Coral Bleaching: A Complete Overview

Editorial Analysis for IAS - Coral Bleaching: A Complete Overview

An Overlook into Coral Bleaching


• The management authority of the world’s largest coral reef system, Australia’s Great Barrier Reef, confirmed on March 25 that the reef is experiencing a mass coral bleaching event.
• This is the sixth time that the coral reef system is being hit by a widespread and damaging bleaching event and the fourth time in six years that such an event has occurred.

What exactly is it?

• Corals are marine invertebrates or animals not possessing a spine. Each coral is called a polyp and thousands of such polyps live together to form a colony, which grows when polyps multiply to make copies of themselves.
• Corals are of two types — hard coral and soft coral.
• Hard corals, also called hermatypic or ‘reef building’ corals extract calcium carbonate (also found in limestone) from the seawater to build hard, white coral exoskeletons. Soft coral polyps, however, borrow their appearance from plants, attach themselves to such skeletons and older skeletons built by their ancestors.
• Soft corals also add their own skeletons to the hard structure over the years and these growing multiplying structures gradually form coral reefs.
• They are the largest living structures on the planet.
• Corals share a symbiotic relationship with single-celled algae called zooxanthellae. The algae provides the coral with food and nutrients, which they make through photosynthesis, using the sun’s light. In turn, the corals give the algae a home and key nutrients.


About Coral Bleaching:

• When corals are stressed in their environment, such as by changes in temperature, pollution, or excessive levels of ocean acidity, they bleach.
• When coral polyps are agitated, the zooxanthellae, or food-producing algae, inside them begin to produce reactive oxygen species, which are harmful to the corals.
• As a result, corals eject the color-producing zooxanthellae from their polyps, revealing their pale white exoskeleton and giving them a bleached appearance.
• This also puts an end to the symbiotic interaction that allows corals to thrive and survive.
• Bleached corals can survive depending on the severity of the bleaching and the return of normal sea temperatures.
• The zooxanthellae can return to the corals and reestablish the alliance if the heat pollution subsides over a few weeks, but catastrophic bleaching and death are likely.



• Even while coral reefs only cover 1% of the bottom, they support approximately 25% of marine species, including fish, turtles, and lobsters.
• Reef-supported marine life feeds the world’s fishing businesses. Even whales and huge clams rely on the reefs to survive.
• Furthermore, coral reef ecosystems provide $2.7 trillion in yearly economic value through commerce in goods and services, as well as tourism.
• In pre-COVID Australia, the Barrier Reef earned $4.6 billion in yearly tourism revenue and employed over 60,000 people, including divers and tour guides.
• Coral reefs provide protection from storm waves in addition to adding economic value and supporting aquatic life.
• If there are enough fish species that can graze on the weeds, dead reefs can be revived over time.

Great Barrier Reef:

• The United Nations Intergovernmental Panel on Climate Change (IPCC) has reported that the great barrier reef is in great danger.
• After this even the authorities in Australia have confirmed that mass bleaching phenomenon is affecting the coral ecosystem.
• It’s a first that the current bleaching event has occurred during a La Niña weather pattern.