Why Do Mussels Matter?

By Brandon Peoples

If you’re like me, you’ll be hitting the creeks this spring to catch a trout or smallmouth bass.  But did you know that as you wade along, the very stream bed you walk on is teeming with life?  In fact, much of the stream bed itself is alive…

Mussels are diverse and often mistaken for rocks (source).

Many of the hard “rocks” you’re walking on may in fact be mussels.  Mussels are mollusks, which means they are related to snails and clams.  Although some mussels can cling to hard structures, most freshwater mussels native to the US are purely bottom dwellers.

Freshwater mussels have one of the most unique life cycles of any aquatic organism.  After spawning occurs in spring, a female mussel will keep her brood inside her shell.  When the juvenile mussels (called glochidia) are old enough to be released, the female uses a fish to disperse them.  That’s right—mussels send their kids out on the gills of fishes.

How does she do this?

Mussels have artificial lures that sometimes resemble fish (source).

Many mussels have very special adaptations to lure fish in close enough to deposit glochidia.  Just like I use bait to catch a bass, mussels’ lures resemble small fish or crayfish.  Once the interested fish gets close enough to the mussel, she releases her young and they attach to the fish’s gills.  Sometimes with small fish, the mussel will swallow the fish whole; she then releases the captured fish to swim away with her brood.  After a couple of weeks, the baby mussels fall off the fish, to hopefully begin their new lives.

Be sure to watch the video below about these "fishing lures".

Mussels have one of the most important jobs in the river: they are natural biofilters.  Mussels can filter up to 40 liters of water each day, feeding on algae and bacteria floating in the water.  Many scientists believe that filtration by mussels may be critical to keeping our rivers and lakes clean.

Unfortunately, things haven’t gone so well for freshwater mussels.  There are approximately 300 species of mussels in North American freshwaters, and over half of them are imperiled (vulnerable to extinction).  Over 30 mussel species are believed to already be extinct.

Mussel shells were often used to make buttons (source).

In large rivers such as the Illinois and Mississippi, freshwater mussels first began to be harvested because some of them produced pearls.  Mussel harvest reached its peak in the early 1900s when they were used extensively for making buttons for clothing.  By the mid 1930s, mussels had been grossly overharvested; entire mussel beds were gone.

In the southeastern US, which is home to one of the richest aquatic fauna in the world, declines of mussel populations were made worse by extensive dam construction and water quality degradation.  To make matters worse, the widespread establishment of exotic zebra mussels has had significant impact on native mussel populations.

There is still hope for the threatened bivalves.  Groups across the country—from federal agencies, to private citizen groups, to university research groups—are working to stabilize populations of imperiled mussels.

Researchers surveying a river for mussels (source).

In addition to habitat protection and restoration, many labs across the US actively propagate mussels for reintroduction.  Like many of its counterparts, the Freshwater Mollusk Conservation Center (FMCC) at Virginia Tech grows native mussels to learn more about their life-history requirements, and to eventually release them into their native streams.  In the past five years, thousands of juvenile mussels of multiple species have been released.  Hopefully, some of them will live to maturity and begin reproducing.

Mussels have had a large influence on our society, and we’ve had a larger influence on their very existence. Mussel conservationists hope to do a better job, so these natural biofilters can hang on and keep doing what they do best.