Michigan is home to 43 species of native freshwater mussels, 30 of which are considered to be at risk of extinction. Among the many factors that threaten the hard-shelled bottom dwellers are competition from invasive zebra and quagga mussels, water pollution, and—especially—dams. Michigan is home to 43 species of native freshwater mussels, 30 of which are considered to be at risk of extinction. Among the many factors that threaten the hard-shelled bottom dwellers are competition from invasive zebra and quagga mussels, water pollution, and—especially—dams. Plants & Animals Ecology Phys.org – latest science and technology news stories