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Coral reefs are one of the ecosystems most sensitive to climate change. The recent loss and degradation of coral reef ecosystems is expected to continue even if global warming is limited to 1.5°C above pre-industrial levels. There is therefore an urgent need to develop new technologies and management approaches to coral reef conservation. Emerging technologies, however, bring new challenges for decision making as they are associated with novel risks and impacts on the reef system. We argue that accounting for multiple biophysical thresholds and identifying key decisions in the planning process are crucial to avoid perverse outcomes in coral reef conservation. We identify opportunities to apply an Adaptation Pathways (AP) framework combined with a 'values, rules and knowledge' approach to facilitate long-term and large-scale coral reef conservation by explicitly considering uncertainty with climate change impacts in the decision-making process. The AP process can be used to reconcile the diverse values of stakeholders, scientific and cultural knowledge about the system, and the policy and regulatory context within which management must occur, in order to achieve robust long-term management. Climate change is a key driver of global coral reefs decline, with current management practices are expected to be insufficient in a changing world. Long-term strategic planning is needed to reduce risks of failure in coral reef conservation. Adaptation Pathways are a promising decision approach to develop a shared view of the changing systems and challenges for the conservation of coral reefs. [ABSTRACT FROM AUTHOR]

Climate change is impacting coral reefs now. Recent pan-tropical bleaching events driven by unprecedented global heat waves have shifted the playing field for coral reef management and policy. While best-practice conventional management remains essential, it may no longer be enough to sustain coral reefs under continued climate change. Nor will climate change mitigation be sufficient on its own. Committed warming and projected reef decline means solutions must involve a portfolio of mitigation, best-practice conventional management and coordinated restoration and adaptation measures involving new and perhaps radical interventions, including local and regional cooling and shading, assisted coral evolution, assisted gene flow, and measures to support and enhance coral recruitment. We propose that proactive research and development to expand the reef management toolbox fast but safely, combined with expedient trialling of promising interventions is now urgently needed, whatever emissions trajectory the world follows. We discuss the challenges and opportunities of embracing new interventions in a race against time, including their risks and uncertainties. Ultimately, solutions to the climate challenge for coral reefs will require consideration of what society wants, what can be achieved technically and economically, and what opportunities we have for action in a rapidly closing window. Finding solutions that work for coral reefs and people will require exceptional levels of coordination of science, management and policy, and open engagement with society. It will also require compromise, because reefs will change under climate change despite our best interventions. We argue that being clear about society's priorities, and understanding both the opportunities and risks that come with an expanded toolset, can help us make the most of a challenging situation. We offer a conceptual model to help reef managers frame decision problems and objectives, and to guide effective strategy choices in the face of complexity and uncertainty. [ABSTRACT FROM AUTHOR]

Environmental policy instruments often require that natural resource managers safeguard the resilience of ecosystems. However, 'resilience' has been a difficult concept to operationalise. Two forms of resilience are recognised in the ecological literature. 'Ecological resilience' concerns ecosystems that possess alternative equilibrial states (attractors) and has been operationalised in a few systems. 'Engineering resilience' was developed for ecosystems with a single attractor, but its use is confined to systems that gravitate towards a stable equilibrium., We present a general method to quantify engineering resilience that can be applied irrespective of an ecosystem's stability or proclivity to obey multiple attractors. The technique uses a system model to distinguish the effects of globally driven (and essentially unmanageable) stressors, such as climate change and ocean acidification, from regional- and local-scale (manageable) stressors on the ecosystem., We illustrate the technique using a simple coral reef model and find it able to calculate the impacts of managing crown-of-thorns starfish against a background of increasing stress from climate change and ocean acidification., Resilience analyses using our approach help assess the relative importance of local- or regional-scale management interventions under varying degrees of global environmental change, even if they preside over long-term ecosystem decline. Several frameworks of varying complexity are provided to guide the linkage of resilience metrics to environmental decision-making. [ABSTRACT FROM AUTHOR]

Reviews suggest that that the biogeochemical threshold for sustained coral reef growth will be reached during this century due to ocean acidification caused by increased uptake of atmospheric CO2. Projections of ocean acidification, however, are based on air-sea fluxes in the open ocean, and not for shallow-water systems such as coral reefs. Like the open ocean, reef waters are subject to the chemical forcing of increasing atmospheric pCO2. However, for reefs with long water residence times, we illustrate that benthic carbon fluxes can drive spatial variation in pH, pCO2 and aragonite saturation state (Ωa) that can mask the effects of ocean acidification in some downstream habitats. We use a carbon flux model for photosynthesis, respiration, calcification and dissolution coupled with Lagrangian transport to examine how key groups of calcifiers (zooxanthellate corals) and primary producers (macroalgae) on coral reefs contribute to changes in the seawater carbonate system as a function of water residence time. Analyses based on flume data showed that the carbon fluxes of corals and macroalgae drive Ωain opposing directions. Areas dominated by corals elevate pCO2 and reduce Ωa, thereby compounding ocean acidification effects in downstream habitats, whereas algal beds draw CO2 down and elevate Ωa, potentially offsetting ocean acidification impacts at the local scale. Simulations for two CO2 scenarios (600 and 900 ppm CO2) suggested that a potential shift from coral to algal abundance under ocean acidification can lead to improved conditions for calcification in downstream habitats, depending on reef size, water residence time and circulation patterns. Although the carbon fluxes of benthic reef communities cannot significantly counter changes in carbon chemistry at the scale of oceans, they provide a significant mechanism of buffering ocean acidification impacts at the scale of habitat to reef. [ABSTRACT FROM AUTHOR]

Changes in the carbonate chemistry of coral reef waters are driven by carbon fluxes from two sources: concentrations of CO2 in the atmospheric and source water, and the primary production/respiration and calcification/dissolution of the benthic community. Recent model analyses have shown that, depending on the composition of the reef community, the air-sea flux of CO2 driven by benthic community processes can exceed that due to increases in atmospheric CO2 (ocean acidification). We field test this model and examine the role of three key members of benthic reef communities in modifying the chemistry of the ocean source water: corals, macroalgae, and sand. Building on data from previous carbon flux studies along a reef-flat transect in Moorea ( French Polynesia), we illustrate that the drawdown of total dissolved inorganic carbon ( CT) due to photosynthesis and calcification of reef communities can exceed the draw down of total alkalinity ( AT) due to calcification of corals and calcifying algae, leading to a net increase in aragonite saturation state (Ωa). We use the model to test how changes in atmospheric CO2 forcing and benthic community structure affect the overall calcification rates on the reef flat. Results show that between the preindustrial period and 1992, ocean acidification caused reef flat calcification rates to decline by an estimated 15%, but loss of coral cover caused calcification rates to decline by at least three times that amount. The results also show that the upstream-downstream patterns of carbonate chemistry were affected by the spatial patterns of benthic community structure. Changes in the ratio of photosynthesis to calcification can thus partially compensate for ocean acidification, at least on shallow reef flats. With no change in benthic community structure, however, ocean acidification depressed net calcification of the reef flat consistent with findings of previous studies. [ABSTRACT FROM AUTHOR]

The onset of large-scale coral bleaching events is routinely estimated on the basis of the duration and intensity of thermal anomalies determined as degree heating weeks. Degree heating weeks, however, do not account for differential rates of heating. This study aimed to explore the relationship between different rates of heating above the documented regional winter threshold, and resultant bleaching of the reef-building coral Acropora formosa. Under a relatively low light field, rapid heating of 1°C day-1 from 29°C to 32°C lead to a 17.6% decline in Fv/Fm, concurrent with a rapid increase in xanthophyll de-epoxidation sustained into the dark, whereas slower heating rates of 0.5°C day-1 lead to no decline in Fv/Fm and no change in dark-adapted xanthophyll cycling. At the winter bleaching threshold of 30°C, areal net O2 evolution exceeded the control values for rapidly heated corals, but was lower than the controls for slowly heated corals. At the maximum temperature of 33°C, however, both treatments had net O2 fluxes that were 50% of control values. At 30°C, only symbiont densities in the slowly heated controls were reduced relative to controls values. By 33°C, however, symbiont densities were 55% less than the controls in both treatments. The rate of heat accumulation was found to be an important variable, with rapidly heated corals attaining the same bleaching status and loss of areal O2 production for half the degree heating week exposure as slowly heated corals. The study revealed that it is incorrect to assume that significant dark acclimation disables non-photochemical quenching, because 75% of an increased xanthophyll pool was found to be in the de-epoxidated state following rapid heat accumulation. This has important ramifications for the interpretation of chlorophyll fluorescence data such as dark adapted Fv/Fm. [ABSTRACT FROM AUTHOR]

We analyzed the contributions of clouds, turbidity, and tides to variations in irradiance and predicted benthic primary productivity on a coastal coral reef over a period of 2 yr (2001-2002). At 1.5 m below lowest astronomical tide (3.8-m tidal range), attenuation by suspended solids (turbidity) accounted for 74-79% of the total annual variation in irradiance, clouds for 14-17%, and tides for 7-10%. With increasing depth, the contribution from turbidity to irradiance variation increased asymptotically toward 95%. Fourier (spectral) analyses indicated that the benthic irradiance regime followed strong 8-week periodicities and weaker 2-4-week periodicities. The 8-week cycle was driven primarily by turbidity and secondarily by clouds and matches the periodicity of the intraseasonal Madden-Julian atmospheric oscillation. The weaker 3-4-week irradiance cycle was driven by turbidity; the 2-week cycle was driven by tides and, to a lesser extent, clouds. Comparisons of the benthic irradiance pattern with predictions of physiologically optimal irradiance levels (parameter Ek) for the coral Turbinaria mesenterina suggested that corals at the site alternate between states of potential light limitation and light stress, with a 2-8-week periodicity caused mainly by variations in turbidity. The effect of external sources of light reduction, such as episodic runoff events, on the energetics of benthic primary producers is likely to vary critically with the timing of such events. [ABSTRACT FROM AUTHOR]