When you think about endangered species, what do you picture? Pandas? What if you learned that the most endangered group of animals in the Midwest — including Ohio — aren’t cute and fuzzy mammals that melt your heart, but hard-shelled critters that look like rocks, living hidden lives at the bottom of rivers, lakes and streams?
That’s the challenge for Andrew Phipps and others involved in projects to conserve and help restore decimated populations of the humble freshwater mussel.
Get to know them
“We want folks to get to know these animals; people don’t care about what they don’t know,” said Phipps, a mussel biologist with the U.S. Fish and Wildlife Service’s White Sulphur Springs National Fish Hatchery, in the highlands of West Virginia.
“What we want is for people to view mussels like they do pandas,” he said.
One way is to show how essential they are to freshwater ecosystems. Their methods of feeding make them fantastic filterers. Studies show an adult mussel can filter up to a gallon of water an hour, 24 hours a day. Another way is to show how absolutely fascinating mussels are. Yes, fascinating.
They may not have a brain, and only one foot to stand on, but mussels are perhaps one of the most clever — even devious — creatures on Earth when it comes to reproduction. They need fish — different species of fish for different kinds of mussels — to serve as hosts for their hitch-hiking young. As they travel, the fish hosts allow the young to grow into juvenile mussels — and avoid washing downstream to unsuitable habitat.
Female mussels “catch” those fish using methods that even the most seasoned angler might envy. How about using lures that include worms, crayfish, minnows and even a wet fly like the ones used for fly fishing? Or — a technique so good it’s almost criminal — snapping one’s shell shut on the nose of a fish and holding it hostage until its gills are stuffed with mussel larvae?
Mussels do all this and more, right here in the Ohio River basin where Phipps and his crew do most of their work. More on the mussel’s interesting sex life later. Oh, and they can live for 70, 80 or 100 years in North America, while some in Siberia top 150 years.
Their shells come in a variety of colors and shapes from round, to oblong, to lance shaped, and range from one inch to almost a foot in diameter. At the dawn of the 20th century, the Ohio River basin was home to 127 of the nearly 300 species of mussels native to North America. That’s more than all the species in Asia, and more than those in all the countries of Europe combined, Phipps said.
Human interference
Since then, human activity that changed their environment has resulted in 11 of those species becoming extinct, and 46 that are endangered, threatened or “state species of concern.” That human activity started with the birth of the button industry in the late 1800s. Before the invention of plastic, mussel shells were used to make buttons.
“There are pictures of men standing on piles of mussel shells that are as big as a house,” he said.
Another business that exploited mussels for their shells was the cultured pearl industry, which developed in the 1960s but still continues today, mostly overseas. Pellets are cut from mussels’ shells and implanted in oysters, which then cover them in layers to create pearls. Add pollution, dredging and dams, and the result was mussels’ demise.
“No other group of animals in the Midwest is so gravely imperiled,” the FWS says in an article titled America’s Mussels: Silent Sentinels.
“To put this in perspective, The Nature Conservancy reports that about 70% of mussels in North America are extinct or imperiled, compared to 16.5% of mammalian species and 14.6 percent of bird species.”
“Across the range, they are in decline,” Phipps said of the mollusks. “They’re the most prevalent group on the endangered species lists now.”
Silent sentinels
Why are they “silent sentinels”? As mussels go, so goes the health of the aquatic ecosystem. They’re the underwater version of the canary in the coal mine.
On the mussel’s gills are scillia, like little fingers, that sort out the particles floating by in the water. They put what they want in their mouths and get rid of what they don’t. What they get rid of is called “pseudo feces” because it’s not eaten or digested, so it’s not actual poop.
But the mussels do pull unwanted gunk “out of the water column and put it down in the sediment, so it doesn’t get on fish or into the environment,” Phipps said. “Mussels filter many millions of gallons of water per day.”
They’re not dying because they’re delicate creatures, the FWS article points out. In fact, they’re pretty tough cookies. They can absorb heavy metals, like copper, and have a good system for getting rid of them, Phipps said. They can even shut themselves up tightly to avoid pollution — as long as it’s only temporary.
“When they’re overloaded with too much sediment, heavy metals, chemicals and organics, like agricultural runoff, it’s like the water filter at your house becoming so clogged that it doesn’t work anymore,” he said.
Dredging to allow barges and boats to pass can destroy mussels’ habitat, plus adds a blanket of silt to the bottoms of rivers and streams, which are normally porous and complete with their own systems of water and oxygen.
Development and modern farming methods also add to the silt problem, which can suffocate mussels, eliminate fish spawning habitat and destroy microorganisms that keep rivers and streams healthy. Meanwhile, dams block the fish that carry the mussels’ larvae, effectively isolating mussels above the dam and halting their ability to reproduce.
Reproductive process
Back to the mussel’s sex life. Mussels come to the surface to mate in the early spring. That’s the surface of the sediment on the bottom, not the surface of the water, Phipps explained. Males release sperm into the water. Females catch it in their gills, then move it to their ovaries. The fertilized eggs then migrate back up to the female’s “marsupial” gills.
Mussels that are short-term breeders will hang onto the eggs till late spring or early summer. Long-term breeders mate in the fall and hold the eggs over the winter. Either way, when the eggs become larvae and are ready to release, the female has to go fishing, Phipps said.
Again, she’s usually looking for a specific type of fish. Take one of the Ohio River mussels called the pocketbook. She’s looking for bass — largemouth, smallmouth, either one will do.
Fishing lures
To attract them, she creates a very convincing lure from the fleshy skin along her gills. The lure not only looks like a darter fish, one of the bass’s favorites, but even wiggles like one. The lure is in two halves, and the mussel pushes a gill filled with larvae up through the middle. As the bass grabs the lure, the packet of larvae explodes in its mouth.
The rainbow mussel, also an Ohio River inhabitant, is only looking for rock bass. Her lure looks like a crayfish, the rock bass’s favorite food. She can even make it “walk” across the bottom to look even more enticing.
Other types of mussels produce packets of larvae that look like worms: Red worms, flatworms, “and really cool ones that look like blackfly larvae,” Phipps said. “You can’t tell the difference between those and the real ones.”
But perhaps the most amazing group of mussels, like the snuffbox or northern riffleshell, are the ones that employ “active capture,” Phipps said. Both of those Ohio River natives have a big bulge in their shells; big enough for babies to brood, and also to serve as a trap. These mussels go to the surface of the sediment and open their shells, exposing a very tiny lure.
When a darter fish comes along, the mussel “clamps down on its head, forming a tight compartment,” Phipps said. The mussel doses the fish with the proper amount of larvae, then releases it unharmed, he said.
All of these “fishing” techniques have the same result: Exploding packets of larvae. Once they are released from the packets, the larvae’s little shells spring open, revealing sensor hairs.
“When they sense that they’re close to the fish, they snap closed on the gills,” Phipps said.
This makes the fish cover the larvae with cysts. Which only helps the larvae to get under the fish’s skin. Some species ride on the fish for a couple of weeks — getting protein, fat and other nutrients from the fish’s blood — while others stay on over the winter.
When they become juveniles, the little mussels release their grip and the fish swims away, usually none the worse for wear. The juveniles then begin life on the bottom, wherever they happen to be.
Phipps notes the brilliance of the mussels’ strategies: They produce thousands of offspring, but have to go above and beyond to ensure that those babies get to a place where they can survive.
“Something with one fleshy foot can’t move very far,” he said. “But put the babies on a fish and they can go upstream, downstream, pretty much anywhere.”
Mussel conservation
The White Sulphur Springs hatchery is one of the agencies involved in mussel conservation and restoration in the Ohio River basin and elsewhere. There, scientists try to restore mussel populations that have been harmed by road and bridge projects, dredging, chemical spills, or dams.
To do this, Phipps said, they use a syringe to collect larvae from the female mussels’ gills, then deposit it onto host fish. They hold those fish for three or four weeks in special tanks until the juvenile mussels are ready to drop off. Then, the scientists collect the baby mussels and raise them in the hatchery for several months to a year.
When they’re big enough, they’re tagged and released into areas where additional mussels are needed. And if you think about it, that’s pretty much everywhere. At least everywhere that we want clean water.
