NASA predicts a 99% decline in corals at 2C warming which could occur by 2050.

Vanishing Corals, Part One: NASA Data Helps Track Coral Reefs – Climate Change: Vital Signs of the Planet

The greatest expansion of ocean life (including the appearance of corals and shellfish) occurred 540 million years ago, with CO2 levels fifteen times higher than now and temperatures 15C warmer.

When life exploded

Global temperature and atmospheric CO2 over geological time (600 mya)…. | Download Scientific Diagram

The world’s largest coral reef has record amounts of coral

Highest coral cover in central, northern Reef in 36 years | AIMS

In 1954, the US blew up a hydrogen bomb at Bikini Island and raised water temperatures 99,000F.  Corals are thriving there now.

National Geographic News Photo Gallery: CCorals Flourish at ”Nuked” Atoll