Corals are one of the most amazing living creatures on the planet, with an incredible array of shapes and colors. These wonderful structures are mostly found on reefs, however, these reefs are under threat. 

The Great Barrier Reef has recently suffered from its third mass coral bleaching event, after two occurring in 2016 and 2017. This was after the Climate Council of Australia reporting that 93% of reefs in the Great Barrier Reef have suffered bleaching in 2016. The reefs of the world are dying and we will soon not have them unless we as a society change. 

Coral reefs are important to life. A quarter of marine life depends on coral reefs at some point in their life cycle even though corals are only found in under 1% of the planet’s oceans. So many species of fish and invertebrates rely on coral and form a symbiotic partnership with them. This relationship is vital in sustaining the life of these creatures.   

Unfortunately, the diverse reefs around the world are threatened by global warming and human interference. One of these problems that coral reefs face is that of bleaching. But what is coral bleaching and what causes it?

What Is Coral Bleaching?

In order to understand what coral bleaching is, it is important to understand the partnership that corals have with zooxanthellae. These are tiny organisms that live within the coral’s tissue and they get their energy from the sunlight. Then, the corals will feed off them. In return, the corals provide these organisms with protection and a place to live. 

The zooxanthellae are really important in order for sustaining the coral’s health as they provide corals with essential nutrients. These organisms also give the corals the wonderful and exciting array of colors they have. Having the zooxanthellae living within their tissues allows the coral to expand and grow. 

Coral bleaching refers to the phenomena in which corals lose their colors and appear white. This is caused by the corals expelling the zooxanthellae that live within them. The coral itself is not dead, but when bleaching occurs the coral’s life is threatened. The corals are very vulnerable at this point and therefore often die. 

What Factors Cause Bleaching?

This is a rather worrying phenomenon and does sometimes happen naturally. However, human causes have made bleaching occur more rapidly and widespread bleaching events have killed a lot of reefs. In order to protect the coral reefs of the world, we must understand what causes the bleaching and what humanity has to do to protect the corals. 

There are an array of reasons for coral bleaching, but it mostly happens when a change occurs in the coral’s habitat and thus causes stress. 

Warmer Waters

A big change that can cause corals to bleach is when the waters they live in have a change of temperature. If the waters get warmer, this will stress the corals and therefore trigger the bleaching to occur. 

This is one of the main causes of coral bleaching and it is directly linked to global warming. Right now, the ocean is absorbing the majority of greenhouse gas emissions with one study by the Intergovernmental Panel on Climate Change suggesting that 93% of the excess heat from greenhouse gasses since the 1970s.

Because of this, the temperature in the world’s oceans is increasing. The US National Oceanic and Atmospheric Administration (NOAA) studies the temperature of the oceans and has found that the temperature increases about 0.13°C per decade. This increase has been going on for at least 100 years and things will only get worse unless we act now.

Because the temperatures of the oceans are rising, delicate ecosystems around the world are being threatened. Coral reefs are one of them. Because the temperatures of the water is going up, corals get stressed and the bleaching process occurs. 


Polluted waters around coral reefs are also known to cause bleaching. Discarded waste from industry and humans run into the sea and the chemicals harm the corals, killing the zooxanthellae or stressing the corals enough to expel the zooxanthellae. 

Scientists at the Polytechnic University of the Marche Region in Italy conducted a study in which they examined corals and chemicals that humans use. Specifically, they looked at chemicals that are commonly found in sunscreen. 

The study found that four common ingredients that are found in sunscreen can cause viral infections within the zooxanthellae. This caused the zooxanthellae to explode, thus causing bleaching. 

These everyday products that we use are causing corals around the world to die and we must be aware of what we do that might directly harm the reefs. 

What Is The Significance of Coral Bleaching?

Unfortunately, the effects of coral bleaching are already causing extreme and unrepairable damage to the reefs of the oceans. 

The Great Barrier Reef

According to the BBC, The Great Barrier Reef has lost over half its corals since 1995. This is because of the warmer waters that have caused bleaching. The corals on the Great Barrier Reef are struggling to recuperate and become stable because of the amount of death surrounding them. 

The Great Barrier Reef has existed for millions of years, with corals thriving and growing on the top of deceased corals. However, because of the acceleration of coral bleaching and deaths, the reef cannot keep up. 

It is not just the corals that feel the devastating effects of global warming and pollution. 1,800 species of fish, 5,000 types of mollusks, and over a hundred species of sharks all rely on the Great Barrier Reef, inhabiting the waters, feeding, or finding protection within the incredible fauna. The diversity of the creatures in such a small part of the ocean is a natural wonder, and all these creatures are under threat. 

Caribbean Coral Reefs

The coral reefs in the Caribbean have been significantly affected because of coral bleaching. According to The Guardian, the coral reefs in the region have all declined by over 50% in the last fifty years. Scientists predict that all the coral reefs in the Caribbean will be gone in the next twenty years unless we act now.  

What Can We Do?

The ocean is under severe threat and so much irreversible damage has already happened. However, there is power in the people and if we work together we can save the corals. 

Spreading the word and putting pressure on policymakers are things that we can do personally to assist in the protection of the coral reefs. In writing letters to our politicians and supporting conservationist groups we can make our voices heard.

Another thing we can do to assist in the protection of the coral reefs is to be aware of the products we are using and what chemicals might be in them. We may feel like we are not really connected to the ocean, but everything is connected! The products we use might end up in the oceans and thus cause damage to the coral reefs. 

The world is now waking up the crisis that we are all in, and making our voices heard and spreading the word means that we can change things!


Everything You Need to Know About Coral Bleaching—And How We Can Stop It. World Wildlife Fund. Retrieved 7 January 2021, from  

Ocean warming. (2018, December 5). IUCN. 

Tibbetts J. (2008). Bleached, But Not By The Sun: Sunscreen Linked to Coral Damage. Environmental health perspectives, 116(4).

What is coral? What are the causes, impacts, and solutions of coral bleaching? Greenpeace East Asia. Retrieved 7 January 2021, from  

What is Coral Bleaching and What Causes It – Fight For Our Reef. (2020, December 18). Australian Marine Conservation Society.