What coral bleaching reveals about climate change

The word’s largest living structure, Australia’s Great Barrier Reef, suffered massive coral bleaching this year – an unprecedented second year in a row. This marine system half the size of France has suffered four major bleaching events in less than 20 years, namely in 1998, 2002, 2016, and 2017.

What is coral bleaching

Zooxanthellae are tiny, colourful marine algae that live inside corals, providing them with colour and food. Bleaching (corals turning white or very pale) is the result of this symbiotic algae being expelled due to stressors like pollution, excessive sunlight or unusually high water temperatures.

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Photo taken by marine biologist Brett Monroe Garner on the Great Barrier Reef between Port Douglas and Cairns show bleaching of corals. Photograph: Brett Monroe Garner/Greenpeace

Without algae, corals turn pale, grow weak and become more susceptible to disease. While bleaching does not lead to immediate death, the corals will die if conditions don’t improve fast enough.

coral bleaching
Image source: National Oceanic and Atmospheric Administration. Click here for larger view.

A catastrophe 30 years too early

According to a National Geographic article, 2016’s bleaching event at the Great Barrier Reef was the worst ever. It struck the northern portion of the reef, killing about 67% of the corals along a 500-mile stretch north of Cairns. All that damage was done in less than a year. In comparison, just a few years ago, scientists showed that it had taken more than 25 years to kill just over half of the corals on other stretches of the reef.

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Mature staghorn coral comparison between the short period of February 2016 and April 2016. Picture: Terry Hughes et al./Nature
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Great Barrier Reef before and after photos shot by Professor Terry Hughes. — Picture: Terry Hughes et al./Nature

Professor Terry Hughes, director of the Arc Centre of Excellence’s Coral Reef Studies project at James Cook University, told environmental journal Nature that scientists didn’t expect to see this level of destruction for another 30 years.

This year, aerial surveys revealed some troubling results: the central section that was mostly spared last year has been hit, allowing existing damage to spread another 640km.

A Global Problem

Coral bleaching is a problem that extends beyond Australia.

In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined. (Information source)

Even corals in Singapore are not spared. In June 2016, coral reefs along the fringes of the Southern Islands and in the north-east of Singapore were reported to be bleaching, due to the higher-than-usual sea temperatures triggered by the El Nino.

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Bleached coral at Big Sister’s Island in June. ST PHOTO: LIM YAOHUI

Corals take at least a decade to recover

The fastest-growing corals take a decade or more to make a decent recovery, while slower-growing corals take far longer. That said, corals are resilient creatures. If conditions do improve, many corals can be recolonised by algae and recover.

Climate change and what we can do

Climate change is one of the biggest global environmental challenges today. The use of energy, which is primarily produced through the burning of fossil fuels, is one of the main culprits. Greenhouse gas emissions drive ocean temperatures up, which threatens the future of coral reefs, and the natural environment as a whole.

To learn about the science of climate change and practical ways to use energy efficiently, download the brochure Climate Change: How It Affects You, created by Singapore’s National Environment Agency. Or watch the video below:

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