To those interested in shell dissolution:
 
        We have found that in freshwater lakes with pH values in the 7-8
range, unionid mussels often experience shell dissolution rates equivalent
to up to 20% of their shell length annually.  We published this information
in Nature a couple of years ago.  We attribute this loss of shell to
long-term shell closure, probable anaerobic respiration and decreased pH of
the inter-pallial fluid.  This shell loss is quite detrimental to the
animals, because the periostracum does not disappear, but curls around the
siphons making shell closure impossible.  We are seeing mass mortality in
areas where this is common, and it appears to occur over much of the
continent.  I have sought negative growth rates in marine systems, have
found many but also have seen that most are swept under the rug.  Leonardo
da Vinci suggested 600 years ago that one thing in nature that we can count
on is that bivalves add one new ring with each passing year.  Poor
Leondardo's foundations may have been shaken.
 
        Best wishes,
 
        John A. Downing, Professor
        Iowa State University
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