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Saving Coral Reef Ecosystems

What is the compelling question or challenge?

Coral reefs are economically and biologically irreplaceable ecosystems, existentially threatened by climate change. Can science and engineering save coral reefs before the end of the century?

What do we know now about this Big Idea and what are the key research questions we need to address?

The survival of coral reefs is gravely threatened by climate change. Darling and Côté (1) write that two factors, intrinsic resistance (phenotype) and extrinsic resistance (location), determine the resiliency of any ecosystem to climate change and describe possible approaches for coral reef conservation and renewal. In order to increase the chances that coral reefs will continue to support marine diversity, a broad and ambitious multidisciplinary research program is vital.

Research efforts are required to develop new knowledge on biological mechanisms and diversity, ecological function and the interactions between ocean reefs and anthropologic systems. A particular need is for better understanding the mechanisms and mitigating the consequences of twin causes of coral stress: global warming and ocean acidification.

Question 1: What are the key aspects of coral reef resilience to ocean acidification?

Acidification alters the thermodynamic stability of the calcium carbonate skeleton in seawater, potentially preventing corals from building the rocky structures that provide the entire reef ecosystem its essential scaffolding and infrastructure. A recent discovery (2) on the mechanism of coral biomineral formation, however, suggests that some coral species may possess resistance to changes in ocean chemistry. In at least one species of coral (Stylophora pistillata) the skeleton is deposited not one ion at a time from sea water but one particle at a time from vesicles inside the polyp. Because animals, including coral polyps, actively regulate their internal chemistry, independent of the water in which they swim or live, coral reefs may be able to fight off the effect of surrounding ocean water chemistry. This would certainly lead to stress and require a larger metabolic investment in coral reef building, but it provides hope that one threat from climate change might not be existential.

Question 2: What are the key aspects of coral reef resilience to ocean warming?

Warming causes coral bleaching – above 29 °C coral polyps eject their photosynthesizing zooxanthellae symbionts. Coupled climate and ocean models predict that the current temperature limits for ocean corals will move towards higher latitudes faster than any species can evolve and adapt, and faster than corals could migrate naturally. Currently, the human fight against coral bleaching is being waged by the propagation of corals by collecting fragments, growing them in coral gardens and replacing juveniles onto the bleached reef. This could be extended to transplanting corals into cooler waters, at unprecedentedly high latitudes. The preservation of DNA from both coral and symbionts is essential to preserve and understand diversity and intrinsic resistance.

Question 3: Which new models for complex ecosystem resilience can guide intervention strategies?

Once the science of coral reef resilience is understood, a range of engineering or ecological interventions may be conceived. Highly technical efforts might include ocean cooling or decarbonation. Such extreme bio-geo-engineering is controversial and will become more so, but it is inevitable that populations whose livelihoods are tethered to the survival of coral reef ecosystems will call for action.

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