Mussels can adapt to their acidifying ocean by changing the composition of their hard parts. In an ever more corrosive environment, mussels changed the mineralogical makeup of their calcareous shells. Shells normally consist of calcium carbonate which is ordered in a crystalline fashion, with strong and resistant properties. However, under ocean acidification conditions, with a lower pH, the calcium carbonate of these experimental mussel shells consisted of much more amorphous calcium carbonate, leaving the shells more vulnerable to predation by crabs and seagulls and the crushing forces of waves. This is a very strong example of secondary effects of ocean acidification, where organisms suffer from the consequences of climate change in an almost cryptic way. The danger sits in the fact that these changes on an organism level might go by unnoticed, until it is too late.