Coral Bleaching: Reasons and Impacts

Coral bleaching is the loss of intracellular endosymbionts through either expulsion or loss of algal pigmentation. When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn white.

Reasons for coral bleaching

Both biotic and abiotic factors cause coral bleaching

• Increased or reduced water temperatures.
• Oxygen starvation caused by an increase in zooplankton levels as a result of overfishing.
• Increased solar irradiance (photosynthetically active radiation and ultraviolet band light).
• Changes in water chemistry (in particular acidification).
• Increased sedimentation (due to silt runoff).
• Bacterial infections.
• Coral eating crown of thorns starfish
• Changes in salinity.
• Cyanide fishing
• Elevated sea levels due to global warming.
• Mineral dust from African dust storms caused by drought.

Mass coral bleaching events occur at a regional or global scale and are triggered by periods of elevated thermal stress resulting from increased sea surface temperatures.

Impact

The Intergovernmental Panel on Climate Change (IPCC) sees this as the greatest threat to the world’s reef systems. Since countless sea life depends on the reefs for shelter and protection from predators, the extinction of the reefs would ultimately create a domino effect that would trickle down to the many human societies that depend on those fish for food and livelihood. There has been a 44% decline over the last 20 years in the Florida Keys, and up to 80% in the Caribbean reef alone.