Vulnerability of global coral reef habitat suitability to ocean warming, acidification and eutrophication

Abstract

Coral reefs are threatened by global and local stressors. Yet, reefs appear to respond differently to different environmental stressors. Using a global dataset of coral reef occurrence as a proxy for the long‐term adaptation of corals to environmental conditions in combination with global environmental data, we show here how global (warming: sea surface temperature; acidification: aragonite saturation state, Ωarag) and local (eutrophication: nitrate concentration, and phosphate concentration) stressors influence coral reef habitat suitability. We analyse the relative distance of coral communities to their regional environmental optima. In addition, we calculate the expected change of coral reef habitat suitability across the tropics in relation to an increase of 0.1°C in temperature, an increase of 0.02 μmol/L in nitrate, an increase of 0.01 μmol/L in phosphate and a decrease of 0.04 in Ωarag. Our findings reveal that only 6% of the reefs worldwide will be unaffected by local and global stressors and can thus act as temporary refugia. Local stressors, driven by nutrient increase, will affect 22% of the reefs worldwide, whereas global stressors will affect 11% of these reefs. The remaining 61% of the reefs will be simultaneously affected by local and global stressors. Appropriate wastewater treatments can mitigate local eutrophication and could increase areas of temporary refugia to 28%, allowing us to ‘buy time’, while international agreements are found to abate global stressors.

The coral conservation crisis: interacting local and global stressors reduce reef resiliency and create challenges for conservation solutions

“…While it is estimated that 6% of reefs across the globe will not be affected by either local or global stressors, 11% of reefs will be threatened solely by global factors alone, 22% solely from local factors, and 61% from the combined effects of local and global drivers of environmental change [14]. Globally, ocean warming and acidification are compromising carbonate accretion of coral reefs, resulting in less diverse reef communities [15,16].…”

“…However, the potential of local action to offset global consequences on coral reefs is relatively unknown because it is difficult to assess across ecological scales in an experimental setting. Therefore, it becomes increasingly important to implement management and monitoring strategies that document the interaction of local and global drivers of environmental change to identify potential mitigation strategies [14]. The primary sources of human-induced impacts result from land-use change and terrestrial runoff, which have increased sedimentation and eutrophication on nearshore coral reefs [70].…”

“…In the Florida Keys, the local and regional variability of nitrogen enrichment increased the risk of coral bleaching, mortality, and disease under temperature stress [32]. Numerous studies confirm that appropriate wastewater treatment would mitigate local eutrophication and, in response, increase reef refugia areas by 28% across the globe, giving reefs time while climate change is addressed at a global scale [14,25].…”

“…In contrast, local factors can be dealt with immediately and directly. For example, appropriate wastewater treatments can mitigate local eutrophication and increase temporary refugia areas to 28%, allowing coral reefs to be relieved of the local stressor while international agreements are found to abate global stressors [14]. It is suggested that managers spend time identifying coral reef locations that, in the absence of other impacts, are most likely to have a heightened chance of surviving projected climate changes relative to other reefs and protect those reefs ( Fig.…”

“…To plan, mitigate, and restore the future of coral reefs, it is essential to acknowledge that 61% of reefs are simultaneously affected by local and global stressors. It cannot be a 'one size fits all' solution for reef protection [14]. Our review recommends actionable science-based advancements based on a local risk assessment that are unique to each region or reef system.…”