Coral reef and corals are different things. A coral is just an animal. Will settle in any suitable place reached by sea currents. If the currents in their place

Coral reef and corals are different things. A coral is just an animal. Will settle in any suitable place reached by sea currents. If the currents in their place go from poles to equator will never survive to settle there. A coral reef needs 1000 years and several submarine mounts to appear. It hosts tens of thousands of species interacting together, is more complex than the more complex software that we could imagine and not all of those species can just move with the coral and survive in the new area. Algae for example, that are of crucial importance in the survival of the reef, both as symbionts but also as competitors. Wipe the 10% of the species, just the rare ones, and you will have still a stunning "virgin" coral reef but is neither healthy nor sustainable long term. Wipe all the uncommon species of coral and Acropora will refill all empty space so technically there is plenty of coral still. Wipe all sharks and there will be a chain of unexpected consequences down on the food chain. The reef works as a whole entity. Is about quantity but also about quality of the remaining corals.