The partnering of coral and zooxanthellae was once a powerful evolutionary achievement between them they built the reef. And now, between them, they may just let it go, dust to dust, coral reefs to their constituent parts. The Gogo reef was a different kind of reef, no symbiosis between polyp and algae, more a community of sponges and sea mosses that formed hard skeletons. Oceans come and oceans go. Once they cut a deal with the corals, but they didn't mean forever.
Deals come apart and circumstances change.
The earth gets warmer and corals get a dose of stress. There is an important lesson to be learned in the long-term view, from the coral fossil record. Corals are good predictors of mass extinction events. The corals nearly died out with the dinosaurs when a comet slammed into the earth some 65 million years ago. The ancient Greeks believed that comets come when the gods are angry.