Fourth Global Coral Bleaching Event

Syllabus: GS3/ Biodiversity and Conservation

Context

According to the National Oceanic and Atmospheric Administration (NOAA), the mass bleaching of coral reefs around the world since 2023 is now the most extensive on record.

77% of the world’s coral reef areas – from the Atlantic to the Pacific to the Indian oceans – have so far been subjected to bleaching-level heat stress.
The NOAA coral reef authority declared the global bleaching event in 2024, making it the fourth of its kind since 1998.
- Mass bleaching events on the Great Barrier Reef have been documented with full-scale surveys in 1998, 2002, 2016, 2017, 2020, 2022 and 2024.
The previous record from the 2014 to 2017 mass bleaching affected just below 66 percent of the world’s reef area.
In coming months and years scientists will conduct underwater assessments of dead corals to help tally up the severity of the damage.

Corals are invertebrates that belong to a large group of animals called Cnidaria.
- Corals are formed by multiple small, soft organisms known as polyps.
- They secrete a rocky chalk-like (calcium carbonate) exoskeleton around themselves for protection.
- Coral reefs are therefore created by millions of tiny polyps forming large carbonate structures.
Appearance: Corals range in colour from red to purple and even blue, but are most commonly shades of brown and green.
- Coral are bright and colorful because of microscopic algae called zooxanthellae.
There are three types of coral reefs – fringing reefs, barrier reefs and atolls.
- Fringing reefs form along shorelines, barrier reefs form in open water and atolls are circular reefs that have formed around sunken volcanoes.
Significance: They provide food, shelter, resting and breeding grounds to a quarter of all marine life, acting as nurseries and refuges to protect critical biodiversity.
- They also support more than 1 billion people living in coastal regions around the world by providing food, livelihoods and recreation.

Coral bleaching occurs when corals expel the colourful algae living in their tissues.
Without these helpful algae, the corals become pale and are vulnerable to starvation and disease.
A bleached coral is not dead, but ocean temperatures need to cool off for any hope of recovery.
At least 14% of the world’s remaining corals were estimated to have died in the previous two global bleaching events.
Scientists had previously projected that coral reefs would cross a tipping point at 1.5 degrees Celsius (2.7 F) of global warming, whereby up to 90% of reefs would be lost.
- The latest record bleaching adds to growing evidence that reefs have already passed a point of no return at just 1.3 C (2.3 F) of warming.

The leading cause of coral bleaching is climate change.
- A warming planet means a warming ocean, and a change in water temperature—as little as 2 degrees Fahrenheit—can cause coral to drive out algae.
Coral also bleaches for other reasons, like extremely low tides, pollution, or too much sunlight.
The ongoing bleaching has been made worse by El Nino, a natural climate pattern that can temporarily warm some oceans, which ended in May.

Coral bleaching matters because once these corals die, reefs rarely come back.
With few corals surviving, they struggle to reproduce, and entire reef ecosystems, on which people and wildlife depend, deteriorate.
This would have dire implications for ocean health, subsistence fisheries and tourism.

Wildlife: Thousands of marine animals depend on coral reefs for survival.
- Coral reefs provide shelter, spawning grounds, and protection from predators.
- They also support organisms at the base of ocean food chains.
- As reef ecosystems collapse, already at-risk species may face extinction.
Humans: Coral reefs are natural barriers that absorb the force of waves and storm surges, keeping coastal communities safe.
- Every year, reefs provide about $2.7 trillion in goods and services, according to a 2020 estimate by the Global Coral Reef Monitoring Network.
- Bleached coral also compounds the overfishing crisis by removing links in the food web and depriving some fish of a place to spawn and develop.
- Reef tourism brings in billions of dollars each year and supports thousands of jobs.

Corals can recover from bleaching over time, but only if temperatures drop and conditions return to normal.
When this happens, the algae returns and the corals gradually regain their health.

Strengthening Marine Protected Areas (MPAs).
Implementing coral restoration techniques, such as coral gardening and breeding resilient coral species, to enhance recovery after bleaching events.
Advocating for global efforts to reduce greenhouse gas emissions to limit temperature increases and ocean acidification.
Increasing investment in research to better understand coral resilience, bleaching triggers, and recovery processes, alongside developing advanced monitoring technologies.

Source: TH

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