By comparison, the waters of the South Pacific are still pristine, and those of the Caribbean are human dumping grounds. We could drop millions of herbivores into the Caribbean and the environment still wouldn't be favorable to stony coral growth. If we could magically remove 90% of the algae from the reefs of the Caribbean, it wouldn't be stony corals that took its place. It would be some other organism that's better suited to higher nutrients, like sponges.