of oceans and amphibians

From the worrywart file, and perhaps relevant to my earlier post on the world's most pressing problem, come these two articles in the SF Chron: Greenhouse gas turning oceans acidic, and Extinction crisis for amphibians: Frogs, toads and other species dying off. So if significant links in the oceanic and terrestrial food chains break, that's not good, right?

How much change in the global ecosystem, and how fast, is too much change, too fast? How well-damped is the system, and is there a point when it swings into instability?