THE CORAL BLEACHING CRISIS
- Clementine Saliot
- Jun 6
- 3 min read
THE CORAL BLEACHING CRISIS
The planet is currently undergoing of the most extensive and severe coral bleaching event ever recorded. Beginning early 2023 and continuing into 2025, this crisis has already affected nearly 84% of coral reef areas across all tropical oceans, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). It marks the fourth global bleaching event in history and the second within the last decade, scientists are calling it a "planet-scale emergency." All around the world, the Great Barrier Reef, the Caribbean, the Pacific islands and East Africa, corals are turning white, indicating the extreme physiological stress they are going through.
What is coral bleaching?
Coral bleaching occurs when corals expel the zooxanthellae algae that live within their tissues. This process is triggered by physiological stress they experience, primarily caused by the rising ocean temperatures that exceed the coral’s tolerance levels. Events like El Nino and human driven global warming further amplify this stress, making the global bleaching crisis particularly severe. In addition to the rise of ocean temperatures, ocean acidification, caused by the increase of Carbon Dioxide levels in the water, further weakens and damages the coral reefs. Pollution and overfishing also threaten coral ecosystems, as it disrupts the natural balance of life of the ecosystem. The coral issue lies in the fact that the various stressors like the rising temperatures, ocean acidification, and human induced factors, cause the corals to expel the zooxanthellae algae. These are algae which are crucial to coral health, as they provide approximately 90% of the coral’s energy and are responsible for the coral’s vibrant color. Therefore, when corals expel their algae under stressful conditions, they also lose both their vibrant color and their energy source, making them more vulnerable to disease or death.
The most common cause of this stress is prolonged exposure to high sea surface temperatures. When ocean heat persists for too long, corals become bleached. If the heat stress lasts more than a few weeks, the corals may die. Recovery, when possible, can take years — and in many cases, repeated bleaching events mean reefs are simply not bouncing back.
According to NOAA, bleaching has been confirmed in 54 countries and territories, affecting every major ocean basin. Furthermore, bleaching has been recorded from the 1st of January 2023 to 30th of April 2024, and the phenomenon has intensified through early 2025 due to continuing ocean heatwaves.
Why it matters
Coral reefs support an estimated 25% of all marine life even though they cover less than 1% of the seafloor, they are essential to ocean biodiversity, providing food and shelter to thousands of species. Their decline disrupts entire food chains and increases extinction risk for reef-dependent species. Aside from being important for marine ecosystems, reefs also play a vital role in protecting coastlines from storms and rising seas, especially for small island environments. Reefs also serve as carbon sinks, absorbing atmospheric carbon dioxide which is essential for regulating the climate and the ocean’s chemistry. In fact, the collapse of reef ecosystems could have extremely problematic consequences, including the acceleration of ocean acidification which would then reduce the ocean’s ability to absorb greenhouse gases - worsening the climate crisis.
This global coral bleaching event shows us a brutal consequence of global warming, primarily caused by human activity. According to scientists quoted in The Guardian, this may be a “tipping point” for many reef systems if urgent climate mitigation doesn’t occur.
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