Hidden Treasures of the Harpeth

by Louis Levine

I grew up in Nashville and have many fond memories of my dad taking our family rock collecting along Hwy 70 and wading in the nearby Harpeth. I was always picking up interesting odds and ends, as I still do, and probably found my first freshwater mussels on one of these outings. Now, forty years later, I wish I had kept more of my early finds since some species have already become extinct in my lifetime.

Pink Heelsplitter (Potamilus alatus)

I have come to appreciate the often overlooked freshwater mussel for its diversity, subtlety, and beauty. Unfortunately, this group of animals is one of the most endangered in the world. More than two dozen species have died out in Tennessee over the last one hundred years and several more are listed as threatened or endangered. In fact, the Tennessee Wildlife Resources Agency protects all mussels and requires a permit to collect any shell live or dead. About ten species are commercially harvested for the cultured pearl industry.

Most of our freshwater mussels belong to the family Unionidae. There are a few other families represented in Tennessee which include the tiny fingernail or pea clams, the Asian Clam, the Zebra Mussel, and the Spectacle-case. Worldwide, there are around 300 Unionid species and our state has nearly 130 of the total.

Only Alabama has more mussel diversity. The best populations that still survive are in the Duck and Clinch Rivers, where it is possible to encounter more than forty varieties in some locations.

The Harpeth before 1960 supported approximately twenty-five species and still has over a dozen well-represented species. The major factors affecting today’s mussels are pollution and loss of habitat. The unique natural history of these animals makes them good environmental health indicators.

They are filter feeders which makes them particularly vulnerable to pollutants in the surrounding water, and variation in water temperature has an adverse effect on their ability to breed. They have a parasitic larval stage which must feed on the gills of specific host fish, and, in one case, host salamander. Without these complementary species, the mussels cannot survive. Few species tolerate silty water, with the majority preferring fast-moving, highly oxygenated water with a gravel substrate.

Threeridge (Amblema plicata)

Common names for our shells are usually colorful and descriptive. Some of the species I have encountered around the Narrows of the Harpeth have been Threeridge, Pistol-grip, Fluted Shell, White Heelsplitter, Pink Heelsplitter, Spike, Deertoe, Purple Wartyback, Pocketbook, and Fragile Papershell. Most of the shells you’ll find are worn and old dead specimens. Muskrats feed on the smaller shells, especially Asian clams which are not native to this country, and often leave them in small mounds on the shore. Recently introduced otters seem to also be dining on mussels.

Live shells are usually partially imbedded in the gravel and can be easily overlooked.

The definitive reference book is The Freshwater Mussels of Tennessee, written by Paul Parmalee and Arthur Bogan, and published in 1998.

Louis Levine offers wildlife programs for scouts, camps, schools and birthdays. Contact him at (615) 352-2134 or email louis.levine@earthlink.net.

-From Voices for the Harpeth, 2004