Coral Bleaching

Topic: Environmental Pollution and Degradation

Why in the news?

• The ongoing fourth global coral bleaching (GCBE4) event that began in January 2023 is now the most widespread and surpassed the coral bleaching levels of 2014-2017 by over 11 per cent, according to the United States National Oceanic and Atmospheric Administration (NOAA).
• The record breaking, severe and intense global bleaching event has been recorded in almost half the amount of time than the previous event.

Source: Down To Earth 

About Coral Bleaching:

• It occurs when corals experience stress in their environment due to changes in temperature, pollution or high levels of ocean acidity.
• Under stressed conditions, the zooxanthellae or food-producing algae living inside coral polyps start producing reactive oxygen species, which are not beneficial to the corals.
  • Subsequently, the corals expel the colour-giving zooxanthellae from their polyps, which exposes their pale white exoskeleton, giving the corals a bleached appearance.
  • This also ends the symbiotic relationship that helps the corals to survive and grow.
• Causes:
  • Change in Ocean Temperature: Increased Ocean temperature caused by climate change is the leading cause of coral bleaching.
  • Runoff and Pollution: Storm generated precipitation can rapidly dilute ocean water and runoff can carry pollutants, which can bleach near shore corals.
  • Overexposure to sunlight: When temperatures are high, high solar irradiance contributes to bleaching in shallow water corals.
  • Extremely low tides: Exposure to the air during extremely low tides can cause bleaching in shallow corals.
• Effects:
  • Bleached corals are likely to have reduced growth rates, decreased reproductive capacity, increased susceptibility to diseases and elevated mortality rates.
  • Changes in coral community composition can occur when more susceptible species are killed by bleaching events.