Climate Change: A death note for coral reefs?

Be it the Great Barrier Reef, the New Caledonian Reef, the Red Sea Coral Reef, or reefs in the waters of the Great Chagos Archipelagos – coral reefs are intricate and majestic living marine architectures which form the vibrant cities of our oceans. They cover a mere 0.1% of the sea, yet they are home to around 25% of the marine biodiversity¹. It is therefore unsurprising that life across coral reefs can get as busy as cities like London or New York. Akin to such metropolises, the disappearance of coral reefs seems very unlikely; yet, we are losing them at an alarming rate. While their loss can be attributed to several factors including pollution and destructive fishing practices, coral bleaching due to climate change is the biggest threat today – jeopardising their very existence. 

Coral bleaching has already claimed around 50% of the world’s coral reefs leading to the endangerment of several dependent marine species. This destruction directly impacts humans in multiple ways – from our fishery industries to our ability to discover new drugs against diseases as deadly as cancer. So, what is coral bleaching? As the name suggests, it literally means the corals losing their vivid colours. Let’s take a minute and appreciate their anatomy to better understand how this happens. A coral is an animal which consists of anything from thousands to millions of other tiny soft-bodied animals known as polyps². Each polyp holds heaps of colourful microscopic plants (known as microalgae) embedded in its body. Both the microalgae and the corals share a mutualistic relationship. The microalgae are sheltered and are supplied with food (in the form of the coral wastes) for photosynthesis – a process through which they manufacture vital nutrients (for both them and the corals) and oxygen. In this way, the corals dispose of their waste and are supplied with oxygen as well as essential nutrients for them to survive and thrive³. Do not be fooled though, this is an oversimplification of this harmonious and beneficial relationship. In reality, the latter is utterly complex and even more delicate. 

In the event of a stressful situation – especially the rise in the seawater temperature, this mutualistic relationship is disrupted, and corals bleach by expelling their colourful microalgae, leaving them snow white. Depending on the period of stress that they are subjected to, corals may never recover their microalgae which ultimately leads to their death due to starvation⁴. ‘Chasing Corals’ — a must-watch documentary — captured this gruesome reality during the last mass coral bleaching events which started in 2014⁵. It reveals stretches of coral reef graveyards, dead as far as you can see and invaded by seaweed — heart-breaking would be the one word to describe it. Be wary, if you are among those who have a sweet spot for marine life, it would be almost impossible to retain your tears as the images unfold in front of you. The year 2017 marked the culmination of an unprecedented three year back-to-back mass coral bleaching events which took place on a global scale owing, primarily, to climate change-driven rise in the seawater temperature which was further exacerbated by El Niño⁶.

El Niño is a natural phenomenon and involves the occurrence of unusually warm water in the Pacific Ocean⁷, while the unprecedented rate at which our climate is changing and the consequential temperature rise are human-driven.  Let’s briefly review the science. Climate change is the outcome of an upward shift in the Earth’s atmospheric greenhouse gases caused by agriculture and the burning of fossil fuels, among others. The greenhouse gases (which are mainly carbon dioxide, methane and water vapour) have the property to absorb infrared radiation and to emit it back to the Earth’s surface thereby confining heat energy to the Earth’s atmosphere. There is a delicate balance though. Too little of atmospheric greenhouse gases would be detrimental to life, while too much will result in the Earth cooking. Right now, we are being cooked, and on the verge of being overcooked if the world continues with the business-as-usual agenda.

For decades, the oceans have profusely absorbed excess heat generated by the surplus of greenhouse gases in our atmosphere, thereby warming the oceans. As the years pass by, it is apparent that thermal stress in the marine environment is being amplified at an exponential rate as depicted by the above-mentioned recent back-to-back mass coral bleaching events. From 2014 to 2017, it has been reported that 70% of the world’s coral reefs have been affected while in over two decades, we have lost over 50% of the world’s coral reefs due to mainly global climate change worsened by other factors including El Niño⁸. At this rate, the collapse of an entire ecosystem is imminent. In fact, scientists predict that by 2050, 90% of the coral reefs around the globe will be wiped out. Some even dare to say that the future seas will be slimy, teeming with jellyfish⁹. Why should we care? If this scenario becomes a reality, the marine ecological collapse will have a ripple effect on our civilisation and will affect us all – from our ability to breathe to our food security and our economies.

There is still a reason to be optimistic though. The 10% of coral reefs that will survive will be pretty resilient. In fact, such occurrences have already been reported. On the Great Barrier Reef in Australia, scientists have observed that between the last two consecutive bleaching events, which occurred in 2016 and 2017, coral reefs took longer to bleach in 2017 even when subjected to higher temperatures¹⁰. Interestingly, others have reported that in other parts of the world adaptive mechanisms and, probably even more importantly, natural selection for heat-tolerant corals have been observed. While scientists may disagree on many aspects concerning the future of coral reefs in a steadily warming ocean, almost all of them firmly believe that for corals to survive in the twenty-first century, they need time to adapt to the changing environment. Indeed, the evolution of such an organism cannot happen overnight. Therefore, the problem which they face today can be described as a race between how fast they can adapt and that of the changing climate¹¹.

Today, time seems to be a luxury which coral reefs do not have to allow their evolution into climate change resilient species. Yet, time is the prime prerequisite to prevent a global marine ecological collapse. There is still hope for the world’s coral reefs, as long as we slow down climate change.

This article was specialist edited by Kym Bain and copy-edited by Dzachary Zainudden.

1. For more information check out this website: https://www.scientificamerican.com/article/scientists-are-taking-extreme-steps-to-help-corals-survive/
2. https://www.nationalgeographic.com/animals/invertebrates/group/corals/
3. For more information check out this website:   https://oceanservice.noaa.gov/facts/coral.html
4. https://e360.yale.edu/features/how_long_can_oceans_continue_to_absorb_earths_excess_heat
5.  https://www.netflix.com/title/80168188
6. https://www.climate.gov/news-features/understanding-climate/unprecedented-3-years-global-coral-bleaching-2014%E2%80%932017
7. https://oceanservice.noaa.gov/facts/ninonina.html
8. https://www.scientificamerican.com/article/scientists-are-taking-extreme-steps-to-help-corals-survive/ 
9. https://www.nytimes.com/2012/07/14/opinion/a-world-without-coral-reefs.html
10. https://www.nytimes.com/2018/12/10/climate/coral-reefs-natural-selection.html  
11. https://news.stanford.edu/news/2009/may20/corals-052009.html