diseases have contributed significantly to the decline in coral cover in the Caribbean. As many as twenty diseases have been described for Caribbean corals, but few have known etiologies. Here we report on disease signs that were accompanied by high densities of motile, holotrich ciliates, on two species of Caribbean corals, Orbicella faveolata and Siderastrea siderea, which were field collected and maintained in aquaria. A visually estimated increase in ciliate density in the tissue of the coral colonies reflected a putative progression of three ‘different’ disease signs: white-plague-like, brown-band-like, and brown-jelly-like signs. The latter two diseases have previously only been described for corals in the Indo-Pacific, and in aquaria, respectively. Although it remains unclear whether these ciliates are primary pathogens or secondary opportunists, increasing evidence suggests that motile ciliates may play a role in Caribbean-coral diseases.
Coral-reef ecosystems are experiencing frequent and severe disturbance events that
are reducing g... more Coral-reef ecosystems are experiencing frequent and severe disturbance events that are reducing global coral abundance and potentially overwhelming the natural capacity for reefs to recover. While mitigation strategies for climate warming and other anthropogenic disturbances are implemented, coral restoration programmes are being established worldwide as an additional conservation measure to minimise coral loss and enhance coral recovery. Current restoration efforts predominantly rely on asexually produced coral fragments — a process with inherent practical constraints on the genetic diversity conserved and the spatial scale achieved. Because the resilience of coral communities has hitherto relied on regular renewal with natural recruits, the scaling-up of restoration programmes would benefit from greater use of sexually produced corals, which is an approach that is gaining momentum. Here we review the present state of knowledge of scleractinian coral sexual reproduction in the context of reef restoration, with a focus on broadcast-spawning corals. We identify key knowledge gaps and bottlenecks that currently constrain the sexual production of corals and consider the feasibility of using sexually produced corals for scaling-up restoration to the reef- and reef-system scales.
Corals of the eastern tropical Pacific live in a marginal and oceanographically dynamic environme... more Corals of the eastern tropical Pacific live in a marginal and oceanographically dynamic environment. Along the Pacific coast of Panamá, stronger seasonal upwelling in the Gulf of Panamá in the east transitions to weaker upwelling in the Gulf of Chiriquí in the west, resulting in complex regional oceanographic conditions that drive differential coral‐reef growth. Over millennial timescales, reefs in the Gulf of Chiriquí recovered more quickly from climatic disturbances compared with reefs in the Gulf of Panamá. In recent decades, corals in the Gulf of Chiriquí have also had higher growth rates than in the Gulf of Panamá. As the ocean continues to warm, however, conditions could shift to favor the growth of corals in the Gulf of Panamá, where upwelling may confer protection from high‐temperature anomalies. Here we describe the recent spatial and temporal variability in surface oceanography of nearshore environments in Pacific Panamá and compare those conditions with the dynamics of contemporary coral‐reef communities, during and after the 2016 coral‐bleaching event. Although both gulfs have warmed significantly over the last 150 years, thermal maxima in the Gulf of Chiriquí are increasing faster, and ocean temperatures there are becoming more variable than in the recent past. In contrast to historical trends, we found that coral cover, coral survival, and coral growth‐rates were all significantly higher in the Gulf of Panamá. Corals bleached extensively in the Gulf of Chiriquí following the 2015–2016 El Niño event, whereas upwelling in the Gulf of Panamá moderated the high temperatures caused by El Niño, allowing the corals largely to escape thermal stress. As the climate continues to warm, upwelling zones may offer a temporary and localized refuge from the thermal impacts of climate change, while reef growth in the rest of the eastern tropical Pacific continues to decline.
Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determinin... more Thermal-stress events are changing the composition of many coral reefs worldwide. Yet, determining the rates of coral recovery and their long-term responses to increasing sea-surface temperatures is challenging. To do so, we first estimated coral recovery rates following past disturbances on reefs in southern Japan and Western Australia. Recovery rates varied between regions, with the reefs in southern Japan showing more rapid recovery rates (intrinsic rate of increase, r = 0.38 year −1) than reefs in Western Australia (r = 0.17 year −1). Second, we input these recovery rates into a novel, nonlinear hybrid-stochastic-dynamical system to predict the responses of Indo-Pacific coral populations to complex inter-annual temperature cycles into the year 2100. The coral recovery rates were overlaid on background increases in global sea-surface temperatures, under three different climate-change scenarios. The models predicted rapid recovery at both localities with the infrequent and low-magnitude temperature anomalies expected under a conservative climate-change scenario, Representative Concentration Pathway (RCP) 4.5. With moderate increases in ocean temperatures (RCP 6.0) the coral populations showed a bimodal response, with model runs showing either recovery or collapse. Under a business-as-usual climate-change scenario (RCP 8.5), with frequent and intense temperature anomalies, coral recovery was unlikely. The rapid rate of contemporary climate change is seriously affecting terrestrial and marine populations 1,2 , particularly on tropical coral reefs where corals have been living close to their upper thermal limits for millennia 3-5. Although corals on tropical reefs are adapted to warm waters, they rarely experience an annual temperature range greater than a few degrees Celsius. Warmer than average temperatures combined with high seasonal irradiance can cause a dysfunction in the coral-dinoflagellate symbiosis that leads to coral bleaching, and under extreme conditions leads to mortality 6-10. There is, however, considerable variability in the range of thermal tolerances among the eight hundred or more extant coral species 11-13 , and there are substantial differences in the rates of population and community recovery from thermal disturbances 14,15. The rate of recovery from a disturbance is a function of a system's stability and resilience 16,17. Stable, resilient systems recover rapidly; whereas unstable, non-resilient systems recover slowly, or even collapse after disturbances 18. Moreover, the slowing of recovery usually indicates that a system is deteriorating and may be approaching a critical threshold, beyond which the system switches to an alternate and often undesirable state 19,20. Indeed, understanding the rates of change and the resilience of systems has become central to our understanding of modern ecology 21,22. On modern coral reefs, we frequently ask the question: how quickly will a reef recover from a given distur-bance? It is challenging to answer this question, particularly given the complexity of coral reefs and the multitude of nuances that influence recovery 23,24. Recovery depends on many interacting factors, including species composition and environmental and geographic vicissitudes. Understanding these factors and accurately predicting the recovery rates of coral populations is critical in a rapidly changing climate 25 , which is characterized by ocean warming and an increase in the frequency of acute thermal-stress events 5. There is, therefore, a need for models that accurately predict the dynamics of coral populations and determine the likelihood of recovery under future climate-change scenarios RCP 4.5, 6.0, and 8.5 26. Many models explore the dynamics of coral populations 25-28 , although most models are built on the traditional foundation of Leslie and Lefkovitch matrices 29-31. The matrix approach is convenient, but does not capture the instantaneous dynamics of a population. A system of differential equations captures the dynamics of
Expert and intelligent systems based on computer-vision algorithms are becoming a common part of ... more Expert and intelligent systems based on computer-vision algorithms are becoming a common part of our daily lives, as they help us solve problems in areas such as medicine, agriculture, transportation, and ecology. In this paper, we focus on the application of computer vision in marine ecology. Here, we propose a new algorithm for mosaicing images of coral reefs captured by scuba divers using hand-held cameras during reef surveys. Such images often capture partial views of the surveyed area that are then collated into mosaics of the reef assemblages. Accurate mosaics will help coral-reef researchers rapidly assess not only the status of coral reefs, but also determine rates of recovery or rates of decline using longitudinal data. Most standard mosaicing algorithms distort the images, however, and moving objects and paral-lax errors, which usually happen in underwater images, hinder mosaic construction. To overcome these issues, our new algorithm uses a two-step approach that first detects and then removes loops and low-quality regions from an estimated camera trajectory. The algorithm then stitches the remaining images by warping parallax-affected image regions with a geometric transformation different from the one used for parallax-unaffected regions. We tested our method on images captured during a large spatial survey of coral reef sites throughout the Caribbean region. Our method obtained better-quality mosaics than other state-of-the-art algorithms.
Outbreaks of coral diseases continue to reduce global coral populations. In the Caribbean, yellow... more Outbreaks of coral diseases continue to reduce global coral populations. In the Caribbean, yellow band is a severe and widespread disease that commonly affects corals of the Orbicella spp. complex, significantly impeding coral reproduction, and hindering the natural recovery of Orbicella spp. populations. Caribbean yellow-band disease (CYBD) lesions may be severe, and often result in the complete loss of coral tissue. The slow spread of CYBD, however, provides an opportunity to test methods to mitigate the disease. Here we report the results of in situ experiments, conducted within Buck Island Reef National Monument in St. Croix, USVI, to test the effectiveness of three techniques to minimize disease impact on Orbicella faveolata: (1) shading, (2) aspirating, and (3) chiseling a " firebreak " to isolate the lesion. Neither shading nor aspirating the diseased tissue significantly reduced CYBD tissue loss. However, chiseling reduced the rate and amount of tissue lost by 31%. While 30–40% of the chiseled lesions appeared to be free of disease signs 12–16 months after treatment, success significantly and steadily declined over 23 months, indicating a possible lack of long-term viability of the technique. The results of this study demonstrate that creating a " firebreak " between diseased and healthy-appearing tissue slows the spread of the disease and may prolong the life of O. faveolata colonies. The firebreak method yielded the best results of all the techniques tested, and also required the least amount of effort and resources. However, we do not recommend that this treatment alone be used for long-term disease mitigation. Rather, we propose that modifications of this and other treatment options be sought. The results also highlight the need for extended monitoring of CYBD after any treatment, due to the slow but variable rate and pattern of tissue loss in this disease.
Recent outbreaks of coral diseases in the Caribbean have been linked to increasingly stressful se... more Recent outbreaks of coral diseases in the Caribbean have been linked to increasingly stressful sea-surface temperatures (SSTs). Yet, ocean warming is spatially heterogeneous and therefore has the potential to lead to hotspots of disease activity. Here, we take an epidemiological approach to examine spatial differences in the risk of white-band disease on Acropora spp. and yellow-band disease on Orbicella spp. in the Caribbean. Our analysis involved examining the spatial patterns of disease prevalence, and creating a Bayesian-risk model that tested for regional differences in disease risk. The spatial examination of disease prevalence showed several clusters of white-band disease, including high prevalence in the Turks and Caicos, Jamaica, Puerto Rico, the Virgin Islands, and Belize, whereas yellow-band disease seemed most prevalent along the Yucatan Peninsula. The Bayesian-risk model showed regional clusters of white-band disease near the southern Dominican Republic, Puerto Rico, the Virgin Islands, and the Lesser Antilles, whereas the risk of yellow-band disease was highest in the southern Caribbean. The relative risk of both diseases increased with warmer SSTs. The Bayesian-risk model allowed us to predict where we should expect future outbreaks of coral diseases at a regional scale, and suggests regions where the implementation of disease mitigation plans may be most urgent.
With the current rapid rate of climate change, coral communities are being repeatedly subjected t... more With the current rapid rate of climate change, coral communities are being repeatedly subjected to anomalously high thermal-stress events. Most global models predict that within the next 100 years, few reef corals will survive in tropical oceans. Yet thermal stresses have long been spatially and temporally variable across the oceans, and coral communities in different geographic regions are likely to be inherently different in their capacity to tolerate thermal stress. Using a spatially explicit Bayesian approach, we examined the response of coral communities to the hazards of climate-change associated thermal stress. We used the rates of change in sea-surface temperatures and the maximum sea-surface temperatures from 1980 to 2012 as predictive covariates of global records of coral bleaching over the same time period. There were negative relationships between the rates of change in sea-surface temperatures and coral bleaching, although the results were misleading because the highest rates of change in sea-surface temperatures were recorded at high latitudes, where average sea-surface temperatures are characteristically cooler than at low latitudes. Also, the results suggested that the most hazardous localities for corals, which experienced the highest maximum sea-surface temperatures, were in the northern hemisphere, particularly in the northern and western Indian Ocean, and along the rim of the eastern and western Pacific Ocean. Coral populations in these localities have suffered the greatest mortality. When a capacity to adapt to thermal stress was considered in the model, several localities responded positively, particularly corals in the Hawaiian Islands, the northern Marshall Islands, Micronesia, the Line Islands, the Cook Islands, the southern Great Barrier Reef, and along the coast of Brazil.
The putative increase in coral diseases in the Caribbean has led to extensive declines in coral p... more The putative increase in coral diseases in the Caribbean has led to extensive declines in coral populations. Coral diseases are a consequence of the complex interactions among the coral hosts, the pathogens, and the environment. Yet, the relative influence that each of these components has on the prevalence of coral diseases is unclear. Also unknown is the extent to which historical thermal-stress events have influenced the prevalence of contemporary coral diseases and the potential adjustment of coral populations to thermal stress. We used a Bayesian approach to test the hypothesis that in 2012 the relative risk of four signs of coral disease (white signs, dark spots, black bands, and yellow signs) differed at reef locations with different thermal histories. We undertook an extensive spatial study of coral diseases at four locations in the Caribbean region (10 3 km), two with and two without a history of frequent thermal anomalies (;4–6 years) over the last 143 years (1870–2012). Locations that historically experienced frequent thermal anomalies had a significantly higher risk of corals displaying white signs, and had a lower risk of corals displaying dark spots, than locations that did not historically experience frequent thermal anomalies. By contrast, there was no relationship between the history of thermal stress and the relative risk of corals displaying black bands and yellow signs, at least at the spatial scale of our observations.
Elevated seawater temperatures during the late summer have the potential to negatively affect the... more Elevated seawater temperatures during the late summer have the potential to negatively affect the development and survivorship of the larvae of reef corals that are reproductive during that time of year. Acropora palmata, a major Caribbean hermatype, reproduces annually during August and September. A. palmata populations have severely declined over the past three decades, and recovery will require high recruitment rates. Such recruitment will be limited if larval supply is reduced by elevated temperatures. The effects of elevated temperatures on development, survival, and larval settlement of A. palmata were investigated by culturing newly fertilized eggs at temperatures ranging from 27.5 to 31.5 degrees C. Development was accelerated and the percentage of developmental abnormalities increased at higher temperatures. Embryo mortality peaked during gastrulation, indicating that this complex developmental process is particularly sensitive to elevated temperatures. Larvae cultured at 3...
Elevated seawater temperatures during the late summer have the potential to negatively affect the... more Elevated seawater temperatures during the late summer have the potential to negatively affect the development and survivorship of the larvae of reef corals that are reproductive during that time of year. Acropora palmata, a major Caribbean hermatype, reproduces annually during August and September. A. palmata populations have severely declined over the past three decades, and recovery will require high recruitment rates. Such recruitment will be limited if larval supply is reduced by elevated temperatures. The effects of elevated temperatures on development, survival, and larval settlement of A. palmata were investigated by culturing newly fertilized eggs at temperatures ranging from 27.5 to 31.5 degrees C. Development was accelerated and the percentage of developmental abnormalities increased at higher temperatures. Embryo mortality peaked during gastrulation, indicating that this complex developmental process is particularly sensitive to elevated temperatures. Larvae cultured at 3...
Over the last half-century, coral diseases have contributed to the rapid decline of coral populat... more Over the last half-century, coral diseases have contributed to the rapid decline of coral populations throughout the Caribbean region. Some coral diseases appear to be potentially infectious, yet little is known about their modes of transmission. This study experimentally tested whether dark-spot syndrome on Siderastrea siderea was directly or indirectly transmissible to neighboring coral colonies. We also tested whether open wounds were necessary to facilitate disease transmission. At the completion of the experiments, we sampled bacterial communities on diseased, exposed, and healthy coral colonies to determine whether bacterial pathogens had transmitted to the susceptible colonies. We saw no evidence of either direct or waterborne transmission of dark-spot syndrome, and corals that received lesions by direct contact with diseased tissue, healed and showed no signs of infection. There were no significant differences among bacterial communities on healthy, exposed, and diseased colonies, although nine individual ribotypes were significantly higher in diseased corals compared with healthy and exposed corals, indicating a lack of transmission. Although our experiments do not fully refute the possibility that dark-spot syndrome is infectious and transmissible, our results suggest that in situ macroscopic signs of dark-spot syndrome are not always contagious.
Over the past 40 years, two of the dominant reef-building corals in the Caribbean, Acropora palma... more Over the past 40 years, two of the dominant reef-building corals in the Caribbean, Acropora palmata and Acropora cervicornis, have experienced unprecedented declines1, 2. That loss has been largely attributed to a syndrome commonly referred to as white-band disease1, 3. Climate change-driven increases in sea surface temperature (SST) have been linked to several coral diseases4, 5, yet, despite decades of research, the attribution of white-band disease to climate change remains unknown. Here we hindcasted the potential relationship between recent ocean warming and outbreaks of white-band disease on acroporid corals. We quantified eight SST metrics, including rates of change in SST and contemporary thermal anomalies, and compared them with records of white-band disease on A. palmata and A. cervicornis from 473 sites across the Caribbean, surveyed from 1997 to 2004. The results of our models suggest that decades-long climate-driven changes in SST, increases in thermal minima, and the breach of thermal maxima have all played significant roles in the spread of white-band disease. We conclude that white-band disease has been strongly coupled with thermal stresses associated with climate change, which has contributed to the regional decline of these once-dominant reef-building corals.
Coral diseases have contributed significantly to the decline in coral cover in the Caribbean. As ... more Coral diseases have contributed significantly to the decline in coral cover in the Caribbean. As many as twenty diseases have been described for Caribbean corals, but few have known etiologies. Here we report on disease signs that were accompanied by high densities of motile, holotrich ciliates, on two species of Caribbean corals, Orbicella faveolata and Siderastrea siderea, which were field collected and maintained in aquaria. A visually estimated increase in ciliate density in the tissue of the coral colonies reflected a putative progression of three ‘different’ disease signs: white-plague-like, brown-band-like, and brown-jelly-like signs. The latter two diseases have previously only been described for corals in the Indo-Pacific, and in aquaria, respectively. Although it remains unclear whether these ciliates are primary pathogens or secondary opportunists, increasing evidence suggests that motile ciliates may play a role in Caribbean-coral diseases.
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are reducing global coral abundance and potentially overwhelming the natural capacity for reefs
to recover. While mitigation strategies for climate warming and other anthropogenic disturbances
are implemented, coral restoration programmes are being established worldwide as an additional
conservation measure to minimise coral loss and enhance coral recovery. Current restoration
efforts predominantly rely on asexually produced coral fragments — a process with inherent practical constraints on the genetic diversity conserved and the spatial scale achieved. Because the
resilience of coral communities has hitherto relied on regular renewal with natural recruits, the
scaling-up of restoration programmes would benefit from greater use of sexually produced corals,
which is an approach that is gaining momentum. Here we review the present state of knowledge
of scleractinian coral sexual reproduction in the context of reef restoration, with a focus on broadcast-spawning corals. We identify key knowledge gaps and bottlenecks that currently constrain
the sexual production of corals and consider the feasibility of using sexually produced corals for
scaling-up restoration to the reef- and reef-system scales.
are reducing global coral abundance and potentially overwhelming the natural capacity for reefs
to recover. While mitigation strategies for climate warming and other anthropogenic disturbances
are implemented, coral restoration programmes are being established worldwide as an additional
conservation measure to minimise coral loss and enhance coral recovery. Current restoration
efforts predominantly rely on asexually produced coral fragments — a process with inherent practical constraints on the genetic diversity conserved and the spatial scale achieved. Because the
resilience of coral communities has hitherto relied on regular renewal with natural recruits, the
scaling-up of restoration programmes would benefit from greater use of sexually produced corals,
which is an approach that is gaining momentum. Here we review the present state of knowledge
of scleractinian coral sexual reproduction in the context of reef restoration, with a focus on broadcast-spawning corals. We identify key knowledge gaps and bottlenecks that currently constrain
the sexual production of corals and consider the feasibility of using sexually produced corals for
scaling-up restoration to the reef- and reef-system scales.