Coral bleaching in 2020: The Great Barrier Reef and beyond

Written by Evan Quinter

Last week, Dr. Terry Hughes and Dr. Morgan Pratchett, scientists with the ARC Centre of Excellence in Coral Reef Studies (ARC), published the results of a two-week survey across the Great Barrier Reef (GBR). After conducting aerial and underwater assessments of 1,036 reefs, they discovered the GBR is undergoing a massive bleaching event. This is the first time where severe bleaching is recorded in all regions of the GBR, defining the 2020 wave as the most widespread bleaching event ever recorded (Figure 1). 

A close up of a map

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Figure 1: Maps of the GBR during the past three massive bleaching events. Notice how the most severe bleaching areas expand southward with each year. Photo credit to ARC 

Additionally, this year demonstrates the second harshest bleaching, preceded only by the mass bleaching in 2016. It’s important to note that the 2016 bleaching occurred during an El Niño period, part of the El Niño-Southern Oscillation (ENSO) atmospheric cycle that generates warmer and dryer conditions in Australia. However, 2020 is not an El Niño year, and still February of this year yielded the highest sea surface temperatures recorded in northern Australia (Figure 2). These extreme temperatures did not occur through natural causes; they are the result of increasing greenhouse gas emissions into the atmosphere

A graph showing sea temperatures in February around the Great Barrier Reef were the warmest on record
Figure 2: Sea surface temperatures in February 2020 were the highest recorded in the past 120 years, photo credit to the Bureau of Meteorology

The scientists found that 25.1% of surveyed reefs displayed signs of severe bleaching, with an additional 35% of reefs showing modest bleaching. Such high bleaching rates are expected to result in high coral mortality across the GBR.  As this is the third major bleaching event over the past five years, it is clear the recovery times are shrinking by the year. This is our new reality, where intense climate events occur with such frequency that coral cannot heal, and the ecosystem is in danger of collapse.

Coral bleaching occurs in particularly warm water, where corals are stressed to the point of expelling their symbiotic algae, zooxanthellae. The absence of algae exposes the underlying white aragonite skeleton, leaving the coral looking bleached. Without the photosynthetic microbes to provide food, coral need to actively hunt for their food or starve. Although coral bleaching does not immediately result in death, coral can only survive in this state for a short period of time before they are overgrown by competitive algae. 

The window for saving the world’s coral reefs is rapidly closing
Figure 3: The resulting appearance of a bleached coral colony, Photo credit to ARC

The GBR is not the only reef suffering this year. During February and March 2020, ARC researchers surveyed offshore reefs throughout the Coral Sea off the east coast of Australia. Of those studied, over half of the reefs experienced bleaching, some reefs with bleaching rates as high as 90%. Washed out coral colonies appeared down to 20 meters, demonstrating that even deep reefs, theorized to serve as potential refuge nurseries for some hard coral species, are stressed from warmer temperatures. In addition, the Maldives Marine Research Institute also reported dire trends for the upcoming weeks as temperatures are predicted to exceed the tolerable threshold. Sadly, coastal communities and island nations rely on reef ecosystems for economic security, natural resources, and cultural connectivity, global mass bleaching jeopardizes it all. 

Now, I know some of us may suffer from bad news fatigue, where each new headline seems to join a mill of depressive stories. And in the context of the global crises, like the COVID-19 pandemic and climate change, it makes sense to feel dismayed and overwhelmed. However, we cannot give up! Dr. David Wachenfeld, chief scientist at Great Barrier Reef Marine Park Authority said

“My greatest fear is that people will lose hope for the reef. Without hope there’s no action.” 

Let’s not lose hope. We still have the power to lessen our impact on the environment and move towards a brighter future. Now is the time to fight for the conservation of reef ecosystems, and it will take a collective effort, from coral reef scientists and community leaders to anyone interested in environmental advocacy, to secure the sustainability of reefs. We need to focus on the leading ailment to reef health – greenhouse gas emissions. By pushing for emission reduction strategies, such as stricter regulations and carbon taxing, we can mitigate the effects of climate change and preserve coral reefs.

 If you’d like to get involved or show your support, I’ve included local and international organizations below, which focus on coral reef research and conservation. Keep hope, enact change! 

The Coral Reef Alliance:

Coral Guardian: 

ARC Centre of Excellence in Coral Reef Studies:

Maldives Marine Research Institute:

Great Barrier Reef Foundation: 

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