It is true that much environmental science has become intellectual finger-waving with dire warnings of events to come. However, there are a number of holes in the Scripps paper. This includes repeated references to the Yucatan Penninsula site where pH fluctuations are the norm. In fact, any site where you get regular flushing of freshwater (think estuaries) you will get large fluctuations in pH naturally. Like global warming, ocean acidification is more of an increase in the world wide norm.
It has been a while since I've taken a class on this, but I think I remember three types of bioavailable calcium, all of which disintegrate at different rates in decreased pH. The one utilized by pelagic gastropods (not mussels) is the most vulnerable to acidification. When I was learning about this stuff, it was pointed out that pelagic gastropods don't serve much of a purpose around coastal shore lines like the site at the Yucatan, but are a staple of the base of the food chain for southern pelagic ecosystems.
They did mention in the Scripps article that the open ocean does fluctuate somewhat in pH, a fact that has been known for a long time. The worry is what will happen if the upper limit of the fluctuation increases? Nobody knows for sure.
