Coral Bleaching Definition And 4 Natural Causes

coral bleaching

Coral bleaching is one of the most significant and under-reported environmental issues today. It has been observed in many parts of the world, including Australia’s Great Barrier Reef (GBR).

Coral bleaching definition

Coral bleaching is a process where the coral polyps expel algae from their tissues. Coral bleaching can be either caused by physical stress or due to changes in temperature, acidity, and light levels. This is an indication that the coral polyps are under stress from environmental disturbances.

Coral bleaching does not always lead to the death of all corals, but it can also cause significant changes in the composition and structure of the coral community on a reef. Corals have evolved complex symbiotic partnerships with algae known as zooxanthellae. This partnership has a mutually beneficial relationship because the algae provide food to the coral polyps and also supply them with oxygen. When environmental disturbances occur, this symbiotic partnership can be disrupted which causes bleaching.

What Causes Coral Bleaching?

coral bleaching

Coral bleaching occurs when the symbiotic algae living in coral tissues (zooxanthellae) are expelled due to changes caused by high water temperatures or acidification. This leaves corals vulnerable and susceptible to disease, which can lead to death without rapid intervention. Coral reefs provide habitats for about 25% of all marine life on Earth. When these habitats are destroyed, the ecosystem suffers.

Coral reef ecosystems provide many benefits to humanity including shoreline protection and recreation opportunities. Coral reefs also have significant economic value—the GBR is worth $33 billion annually from tourism alone.

Reefs also help regulate climate by absorbing CO₂ gas dissolved in seawater and converting it to calcium carbonate, the material that builds coral reefs.

Caddisfly Life Cycle

The most effective way of reducing climate change is by implementing a transition from fossil fuel-based energy production to renewable sources such as solar and wind power.

The second best option would be for countries with high CO₂ emissions (such as Australia) to plant more trees that will absorb CO₂ and provide a more sustainable energy source.

Why is coral bleaching bad?

Coral bleaching is bad because it can lead to coral death. Global warming is one of the factors that cause this, as warmer water temperatures cause corals to expend energy and produce disease-causing proteins called heat-shock proteins. When they are under stress from being too warm or losing too many algae, their colors start turning white.

Coral bleaching is usually temporary, but if the stress continues for a long time, and particularly an extended period of very warm water temperatures that we’re seeing now or in 2005-2007 when this happened last, corals may die.

The National Oceanographic and Atmospheric Administration released “the most up-to-date global coral bleaching event maps” that show “where in the world corals are most at risk.”

If coral reefs die, it will have a huge impact on coastal communities and economies. Coral reef protection is important because they provide food security for over 275 million people globally, generate income from tourism (over $30 billion annually), act as wave breakers and storm buffers, protect the shoreline from erosion, maintain water quality by filtering out pollution, and provide coastal protection from tsunamis.

Coral reefs are also a beautiful part of our environment that has been around for 500 million years!

What are the four causes of coral bleaching?

coral bleaching

Causes of coral bleaching can include:

  • Global warming/climate change;
  • Thermal stress (e.g., unusually hot water);
  • Pollution, e.g., from agricultural runoffs or sewage outflows; and
  • The arrival of destructive invasive species.

What are the effects of coral bleaching?

  • The main effect of coral bleaching is the loss of living corals. This decreases biodiversity and leads to the destruction of reefs, which impacts animal populations. Coral deaths also cause economic losses for communities dependent on tourism.
Mud Fiddler Crab (Uca Rapax)

The most important factor in predicting a reef’s vulnerability to climate change is its proximity to the equator. The closer a reef is to the equator, the more likely it will be affected by coral bleaching.

The prevalence of human activities such as fishing and coastal development also play a role in predicting vulnerability because they may cause stress on reefs that can increase their risk for bleaching events.

How to prevent coral bleaching

Coral bleaching is a natural process that occurs when ocean temperatures rise. It can be caused by both global warming and localized issues such as agricultural runoff, but the most significant cause of coral bleaching in recent years has been increased water temperature.

When corals are exposed to unusually high levels of sunlight for an extended period of time they expel the algae that live in their tissues. This makes the corals vulnerable to infection and death, as they no longer have any symbiotic algae for food or protection from predators.

Solutions include:

  • reducing carbon emissions to reduce global warming.
  • cutting back on single-use plastics such as straws and baggies which release chemicals into our waterways when discarded and
  • reducing the amount of fertilizer we use in our yards.

Coral bleaching Great Barrier Reef

coral bleaching

Coral bleaching has been a significant problem for the Great Barrier Reef. This is because of climate change and warmer water temperatures, which are damaging to coral reefs by causing them to lose their source of protection and become more susceptible to disease. Coral have high levels of algae living inside them – this provides it with nutrients so that it can survive. The warmer water temperatures cause the coral to reject these algae, which means that they are left without a key source of nutrients and protection.

The Great Barrier Reef is made up of more than 900 individual reefs and spans over 2300km in length – it’s also home to more than 600 different types of corals. If we continue with the current climate change trends, we could lose most of the Great Barrier Reef by 2030 because it’s predicted that 93% of the coral will be lost. Scientists have raised concerns about what this may mean for other marine life and tourism in Australia.

Tubifex Worms - Culturing And 2 Weird Reproduction System

Factors responsible for coral bleaching

A few factors that are responsible for coral bleaching are:

  • Rising air and water temperatures.
  • Increased ocean acidity levels due to CO ² emissions
  • Overfishing of marine life, which increases nutrients in the oceans.

These factors lead to higher stress on the corals making them more vulnerable when it comes to dealing with changes like low light or high light, low nutrients or high nutrients.

Ocean acidification and coral bleaching

coral bleaching

Coral bleaching occurs when the oceans become more acidic because of global warming. When acid levels rise, symbiotic algae that live in corals flocculate and lose their coloration, making it impossible for them to grow or reproduce. This process leaves coral reefs unable to sustain life and leads to a greater risk of mass species die-off.


Coral bleaching is an environmental stress response that causes coral to expel the algae living in their tissues, which provide them with food and color. The corals then turn white, or “bleached.”

In 1998, scientists had observed a severe global bleaching event for the first time, affecting over 60% of reefs globally. This was followed by a second major bleach event in 2010.

A new study published in Nature on Wednesday, Oct 18th found that the bleaching events of 1998 and 2010 were caused by unusually high water temperatures linked to global warming. This is leading some scientists to sense an environmental catastrophe coming for coral reefs globally if we don’t reduce our carbon emissions soon enough.