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Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs
Global Change Biology
Abstract
Coral reefs and the services they provide are seriously threatened by ocean acidification and climate change impacts like coral bleaching. Here, we present updated global projections for these key threats to coral reefs based on ensembles of IPCC AR5 climate models using the new Representative Concentration Pathway (RCP) experiments. For all tropical reef locations, we project absolute and percentage changes in aragonite saturation state (Ωarag) for the period between 2006 and the onset of annual severe bleaching (thermal stress >8 degree heating weeks); a point at which it is difficult to believe reefs can persist as we know them. Severe annual bleaching is projected to start 10-15 years later at high-latitude reefs than for reefs in low latitudes under RCP8.5. In these 10-15 years, Ωarag keeps declining and thus any benefits for high-latitude reefs of later onset of annual bleaching may be negated by the effects of acidification. There are no long-term refugia from the effects of both acidification and bleaching. Of all reef locations, 90% are projected to experience severe bleaching annually by 2055. Furthermore, 5% declines in calcification are projected for all reef locations by 2034 under RCP8.5, assuming a 15% decline in calcification per unit of Ωarag. Drastic emissions cuts, such as those represented by RCP6.0, result in an average year for the onset of annual severe bleaching that is ~20 years later (2062 vs. 2044). However, global emissions are tracking above the current worst-case scenario devised by the scientific community, as has happened in previous generations of emission scenarios. The projections here for conditions on coral reefs are dire, but provide the most up-to-date assessment of what the changing climate and ocean acidification mean for the persistence of coral reefs.
... Projecting trajectories of future net carbonate production is, however, challenging because the manifestation of the effects of OA and warming will not occur uniformly in space and time across the world's reef regions [23][24][25] . Many different regional effects will impact temperature and aragonite saturation state (Ω Ar ) differently 26,27 . For instance, effects from the El Niño-Southern Oscillation (ENSO), polar amplification and the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) cause sea surface temperature rise to vary greatly across regions under climate change 28 . ...
... For instance, effects from the El Niño-Southern Oscillation (ENSO), polar amplification and the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) cause sea surface temperature rise to vary greatly across regions under climate change 28 . This adds to the uncertainties regarding the onset and severity of annual bleaching due to marine heatwaves 26 . Further, there is great variability in the calcification responses to warming and OA among different coral species, and the flexibility in the ability of some corals to maintain calcification rates over a broad range of Ω Ar conditions [29][30][31] . ...
... Max DHW projections were then used to forecast annual bleaching. The onset of annual severe bleaching (ASB) conditions is described as the annual surpassing of > 8 DHWs accumulating during a 3-month period 26 . Eight DHWs is higher than the world average bleaching predictor 62 , but at this greater threshold, interspecies differences in sensitivity are covered and it is likely that most coral species will bleach 63 . ...
For reef framework to persist, calcium carbonate production by corals and other calcifiers needs to outpace loss due to physical, chemical, and biological erosion. This balance is both delicate and dynamic and is currently threatened by the effects of ocean warming and acidification. Although the protection and recovery of ecosystem functions are at the center of most restoration and conservation programs, decision makers are limited by the lack of predictive tools to forecast habitat persistence under different emission scenarios. To address this, we developed a modelling approach, based on carbonate budgets, that ties species-specific responses to site-specific global change using the latest generation of climate models projections (CMIP6). We applied this model to Cheeca Rocks, an outlier in the Florida Keys in terms of high coral cover, and explored the outcomes of restoration targets scheduled in the coming 20 years at this site by the Mission: Iconic Reefs restoration initiative. Additionally, we examined the potential effects of coral thermal adaptation by increasing the bleaching threshold by 0.25, 0.5, 1 and 2˚C. Regardless of coral adaptative capacity or restoration, net carbonate production at Cheeca Rocks declines heavily once the threshold for the onset of annual severe bleaching is reached. The switch from net accretion to net erosion, however, is significantly delayed by mitigation and adaptation. The maintenance of framework accretion until 2100 and beyond is possible under a decreased emission scenario coupled with thermal adaptation above 0.5˚C. Although restoration initiatives increase reef accretion estimates, Cheeca Rocks will only be able to keep pace with future sea-level rise in a world where anthropogenic CO2 emissions are reduced. Present results, however, attest to the potential of restoration interventions combined with increases in coral thermal tolerance to delay the onset of mass bleaching mortalities, possibly in time for a low-carbon economy to be implemented and complementary mitigation measures to become effective.
... As indicated earlier, considerable environmental unsuitability has already occurred due to localized human drivers, particularly along continental masses and tropical regions (S4 and S5 Figs). Going forward, environmental unsuitability by heatwaves is projected to occur first in tropical areas and later at higher latitudes (S2 Fig), while environmental unsuitability by acidification is projected to occur first in higher latitudes and later at tropical areas (S3 Fig; see also [6,18]). Environmental unsuitability by storms spreads earlier in pantropical areas towards higher latitudes and the tropics (S6 Fig). ...
... Considerable attention has been given to the issue of climate change, especially as it relates to changes in temperature and acidification on coral reefs [6,18,19]. These studies all highlighted a dire prognosis for the world's coral reefs around the middle of the century (e.g., significant environmental crises have been projected to occur from 2050 to 2080 under projected changes of temperature and/or acidification [6,[18][19][20][21]). ...
... Considerable attention has been given to the issue of climate change, especially as it relates to changes in temperature and acidification on coral reefs [6,18,19]. These studies all highlighted a dire prognosis for the world's coral reefs around the middle of the century (e.g., significant environmental crises have been projected to occur from 2050 to 2080 under projected changes of temperature and/or acidification [6,[18][19][20][21]). While concurring with these prior results, our study suggests that assessing suitability from too few variables might underestimate the dangers of human disturbances on coral reefs, as supported by studies investigating effects of cumulative stressors at a local scale [22][23][24][25][26] and studies on planetary and biodiversity boundaries [27,28]. ...
Anthropogenic disturbances are posing unprecedented challenges to the persistence of ecosystems worldwide. The speed at which these disturbances reach an ecosystem’s tolerance thresholds will determine the time available for adaptation and conservation. Here, we aim to calculate the year after which a given environmental stressor permanently exceeds the bounds of an ecosystem’s tolerance. Ecosystem thresholds are here defined as limits in a given stressor beyond which ecosystems have showed considerable changes in community assembly and functioning, becoming remnants of what they once were, but not necessarily leading to species extirpation or extinction. Using the world’s coral reefs as a case example, we show that the projected effects of marine heatwaves, ocean acidification, storms, land-based pollution, and local human stressors are being underestimated considerably by looking at disturbances independently. Given the spatial complementarity in which numerous disturbances impact the world’s coral reefs, we show that the timelines of environmental suitability are halved when all disturbances are analyzed simultaneously, as opposed to independently. Under business-as-usual scenarios, the median year after which environmental conditions become unsuitable for the world’s remaining coral reefs was, at worse, 2050 for any one disturbance alone (28 years left); but when analyzed concurrently, this date was shortened to 2035 (13 years left). When analyzed together, disturbances reduced the date of environmental suitability because areas that may remain suitable under one disturbance could become unsuitable by any of several other variables. The significance of co-occurring disturbances at reducing timeframes of environmental suitability was evident even under optimistic scenarios. The best-case scenario, characterized by strong mitigation of greenhouse gas emissions and optimistic human development, resulted in 41% of global coral reefs with unsuitable conditions by 2100 under any one disturbance independently; yet when analyzed in combination up to 64% of the world’s coral reefs could face unsuitable environmental conditions by one disturbance or another. Under the worst-case scenario, nearly all coral reef ecosystems worldwide (approximately 99%) will permanently face unsuitable conditions by 2055 in at least one of the disturbances analyzed. Prior studies have indicated the projected dire effects of climate change on coral reefs by mid-century; by analyzing a multitude of projected disturbances, our study reveals a much more severe prognosis for the world’s coral reefs as they have significantly less time to adapt while highlighting the urgent need to tackle available solutions to human disturbances.
... ASB describes the timeframe during which reefs are expected to experience severe bleaching events annually that result in large reductions in live coral and are not predicted to recover [60]. Heat stress for corals is quantified when sea surface temperature (SST) exceeds 1˚C above the maximum monthly mean, and the indicator is cumulative during a three-month period [61,62]. ASB is expected to occur above eight Degree Heating Weeks (DHWs), which may reflect a 1˚C exceedance over eight weeks, 2˚C for four weeks, etc., during the 3-month window. ...
... For this assessment process, such datasets were also combined with a trait-based approach to estimate individual species' vulnerability and resiliency to decline. Most studies on the loss of corals typically focus on the severity of coral reef loss at either regional or global levels [20,21,33,61,[73][74][75]. While insights at the biome/ecosystem level are important for corals, changes in species composition are more relevant for measures of biodiversity and may be of higher priority to management/conservation plans [76]. ...
Atlantic reef-building corals and coral reefs continue to experience extensive decline due to increased stressors related to climate change, disease, pollution, and numerous anthropogenic threats. To understand the impact of ocean warming and reef loss on the estimated extinction risk of shallow water Atlantic reef-building scleractinians and milleporids, all 85 valid species were reassessed under the IUCN Red List Categories and Criteria, updating the previous Red List assessment of Atlantic corals published in 2008. For the present assessment, individual species declines were estimated based on the modeled coral cover loss (1989–2019) and projected onset of annual severe bleaching events (2020–2050) across the Atlantic. Species traits were used to scale species’ relative vulnerability to the modeled cover declines and forecasted bleaching events. The updated assessments place 45.88%–54.12% of Atlantic shallow water corals at an elevated extinction risk compared to the previous assessments conducted in 2008 (15.19%–40.51%). However, coral cover loss estimates indicate an improvement in reef coverage compared to the historic time-series used for the 2008 assessments. Based on this, we infer that, although remaining dangerously high, the rate of Atlantic reef coral cover decline has surprisingly slowed in recent decades. However, based on modeled projections of sea-surface temperature that predict the onset of annual severe bleaching events within the next 30 years, we listed 26 (out of 85) species as Critically Endangered in the IUCN Red List. Each of these species had previously been listed under a lower threatened category and this result alone highlights the severe threat future bleaching events pose to coral survival and the reef ecosystems they support.
... This relationship can be disrupted at just 1-2°C above mean summer sea surface temperatures in a process known as bleaching [3], often leading to mortality [4,5] or impacts on growth and fecundity [6,7]. Due to the increasing frequency of marine heatwaves, mass coral bleaching events are projected to become the norm annually by mid-century [8,9]. As such, many studies have focused on the response of reef-building corals to thermal stress alone [10][11][12]. ...
... As such, many studies have focused on the response of reef-building corals to thermal stress alone [10][11][12]. However, as corals are calcifying organisms that build aragonite skeletons, lower seawater pH and aragonite saturation due to ocean and coastal acidification [9] represent an additional drain on the energy required to maintain homeostasis [13,14]. Thus, understanding how corals respond to the interactive effects of temperature and acidification will be essential to more accurately predict their future persistence in a changing climate [10]. ...
As environments are rapidly reshaped due to climate change, phenotypic plasticity plays an important role in the ability of organisms to persist and is considered an especially important acclimatization mechanism for long-lived sessile organisms such as reef-building corals. Often, this ability of a single genotype to display multiple phenotypes depending on the environment is modulated by changes in gene expression, which can vary in response to environmental changes via two mechanisms: baseline expression and expression plasticity. We used transcriptome-wide expression profiling of eleven genotypes of common-gardened Acropora cervicornis to explore genotypic variation in the expression response to thermal and acidification stress, both individually and in combination. We show that the combination of these two stressors elicits a synergistic gene expression response, and that both baseline expression and expression plasticity in response to stress show
genotypic variation. Additionally, we demonstrate that front-loading of a large module of co-expressed genes is associated with greater retention of algal symbionts under combined stress. These results illustrate that variation in the gene expression response of individuals to climate change stressors can persist even when individuals have shared environmental histories, affecting their performance under future climate change scenarios.
... The increasing carbon dioxide in the atmosphere is contributing to rising sea surface temperatures (SST) and surging ocean acidification. Under current climate change estimates, both phenomena are expected to worsen (van Hooidonk et al., 2014). Despite emissions being steady, the world's oceans are experiencing continuous temperature rise and unavoidable changes in carbonate chemistry (IPCC, 2014). ...
... The second and third phases of coral reef transition show alarming conditions since the likelihood of sand transformation into a mixed habitat, or coral reefs is very small. This state also harms fish reefs' biomass and density since the sand, and adjacent habitat is higher than 20% (Sievers et al., 2020). If we ignore the transition change and only focus in Table 2, in that case, we can conclude that the coral reef's condition in the study area is normal since it fluctuates annually. ...
This study looks at how the benthic habitat on Ayau Island; one of Indonesia's most significant coral reef habitats has changed from 2015 to 2019 and the linkage with local sea temperature trends. This study used Landsat 8 Operational Land Imager and National Oceanic and Atmospheric Administration satellite remote sensing data and field data. The Landsat 8 satellite image processing includes atmospheric correction, sunglint correction, water column correction, image classification, and accuracy assessment. These steps were employed to understand change detection. The result revealed that the coral reef and seagrass decreased by 9.9 and 74.9% during the study period. However, the transition change was dynamic, with an annual rate of − 82.5 ha/year for coral reefs and − 108.95 ha/year for seagrass. The highest decrease in both benthic habitats occurred during the El-Nino Event, where the Sea Surface Temperature anomaly reached 1.5 °C. The massive habitat loss is alarming; thus, climate change mitigation and adaptation in the local context must be addressed.
... This trend is likely influenced by the West Sea's geographical characteristics, such as its relatively shallow depth and semi-enclosed waters. Marine heatwaves driven by global climate change pose significant threats to marine ecosystems, such as coral bleaching and fluctuations in fish populations, as documented in previous studies [26][27][28] . Furthermore, rising sea temperatures and marine heatwaves have been linked to large-scale fish die-offs 29 . ...
Coastal ecosystems surrounding the Korean Peninsula are undergoing rapid environmental changes driven by global climate warming, highlighting the need for efficient methods to monitor marine biodiversity. This study aimed to analyze fish communities across four coastal regions: the East Sea, South Sea, West Sea, and Jeju using environmental DNA (eDNA) metabarcoding. Underwater drones were employed to collect water samples. A total of 63 sampling sites were surveyed, detecting 167 fish species from 72 families, encompassing tropical, subtropical, temperate, boreal, polar, and deep-water taxa. The East Sea hosted a mix of cold- and warm-water species, while Jeju exhibited a relatively high proportion of tropical and subtropical fish. Additionally, 13 alien species were identified, underscoring the utility of eDNA for the early detection of non-native taxa expanding their ranges in response to ongoing warming trends. This study further validated that eDNA sampling using underwater drones offers a rapid, non-invasive approach to biodiversity assessments, effectively addressing many of the limitations associated with traditional survey techniques. Collectively, these findings highlight the potential of eDNA to generate critical and timely data on fish assemblages the emergence of alien species, providing valuable insights to inform proactive resource management, and climate change research in marine ecosystems.
Supplementary Information
The online version contains supplementary material available at 10.1038/s41598-025-02685-6.
... Ocean Acidification Projections estimate future ocean pH decreases due to CO 2 absorption, impacting marine ecosystems, coral reefs, shellfish, and biodiversity, based on climate models and emission scenarios (cf. [86,88,24]). Let be a set of marine regions (e.g., different areas of the ocean). ...
A fuzzy set generalizes classical set theory by assigning each element a membership value within [0, 1], allowing for the representation of partial or uncertain membership. It is well established that fuzzy sets can be further extended to Hyperfuzzy sets and SuperHyperfuzzy sets. However, as these concepts have been introduced only recently, their practical applications remain largely unexplored. In this paper, we investigate potential applications of Fuzzy sets, Hyperfuzzy sets, and SuperHyperfuzzy sets in the context of climate change and environmental factors. Additionally, we introduce the Forest Fuzzy Set, Forest Hyperfuzzy Set, and Forest SuperHyperfuzzy Set, and explore their possible applications. Furthermore, Hyperfuzzy sets and SuperHyperfuzzy sets are known to be associated with Hyperstructure and SuperHyperstructure concepts. While our primary focus is on the aforementioned extensions, we also provide a brief discussion on TreeStructure and ForestStructure by considering their definitions in the context of Hyperstructure and SuperHyperstructure.
... However, owing to their proximity to human populations, shallow-water coral reefs are subject to a variety of local impacts, such as overfishing, eutrophication, pollution related to agriculture and industry, and mass tourism (Leão and Kikuchi 2005). In addition to these threats, coral reefs are widely recognized as the ecosystem that is most threatened by climate change impacts, especially ocean acidification and warming (e.g., Fabricius et al. 2011;van Hooidonk et al. 2014). ...
Small metazoans, especially harpacticoid copepods, are an important component in the benthic food webs of benthic environments. However, studies on the effects of elevated CO 2 and temperature on these animals are scarce and those that do exist focus mainly on the individual species level. A laboratory experiment was conducted to evaluate the impact of different climate change scenarios on a community of harpacticoid copepods from a coral reef environment. Samples were collected from the coral reef subtidal zone of Serrambi beach (Ipojuca, Pernambuco, Brazil), using colonized artificial substrate units. The units were exposed to control treatments and to three climate change scenarios and were collected after 14 and 29 days. A highly diverse community of harpacticoids was analyzed [H′(log 2 ) = 4.37]. Changes in the community structure were observed, and the response of the copepod community structure to the different scenarios varied according to the sampling period. The maintenance of a highly diverse community enabled a complex pattern of responses to be observed at a species level with three different response patterns to the changing seawater conditions: sensitive species represented by Tisbe sp., Stenhelia sp. and Ameira sp.; mildly sensitive represented by Cyclopoida and Dactylopusia sp.; resistant or opportunist represented by Ectinosoma sp.1, Ectinosoma sp.2 and Mesochra sp. The increase in malformed adult animals in the most severe scenario indicated that species that do not suffer mortality are not exempt from sublethal symptoms. Harpacticoid organisms are shown as reliable tools to assess climate change in coral reef environments.
... Dove et al., 2013). Based on such studies, numerical and statistical models have been developed and used to evaluate the impact of temperature and ocean acidification 65 changes on coral reefs, often regionally (Evenhuis et al., 2015;Buddemeier et al., 2008;Sully et al., 2022), but also globally (Kleypas et al., 1999;Donner et al., 2005;Silverman et al., 2009;Frieler et al., 2012;Couce et al., 2013;van Hooidonk et al., 2014;Eyre et al., 2018;Cornwall et al., 2021). Among the models used to evaluate the impact on coral reefs during the next century globally, some considered the impact of future temperature change (Donner et al., 2005), others the impact of Ωar change (Kleypas et al., 1999, Eyre et al., 2018, and some both variables simultaneously (Silverman et al., 2009;Frieler et al., 70 2012;Couce et al., 2013;van Hooidonk et al., 2016;Cornwall et al., 2021;Cornwall et al., 2023). ...
Coral reefs are under threat due to climate change and ocean acidification. However, large uncertainties remain concerning future carbon dioxide emissions, climate change and the associated impacts on coral reefs. While most previous studies have used climate model outputs to compute future coral reef carbonate production, we use a coral reef carbonate production module embedded in a global carbon-climate model. This enables the simulation of the response of coral reefs to projected changes in physical and chemical conditions at finer temporal resolution. The use of a fast-intermediate complexity model also permits the simulation of a large range of possible futures by considering different greenhouse gas concentration scenarios (Shared Socioeconomic Pathways (SSPs)), different climate sensitivities (hence different levels of warming for a given level of acidification), as well as the possibility of corals adapting their thermal bleaching thresholds. We show that without thermal adaptation, global coral reef carbonate production decreases to less than 25 % of historical values in most scenarios over the twenty-first century, with limited further declines between 2100 and 2300 irrespective of the climate sensitivity. With thermal adaptation, there is far greater scenario variability in projections of reef carbonate production. Under high-emission scenarios the rate of twenty-first century declines is attenuated, with some global carbonate production declines delayed until the twenty-second century. Under high-mitigation scenarios, however, global coral reef carbonate production can recover in the twenty-first and twenty-second century, and thereafter persists at 50–90 % of historical values, provided that the climate sensitivity is moderate.
... For example, 39% of the world's reefs had been exposed to at least one severe heatwave between 1990-2020, corresponding to the potential loss of 14% of the genetic diversity in Acropora corals. By 2055, 90% of the world's reefs might be exposed to severe heatwaves (52), resulting in a potential loss of~50% of the global Acropora genetic diversity (Fig. 4D). Accounting for genomic vulnerability, the worldwide fraction of at-risk reefs is reduced to 20%, corresponding to a potential Acropora genetic loss of~6%. ...
The dramatic decline of reef-building corals calls for a better understanding of coral adaptation to ocean warming. Here, we characterized genetic diversity of the widespread genus Acropora by building a genomic database of 547 coral samples from different oceanic regions—from the Great Barrier Reef to the Persian Gulf. Through genome-environment associations, we found that different Acropora species showed evolutionary signals of heat-adaptation in the same genomic regions, pointing to genes associated with molecular heat shock responses and symbiosis. These adaptive signals were uncommon in Acropora populations exposed to less than two heatwaves, indicating a potential genomic vulnerability to future heat exposure. We showed that genomic vulnerability estimates corroborate local and global patterns of coral decline, and used these estimates to reassess global coral reef conservation risks and priorities.
... This assumption permits the estimation of reef cells (e.g., 0.5°× 0.5°pixels on the Earth's surface) that are at risk of 'long-term degradation' 14,15 or 'severe bleaching events' [41][42][43] , according to the threshold and frequency of events set. Although these models have the advantage of utilizing a method that can be applied to broad geographical scales and incorporate other moderating factors without the need for detailed in situ data, they rarely perform any direct assessments of biological or ecological processes 14,15,[44][45][46] . This approach was the most prevalent model type in our analysis (32%) (Fig. 1a) and attracted a disproportionately higher number of cumulative citations (68%) than all other model types (Fig. 1b). ...
Climate change impact syntheses, such as those by the Intergovernmental Panel on Climate Change, consistently assert that limiting global warming to 1.5 °C is unlikely to safeguard most of the world’s coral reefs. This prognosis is primarily based on a small subset of available models that apply similar ‘excess heat’ threshold methodologies. Our systematic review of 79 articles projecting coral reef responses to climate change revealed five main methods. ‘Excess heat’ models constituted one third (32%) of all studies but attracted a disproportionate share (68%) of citations in the field. Most methods relied on deterministic cause-and-effect rules rather than probabilistic relationships, impeding the field’s ability to estimate uncertainty. To synthesize the available projections, we aimed to identify models with comparable outputs. However, divergent choices in model outputs and scenarios limited the analysis to a fraction of available studies. We found substantial discrepancies in the projected impacts, indicating that the subset of articles serving as a basis for climate change syntheses may project more severe consequences than other studies and methodologies. Drawing on insights from other fields, we propose methods to incorporate uncertainty into deterministic modeling approaches and propose a multi-model ensemble approach to generating probabilistic projections for coral reef futures.
... We grew Pacific oyster spat at pCO 2 levels of 800, 1,600, and 2,800 μatm (Table S1) to assess the effect of acidification on the spat microbiome. Previous studies have shown that changes in pH as a result of pCO 2 influence the physiology of marine organisms such as corals and oysters (107)(108)(109) and also play a role in shifting the composition of the microbiome (47)(48)(49)(50). Therefore, we expected pCO 2 to affect the biology of the spat and, thus, influence the microbiome. ...
Pacific oysters (Magallana gigas, a.k.a. Crassostrea gigas), the most widely farmed oysters, are under threat from climate change and emerging pathogens. In part, their resilience may be affected by their microbiome, which, in turn, may be influenced by ocean warming and acidification. To understand these impacts, we exposed early-development Pacific oyster spat to different temperatures (18°C and 24°C) and pCO2 levels (800, 1,600, and 2,800 µatm) in a fully crossed design for 3 weeks. Under all conditions, the microbiome changed over time, with a large decrease in the relative abundance of potentially pathogenic ciliates (Uronema marinum) in all treatments with time. The microbiome composition differed significantly with temperature, but not acidification, indicating that Pacific oyster spat microbiomes can be altered by ocean warming but is resilient to ocean acidification in our experiments. Microbial taxa differed in relative abundance with temperature, implying different adaptive strategies and ecological specializations among microorganisms. Additionally, a small proportion (~0.2% of the total taxa) of the relatively abundant microbial taxa were core constituents (>50% occurrence among samples) across different temperatures, pCO2 levels, or time. Some taxa, including A4b bacteria and members of the family Saprospiraceae in the phyla Chloroflexi (syn. Chloroflexota) and Bacteroidetes (syn. Bacteroidota), respectively, as well as protists in the genera Labyrinthula and Aplanochytrium in the class Labyrinthulomycetes, and Pseudoperkinsus tapetis in the class Ichthyosporea were core constituents across temperatures, pCO2 levels, and time, suggesting that they play an important, albeit unknown, role in maintaining the structural and functional stability of the Pacific oyster spat microbiome in response to ocean warming and acidification. These findings highlight the flexibility of the spat microbiome to environmental changes.
IMPORTANCE
Pacific oysters are the most economically important and widely farmed species of oyster, and their production depends on healthy oyster spat. In turn, spat health and productivity are affected by the associated microbiota; yet, studies have not scrutinized the effects of temperature and pCO2 on the prokaryotic and eukaryotic microbiomes of spat. Here, we show that both the prokaryotic and, for the first time, eukaryotic microbiome of Pacific oyster spat are surprisingly resilient to changes in acidification, but sensitive to ocean warming. The findings have potential implications for oyster survival amid climate change and underscore the need to understand temperature and pCO2 effects on the microbiome and the cascading effects on oyster health and productivity.
... In this ecosystem, the recent large declines in coral abundance (Hughes et al. 2018) highlight the value of understanding the conditions favoring recruitment and population recovery (Graham et al. 2011;Holbrook et al. 2018). In many tropical marine locations, disturbances including bleaching, diseases, and severe storms, have depressed coral cover to such an extent that population recovery is generally considered unlikely (Veron et al. 2009;Hooidonk et al. 2014;Hoegh-Guldberg et al. 2018), due mostly to low densities of coral recruits (Graham et al. 2011(Graham et al. , 2015Gilmour et al. 2013). Examples of recovery of coral communities following disturbances (Graham et al. 2011), provide opportunities to study the factors promoting population growth, with which high coral recruitment is often associated (Graham et al. 2011;Nakamura et al. 2022). ...
Understanding population dynamics is a long-standing objective of ecology, but the need for progress in this area has become urgent. For coral reefs, achieving this objective is impeded by a lack of information on settlement versus post-settlement events in determining recruitment and population size. Declines in coral abundance are often inferred to be associated with reduced densities of recruits, which could arise from mechanisms occurring at larval settlement, or throughout post-settlement stages. This study uses annual measurements from 2008 to 2021 of coral cover, the density of coral settlers (S), the density of small corals (SC), and environmental conditions, to evaluate the roles of settlement versus post-settlement events in determining rates of coral recruitment and changes in coral cover at Moorea, French Polynesia. Coral cover, S, SC, and the SC:S ratio (a proxy for post-settlement success), and environmental conditions, were used in generalized additive models (GAMs) to show that: (a) coral cover was more strongly related to SC and SC:S than S, and (b) SC:S was highest when preceded by cool seawater, low concentrations of Chlorophyll a, and low flow speeds, and S showed evidence of declining with elevated temperature. Together, these results suggest that changes in coral cover in Moorea are more strongly influenced by post-settlement events than settlement. The key to understanding coral community resilience may lie in elucidating the factors attenuating the bottleneck between settlers and small corals.
... Areas not subject to climate-related stress will become increasingly rare in the next century. Contrasting gradients in projected heat stress and acidification suggest that few locations will be true climate refuges maintaining twentieth-century conditions (van Hooidonk et al. 2014). Strategies that manage and mitigate local stressors increase the ability of corals to withstand the consequences of global stressors. ...
Resilience-based management strategies are gaining attention as tools to improve coral survival and recovery under increasingly stressful conditions. Prioritizing locations to implement these strategies depends on knowing where corals already show potential signs of resilience and how environmental conditions may shift with climate change. We synthesized environmental conditions and coral cover trends in Guam and American Samoa using present-day climate conditions and 2 future climate scenarios: Representative Concentration Pathways 4.5 and 8.5. We examined the spatial overlap between favorable and unfavorable environmental conditions and locations where coral reefs have maintained or increased coral cover over the past decade. Locations representing 4 combinations of the aforementioned characteristics may be subject to different management strategies: (1) conservation and restoration of robust corals, (2) restoration of declining corals, (3) conservation of genetic material of robust corals and stressor mitigation, and (4) no clear strategy for declining corals. We estimated areas in which multiple management actions could be performed based on these combinations. Under present-day climate conditions, the conservation of genetic material and stressor mitigation were overrepresented in Guam, comprising 23% of the study area; this declined to 15% in future climate scenarios. Coral restoration was at first underrepresented (0%). In American Samoa, the proportional area for each strategy remained consistent regardless of climate. Coral restoration was overrepresented, comprising 54% to 56% of the study area, whereas the conservation of genetic material and stressor mitigation were underrepresented (9% to 11%, respectively). Our approach offers a rapid way to assess where potential management actions could be applied based on data aggregated over large spatial extents, which can complement more detailed, labor-intensive assessments of reef community dynamics, particularly if distinct coral communities inform the boundaries of aggregation units. These results may guide managers in selecting ecologically suitable locations for implementing resilience-based management strategies for coral reefs.
... Living close to their thermal limit, however, shallow corals are threatened by the global increase in sea surface temperatures (SSTs) and subsequent coral bleaching; current estimates suggest that 70-90% of the reefs will be lost with a 1.5°C rise and 99% if the increase in temperatures reaches 2°C 4,5 . Bleaching events are increasing in their severity, frequency and duration 6,7 , yet our knowledge of the impacts of these events is centred around shallow-water coral reefs. Mesophotic coral ecosystems (MCEs) reside between the depths of 30-150 m and have been estimated to occupy two-thirds of the total depth range of zooxanthellate coral environments 8,9 . ...
As global temperatures continue to rise, shallow coral reef bleaching has become more intense and widespread. Mesophotic coral ecosystems reside in deeper (30–150 m), cooler water and were thought to offer a refuge to shallow-water reefs. Studies now show that mesophotic coral ecosystems instead have limited connectivity with shallow corals but host diverse endemic communities. Given their extensive distribution and high biodiversity, understanding their susceptibility to warming oceans is imperative. In this multidisciplinary study of an atoll in the Chagos Archipelago in the central Indian Ocean, we show evidence of coral bleaching at 90 m, despite the absence of shallow-water bleaching. We also show that the bleaching was associated with sustained thermocline deepening driven by the Indian Ocean Dipole, which might be further enhanced by internal waves whose influence varied at a sub-atoll scale. Our results demonstrate the potential vulnerability of mesophotic coral ecosystems to thermal stress and highlight the need for oceanographic knowledge to predict bleaching susceptibility and heterogeneity.
... Aldabra reefs showed high recovery, with the lagoon having the highest resilience (Koester et al. 2020). There is a predicted and expected increase in future bleaching events (Van Hooidonk et al. 2014). The predicted intervals in between these bleaching events may become too short for even Aldabra's reef to recover (Koester et al. 2020), which will have an effect on sea turtle habitats and food item availability. ...
Changes in marine ecosystems from human stressors, and concerns over how species will respond to these changes have emphasized the importance of understanding and monitoring crucial demographic parameters for population models. Long-lived, migratory, marine vertebrates such as sea turtles are particularly vulnerable to changes. Life-history parameters like growth-in-body size can be largely influenced by environmental processes which can impact population growth. We analyzed a 40-year (1981–2021) capture-mark-recapture dataset from the protected UNESCO World Heritage Site, Aldabra Atoll, Seychelles, to estimate key population parameters, including body growth, for immature green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata). Curved carapace length (CCL) range was 34.3–110.9 cm (mean ± SD: 51.0 ± 11.4 cm, n = 1191) for green turtles and 28.7–89.4 cm (47.7 ± 14.4 cm, n = 538) for hawksbill turtles. Recapture events, with an 11-month minimum period, revealed a mean annual growth rate of 3.2 ± 1.5 cm year⁻¹ for green turtles (n = 75) and 2.8 ± 1.4 cm year⁻¹ for hawksbill turtles (n = 110). Hawksbill turtles exhibited a non-monotonic growth rate while no significant growth-size relationship was detected for green turtles. Green turtle mean annual growth per 10-cm size class was highest in the larger size classes (50‒69.9 cm). Hawksbill turtle growth rate was highest in the larger size classes (50‒69.9 cm) then declined in the largest size class (70‒79.9 cm). Green turtles and hawksbill turtles may spend > 8 and 18 years, respectively, using Aldabra, Seychelles, as a foraging ground.
... This rise in ocean temperature will probably force coral to colonize higher latitudes that currently lack reefs [198][199][200]. However, various factors, including the need for a suitable substrate [201], connectivity to other reefs [202], ocean acidification [203], and light intensity [204], may outweigh the advantages of reefs as they expand to high latitudes [193]. ...
Simple Summary
Coral reefs are vital ecosystems with high biodiversity and ecological services for coastal communities. Climate change is accelerating, with detrimental consequences on coral reefs and related communities, but it is challenging to keep up with the literature given its current rapid expansion. The current review foresees three future trends in the area of coral reefs and climate change, including (i) incorporating future scenarios, (ii) climate-induced temperature changes, and (iii) adaptation strategies, which are expected to move society closer to the following Sustainable Development Goal: 13 Climate Action.
Abstract
In this scientometric review, we employ the Web of Science Core Collection to assess current publications and research trends regarding coral reefs in relation to climate change. Thirty-seven keywords for climate change and seven keywords for coral reefs were used in the analysis of 7743 articles on coral reefs and climate change. The field entered an accelerated uptrend phase in 2016, and it is anticipated that this phase will last for the next 5 to 10 years of research publication and citation. The United States and Australia have produced the greatest number of publications in this field. A cluster (i.e., focused issue) analysis showed that coral bleaching dominated the literature from 2000 to 2010, ocean acidification from 2010 to 2020, and sea-level rise, as well as the central Red Sea (Africa/Asia), in 2021. Three different types of keywords appear in the analysis based on which are the (i) most recent (2021), (ii) most influential (highly cited), and (iii) mostly used (frequently used keywords in the article) in the field. The Great Barrier Reef, which is found in the waters of Australia, is thought to be the subject of current coral reef and climate change research. Interestingly, climate-induced temperature changes in “ocean warming” and “sea surface temperature” are the most recent significant and dominant keywords in the coral reef and climate change area.
... As the ASB is highly sensitive to the Maximum of the Monthly Mean (MMM) and the emission scenario used, the year of onset of ASB should be used with care, although spatial patterns are reliable and arguably more useful when trying to find out what areas should be prioritized in terms of management. For example, eight DHWs is higher than the mean optimum bleaching predictor of 6.1 DHWs for the globe [84]; i.e., at 8 DHWs there is a greater degree of confidence that thermal stress will be sufficient for bleaching to occur [85]. ...
Coral reefs face an uncertain future under global climate change, with thermal-induced bleaching increasing in frequency such that corals will soon experience annual severe bleaching (ASB). Marine Protected Areas (MPAs) are therefore becoming increasingly important as a conservation tool. Here we evaluate (i) Indonesia’s coral reefs’ spatial variation in ASB, (ii) whether reefs projected to have a later onset of ASB (i.e. possible climate refugia) are protected within MPAs, and (iii) the ASB risk profiles for reefs related to MPAs receiving priority investments. Our results highlight considerable variability across Indonesia’s reefs being at risk of ASB. The ASB risk before 2028 is greater for coral reefs protected by MPAs versus those outside MPA boundaries. The ASB risk before 2025 is greater for coral reefs protected by priority MPAs versus those protected by non-priority MPAs. Overall, our results show that only ∼45% of the coral reef areas that are currently located within MPAs will likely act as thermal refugia (ASB > 2044). This is unsurprising given that the MPA network in Indonesia has been established over many decades, with most MPAs designated before suitable bleaching risk projections were available to inform MPA placement. Our results highlight the scope to further incorporate potential climate refugia for reefs into new MPA designations. This study also provides strategic information, which can support the development of Indonesia’s long-term MPA and coral reef conservation strategy to effectively manage, mitigate, and adapt to the impacts of climate change on coral reefs.
... However, coral reefs are presumed to be the most threatened by ocean acidification (Hoegh-Guldberg et al. 2007; Kleypas and Yates 2009;Fabricius et al. 2011;IPCC 2014;van Hooidonk et al. 2014). And, it is widely accepted that the reduction in ocean pH will have negative effects on benthic organisms, mainly through physiological and/or metabolic disturbances that can affect their growth and survival (Byrne et al. 2010;Findlay et al. 2010;Anthony et al. 2011;Dissanayake et al. 2011;Wood et al. 2011). ...
A mesocosm experiment was designed to study the effects of acidification on the phytal nematofauna of a coral reef. We hypothesized that phytal nematodes are responsive to different seawater acidification levels and that their assemblage structure and functional indicators (combination of maturity index and trophic diversity index) are useful to evaluate the effects of acidification. Artificial substrate units (ASU) were first colonized in a coral reef zone (Recife de Fora Municipal Marine Park, Porto Seguro, Bahia, Brazil) to obtain standardized assemblage samples. ASUs were transferred to laboratory and exposed to control and three levels of seawater acidification (pH reduced by 0.3, 0.6 and 0.9 units below field levels) and collected after 15 and 30 d. Contrary to our expectations that acidification may change the taxonomic structure of nematodes, while the functional structure may deviate from the expected under high levels of acidification, we found that univariate functional indicators of the community (index of trophic diversity and maturity index) did not show significant differences between the control and experimental treatments throughout the exposure period. It is probably because the frequent exposure of shallow-water nematodes to rather large environmental variations leads the faunal response to acidification to be complex and subtle. On the other hand, the density of the life-history strategy groups 3 and 4 and the structure of nematode assemblages were significantly affected by different pH levels throughout the exposure period. Both history strategy groups include all kinds of feeding groups. These results suggest that the impact of pH changes predicted by the years 2100 and 2300 may be strong enough to provide different traits or life-history strategies of nematodes to take advantage under changing conditions.
... Ocean acidification lowers coral growth rates and impairs recovery following disturbance ( Van Hooidonk et al. 2014). Conversely, increased CO 2 may benefit adjacent seagrass beds and mangrove forests areas by enhancing photosynthesis and productivity (Unsworth et al. 2012;Wang et al. 2015). ...
Good governance is one of the principles to ensure the effectiveness of Marine Protected Areas (MPA) management. Governance refers to the formal and informal structures and processes, agencies, and institutions, technical expertise, and traditions that shape management. This could refer to the national and local legislative and regulatory frameworks, the roles and responsibilities of different agencies and individuals, and the processes and relationships through which these are carried out. Management on the other hand, comprises the different tools available to the management authority. This chapter discusses the formal governance – which is governance by government – of MPAs in Indonesia in term of institutional framework and the current challenges. Global MPA governance will be provided as a sharing experience.
... Ocean acidification lowers coral growth rates and impairs recovery following disturbance ( Van Hooidonk et al. 2014). Conversely, increased CO 2 may benefit adjacent seagrass beds and mangrove forests areas by enhancing photosynthesis and productivity (Unsworth et al. 2012;Wang et al. 2015). ...
Good governance is a key indicator for effective management of Marine Protected Areas (MPAs). Community involvement is an integral part of this governance. Community involvement is important to ensure that people’s inclusive rights in the sustainable use of marine resources can be fulfilled, that knowledge and practices of community-based management (customary and modern society) are recognized and accommodated in MPA management plans. This chapter provides an introduction to the principles of governance and how they are applied within the formal Indonesian MPA context. This
includes literature review and case studies on how communities are involved in MPA governance, and the importance of community ownership and appropriateness to the local context. The final section of this chapter highlights opportunities for an increased role that communities can play in the governance of MPAs in Indonesia. With a rich and diverse history of local and customary wisdom for managing marine resources, there are opportunities to revitalize and transform customary institutions to co-manage effective and inclusive MPAs to achieve positive conservation and socio-economic outcomes.
... The consequences of bleaching can be affected by local stressors, with turbidity, wave exposure, macroalgae cover, and urchin abundance all significantly affecting changes in coral cover in the year after heat-induced bleaching (Donovan et al., 2021). The frequency of coral bleaching has increased in recent years, with annual bleaching events predicted by 2055 and periods of annual bleaching already occurring on some reefs (Van Hooidonk et al., 2014;Hughes et al., 2017;Slattery et al., 2019). Bleaching susceptibility differs between cnidarian groups (anemone, octocoral, stony coral, etc.) and between stony coral species, where growth forms and even size classes within species are reported to have differential bleaching susceptibilities (Loya et al., 2001;Brandt, 2009;Fabricius et al., 2011;Grottoli et al., 2014). ...
Coral reefs are amongst the most biodiverse ecosystems on earth, and while stony corals create the foundational complexity of these ecosystems, octocorals and anemones contribute significantly to their biodiversity and function. Like stony corals, many octocorals contain Symbiodiniaceae endosymbionts and can bleach when temperatures exceed the species’ upper thermal limit. Here, we report octocoral bleaching susceptibility and resistance within the subtropical Lord Howe Island coral reef ecosystem during and after marine heatwaves in 2019. Octocoral and anemone surveys were conducted at multiple reef locations within the Lord Howe Island lagoon during, immediately after, and 7 months after the heatwaves. One octocoral species, Cladiella sp. 1, experienced bleaching and mortality, with some bleached colonies detaching from the reef structure during the heatwave (presumed dead). Those that remained attached to the benthos survived the event and recovered endosymbionts within 7 months of bleaching. Cladiella sp. 1 Symbiodiniaceae density (in cells per µg protein), chlorophyll a and c 2 per µg protein, and photosynthetic efficiency were significantly lower in bleached colonies compared to unbleached colonies, while chlorophyll a and c 2 per symbiont were higher. Interestingly, no other symbiotic octocoral species of the Lord Howe Island lagoonal reef bleached. Unbleached Xenia cf crassa colonies had higher Symbiodiniaceae and chlorophyll densities during the marine heatwave compared to other monitoring intervals, while Cladiella sp. 2 densities did not change substantially through time. Previous work on octocoral bleaching has focused primarily on gorgonian octocorals, while this study provides insight into bleaching variability in other octocoral groups. The study also provides further evidence that octocorals may be generally more resistant to bleaching than stony corals in many, but not all, reef ecosystems. Responses to marine heating events vary and should be assessed on a species by species basis.
... Species richness anomalies in a diverse array of clades have been found to occur along altitudinal, ecological, and latitudinal gradients, as well as across distribution disjunctions (Kerkhoff et al., 2014;Rahbek, 1995;Rex et al., 2000;Van Hooidonk et al., 2014;Willig & Lyons, 1998). One of the most well-known species richness anomalies is seen in disjunctly distributed genera between eastern Asia (EA) and eastern North America (ENA). ...
Aim
While the floras of eastern Asia (EA) and eastern North America (ENA) share numerous genera, they have drastically different species richness. Despite an overall similarity in the quality of their temperate climates, the climate of EA is more spatially heterogeneous than that of ENA. Spatial environmental heterogeneity has been found to play a key role in influencing species richness in some regions. Here, we tested the following hypotheses: (a) EA species will occupy larger climatic niches than their ENA congeners, (b) congeners of EA‐ENA disjunct genera will occupy statistically equivalent climatic niches, and (c) congeners of EA‐ENA disjunct genera will occupy more similar climatic niches than expected by their respective physiographic context.
Location
North America and Asia.
Time period
Present.
Major taxa studied
Seed plants.
Methods
Predictions generated by ecological niche models (ENMs) were compared for 88 species across 31 EA‐ENA disjunct genera. ENM predictions were assessed for geographic and ecological breadth. Tests for niche equivalency and similarity were performed for congeneric species pairs to determine if species of disjunct genera have experienced niche conservatism or divergence.
Results
EA species tend to occupy greater amounts of climatic niche space than their close relatives in ENA. Over two‐thirds of the conducted niche comparisons show that EA‐ENA congeners either occupy equivalent climatic niche space within these broader climatic regimes or occupy non‐equivalent niches that are as similar as expected given their physiographic contexts.
Main conclusions
EA species tend to occupy larger climatic niches, and congeners of EA‐ENA disjunct genera tend to occupy equivalent/similar niche space within their respective distributions, with differences in occupied niches possibly due to their respective physiographic contexts, highlighting how niche‐neutral processes and niche conservatism may affect the distributions of disjunct species.
... Ocean acidification lowers coral growth rates and impairs recovery following disturbance ( Van Hooidonk et al. 2014). Conversely, increased CO 2 may benefit adjacent seagrass beds and mangrove forests areas by enhancing photosynthesis and productivity (Unsworth et al. 2012;Wang et al. 2015). ...
Marine Protected Areas Management in Indonesia: Status and Challenges report is a part of the MPA Vision framework for 2030, initiated by MMAF (The Ministry of Marine Affairs and Fisheries of Indonesia) along with a consortium of NGOs (WWF-Indonesia, CTC, WCS-IP, YKAN, CII, RARE). It is intended to review the status and trends of marine protected areas in Indonesia. The document uses a knowledge based approach in describing the condition of marine protected areas in Indonesia, with four main topics, namely: (1) marine protected areas Governance in Indonesia; (2) marine protected areas Implementation in Indonesia – Progress Towards National and Global Targets; (3) Balancing Biodiversity Conservation and Sustainable Use in marine protected areas; and (4) Building the marine protected areas Network – New Threats and Approaches to Improve marine protected areas Outcomes.
... This increase in ocean temperature will also likely open higher latitudes for coral colonization, which presently do not have reefs (Greenstein & Pandolfi, 2008;Precht & Aronson, 2004;Yamano et al., 2011). However, any potential benefits that reefs may have expanding to high latitudes may be offset by ocean acidification (van Hooidonk et al., 2014). ...
Marine heatwaves can cause coral bleaching and reduce coral cover on reefs, yet few studies have identified “bright spots,” where corals have recently shown a capacity to survive such pressures. We analyzed 7714 worldwide surveys from 1997 to 2018 along with 14 environmental and temperature metrics in a hierarchical Bayesian model to identify conditions that contribute to present‐day coral cover. We also identified locations with significantly higher (i.e., “bright spots”) and lower coral cover (i.e., “dark spots”) than regionally expected. In addition, using 4‐km downscaled data of Representative Concentration Pathways (RCPs) 4.5 and 8.5, we projected coral cover on reefs for the years 2050 and 2100. Coral cover on modern reefs was positively associated with historically high maximum sea‐surface temperatures (SSTs), and negatively associated with high contemporary SSTs, tropical‐cyclone frequencies, and human‐population densities. By 2100, under RCP8.5, we projected relative decreases in coral cover of >40% on most reefs globally but projected less decline on reefs in Indonesia, Malaysia, the central Philippines, New Caledonia, Fiji, and French Polynesia, which should be focal localities for multinational networks of protected areas.
... Prioritising present thermal refugia in management strategies may provide stepping stones for migrating corals to more favourable habitats [65]. However, concomitant ocean acidification is likely to limit the poleward extent of reef-accreting corals due to reductions in aragonite saturation state [74]. In future research, our projections can be used to estimate future thermal stress at high latitudes for corals adapted to tropical baseline temperatures in different locations around the world. ...
Thermal refugia underpin climate-smart management of coral reefs, but whether current thermal refugia will remain so under future warming is uncertain. We use statistical downscaling to provide the highest resolution thermal stress projections (0.01°/1 km, >230,000 reef pixels) currently available for coral reefs and identify future refugia on locally manageable scales. Here, we show that climate change will overwhelm current local-scale refugia, with declines in global thermal refugia from 84% of global coral reef pixels in the present-day climate to 0.2% at 1.5°C, and 0% at 2.0°C of global warming. Local-scale oceanographic features such as upwelling and strong ocean currents only rarely provide future thermal refugia. We confirm that warming of 1.5°C relative to pre-industrial levels will be catastrophic for coral reefs. Focusing management efforts on thermal refugia may only be effective in the short-term. Promoting adaptation to higher temperatures and facilitating migration will instead be needed to secure coral reef survival.
... Moreover, by threatening reef-building corals, HAB also exerts indirect deleterious effects on these marine mammals. Indeed, these corals already suffer from rapid degradation due to ocean acidification and elevated sea surface temperatures, these same effects potentializing the toxicity and the growth of K. brevis [102]. Thus, quantitative proteomics is also studied using the ITRAQ approach and LC-MS/MS analysis on the P. astreoides population with K. brevis treatment. ...
Harmful algal blooms (HAB), and the consequent release of toxic metabolites, can be responsible for seafood poisoning outbreaks. Marine wildlife can accumulate these toxins throughout the food chain, which presents a threat to consumers’ health. Some of these toxins, such as saxitoxin (STX), domoic acid (DA), ciguatoxin (CTX), brevetoxin (BTX), tetrodotoxin (TTX), and β-N-methylamino-L-alanine (BMAA), cause severe neurological symptoms in humans. Considerable information is missing, however, notably the consequences of toxin exposures on changes in gene expression, protein profile, and metabolic pathways. This information could lead to understanding the consequence of marine neurotoxin exposure in aquatic organisms and humans. Nevertheless, recent contributions to the knowledge of neurotoxins arise from OMICS-based research, such as genomics, transcriptomics, proteomics, and metabolomics. This review presents a comprehensive overview of the most recent research and of the available solutions to explore OMICS datasets in order to identify new features in terms of ecotoxicology, food safety, and human health. In addition, future perspectives in OMICS studies are discussed.
Motivation
Timing, duration and severity of marine heatwaves are changing rapidly in response to anthropogenic climate change, thereby increasing the frequency of coral bleaching events. Mass coral bleaching events result from cumulative heat stress, which is commonly quantified through degree heating weeks (DHW). Here we introduce CoralBleachRisk, a daily‐resolution global dataset that characterises sea surface temperatures, heat stress anomalies and the timing, duration and magnitude of severe coral bleaching conditions from the recent past (1985) to the future (2100) under three contrasting Shared Socioeconomic Pathways. Our projections are downscaled to a 0.5° resolution (~50 km), bias‐corrected and validated using remotely sensed data of sea surface temperatures and a global dataset of historical coral bleaching events. An accompanying online software tool allows non‐specialist users to access aggregated metrics of coral bleaching risk and generate time series projections of coral vulnerability for Earth's coral reefs. Our dataset enables regional to global comparisons of future trends in severe coral bleaching risk.
Main Types of Variables Contained
Sea surface temperature (SST), SST anomaly, DHW, annual timing and duration of Bleaching Alerts.
Spatial Location
Global.
Time Period
1985–2100.
Major Taxa and Level of Measurement
Coral communities.
Software Format
Netcdf (.nc).
Coral reefs are facing bleaching threats due to climate change. Previous analyses primarily quantify this risk by assessing the average global menace. However, various local factors amplify the effects of climate change in some regions, making the phenomenon spatially heterogeneous. Thus, this study examines the spatially varying effects of sea surface temperature (SST) on coral bleaching using Geographically Weighted Regression (GWR) to better understand regional variations in coral vulnerability. This machine learning algorithm incorporates geo-localization of observations to capture regionally varying relationships in the data, offering insights into the geographical patterns of the local factors influencing SST effects. The analyses use Coral Check’s 7,941 globally distributed observations of coral health, collected by professional scientists as well as trained and certified citizen scientists. These observations were assembled by marine experts and followed a standardized transect protocol. The research identifies areas most vulnerable to temperature-induced coral bleaching. First, stationary models revealed a statistically significant relationship between SST and coral bleaching, highlighting the critical global impact of temperature on coral reefs. Second, the GWR emphasizes that the most sensitive to temperature-induced bleaching are in Southern Africa and Southeast Asia. Third, this study predicts the implications of this impact using IPCC’s representative concentration pathways of climate change, namely RCP 4.5 and RCP 8.5. The estimates reveal that by 2050 several seas around the equator will experience the highest levels of temperature-led coral bleaching. The findings underscore the need for a differentiated approach under the Paris Agreement on climate change to address coral reef bleaching and identify hotspot regions where targeted assistance is necessary.
Warm-water coral reefs are facing unprecedented human-driven threats to their continued existence as biodiverse functional ecosystems upon which hundreds of millions of people rely. These impacts may drive coral ecosystems past critical thresholds, beyond which the system reorganises, often abruptly and potentially irreversibly; this is what the Intergovernmental Panel on Climate Change (IPCC, 2022) define as a tipping point. Determining tipping point thresholds for coral reef ecosystems requires a robust assessment of multiple stressors and their interactive effects. In this perspective piece, we draw upon the recent global tipping point revision initiative (Lenton et al., 2023a) and a literature search to identify and summarise the diverse range of interacting stressors that need to be considered for determining tipping point thresholds for warm-water coral reef ecosystems. Considering observed and projected stressor impacts, we endorse the global tipping point revision's conclusion of a global mean surface temperature (relative to pre-industrial) tipping point threshold of 1.2 °C (range 1–1.5 °C) and the long-term impacts of atmospheric CO2 concentrations above 350 ppm, while acknowledging that comprehensive assessment of stressors, including ocean warming response dynamics, overshoot, and cascading impacts, have yet to be sufficiently realised. These tipping point thresholds have already been exceeded, and therefore these systems are in an overshoot state and are reliant on policy actions to bring stressor levels back within tipping point limits. A fuller assessment of interacting stressors is likely to further lower the tipping point thresholds in most cases. Uncertainties around tipping points for such crucially important ecosystems underline the imperative of robust assessment and, in the case of knowledge gaps, employing a precautionary principle favouring lower-range tipping point values.
Influential projections of coral reef futures have used Degree Heating Months—a monthly reformulation of the well-validated Degree Heating Weeks index. Here we show that heat stress predictions using the 2 metrics differ substantially, with 33–1,584% additional bleaching predicted under many climate models when using Degree Heating Months. Coral cover projections for 2030–2050 differ by a factor of 2 between the 2 metrics, reducing the credibility of forecasts that use Degree Heating Months as it is currently applied.
Rhodolith beds play a crucial role in enhancing local biodiversity by providing habitat for a wide variety of marine species. Despite ecosystem services provided, these species have been lost due to disturbances associated with ongoing environmental changes. Their calcification and slow growth of these organisms make them more vulnerable to increasing ocean acidification and warming. The predictive modelling is one technique to find the most suitable places to search these habitats by selecting environmental variables that are known to influence the rhodoliths physiology, associated with occurrence and abundance data. The settlement, distribution and abundance of rhodolith beds throughout the world have been associated with environmental factors such as temperature, light, nutrients and currents. To find the most suitable areas on the Brazilian coast, a recent study used these environmental factors together with results of biomass of rhodolith bed and occurrence data. The models available to Brazil indicate 167,379–229,718 km 2 of niche suitability from south to north of Brazilian coast. Despite the large suitable areas of occurrence along the coast, only a few beds are in environmental protection areas, such as Fernando de Noronha, Abrolhos and Santa Catarina and the Vitória-Trindade chain, and most of them are threatened by coastal pollution and oil exploitation. Conservation policies are needed to protect these organisms and respective environments that are responsible for ecological cascades that find in Brazilian coast their planetary largest refuge.
Abstract
Coral reefs are regarded as one of the most diverse, productive as well as sensitive ecosystems existing across the world. Major coral reefs across the Pacific Ocean exhibit a vast variety of species, the majority of which are under threat, largely due to changes in past conducive climatic and oceanic parameters. The present study involves the mapping of coral reefs at select islands of Great Barrier Reefs (Heron Island), Fiji (Namena Island), and Cook Island (Aitutaki Island) using Landsat 7 (ETM+) and Landsat 8 (OLI/ TIRS) satellite data for the years 2002 and 2020. Depth invariant bottom index (DII) is applied for water column correction and identification of bottom type submerged and heterogeneous coral reef classes. Maximum likelihood classifier (supervised classification) is performed to characterize various classes of the coral community. Turbidity values (10.4 – 53 Nephelometric Turbidity unit (NTU)), (4.74–26.1NTU), and (14.56–73.56 NTU) for Heron, Namena, and Aitutaki Islands indicate a pronounced effect of sedimentation due to an increase in Sea level rise and anthropogenic activities. Increasing trend of oceanic parameters viz. SST, PAR, salinity, and sea level rise indicated an adverse impact on coral health and triggered coral bleaching along these Islands especially due to El Niño events in the years 2015–2016. We identified the coral mortality for 18 years of period as 16.1 %, 20.2 % and 11. 2 % in Heron, Namena, and Aitutaki Island respectively. The study provides a holistic impact assessment of various anthropogenic activities and climate change on the health of the coral reef ecosystem.
Bibliográficamente, se identificó que no existe una definición clara y específica del concepto de “estado de conservación” aplicable a los sistemas arrecifales, debido a que los conceptos actuales se guían por múltiples intereses, aunque la definición más utilizada, se deriva de la descripción de la condición actual en relación a la encontrada en un tiempo anterior.
Para comprender el concepto de “estado del sistema”, se evaluaron los conceptos de “salud”, "daño", "deterioro" e “impacto”, encontrando que el concepto de salud es una analogía a la salud en el bienestar humano, por lo que es difícil de caracterizar y cuantificar, sin embargo, los conceptos de daño, impacto y deterioro, muestran connotaciones ecológicas, “daño” como el impacto únicamente negativo en el sistema, “deterioro” como la pérdida total de las características biológicas del sistema, e “impacto” como el efecto positivo o negativo de variables o estresores sobre el sistema. El deterioro y daño se ven reflejados en la cobertura coralina, la cual es indicadora de la biomasa en crecimiento hasta sus propios límites naturales, resultando el parámetro más viable a cuantificar como grado del estado energético del sistema.
Como objetivo principal, en un principio se propuso la elaboración de un índice para cuantificar variables de impacto arrecifal, sin embargo, al profundizar en conceptos relacionados a la temática a resolver, se encontró que era más recomendable considerar un nuevo objetivo, por lo que se propuso el desarrollo de una herramienta denominada “Herramienta de Evaluación Cuantitativa del Estado del Sistema Arrecifal” (HECESA), para esquematizar y cuantificar variables de impacto arrecifal, identificando los posibles impactos positivos y negativos en el sistema y considerando como variable dependiente a la biomasa coralina
Para la evaluación del uso de la herramienta se realizaron muestreos en el arrecife Tuxpan en Veracruz, donde se comprobó la eficiencia y viabilidad de la herramienta al cuantificar exitosamente las variables. La herramienta no predice si el estado del sistema está conservado o no, sino que solamente cuantifica el grado de impacto que puede afectar la acumulación de biomasa coralina. En comparación con métodos tradicionales, la herramienta refleja de manera más eficiente la situación del arrecife, ya que compara el impacto del daño sobre la cobertura viva habitada, mostrando el área realmente impactada. En el caso del arrecife Tuxpan, se concluyó que, al ser un arrecife poco complejo estructuralmente y poco diverso, se trata de un arrecife en proceso de colonización de un ambiente hostil.
Timing, duration, and severity of marine heatwaves are changing rapidly in response to anthropogenic climate change, thereby increasing the frequency of coral bleaching events. Mass coral bleaching events occur because of cumulative heat stress, which is commonly quantified through Degree Heating Weeks (DHW). Here we introduce CoralBleachRisk , a daily-resolution global dataset that characterises sea surface temperatures, heat stress anomalies, and the timing, duration, and magnitude of severe coral bleaching conditions from the recent past (1985) to the future (2100) under three contrasting Shared Socioeconomic Pathways. Our projections are downscaled to a 0.5° resolution (~50km), bias-corrected and validated using remotely sensed data of sea surface temperatures and a global dataset of historical coral bleaching events. An accompanying online software tool allows non-specialist users to access aggregated metrics of coral bleaching risk and generate time series projections of coral vulnerability for Earth’s coral reefs. More broadly, our dataset enables regional to global comparisons of future trends in severe coral bleaching risk and the identification of potential climate refugia for corals.
Humans have relied on oceans since time immemorial and have exploited them for natural resources and recreational activities. With the advancement of technologies, rapid population growth and land-use change, the dependability on marine ecosystems has increased tremendously. Anthropogenic activities are causing increased global temperatures, altered weather conditions, melting glaciers, rising sea levels, acidification etc. The biological processes of marine ecosystems are getting affected indirectly or directly from the molecular level to rock pools to ocean basins, thus impacting overall ecosystem services. Out of various disturbances being caused by humans, global warming has been one of the most threatening factors with other anthropogenic inputs such as nutrient enrichment, sewage and microplastics, thereby causing significant changes in the symbiotic relationship between algae and corals. The coral associations with algae, macroalgae and other groups play a very important role in the functioning of ocean ecosystems and are very sensitive to anthropogenic inputs. The symbiotic association of algae with corals results in enriched biodiversity as well as it maintains the biogeochemistry of oceans and open coastal areas. The review outlines the importance of algal associations towards the maintenance of coral reefs, along with discussing the ecological services offered by them. One of the sections also discusses the impact of anthropogenic activities on the association between corals and algae. Also, the potential adaptive response of corals to the changing climatic conditions, and conservation strategies for the conservation of coral ecosystems to ensure a sustainable environment have also been discussed.
Graphical Abstract
In recent decades, great research efforts have been made to understand how specific anthropogenic drivers impact coastal marine ecosystems and their services. Nevertheless, we still lack a synthesis of the existing knowledge on single and multiple anthropogenic drivers impacts to coastal marine systems, which is necessary to guide future work.
The objective of this paper is to assess the current knowledge on the impacts of anthropogenic drivers and their interactions on coastal marine ecosystem services, with emphasis on abiotic drivers as dissolved nutrients (eutrophication or de‐eutrophication), temperature (warming), pH (acidification) and oxygen (hypoxia). We performed a systematic review of the literature consisting of 164 papers using the PRISMA method (Preferred Reporting Items for Systematic Reviews and Meta‐Analyses). We only include English‐written papers, we exclude non‐English papers to avoid potential errors in representing or interpreting scientific information due to language limitations among the authors.
The results show that coastal marine ecosystem service research has largely focused on single drivers, while multiple driver assessments are less common.
Assessments partially integrate multiple driver complexity, but they do not consider (1) relations and feedbacks between drivers; 2() social processes dynamics; and (3) temporal and spatial scales.
Synthesis and applications. We have reviewed the current scientific knowledge on how human drivers affect coastal marine ecosystem services. We found that understanding the combined effects of different drivers and considering various time and space scales is still a pending issue. Ignoring multiple drivers, their interactions and time and space scales limits our understanding of reality, and results in high levels of uncertainty. This affects policies and actions, as they rely on uncertain information. Thus, incomplete knowledge leads to poor management of coastal ecosystem services. To improve this, we propose research framework to better consider multiple drivers and time and space factors.
Reef-building corals host diverse dinoflagellate algal symbionts (Family Symbiodiniaceae) whose identity can influence host thermotolerance and whose relative abundance can be dynamic. Breakdown in this symbiosis during “bleaching” events can promote changes in symbiont communities in favour of thermotolerant types, particularly in the genus Durusdinium. We employed experimental bleaching to manipulate the symbiont communities of three common Caribbean reef-building species (Montastraea cavernosa, Orbicella faveolata, and Siderastrea siderea) and tested whether seasonal differences in the corals’ symbiont communities at the time of their collection affected their responses to manipulation. In O. faveolata and S. siderea, a minimum threshold of initial background proportion Durusdinium trenchii shaped recovery from bleaching with mainly Durusdinium. In contrast, in M. cavernosa, Durusdinium became highly dominant after recovery even when it was undetectable prior to bleaching. Seasonal changes were also detected in M. cavernosa and S. siderea dominated by Cladocopium, with significant increases and decreases, respectively, in symbionts per host cell in October (following annual temperature maxima) compared to the previous April (following temperature minima). These results demonstrate how background symbionts and seasonal differences in symbiont density can affect the disturbance and recovery dynamics of algal symbiont communities in different coral species, and prompt further research into how seasonal changes in algal symbiosis might inform projected future bleaching, which is increasingly relevant in light of predicted winter warming and prolonged warm summer temperatures under climate change.
Marine heatwaves and regional coral bleaching events have become more frequent and severe across the world's oceans over the last several decades due to global climate change. Observational studies have documented spatiotemporal variation in the responses of reef-building corals to thermal stress within and among taxa across geographic scales. Although many tools exist for predicting, detecting, and quantifying coral bleaching, it remains difficult to compare bleaching severity (e.g., percent cover of bleached surface areas) among studies and across species or regions. For this review, we compiled over 2,100 in situ coral bleaching observations representing 87 reef-building coral genera and 250 species of common morphological groups from a total of 74 peer-reviewed scientific articles, encompassing three broad geographic regions (Atlantic, Indian, and Pacific Oceans). While bleaching severity was found to vary by region, genus, and morphology, we found that both genera and morphologies responded differently to thermal stress across regions. These patterns were complicated by (i) inconsistent methods and response metrics across studies; (ii) differing ecological scales of observations (i.e., individual colony-level vs. population or community-level); and (iii) temporal variability in surveys with respect to the onset of thermal stress and the chronology of bleaching episodes. To improve cross-study comparisons, we recommend that future surveys prioritize measuring bleaching in the same individual coral colonies over time and incorporate the severity and timing of warming into their analyses. By reevaluating and standardizing the ways in which coral bleaching is quantified, researchers will be able to track responses to marine heatwaves with increased rigor, precision, and accuracy.
Ocean acidification is a major threat to marine ecosystems. It is caused by increasing carbon dioxide concentrations in the atmosphere due to anthropogenic emissions and has socio-ecological and socio-economic ramifications for many countries. However, in some critical areas like the Philippines, a known center of marine biodiversity, no legislation currently exists to manage it. This could be due to lack of understanding of the problem, conflicting priorities, or difficulties in implementation common to many developing countries. We consider a possible incremental pathway for the mitigation of ocean acidification impacts on Philippine marine ecosystems using existing laws on marine pollution. This could complement longer term efforts to formalize legislation and institutionalize efforts to address its effects in the country. The approach may possibly be applied in other areas where no specific legislation exists to address crucial environmental problems.
Oceanic thermal anomalies are increasing in both frequency and strength, causing detrimental impacts to coral reef communities. Water temperatures beyond the corals optimum threshold causeing coral bleaching and mass mortality, impacting our global coral reef ecosystems, including marginal high-latitude reefs. Coral bleaching and mortality were observed at the southernmost coral reef, Lord Howe Island Marine Park, during the summer of 2019, coinciding with anomalously high sea surface temperatures across the reef system from January-April. Here we document the extent of coral impacts within the Lord Howe Island lagoonal reef and the recovery from bleaching eight-months later. Significant differences in bleaching prevalence were observed across the lagoonal coral reef, ranging from 16 to 83% across offshore and inshore reef regions and with variable onset timing. Coral mortality of up to 40% was recorded in the reef’s most severely impacted near-shore area. The four most dominant species, Stylophora pistillata, Pocillopora damicornis, Porites spp. and Seriatopora hystrix, were the most susceptible to bleaching, with all coral colonies found either bleached or dead at the most affected inshore site during and following peak heat stress. Interestingly, during the eight-months following bleaching, there was no evidence of bleaching recovery (i.e., re-establishment of symbiosis) at the offshore lagoonal site. However, there was a significant increase in the abundance of healthy coral colonies at the inshore site, suggesting the recovery of the surviving bleached corals at this site. Importantly, we found no evidence for bleaching or mortality in the Acropora spp. and minimal bleaching and no mortality in Isopora cuneata during the study period, typically highly susceptible species. Given the isolation of high-latitude reefs such as Lord Howe Island, our results highlight the importance of understanding the impacts of bleaching, mortality and bleaching recovery on coral population structure and resilience of high-latitude coral reefs.
The Great Barrier Reef (GBR) is predicted to undergo its sixth mass coral bleaching event during the Southern Hemisphere summer of 2021-2022. Coral bleaching-level heat stress over the GBR is forecast to start earlier than any previous year in the satellite record (1985-present). The National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) near real-time satellite-based heat stress products were used to investigate early-summer sea surface temperature (SST) and heat stress conditions on the GBR during late 2021. As of 14 December 2021, values of instantaneous heat stress (Coral Bleaching HotSpots) and accumulated heat stress over a 12-week running window (Degree Heating Weeks) on the GBR were unprecedented in the satellite record. Further, 89% of GBR satellite reef pixels for this date in 2021 had a positive seven-day SST trend of greater than 0.2 degrees Celsius/week. Background temperatures (the minimum temperature over the previous 29 days) were alarmingly high, with 87% of GBR reef pixels on 14 December 2021 being greater than the maximum SST over that same 29-day period for any year from 1985-2020. The GBR is starting the 2021-2022 summer season with more accumulated heat than ever before, which could have disastrous consequences for the health, recovery, and future of this critical reef system.
Climate change, rigorously heralded more than thirty years ago as a real threat, has become the most pressing and pernicious global problem for the entire planet. In conjunction with local impacts such as fishing, eutrophication or the invasion of alien species, to give just a few examples, the acidification of the oceans and the warming of the sea began to show its effects more than twenty years ago. These signals were ignored at the time by the governing bodies and by the economic stakeholders, who now see how we must run to repair the huge inflicted damage. Today, different processes are accelerating, and the thermodynamic machine has definitely deteriorated. We see, for example, that the intensity and magnitude of hurricanes and typhoons has increased. Most models announce more devastation of flash floods and a decomposition in the water cycle, which are factors directly affecting ecosystems all over the world. Important advances are also observed in the forecasting of impacts of atmospheric phenomena in coastal areas with more and more accurate models. Rising temperatures and acidification already affect many organisms, impacting the entire food chain. All organisms, pelagic or benthic, will be affected directly or indirectly by climate change at all depths and in all the latitudes. The impact will be non-homogeneous. In certain areas it will be more drastic than in others, and the visualization of such impacts is already ongoing. Some things may be very evident, such as coral mortalities in tropical areas or in the surface waters of the Mediterranean, while others may be less visible, such as changes in microelement availability affecting plankton productivity. In fact, primary productivity in microalgae, macroalgae and phanerogams is already beginning to feel the impact of warmer, stratified and nutrient-poor waters in many parts of the planet. Nutrients are becoming less available, temperature is rising above certain tolerance limits and water movement (turbulence) may change in certain areas favoring certain species of microplankton instead of others. All these mechanisms, together with light availability (which, in principle, is not drastically changing except for the cloudiness), affect the growth of the organisms that can photosynthesize and produce oxygen and organic matter for the rest of the trophic chain. That shift in productivity completely changes the rest of the food chain. In the Arctic or Antarctic, the problem is slightly different. Life depends on the dynamics of ice that is subject to seasonal changes. But winter solidification and summer dissolution is undergoing profound changes, causing organisms that are adapted to that rhythm of ice change to be under pressure. The change is more evident in the North Pole, but is also visible in the South pole, where the sea ice cover has also dramatically changed. In the chapter there is also a mention about the general problem of the water currents and their profound change do greenhouse gas effects. The warming of the waters and their influence on the marine currents are also already affecting the different ocean habitats. The slowdown of certain processes is causing an acceleration in the deoxygenation of the deepest areas and therefore an impact on the fragile communities of cold corals that populate large areas of our planet. Many organisms will be affected in their dispersion and their ability to colonize new areas or maintain a connection between different populations. The rapid adaptations to these new changes are apparent. Nature is on its course of restart from these new changes, but in this transitional phase the complexity and interactions that have taken thousands or millions of years to form can fade away until a new normal is consolidated.
Changes in marine ecosystems from human stressors, and concerns over how species will respond to these changes have emphasized the importance of understanding and monitoring crucial demographic parameters for population models. Long-lived, migratory, marine vertebrates such as sea turtles are particularly vulnerable to changes. Life-history parameters like growth in body size can be largely influenced by environmental processes which can impact population growth. We analyzed a 40-year (1981–2021) capture-mark-recapture dataset from the protected UNESCO World Heritage Site, Aldabra Atoll, Seychelles, to estimate key population parameters, including body growth, for immature green turtles ( Chelonia mydas ) and hawksbill turtles ( Eretmochelys imbricata ). Curved carapace length (CCL) ranged from 34.3–110.9 cm (mean ± SD: 51.0 ± 11.4 cm, n = 1191) for green turtles and 28.7–89.4 cm (47.7 ± 14.4 cm, n = 538) for hawksbill turtles. Recapture events, with an 11-month minimum period, revealed a mean annual growth rate of 3.2 ± 1.5 cm year-1 for green turtles (n = 75) and 2.8 ± 1.4 cm year-1 for hawksbill turtles (n = 110). Hawksbill turtles exhibited a non-monotonic growth rate while no significant growth-size relationship was detected for green turtles. Green turtle mean annual growth per 10-cm size class was highest in the larger size classes. Hawksbill turtle growth rate was highest in the larger size classes (50‒69.9 cm) then declined in the largest size class (80‒79.9 cm). Per the growth functions, green turtles and hawksbill turtles may spend > 8 and 18 years, respectively, using Aldabra as a foraging ground.
Coral reefs are critically important to the economic development of most tropical countries. However, they have faced multi-stressors from natural and anthropogenic disturbances, particularly from coastal development, tourism, overfishing, and coral bleaching. Consequently, the loss of vulnerable species from coral communities is occurring at an accelerating rate. Many coral species are particularly at risk. Coral reef recovery following severe disturbances depends on several complicated factors, including resistance and tolerance to stresses, recruitment rate, reef connectivity, and local stressors. Maintaining reef framework is also very important, particularly bioerosion rate at a degraded reef. As global climate change potentially causes more frequent and severe coral bleaching events, identifying and conserving coral reef refugia is critically important. Most coral reefs are in a type of marine protected areas that intensively require scientific data for management. The achievements of passive and active coral reef restoration projects in the Western Pacific are necessarily considered for the improvement of coral reef management plans. In this chapter, we synthesize important information on coral reef biodiversity decline and extinction risk; coral reef recovery after disturbances; coral reef resilience; coral reef connectivity; coral reef bioerosion; coral reef refugia under global change; marine protected area networks; and passive and active restoration of degraded coral reefs.KeywordsCoral ecologyBiodiversityExtinction riskRecoveryResilienceConnectivityBioerosionRefugiaClimate changeMarine protected areaRestoration
ABSTRACT FRENCH-Chapitre 1:
Il existe des interactions étroites entre le climat terrestre et le vivant et ceci depuis les origines. En étudiant l’histoire de la vie sur Terre, on comprend que l’atmosphère l’a probablement créée et que le vivant n’a pas cessé de modifier cette atmosphère en réaction aux pressions de sélection issues des grandes transitions qu’a subie la Terre. Le vivant s’est adapté aux perturbations en se stabilisant grâce à la spécialisation et à l’organisation.
FRENCH-BOOK: En plus d’un hymne à la biodiversité marine, cet ouvrage a pour objectif d’aider les décideurs à mieux comprendre le rôle de la planète bleue dans le climat et l’importance de la prendre en considération dans chacune des décisions politiques de ce XXIème siècle.
ENGLISH-Chapter-1: There are close interactions between the Earth's climate and life, and this has been the case since the beginning. By studying the history of life on Earth, we understand that the atmosphere probably created it and that life has not stopped modifying this atmosphere in response to the selection pressures resulting from the major transitions that the Earth has undergone. Life has adapted to perturbations by stabilizing itself through specialization and organization. ENGLISH-BOOK: In addition to being a hymn to marine biodiversity, this book aims to help decision-makers to better understand the role of the blue planet in the climate and the importance of taking it into consideration in each of the political decisions of this 21st century.
The Great Barrier Reef (GBR) is predicted to undergo its sixth mass coral bleaching event during the Southern Hemisphere summer of 2021-2022. Coral bleaching-level heat stress over the GBR is forecast to start earlier than any previous year in the satellite record (1985-present). The National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) near real-time satellite-based heat stress products were used to investigate early-summer sea surface temperature (SST) and heat stress conditions on the GBR during late 2021. As of 14 December 2021, values of instantaneous heat stress (Coral Bleaching HotSpots) and accumulated heat stress over a 12-week running window (Degree Heating Weeks) on the GBR were unprecedented in the satellite record. Further, 89% of GBR satellite reef pixels for this date in 2021 had a positive seven-day SST trend of greater than 0.2 degrees Celsius/week. Background temperatures (the minimum temperature over the previous 29 days) were alarmingly high, with 87% of GBR reef pixels on 14 December 2021 being greater than the maximum SST over that same 29-day period for any year from 1985-2020. The GBR is starting the 2021-2022 summer season with more accumulated heat than ever before, which could have disastrous consequences for the health, recovery, and future of this critical reef system.
Anthropogenic climate change has caused widespread loss of species biodiversity and ecosystem productivity across the globe, particularly on tropical coral reefs. Predicting the future vulnerability of reef‐building corals, the foundation species of coral reef ecosystems, is crucial for cost‐effective conservation planning in the Anthropocene. In this study, we combine regional population genetic connectivity and seascape analyses to explore patterns of genetic offset (the mismatch of gene–environmental associations under future climate conditions) in Acropora digitifera across 12 degrees of latitude in Western Australia. Our data revealed a pattern of restricted gene flow and limited genetic connectivity among geographically distant reef systems. Environmental association analyses identified a suite of loci strongly associated with the regional temperature variation. These loci helped forecast future genetic offset in gradient forest and generalized dissimilarity models. These analyses predicted pronounced differences in the response of different reef systems in Western Australia to rising temperatures. Under the most optimistic future warming scenario (RCP 2.6), we predicted a general pattern of increasing genetic offset with latitude. Under the extreme climate scenario (RCP 8.5 in 2090–2100), coral populations at the Ningaloo World Heritage Area were predicted to experience a higher mismatch between current allele frequencies and those required to cope with local environmental change, compared to populations in the inshore Kimberley region. The study suggests complex and spatially heterogeneous patterns of climate‐change vulnerability in coral populations across Western Australia, reinforcing the notion that regionally tailored conservation efforts will be most effective at managing coral reef resilience into the future.
A review of progress in oceanographic research in the tropics over the past decade is provided. Physical and biogeochemical oceanographic perspectives regarding directions for the next decade are proposed, with a special focus on the El Niño-Southern Oscillation (ENSO) in the tropical Pacific. Although physical understanding of the ENSO has considerably advanced and its dynamical prediction has now become possible, our understanding of mechanisms and ability to predict variations in the material cycles, biological production, and biodiversity associated with the ENSO is still rudimentary. Because effects of internal natural climate variability on the marine system (e.g., ocean warming, acidification, and deoxygenation) have become more serious with global warming, comprehensive understanding and more accurate prediction of the ENSO and its effects on the tropical ocean system are becoming increasingly important. This research will also be key to anticipating changing societal needs as ocean conditions change. In particular, basin-scale studies based on Biogeochemical Argo floats and earth system models, process-oriented studies based on ship/buoy observations and experiment/observation by local research stations, and feedback between the basin-scale studies and the process-oriented studies will be key in the coming decade. The tropical Pacific is an optimal testbed for innovative cross-disciplinary programs that contribute to better understanding and prediction of the ocean system, because its interannual variations associated with the ENSO are highly predictable relative to other oceans.
Using results from four coupled global carbon cycle-climate models combined with in situ observations, we estimate the combined effects of future global warming and ocean acidification on potential habitats for tropical/subtropical and temperate coral communities in the seas around Japan. The suitability of the coral habitats are identified primarily on the basis of the currently observed ranges for temperature and saturation states Ω with regard to aragonite (Ωarag). We find that under the "business as usual" SRES A2 scenario, coral habitats will expand northward by several hundred kilometers by the end of this century. At the same time, coral habitats are projected to become sandwiched between the tropical regions, where the frequency of coral bleaching will increase, and the temperate-to-subpolar latitudes, where Ωarag will become too low to support sufficiently high calcification rates. As a result, the area of coral habitats around Japan that is suitable to tropical-subtropical communities will be reduced by half by the 2020s to 2030s, and is projected to disappear by the 2030s to 2040s. The suitable habitats for the temperate coral communities are also becoming smaller, although at a less pronounced rate due to their higher tolerance for low Ωarag.
Until recently, research into the consequences of oceanic uptake of CO2 for corals focused on its effect on physiological processes, in particular, calcification. However, events early in the life history of corals are also likely to be vulnerable to changes in ocean chemistry caused by increases in the atmospheric concentration of CO2 (ocean acidification). We tested the effect of reduced pH on embryonic development, larval survivorship and metamorphosis of 3 common scleractinian corals from the Great Barrier Reef. We used 4 treatment levels of pH, corresponding to the current level of ocean pH and 3 values projected to occur later this century. None of the early life-history stages we studied were consistently affected by reduced pH. Our results suggest that there will be no direct ecological effects of ocean acidification on the early life-history stages of reef corals, at least in the near future.
The question at once arises, how is it that even the stoutest corals, resting with broad base upon the ground, and doubly secure from their spreading proportions, become so easily a prey to the action of the same sea which they met shortly before with such effectual resistance? The solution of this enigma is to be found in the mode of growth of the corals themselves. Living in communities, death begins first at the base or centre of the group, while the surface or tips still continue to grow, so that it resembles a dying centennial tree, rotten at the heart, but still apparently green and flourishing without, till the first heavy gale of wind snaps the hollow trunk, and betrays its decay. Again, innumerable boring animals establish themselves in the lifeless stem, piercing holes in all directions into its interior, like so many augurs, dissolving its solid connexion with the ground, and even penetrating far into the living portion of these compact communities. --L. Agassiz, 1852 4.1 INTRODUCTION Coral reefs are among the Earth's most biologically diverse ecosystems, and many of the organisms contributing to the high species diversity of reefs normally weaken them and convert massive reef structures to rubble, sand and silt. The various activities of those reef species that cause coral and coralline algal erosion are collectively termed bioerosion, a name coined by Neumann (1966). A bioeroder is any organism that, through its assorted activities, erodes and weakens the calcareous skeletons of reef-building species. Although an extensive terminology has been adopted only during the past three decades, bioerosion has been recognized as an important process in reef development and maturation for more than a century (e.g., Darwin, 1842; Agassiz, 1852). Traces of biologically-induced erosion in ancient reef structures indicate that bioerosion has probably had some effect on reef carbonate budgets since Precambrian and Cambrian times (Vogel, 1993).
Ocean acidification is projected to shift coral
reefs from a state of net accretion to one of net dissolution
this century. Presently, our ability to predict global-scale
changes to coral reef calcification is limited by insufficient
data relating seawater carbonate chemistry parameters to in
situ rates of reef calcification. Here, we investigate diel and
seasonal trends in carbonate chemistry of the Davies Reef
flat in the central Great Barrier Reef and relate these trends
to benthic carbon fluxes by quantifying net ecosystem calcification
(nec) and net community production (ncp). Results
show that seawater carbonate chemistry of the Davies Reef
flat is highly variable over both diel and seasonal cycles.
pH (total scale) ranged from 7.92 to 8.17, pCO2 ranged
from 272 to 542 μatm, and aragonite saturation state (arag)
ranged from 2.9 to 4.1. Diel cycles in carbonate chemistry
were primarily driven by ncp, and warming explained 35%
and 47% of the seasonal shifts in pCO2 and pH, respectively.
Daytime ncp averaged 37±19 mmolCm−2 h−1 in
summer and 33±13 mmolCm−2 h−1 in winter; nighttime
ncp averaged −30±25 and −7±6 mmolCm−2 h−1
in summer and winter, respectively. Daytime nec averaged
11±4 mmol CaCO3 m−2 h−1 in summer and
8±3 mmol CaCO3 m−2 h−1 in winter, whereas nighttime
nec averaged 2±4 mmol and −1±3 mmol CaCO3 m−2 h−1
in summer and winter, respectively. Net ecosystem calcification
was highly sensitive to changes in arag for both
seasons, indicating that relatively small shifts in arag may
drive measurable shifts in calcification rates, and hence
carbon budgets, of coral reefs throughout the year.
Ocean acidification is projected to shift coral reefs from a state of
net accretion to one of net dissolution this century. Presently, our
ability to predict global-scale changes to coral reef calcification is
limited by insufficient data relating seawater carbonate chemistry
parameters to in situ rates of reef calcification. Here, we investigate
natural trends in carbonate chemistry of the Davies Reef flat in the
central Great Barrier Reef on diel and seasonal timescales and relate
these trends to benthic carbon fluxes by quantifying net ecosystem
calcification (nec) and net community production (ncp). Results show
that seawater carbonate chemistry of the Davies Reef flat is highly
variable over both diel and seasonal timescales. pH (total scale) ranged
from 7.92 to 8.17, pCO2 ranged from 272 to 542 μatm, and
aragonite saturation state (Ωarag) ranged from 2.9 to
4.1. Diel cycles in carbonate chemistry were primarily driven by ncp,
and warming explained 35% and 47% of the seasonal shifts in
pCO2 and pH, respectively. Daytime ncp averaged 36 ±
19 mmol C m-2 h-1 in summer and 33 ± 13
mmol C m-2 h-1 in winter; nighttime ncp averaged
-22 ± 20 and -7 ± 6 mmol C m-2 h-1
in summer and winter, respectively. Daytime nec averaged 11 ± 4
mmol CaCO3 m-2 h-1 in summer and 8
± 3 mmol CaCO3 m-2 h-1 in
winter, whereas nighttime nec averaged 2 ± 4 mmol and -1 ±
3 mmol CaCO3 m-2 h-1 in summer and
winter, respectively. Net ecosystem calcification was positively
correlated with Ωarag for both seasons. Linear
correlations of nec and Ωarag indicate that the Davies
Reef flat may transition from a state of net calcification to net
dissolution at Ωarag values of 3.4 in summer and 3.2 in
winter. Diel trends in Ωarag indicate that the reef
flat is currently below this calcification threshold 29.6% of the time
in summer and 14.1% of the time in winter.
We analyse the ability of CMIP3 and CMIP5 coupled ocean–atmosphere general circulation models (CGCMs) to simulate the tropical Pacific mean state and El Niño-Southern Oscillation (ENSO). The CMIP5 multi-model ensemble displays an encouraging 30 % reduction of the pervasive cold bias in the western Pacific, but no quantum leap in ENSO performance compared to CMIP3. CMIP3 and CMIP5 can thus be considered as one large ensemble (CMIP3 + CMIP5) for multi-model ENSO analysis. The too large diversity in CMIP3 ENSO amplitude is however reduced by a factor of two in CMIP5 and the ENSO life cycle (location of surface temperature anomalies, seasonal phase locking) is modestly improved. Other fundamental ENSO characteristics such as central Pacific precipitation anomalies however remain poorly represented. The sea surface temperature (SST)-latent heat flux feedback is slightly improved in the CMIP5 ensemble but the wind-SST feedback is still underestimated by 20–50 % and the shortwave-SST feedbacks remain underestimated by a factor of two. The improvement in ENSO amplitudes might therefore result from error compensations. The ability of CMIP models to simulate the SST-shortwave feedback, a major source of erroneous ENSO in CGCMs, is further detailed. In observations, this feedback is strongly nonlinear because the real atmosphere switches from subsident (positive feedback) to convective (negative feedback) regimes under the effect of seasonal and interannual variations. Only one-third of CMIP3 + CMIP5 models reproduce this regime shift, with the other models remaining locked in one of the two regimes. The modelled shortwave feedback nonlinearity increases with ENSO amplitude and the amplitude of this feedback in the spring strongly relates with the models ability to simulate ENSO phase locking. In a final stage, a subset of metrics is proposed in order to synthesize the ability of each CMIP3 and CMIP5 models to simulate ENSO main characteristics and key atmospheric feedbacks.
The rise in atmospheric CO2 has caused significant decrease in sea surface pH and carbonate ion (CO32-) concentration. This decrease has a negative effect on calcification in hermatypic corals and other calcifying organisms. We report the results of three laboratory experiments designed specifically to separate the effects of the different carbonate chemistry parameters (pH, CO32-, CO2 [aq], total alkalinity [AT], and total inorganic carbon [C T]) on the calcification, photosynthesis, and respiration of the hermatypic coral Acropora eurystoma. The carbonate system was varied to change pH (7.9-8.5), without changing CT; CT was changed keeping the pH constant, and CT was changed keeping the pCO2 constant. In all of these experiments, calcification (both light and dark) was positively correlated with CO32- concentration, suggesting that the corals are not sensitive to pH or CT but to the CO 32- concentration. A decrease of ∼30% in the CO 32- concentration (which is equivalent to a decrease of about 0.2 pH units in seawater) caused a calcification decrease of about 50%. These results suggest that calcification in today's ocean (pCO2 = 370 ppm) is lower by ∼20% compared with preindustrial time (pCO2 = 280 ppm). An additional decrease of ∼35% is expected if atmospheric CO 2 concentration doubles (pCO2 = 560 ppm). In all of these experiments, photosynthesis and respiration did not show any significant response to changes in the carbonate chemistry of seawater. Based on this observation, we propose a mechanism by which the photosynthesis of symbionts is enhanced by coral calcification at high pH when CO2(aq) is low. Overall it seems that photosynthesis and calcification support each other mainly through internal pH regulation, which provides CO32- ions for calcification and CO2(aq) for photosynthesis. © 2006, by the American Society of Limnology and Oceanography, Inc.
The latest carbon dioxide emissions continue to track the high end of
emission scenarios, making it even less likely global warming will stay
below 2 °C. A shift to a 2 °C pathway requires immediate
significant and sustained global mitigation, with a probable reliance on
net negative emissions in the longer term.
We use a coupled climate/carbon-cycle model to examine the consequences of stabilizing atmospheric CO2 at different levels for ocean chemistry. Our simulations show the potential for major damage to at least some ocean ecosystems at atmospheric CO2 stabilization levels as low as 450 ppm. Before the industrial revolution, more than 98% of corals reefs were surrounded by waters that were >3.5 times saturated with respect to their skeleton materials (aragonite). If atmospheric CO2 is stabilized at 450 ppm only 8% of existing coral reefs will be surrounded by water with this saturation level. Also at this CO2 level 7% of the ocean South of 60°S will become undersaturated with respect to aragonite, and parts of the high latitude ocean will experience a decrease in pH by more than 0.2 units. Results presented here provide an independent and additional basis for choosing targets of atmospheric CO2 stabilization levels.
The ability of corals to cope with environmental change, such as increased temperature, relies on the physiological mechanisms of acclimatisation and long-term genetic adaptation. We experimentally examined the bleaching sensitivity exhibited by 2 species of coral, Pocillopora damicornis and Turbinaria reniformis, at 3 locations across a latitudinal gradient of almost 6 degrees on the Great Barrier Reef (GBR), Target bleaching temperature was reached by using a ramping rate of 0.2 degrees C/h. We found that the bleaching sensitivity and recovery of both species differed between corals with clade D symbionts and those with clade C. However, in F damicornis bleaching susceptibility corresponded more strongly with latitude than with zooxanthella type and hence, temperature history, suggesting that local adaptation has occurred. The observed bleaching sensitivity was shown by a decrease in photochemical efficiency (F-v/F-m) in both species of coral. The rate of recovery in T reniformis was highest in explants containing clade D symbionts. The occurrence of clade D in the northern section of the GBR may reflect a long-term response to high sea water temperatures, while the presence of clade D in low abundance in T reniformis at Heralds Prong Reef and Percy Island may be a result of recent bleaching events.
We have analyzed the seasonal variations of global mean surface air temperature (SAT) and surface energy budgets of 17 AR4 models. Considerable differences in the amplitude of seasonal cycle (A) in the global mean SAT in the pre-industrial control simulations among the models have been traced, to a large degree, to differences in their simulated clear-sky downward longwave radiation (LW "«) and latent heat flux (LH). We suggest that water vapor feedback process influence the seasonal changes of SAT through its roles on the seasonal variations of LW "« and LH. This implies that the simulated seasonal change of global mean SAT might contain a clue about the sensitivity of water vapor feedback and the A of in SAT thus provides some constraint on climate sensitivity since both are subject to the same feedback process.
The concentration of CO2 in the atmosphere is projected to reach twice the preindustrial level by the middle of the 21st century. This increase will reduce the concentration of CO32- of the surface ocean by 30% relative to the preindustrial level and will reduce the calcium carbonate saturation state of the surface ocean by an equal percentage. Using the large 2650 m3 coral reef mesocosm at the BIOSPHERE-2 facility near Tucson, Arizona, we investigated the effect of the projected changes in seawater carbonate chemistry on the calcification of coral reef organisms at the community scale. Our experimental design was to obtain a long (3.8 years) time series of the net calcification of the complete system and all relevant physical and chemical variables (temperature, salinity, light, nutrients, Ca2+,pCO2,TCO2, and total alkalinity). Periodic additions of NaHCO3, Na2CO3, and/or CaCl2 were made to change the calcium carbonate saturation state of the water. We found that there were consistent and reproducible changes in the rate of calcification in response to our manipulations of the saturation state. We show that the net community calcification rate responds to manipulations in the concentrations of both Ca2+ and CO32- and that the rate is well described as a linear function of the ion concentration product, [Ca2+]0.69[CO32-]. This suggests that saturation state or a closely related quantity is a primary environmental factor that influences calcification on coral reefs at the ecosystem level. We compare the sensitivity of calcification to short-term (days) and long-term (months to years) changes in saturation state and found that the response was not significantly different. This indicates that coral reef organisms do not seem to be able to acclimate to changing saturation state. The predicted decrease in coral reef calcification between the years 1880 and 2065 A.D. based on our long-term results is 40%. Previous small-scale, short-term organismal studies predicted a calcification reduction of 14-30%. This much longer, community-scale study suggests that the impact on coral reefs may be greater than previously suspected. In the next century coral reefs will be less able to cope with rising sea level and other anthropogenic stresses.
Census-based approaches can provide important measures of the ecological processes controlling reef carbonate production states. Here, we describe a rapid, non-destructive approach to carbonate budget assessments, termed ReefBudget that is census-based and which focuses on quantifying the relative contributions made by different biological carbonate producer/eroder groups to net reef framework carbonate production. The methodology is presently designed only for Caribbean sites, but has potential to be adapted for use in other regions. Rates are calculated using data on organism cover and abundance, combined with annual extension or production rate measures. Set against this are estimates of the rates at which bioeroding species of fish, urchins and internal substrate borers erode reef framework. Resultant data provide a measure of net rates of biologically driven carbonate production (kg CaCO3 m(-2) year(-1)). These data have potential to be integrated into ecological assessments of reef state, to aid monitoring of temporal (same-site) changes in rates of biological carbonate production and to provide insights into the key ecological drivers of reef growth or erosion as a function of environmental change. Individual aspects of the budget methodology can also be used alongside other census approaches if deemed appropriate for specific study aims. Furthermore, the methodology spreadsheets are user-changeable, allowing local or new process/rate data to be integrated into calculations. Application of the methodology is considered at sites around Bonaire. Highest net rates of carbonate production, +9.52 to +2.30 kg CaCO3 m(-2) year(-1), were calculated at leeward sites, whilst lower rates, +0.98 to -0.98 kg CaCO3 m(-2) year(-1), were calculated at windward sites. Data are within the ranges calculated in previous budget studies and provide confidence in the production estimates the methodology generates.
Climate-change impacts on coral reefs are expected to include
temperature-induced spatially extensive bleaching events. Bleaching
causes mortality when temperature stress persists but exposure to
bleaching conditions is not expected to be spatially uniform at the
regional or global scale. Here we show the first maps of global
projections of bleaching conditions based on ensembles of IPCC AR5 (ref.
) models forced with the new Representative Concentration Pathways
(RCPs). For the three RCPs with larger CO2 emissions (RCP
4.5, 6.0 and 8.5) the onset of annual bleaching conditions is associated
with ~ 510ppm CO2 equivalent; the median year of all
locations is 2040 for the fossil-fuel aggressive RCP 8.5. Spatial
patterns in the onset of annual bleaching conditions are similar for
each of the RCPs. For RCP 8.5, 26% of reef cells are projected to
experience annual bleaching conditions more than 5 years later than the
median. Some of these temporary refugia include the western Indian
Ocean, Thailand, the southern Great Barrier Reef and central French
Polynesia. A reduction in the growth of greenhouse-gas emissions
corresponding to the difference between RCP 8.5 and 6.0 delays annual
bleaching in ~ 23% of reef cells more than two decades, which might
conceivably increase the potential for these reefs to cope with these
changes.
Global-scale deteriorations in coral reef health have caused major shifts in species composition. One projected consequence is a lowering of reef carbonate production rates, potentially impairing reef growth, compromising ecosystem functionality and ultimately leading to net reef erosion. Here, using measures of gross and net carbonate production and erosion from 19 Caribbean reefs, we show that contemporary carbonate production rates are now substantially below historical (mid- to late-Holocene) values. On average, current production rates are reduced by at least 50%, and 37% of surveyed sites were net erosional. Calculated accretion rates (mm year(-1)) for shallow fore-reef habitats are also close to an order of magnitude lower than Holocene averages. A live coral cover threshold of ~10% appears critical to maintaining positive production states. Below this ecological threshold carbonate budgets typically become net negative and threaten reef accretion. Collectively, these data suggest that recent ecological declines are now suppressing Caribbean reef growth potential.
Using results from four coupled global carbon cycle-climate models combined with in situ observations, we estimate the effects of future global warming and ocean acidification on potential habitats for tropical/subtropical and temperate coral communities in the seas around Japan. The suitability of coral habitats is classified on the basis of the currently observed regional ranges for temperature and saturation states with regard to aragonite (Ωarag). We find that, under the "business as usual" SRES A2 scenario, coral habitats are projected to expand northward by several hundred kilometers by the end of this century. At the same time, coral habitats are projected to become sandwiched between regions where the frequency of coral bleaching will increase, and regions where Ωarag will become too low to support sufficiently high calcification rates. As a result, the habitat suitable for tropical/subtropical corals around Japan may be reduced by half by the 2020s to 2030s, and is projected to disappear by the 2030s to 2040s. The habitat suitable for the temperate coral communities is also projected to decrease, although at a less pronounced rate, due to the higher tolerance of temperate corals for low Ωarag. Our study has two important caveats: first, it does not consider the potential adaptation of the coral communities, which would permit them to colonize habitats that are outside their current range. Second, it also does not consider whether or not coral communities can migrate quickly enough to actually occupy newly emerging habitats. As such, our results serve as a baseline for the assessment of the future evolution of coral habitats, but the consideration of important biological and ecological factors and feedbacks will be required to make more accurate projections.
The El Niño–Southern Oscillation (ENSO) is a naturally occurring fluctuation that originates in the tropical Pacific region and affects ecosystems, agriculture, freshwater supplies, hurricanes and other severe weather events worldwide. Under the influence of global warming, the mean climate of the Pacific region will probably undergo significant changes. The tropical easterly trade winds are expected to weaken; surface ocean temperatures are expected to warm fastest near the equator and more slowly farther away; the equatorial thermocline that marks the transition between the wind-mixed upper ocean and deeper layers is expected to shoal; and the temperature gradients across the thermocline are expected to become steeper. Year-to-year ENSO variability is controlled by a delicate balance of amplifying and damping feedbacks, and one or more of the physical processes that are responsible for determining the characteristics of ENSO will probably be modified by climate change. Therefore, despite considerable progress in our understanding of the impact of climate change on many of the processes that contribute to El Niño variability, it is not yet possible to say whether ENSO activity will be enhanced or damped, or if the frequency of events will change.
Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
A coral reef represents the net accumulation of CaCO3 produced by corals and other calcifying organisms. If calcification declines, then reef-building capacity also declines. Coral reef calcification depends on the saturation state of the carbonate mineral aragonite of surface waters. By the middle of next century, increased CO2 concentration will decrease aragonite saturation state in the tropics by 30%, and biogenic aragonite precipitation by 14–30%. Coral reefs are particularly threatened, since reef-building organisms secrete metastable forms of CaCO3, but the biogeochemical consequences on other calcifying marine ecosystems may be equally severe.
Experiments have shown that ocean acidification due to rising atmospheric carbon dioxide concentrations has deleterious effects on the performance of many marine organisms. However, few empirical or modelling studies have addressed the long-term consequences of ocean acidification for marine ecosystems. Here we show that as pH declines from 8.1 to 7.8 (the change expected if atmospheric carbon dioxide concentrations increase from 390 to 750ppm, consistent with some scenarios for the end of this century) some organisms benefit, but many more lose out. We investigated coral reefs, seagrasses and sediments that are acclimatized to low pH at three cool and shallow volcanic carbon dioxide seeps in Papua New Guinea. At reduced pH, we observed reductions in coral diversity, recruitment and abundances of structurally complex framework builders, and shifts in competitive interactions between taxa. However, coral cover remained constant between pH 8.1 and ~7.8, because massive Porites corals established dominance over structural corals, despite low rates of calcification. Reef development ceased below pH 7.7. Our empirical data from this unique field setting confirm model predictions that ocean acidification, together with temperature stress, will probably lead to severely reduced diversity, structural complexity and resilience of Indo-Pacific coral reefs within this century.
Rapidly rising levels of atmospheric CO2 are not only causing
ocean warming, but also lowering seawater pH hence the carbonate
saturation state of the oceans, on which many marine organisms depend to
calcify their skeletons. Using boron isotope systematics, we show how
scleractinian corals up-regulate pH at their site of calcification such
that internal changes are approximately one-half of those in ambient
seawater. This species-dependent pH-buffering capacity enables
aragonitic corals to raise the saturation state of their calcifying
medium, thereby increasing calcification rates at little additional
energy cost. Using a model of pH regulation combined with abiotic
calcification, we show that the enhanced kinetics of calcification owing
to higher temperatures has the potential to counter the effects of ocean
acidification. Up-regulation of pH, however, is not ubiquitous among
calcifying organisms; those lacking this ability are likely to undergo
severe declines in calcification as CO2 levels increase. The
capacity to up-regulate pH is thus central to the resilience of
calcifiers to ocean acidification, although the fate of zooxanthellate
corals ultimately depends on the ability of both the photosymbionts and
coral host to adapt to rapidly increasing ocean temperatures.
Ocean acidification (OA) is a relatively young yet rapidly developing scientific field. Assessing the potential response(s) of marine organisms to projected near-future OA scenarios has been at the forefront of scientific research, with a focus on ecosystems (e.g., coral reefs) and processes (e.g., calcification) that are deemed particularly vulnerable. Recently, a heightened emphasis has been placed on evaluating early life history stages as these stages are generally perceived to be more sensitive to environmental change. The number of acidification-related studies focused on early life stages has risen dramatically over the last several years. While early life history stages of corals have been understudied compared to other marine invertebrate taxa (e.g., echinoderms, mollusks), numerous studies exist to contribute to our status of knowledge regarding the potential impacts of OA on coral recruitment dynamics. To synthesize this information, the present paper reviews the primary literature on the effects of acidification on sexual reproduction and early stages of corals, incorporating lessons learned from more thoroughly studied taxa to both assess our current understanding of the potential impacts of OA on coral recruitment and to inform and guide future research in this area.
Ocean warming and acidification from increasing levels of atmospheric CO2 represent major global threats to coral reefs, and are in many regions exacerbated by local-scale disturbances such as overfishing and nutrient enrichment. Our understanding of global threats and local-scale disturbances on reefs is growing, but their relative contribution to reef resilience and vulnerability in the future is unclear. Here, we analyse quantitatively how different combinations of CO2 and fishing pressure on herbivores will affect the ecological resilience of a simplified benthic reef community, as defined by its capacity to maintain and recover to coral-dominated states. We use a dynamic community model integrated with the growth and mortality responses for branching corals (Acropora) and fleshy macroalgae (Lobophora). We operationalize the resilience framework by parameterizing the response function for coral growth (calcification) by ocean acidification and warming, coral bleaching and mortality by warming, macroalgal mortality by herbivore grazing and macroalgal growth via nutrient loading. The model was run for changes in sea surface temperature and water chemistry predicted by the rise in atmospheric CO2 projected from the IPCC's fossil-fuel intensive A1FI scenario during this century. Results demonstrated that severe acidification and warming alone can lower reef resilience (via impairment of coral growth and increased coral mortality) even under high grazing intensity and low nutrients. Further, the threshold at which herbivore overfishing (reduced grazing) leads to a coral–algal phase shift was lowered by acidification and warming. These analyses support two important conclusions: Firstly, reefs already subjected to herbivore overfishing and nutrification are likely to be more vulnerable to increasing CO2. Secondly, under CO2 regimes above 450–500 ppm, management of local-scale disturbances will become critical to keeping reefs within an Acropora-rich domain.
This paper summarizes the development process and main characteristics of the Representative Concentration Pathways (RCPs), a set of four new scenarios developed for the climate modeling community as a basis for long-term and near-term modeling experiments. The four RCPs together span the range of year 2100 radiative forcing values found in the open literature, i.e. from 2.6 to 8.5 W/m2. The RCPs are the product of an innovative collaboration between integrated assessment modelers, climate modelers, terrestrial ecosystem modelers and emission inventory experts. The resulting product forms a comprehensive data set with high spatial and sectoral resolutions for the period extending to 2100. Land use and emissions of air pollutants and greenhouse gases are reported mostly at a 0.5 x 0.5 degree spatial resolution, with air pollutants also provided per sector (for well-mixed gases, a coarser resolution is used). The underlying integrated assessment model outputs for land use, atmospheric emissions and concentration data were harmonized across models and scenarios to ensure consistency with historical observations while preserving individual scenario trends. For most variables, the RCPs cover a wide range of the existing literature. The RCPs are supplemented with extensions (Extended Concentration Pathways, ECPs), which allow climate modeling experiments through the year 2300. The RCPs are an important development in climate research and provide a potential foundation for further research and assessment, including emissions mitigation and impact analysis.
Elevated ocean temperatures can cause coral bleaching, the loss of colour from reef-building corals because of a breakdown of the symbiosis with the dinoflagellate Symbiodinium. Recent studies have warned that global climate change could increase the frequency of coral bleaching and threaten the long-term viability of coral reefs. These assertions are based on projecting the coarse output from atmosphere–ocean general circulation models (GCMs) to the local conditions around representative coral reefs.
Here, we conduct the first comprehensive global assessment of coral bleaching under climate change by adapting the NOAA Coral Reef Watch bleaching prediction method to the output of a low- and high-climate sensitivity GCM. First, we develop and test algorithms for predicting mass coral bleaching with GCM-resolution sea surface temperatures for thousands of coral reefs, using a global coral reef map and 1985–2002 bleaching prediction data. We then use the algorithms to determine the frequency of coral bleaching and required thermal adaptation by corals and their endosymbionts under two different emissions scenarios.
The results indicate that bleaching could become an annual or biannual event for the vast majority of the world's coral reefs in the next 30–50 years without an increase in thermal tolerance of 0.2–1.0°C per decade. The geographic variability in required thermal adaptation found in each model and emissions scenario suggests that coral reefs in some regions, like Micronesia and western Polynesia, may be particularly vulnerable to climate change. Advances in modelling and monitoring will refine the forecast for individual reefs, but this assessment concludes that the global prognosis is unlikely to change without an accelerated effort to stabilize atmospheric greenhouse gas concentrations.
Water quality and criculation in Florida Bay (a shallow, subtropical estuary in south Florida) are highly dependent upon the
development and evolution of carbonate mud banks distributed throughout the Bay. Predicting the effect of natural and anthropogenic
perturbations on carbonate sedimentation requires an understanding of annual, seasonal, and daily variations in the biogenic
and inorganic processes affecting carbonate sediment precipitation and dissolution. In this study, net calcification rates
were measured over diurnal cycles on 27 d during summer and winter from 1999 to 2003 on mud banks and four representative
substrate types located within basins between mud banks. Substrate types that were measured in basins include seagrass beds
of sparse and intermediate densityThalassia sp., mud bottom, and hard bottom communities. Changes in total alkalinity were used as a proxy for calcification and dissolution.
On 22 d (81%), diurnal variation in rates of net calcification was observed. The highest rates of net carbonate sediment production
(or lowest rates of net dissolution) generally occurred during daylight hours and ranged from 2.900 to −0.410 g CaCO3 m−2d−1. The lowest rates of carbonate sediment production (or net sediment dissolution) occurred at night and ranged from 0.210
to −1.900 g CaCO3 m−2 night−1. During typical diurnal cycles, dissolution during the night consumed an average of 29% of sediment produced during the day
on banks and 68% of sediment produced during the day in basins. Net sediment dissolution also occurred during daylight, but
only when there was total cloud cover, high turbidity, or hypersalinity. Diurnal variation in calcification and dissolution
in surface waters and surface sediments of Florida Bay is linked to cycling of carbon dioxide through photosynthesis and respiration.
Estimation of long-term sediment accumulation rates from diurnal rates of carbonate sediment production measured in this study
indicates an overall average accumulation rate for Florida Bay of 8.7 cm 1000 yr−1 and suggests that sediment dissolution plays a more important role than sediment transport in loss of sediment from Florida
Bay.
Future widespread coral bleaching and subsequent mortality has been projected using sea surface temperature (SST) data derived
from global, coupled ocean–atmosphere general circulation models (GCMs). While these models possess fidelity in reproducing
many aspects of climate, they vary in their ability to correctly capture such parameters as the tropical ocean seasonal cycle
and El Niño Southern Oscillation (ENSO) variability. Such weaknesses most likely reduce the accuracy of predicting coral bleaching,
but little attention has been paid to the important issue of understanding potential errors and biases, the interaction of
these biases with trends, and their propagation in predictions. To analyze the relative importance of various types of model
errors and biases in predicting coral bleaching, various intra- and inter-annual frequency bands of observed SSTs were replaced
with those frequencies from 24 GCMs 20th century simulations included in the Intergovernmental Panel on Climate Change (IPCC)
4th assessment report. Subsequent thermal stress was calculated and predictions of bleaching were made. These predictions
were compared with observations of coral bleaching in the period 1982–2007 to calculate accuracy using an objective measure
of forecast quality, the Peirce skill score (PSS). Major findings are that: (1) predictions are most sensitive to the seasonal
cycle and inter-annual variability in the ENSO 24–60months frequency band and (2) because models tend to understate the seasonal
cycle at reef locations, they systematically underestimate future bleaching. The methodology we describe can be used to improve
the accuracy of bleaching predictions by characterizing the errors and uncertainties involved in the predictions.
KeywordsCoral bleaching–Climate change–Coupled ocean–atmosphere general circulation models
Marginal reef habitats are regarded as regions where coral reefs and coral communities reflect the effects of steady-state or long-term average environmental limitations. We used classifications based on this concept with predicted time-variant conditions of future climate to develop a scenario for the evolution of future marginality. Model results based on a conservative scenario of atmospheric CO2 increase were used to examine changes in sea surface temperature and aragonite saturation state over the Pacific Ocean basin until 2069. Results of the projections indicated that essentially all reef locations are likely to become marginal with respect to aragonite saturation state. Significant areas, including some with the highest biodiversity, are expected to experience high-temperature regimes that may be marginal, and additional areas will enter the borderline high temperature range that have experienced significant ENSO-related bleaching in the recent past. The positive effects of warming in areas that are presently marginal in terms of low temperature were limited. Conditions of the late 21st century do not lie outside the ranges in which present-day marginal reef systems occur. Adaptive and acclimative capabilities of organisms and communities will be critical in determining the future of coral reef ecosystems.
Calcification rates in stony corals are expected to decline significantly in the near future due to ocean acidification. In this study we provide a global estimate of the decline in calcification of coral reefs as a result of increase in sea surface temperature and partial pressure of CO2. This estimate, unlike previously reported estimates, is based on an empirical rate law developed from field observations for gross community calcification as a function of aragonite degree of saturation (Warag), sea surface temperature and live coral cover. Calcification rates were calculated for more than 9,000 reef locations using model values of Warag and sea surface temperature at different levels of atmospheric CO2. The maps we produced show that by the time atmospheric partial pressure of CO2 will reach 560 ppm all coral reefs will cease to grow and start to dissolve.
A coral reef represents the net accumulation of calcium carbonate (CaCO3) produced by corals and other calcifying organisms. If calcification declines, then reef-building capacity also declines. Coral reef calcification depends on the saturation state of the carbonate mineral aragonite of surface waters. By the middle of the next century, an increased concentration of carbon dioxide will decrease the aragonite saturation state in the tropics by 30 percent and biogenic aragonite precipitation by 14 to 30 percent. Coral reefs are particularly threatened, because reef-building organisms secrete metastable forms of CaCO3, but the biogeochemical consequences on other calcifying marine ecosystems may be equally severe.
Over the past 30 years, warm thermal disturbances have become commonplace on coral reefs worldwide. These periods of anomalous sea surface temperature (SST) can lead to coral bleaching, a breakdown of the symbiosis between the host coral and symbiotic dinoflagellates which reside in coral tissue. The onset of bleaching is typically predicted to occur when the SST exceeds a local climatological maximum by 1 degrees C for a month or more. However, recent evidence suggests that the threshold at which bleaching occurs may depend on thermal history. This study uses global SST data sets (HadISST and NOAA AVHRR) and mass coral bleaching reports (from Reefbase) to examine the effect of historical SST variability on the accuracy of bleaching prediction. Two variability-based bleaching prediction methods are developed from global analysis of seasonal and interannual SST variability. The first method employs a local bleaching threshold derived from the historical variability in maximum annual SST to account for spatial variability in past thermal disturbance frequency. The second method uses a different formula to estimate the local climatological maximum to account for the low seasonality of SST in the tropics. The new prediction methods are tested against the common globally fixed threshold method using the observed bleaching reports. The results find that estimating the bleaching threshold from local historical SST variability delivers the highest predictive power, but also a higher rate of Type I errors. The second method has the lowest predictive power globally, though regional analysis suggests that it may be applicable in equatorial regions. The historical data analysis suggests that the bleaching threshold may have appeared to be constant globally because the magnitude of interannual variability in maximum SST is similar for many of the world's coral reef ecosystems. For example, the results show that a SST anomaly of 1 degrees C is equivalent to 1.73-2.94 standard deviations of the maximum monthly SST for two-thirds of the world's coral reefs. Coral reefs in the few regions that experience anomalously high interannual SST variability like the equatorial Pacific could prove critical to understanding how coral communities acclimate or adapt to frequent and/or severe thermal disturbances.
This article identifies ecological goods and services of coral reef ecosystems, with special emphasis on how they are generated. Goods are divided into renewable resources and reef mining. Ecological services are classified into physical structure services, biotic services, biogeochemical services, information services, and social/cultural services. A review of economic valuation studies reveals that only a few of the goods and services of reefs have been captured. We synthesize current understanding of the relationships between ecological services and functional groups of species and biological communities of coral reefs in different regions of the world. The consequences of human impacts on coral reefs are also discussed, including loss of resilience, or buffer capacity. Such loss may impair the capacity for recovery of coral reefs and as a consequence the quality and quantity of their delivery of ecological goods and services. Conserving the capacity of reefs to generate essential services requires that they are managed as components of a larger seascape-landscape of which human activities are seen as integrated parts.
Mass coral bleaching events have become a widespread phenomenon causing
serious concerns with regard to the survival of corals. Triggered by
high ocean temperatures, bleaching events are projected to increase in
frequency and intensity. Here, we provide a comprehensive global study
of coral bleaching in terms of global mean temperature change, based on
an extended set of emissions scenarios and models. We show that
preserving >10% of coral reefs worldwide would require limiting
warming to below 1.5°C (atmosphere-ocean general circulation models
(AOGCMs) range: 1.3-1.8°C) relative to pre-industrial levels. Even
under optimistic assumptions regarding corals' thermal adaptation,
one-third (9-60%, 68% uncertainty range) of the world's coral reefs are
projected to be subject to long-term degradation under the most
optimistic new IPCC emissions scenario, RCP3-PD. Under RCP4.5 this
fraction increases to two-thirds (30-88%, 68% uncertainty range).
Possible effects of ocean acidification reducing thermal tolerance are
assessed within a sensitivity experiment.
The program CO2SYS performs calculations relating parameters of the carbon dioxide (COâ) system in seawater and freshwater. The program uses two of the four measurable parameters of the COâ system [total alkalinity (TA), total inorganic COâ (TCOâ), pH, and either fugacity (fCOâ) or partial pressure of COâ (pCOâ)] to calculate the other two parameters at a set of input conditions (temperature and pressure) and a set of output conditions chosen by the user. It replaces and extends the programs CO2SYSTM.EXE, FCO2TCO2.EXE, PHTCO2.EXE, and CO2BTCH.EXE, which were released in May 1995. It may be run in single-input mode or batch-input mode and has a variety of options for the various constants and parameters used. An on-screen information section is available that includes documentation on various topics relevant to the program. This program may be run on any 80 x 86 computer equipped with the DOS operating system by simply typing CO2SYS at the prompt after loading the executable file CO2SYS.EXE.
Sea temperatures in many tropical regions have increased by almost 1°C over the past 100 years, and are currently increasing at ~1-2°C per century. Coral bleaching occurs when the thermal tolerance of corals and their photosynthetic symbionts (zooxanthellae) is exceeded. Mass coral bleaching has occurred in association with episodes of elevated sea temperatures over the past 20 years and involves the loss of the zooxanthellae following chronic photoinhibition. Mass bleaching has resulted in significant losses of live coral in many parts of the world. This paper considers the biochemical, physiological and ecological perspectives of coral bleaching. It also uses the outputs of four runs from three models of global climate change which simulate changes in sea temperature and hence how the frequency and intensity of bleaching events will change over the next 100 years. The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades. Events as severe as the 1998 event, the worst on record, are likely to become commonplace within 20 years. Most information suggests that the capacity for acclimation by corals has already been exceeded, and that adaptation will be too slow to avert a decline in the quality of the world's reefs. The rapidity of the changes that are predicted indicates a major problem for tropical marine ecosystems and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale.
To date, meta-analyses of effects of acidification have focused on the overall strength of evidence for statistically significant responses; however, to anticipate likely consequences of ocean acidification, quantitative estimates of the magnitude of likely responses are also needed. Herein, we use random effects meta-analysis to produce a systematically integrated measure of the distribution of magnitudes of the response of coral calcification to decreasing ΩArag . We also tested whether methodological and biological factors that have been hypothesized to drive variation in response magnitude explain a significant proportion of the among-study variation. We found that the overall mean response of coral calcification is ~15% per unit decrease in ΩArag over the range 2 < ΩArag < 4. Among-study variation is large (standard deviation of 8% per unit decrease in ΩArag ). Neither differences in carbonate chemistry manipulation method, study duration, irradiance level, nor study species growth rate explained a significant proportion of the among-study variation. However, studies employing buoyant weighting found significantly smaller decreases in calcification per unit ΩArag (~10%), compared with studies using the alkalinity anomaly technique (~25%). These differences may be due to the greater tendency for the former to integrate over light and dark calcification. If the existing body of experimental work is indeed representative of likely responses of corals in nature, our results imply that, under business as usual conditions, declines in coral calcification by end-of-century will be ~22%, on average, or ~15% if only studies integrating light and dark calcification are considered. These values are near the low end of published projections, but support the emerging view that variability due to local environmental conditions and species composition is likely to be substantial.
The apparent dissociation constants of carbonic acid in seawater were determined as functions of temperature (2-35°C) and salinity ( 19-43%) at atmospheric pressure by measurement of K'1 and the product K', K',. At 35sa salinity and 25°C the measured values were pE1 = 6.600 and pK'2 = 9.115; at 35% and 2°C the measured values were pK'1 = 6.177 and pKPz = 9.431.
A weekly 18 spatial resolution optimum interpolation (OI) sea surface temperature (SST) analysis has been produced at the National Oceanic and Atmospheric Administration (NOAA) using both in situ and satellite data from November 1981 to the present. The weekly product has been available since 1993 and is widely used for weather and climate monitoring and forecasting. Errors in the satellite bias correction and the sea ice to SST conversion algorithm are discussed, and then an improved version of the OI analysis is developed. The changes result in a modest reduction in the satellite bias that leaves small global residual biases of roughly 20.038C. The major improvement in the analysis occurs at high latitudes due to the new sea ice algorithm where local differences between the old and new analysis can exceed 18C. Comparisons with other SST products are needed to determine the consistency of the OI. These comparisons show that the differences among products occur on large time- and space scales with monthly rms differences exceeding 0.58C in some regions. These regions are primarily the mid- and high-latitude Southern Oceans and the Arctic where data are sparse, as well as high- gradient areas such as the Gulf Stream and Kuroshio where the gradients cannot be properly resolved on a 18 grid. In addition, globally averaged differences of roughly 0.05 8C occur among the products on decadal scales. These differences primarily arise from the same regions where the rms differences are large. However, smaller unexplained differences also occur in other regions of the midlatitude Northern Hemisphere where in situ data should be adequate.
Large-scale coral bleaching episodes are potentially major disturbances to coral reef systems, yet a definitive picture of
variation in assemblage response and species susceptibilities is still being compiled. Here, we provide a detailed analysis
of the bleaching response of 4160 coral colonies, representing 45 genera and 15 families, from two depths at four sites on
reefs fringing inshore islands on the Great Barrier Reef. Six weeks after the onset of large-scale bleaching in 1998, between
11 and 83% of colonies along replicate transects were affected by bleaching, and mortality was 1 to 16%. There were significant
differences in bleaching response between sites, depths and taxa. Cyphastrea, Turbinaria and Galaxea were relatively unaffected by bleaching, while most acroporids and pocilloporids were highly susceptible. The hydrocorals
(Millepora spp.) were the most susceptible taxa, with 85% mortality. Spatial variation in assemblage response was linked to the taxonomic
composition of reef sites and their bleaching history. We suggest, therefore, that much of the spatial variation in bleaching
response was due to assemblage composition and thermal acclimation.
The published experimental data of Hansson and of Mehrbach et al. have been critically compared after adjustment to a common pH scale based upon total hydrogen ion concentration. No significant systematic differences are found within the overall experimental error of the data. The results have been pooled to yield reliable equations that can be used to estimate for seawater media a salinities from 0 to 40 and at temperatures from 2 to 35°C.
Sea surface temperatures were warmer throughout 1998 at Sesoko Island, Japan, than in the 10 preceding years. Temperatures peaked at 2.8 °C above average, resulting in extensive coral bleaching and subsequent coral mortality. Using random quadrat surveys, we quantitatively documented the coral community structure one year before and one year after the bleaching event. The 1998 bleaching event reduced coral species richness by 61% and reduced coral cover by 85%. Colony morphology affected bleaching vulnerability and subsequent coral mortality. Finely branched corals were most susceptible, while massive and encrusting colonies survived. Most heavily impacted were the branched Acropora and pocilloporid corals, some of which showed local extinction. We suggest two hypotheses whose synergistic effect may partially explain observed mortality patterns (i.e. preferential survival of thick-tissued species, and shape-dependent differences in colony mass-transfer efficiency). A community-structural shift occurred on Okinawan reefs, resulting in an increase in the relative abundance of massive and encrusting coral species.