Zoetwatermosselen en hun verwerking tot knopen. Opkomst en ondergang van de parelmoerknopen industrie in de Verenigde Staten van Amerika

Already early in the 19th century pearl-shell of fresh water clams was used in North America for the production of buttons. In 1889, Johann Fredrick Boepple migrated from Germany to the U.S. and incepted a pearl-shell button industry on the banks of the Mississippi river in Muscatine, Iowa. People and children working in those factories were exploited and soon stroke for better wages. At the same time, over-fishing exhausted mussel populations. In the 1940's plastic buttons gradually took over and the pearl-shell button industry collapsed. Furthermore, around 1850 and in 1960-1980 'gold-rushes' developed on fresh water mussels: the first to find pearls, the second to harvest mussels for the production of mother-of-pearl nuclei to elicit 'cultivated' pearls in fresh water mussels in Japan. All North American species of fresh water mussels survived the assaults, but some of them are now considered 'critically endangered' and enjoy protection by the Federal Endangered Species Act of 1976.