Coral dieing on Great Barrier Reef question

I read an article on Yahoo today that claimed the coral on the Great Barrier Reef was dieing because of increase in water temperature of 1/2 degree over the last century. I no longer have a reef tank but when I did the corals were not very sensitive to those kind of minor changes in temperature. I had daily swings of +-1 degrees Celsius (Halides and chillers working against each other) without any noticable problems with corals. I had seasonal changes of as much as 3 degrees Celsius without too many problems, some stress but no dieing. Can someone explain this contradiction to me? Are these corals different?

Thanks

Marc

Quote below:

'The sea temperature over the last century has risen by just half a degree Celsius.

But corals tend to live within one to two degrees of their maximum temperature threshold and a tiny increase is therefore enough to ensure a major impact.

Bleaching occurs when coral becomes stressed. It involves a breakdown in the symbiotic relationship between the coral and algae and in severe cases the coral will die. '

It is increase in mean temperature in the last century. It means faster metabolism, and corals containing zooxanthellae suffer from 'oxygen poisning'.

The 3C temp different is not a problem when the temp is within the acceptable temp range of what the corals can live within. But 1C is when the temp is above this limit. This should give you a good explanation ...

Ok, so your saying that 1/2 degree average increase translates into a new maximum temperature that is above what the corals can tolerate. Hmm, I'm still not entirely convinced, because this would imply that the maximum temperature has always been very close to lethal for the corals and a minor shift in the overall temperture range caused the die off.. Unless there is also an increase in the temperatures standard deviation so that an average increase of 1/2 degree might translate into a several degree rise in the maximum temp. Assuming this is correct and happened over a period of a century, wouldn't there be a gradual die off and replacement. The less tolerent corals die first then are replaced by more temperature tolerant corals.

Nope, but do realize that 1/2 degree for the world's ocean avg might have taken place locally at a much higher temp.

I have to agree with JC on this one.. the 1/2 degree may not on the surface (no pun there) seem like a diddly but when you realize that that 1/2 was gained throught the heat absorbtion of only a small percentage of the ocean then you begin to see how in some areas its of no consequence -because the weren't involved in the heating- and devestational in other areas because their relative temps were +4 +5 even +10 degrees above normal for extended periods.