RISING OCEAN TEMPERATURE
Corals are sensitive to changes in temperature, and an increase of just two degrees Celsius over a few weeks to months can be enough to cause catastrophic coral bleaching. When corals are stressed from the warmer water, they expel their photosynthetic zooxanthellae algae which are critical to their survival.
Once the zooxanthellae algae leaves, the corals turn a ghostly white colour and it is difficult for them to survive. When corals are bleached, harmful algae taking over the corals. And with the loss of herbivorous fish, these algae can quickly out-compete and kill the coral.