Mussel Power
by Mary Ball

Students create student-written books about freshwater mussels.

Finding Mussel Shells

Since live mussels are often nearly completely buried in mud or sand, it is difficult to view them without disturbing their habitat. It is easiest to find shells along streams in the winter and spring after heavy rains have caused the rivers to overflow their banks. When the water goes down, there will be empty mussel shells along the banks.

Background

In an article in the Tennessee Conservationist, Rob Simbeck tells the story of how Tennessee pearls became an important resource in the state. According to Simbeck, "Charles Bradford and James Johnson were just looking for bait. The Murfreesboro boys were fishing in the Caney Fork River in the early 1880s when, on opening one of the mussels they had pulled from the mouth of Indian Creek, they found a large white pearl. They took it to William Wendel, a local druggist, who sent it off to Tiffany's in New York. A few days later the boys had a check for a then-impressive $83. More than 100 years later, through boom and bust, and despite pollution, over-harvesting, 9creation of) dams and the vicissitudes of fashion, mussels are bringing $40 million a year into Tennessee, and the freshwater pearl has been, since 1979, the official state gem."

According to Steve Adams' article in a later issue of the same magazine, "The turn of the century ushered in a new era when the Japanese discovered the principles of pearl culturing. The mantle of an oyster is implanted with a shell bead nucleus together with a sliver of the mantle tissue from another oyster. The oyster will coat the nucleus with successive layers of nacre (pronounced "NAY-ker"), which, like the mother-of-pearl layer that lines the inner walls of mollusk shells, forms the outer hull of a cultured pearl.

The substance is identical to the mineral aragonite. Thus a cultured pearl is a thin layer of pearl material surrounding a bead cut from a shell. Whether a cultured pearl came from Japan or America, with rare exceptions the shell bead nucleus came from Tennessee! Both oysters and mussels reject most foreign material, so the proverbial grain of sand irritant at the center of natural pearls is a myth. Much research has been put into nucleating material for cultured pearls, and the thick shells of the Unio family of mussels found in the Tennessee river proved to be ideal."

Simbeck points out that, "Not long after the turn of the century, the rate of depletion was concerning a number of people. W.E. Myer of Carthage, speaking before the Tennessee Academy of Science in 1914, decried 'the heedless total working out and total destruction of every mussel in each mussel bed and leaving no mussels to reproduce the race.' Despite his implied protestations against greed in pearl-gathering, Myer, whose brother was a major New York pearl dealer, was one of many (explorer Hernando DeSoto had been the first) to dig up the graves of Indian mound builders looking for the popular gem. The Indians had long been avid consumers of the mussels, both for food and for adornment, and archaeological excavations have often turned up large heaps of shells. It remains to be seen whether those efforts can turn the tide in the effort to improve conditions for our most fragile state symbol, one extremely sensitive to the kinds of problems that growth and pollution bring."

References:

Gemstones of Tennessee by Steve Adams, The Tennessee Conservationist, March/April, 1993.
The Freshwater Pearl: A Tennessee State Gem, by Rob Simbeck The Tennessee Conservationist, November/December 1991.

Focus:

Freshwater mussels have been and are an important natural resource in Tennessee.

Materials:

• mussel shells (optional)
• Copies of the mussel life cycle and copies of charts summarizing mussel importance
• mussel model pieces cut using pattern assemble using instructions

Procedure:

Look over other activities on mussels for background information that may be helpful and for ideas for presentation and follow-up.

Pass out copies of the life cycle of freshwater mussels and briefly go through the stages of the life cycle.

1. The tiny "offspring" begin development inside the gills of their "mother". (NOTE: Sperm released into the water fertilize the female's eggs. The young mussels are called "glochidia" (pronounced "glow-KID-ee-uy"). Whether or not you want to include this information is up to you.)
2. After being released into the water, these "youngsters" attach to the gills of fish, getting protection and a free ride to a new location. Some are very particular about what kind of fish they attach to.
3. As the youngsters filter tiny suspended particles of food from the water, they grow and finally drop to the bottom, where they half-bury themselves and remain.
4. Once mature, the full-grown mussels begin the cycle again.

If mussel shells are available, let students examine them, noting the muscle attachment points, the "mother-of-pearl", the hinge, and the growth lines on the outer covering.

Use the pattern to cut out 2 valves, 2 mantle pieces, 2 gill pieces, and 1 foot piece for each student. (There are actually 2 pair of gills on each side of the foot, but this would create a longer book.)

Students are to assemble the pieces according to the diagram on the sheet showing the life cycle. Either staple the pieces together along the hinge edge, or use tape to attach the pieces to each other.

Once assembled, the "model" of a mussel is to be used like a "theme notebook" to write a report on the importance of freshwater mussels to humans and to their aquatic communities.

Provide copies of the charts, reference materials, back issues of the Tennessee Conservationist, etc. as resource materials. Students may exercise creativity in their writing by following a diary format, or a newspaper article format. (Do NOT allow them to "copy from the encyclopedia"!)

Finished "books" could be made available for "check-out" or displayed.