At only an inch and a half long, Alasmidonta heterodon is the tiniest of the Northeast's freshwater mussels. But in spite of its size, the dwarf wedge mussel plays a starring role in the ecology of our region. An "indicator species," its presence (or lack thereof) shows the relative health of an ecosystem; when the wedge mussel population shrinks, we know that its habitat is in trouble, too.

And right now, things are not looking too good for the tiny critter, says Tom French, assistant director of the Massachusetts Division of Fish and Wildlife. The mussel, which boasts a distinctive wedge-shaped point on the posterior end of its smooth brown shell, is a parasite. As such, it must be able to easily reach its host fish — the sculpin, darter, and juvenile salmon found in clear, cold coastal waters. Fertilization of the mussel egg actually occurs in the gills of the fish.

But because damming has so dramatically altered stream beds and because the fish are anadromous, migrating long distances from ocean to fresh water for spawning, it has become more difficult for mussel and fish to meet, French says. In addition, the pristine water quality they both require has been degraded by sediments and chemicals from agriculture, golf courses, and development. Collection of the mussel's pearls and shells for jewelry — now largely supplied by freshwater pearl farms — has also taken a toll.

As a result, though the wedge mussel was once found in more than 70 places in the Northeast, its territory currently comprises fewer than a dozen waterways from New Hampshire to North Carolina. In fact, in May 2000, the Canadian Species at Risk Act listed the dwarf wedge mussel as being extirpated in that country and the U.S. Fish and Wildlife Service currently considers the species endangered.

Keeping track of small mussels isn't easy. Because they're buried in the sand, it takes a skilled eye — often in the form of a snorkeler — to count them for surveys. Scientists look for signs including dead shells and the tiny squiggly line the mussel's single "foot" leaves behind in the sandy stream bottom. Once the habitats are determined, says French, his agency and others work to protect them from further degradation.

While the lesson of the dwarf wedge mussel is a mantra for these scientists (if they aren't doing well, our water isn't either), the reverse is also true. In places where water quality is improving, like along certain stretches of the Connecticut River, this mussel lives a remarkable 10 years or longer.