Original Paper: Beyer, H.L., Kennedy, E.V., Beger, M., Chen, C.A., Cinner, J.E., Darling, E.S., Eakin, C.M., Gates, R.D., Heron, S.F., Knowlton, N. and D.O. Obura. 2018. “Risk‐sensitive planning for conserving coral reefs under rapid climate change.” Conservation Letters 11(6), p.e12587. https://onlinelibrary.wiley.com/doi/full/10.1111/conl.12587
Featured Image Source: American Samoa, Swain Island. Credit: NOAA/NMFS/PIFSC/CRED, Oceanography Team. Flickr
What’s so Special About Coral?
Coral reefs are the world’s most diverse ecosystems despite making up less than one percent of the ocean floor. Home to many underwater creatures, it is estimated that about 25% of all ocean life depends on reefs. Reefs provide food, housing, and spawning and nursery areas to ocean life; they are important sources of income for over 500 million people worldwide; and they provide a number of essential ecosystem services, such as serving as barriers for storms.
However, losses of coral reefs have become more and more frequent over the last few decades. Mass coral bleaching events have been documented as early as the 1990s. Corals bleach when ocean temperatures rise. The corals become stressed and they expel the symbiotic algae living inside them. These algae are what give corals their vibrant colors, as corals themselves are white. When the algae are expelled, this is called a bleaching event since all you can see when this occurs is the remaining white coral skeleton. Corals can live in a dormant state for only a few days to a few weeks without algae, at which point they cannot be revived. If water temperatures return to normal, corals can go back to their unbleached state.
Let’s Face the Facts
Recordings of coral bleaching events are fairly common among recent environmental news reports, and there is a lot of evidence-based research suggesting that anthropogenic climate change kills off areas of coral reefs worldwide each year. The Paris Agreement was adopted in 2015 to address this issue of anthropogenic climate change.
Its main goal was to limit the increase of global average temperatures below 2°C above pre-industrial levels. A 2°C increase might not seem like a big deal, but a spike in ocean temperature of only 1-2°C, sustained over a few weeks, is enough to cause a bleaching event! And these measures may not be enough – using projections found by the Intergovernmental Panel on Climate Change, 70-90% of corals will degrade with a 1.5°C increase in temperature, with 99% degradation at a 2°C increase. For an in-depth visual look at a bleaching event over the course of just a few months, you can check out the Netflix documentary “Chasing Coral” (2017).
Though these events are frequently documented, research based around conserving corals is often looked at as a no-win situation. Bleaching events are difficult to predict far in advance and humans have been unsuccessful at mitigating the increase in global average temperatures. And bleaching events due to warming are not the only threats for coral reefs posed by climate change.
Declining water quality, overfishing, ocean acidification, nutrient availability from increased urbanization, storms, ocean warming, and other global stressors combined are predicted to lead to the disappearance of most of the world’s corals by mid-century, even if the emission goals set by the Paris Agreement are met.
In a number of cases, conservation groups have spent time, money, and other valuable resources trying to slow down coral degradation in threatened areas, only to have the corals eventually bleach a short time later. Therefore, many outlooks on the future of coral reefs are solemn – if global temperatures continue to rise, this phenomenon is something that cannot be mitigated using current conservation efforts. On one hand, increases in global surface temperatures need to halt for bleaching events to stop, which means globally countries need to meet or exceed their targets identified in the Paris Agreement. But this does not mean conservation organizations can’t find more effective ways of mitigating coral reef loss. What if there is a better way we can plan for the future?
Investing in the Future of Corals
Authors, Beyer and colleagues, published a study in 2018 with the idea of approaching coral conservation from another angle. They used Modern Portfolio Theory, a mathematical framework used in investing, to identify reefs around the world that would provide the most “return,” or would be the most beneficial to conserve. The framework uses correlations to distinguish reefs that would provide the least amount of risk, but would be the largest benefit to conserve, and it takes into account a degree of uncertainty in the investments, which is expected when dealing with reef conservation.
Climate change presents unique challenges for conservation since it can create a number of continuously changing and uncertain conditions. This means that what might work to mitigate coral degradation in one area might not work in another due to different areas experiencing varying effects of climate change. Therefore, absolute predictions of future reef behavior are extremely difficult to predict, and limited conservation resources may be targeted at reefs that are at high-risk for degradation, leading to low conservation success. However, the model provided by this framework aims to coordinate reef conservation efforts globally to reduce risk of widespread failure and plan strategically.
The framework goal was to identify a set of bioclimatic units containing approximately 500 km2 of reefs, and it focused on 30 metrics relevant to reef ecology, which spanned five major themes. None of the metrics in these themes are able to be managed directly, so it was important to identify and map out areas most affected by these metrics. The goal was to maximize the chance these less-affected reefs are secure in the future, since those coral populations that remain after the mass die-off due to climate change would be vital sources of larvae that can replenish reefs once ocean temperatures stabilize.
Is There Any Hope for Our Reefs?
Results of the study indicated that areas of the world that are projected to experience lower levels of threats under these metrics contained between them 95% of the documented species of coral. These areas included parts of central and western Southeast Asia, Australia, Cuba, and the Bahamas, with 31 countries in total. On the opposite scale, Hawaii, the Meso-American Reef, and Western Australia were regions that had reefs of high ecological and social value, but the framework projected them to suffer higher levels of impacts.
As the authors state, there is little doubt that the future of coral reefs hangs in the balance. But by using an interdisciplinary approach, the future of our reefs might not be so bleak. Using this framework, the likelihood of conservation success is improved and risks are reduced. In particular, the study identified conservation hotspots – areas where there was currently limited conservation attention, but where climate impacts were low. Conservation efforts should be focused more on these areas, and this framework could be extremely important in the overall future of coral reefs, as well as in other areas of conservation.
And you can help too! Upholding the Paris Agreement represents our best chance for saving reefs and other ecological areas around the world. We, as the global community, can work together to reduce our emissions and work towards the world’s targets as agreed to in Paris.
Knowlton, N. “Corals and coral reefs.” Smithsonian Ocean, Smithsonian, 2018, ocean.si.edu/ocean-life/invertebrates/corals-and-coral-reefs
Australian Institute of Marine Science. “Coral bleaching events.” Australian Institute of Marine Science, Australian Government, 2011, https://www.aims.gov.au/docs/research/climate-change/coral-bleaching/bleaching-events.html
IUCN. “Coral reefs and climate change.” IUCN Issues Brief, International Union for Conservation of Nature, 2019, https://www.iucn.org/resources/issues-briefs/coral-reefs-and-climate-change