Climate Change and Carbon Threats to Coral Reefs

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The preservation of coral reefs un- der a changing climate requires a coordinated approach that inte- grates observational, experimental, and modeling efforts ...
Climate Change and Carbon Threats to Coral Reefs National Meteorological and Ocean Services as Sentinels by

Claire M. Spillman, Scott F. Heron, Mark R. Jury, and Kenneth R. N. Anthony


he preservation of coral reefs under a changing climate requires a coordinated approach that integrates observational, experimental, and modeling efforts with practical management and sound government policy. Coral reefs are among the most species-rich habitats in the world, but also among the most vulnerable to our current high-emission path. Observations of the climate system have shown an increase in global average surface temperature during the twentieth century, with an increased rate of warming since 1950. This has been attributed to increased levels of Fig. 1. Links between carbon emissions and factors reducing coral anthropogenic carbon dioxide (CO2) reef resilience due to ocean acidification, warming, tropical cyclones, in the atmosphere since the preindus- and sea level [adapted from Anthony and Marshall (2009)]. trial era, primarily due to the human activities of fossil fuel combustion and forest logging. The Intergovernmental Panel on tures, widespread melting of snow and ice, and rising Climate Change (IPCC)’s 2007 Fourth Assessment global average sea level. Report states that warming of the climate system is Ocean warming increases the risk of extensive unequivocal, as is now evident from observations of coral bleaching events and mass mortalities. Ocean increases in global average air and ocean tempera- acidification, via increased absorption of CO2 by seawater, can reduce the capacity of coral reefs to grow and maintain their structure and function. Many of the world’s coral reefs are already degraded Affiliations : S pillman —Centre for Australian Weather and Climate Research (CAWCR), Melbourne, Australia; Heron — due to marine pollution, overfishing, and local-scale Coral Reef Watch, NOAA, and the School of Engineering and disturbances; to ensure reefs can cope with potential Physical Sciences, James Cook University, Townsville, Australia; impacts of global warming and ocean acidification, Jury—University of Puerto Rico, Mayaguez, Puerto Rico, and improved reef management is essential. University of Zululand, KwaDlangezwa, South Africa; A nthony— Here, we summarize some of the linkages between Australian Institute of Marine Science, Townsville, Australia atmospheric CO2 and the physical and chemical Corresponding Author : Dr. Claire M. Spillman, Centre processes that it drives: climate change, increased sea for Australian Weather and Climate Research (CAWCR), a partnership between the Australian Bureau of Meteorology and surface temperatures, ocean acidification, tropical cyCSIRO, Bureau of Meteorology, GPO Box 1289, Melbourne, VIC clone frequency/severity, and sea level rise (Fig. 1). We 3001, Australia then draw links between these processes and specific E-mail: [email protected] threats to coral reef ecosystems. Finally, we propose a DOI:10.1175/BAMS-D-11-00009.1 strategic framework for how observations and forecasting systems can be coordinated as part of national me©2011 American Meteorological Society teorological and ocean services, alerting reef managers AMERICAN METEOROLOGICAL SOCIETY

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and policy makers to areas at high risk from both local and global pressures. C LI M ATE C H A NGE AND COR AL REEFS. Warming of the tropical ocea ns is one obser ved manifestation of changes in the climate system (Fig. 2). Elevated ocean temperature has been established as the Fig. 2. Time series of NOAA observed and GFDL model-projected SST in the primary cause of mass cor- zone 30°N–30°S based on IPCC-AR4 A1B scenario, both smoothed with an al bleaching events. Coral 18-month running mean. Data derived from the International Research Instibleaching results from the tute for Climate and Society (IRI) database ( loss of symbiotic algae from coral tissues during times of stress. Mortality, due of carbonate ions, the building blocks for corals. The to bleaching and/or subsequent disease, can occur consequences will be several-fold. First, acidification following prolonged thermal stress, leading to loss leads to reduced coral growth, potentially promoting of reef structure and habitats. The intensity and scale a shift from net reef growth to net dissolution. Second, of observed bleaching events have increased since reduced calcification will lead to a weakening of reef the 1960s, and major bleaching events in 1997–98 structures, and hence increased vulnerability to storm (Fig. 3), 2002, 2005, and 2010 have impacted entire damage. The combined effect for coral reefs is reduced reef systems. Projections for most IPCC scenarios resilience and ecosystem function. With CO2 concenpredict a rise in sea surface temperatures (SST) of trations predicted to rise further in the twenty-first at least 2°C in the twenty-first century (Fig. 2). This century, the rapid change in ocean carbon chemistry is is likely to push most coral reefs close to or beyond likely to outpace the potential for evolutionary adaptatheir threshold for bleaching more often, reducing tion to ocean acidification. their ability to recover from such events. A warming climate is also likely to affect the freCoral reefs are also under growing threat from quency and intensity of tropical cyclones (hurricanes, ocean acidification, resulting from increasing CO2 con- typhoons), as warm sea surface temperatures are centrations in the atmosphere. Increased absorption necessary for cyclogenesis. Some studies suggest an of this CO2 by ocean surface waters leads to a decline increase in the severity of storms but a decrease in the in marine pH and a reduction in the concentration number of events under climate change, though this is still under debate within the scientific community. Cyclones can be extremely destructive to coral reefs, as the waves they generate can relocate large coral colonies and reduce reefs to rubble (Fig. 4). Reefs already weakened by bleaching and ocean acidification will be at greater risk of physical destruction from tropical cyclones. However, storms can also mitigate thermal bleachFig. 3. Location of the coral reefs affected in the 1997–98 global bleaching ing risk, as localized cooling event. Red, yellow, and blue dots indicate severe, moderate, and low bleach- can result from wind-driven water mixing and increased ing, respectively (Reefbase; 1582 |

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cloud cover, while the latter also reduces light pressure to ameliorate bleaching risk. Sea level rise is another consequence of climate change. Since 1990, global warming has contributed approximately 1.6 mm per year to global average sea level (Fig. 5), which is estimated to increase by as much as 60 cm during this century. Sea level rise over coral reefs provides corals with greater space to grow upward. It is possible for coral reef growth to keep pace with gradual sea level rise unless compromised by ocean acidification. However, increasing water depth and reduced water quality from enhanced sediment suspension can reduce light availability and may cause deeper coral reefs to “drown” if they do not receive enough sunlight to support photosynthesis. The downstream consequences of CO2 emissions, via ocean acidification and ocean warming driven by climate change, intense storms, and sea level rise (Fig. 1), can have far-reaching implications for the health and functioning of coral reef ecosystems. Importantly, global impacts of increased CO2 are likely to occur in combination with regional or local-scale disturbances already experienced by many coral reefs, such as poor water quality and destructive fishing practices. These can act together to significantly degrade the resilience of coral reefs to the point that reefs are unable to recover from even minor disturbances. Coordinated action at national levels to promote management for reef resilience is imperative to secure the survival of global coral reefs under climate change and ocean acidification. THE ROLE OF METEOROLOGICAL AND OCEAN SERVICES. With growing recognition of the potential impacts of global change on coral reefs and coastal ecosystems, meteorological and ocean services are increasingly called upon to provide support to real-time oceanography, marine biology, and coastal management. Here, we suggest a framework for the role of meteorological and ocean services in providing information and forecasts for coral reefs that consider multiple environmental factors at different temporal and spatial scales (Fig. 6). Participation in (and support of) regional and global observation networks is an important role of meteorological and ocean services. Meteorological services participate by contributing observations, providing instruments and processing, and transmitting and storing data. In turn, they benefit from access to extensive datasets that can be used to develop and implement a broad range of ocean products and AMERICAN METEOROLOGICAL SOCIETY

Fig. 4. A Porites colony in Western Australia was propelled onto the reef flat as Cyclone Fay passed in Mar 2005 (Australian Institute of Marine Science).

services, including those needed to monitor and protect coral reefs (Fig. 6). Examples of such products include those developed by the NOAA Coral Reef Watch program for determining coral bleaching and disease risk due to thermal stress using satellitederived SST. Additionally, NOAA also provides in situ oceanographic monitoring at tropical reef locations. In addition to observation-based nowcasts and reanalyses, high-quality data are essential for accurate numerical weather prediction (storms and waves), seasonal forecasting (thermal stress), and climate modeling (ocean acidification and sea level rise). Numerical weather prediction has long been an undertaking of national meteorological services, with forecasts of events such as cyclones and storm surges produced operationally. In recent decades, these capabilities have expanded to include ocean forecasting, both on seasonal and climatic timescales, as recognition of the impact on regional climate of large-scale drivers such as the El Niño–Southern Oscillation has increased. The Australian Bureau of Meteorology currently provides global seasonal ocean forecasts, December 2011

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public education, and proactive management responses to reef threats, and also provides improved guidance for government policy and increased global awareness of the impacts of climate change on coral reefs. Targeted reef ser vices must be well designed in order to reliably provide useful Fig. 5. Time series of sea levels averaged over the zone 30°N–30°S, based on gauge information in near real-time data from the Joint Archive for Sea Level (JASL; that allows for rapid manageUHSLC/jasl.html), accessed via Climate Explorer ( ment responses to reef threats. National meteorological serhigh-resolution five-day ocean forecasts (BLUElink), vices often have the mandate and operational infratidal predictions, tsunami warning services, and structure to support products that research institutes ocean surface wave predictions. In particular, sea- lack, emphasizing their role as the logical coordinator sonal dynamical SST forecasts are provided using the of such systems. Formal communication pathways bePredictive Ocean Atmosphere Model for Australia tween relevant agencies are essential to insure systems (POAMA) for the monitoring of coral bleaching risk meet the requirements for effective reef management. on the Great Barrier Reef. NOAA also produces a The use of interactive viewing platforms that allow global statistical seasonal outlook for thermal stress the simultaneous display of multiple products, plus for reefs. Such advance warning of anomalous warm well designed websites that draw together all available conditions and other threats to reef health allows for resources in a clear and logical manner, are excellent proactive management. tools in creating a usable reef service. As public engageObservations, data-based products, and model ment is important for promoting stewardship of coral forecasts provided by national meteorological and reefs, tools that can also be utilized for community ocean services—both currently and in the future—could be used to inform reef warning systems. However, often these products are not integrated to form a coordinated, tailored service for reef management. National meteorological services are the logical agencies to coordinate such systems, due to their strengths in numerical prediction, climate modeling, and operational capabilities. The development of multifaceted systems that include information and forecasts of tropical cyclones, storm surge, and thermal stress on daily-to-seasonal time scales, together with predictions for ocean acidification and sea level rise at decadal time scales, is crucial for best-practice reef management. The inclusion of both pulse-type risks (stochastic disturbances) and press- Fig . 6. Framework describing the role of national meteorological type stressors in an alert framework and ocean services in addressing carbon, climate change, and coral allows for better future planning, reef issues. 1584 |

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education are doubly useful. Lastly, integration of reef ecosystems research into the development of systems that alert management agencies to coral reef threats is an important feedback mechanism for continuous improvement of forecasting capabilities. THE WAY FORWARD. The development of operational cross-disciplinary reef services will provide improved risk and vulnerability assessments for coral reefs, and can assist in the development of monitoring, conservation, and adaptation strategies. First, for the development of effective systems, close collaboration between meteorological and ocean services, reef management agencies, and the science community is essential. Systems must address the requirements of reef management agencies and be useful, reliable, and informative, with limitations well documented. Collaborative programs between management agencies and meteorological services can develop plans for warning systems and determine how they would best be assimilated into existing response plans and management frameworks. Second, the creation of multidisciplinary, crossinstitutional research programs that underpin such services is important, particularly for the investigation of reef ecosystem responses to global warming and ocean acidification, and assessment of associated impacts on ecological, social, and economic systems. Further research is required to enhance modeling capabilities, particularly in determining the impacts of climate change on large-scale drivers and subsequent teleconnections with reef regions, coastal circulation, cyclone generation, and wave regimes. This would lead to improved predictions, assessments, and management of the impacts of climate change and ocean acidification on coral reef systems. Targeted, coordinated reef services, which incorporate the multiple threats of storm surge, thermal stress, ocean acidification, and sea level rise, are recommended to help address the substantial challenge of securing the long-term health and resilience of coral reefs. Other coastal ecosystems and communities that are similarly at risk under climate change will also benefit from such integrated systems. Provision of reliable forecasts, high-quality data, and applied reef products at multiple scales will enable reef managers and stakeholders to plan better for local-scale disturbances as well as climate change. The interactions and potential feedbacks between global CO2 effects and local/regional disAMERICAN METEOROLOGICAL SOCIETY

turbances affecting reef health heighten the urgency of the development of coordinated strategies for reef conservation. ACKNOWLEDGMENTS. The authors would like to thank M. V. K. Sivakumar (WMO) and Peter Dexter (Bureau of Meteorology) for initializing this discussion and for their helpful suggestions. The manuscript contents are solely the opinions of the authors and do not constitute a statement of policy, decision, or position on behalf of NOAA or the U.S. Government, nor on behalf of the Australian Institute of Marine Science or the Australian Government.

FOR FURTHER READING Anthony, K. R. N., and P. A. Marshall, 2009: Coral reefs and climate change. Marine Climate Change Impacts and Adaptation Report Card for Australia 2009, E. S. Poloczanska, A. J. Hobday, and A. J. Richardson, Eds. NCCARF. [Available online at www. Coral_Reefs_Final.pdf.] ——, J. A. Maynard, G. Diaz-Pulido, P. J. Mumby, P. A. Marshall, L. Cao, and O. Hoegh-Guldberg, 2011: Ocean acidification and warming will lower coral reef resilience. Global Change Biol., 17, 1798–1808. Baker, A. C., P. W. Glynn, and B. Riegl, 2008: Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuar. Coast. Shelf Sci., 80, 435–471. Donner, S. D., 2009: Coping with commitment: Projected thermal stress on coral reefs under different future scenarios. PLoS One, 4, e5712. Dubinsky, Z., and N. Stambler, Eds., 2010: Coral Reefs: An Ecosystem in Transition. Springer, 561 pp. Hoegh-Guldberg, O., and Coauthors, 2007: Coral reefs under rapid climate change and ocean acidification. Science, 318, 1737–1742. Knutson, T. R., and Coauthors, 2010: Tropical cyclones and climate change. Nature Geosci., 3, 157–163. Manzello, D. P., M. Brandt, T. B. Smith, D. Lirman, J. C. Hendee, and R. S. Nemeth, 2007: Hurricanes benefit bleached corals. PNAS, 104, 12,035–12,039. Massel, S. R., and T. J. Done, 1993: Effects of cyclone waves on massive coral assemblages on the Great Barrier Reef: Meteorology, hydrodynamics and demography. Coral Reefs, 12, 153–166. Ogston, A. S., and M. E. Field, 2010: Predictions of turbidity due to enhanced sediment resuspension resulting December 2011

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from sea-level rise on a fringing coral reef: Evidence from Molokai, Hawaii. J. Coast. Res., 26, 1027–1037. Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor, and H. L. Miller, Eds., 2007: Climate Change 2007: The Physical Science Basis. Cambridge University Press, 996 pp. Spillman, C.  M., 2011: Operational real-time seasonal forecasts for coral reef management. J. Oper. Oceanogr., 4, 13–22. van Oppen, M. J. H., and J. M. Lough, Eds., 2009: Coral Bleaching: Patterns, Processes, Causes and Consequences. Springer, 178 pp.

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Webster, P. J., G. J. Holland, J. A. Curry, and H. R. Chang, 2005: Changes in tropical cyclone number, duration, and intensity in a warming environment. Science, 309, 1844–1846. Web Resources Operational BLUElink and POAMA forecasts: NOAA Coral Reef Watch: