I think the comment about corals would make sense if both growth and death occurred at the same rate. But it doesn't. It takes coral and awful long time to establish itself and grow, but you can have a massive die-off in a single season. So we're starting to see some large die-offs in warmer waters. Maybe in a few hundred years it will balance out, but that's not really too comforting if you are dependent on fish now that lives off of the coral.
I have been hearing about large scale reef destruction (pick a cause, any cause) for over 30 years now since the Frog in scuba gear started his junk science soap opera for National Geographic, yet I am not aware of any reef that has ceased to exist in that time.
Are you?
And where is the evidence that a degree or two change in water temp. will kill them off just like that?