Management strategies for coral reefs and people under global environmental

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A two-tiered approach for global assessment to inform climate investment and action

To avoid the challenges described above and to move towards a more transparent approach to global indicator assessments that can be used to identify climate action, a simplification and harmonization of assessments is needed to understand the impacts of climate change at the global level for coastal human populations. Specifically, we suggest a two-tiered approach for classifying existing studies to better identify common elements, and guide further global analysis (Figure 1.3.):
1. GLOBAL LEVEL IMPACT ASSESSMENTS (first tier): At the global level, we should focus on simplified and more standardized scoping studies for which good global data are available. These simpler approaches should link climate change directly to impact, be limited to impacts, and not include measures of adaptive capacity so as to clearly separate development issues from threats driven by climate change. A focus on global-level impact assessments can help identify countries where:
a. climate action may be warranted (mitigation, adaptation or other).
b. additional, finer scaled vulnerability assessments may provide crucial information to set up appropriate policy action.
c. monitoring and science may yield socially relevant results.
The scores used to rank countries could be presented by impact or as a summary measure of how high-ranked countries scored across the impacts considered. Global-level scoping analyses based on impacts are meant to guide more refined and more data-intensive local level analyses, but do not aim to replace such local level analyses. This has been attempted recently (Barange et al., 2014). Ideally, such analyses are accompanied by a global scale analysis of technical, economic and social costs of action for comparison to potential benefits from impact mitigation and adaptation.

Why sea surface temperature and ocean acidification matter

Coral bleaching, mortality, and disease caused by elevated sea surface temperature, have direct impacts on coral reef ecosystems (Chapter 2). Sustained bleaching events can cause coral reef death (Hoegh-Guldberg, 1999). Historically, the time between mass mortality events allowed coral reef ecosystems to recover from the damage caused by coral bleaching as new coral larvae could settle and grow in damaged areas. As these mortality events become more frequent, it is harder for coral reef ecosystems to recover. Coral bleaching has been shown to damage coral reef ecosystems (Donner et al., 2005; Fabricius et al., 2008) and can lead to bioerosion if corals die, eventually leading to the loss of reef height and structural complexity, also known as rugosity (Alvarez-filip et al., 2009). Reef structure provides shoreline protection (Fernando et al., 2005; Sheppard et al., 2005). Ferrario et al. (2014) found that coral reefs can dissipate approximately 97% of wave energy. The reef crest is the most important attenuation factor, contributing to 86% of wave attenuation. Roughness or rugosity is the next most important attenuation factor (Ferrario et al., 2014). Moreover, the three-dimensional structure of coral reefs also provide habitat for reef fish and other organisms that support the livelihoods of coastal areas (Wilson et al., 2006). To maintain these services, reefs must not only maintain their structure, but must keep pace with sea level rise. The ability of coral reef ecosystems to recover from damaging events is likely to be suppressed by the elevated sea surface temperature and OA expected to occur in a high-CO2 world. Van Hooidonk et al. (Maynard et al., 2015b; van Hooidonk et al., 2014) used projections under the Intergovernmental Panel on Climate Change’s RCP8.5 emissions scenario to show the potential spatial distribution of sustained, future high sea surface temperatures measured as the year when an area experiences at least 8 degrees Celsius degree-heating weeks (DHW) annually. A degree heating week is a standard measure of heat accumulation over the previous twelve weeks and represents the number of weeks an area has experienced temperatures in excess of 1 degree Celsius above the highest mean summer time temperature. Here we use this same threshold of 8 DHWs to indicate where future increases in sea surface temperature will lead to sustained bleaching and a high likelihood of coral mortality. Changes in ocean carbonate chemistry due to increasing atmospheric CO2, known as OA and often measured by aragonite saturation state (Ωar), also poses a severe threat to corals and reef ecosystems (Hoegh-Guldberg et al., 2014). While much of the research focus, and debate, to date has been on the role of OA in the reduction of calcification rates on coral reefs (Albright et al., 2016; Howes et al., 2015; Yeakel et al., 2015), OA can significantly impair other ecological and physiological functions. For instance, coral larval success may be impaired at much more modest levels of OA. Ωar levels of 3.1 or less, a level some coral reefs will experience in the next decade, are known to impair larval recruitment of some corals (Albright et al., 2010; Manzello et al., 2014). Similar levels of OA can also reduce growth rates in some corals (Chan and Connolly, 2013). Experimental evidence shows that increased OA and thermal stress combined have a greater harmful effect on both larval success and growth rates than either factor alone (Albright and Mason, 2013), which could make coral recovery even more difficult when both stressors occur simultaneously (and at less severe levels than those required to induce harm by either stressor alone). Additionally, a variety of other coral reef organisms have also been shown to suffer from thermal stress and OA (Lürig and Kunzmann, 2015; Yang et al., 2015).

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Where are the greatest potential risks to reefs and people in a high- CO2 world?

We use an indicator approach to identify places where key environmental factors driven by a high-CO2 world may put coral reef-dependent people most at risk (Ekstrom et al., 2015). Mapping indicators has been proposed as a way 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” to combat global environmental change (Lürig and Kunzmann, 2015). As such, an indicator approach allows for a focus on a spatial understanding of key characteristics of the social-ecological system, even in the absence of a complete set of science and data that would be needed to create more complex models of ecological processes and people’s responses to change in ecosystem conditions.
To identify where people are at risk from CO2-driven threats to coral reefs, we map indicators of two key aspects of current human dependence on coral reefs (people who benefit from the shoreline protection provided by reefs and reef-related fisheries) and two key indicators of oceanic change in a high CO2 world (the onset of high thermal stress in terms of the year that sea surface temperature reaches 8 DHW annually (Maynard et al., 2015b; van Hooidonk et al., 2014) and the expected level of OA in year 2050). Recent studies show that the precise role that increased sea surface temperature and OA have on coral reef ecosystem conditions and health is complicated (McClanahan et al., 2015; Mongin et al., 2016b; Yeakel et al., 2015) and may vary regionally (Roff and Mumby, 2012). With that in mind, these indicators are not intended to be predictive of coral reef death. Instead, we use an indicator approach to reflect the spatial distribution of the intensity of environmental stress on corals that could result from increased levels of atmospheric CO2 that are projected to occur during the twenty first century, if emissions continue under assumptions of business as usual (Alexander et al., 2013).

Constructing a typology for management strategies of coral reefs and people under GEC

The typology presented in Gattuso et al. (2015) classifies management strategies into four major categories: mitigate, protect, repair, and adapt. This typology was designed to broadly identify actions to tackle climate change and ocean acidification for ocean ecosystems and the services they provide. To apply this typology to management strategies that tackle the impacts of GEC on coral reefs ecosystems and ecosystem services, we created sub-categories that take into account specific aspects of coral reef management (Figure 4.1.). When refining Gattuso et al.’s typology to deal with coral reefs ecosystems, the same four categories of management strategies can be used: reduction of global and local environmental hazards (mitigate), repairing and restoring damaged reefs and associated ecosystems (repair), protecting existing healthy ecosystems to improve resilience and maintain ecosystem functions (protect), and adapting human societies to the reduction of ecosystem services when damage from global and local environmental change is not avoidable (adapt) (Burke et al., 2011; Gattuso et al., 2015; Mumby and Anthony, 2015).

Table of contents :

Table of content
List of annexes
List of figures
List of tables
List of abbreviations / correspondance en français
Scientific production
Introduction générale
Chapter 1. Conceptual advances on global scale assessments of marine and coastal vulnerability
Chapter 2. Multiple stressors and ecological complexity require a new approach to coral reef research
Chapter 3. Coral reefs and people in a high-co2 world: where can science make a difference to people?
Chapter 4. Management strategies for coral reefs and people under global environmental
change: 25 years of scientific research
Chapter 5. The role of ecological limits in prioritizing impacts, resilience, and action for coral
reefs under global environmental change
Discussion générale
Fully detailed table of content
Short abstract
Résumé court


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