biggest producer of co2 is not coal, page-19

That will certainly help for some of the corals. Interesting work. But I suspect it is species dependent, as this article in the same journal attests, with a suggestion of no reef development below pH 7.7. Obviously the fossil record shows that during very extreme CO2 conditions such as during the Permian extinction then corals reefs are lost.

http://www.nature.com/nclimate/journal/v1/n3/full/nclimate1122.html

Also, still have the problems for the carbonate dependent phytoplankton and the like, at the base of the food chain.