By Abbie Gascho Landis
I stand, dripping, in Alabama’s Paint Rock River, and what looks like a rock in my hand is alive. She is a native freshwater mussel called a snuffbox. Her apricot-sized shell meets in a blunted edge, forming a curving triangle, which is mottled yellowish and dark brown. I have lifted her from the river’s cobbled bottom, where she blends in with the stones around her. Unlike the rocks, though, the mussel’s shell sits slightly agape on river bottom as she inhales and exhales the river.
The Paint Rock River tugs gently at my knees, my sandal straps. My husband, a mussel biologist, watches our four-year-old son turn somersaults in the water as our two-year-old daughter eats pretzels on the sandbar. We have come to this northeastern corner of Alabama to meet the Paint Rock, a freely-flowing tributary of the Tennessee River. Once suffering from typical damages to a river system—including agricultural run-off, forestry practices, trash, septic leakage, and industry—the Paint Rock River now flourishes with exceptional diversity. The Nature Conservancy, collaborating with many others, restored and protected stream sites and riparian buffers in the watershed. Now the river system supports over one hundred fish species, and about forty-five mussel species, including twelve globally rare mussels. We have come to see mussels like the one I hold.
On my palm, she feels alive. Her weight presses my skin. A squirt of water arcs from between her shell halves, delighting me. Mussels like this endangered snuffbox, Epioblasma triquetra, can filter almost a liter of water each hour, and a community of them—such as we find in the Paint Rock River—can clean up to 100% of the water flowing past them. Nestled into the river bottom, this snuffbox has two openings in her soft body, poised just beyond her parted shell edges. One opening draws in water the way we might draw a breath, but the mussel’s relationship with water is even more intimate and complicated than ours with the air around us.
The water flows across her gill leaflets in the way a breeze might rifle the pages of an open book. The pages of these gills are selectively porous and lined with beating, hair-like cilia. Mussel gills absorb oxygen from the water and sort particles as edible or non-edible. They chase the edible algae and other plankton towards the mussel’s mouth. They also capture sperm launched from an upstream male mussel to fertilize the female’s eggs. When fertilized eggs become larval mussels, the maternal gills expand to form marsupial compartments, sealing these babies from the river while they are brooding. This snuffbox mussel can multi-task better than I can as a working mom.
Then she must accomplish what seems impossible—to install her larval babies onto the gills of a fish. Native freshwater mussels of the Unionid family require fish hosts for their offspring. Some species’ larvae can transform into their free-living juvenile stage on many types of fish. Some, including this snuffbox, must use a particular fish species. For the snuffbox, a logperch.
Tactics vary among mussel species for getting their babies onto fish gills. Many mussel females display part of their body as a lure, decorated by millennia of evolution to mimic the favorite prey of the necessary host fish, such as minnows, worms, or crayfish. The mussel can display this lure from between her shell edges, waggling it just above her baby-filled gills. When a fish strikes, the gills burst. Larval mussels explode into the fish’s face. The snuffbox holds her lure just inside her shell edges, which are lined with serrations. When a logperch strikes the lure, the snuffbox can clamp her shell onto its head, holding it to allow her Pac-man-shaped larvae to clamp onto the fish’s gills.
I rotate my hand to see the tiny teeth along the snuffbox’s shell edge. As I peer at her, a white slug seems to ooze from her shell. She is extending her muscular foot, probing between my fingers for stability. I am breathless at this interaction. Mussels use their foot to creep across river bottom and to dig themselves into the sand or mud or pebbles. They can only succeed in living where the substrate is stable, where they will not wash away with it.
I feel like I could live almost anywhere, but this mussel cannot. She must have a stable creek or river bottom, which is not disrupted by dredges or other machinery. She needs logperch in her creek or river. Without logperch, she will fail to reproduce, even if plenty of male mussels live nearby. She requires clean water. Mussels live in complete reciprocity with water, as it flows through their filtering bodies, giving them food and oxygen. A mussel’s body and a river’s water change each other. They are inextricable.
Lowering the snuffbox back down through the water—from the surface to her place on the bottom—my arm joins my legs underwater. I am less intimate with the river than this mussel, but I cannot live without it. Through my snorkel mask, I see the prominent veins in my lowered hand, the streams coursing inside of me. On the inside of my wrist, two tributaries meet, draining the watershed of my hand. Our bodies are a spongy loam, mostly water, also vulnerable to the damaged, but resilient health of rivers and fresh water.
In 2017, saying that we need clean water to survive seems trite—old news. Our pre-school kids, playing just downstream of me, already denounce pollution. They take for granted that adults want clean water, too. In 2017, however, we see protection of waters backsliding, as the U.S. Environmental Protection Agency suffers from ill-qualified leadership. If the Clean Water Act is undermined, we face the return of freshwater damages that will be hard to explain to our children. Fortunately, there are still mussels in healthy rivers to point a way forward. We can look to mussels as water filters and as indicators, knowing that their fate—their extinctions or their survival—is coupled to our own, water-dependent lives.
Abbie Gascho Landis, author of Immersion: The Science and Mystery of Freshwater Mussels, is a writer, veterinarian, and naturalist in upstate New York. Find her on Twitter @abbiergl or abbiegascholandis.com.