You may be wondering, what’s the big deal with all these mussels? Don't they just sit around in the river? Well, mussels are in fact a very important link in the river ecosystem and play an important role in your life as well!
Historically, mussels have been very valuable to humans
Based on piles of mussel shells found near river banks of archeological sites, we can conclude that Native Americans used mussels in some way or another. The mussels that we eat today come from salt water because freshwater mussels do not taste very good.
These mussel species are all
However, if Native Americans only had access to freshwater mussels, it is quite possible that they used them for food. Other uses included tools, spoons, and jewelry from the pearls that mussels produce. By the 1900s, European settlers found a use for mussels too, making buttons out of the hard, durable shells. During this time, thousands of pounds of mussels were harvested each year for the textile industry, with no respect to environmental impact. By the 1940s, plastic was invented and it replaced mussels to make buttons. This lessened the demand for mussels, but the damage was already done. Over 40 years of harvesting mussels left many species impaired. Fortunately, some native populations began to recover over time.
However, this was not the end of hardships for the mussels. Other problems that the mussels still face today relate to the effects from farming and industrialization on rivers. Before we understand how these actions impair the life of a mussel, it is important to learn about their habitat, how they function, and what they need to survive.
Suitable habitats for mussels range from small ponds and streams to large lakes and rivers.
Common Name - Scientific Name
**federally listed endangered (2)
Here is some helpful watershed vocab!
Unlike some of their other aquatic friends, mussels do not have fins to allow them to swim to their food. Instead, they wait for food to come to them. They are called filter feeders and they rely on the water currents to bring nutrients to them. One mussel alone can filter up to 8 gallons of water each day! Mussels remove pollutants like E. coli bacteria, silt, and suspended organic nutrients. This improves water quality, benefiting other aquatic wildlife and humans!
Mussels go through a very unique life cycle, and can live up to 70 years! It all begins when fertilized eggs in the females develop into larvae, called glochidia. These glochidia need to survive off the blood from fish for the first few weeks of their life, and then disperse throughout the river. To accomplish this, mussels must "trick" fish. The video below demonstrates how mussels have evolved to entice fish and fool them into thinking the sac that holds the glochidia is a food source. When the fish try to bite the sac, the mussels are able to disperse their glochidia onto the fish.
(This video was shot in Missouri, but the same species starring in this video are also found in the Harpeth: The Lampsilis mussel, bass, darters, and striped shiners)
The glochidia attach themselves to the gills, fins, or body of fish where they can then feed off their host. Since this causes no harm or pain to the fish, but benefits the mussels, it is an example of commensalism. After a glochidium receives enough nutrients from the fish, it releases itself, drifts to the bottom of the river, and begins its life as a juvenile. This next stage usually lasts 2-9 years until it matures and is able to reproduce. Once in adult stage, the mussel can live 60 – 70 years under the right conditions.
Mussels play a key role in the ecosystem of a river. Mussels filter the water, creating a healthy and happy environment for surrounding fish, especially those most sensitive to pollution. They also provide food for fish, as well as muskrats, birds, otters, and raccoons living in or near the river. Mussels and fish are very much interdependent. While the mussels provide food for certain fish, some mussel species rely on specific fish for their glochidium to attach to. If one goes extinct, there is a strong possibility that the other will eventually go extinct as well, reducing biodiversity and ecosystem health overall. The impacts go beyond aquatic species to human populations. Extinction of mussels would mean that a natural pollution filter would disappear, increasing the pollution levels in waters. Extinction of fish species that rely on mussels would mean that fishermen will be disappointed when their favorite fish disappear.
We also rely on mussels as bio indicators, meaning they can indicate how clean the water is. All mussel species are affected by pollution, but some species are more tolerant than others. If we know which species are present in a river segment, each species' tolerance to pollution, and the number of individuals present, we can determine the water quality in that area.
Hardships the mussels face today
When European settlers began to clear land of trees and vegetation for farming and industrial use, the amount of sediment and pollutants entering into the river as polluted runoff increased. Although mussels can filter out silt and pollutants, too much sediment is bad because it can cover the mussels and suffocate them completely. Sediment also fills in the small spaces in gravel beds where some mussels live, forcing them out, and they cannot adapt to this habitat change. As if the extra sediment in rivers isn’t bad enough, many times the sediment is filled with pollutants like fertilizers from farmlands, or chemicals from industrialized areas. As chemicals like ammonia and heavy metals filter through the mussels, they can accumulate in the tissue of the mussels, causing them to die. If too many nutrients from fertilizers are delivered to the river, the growth of algae and aquatic plants will also increase. This will actually reduce the flow of water, thus reducing the flow of good nutrients into mussels, and over time reduce the supply of oxygen. Currently, the two major pollution issues affecting the Harpeth are over-sedimentation, and nutrient overload.
Dams along rivers have also posed a great obstacle for freshwater mussels, literally. Dams constructed in rivers limit the movement of aquatic wildlife between the upstream and downstream sides of the dam. This is especially harmful if mussels are stuck on one side of the dam, and the fish they rely on to disperse their glochidia are on the other side. Luckily, the entire Harpeth River has been dam-free since July 2012, with the removal of the lowhead dam in Franklin, making it completely free-flowing. This is great news for the mussels that call the Harpeth River their home!
Tennessee is a very special place for mussels. Pre-industrialization, 300 different mussel species lived in the U.S., of which 130 were found in Tennessee. Though the overall number of mussel species has decreased, Tennessee still contains the second most diverse mussel population in the United States. According to the Tennessee Wildlife Resources Agency, 42 known species found in this state are on the federal endangered species list, and 2 are listed as threatened. Freshwater mussels are more at risk of extinction than any other group of animals across the entire United States.
Economic uses today
Today, there is a high demand for mussels in the pearl industry, specifically in Japan and China. Pearls used for jewelry come from oysters, but what many people don’t know is that in the very center of most oyster pearls is a little piece of freshwater mussel! Both mussels and oysters contain a substance called nacre. When a foreign object is lodged inside an oyster or mussel, it continually coats the object with nacre to reduce irritation. The result is a magnificent pearl! However, finding a natural pearl in a mollusk is extremely rare, and takes a lot of time and effort. That all changed though when a man, Kokichi Mikimoto, decided to “create” his own pearls. He lodged foreign objects inside oysters, and then waited, in hopes of finding pearls. When it was finally time to pull his oysters from the water, he was happy to find he had indeed created a pearl!
After much experimentation with inserting various objects into the oysters, it was finally concluded that the best substance to use for creating a pearl is in fact a piece of freshwater mussel shell. Small sections of mussel shells are extracted, rounded, polished, and then inserted into the oyster to serve as the “nuclei” of the pearl. After many coatings in the oyster’s nacre, and a waiting period of 2 – 6 years, a pearl is created. Today, about 80% of freshwater mussels exported from the U.S. come from Tennessee! Each year, 2 – 5 million pounds of mussels are exported, which brings 2 – 6 million dollars into Tennessee.
Since much attention has been brought to mussels lately, there are many regulations for harvesting mussels. In Tennessee, there are only 10 different species which can be removed from their environment, and they must be a certain size to ensure juvenile mussels are not taken before they have a chance to reproduce.
What can you do to help?
The best way to help these mighty mussels is to consciously reduce, or eliminate when possible, actions that lead to pollution. You can do this by minimizing the use of fertilizers as much as possible and following application directions, leaving streamside vegetation as is, keep livestock out of streams, and reporting any suspected water pollution problems. When you are playing in the river, make sure to not disrupt the mussels or remove them from the river.
Photos courtesy of TWRA