Coral Reef Ecosystems under Climate Change and Ocean Acidification

Abstract

Coral reefs are found in a wide range of environments, where they provide food and habitat to a large range of organisms as well as providing many other ecological goods and services. Warm-water coral reefs, for example, occupy shallow sunlit, warm, and alkaline waters in order to grow and calcify at the high rates necessary to build and maintain their calcium carbonate structures. At deeper locations (40-150 m), "mesophotic" (low light) coral reefs accumulate calcium carbonate at much lower rates (if at all in some cases) yet remain important as habitat for a wide range of organisms, including those important for fisheries. Finally, even deeper, down to 2,000 m or more, the so-called "cold-water" coral reefs are found in the dark depths. Despite their importance, coral reefs are facing significant challenges from human activities including pollution, over-harvesting, physical destruction, and climate change. In the latter case, even lower greenhouse gas emission scenarios (such as Representative Concentration Pathway RCP 4.5) are likely drive the elimination of most warm-water coral reefs by 2040-2050. Cold-water corals are also threatened by warming temperatures and ocean acidification although evidence of the direct effect of climate change is less clear. Evidence that coral reefs can adapt at rates which are sufficient for them to keep up with rapid ocean warming and acidification is minimal, especially given that corals are long-lived and hence have slow rates of evolution. Conclusions that coral reefs will migrate to higher latitudes as they warm are equally unfounded, with the observations of tropical species appearing at high latitudes "necessary but not sufficient" evidence that entire coral reef ecosystems are shifting. On the contrary, coral reefs are likely to degrade rapidly over the next 20 years, presenting fundamental challenges for the 500 million people who derive food, income, coastal protection, and a range of other services from coral reefs. Unless rapid advances to the goals of the Paris Climate Change Agreement occur over the next decade, hundreds of millions of people are likely to face increasing amounts of poverty and social disruption, and, in some cases, regional insecurity.

Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia

“…Further studies of coral pH cf and Ca 2+ upregulation across a wide range of Indo‐Pacific coral genera are required to better establish how the response of coral calcification rates to the combined effects of future OA and warming will vary geographically. Finally, coral bleaching due to marine heatwaves is currently the foremost threat to coral reef survival (Hoegh‐Guldberg, Poloczanska, Skirving, & Dove, ; Hughes et al, ), especially given that the capacity to maintain relatively high pH cf is impaired in thermally stressed corals with resultant declines in calcification rates (D'Olivo & McCulloch, ). The future vitality of coral reefs ultimately depends on the success of global efforts to rapidly and substantially reducing CO 2 emissions to reduce the impacts of ocean warming and OA.…”

Thresholds and drivers of coral calcification responses to climate change

“…Climate change and associated ocean acidification and warming (OAW) have been linked to some of the major coral reef crises in Earth's history (Pandolfi, Connolly, Marshall, & Cohen, ). The current anthropogenic increase in atmospheric CO 2 concentrations is causing environmental change at an unprecedented rate (IPCC, ), with deleterious repercussions for coral reef communities (Baker, Glynn, & Riegl, ; Hoegh‐Guldberg, Poloczanska, Skirving, & Dove, ). One potential repercussion is the decline in calcification rates of scleractinian corals (Anthony, Kline, Diaz‐Pulido, Dove, & Hoegh‐Guldberg, ; Dove et al., ; Schoepf et al., ), which could shift coral reef carbon budgets from net growth to net dissolution (Dove et al., ), leading to substantial ecological and socioeconomic impacts throughout the tropics (Moberg & Folke, ).…”

Ecosystem‐based management of coral reefs under climate change

“…A recent review by Hoegh‐Guldberg et al. () suggests that there is little evidence to show corals can adapt fast enough, especially considering their long generation times.…”