These unphotogenic bivalves may not be as majestic as a humpback whale or as cuddly as a panda — but our impact on their environment can be just as devasting, and more immediate.
Twenty minutes east of Wichita, the sound of traffic from Highway 254 mingling with the calls of blue jays overhead, Amanda Reed ’00/02 stops, shovel and sifter in hand, and surveys the scene. Before her is Whitewater Creek, part of the Walnut River basin. It’s a shallow, sluggish current maybe 10 feet across, making about as much noise as a $19.95 serenity fountain. Exposed tree roots grip the high banks, and the smell is wet with decay. At the base of a tree, an abandoned air conditioner rusts quietly. “It’s pretty, isn’t it?” says Reed. “Except for the trash.”
Clad in brown chest waders, Reed slogs into the creek, loads up her sifter with muck from the bottom, and starts picking through it. It’s an action that must be second nature by now — from May through November of 2001, she did this every day from 8 a.m. to dark, sampling 87 sites throughout the basin for her graduate thesis in biology. What she’s looking for are mussels — both living individuals and the shells of dead ones. She looks for them by sifting, by crawling on her hands and knees, and, if the water’s too deep, “You learn to feel them with your feet.” Today, she finds only the empty shells of a giant floater (Pyganodon grandis) and a mapleleaf (Quadrula quadrula). It’s not a wasted trip, though; she proudly displays snails, two types of dragonfly larvae, and a freshly dead crawdad. She admits to getting sidetracked throughout her study, catching fish and crawdads with the sifter — “My goal was to catch a water snake. But they’re just too fast.”
Shell Shock
There’s a method to Reed’s muddiness, however. Back in 1980, Rose Hacker ’80, also a WSU grad student, conducted a study “to determine the distribution and abundance of unionid mussels in the Walnut River Basin … and to determine what changes had taken place in the distribution of mussels since earlier studies and what factors may have contributed to these changes.” Hacker studied a total of 120 sites, about five miles apart, and found evidence of 21 species, of which 18 were represented by fresh material. She compared her data with three studies made between 1885 and 1906, which documented 25 species in all. Using detailed maps Hacker left behind, Reed attempted to duplicate her study at as many sites as possible. Where Hacker had found a slight decline in mussel populations, Reed found decimation — of the 18 species found living in 1980, only eight remain.
“The thing about mussels is … ,” sighs Reed, and then launches into a rapid-fire overview of their multistage life cycle. The female’s eggs are in her gills, and are fertilized there. They hatch into larvae called glochidia, which leave the mother and attach themselves to a fish host, feeding on its blood. Glochidia develop into tiny adult mussels — “we’re talking a quarter of a millimeter by a quarter of a millimeter,” says Reed — and then drop off into the substrate. If all goes well, they stay buried there for as much as 10 years, reach adulthood, and continue the cycle.
But so much can go wrong. The miniscule adults are easy prey for fish, crayfish, even insects — and if they fall into substrate that’s too deep or too rocky, they’ll die. Then, if the mussels can manage to survive the lengthy turnover between infancy and maturity, their water-borne method of reproduction requires a large number of other mature adults nearby on the streambed. Even without human interference, it seems amazing that they carry on at all.
Precarious Position
The delicate, slow-moving life of mussels, however, is particularly susceptible to disruption by man. Every species has a particular “microenvironment” — for instance, some, called lodic, prefer quick-moving water, others slow (“lentic”). “When you impound water, like El Dorado Lake [completed in 1981], it kills lodic species. Humans have control of the flow, and it can slow down the streams coming out of or into the lake.” Reed says all of the eight species she found alive were lentic.
Other human factors can quickly upset a mussel’s tenuous existence. Few of these are meant to affect the mussels directly — though, at the beginning of the last century, mussels were harvested in huge numbers for use as decorative buttons, a multimillion dollar industry until the advent of plastics. Now the problem has little to do with the animals themselves, but what Reed refers to as “mistreatment” of their environment. Reed names some human disturbances, and their repercussions: “If you farm right up to the edge of the water, it increases erosion, and washes away rocks. Paving the ground makes it unable to absorb moisture, so everything runs off into the river. Cows come to drink in the river, and leave behind waste full of fecal coliform bacteria, which use up oxygen the mussels need — and sometimes cows just stomp on the shells. One thing that’s happened a lot in Cowley County is dredging — pulling up rocks out of the substrate to use elsewhere — mussels live in the substrate, and then it’s gone. It makes the water too deep to sample.”
Hacker says, “There was definite evidence of human interference all along the river [in 1980]: cropland, oil wells and impoundments. … The results of my study seemed to indicate that the species which seemed to be increasing were those that were tolerant of intermittency, silt and pollution. They are thin-shelled, grow rapidly and reach sexual maturity earlier than other species. The declining and/or extinct species were mostly heavy-shelled, long-lived, late-maturing, more sensitive to silt and pollution.”
This trend was borne out by Reed’s study. While she can’t vouch directly for the presence of pollutants in the Walnut, she points out that mussel species known to be sensitive to pollution have died out in the river. Pollution can come from wastewater treatment plants and effluent from industry, or runoff from farms. “Because mussels can’t move and find a better place to live, they’re good water-quality indicators,” she says. “Sometimes direct measurement [of water quality] can be inaccurate because a river’s a flowing system — it changes every day.”
Long-Term, Not Quick Fixes
Though Reed could be described as an “environmentalist” — she prefers “nature lover” — she readily admits that the damage to the river cannot be reversed. “I live just like everybody else,” she says. “I like water treatment plants, all that. I’m talking long-term, that people need to be thinking of the next hundred years, gradually improving things, instead of just thinking of right now.” So she doesn’t have any ready answers to the question, “How can the mussels be saved?”
But she does have suggestions. For example, she advocates the use of “buffer zones,” a line of grass or trees between a farmer’s field and the river; these sturdy plants will absorb pesticides and survive, while preventing the chemicals from reaching the water. There’s a similar technique called “no-till” or “no-plow.” Often, after harvest, farmers clear all the plant debris from their fields. This, again, leaves no vegetable matter to soak up possible pollutants. Beyond that, she says, “We need to have respect for it, the way we use the land, the way we use the water.”
Falling In Love
Mussels aren’t cute or furry or big-eyed. Most Kansans don’t even know they exist in the state. But these two women who spent days counting their shells and searching for their young came away fascinated — and concerned.
Reed, who knew little about mussels before wsu biology professor Don Distler suggested the project, has “fallen in love” with them. She grins widely as she describes their various methods for attracting host fish to the glochidia: “Some of them have mantle flaps that are colored and wave in the water to attract fish, and then when the fish is over them, they sense it — they don’t even have eyes! — and then they release the glochidia. Or some of them package the glochidia into little bundles that look like worms or insect larvae. I mean, isn’t that cool?”
Hacker has similar affection for the bivalves: “I gained an appreciation for freshwater mussels as the silent monitors of the health of a body of water, whether a river or a lake. Their dependence upon specific species of fish for the survival of their offspring struck me as a call to be more aware of the interconnectedness of us all. If we continue our trend of consumerism, with little regard for our environment, not only will the mussels suffer, we will find ourselves struggling for survival.”
In the end, mussels matter.
— By Anna Perleberg
