Coral Bleaching: What Is It and Is There Anything We Can Do About It?

coral bleaching

While coral bleaching is basically a normal process that corals undergo, it’s not good for them or the marine environment. When it happens en mass, it can be devastating for reefs and all the marine life that depends on them.

Since a quarter of sea life depends on reefs and the ecosystems they create, the death of the world’s reefs would have serious consequences for all sea life. If the reefs go, so too do the fishing communities, tourism industries, and various economies that centre around them.

Australia, home to the world’s largest reef system, could be doing more to protect it. Earlier this month, a government agency quietly released a crucial report on the health of the Great Barrier Reef and, specifically, the extent of coral bleaching. The report found that 91% of reefs surveyed had experienced bleaching in 2021 and 2022, the sixth mass bleaching event in 24 years.

So, what exactly is coral bleaching? How bad is the current state of the world’s reefs, and can we do anything to stop this process from happening? Here’s what you need to know:

What is Coral Bleaching?

Put simply, when corals get stressed they simply give up and, let’s be honest, it’s highly relatable behaviour.

Corals are technically invertebrate animals, like crabs or spiders, that are not really one thing. They are ‘colonial organisms,’ meaning they’re made up of lots of different distinct species all living symbiotically together.

Hard corals, the kinds you think of when you picture a coral, are really soft tubes that filter seawater and use the calcium in it to build up a hard exoskeleton around themselves. On the surface of these exoskeletons are microscopic algae known as zooxanthellae, which help the coral by cleaning it and providing nutrients, getting carbon dioxide and ammonium from it in return, so that they can photosynthesise. It’s a delicately balanced relationship.

The algae living in the coral is actually what gives the coral its colour, otherwise, it would be white since it’s made up of calcium. Essentially, coral bleaching is the zooxanthellae in coral being expelled by the coral organism when it gets stressed.

What does coral get stressed about? Well, lots of things, including pollution, chemicals in sunscreen, and acidity, but the main one is if the water is too warm; the coral doesn’t like it and their symbiotic relationship with the algae living on it breaks down; the algae leave and the coral turns white.

Bleached coral is not actually dead, although, without the algae, the coral is very likely to starve or die of disease.

Since 1950, the world has lost half of its coral reef systems. Over the past 40 years or so, almost all the remaining coral on Earth has been affected by bleaching. In 2016, during an El Niño event, 70 per cent of the world’s reefs experienced some form of bleaching. The Intergovernmental Panel on Climate Change says bleaching is the greatest threat to the world’s reefs, with 60 per cent at immediate risk of being lost.

In Australia, as per the government’s ‘Reef Snapshot’ report, above average water temperatures over the summer we’ve just had caused coral bleaching throughout the entire 2,300km reef system. The most affected areas were reefs between, roughly, Mackay and Cooktown, a 1,000km stretch where 90 per cent of coral is thought to have bleached.

Lissa Schindler, a campaign manager with the Australian Marine Conservation Society, said that the report was “devastating news for anyone who loves the reef.”

“Although bleaching is becoming more and more frequent, this is not normal and we should not accept that this is the way things are. We need to break the norms that are breaking our reef,” said Schindler.

Worryingly, this is the first bleaching event on the reef recorded during a La Niña year, when ocean temperatures are typically cooler. These events are expected to occur more frequently as we fail to deal with climate change.

Is There Anything We Can Do to Stop Coral Bleaching?

The most important action we could take to stop coral bleaching would be to end fossil fuel emissions, right now.

In response to the Reef Snapshot report, Dr Simon Bradshaw, Director of Research at the Climate Council, said: “This is an issue that cannot be solved with big shiny funding announcements.”

“The science is very clear, in order to protect the world’s reefs from total destruction, we must dramatically reduce emissions in the 2020s.”

“Not 30 years from now, this decade,” said Bradshaw.

While that would be ideal, even stopping now wouldn’t solve everything. In the short-term, much of the warming we are experiencing and are yet to experience is locked in. Carbon dioxide in the atmosphere takes between six and 30 years to affect the temperature of the planet, meaning all the warming we’ve already experienced is from carbon dioxide we released decades ago.

On top of that, carbon dioxide, as it’s absorbed into the ocean, causes a rise in acidity which also stresses corals as well as most other things that live in it. Scientists are pretty sure we’re very close to a tipping point with ocean acidity that would lead to the mass extinction of all marine life (if that’s the kind of thing you want to read about) and by then, the coral will be the least of our concerns.

That aside, coral bleaching is reversible, as the coral is not actually dead, as stated above. Cooling temperatures, a lowering of harmful chemicals in the water, and reversing acidity will return the algae to their coral homes and the colour to the coral. In order for that to happen, corals need time to recover, with some estimates saying a decade or more of good environmental conditions are necessary.

The problem is that bleaching events are happing in the same areas in back-to-back seasons, giving the coral very little time to recover. When this happens, corals die off for good.

We can, however, do our best to give them a break. Reducing our own direct impact on the reefs by cutting pollution in the oceans, banning fishing on the reefs, and protecting them from boat damage will all give coral the best shot at recovery. Marine protection organisations like the Coral Reef Alliance are working hard on implementing these measures worldwide, and collaborating with local community groups to enforce protections, divert pollution, and offer alternative employment options to fishing.

Rapidly stopping the release of carbon dioxide into the atmosphere, by shutting coal and gas-fired power plants and transitioning whole industries like transport to renewable sources, is however still the best thing we as a species can do to reverse coral bleaching. Scientists say there is still time to save the reefs if we act now.

Not all reefs are uniformly affected by bleaching. Some, like those in French Polynesia and other Pacific Islands, have been protected from bleaching events and survive as an oasis of pristine habitat in an otherwise globally dire system. Protecting these places is now a top priority for conservationists, who believe it is still possible to preserve at least some of the world’s underwater paradises.

If we don’t act soon, change our ways, and focus on protecting what we still can, it will be a very colourless undersea world in the future.

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