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July 2010 cover image 12 Why Water Matters

Below the surface

Freshwater mussels are disappearing from Texas waters.

By Kathryn Hunter

Camouflaged to suit their surroundings and buried in sand or mud, freshwater mussel species like the washboard (Megalonaias nervosa) may live for more than 100 years and grow up to a foot long without attracting more than the attention of a passing minnow. Freshwater mussels, though one of the most varied and fascinating groups of animals in the U.S., often are overlooked and underappreciated by the humans who share their waterways.

Many freshwater mussel species are disappearing from Texas waters as quietly as they once inhabited them. In January 2010, 15 of the 52 species found in Texas were placed on the state threatened list, and 11 are being reviewed by the U.S. Fish and Wildlife Service as possible candidates for the federal list of threatened and endangered species.

“The reason we’ve listed these 15 species as threatened is that we’re pretty certain at this point these species are extremely rare,” says Wendy Gordon, leader of the Nongame and Rare Species Program for the Texas Parks and Wildlife Department. “It’s possible that we may come up with some populations that were previously unknown, but some of these species haven’t been seen in a decade or more, and truthfully, we don’t know if they’re gone from the state.”

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Gordon describes the state listing as a stepping stone. The listing makes the collection or possession of the threatened species a Class C misdemeanor. Without a permit, an individual is prohibited from handling the mussels, whether alive or dead.

Mussels are filter feeders, using a siphon to suck drifting plankton and oxygen through their gills, while a muscular “foot” allows them to stay rooted in place or to move slowly. Freshwater mussels rarely move more than 100 yards in a lifetime and often stay in a single spot. For this reason, they are particularly susceptible to water quality problems and habitat degradation, as well as illegal harvesting and competition with invasive species.

The presence of freshwater mussels is a sign of a healthy aquatic system, and their feeding process serves to further purify the water. The sudden disappearance of mussels in an area often indicates water pollution problems or other environmental concerns that are likely to affect other aquatic and terrestrial species.

Freshwater mussels may also play a vital role in processes that are still not completely understood. Many species of mussels release larval young, called glochidia, which attach to host fish species, create a cyst and then, after riding along for a short period of time, fall from the fish as a tiny but fully developed mussel. Researchers believe that this parasitic relationship may help protect the host fish against other infestations for up to six months afterward.

To attract their host fish, some species use complex “lures.” For example, the Texas fatmucket (Lampsilis bracteata) displays a fishlike lure made up of mantle tissue to draw the fish closer.

Gordon says mussels benefit from any efforts that keep the water cleaner and clearer, such as planting native grasses, maintaining riparian buffers, limiting erosion and using alternative sources of water such as stock tanks for livestock.

Marsha May, a TPWD biologist and Texas Nature Tracker coordinator, administers the Texas Mussel Watch program, training and certifying citizens to collect data about the mussels in the waters near their homes. Several teachers and professors have incorporated these mussel surveys into their lessons, collecting data every year from the same location, which allows researchers to determine how mussel populations have changed over time.

“I’m very optimistic because I’ve been involved in Texas Mussel Watch for nine years, and I’m seeing more interest than I’ve ever seen before,” May says.

To learn more about Texas Mussel Watch, visit www.tpwd.state.tx.us/tracker

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