1. Heron, S.F., C.M. Eakin, F. Douvere, K. Anderson, J.C. Day, E. Geiger, O. Hoegh-Guldberg, R. van Hooidonk, T. Hughes, P. Marshall, and D. Obura. Impacts of climate change on world heritage coral reefs: A first global scientific assessment. UNESCO World Heritage Centre, 12 pp., 2017

    Abstract:

    No abstract.

  2. Maynard, J.A., P.A. Marshall, B. Parker, E. Mcleod, G. Ahmadia, R. van Hooidonk, S. Planes, G.J. Williams, L. Raymundo, R. Beeden, and J. Tamelander. A guide to assessing coral reef resilience for decision support. United Nations Environment Programme, Nairobi, Kenya, 44 pp., 2017

    Abstract:

    No abstract.

  3. Okazaki, R.R., E.K. Towle, R. van Hooidonk, C. Mor, R.N. Winter, A.M. Piggot, R. Cunning, A.C. Baker, J.S. Klaus, P.K. Swart, and C. Langdon. Species-specific responses to climate change and community composition determine future calcification rates of Florida Keys reefs. Global Change Biology, 23(3):1023-1035, doi:10.1111/gcb.13481 2017

    Abstract:

    Anthropogenic climate change compromises reef growth as a result of increasing temperatures and ocean acidification. Scleractinian corals vary in their sensitivity to these variables, suggesting species composition will influence how reef communities respond to future climate change. Because data are lacking for many species, most studies that model future reef growth rely on uniform scleractinian calcification sensitivities to temperature and ocean acidification. To address this knowledge gap, calcification of 12 common and understudied Caribbean coral species was measured for two months under crossed temperatures (27, 30.3°C) and CO2 partial pressures (pCO2) (400, 900, 1300 μatm). Mixed-effects models of calcification for each species were then used to project community-level scleractinian calcification using Florida Keys reef composition data and IPCC AR5 ensemble climate model data. Three of the four most abundant species, Orbicella faveolata, Montastraea cavernosa, and Porites astreoides, had negative calcification responses to both elevated temperature and pCO2. In the business-as-usual CO2 emissions scenario, reefs with high abundances of these species had projected end-of-century declines in scleractinian calcification of >50% relative to present-day rates. Siderastrea siderea, the other most common species, was insensitive to both temperature and pCO2 within the levels tested here. Reefs dominated by this species had the most stable end-of-century growth. Under more optimistic scenarios of reduced CO2 emissions, calcification rates throughout the Florida Keys declined <20% by 2100. Under the most extreme emissions scenario, projected declines were highly variable among reefs, ranging 10–100%. Without considering bleaching, reef growth will likely decline on most reefs, especially where resistant species like S. siderea are not already dominant. This study demonstrates how species composition influences reef community responses to climate change and how reduced CO2 emissions can limit future declines in reef calcification.

  4. van Hooidonk, R., J.A. Maynard, J. Tamelander, J. Gove, G. Ahmadia, L. Raymundo, G. Williams, S. Heron, D. Tracey, B. Parker, and S. Planes. Coral bleaching futures—downscaled projections of bleaching conditions for the world’s coral reefs, implications of climate policy and management responses. United Nations Environment Programme, Nairobi, Kenya, 68 pp., 2017

    Abstract:

    No abstract.

  5. Eisenlord, M.E., M.L. Groner, R.M. Yoshioka, J. Elliott, J. Maynard, S. Fradkin, M. Turner, K. Pyne, N. Rivlin, R. van Hooidonk, and C.D. Harvell. Ochre star mortality during the 2014 wasting disease epizootic: Role of population size structure and temperature. Philosophical Transactions of the Royal Society B, 371(1689):20150212, doi:10.1098/rstb.2015.0212 2016

    Abstract:

    Over 20 species of asteroids were devastated by a sea star wasting disease (SSWD) epizootic, linked to a densovirus, from Mexico to Alaska in 2013 and 2014. For Pisaster ochraceus from the San Juan Islands, South Puget Sound, and Washington outer coast, time-series monitoring showed rapid disease spread, high mortality rates in 2014, and continuing levels of wasting in the survivors in 2015. Peak prevalence of disease at 16 sites ranged to 100%, with an overall mean of 61%. Analysis of longitudinal data showed disease risk was correlated with both size and temperature and resulted in shifts in population size structure; adult populations fell to one quarter of pre-outbreak abundances. In laboratory experiments, time between development of disease signs and death was influenced by temperature in adults but not juveniles, and adult mortality was 18% higher in the 19°C treatment compared to the lower temperature treatments. While larger ochre stars developed disease signs sooner than juveniles, diseased juveniles died more quickly than diseased adults. Unusual 2-3°C warm temperature anomalies were coincident with the summer 2014 mortalities. We suggest these warm waters could have increased the disease progression and mortality rates of SSWD in Washington State.

  6. Heron, S.F., J.A. Maynard, R. van Hooidonk, and C.M. Eakin Warming trends and bleaching stress of the world’s coral reefs, 1985-2012. Nature Scientific Reports, 6:38402, doi:10.1038/srep38402 2016

    Abstract:

    Coral reefs across the world’s oceans are in the midst of the longest bleaching event on record (from 2014 to at least 2016). As many of the world’s reefs are remote, there is limited information on how past thermal conditions have influenced reef composition and current stress responses. Using satellite temperature data for 1985–2012, the analysis we present is the first to quantify, for global reef locations, spatial variations in warming trends, thermal stress events and temperature variability at reef-scale (~4 km). Among over 60,000 reef pixels globally, 97% show positive SST trends during the study period with 60% warming significantly. Annual trends exceeded summertime trends at most locations. This indicates that the period of summer-like temperatures has become longer through the record, with a corresponding shortening of the "winter" reprieve from warm temperatures. The frequency of bleaching-level thermal stress increased three-fold between 1985–91 and 2006–12 – a trend climate model projections suggest will continue. The thermal history data products developed enable needed studies relating thermal history to bleaching resistance and community composition. Such analyses can help identify reefs more resilient to thermal stress.

  7. Keith, S.A., J.A. Maynard, A.J. Edwards, J.R. Guest, A.G. Bauman, R. van Hooidonk, S.F. Heron, M.L. Berumen, J. Bouwmeester, S. Piromvaragorn, C. Rahbek, and A.H. Baird. Coral mass spawning predicted by rapid seasonal rise in ocean temperature. Proceedings of the Royal Society of London B, 283(1830):20160011, doi:10.1098/rspb.2016.0011 2016

    Abstract:

    Coral spawning times have been linked to multiple environmental factors; however, to what extent these factors act as generalized cues across multiple species and large spatial scales is unknown. We used a unique dataset of coral spawning from 34 reefs in the Indian and Pacific Oceans to test if month of spawning and peak spawning month in assemblages of Acropora spp. can be predicted by sea surface temperature (SST), photosynthetically available radiation, wind speed, current speed, rainfall, or sunset time. Contrary to the classic view that high mean SST initiates coral spawning, we found rapid increases in SST to be the best predictor in both cases (month of spawning: R2 = 0.73, peak: R2 = 0.62). Our findings suggest that a rapid increase in SST provides the dominant proximate cue for coral mass spawning over large geographical scales. We hypothesize that coral spawning is ultimately timed to ensure optimal fertilization success.

  8. Maynard, J., R. van Hooidonk, C.D. Harvell, C.M. Eakin, G. Liu, B.L. Willis, G.J. Williams, M. Groner, A. Dobson, S.F. Heron, R. Glenn, K. Reardon, and J.D. Shields. Improving marine disease surveillance through sea temperature monitoring, outlooks, and projections. Philosophical Transactions of the Royal Society B, 371(1689):20150208, doi:10.1098/rstb.2015.0208 2016

    Abstract:

    To forecast marine disease outbreaks as oceans warm requires new environmental surveillance tools. We describe an iterative process for developing these tools that combines research, development, and deployment for suitable systems. The first step is to identify candidate host-pathogen systems. The 24 candidate systems we identified include sponges, corals, oysters, crustaceans, sea stars, fishes, and sea grasses (among others). To illustrate the other steps, we present a case study of epizootic shell disease (ESD) in the American lobster. Increasing prevalence of ESD is a contributing factor to lobster fishery collapse in southern New England (SNE), raising concerns disease prevalence will increase in the northern Gulf of Maine under climate change. The lowest maximum bottom temperature associated with ESD prevalence in SNE is 12°C. Our seasonal outlook for 2015 and long-term projections shows bottom temperatures greater than or equal to 12°C may occur in this and coming years in the coastal bays of Maine. The tools presented will allow managers to target efforts to monitor the effects of ESD on fishery sustainability and will be iteratively refined. The approach and case example highlight that temperature-based surveillance tools can inform research, monitoring, and management of emerging and continuing marine disease threats.

  9. Maynard, J.A., R. Beeden, M. Puotinen, J.E. Johnson, P. Marshall, R. van Hooidonk, S.F. Heron, M. Devlin, E. Lawrey, J. Dryden, N. Ban, D. Wachenfeld, and S. Planes. Great Barrier Reef no-take areas include a range of disturbance regimes. Conservation Letters, 9(3):191-199, doi:10.1111/conl.12198 2016

    Abstract:

    Exposure to disturbance is rarely considered in marine protected area planning. Typically, representing and replicating the habitat types present within protected areas is used to spread the risk of protecting frequently disturbed sites. This was the approach used during the 2004 re-zoning of the Great Barrier Reef Marine Park (GBRMP) via the Representative Areas Program. Over 10 years later, we examine whether the risk was spread by mapping exposure of coral reefs in the GBRMP to four disturbances that cause coral mortality: bleaching, tropical cyclones, crown-of-thorns starfish outbreaks, and freshwater inundation. Our objectives were to: (1) assess whether no-take areas include a range of disturbance regimes; and (2) identify coral reef areas with lower relative exposure. At least 13% and an average of 31% of reef locations in each of 11 exposure classes are included within no-take areas. A greater proportion of low-exposure areas are within no-take areas than high-exposure areas (34.2% vs. 28.3%). The results demonstrate the value of risk spreading when exposure data are not available, while also showing that regularly assessing exposure increases capacity for adaptive, resilience-based reef management.

  10. Pendleton, L., A. Comte, C. Langdon, J.A. Ekstrom, S.R. Cooley, L. Suatoni, M.W. Beck, L.M. Brander, L. Burke, J.E. Cinner, C. Doherty, P.E.T. Edwards, D. Gledhill, L.-Q. Jiang, R.J. van Hooidonk, L. Teh, G.G. Waldbusser, and J. Ritter. Coral reefs and people in a high CO2 world: Where can science make a difference to people? PLoS ONE, 11(11):e0164699, doi:10.1371/journal.pone.0164699 2016

    Abstract:

    Increasing levels of carbon dioxide in the atmosphere put shallow, warm-water coral reef ecosystems, and the people who depend upon them, at risk from two key global environmental stresses: (1) elevated sea surface temperature (that can cause coral bleaching and related mortality); and (2) ocean acidification. These global stressors: cannot be avoided by local management; compound local stressors; and hasten the loss of ecosystem services. Impacts to people will be most grave where (a) human dependence on coral reef ecosystems is high, (b) sea surface temperature reaches critical levels soonest, and (c) ocean acidification levels are most severe. Where these elements align, swift action will be needed to protect people’s lives and livelihoods, but such action must be informed by data and science. Designing policies to offset potential harm to coral reef ecosystems and people requires a better understanding of where CO2-related global environmental stresses could cause the most severe impacts. Mapping indicators have been proposed as a way of combining natural and social science data to identify policy actions even when the needed science is relatively nascent. To identify where people are at risk and where more science is needed, we map indicators of biological, physical, and social science factors to understand how human dependence on coral reef ecosystems will be affected by globally-driven threats to corals expected in a high-CO2 world. Western Mexico, Micronesia, Indonesia, and parts of Australia have high human dependence and will likely face severe combined threats. As a region, southeast Asia is particularly at risk. Many of the countries most dependent upon coral reef ecosystems are places for which we have the least robust data on ocean acidification. These areas require new data and interdisciplinary scientific research to help coral reef-dependent human communities better prepare for a high CO2 world.

  11. van Hooidonk, R., J. Maynard, J. Tamelander, J. Gove, G. Ahmadia, L. Raymundo, G. Williams, S.F. Heron, and S. Planes. Local-scale projections of coral reef futures and implications of the Paris Agreement. Nature Scientific Reports, 6:39666, doi:10.1038/srep39666 2016

    Abstract:

    Increasingly frequent severe coral bleaching is among the greatest threats to coral reefs posed by climate change. Global climate models (GCMs) project great spatial variation in the timing of annual severe bleaching (ASB) conditions, a point at which reefs are certain to change and recovery will be limited. However, previous model-resolution projections (~1° × 1°) are too coarse to inform conservation planning. To meet the need for higher-resolution projections, we generated statistically downscaled projections (4-km resolution) for all coral reefs; these projections reveal high local-scale variation in ASB. Timing of ASB varies >10 years in 71 of the 87 countries and territories with >500 km2 of reef area. Emissions scenario RCP4.5 represents lower emissions mid-century than will eventuate if pledges made following the 2015 Paris Climate Change Conference (COP21) become reality. These pledges do little to provide reefs with more time to adapt and acclimate prior to severe bleaching conditions occurring annually. RCP4.5 adds 11 years to the global average ASB timing when compared to RCP8.5; however, >75% of reefs still experience ASB before 2070 under RCP4.5. Coral reef futures clearly vary greatly among and within countries, indicating the projections warrant consideration in most reef areas during conservation and management planning.

  12. Anthony, K.R.N., P.A. Marshall, A. Abdulla, R. Beeden, C. Bergh, R. Black, C.M. Eakin, E.T. Game, M. Gooch, N.A.J. Graham, A. Green, S.F. Heron, R. van Hooidonk, C. Knowland, S. Mangubhai, N. Marshall, J.A. Maynard, P. McGinnity, E. McLeod, P.J. Mumby, M. Nystrom, D. Obura, J. Oliver, H.P. Possingham, R.L. Pressey, G.P. Rowlands, J. Tamelander, D. Wachenfeld, and S. Wear. Operationalizing resilience for adaptive coral reef management under global environmental change. Global Change Biology, 21(1):48-61, doi:10.1111/gcb.12700 2015

    Abstract:

    Cumulative pressures from global climate and ocean change combined with multiple regional and local-scale stressors pose fundamental challenges to coral reef managers worldwide. Understanding how cumulative stressors affect coral reef vulnerability is critical for successful reef conservation now and in the future. In this review, we present the case that strategically managing for increased ecological resilience (capacity for stress resistance and recovery) can reduce coral reef vulnerability (risk of net decline) up to a point. Specifically, we propose an operational framework for identifying effective management levers to enhance resilience and support management decisions that reduce reef vulnerability. Building on a system understanding of biological and ecological processes that drive resilience of coral reefs in different environmental and socio-economic settings, we present an Adaptive Resilience-Based management (ARBM) framework and suggest a set of guidelines for how and where resilience can be enhanced via management interventions. We argue that press-type stressors (pollution, sedimentation, overfishing, ocean warming and acidification) are key threats to coral reef resilience by affecting processes underpinning resistance and recovery, while pulse-type (acute) stressors (e.g., storms, bleaching events, crown-of-thorns starfish outbreaks) increase the demand for resilience. We apply the framework to a set of example problems for Caribbean and Indo-Pacific reefs. A combined strategy of active risk reduction and resilience support is needed, informed by key management objectives, knowledge of reef ecosystem processes and consideration of environmental and social drivers. As climate change and ocean acidification erode the resilience and increase the vulnerability of coral reefs globally, successful adaptive management of coral reefs will become increasingly difficult. Given limited resources, on-the-ground solutions are likely to focus increasingly on actions that support resilience at finer spatial scales, and that are tightly linked to ecosystem goods and services.

  13. Ekstrom, J.A., L. Suatoni, S.R. Cooley, L.H. Pendleton, G.G. Waldbusser, J.E. Cinner, J. Ritter, C. Langdon, R. van Hooidonk, D. Gledhill, K. Wellman, M.W. Beck, L.M. Brander, D. Rittschof, C. Doherty, P.E.T. Edwards, and R. Portela. Vulnerability and adaptation of US shellfisheries to ocean acidification. Nature Climate Change, 5(3):207-214, doi:10.1038/nclimate2508 2015

    Abstract:

    Ocean acidification is a global, long-term problem whose ultimate solution requires carbon dioxide reduction at a scope and scale that will take decades to accomplish successfully. Until that is achieved, feasible and locally relevant adaptation and mitigation measures are needed. To help to prioritize societal responses to ocean acidification, we present a spatially explicit, multidisciplinary vulnerability analysis of coastal human communities in the United States. We focus our analysis on shelled mollusc harvests, which are likely to be harmed by ocean acidification. Our results highlight US regions most vulnerable to ocean acidification (and why), important knowledge and information gaps, and opportunities to adapt through local actions. The research illustrates the benefits of integrating natural and social sciences to identify actions and other opportunities while policy, stakeholders and scientists are still in relatively early stages of developing research plans and responses to ocean acidification.

  14. Maynard, J., R.J. van Hooidonk, C.M. Eakin, M. Puotinen, M. Garren, G. Williams, S.F. Heron, J. Lamb, E. Weil, B. Willis, and C.D. Harvell. Projections of climate conditions that increase coral disease susceptibility and pathogen abundance and virulence. Nature Climate Change, 5(7):688-694, doi:10.1038/nclimate2625 2015

    Abstract:

    Rising sea temperatures are likely to increase the frequency of disease outbreaks affecting reef-building corals through impacts on coral hosts and pathogens. We present and compare climate model projections of temperature conditions that will increase coral susceptibility to disease, pathogen abundance and pathogen virulence. Both moderate (RCP 4.5) and fossil fuel aggressive (RCP 8.5) emissions scenarios are examined. We also compare projections for the onset of disease-conducive conditions and severe annual coral bleaching, and produce a disease risk summary that combines climate stress with stress caused by local human activities. There is great spatial variation in the projections, both among and within the major ocean basins, in conditions favouring disease development. Our results indicate that disease is as likely to cause coral mortality as bleaching in the coming decades. These projections identify priority locations to reduce stress caused by local human activities and test management interventions to reduce disease impacts.

  15. Maynard, J., S. McKagan, L. Raymundo, S. Johnson, G. Ahmadia, L. Johnston, P. Houk, G. Williams, M. Kendall, S. Heron, R. van Hooidonk, and E. McLeod. Assessing relative resilience potential of coral reefs to inform management in the Commonwealth of the Northern Mariana Islands. NOAA Coral Reef Conservation Program, NOAA Technical Memorandum CRCP-22, 153 pp., 2015

    Abstract: No abstract.

  16. Maynard, J.A., S. McKagan, L. Raymundo, S. Johnson, G.N. Ahmadia, L. Johnston, P. Houk, G.J. Williams, M. Kendall, S.F. Heron, R. van Hooidonk, E. Mcleod, D. Tracey, and S. Planes. Assessing relative resilience potential of coral reefs to inform management. Biological Conservation, 192:109-119, doi:10.1016/j.biocon.2015.09.001 2015

    Abstract: Ecological resilience assessments are an important part of resilience-based management (RBM) and can help prioritize and target management actions. Use of such assessments has been limited due to a lack of clear guidance on the assessment process. This study builds on the latest scientific advances in RBM to provide that guidance from a resilience assessment undertaken in the Commonwealth of the Northern Mariana Islands (CNMI). We assessed spatial variation in ecological resilience potential at 78 forereef sites near the populated islands of the CNMI: Saipan, Tinian/Aguijan, and Rota. The assessments are based on measuring indicators of resilience processes and are combined with information on anthropogenic stress and larval connectivity. We find great spatial variation in relative resilience potential with many high resilience sites near Saipan (5 of 7) and low resilience sites near Rota (7 of 9). Criteria were developed to identify priority sites for six types of management actions (e.g., conservation, land-based sources of pollution reduction, and fishery management and enforcement) and 51 of the 78 sites met at least one of the sets of criteria. The connectivity simulations developed indicate that Tinian and Aguijan are each roughly 10× the larvae source that Rota is and twice as frequent a destination. These results may explain the lower relative resilience potential of Rota reefs and indicates that actions in Saipan and Tinian/Aguijan will be important to maintaining a supply of larvae. The process we describe for undertaking resilience assessments can be tailored for use in coral reef areas globally and applied to other ecosystems.

  17. van Hooidonk, R., J.A. Maynard, Y. Liu, and S.-K. Lee. Downscaled projections of Caribbean coral bleaching that can inform conservation planning. Global Change Biology, 21(9):3389-3401, doi:10.1111/gcb.12901 2015

    Abstract:

    Projections of climate change impacts on coral reefs produced at the coarse resolution (~1°) of Global Climate Models (GCMs) have informed debate but have not helped target local management actions. Here, projections of the onset of annual coral bleaching conditions in the Caribbean under Representative Concentration Pathway (RCP) 8.5 are produced using an ensemble of 33 Coupled Model Intercomparison Project phase-5 models and via dynamical and statistical downscaling. A high-resolution (~11 km) regional ocean model (MOM4.1) is used for the dynamical downscaling. For statistical downscaling, sea surface temperature (SST) means and annual cycles in all the GCMs are replaced with observed data from the ~4-km NOAA Pathfinder SST dataset. Spatial patterns in all three projections are broadly similar; the average year for the onset of annual severe bleaching is 2040–2043 for all projections. However, downscaled projections show many locations where the onset of annual severe bleaching (ASB) varies 10 or more years within a single GCM grid cell. Managers in locations where this applies (e.g., Florida, Turks and Caicos, Puerto Rico, and the Dominican Republic, among others) can identify locations that represent relative albeit temporary refugia. Both downscaled projections are different for the Bahamas compared to the GCM projections. The dynamically downscaled projections suggest an earlier onset of ASB linked to projected changes in regional currents, a feature not resolved in GCMs. This result demonstrates the value of dynamical downscaling for this application and means statistically downscaled projections have to be interpreted with caution. However, aside from west of Andros Island, the projections for the two types of downscaling are mostly aligned; projected onset of ASB is within ±10 years for 72% of the reef locations.

  18. Yates, K.K., C. Turley, B.M. Hopkinson, A.E. Todgham, J.N. Cross, H. Greening, P. Williamson, R. van Hooidonk, D.D. Deheyn, and Z. Johnson. Transdisciplinary science: A path to understanding the interactions among ocean acidification, ecosystems, and society. Oceanography, 28(2):212-225, doi:10.5670/oceanog.2015.43 2015

    Abstract:

    The global nature of ocean acidification (OA) transcends habitats, ecosystems, regions, and science disciplines. The scientific community recognizes that the biggest challenge in improving understanding of how changing OA conditions affect ecosystems, and associated consequences for human society, requires integration of experimental, observational, and modeling approaches from many disciplines over a wide range of temporal and spatial scales. Such transdisciplinary science is the next step in providing relevant, meaningful results and optimal guidance to policymakers and coastal managers. We discuss the challenges associated with integrating ocean acidification science across funding agencies, institutions, disciplines, topical areas, and regions, and the value of unifying science objectives and activities to deliver insights into local, regional, and global scale impacts. We identify guiding principles and strategies for developing transdisciplinary research in the ocean acidification science community.

  19. Enochs, I.C., D.P. Manzello, R. Carlton, S. Schopmeyer, R. van Hooidonk, and D. Lirman. Effects of light and elevated pCO2 on the growth and photochemical efficiency of Acropora cervicornis. Coral Reefs, 33(2):477-485, doi:10.1007/s00338-014-1132-7 2014

    Abstract:

    The effects of light and elevated pCO2 on the growth and photochemical efficiency of the critically endangered staghorn coral, Acropora cervicornis, were examined experimentally. Corals were subjected to high and low treatments of CO2 and light in a fully crossed design and monitored using 3D scanning and buoyant weight methodologies. Calcification rates, linear extension, as well as colony surface area and volume of A. cervicornis were highly dependent on light intensity. At pCO2 levels projected to occur by the end of the century from ocean acidification (OA), A. cervicornis exhibited depressed calcification, but no change in linear extension. Photochemical efficiency (F v/F m) was higher at low light, but unaffected by CO2. Amelioration of OA-depressed calcification under high-light treatments was not observed, and we suggest that the high-light intensity necessary to reach saturation of photosynthesis and calcification in A. cervicornis may limit the effectiveness of this potentially protective mechanism in this species. High CO2 causes depressed skeletal density, but not linear extension, illustrating that the measurement of extension by itself is inadequate to detect CO2 impacts. The skeletal integrity of A. cervicornis will be impaired by OA, which may further reduce the resilience of the already diminished populations of this endangered species.

  20. van Hooidonk, R., J.A. Maynard, D. Manzello, and S. Planes. Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs. Global Change Biology, 20(1):103-112, doi:10.1111/gcb.12394 2014

    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.

  21. van Hooidonk, R., J.A. Maynard, and S. Planes. Temporary refugia for coral reefs in a warming world. Nature Climate Change, 3(5):508-511, doi:10.1038/nclimate1829 2013

    Abstract:

    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 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 ~510 ppm 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.

  22. van Hooidonk, R., and M. Huber. Effects of modeled tropical sea surface temperature variability on coral reef bleaching predictions. Coral Reefs, 31(1):121-131, doi:10.1007/s00338-011-0825-4 2012

    Abstract:

    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 24-60 months 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.

  23. van Hooidonk, R.J., D.P. Manzello, J. Moye, M.E. Brandt, J.C. Hendee, C. McCoy, and C. Manfrino. Coral bleaching at Little Cayman, Cayman Islands, 2009. Estuarine, Coastal and Shelf Science, 106:80-84, doi:10.1016/j.ecss.2012.04.021 2012

    Abstract:

    The global rise in sea temperature through anthropogenic climate change is affecting coral reef ecosystems through a phenomenon known as coral bleaching; that is, the whitening of corals due to the loss of the symbiotic zooxanthellae which impart corals with their characteristic vivid coloration. We describe aspects of the most prevalent episode of coral bleaching ever recorded at Little Cayman, Cayman Islands, during the fall of 2009. The most susceptible corals were found to be, in order, Siderastrea siderea, Montastraea annularis, and Montastraea faveolata, while Diplora strigosa and Agaricia spp. were less so, yet still showed considerable bleaching prevalence and severity. Those found to be least susceptible were Porites porites, Porites astreoides, and Montastraea cavernosa. These observations and other reported observations of coral bleaching, together with 29 years (1982-2010) of satellite-derived sea surface temperatures, were used to optimize bleaching predictions at this location. To do this a Degree Heating Weeks (DHW) and Peirce Skill Score (PSS) analysis were employed to calculate a local bleaching threshold above which bleaching was expected to occur. A threshold of 4.2 DHW had the highest skill, with a PSS of 0.70. The method outlined here could be applied to other regions to find the optimal bleaching threshold and improve bleaching predictions.