This is a rather interestingly timed question. I just finished reading a book that got me interested in the actual science behind the issues of global warming. I've just started so I don't have any great insights yet
, but I'll give it a try.
Assuming the significant increase in average ocean temperature is actually happening, I've a couple of thoughts that would explain against your idea.
First and foremost, while the average might be increasing, changes are localized. There are in fact places where the local average temperatures are decreasing. This applies to both land and sea temperatures. So it might be true that the local temperature on say the great barrier reef is increasing causing a decrease in life, but that doesn't mean that a near by location had a sufficient decrease. I say near by because a barren area needs to be settled somehow and the most likely way is from a near by reef.
Most reefs take hundreds, if not thousands of years to fully establish themselves (a quick google gives the age of the GBR at 6,000 to 10,000 years old and the florida keys reef system at 5,000 to 7,000 years old). If there is an event that causes the massive die off of major reef systems in a short period of time, clearly new reefs would not be established in time. Of course, that's not to say that smaller reef systems could not settle. However, if you accept that the average temperature is increasing, and typical growth rates of corals are measure in low centimeters per year, it's unlikely that a new reef would be able to establish itself before local temperatures again increased.
I personally find this to be a fascinating area of knowledge. If you're interested in it, I suggest you do some research beyond just the media hype. You may be surprised to find that much of what you hear in the media does not have scientific backing, or even worse, may contradict what little scientific research there is. And there are, IMO, areas where there is research that should be considered important and are ignored by the media at large.