A small team of scientists with the San Antonio River Authority is wading through the San Antonio River to take stock of the waterway’s mussels species, including some that are candidates for the endangered species list.
Freshwater mussels are in broad decline in the United States, according to the U.S. Fish and Wildlife Service (FWS). About 70% of North American mussels are extinct or imperiled, compared to 16.5% of mammalian species and 14.6% of bird species, according to the FWS website. Scientists across the nation are surveying rivers to find out why.
Three mussel species within the River Authority’s purview are candidates for gaining federal endangered status: the Golden Orb, the Texas Fatmucket, and the Texas Pimpleback. Scientists are surveying the Golden Orb and Texas Fatmucket population, but have yet to locate any examples of the Pimpleback.
Click here to see a full list of candidate species.
Shaun Donovan, senior aquatic biologist with the River Authority, said the baseline study is a way to refine his and his colleagues’ knowledge of what type of mussels are in the river and where they are located. That information will be valuable as local population growth increases the possibility of development along or near the river that could impact the animals.
“If we know what’s there, we can do a better job of not necessarily advocating for them, but protecting the areas and being very conscientious of the fact that they’re there,” Donovan said. “It will give us a knowledge base that’s very important going forward.”
The River Authority began researching freshwater mussels in 2011, but a more comprehensive study of the creatures began in 2014, Donovan said. The efforts resulted in the first set of mussel surveys that have been initiated or completed in the basin in more than 20 years.
So far, the group has surveyed the four Westside creeks (San Pedro, Alazán, Apache, and Martínez creeks) and lower Cibolo Creek east of San Antonio. Now biologists are working in the lower San Antonio River, and from just southeast of Falls City to the river’s confluence with the Guadalupe River.
Donovan said so far they have identified seven different species in the river basin, and he and his team expect to find others as they continue to survey the lower reach of the waterway.
The River Authority’s effort is similar to the one being led by scientists from Texas State University in the Guadalupe, Brazos, and Colorado rivers. The $2.3 million project, backed by the Texas Comptroller’s office, is primarily focused on five species of Central Texas freshwater mussels – the False Spike, Smooth Pimpleback, Texas Fatmucket, Texas Fawnsfoot, and the Texas Pimpleback – that are candidates for the endangered listing. Researchers will learn more about the bivalves, impacts on their environments, and how to restore them.
As for the Golden Orb, the FWS is expected to make its listing decision in 2020, Donovan said, so the River Authority researchers plan to have their field work finished by the end of 2018.
Listing the mussels as endangered could have wide-reaching implications, including serious economic and environmental impacts for San Antonio and the state of Texas. Various habitat protections that often come with such a distinction could affect water distribution from Texas rivers.
“There are different things [the River Authority] is doing to stay more proactive for a potential listing,” Donovan said. “Our biggest goal with this is to make sure that the candidate decision is based on the best science possible.”
The importance of preserving freshwater mussels can often be lost on the average person, Donovan said. As filter feeders, the mollusks are good indicators of water quality and ecosystem health.
“If mussels die, then that’s a bad indicator for fish and other organisms,” Donovan said.
Donovan and Larry Larralde, also an aquatic biologist with the River Authority, attribute the mussels’ population decline to a number of factors, including unmanaged storm water runoff and the damming of rivers. This reduction of water quantity has large impacts on the ecosystem because it directly affects the mussels’ ability to reproduce, Larralde said.
When a mussel is ready to reproduce, it releases glochidia – the microscopic larval stage of some freshwater mussels – which attach to fish and eventually fall off into another part of the river. In a dammed river, fish are unable to travel upstream or downstream to spread the mussel population.
Gravel mining, sedimentation, and urbanization are other factors that affect water quality. If the water quality is poor, mussels – with their limited mobility – suffer since they can’t relocate to a healthier part of the river like fish or other wildlife.
San Antonio and other communities have been working over the last few years to encourage safe, environmentally sensitive practices by all people – including residents, ranchers, and developers – to ensure optimal water quality in the river basins. Larralde said anyone can help preserve water quality by fertilizing responsibly, cleaning up after pets, and using low-impact development methods.
Protecting water quality hasn’t always been a high-profile issue locally, Larralde said, but now “it’s trending in the right direction.
“We’ve done a lot, but there’s a lot that still needs to be done.”