>Shells on the ocean floor appear to act as a buffer against chemical change over thousands of years.  Writing in the March 7 issue of "Nature" magazine, David Anderson of the National Oceanic & Atmospheric Administration's Paleoclimatology Program, & David Archer of the University of Chicago, developed a new method to determine the carbonate ion concentration of seawater, using shells on the ocean floor deposited over thousands of years.<

Actually, the study in Nature examined foraminifera, not mollusks.  Although workers up to the mid 1800's (and apparently some journalists today) thought they were mollusks, they are protists.  They can serve as food for mollusks, however, and so are not entirely irrelevant.

    Dr. David Campbell
    Old Seashells
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That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droigate Spa