Shellfish can survive in fresh water where pH can drop as low as 5, so whats the problem?
Organisms that live in fresh water or in salt water with lower pH have developed adaptive mechanisms that allow them to survive under those conditions. In contrast, marine shellfish that have evolved in seawater with a higher and less variable pH are more susceptible to changes in pH. A good example of this is the natural shift in marine organisms to freshwater organisms living along estuaries. A marine shellfish, Thais gradata, that is found along estuaries tends to have higher rates of dissolution at the freshwater end of the estuary, where pH is lower and varies widely, than it does at the seawater end of the estuary where pH is higher and varies less.
