Southwest Region
Conserving the Nature of America
Southwest Region USFWS facebook page Southwest Region USFWS page Southwest region USFWS Flikr page USFWS YouTube site
San Marcos Mussel Biologists Sciencing the Way to Healthy River Systems and Clean Water
by Al Barrus
April 19, 2018
   

Academy of Natural Sciences of Drexel University Research Associate, Dr. Raymond W. Bouchard, Jr., holding 2 washboard mussels collected as part of a long-term environmental monitoring study on the Sabine River. Credit: Roger L. Thomas/The Academy of Natural Sciences of Drexel University.
Academy of Natural Sciences of Drexel University Research Associate, Dr. Raymond W. Bouchard, Jr., holding 2 washboard mussels collected as part of a long-term environmental monitoring study on the Sabine River. Credit: Roger L. Thomas/The Academy of Natural Sciences of Drexel University.


talking mussel podcast; hand holding a mussel.
Listen to the Talking mussels podcast.
Read the transcript.
Freshwater mussels are easy to miss. They’re nondescript, easily mistaken for rocks, and often spend decades undisturbed, surrounded by mud and gravel.

While they stay out of sight, they’re vital to ecosystems. They remove silt and bacteria from water, improving quality and clarity. If water quality is low, they will close their shells and stop filtering.

In fact, some public water utilities in Europe use mussels to monitor quality. By keeping the mollusks upstream in a cage system, they receive alerts when the bivalves close their shells. And that is a telltale sign that something is in the water. If water quality suffers for too long, mussels die. They’re not unlike canaries in coal mines, but for rivers.

With over 70 percent of North American mussels listed for protection or concern, this is troubling news. Mussels are one of the most threatened animal groups in the U.S. Biologists speculate that a century of habitat alteration in the form of dams, industrial water diversion, and chemical runoff from agriculture has brought these freshwater bivalve mollusks to the brink.

False spike mussel. Credit: Clint Robertson, TPWD.
False spike mussel. Credit: Clint Robertson, TPWD.

The Texas horn shell, for example, was recently listed for protection under the Endangered Species Act. It's native to the Rio Grande watershed, and the last remaining native mussel species in New Mexico. Texas’ watersheds are also seeing steep declines in native mussel populations.

The state is home to over a dozen protected mussel species whose numbers have dwindled in recent decades. There's hope coming in the form of research from scientists at the U.S. Fish and Wildlife Service [USFWS] San Marcos Aquatic Resources Center. Located between San Antonio and Austin, they’re optimistic and hard at work on the cutting edge of mussel science. They’re developing conservation techniques to help strengthen the wild populations of these subtle but ever so vital shellfish.

Aquatic Biologist Josh Abel is a lead mussel scientist in the USFWS Invertebrate and Amphibian Ecology and Conservation Research Program at the San Marcos Aquatic Resources Center. "We're currently working with five species native to Central Texas: the Texas pimpleback, Texas fat mucket, Texas fawns foot, smooth pimpleback and false spike. Four of those species are currently candidates for federal protection and one more is proposed for listing. We're also currently working with the newly endangered Texas horn shell which is found in the Rio Grande drainage," said Abel.

Golden orb mussel in water. Credit: Clint Robertson, TPWD.
Golden orb mussel in water. Credit: Clint Robertson, TPWD.

Texas fatmucket mussel. Credit: Clint Robertson, TPWD.
Texas fatmucket mussel. Credit: Clint Robertson, TPWD.

A major theme of the hatchery’s research is developing science so that hatcheries can breed the mussels: this is called propagation. Their aim is to maintain a genetically diverse captive population or refugia. Perhaps to the most popular example of refugia is Noah’s Ark. It serves as a fail-safe in case the wild population were to disappear.

While the San Marcos hatchery isn’t specifically meant as a rufgium site, they’re developing breeding and refugia techniques that will be free to any hatchery interested in establishing mussel refugia. From the refugia, the mussels can eventually be transplanted to restored river sections in need of these filter-feeding river canaries.

The tricky part is getting the wild habitat back to how it was. Mussels are indiscriminate filter feeders: they ingest anything that is in their water. And so they’re very sensitive to river-bottom conditions. Since they can’t move, they are at the mercy of their neighbor’s habits.

Each mussel species needs a specific habitat. If conditions change too much, they can’t survive. Survival factors for mussels include how fast the water flows, water chemistry, contamination, water temperature, and the amount of silt. If there’s too much silt, they suffocate. Is there enough water flowing year round? Many southwestern rivers dry up because of drought and industrial diversion.

Texas pinpleback2 mussel. Credit: Clint Robertson, TPWD.
Texas pinpleback2 mussel. Credit: Clint Robertson, TPWD.

The conditions that can kill them are called limitations. Learning limitations is a major part of research for San Marcos biologists. Knowledge of these conditions is necessary before they can restore each species back to their original range.

“Most extirpations that have happened and continue to happen with all taxa of animals are mostly because of habitat loss, so that’s the obvious correction that needs to be made before any restocking effort’s going to be successful, water quality and water quantity are concerns that need to be addressed. That’s where the limitations of life history studies can really help elucidate if parameters are suitable for restoration in that area,” said Abel.

Mussel conservationists hope to restore mussels to their old habitats from hatchery refugia. However, they must first assess what caused the mussels to disappear in the first place. (This is called extirpation).

“It's really just going to be correcting those problems. There should be a smoking gun of what caused the extirpation of that population to begin with. A lot of these rivers are highly urbanized, so you're also talking there about water quality. So whatever the issue may be, like a sewage treatment plant from before standards were as high as they are today is a likely culprit. So it's about making sure that those issues are corrected,” said Abel.

Mussels live decades-long lives, and it takes years for them to breed in the wild, so their conservation and reintroduction really takes a long time.

Mussel works its mantle tissue in this short video clip. You can see the mussel tissue wave back and forth in the water. Credit: USFWS.
Mussel works its mantle tissue in this short video clip. You can see the mussel tissue wave back and forth in the water. Credit: USFWS.

“Basically you put a mussel back in the river in a cage system where you can come back and track them, and you just monitor their survival, growth, and health over time. For some of these species it takes several years for them to reach sexual maturity, so you might not know that your efforts have paid off for several years: close to a decade,” said Abel.

The road to mussel recovery isn’t overnight, and the work isn’t easy, but the outcome is well worth the effort.

“Anytime you're restoring a population, in my opinion, that's a victory in and of itself. Your returning things to the way they're supposed to be. In addition to that, mussels are also important in further restoration. Not only are they the goal of restoration but they're a tool that can be utilized for restoration,” said Abel.

The effect of reintroducing native mussels into any ecosystem will have positive effects that radiate into their surroundings, and positively impact recovery of the rest of the system.

“Their presence improves water quality. They can filter a tremendous amount of water. Adults of larger species can filter in excess of 30 gallons a day per mussel. They also help stabilize bank substrate as well as transfer nutrients from the water column to the river bottoms,” said Abel.

For Abel, the set of challenges presented to mussel biologists in the Southwest are especially unique and exciting. “Here in the southwest, we have a really unique group of ecosystems. If you look east to west, eastern Texas to western Arizona - those are as starkly different as you could possibly get in this country.”

Scientists at San Marcos are very much on the frontiers of fish biology. So much is still unknown for freshwater shellfish in this region, so it’s still like the wild west for them. “We're really at the cutting edge for what's known about a lot of those habitats, so mussel work here is probably equivalent to where fish research was a hundred years ago,” said Abel. “That's incredibly exciting as a scientist. It's also great to introduce people to this entire taxon of animals they know little about, and kind of show them the importance of them in our region. Hopefully, mussel restoration here will be a success and that folks can witness and be a part of it in the coming decades.”

Last updated: October 5, 2018