Freshwater Mussels

Freshwater mussels, also known as bivalves, are a type of mollusk, along with snails. Alabama has the greatest diversity of freshwater mussels in the United States with 181 total species.  

Villosa iris. Photo credit: Alan Cressler (Flickr) 

Rainbow (Villosa iris) are found in the Tennessee River Basin, and favor shoal habitats. Its periostracum varies from yellow-brown with green rays.

Mussels are an integral part of water quality, as they filter suspended solids from the water column through their feeding. According to the AABC, “a small mussel can filter over 12 gallons of water per day.” In healthy ecosystems throughout the Southeast, freshwater mollusks historically numbered in the hundreds of millions.” Imagine the filtering power of millions of mussels!  

Unique Biological Cycle 

Mussels have a unique biological cycle as they are mostly sedentary animals that are largely endemic due to this lifestyle. Mussels are considered “obligate parasites,” meaning they require a specific fish host to lay their eggs. They use lures that mimic small fish such as minnows to attract their fish host. When the fish attempts to eat the lure, the mussel injects her larvae into the gills of the fish, who will carry the eggs upstream. The larvae may live on the fish for weeks before dropping off as juvenile mussels.

Specific fish hosts are required for different mussels, although many species share a common host. For example, Southern Pocketbook (Lampsilis ornata) and Southern Rainbow (Villosa vibex) share Black bass (Micropterus spp.) as a host. Darters, which are very common in Alabama, are hosts to several mussel species, including several species of Kidneyshells (Ptychobranchus).

Alabama Native Species Highlights

There are too many mussel species in Alabama to include all of them in this article, so we will highlight just a few. With such a great diversity of mussel species, it can be hard to tell one species from another. Check out the American Museum of Natural History’s Mussel Features resources to learn more about identifying features of mussels. Another interesting feature of mussels is that their shell growth lines can be counted, similarly to tree rings, to approximate the mussel’s age.

Coosa Fiveridge (Amblema elliotti)

Coosa Fiveridge displaying its lure. Photo credit: Alan Cressler (Flickr)

Coosa Fiveridge. Photo credit: Alan Cressler (Flickr)

In the Amblema Family, Alabama has the Coosa Fiveridge and the Threeridge. The Coosa Fiveridge (Amblema elliotti) is endemic, or only found in, the Mobile Basin, primarily in the Coosa and Cahaba rivers. It has a conservation status of Moderate Conservation Concern, meaning that its local populations are vulnerable to deterioration. The Coosa Fiveridge is characterised by three to five ridges that deepen with age. Its outer shell is dark green to black in adults.

Purple Wartyback (Cyclonaias tuberculata)

Purple Wartyback. Photo credit: Alan Cressler (Flickr)

The Purple Wartyback (Cyclonaias tuberculata) is common in the Tennessee River Basin and is considered a low conservation concern. In other areas they may also be known as purple pimplebacks. They prefer riverine habitats with gravel or mud substrates in depths of 2-20 feet. It earns the name from the wart-like bumps on the outside of its shell and the purple nacre, or shiny, rainbow-like inside of the shell. Purple Wartybacks can grow up to 5 inches long.

Eastern Elliptio (Elliptio complanata)

Elliptio complanata. Photo credit: Alan Cressler (Flickr)

Elliptio complanata displaying its lure. Photo credit: Alan Cressler (Flickr)

Eastern Elliptio (Elliptio complanata) and Elephant Ear (Elliptio crassidens) are two of eleven Elliptio species native to Alabama and are of low conservation concern. Eastern Elliptio is commonly found in eastern Alabama, in the headwaters of the Chipola and Chattachooee Rivers. They can grow up to five inches and have a tan to dark brown-black periostracum (outer most shell layer) with green rays.

Elephantear (Elliptio crassidens)

Elliptio crassidens. Photo credit: Alan Cressler (Flickr)

Elephantear (Elliptio crassidens) are commonly found in most Alabama Rivers, with the exception of the Choctawhatchee River system in southeast Alabama. The mussel’s rounded anterior end and pointed posterior take the shape of an elephant’s ear, hence the name. Elephantears are large, growing up to 6 inches in length. Adult mussels’ periostracum is dark brown or black.

Southern Pocketbook (Lampsilis ornata)

There are nine Lampsilis species in Alabama, and many of them have unique names, such as Pink Mucket (Lampsilis abrupta), Lined Pocketbook (Lampsilis binominata), and Southern Fatmucket (Lampsilis straminea).

Lampsilis ornata. Photo credit: Alan Cressler Flickr 

Southern Pocketbooks (Lampsilis ornata) are widespread in the Mobile Basin and common in the Conecuh River system. Southern Pocketbooks are slightly smaller than some of the other native species, averaging around 4 inches in length with high umbos, which are raised, round structures on the shell. They have a tan outer shell with green rays and inner surface color of white or bluish-white.

Black Sandshell (Ligumia recta)

Ligumia recta. Photo credit: Alan Cressler Flickr 

Black Sandshell (Ligumia recta) are of high conservation concern, and are rare in the Tennessee and Mobile River Basins. Black Sandshells can grow up to 8 inches long, and are identified by their long, smooth, greenish-black shells with rays along the periostracum.

Little Spectaclecase (Villosa lienosa)

There are eleven Villosa species in Alabama, with names like Rayed Bean (Villosa fabilis), Alabama Rainbow (Villosa nebulosa)

Villosa lienosa. Photo credit: Alan Cressler (Flickr) 

Little Spectaclecase (Villosa lienosa) are of low conservation concern as they are common in Alabama south of the Tennessee River Basin. Little Spectaclecase, as you may guess from the name, are relatively small, averaging below three inches in length. The periostracum is green to dark brown with green rays, which are not as easy to see as on other species.

Southern Rainbow (Villosa vibex)

Villosa vibex. Photo credit: Alan Cressler (Flickr) 

Southern Rainbow (Villosa vibex) are common and also found throughout Alabama south of the Tennessee River Basin. Like many other species, the outer shell is yellow-green to dark brown and displays several green rays. They grow on average to be about 4 inches in length.

Invasive Species

The majority of Alabama’s native mussels are from the Family Unionidae, with the exception of the endangered Spectaclecase (Cumberlandia monodonta) and invasive Zebra Mussels (Dreissena polymorpha) and Asiatic Claims (Corbicula fluminea). 

If you’ve ever walked through a creek and scooped up a handful of rocks, an Asiatic Claim was likely tagging along. These invasive mussels do not require a host to reproduce, unlike native mussel species, and are widespread throughout Alabama’s waters. Asian claims may be used as bate and are often the delicacy of choice for racoons. 

The spread of invasive mussels can be prevented by properly cleaning boats and other equipment after recreating in a waterbody. Consider these guidelines for clean boating to prevent the spread of invasive species from the Boat U.S. Foundation next time you find yourself out on the water.

Alabama Pearl Fever

According to Alabama Rivers, A Celebration & Challenge by Dr. Bill Deutsch, the Tennessee River Basin once had approximately 350 species of mussels, which is more than any other place in the nation. Many of Alabama’s endangered, threatened, or extinct mussel species once called the Tennessee River home, and the decline of species in the area is largely due to overharvesting which surged during the “Alabama Pearl Fever” in the mid to late 1800s. Hundreds of thousands of mussels were caught using mussel brail boats armed with pronged brail hooks that mussels clamped down on as they were dragged along river bottoms. Alabamians were on the hunt for valuable freshwater pearls, but their desperate search often left them empty handed. While many pearls may not have been found, the shells were not useless to those who caught them, as collected shells became popular materials for buttons.

Overharvesting is only one threat to mussels, as the damming of rivers, water pollution, and pesticides have contributed to species loss. Deutsch notes that “the damming of the Tennessee River… contributed to the greatest loss of mussels. Ten known species extinctions occurred because of impoundments…”

Endangered and Threatened Species

Unfortunately, according to the Alabama Rivers and Streams Network, 58 species are listed as threatened or endangered under the Endangered Species Act. During the past century, over five dozen freshwater species of fish and mollusks have gone extinct.

Nearly 50 species are of high or highest conservation concern, a few being two species of Hillsplitter (Lasmigona), many species of Moccasinshell (Medionidus), and several species of Kidneyshell (Ptychobranchus).

Almost 30 species are extirpated, or locally extinct, from Alabama or completely extinct. At least two extirpated species have conservation and restoration actions underway, including the Dromedary Pearlymussel (Dromus dromas) near Wilson Dam and Oyster Mussel (Epioblasma capsaeformis), near Muscle Shoals, both in the Tennessee River Basin.

View Alabama’s threatened and endangered species list.

Restoration Efforts

While these numbers seem grim, hope is not lost. The mission of the Alabama Aquatic Biodiversity Center (AABC), located in Perry County, AL is to restore threatened species through “propagation and restoration.” According to AABC, “by culturing, restoring, and conserving these species, we can help aid in clean water efforts in Alabama’s waterways.” 

Do you have photos or videos of freshwater mussels? If so, share them with us using the AWW Photo/Video Submission form.