It turns out, though, that both freshwater and saltwater
mussels may be just as important to a healthy Chesapeake
ecosystem as oysters. Today, I’m a believer, fascinated by the
mussels’ life cycles, diversity, and benefits.
The Chesapeake and its tidal rivers host two species of mussels
kin to blue mussels: ribbed mussels and hooked mussels, both
growing one-to-three inches long. A third species, tiny dark
false mussels, appear in upper Bay tributaries in wet years (like
this one) when salinities are low. All three species attach to
hard or firm objects with webs of strong protein fiber. Ribbed
mussels favor strong, deeply-rooted salt marsh cordgrass
stalks. Hooked mussels love oyster shells and rocks. When dark
false mussels find the right salinity, they grow by millions on
dock pilings, boat hulls, and oyster cages.
Like oysters, mussels pump water through their gills, catching
algae, bacteria, suspended decaying plant and animal material,
and fine sediment. They improve water quality by converting
this vast food source into living tissue and packaging sediment
in mucus to expel it to the bottom. Although individual mussels
don’t filter as much water per day as oysters, they make up the
difference with huge numbers. Hooked mussels are particularly
valuable growing in gaps in oyster reefs, where their filtration
synergistically complements that of their neighbors. Ribbed
mussels help to hold salt marsh soils together while adding
benefits to surrounding water clarity. Both feed fish, crabs,
birds, and marsh mammals, including river otters and raccoons.
Meanwhile, above the tide lines, great variations in stream
environments throughout the Chesapeake and Susquehanna
watersheds have allowed a valuable array of freshwater mussel
species to develop. Mussel is something of a misnomer for
these shellfish, because they bury in stream bottoms more like
clams, without the attachment threads of saltwater varieties.
Over the millennia, these living rocks, as some biologists
refer to them, have colonized a variety of stream niches.
Pennsylvania lists 12 species with colorful names like elktoe,
brook floater, northern lance, and rainbow. Maryland hosts 18
species, with overlap on Pennsylvania’s list, plus eight species it
shares with the District of Columbia’s Anacostia River. Virginia’s
Chesapeake drainage grows a dozen, including alewife floater,
tidewater mucket, and creeper. They benefit their streams
through their filtering capacity and opportunistic appetite
for varied food. In turn, they feed other critters like channel
cats, river otters, raccoons, muskrats, and herons. Their rough
bottom beds create habitat for insect larvae and tiny fish that
also feed on organic material and provide food for predator
fish. Once established, those beds tend to last; these shellfish
live astonishingly long lives—50 to 100 years.
Freshwater mussels were once staple foods for upland
American Indian tribes, who also fashioned tools and jewelry
from the colorful shells. Like oysters, mussels absorb the
flavors of their home waters. Today most people—even
appreciative biologists—find them muddy and unpalatable. In
the late nineteenth and early twentieth centuries, fishermen
harvested tons of mussel shells as raw material for buttons,
and some were pulverized to make bases for cultured pearls.
With plastics capturing the button industry, however, we’ve
lost connections with the unobtrusive mussels.
Unfortunately, we’ve disrupted many stream environments
with dams, sediment, channelization, and heavy metals. Several
native species are threatened or endangered. All freshwater
mussels are now protected from harvest, even for fishing bait.
Buried in stream bottoms, the mussels face challenges
spreading their young. Oysters, living in tidal waters that
move both back and forth, reproduce effectively by “broadcast
spawning” for tide and wind to disperse. Mussels, however,
Did you know?
• Some individual freshwater
mussels live for decades, allowing
them to reproduce repeatedly.
Unfortunately, they may also, over
time, ingest and retain pollutants
like heavy metals.
• James spinymussels (top) hold their
places buried in the river’s bottom
by extruding spikes on each side of
their shells as anchors.
• Biologists at Harrison Lake and the
Manning Hatchery have developed
systems for hatching and culturing
multiple native species of
freshwater mussels both in vitro in
the labs and in ponds (middle) for
• Scientists have also developed
a system for tagging mussels by
etching numbers into their shells
with lasers (bottom). The tags will
help to keep track of and gauge
success in the transplanted beds.