The phenomenon of coral bleaching

 GS Paper – 3, Conservation Environmental Pollution & Degradation.


According to the Great Barrier Reef Management Authority, which oversees the world’s biggest coral reef system, Australia’s Great Barrier Reef, the reef is now suffering a widespread coral bleaching event.

For the sixth time in six years, the coral reef system has been attacked by a widespread and destructive bleaching event, and it is the fourth time in the last six years that such an event has taken place. In conjunction with the bleaching event, the United Nations Educational, Scientific, and Cultural Organization (UNESCO) is now conducting a scientific mission in Australia for a period of ten days.

What exactly are corals?

Corals are made up of polyps, which are creatures that are genetically similar to one another. The microscopic algae zooxanthellae, which live within the tissues of these polyps, are responsible for their existence.

Corals and algae have a mutualistic interaction with one another.

ZOOXANTHELLAE rely on the coral to give them with essential nutrients and chemicals for photosynthesis to occur.

In exchange, the zooxanthellae provide the coral with organic products of photosynthesis, such as carbohydrates, which are used by the coral polyps in the production of their calcium carbonate skeletons, as well as other nutrients.

Zooxanthellae, in addition to providing corals with critical nutrients, are responsible for the vibrant colours and patterns found in corals’ natural habitat.

As such, they are referred to as “rainforests of the oceans.”

There are two types of corals: 

  • Corals that are stony and shallow-water in nature—the sort that form reefs.
  • Soft corals and deep water corals are corals that reside in dark, cold water and are soft to the touch.

What is Coral Bleaching and how does it work?

When corals are stressed by changes in environmental circumstances such as temperature, light, or nutrients, they eject the symbiotic algae zooxanthellae that live in their tissues, resulting in the corals turning entirely white in colour. Coral bleaching is the term used to describe this event.

The transparent calcium carbonate tissues, which are visible due to the lack of pigment-producing zooxanthellae, have a faint white colour due to the loss of pigment.

It is possible for corals to recover from stress-induced bleaching if the bleaching is not severe.

Coral bleaching has been occurring on a regular basis in the Caribbean, Indian, and Pacific oceans for some years.

What are the causes of coral bleaching?

Increase in Sea Temperature: Because most coral species reside in seas that are close to the hottest temperature they can endure, even a minor increase in ocean temperature can be detrimental to corals. El Nino raises the temperature of the ocean and causes coral reefs to die.

Ocean Acidification: As carbon dioxide levels rise, the seas absorb an increasing amount of carbon dioxide. This raises the acidity of ocean water and reduces the capacity of corals to build calcareous skeletons, which is critical for their survival in the ocean.

Solar radiation and UV radiation: Shifts in tropical weather patterns result in reduced cloud cover and increased radiation, both of which contribute to coral bleaching and coral reef degradation.

Infectious Diseases: The penetration of bacteria such as Vibrio shiloi affects the photosynthesis of zooxanthellae, which is a kind of algae. Because of the increased potency of these bacteria, higher sea temperatures are being seen.

Chemical Pollution: Increased nutrient concentrations have an adverse effect on corals because they encourage phytoplankton development, which in turn encourages a rise in the number of species that compete with coral for space.

Significant Sedimentation: Land clearance and coastal development cause high rates of erosion and a larger density of suspended silt particles, which can cause a variety of problems.

  • Smother corals after particles have accumulated (sedimentation),
  • lowering the availability of light (turbidity) and
  • It is possible that coral photosynthesis and development will be reduced.
  • Overfishing, pollution from agricultural and industrial runoff, coral mining, and the growth of industrial zones near coral ecosystems are all examples of human-induced threats that have a negative influence on corals.


Changes in coral ecosystems can have an impact on the species that rely on them for food and shelter, such as the fish and invertebrates that rely on living coral for protection and food. The extinction of such marine species has the potential to disrupt the whole food chain.

When corals perish as a result of bleaching, it is possible that genetic and species diversity may decline.

Divers and other tourists are attracted to healthy coral reefs. Tourism might be discouraged by bleached and deteriorated reefs, which can have a negative impact on the local economy.

Coral bleaching has the potential to create significant alterations in fish populations. This can result in fewer catches for fishermen, which has a knock-on effect on the availability of food and the economic activities that support it.

By absorbing continual waves from the ocean, coral reefs shield coasts from increased storm damage, erosion, and floods. People who live near the shore are therefore protected from increased storm damage, erosion, and flooding.

The Best Way Forward

  1. Solutions for ensuring the long-term viability of coral reefs must cross social, economic, and cultural borders to be effective.
  2. Putting a stop to uncontrolled coastal development would go a long way toward reversing the degradation of coral reefs in some areas.
  3. Coral conservation may be aided by encouraging sustainable fishing practises and giving chances for ecotourism.
  4. There is a pressing need to reduce the use of chemically enhanced fertilisers, insecticides, pesticides, and herbicides, which are non-biodegradable and can destroy corals and other marine organisms and ecosystems.
  5. Industrial waste that is harmful to the environment must be processed before it may be dumped in bodies of water.
  6. Water pollution should be avoided wherever feasible by refraining from discharging chemicals or oils into bodies of freshwater.
  7. The implementation of all feasible steps to prevent acts that aggravate global warming, given that climate change is the most serious worldwide danger to coral reef ecosystems.


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