Show Us Your Mussels
Friday December 15, 2006
Every month, in this space, an Ijams staff person presents an article
covering a natural history topic. We choose from an endless supply of
interesting topics that are specifically related to our East Tennessee region.
This month we chose Mussels of EastTennessee.
The natural history
of these mollusks provides a glimpse into the
underwater world of our streams and rivers. Most freshwater mussels are
burrowers, digging into the sand and gravel bottom of our waterways with a
specially adapted foot that holds them to the bottom while they eat. They are filter
feeders that sift water through a siphon for plankton
(microscopic plants and animals).
Nothing tastier to a mussel than some yummy green stuff suspended in the water!
While they are feeding, they
are also cleaning water. As filter feeders, these animals are greatly impacted
by pollution present in the water and specifically by soil that has been washed
into the water through erosion. It interferes with their ability to feed,
reproduce and flourish, in other
words, to survive. It’s estimated that 70% of our freshwater
mussels are extinct, endangered or in need of special protection. Their
complicated reproductive cycle involves luck, luck and more luck. The female
draws sperm to be fertilized into her shell while feeding
A sperm producing male must be in the area,
producing viable sperm and release it into the current that is flowing past the
female. The next bit of luck involves fish that provide a host for the larval
stage of the mussel (glochidia) to
attach themselves to. Some mussel species have developed adaptations that draw
fish to them, such as projections from their shell that look like insects,
worms or other fish food. The female shoots out the larva
in the direction of the fish she has attracted. Once the larvae
attach themselves to a host fish, they develop further for several
weeks before they are ready to take up residence as siphoning bivalves on the
river bottom. The interconnected relationship
of mussels and their reproductive cycle to the habitat and
other species
helps to explain why a vast population is necessary
to successfully sustain a
healthy population. In other words, the more of them there are, the better chance of successful reproduction.
Native mussel species are threatened in ways beyond pollution and
soil erosion.
The non-native species zebra mussel
was first detected in 1988 in Lake St. Claire near Lake Erie in Ohio and is now
considered widespread in the waterways of the eastern United States. Like many
non-native species of plant or
animal, these mussels have few natural predators and, because of their prodigious reproductive
cycle (no larva stage that needs a
fish host), have suffocated and eliminated
many native species of mussel, reducing the
biodiversity of species and weakening the interconnected web of life that
supports a diverse ecosystem.
The impetus for this article was a discussion around the Tennessee
state gem known as the Tennessee pearl. These
exquisite natural gems are produced in several species of mussel and have
supported an aspect of the jewelry
industry since the 1950s. What is often overlooked is the role of the
shells themselves in establishing and supporting the button
industry before the age of plastics. It is estimated that over 80% of the buttons
in our pre-plastic world were made from
mussel shells.
Close to 300 species of native mussels live in the watershed that
is the Mississippi River. They are a
unique and undervalued part of our ecosystem.
Learning their natural history, connecting ourselves
to them and lessening our impact are vital to the future of these animals.
If you’re
interested in learning more about East Tennessee’s
mussel population, visit the permanent exhibit at McClung Museum or the permanent
exhibits area of their website at http://mcclungmuseum.utk.edu. The U.S Fish
and Wildlife Service also has great information
at http://www.fws.gov/news/mussels.html.
An excellent reading resource is The Mussels
of East Tennessee by Paul W. Parmalee and Arthur E. Bogan
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