You might not always see them, but they help keep the Brazos River and its many tributaries clean and clear.
Freshwater mussels have long played an important role in our ecosystem. However, due to a variety of impacts on the ecosystem, freshwater mussel populations are now in peril throughout the country, including throughout the Brazos River basin.
Mussels are often mistaken for rocks, as they lay on the bottom of waterbodies. The U.S. Fish & Wildlife Service described them as “living rocks” due to their lack of movement. Despite not moving often, they still eat by filtering water and can even reproduce without moving.
Described as “vacuum cleaners of the aquatic ecosystem,” mussels can have a life span anywhere between five and 50 years, according to Texas Parks & Wildlife.
In the world, North America has the highest diversity of mussels, but the Nature Conservancy reports that 70 percent of the mussel population has become extinct or imperiled.
In Texas, more than 50 native species have been documented. TPWD said that 15 of those species are listed as threatened at the state level. Six of those included at the state level are candidates for being listed under the U.S. Endangered Species Act.
But how did they get there?
The mussel population has a long history of being used for tools and utensils, as well as serving as a food source. The USFWS said that mussel shells were (and are still being) harvested for other material. By the early 1900s, mussel shells were being used to make pearl buttons. By the late mid-1900s, their shells were being harvested to create “seed pearls.” The USFWS estimates that tons of mussels are harvested in North America every year to be shipped to Japan to be used as seed pearls.
In the Brazos River basin, mussel harvesting has been prohibited in some areas. Texas Parks and Wildlife regulations ban the harvesting of mussels in the Brazos River from the Possum Kingdom dam in Palo Pinto County downstream to FM 2580 in Parker County.
Other than harvesting, the mussel population is dwindling due to a variety of environmental reasons.
Sedimentation and pollution have always been issues that mussels face, but it will only continue. Sediment entering river and streams can bury the bottom and bury mussels living there. The USFW said that mussels cannot live on muddy, sandy bottoms. Sediment that comes with runoff could also contain pesticides or other chemicals, causing more pollution in water.
Another issue plaguing mussel populations is the invasion of exotic species. Zebra mussels have infested several Texas bodies of water, with over 21 of them having documented their presence.
Zebra mussels were first seen in Texas waters in 2009. The USFW said that zebra mussels were a “widespread ecological and economic threat.”
“The problems with the zebra mussel are that they’re not native,” said Brazos River Authority Environment and Compliance Manager Tiffany Morgan. “In a lot of places, they can outcompete the native fauna. There’s not a lot of native predators for [the zebra mussel]. They grow exponentially with very little control. We do have some things that will eat them, but just not enough.”
Zebra mussels have the ability to stick themselves to any hard surface, which includes native mussels. A native mussel could be covered with zebra mussels, which would make it harder to move, eat and reproduce. The USFW said that a native mussel was once documented with over 10,000 zebra mussels covering it.
Much has been done to spread awareness on the effects of zebra mussels, especially through Texas Park & Wildlife’s “Clean, Drain and Dry” campaign.
The USFWS said that there are a variety of reasons the public should care about the declining mussel population. Mussels are indicators of aquatic health. The presence of mussels, according to USFW, signify a healthy aquatic system which would, in turn, mean good fishing and good water quality. Mussels also are natural filters, which help purify the aquatic system. Mussels also present discussions on biodiversity. USFWS said that close to 300 species of mussels have been found in North American river and streams, while only less than 20 species of mussels are found in other parts of the world.
Moving forward, here are tips from the USFWS on how you can help protect mussel populations:
- Limit pesticide use to conserve soil and prevent runoff into nearby lakes and streams.
- Help control soil erosion by planting trees and plants to avoid runoff into freshwater areas.
- Remove aquatic weeds stuck to your boat and boat trailer before using again to prevent the spread of invasive plants and zebra mussels.
- Follow protocol on zebra mussel quarantine, inspection and decontamination programs
You can also help TWPD track mussel populations by adding observations here.