What are the major causes of coral reef bleaching?

Coral reef bleaching is primarily caused by a combination of environmental stressors, with the main factors being:

1. Elevated water temperatures: When ocean temperatures rise above normal levels, corals become stressed and expel the symbiotic algae called zooxanthellae that live within their tissues. These algae provide corals with essential nutrients through photosynthesis, and without them, the corals lose their vibrant colors and become pale or white, hence the term "bleaching."

2. Pollution and poor water quality: Excessive amounts of pollutants, such as agricultural runoff, sewage, and chemicals, can negatively impact coral health and increase their susceptibility to bleaching. These pollutants can disrupt the delicate balance of nutrients and alter the water chemistry, making it harder for corals to recover from stress.

3. Ocean acidification: Increasing levels of carbon dioxide (CO2) in the atmosphere are absorbed by the oceans, leading to a process called ocean acidification. This process lowers the pH of the water, making it more acidic. Acidic waters can hinder the ability of corals to build their calcium carbonate skeletons, making them weaker and more vulnerable to bleaching.

4. Overexposure to sunlight: Corals rely on the symbiotic algae for energy, but excessive sunlight can cause damage to both the corals and the algae. When corals are exposed to prolonged periods of intense sunlight, they can become stressed and expel the algae, resulting in bleaching.

5. Physical damage: Physical disturbances, such as destructive fishing practices, anchor damage, and coral mining, can directly harm corals and weaken their resilience to bleaching. When corals are already stressed or damaged, they are more likely to bleach.

It is important to note that these factors often interact and exacerbate each other, leading to more severe and widespread coral reef bleaching events. Climate change, in particular, plays a significant role in intensifying these stressors and increasing the frequency and severity of coral bleaching worldwide.