Environment and Ecology
Coral Bleaching Event
-
- Context: Scientists have indicated that the fourth global coral bleaching event—the fastest and most widespread on record may have concluded by mid-2025.
- This event was confirmed by the National Oceanic and Atmospheric Administration (NOAA) on April 15, 2024.
- It caused heat stress leading to coral bleaching across 84% of the world’s coral reef areas.
- It is believed to have ended following a coral bleaching event in Western Australia in early 2025.
Coral Reefs
- Coral reefs are formed by tiny marine animals known as coral polyps.
- These animals extract calcium from seawater to build hard external skeletons, which gradually form rock-like structures.
- Although coral reefs cover less than 1% of the ocean floor, they support more than 25% of all marine life.
About Coral Bleaching
- Coral bleaching occurs when corals turn white.
- This happens because they lose the microscopic algae (known as *zooxanthellae*) that live within them and provide both their color and food.
- Bleached corals do not always die, but they become weakened.
- They become susceptible to disease and lack sufficient nutrition; if this stress persists, they may die.
Coral Bleaching Events
- The first global coral bleaching event occurred in 1998.
- The second took place in 2010.
- The third event, occurring between 2014 and 2017, was particularly severe due to intense heat stress and affected approximately 68% of coral reefs worldwide.
Causes of Coral Bleaching
- Climate Change: Rising ocean temperatures are the primary cause. Even a slight temperature increase of around 1°C can lead to coral bleaching.
- Ocean Acidification: As oceans absorb excess carbon dioxide from the atmosphere, the water becomes more acidic. This weakens corals and hinders their ability to build their skeletons.
- Ultraviolet (UV) Radiation: Reduced cloud cover exposes corals to intense sunlight and high levels of UV radiation, causing stress.
- Human Activities: Pollution, overfishing, coastal construction, and coral mining damage coral reefs and increase the likelihood of bleaching.
