What is coral bleaching?

 coral bleaching

The coral and the algae ‘zooxanthellae’ share a symbiotic relationship and 90% of the nutrients that are produced by the algae are transferred to the coral hosts. But this relationship gets affect when corals face stress by changes in conditions such as temperature, light, or nutrients. As a result, they expel the symbiotic algae zooxanthellae living in their tissues, causing them to turn completely white. This phenomenon is known as Coral Bleaching.

Causes of coral bleaching

  1. Rise in sea temperature: Many corals grow optimally in water temperatures between 23°–29° Celsius. A slight increase in ocean temperature can harm corals.
  2. Ocean Acidification: This means increase in the acidity of ocean water due to rise in carbon dioxide and inhibits the corals ability to create calcareous skeletons, which is essential for their survival.
  3. Solar radiation and ultraviolet radiation: Changes in tropical weather patterns result in less cloud cover and more radiations. It leads to more intense UV rays come to the surface of the earth.
  4. Anthropogenic threats: Over-fishing, greenhouse gas emissions, pollution from agricultural and industrial runoff, coral mining, recreational misuse, development of industrial areas near coral ecosystems, micro-plastics, burning of fossil fuels etc. affects corals adversely.         
  5. Chemical pollution: Oil spills, pesticides, heavy metals etc. also damage corals


According to the IPCC’s Global Warming of 1.5˚ C report, if ocean temperatures rise 1.5˚ C, coral reefs are subject to decline 70 to 90 percent more; at 2˚C, we would largely lose all the coral reefs. The day the reefs disappeared, marine biodiversity would suffer huge losses. The ocean bottom would be taken over by forests of seaweed.

For many unique species of fish deep under the ocean, corals are their only safe habitat. A lot of them and some sea turtles will die.

Since corals clean the water, remaining species, including dolphins, would be left to survive in very murky waters. They might soon disappear as well.

What about humans? Will it affect humans also? The answer is ‘Yes’. Since reefs support fish, they also support the fisheries, feeding and giving jobs to 500 million people in tropical countries like Indonesia, Malaysia and the Philippines.

The local tourism industries would crash. No one wants to dive into a forest of seaweed. With no corals left, coastal countries would lose a huge amount of annual income.

Coastlines will not be protect from flooding in extreme storms. Coral provides a natural breakwater, and a buffer against erosion. Without it, water would push local residents out of their homes.

As the ocean spread out, the residents of these densely populated islands would have nowhere to go. The countries might vanish from the planet together with the reefs. Without seafood there would be increase pressure on farms to make up for the shortfall in protein. This might turn into a global food crisis.

 As the damage of coral reefs affect globally, steps need to be taken to conserve them. Otherwise all creatures on earth would be affect and become extinct very soon.

See also : coral Reefs

Leave a Comment