“Even a temperature rise of a few degrees, as the Great Barrier Reef has seen during marine heat waves in recent years, can cause bleaching, in which corals expel the symbiotic bacteria that live inside them and feed them. The increasing acidity caused by excess carbon dioxide absorbed by the ocean makes it hard for corals to build their shells. Sea level rise and stronger storms damage reefs as well. The outlook is bleak.”
My 75 gal I had in the late 90’s - mid 00’s often got up to 84 deg F in the summer and was located in a closet (the tank was in-wall), which resulted in a build-up of CO2 making it difficult to get pH up even with kalk.... my corals grew and thrived. I guess it was because my corals had symbiotic algae and the corals in the Great Barrier Reef have symbiotic bacteria. Maybe they should throw a frag of Pom Pom Xenia in there. After I did that in my 75 gal, a few months later I was culling the stuff and had to rinse it down the garbage disposal.