What is a direct cause of coral bleaching?

Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead

Answer/Explanation: The main cause of coral bleaching is heat stress resulting from high sea temperatures. Temperature increases of only one degree celsius for only four weeks can trigger bleaching events. If this temperatures persist longer periods (eight weeks or more) corals begin to die.