Texas fatmucket mussel conservation provides significant value in regional water filtration efforts

At its regular meeting Sept. 18, the Environmental Commission heard updates on Austin’s freshwater mussel population from Matt Johnson, Texas freshwater mussel conservation and recovery coordinator with the U.S. Fish & Wildlife Service, and Bianca Perez, an environmental scientist with the Watershed Protection Department. Of significant conservation interest was the Texas fatmucket mussel species.

Texas fatmucket mussels “provide a lot of ecosystem services that we don’t really recognize,” said Johnson. “A single freshwater mussel can filter anywhere between 8 to 15 gallons of water a day. When they are filtering, they’re pulling out bacteria, pulling out algae, detritus, sediment, purifying the water … and preventing stream compaction.”

This adds incredible value to the ecosystems these mussels inhabit, which is estimated by David L. Strayer, senior scientist and researcher at the Cary Institute of Ecosystem Studies, to be in the millions of dollars.

Essentially, Texas fatmuckets “do the work for us,” said Johnson.

This species is of specific importance to the region since the Texas fatmucket is geographically separated from other areas. “If we were to lose them, there would be no way to replace them with populations from other areas,” said Johnson. Other mussel species in the area, like the invasive zebra mussel, filter too much from the water – resulting in decreased fish populations, harmful algae blooms, overgrowth of aquatic plant, and other negative impacts on the ecosystem.

Historically, freshwater mussel conservation efforts date back over nearly two decades. In 2007, WildEarth Guardians petitioned the U.S. Fish and Wildlife Service to list six species of freshwater mussels as endangered or threatened under the Endangered Species Act. In 2021, the USFWS proposed listing five of these species as endangered and one as threatened. Included in the list was the Texas fatmucket mussel.

Depending on whether a species is classified as endangered or threatened results in different protections being designated by the Endangered Species Act. An endangered species is classified as “a species which is in danger of extinction throughout all or a significant portion of its range,” and receives full legal protections under the act. A threatened species is classified as “any species likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range,” and receives tailored protections under the act.

Additionally, in 2021 the USFWS designated a critical habitat for all six listed mussel species. Critical habitat identifies geographic areas that are essential to the conservation of federally listed threatened or endangered species and includes necessary physical and biological features. A riverine system with habitat to support all life stages of the mussel species was designated, which provides for the following: suitable substrates and connected instream habitats, adequate flows, adequate water and sediment quality and identified host fish present. An important distinction of critical habitats is that they do not affect land ownership or establish a refuge, wilderness, reserve, preserve or other conservation area. The most important effect of designating such habitat is that federal agencies are required to consult with the USFWS when they undertake, fund or authorize any activity that may affect the species or critical habitat.

Onion Creek was designated as a critical habitat for the Texas fatmucket, consisting of 23.5 miles of river in Travis County. This unit begins at the Interstate 35 bridge crossing downstream to the confluence with the Colorado River. The unit combines the proposed lower and upper Onion Creek subunits. Recent survey data confirms that Texas fatmucket mussels inhabit upper Onion Creek, which had been previously thought to be unoccupied.

The Environmental Commission will consider developing an Onion Creek working group to further aid USFWS’s efforts in protecting the Texas fatmucket mussel population.

The Austin Monitor’s work is made possible by donations from the community. Though our reporting covers donors from time to time, we are careful to keep business and editorial efforts separate while maintaining transparency. A complete list of donors is available here, and our code of ethics is explained here.