Coral Bleaching: Causes, Consequences and Cures

Coral bleaching

You’ve probably heard the term “coral bleaching” thrown around a lot in the news and scientific circles in recent years. However, you may not know exactly what it means, the consequences of it and if it can be fixed.

Coral reefs are large yet intricate underwater structures made up of dead and living invertebrates called corals, as well as thousands of tiny marine animals called polyps. These diverse assortments of species interact with each other and the physical environment around them, bringing in food, nutrients, and oxygen to support whatever lives within it.

So, what is coral bleaching? Well, corals have a mutually beneficial relationship with microscopic algae called zooxanthellae, which it relies upon to survive and thrive. The algae are photosynthetic and live within the tissues of the coral, giving it typically a soft brown colour and providing it with food in return for protection.

When coral becomes stressed due to a change in environmental conditions, the algae leave its host. Without it, the coral is left vulnerable and begins to turn white – coral bleaching. It’s now also very susceptible to disease, and in time, even at risk of starving to death.

Coral bleaching

The first internationally recognised case of coral bleaching was in 1998, and it killed 8 percent of the world’s coral alone, but the Australian Institute of Marine Science (AIMS) has been monitoring mass bleaching events on the Great Barrier Reef since the early 1980s. Wide-scale bleaching events in 1998, 2002, 2006, 2016 and 2017 were caused by unusually warm sea surface temperatures in summer, whilst bleaching in 2008 and 2011 was caused by an influx of freshwater.

Bleaching can interrupt a coral’s chance at reproducing for a year or two, and if it persists and becomes more frequent, the coral has little time to recover and can be left permanently damaged.

The leading causes of coral bleaching are:

  1. Climate change
  2. Direct sunlight
  3. Low tides
  4. Pollution
  5. Construction
  6. Overfishing

According to a recent report by the Washington Post, the world lost 14% of its coral reefs between 2009 and 2018 due to climate change alone. A warming planet means an increase in water temperature, and no matter how slight a rise in degrees, it can interrupt the delicate balance going on in the ecosystem and cause coral to drive out algae. Warmer weather also means hotter conditions above the water, and an overexposure to sunlight or hot, open air – especially during low tides - can bleach coral growing in the shallows.

Pollutions and run-offs as a result of construction in close proximity to the ocean leaves coral prone to bleaching, as dilution and debris will stick to reefs close to the shore. Agricultural run-offs such as fertilisers can change the nitrogen concentration in the water and promote the growth of competitive algae that overgrow corals. Industrial scale fishing has negative repercussions too, as the fish that normally keep the coral clean are taken out of the ocean, leaving the reef overgrown and smothered.

Around the world, coral reefs are home to 25% of all marine animals and plants, but the consequences of bleaching harms humans too.

The decline of coral reefs would threaten around half a billion people who rely on them for food and protection. Reefs help limit erosion and flooding catastrophises for over 500 million residents worldwide, by absorbing the energy of waves as they flow over. People who work in tourism and recreation-based jobs and businesses also rely heavily upon the health of coral reefs.

But it’s not all doom and gloom. Through studying a coral’s reactions, its tolerance levels and its ability to adapt, scientists have noticed that most reefs around the world have remained resilient despite environmental adversity.

There has actually been an increase in global coral cover between 2002 – 2009, showing that it has the potential to recuperate and repopulate.

A reef repairing itself after coral bleaching

Coral reefs in east Asia, for example, had more coral in 2019 than they did in 1983, despite being impacted by mass coral bleaching events. This proves that reefs with a high coral cover to begin with can withstand stress better than expected, and build up a degree of natural resistance.

This is why reef restoration is so important.

Future coral bleaching events are sadly a given, but there are a number of steps we can take to give them a better chance of bouncing back and avoiding irreversible damage.

A proper, politically backed global effort to reduce carbon emissions globally is a good start (and a long overdue one). This will lessen the rise of ocean temperatures worldwide, whilst closer to home, states and regions should focus on delivering good water quality and filtration. Managing the impact of coastal development, trawling and shipping is important too, and businesses should be more aware of their carbon footprint.

Legendary Australian reef researcher and the so-called ‘Godfather of Coral’ Charlie Veron was the recent focus of the ABC’s ‘Australian Story’. Charlie, along with his colleagues, is on a marine mission to protect the Great Barrier Reef from further harm by building a ‘coral ark’. After finding patches of healthy reef amongst the dead coral, Charlie realised that it wasn’t too late to try and reverse the destruction. The painstaking but ingenious process will involve collecting one of every species of coral to create a coral biobank, keeping them alive in aquariums. Then, at a later date and when “the technology is right” it can be integrated back into the ocean to regenerate the reef.

Back on dry land and on a more personal level, we have the power to prevent coral bleaching from becoming an underwater epidemic too. As individuals, the type of sunscreen we choose is having an impact. Whilst it’s vital for protecting ourselves, it needs to protect our oceans too, and that’s why using a reef-safe sunscreen is so important.

Although corals have their own sunscreen-like protective layer, we need to give them a helping hand by limiting the amount of chemicals we bring in to the water on our bodies and equipment, and try to offset our greenhouse gas emissions as much as possible.

So, here are our top 10 tips for reducing the chances of causing coral bleaching:

  1. Eat less seafood, and if you do, choose as locally and responsibly sourced as possible.
  2. Eat less meat! Livestock farming is a major contributor to climate change
  3. Plant trees! We need to restore our forests so they can sequester carbon from the atmosphere.
  4. Support / donate to reef restoration initiatives and projects
  5. Volunteer with beach clean-ups and other environmental charities
  6. Reduce your personal pollution such as household rubbish and plastic waste
  7. Limit the amount of chemicals you use and dispose of them correctly
  8. Practice safe and responsible scuba diving, snorkelling, boating and fishing
  9. Opt for fuel-efficient modes of transport where possible. When flying, find out how you can offset your carbon footprint.
  10. Seek out reef-safe sunscreens and products

And remember, every People4Ocean purchase directly funds non-for-profit initiatives to protect and restore endangered coral reefs worldwide!

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