Context

The US National Oceanic and Atmospheric Administration and International Coral Reef Initiative have confirmed that the world is witnessing its fourth global bleaching event. They have confirmed that the world’s worst ongoing global coral bleaching event has now affected nearly 84 per cent of the world's coral reefs.

What are corals?

Corals are marine invertebrates that belong to the phylum Cnidaria and class Anthozoa. They're best known for forming coral reefs, which are some of the most diverse and vibrant ecosystems on Earth.

• Corals are animals, not plants or rocks.
• Each coral is made up of tiny, soft-bodied organisms called polyps.
• These polyps live in colonies and secrete calcium carbonate (limestone) to build a hard, protective skeleton which is recognized as a coral "structure."

Types of Corals

1. Hard (Stony) Corals

• Build rigid skeletons of calcium carbonate.
• Are the primary builders of coral reefs.
• Examples: brain corals, elkhorn corals, staghorn corals.

2. Soft Corals

• Don’t produce hard skeletons; instead, they have flexible, leathery structures.
• Often resemble plants or trees under water (e.g., sea fans, sea whips).
• While they don’t build reefs, they add to reef diversity and structure.

Causes of Coral Bleaching:

Coral bleaching occurs when corals expel zooxanthellae—algae that provide them with color and up to 90% of their nutrition—due to stress, primarily from increased sea surface temperatures (SSTs). This leads to the whitening of corals, making them vulnerable to disease and death.

·         Increased SSTs: Driven by greenhouse gas emissions, tropical SSTs have risen by ~1°C in 100 years and continue to rise.

·         Marine Heatwaves: Events like the 2020 heatwave bleached 85% of corals in the Gulf of Mannar.

·         El Niño: Triggers regional warming beyond normal thresholds.

·         Shifting Ocean Currents: Altered by changes in temperature, salinity, and wind, impacting coral habitats.

·         Ocean Acidification: Disrupts coral-algae symbiosis.

·         Sedimentation: From coastal dumping and trawling, hampers photosynthesis of zooxanthellae.

Additional threats include biological invasions. Invasive algae like Kappaphycus alvarezii and crown-of-thorns starfish dominate weakened reefs. Xenobiotics—chemical pollutants such as copper, oil, and herbicides—further degrade coral health. Diseases, or epizootics, can also cause severe bleaching and coral mortality.

India’s Coral Conservation Efforts:

• Legal Framework: The Coastal Regulation Zone (CRZ) Notification, 1991, under the Environment Protection Act, 1986, supports reef protection.
• Community Initiatives: The Gulf of Mannar Biosphere Reserve Trust promotes eco-development to reduce fishing pressure.
• Restoration Projects: The Coral Reef Recovery Project (Mithapur) and efforts by the Zoological Survey of India have restored reefs in the Gulf of Kachchh, including reintroducing staghorn corals extinct for 10,000 years.

Conclusion:

The Fourth Global Coral Bleaching Event is a stark warning of how quickly climate change is damaging our oceans. As rising sea temperatures cause widespread coral stress and death, entire ecosystems are at risk. Without urgent global action to reduce emissions and protect reefs, we may lose one of the planet’s most vital and diverse ecosystems.