heres a basic video on what happens to corals long term due to heat. i have heard natural reefs will be GONE in the next 10 years or so due to heat in our enviroment. the symbiotic algae that hosts corals abandon when things get to hot and in turn the coral bleaches and starves. this guy in the video isnt very scientific. a coral is an animal, not a plant but the algae that hosts them, are plants. the coral just feeds off the hosting algae.
and heres a link i had saved about coral reefs being gone. they actaully say it will be due to a carbon dioxide increase which really heat reduces gas exchange and the ammount of oxygen in the water
any long term heat will make corals abandon their hosting algae though, and they will start to bleach.