Thanks for your comment! We will transfer both of these to the original article once we get our commenting situation worked out; thank you.
As to your question -- the difference between these papers is that the 2009 paper compared the size of modern shells to the size of older shells from the past centuries. The shells now are smaller, it concluded, and so the animals must be struggling to build them as large as they once did.
However, it is not entirely conclusive: there could be any number of reasons that an animal would build a smaller shell, unrelated to climate change or acidification.
In the new paper, the authors show microscope photos of the shells physically breaking down--the "patches of weakness" we described above. (You can see photos here.)
Until now, researchers weren't sure they'd see such clear signs of the shells dissolving in the water, and thought maybe smaller shells were the best evidence they could find. The new study showed that this evidence can be observed in the wild without the animals being killed from the weakening shells.
Does that make sense?
Thanks again for your comment and for reading!
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