While many freshwater mussel species native to the US are barely scraping by (see main story), invasive species such as zebra mussels and quagga mussels are making a killing. 'There's a big difference in life cycle," says Monte McGregor, a mollusc specialist at the Kentucky Department of Fish & Wildlife Resources. For starters, zebra and quagga mussels don't require a fish host to nourish and transport their offspring, which means one mussel can pump out millions of free-swimming larvae every spawning season. And once those larvae turn into adults, they ruthlessly outcompete native species.
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