Coral Bleaching- The Doomed Ocean

The warming Earth has been a burning issue for every Environtalist, Climate scientists, and common person. Global warming is affecting every aspect of our life. Global warming is also behind an issue that is related to biodiversity, survival, and recreation. Coral bleaching, it not an unknown term, but there are still many facts and information left to discover. Also called “Rainforest of the sea”, these diverse ecosystems are threatened to disappear. After the major bleaching event in 2016, almost 50% of the corals around the world bleached.

Coral Bleaching is a process in which Microscopic algae called Zooxanthellae leaves the shell of coral pylops due to some stressful conditions and turns white. These conditions can be pollution, a change in temperature, sedimentation, or coastal development.

Coral Reefs and their formation

coral roofs are underwater ecosystems rich in biodiversity. They are formed by the accumulation of single coral polyp. These polyps are joined by an exoskeleton of calcium carbonate(caco3). These coral polyps establish a symbiosis relation with Zooxanthellae. Zooxanthellae is a single-celled alga. It manufactures the food and nutrition for a polyp in the exchange of living space. In stressed conditions like pollution, changes in temperature, and sedimentation zooxanthellae left the coral tissue, therefore, turning them white. pollution means an increase in the level of carbon dioxide. While sedimentation happens because of coastal development, agriculture runoff, or sewage.

Change in temperature can be mistaken only for an increase but that’s not the case. Change in temperature can have two meanings. The Zooxanthellae wants a particular temperature. When the temperature increases 1 degree C it affects corals. The symbiotic relationship starts dissolving which eventually takes to bleaching. Due to a rise in temperature or a drop in temperature coral bleaching can happen. Zooxanthellae are also responsible for the bright color of corals. So when they leave polyps’ tissue coral turns white. These bleached corals can’t starve without algae, hence leaving them very vulnerable. On the website of NOAA, they have put forth an understanding of coral bleaching and its causes.

Causes of coral bleaching

There are many reasons behind coral bleaching. It happens because of two reasons human-based like coastal development or tourism, and nature-based like pollution, storm or predation. Although nature-driven causes are also furthering because of human involvement.

Nature-driven causes of bleaching:

Rise in temperature

The biggest reason behind coral bleaching is the contribution of the rise in temperature. As the world is warming and heat is trapped because of the greenhouse effect, our ocean also has a rise in temperature. When the ideal temperature of coral reefs differs zooxanthellae leaves the tissue turning them white. If the condition goes back to normal then zooxanthellae will return but if the condition persists for a long time, corals may die or can get infected.

Massive coral bleaching events happen because of an increase in temperature. Although lower temperature also triggers bleaching. But there are some cases where the low temperature has resulted in severe coral bleaching, like coral incidence in Florida.

The rise in CO2 level

Pollution is taking its toll on the planet earth. The very same way oceans are also facing this catastrophe. Oceans works as carbon sinks and they absorb more carbon than the tree. As a result, the carbon level in oceans is rising which is leading to acidic oceans. In a normal scenario, oceans are alkaline which is good for many marine species because they carry a skeleton made up of calcium carbonate CACO3. Coral reefs are made up of CACO3 exoskeleton. Corals need 27 to 40% salinity level to make their exoskeleton. Because there is a rise in acidity of the ocean many marine species including corals are unable to make exoskeleton. Because there is a change in the chemical composition of the ocean it can be hard for corals to make exoskeletons to sustain their colonies.

Intense Storm

With the increase in global warming, the intensity of storms is also increasing. As a result, coastal regions are heavily affected therefore coral reefs are no exception. Hurricane or Cyclone takes their energy from the ocean so hotter the ocean more intense the storm will be. Storm destroys coral, make the water murkier and unclear for weeks.

coral reefs are also in danger by earthquakes, Tsunamis, and seasonal variations.

Human-driven causes of bleaching:

Coastal development

Development sounds good and promising with future opportunities. But in most of the case, we only focus on the achievement of goals without giving much thought to the situations surrounding it. It is true that In the case of coastal development local communities have benefited but in almost all case it had a very negative impact on the coastal ocean and their biodiversity. With no exception, the coastal development near coral reefs had distributed the marine life there. Because of the increase in tourist numbers, the pressure on coral reefs had increased. Many resorts and hotels have built on the shorelines for accommodation. In their construction sedimentation increases. Sedimentation is a process in which suspended and heavy particles rest against a solid surface. In this case, because of sedimentation corals become weak and suppressed by algal bloom.


In coral reefs, people always go for diving because reefs are rich in marine life. There are some protocols about how to dive in coral reefs without affecting marine life and corals. In most cases, these rules get neglected. People while diving in coral reefs get too excited that they forget these rules. As well as Boats while throwing their anchor break corals. More the number of people more the damage these corals can get.

Most of the hotels near shoreline don’t think much about sewage treatment plants especially if the local community is poor, not aware. Untreated sewage gets disposed of in the ocean and increases sedimentation. These sediments deposited on the coral surface and block the process of photosynthesis. Lack of photosynthesis can badly affect the growth of zooxanthellae and corals.


Corals reefs are a huge source of food. The high demand for coral fishes for food and trade are making their populations decline very fast. Firstly fishermen practice fishing which is not sustainable as per reef health and fish population. Secondly, they sometimes use dynamite and other methods to break coral reefs so they can reach to more exotic species. These marine lives give balance to the coral reef ecosystems which in the imbalanced condition leads to stress over the reef ecosystems.

Agriculture Runoff

Coral reefs in the vicinity of developing or island country where poverty is a big issue gets very little protection. Although the awareness about these resources and others has increased tremendously in the past few days there is still a big problem of agriculture runoff. The agriculture field near-shore increase the sedimentation and pollution problem. In the case of over-irrigation or rain, The chemicals and fertilizers wash into the sea. They make coastal water unclear, increases the sedimentation, worsening the coral bleaching problem.

Coral predation

After bleaching corals became vulnerable for the attack of predators like large sea stars like crown-of-thorns (Acanthaster planci). These massive starfishes eat over coral tissue. Bleached and affected corals become unprotected. As a result, they can be overtaken by Algal bloom. In low tide conditions, they become exposed to the sun which can dry their tissues. The effect of intense storms is very prominent in low tide areas.

how coral bleaching can affect Us?

Coral reefs sustain 25% of the total marine life of the planet and almost every species depends on them directly or indirectly through the food chain. According to the United Nations Atlas of oceans, coral reefs contain almost 4000 species of fish and 800 species of reef-building corals. As per ICRI (international coral reef initiative), all coral reefs have an economic value of approximately $30 billion per year. Approximately 500 million people depend on coral reefs for tourism, food, or income.

Other than these economic benefits coral reefs act as protective shoreline and reduce the damage of storms. In their absence will lower the protection.

how can we save coral reefs?

The most prominent way to protect coral reefs is switching from coal and petroleum to renewable energy resources like solar and wind. The excess use of exhaustible natural resources is the main reason behind global warming and climate change. When oceans absorb CO2, they turn acidic. The more use of renewable energy will help lower CO2 emissions and thus global warming. If we won’t do anything it then all the reefs will go extinct in 2050.

Tourists should follow the protocols while visiting coral reefs. They should swim and walk carefully without breaking corals. The fishing should follow sustainable practices and the use of dynamite or other destructive material should be banned in coral reefs. We all have to work together in protecting our reefs. We have to protect these biodiverse ecosystems so our future generation will experience them.

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