Populations that have been decimated or lost are being re-established to help filter out the very pollution generated by agriculture, industry, and development that threatened or endangered the species.
Freshwater mussels are "voracious filter feeders able to cycle gallons of water per hour." By taking in phytoplankton and small particles in streams and freshwater tidal habitats, they eject both clearer water and also a nutrient-rich detritus that actually fertilizes the stream and its sediments.
As with some other species, a healthy population of mussels indicates that water is of good water quality.
Mussels are among the earth’s longest living invertebrates. There are about 900 known species. Freshwater mussels live on every continent but Antarctica. Some species survive 100 years and more.
Unfortunately, they become endangered because their long lives mean that they face long-term exposures to pollution and are often the first victims of the increases in silt and theexcess nutrients that come with runoff from developed urban and agricultural land.
The Delaware River once had roughly a dozen native freshwater mussel species. While several still survive in isolated populations, the majority of the river’s mussels—and the species Kreeger’s Freshwater Mussel Recovery Program has, since 2007, focused on — is the Eastern elliptio, a dark shelled mussel up to five inches long with a pearly pink interior. While rare in the tidal estuary, elliptio is common in the river above the reach of the tides at Trenton, New Jersey.
William Lellis of the U.S. Geological Survey (USGS), who surveyed the upper Delaware mussels, estimates there might be as many as two million per river mile. With no dam along the Delaware’s main stem, the American eel, which hosts the mussel’s developing larvae on its gills, can repopulate mussels into beds far upriver, where, as a Wild and Scenic River, the runoff is freer of silt and nutrients than in the highly developed and industrialized estuary. There, the nutrient loads can be very high. The U.S. Environmental Protection Agency’s last National Coastal Condition Report found that the Delaware estuary had more high-nitrogen sites than any other Northeast coastal estuary. Surveys have shown that of 70 Pennsylvania streams, for instance, only four contained any freshwater mussels.
Kreeger realizes it’s critical to find out where and how many mussel beds remain in the estuary, determine where they might still survive if given the chance, and then try to restore those streams to the point where their mussel populations could be rebuilt. (To reach more streams and involve the public in the project, Kreeger has enlisted and trained volunteers to survey mussels in their local streams.) In 2011 and 2012, Kreeger reintroduced mussels into three southeastern Pennsylvania streams and, despite severe flooding, most of the animals survived. The idea, of course, is that, once established, mussels will begin to clean both the water and sediments in their new habitat. Can they do it?