The Minnesota DNR’s Center for Aquatic Mollusk Programs (CAMP) made a breakthrough that may help save the endangered spectaclecase mussel.
Anna Scheunemann counted the juveniles under a microscope.
by CHRIS ROGERS
Like underwater burlesque, female Higgin’s eye mussels wave, shimmy, and jiggle their lures until the fish cannot resist. Mussels usually stay inside their shells, but brooding mothers thrust these lures out into the water and dangle them. On the outside, the lures look just like tiny fish. On the inside, they are crammed with baby mussels. When the fish bites, baby mussels go everywhere, including getting lodged in the fish's gills.
This kind of interaction with fish is at the center of a mystery that has stumped scientists for at least 20 years. Solving that mystery was a key step toward helping an endangered mussel species survive, and this summer, the Minnesota Department of Natural Resources’ (DNR) Center for Aquatic Mollusk Programs (CAMP) in Lake City did it.
Inside a converted warehouse on the far side of Lake City, Mike Davis and Zeb Secrist’s office is decked out with a clam shell the size of a football and a huge sword with a hilt shaped like bat wings and a demon’s head for a pommel. The sword is something Davis stumbled upon while diving in the Twin Cities. He joked about why its owner might have thrown it in the river. On their many trips to the bottom of Minnesota rivers while diving for mussels, the CAMP team members have found a lot of weird things and some useful ones. The warehouse is criss-crossed by an elaborate assembly of pipes, pumps, tanks, and filters that Secrist constructed on a limited budget. In one corner, inside a cooler an old cooler he salvaged from the river bottom and converted into an aquarium, two dozen federally endangered spectaclecase mussels sit, looking happy as clams.
Spectaclecase mussels once spread all up and down the Mississippi, Missouri, Ohio, and Tennessee rivers. Now there are just three strong populations left: two in rivers in southern Missouri and one in the St. Croix River. The U.S. Fish and Wildlife Service (FWS) listed the spectaclecase as federally endangered in 2012. Around 35 other North American freshwater mussels have already gone extinct.
Compared to the Higgin’s eye, spectaclecase mussels' tactic for attracting fish is subdued: they release baby mussels in packages that float around in the water and look like worms. Fish bite them.
That bite is important because while mussels spend most of their sometimes century-long lives in one place, early on in life, they go for a ride. Microscopic mussel larvae called glochidae latch on to the gills of fish, go through a caterpillar-in-the-cocoon-style metamorphosis, then drop off and start their lives as adult mussels. Mussels cannot mature without this stint as a mostly harmless parasite. They depend on host fish to reproduce. Some mussels, like the Higgin’s eye, can grow on a variety of different host fish. Others, such as the snuffbox, can only reach adulthood by latching onto one specific species of fish. The snuffbox’s whole lifecycle has evolved around the logperch. The salamander mussel doesn’t even use a host fish, but depends on its namesake amphibian. Until this summer, nobody knew what the host fish spectaclecase mussels used.
“For an endangered species that we’re trying to recover, if you don’t know how to produce the babies, the recovery actions are basically limited to going to strong populations and taking subsets of animals and taking them to places where you think they would do better,” FWS Mussel Biologist Nathan Eckert explained. “The problem with spectaclecase is that there are not enough of them that you can take without gutting the population you’re taking them from.”
Identifying the mystery host fish was step number one in the FWS’ plan to protect the spectaclecase mussel from extinction.
“A lot of people tried everything they could think of,” Davis said. Scientists tried sunfish, catfish, walleye, shiners, minnows, gar, sculpins, hogsuckers, madtoms, greenside darters, orangethroat darters, rainbow darters, and Missouri saddled darters. In 2000, Missouri State University graduate student Michael Baird scoured for clues and tested 35 likely species — from channel catfish to mole salamanders. In an interview this summer, Baird remembered finding one glochidae on a mooneye fish, but he could never quite identify what mussel species it was. Before Baird, University of Minnesota Biologist Mark Hove tested 20 species, everything from longnose dace to tiger salamanders. FWS researchers tried again with more potential hosts in 2006, and a senior research biologist for the U.S. Geological Survey tried in 2008. Over the last 20 years, Hove worked on five different studies, including one with CAMP Malacologist Benard Sietman that featured the cheery title “Spectaclecase host studies produce more negative results.” “People were starting to get kind of desperate,” Sietman said. Researchers started wondering: “Do these have something totally unexpected as a host — some other animal? Because none of the fish worked,” Sietman explained. The CAMP team tried turtles, mudpuppies, and crayfish. According to the FWS, various scientists tried over 60 species of fish, amphibians, and crustaceans before Sietman and the CAMP team struck gold this summer.
Like past researchers, Sietman and the CAMP team looked for clues that could help narrow the search. The St. Croix Falls Dam cuts the river in half, blocking fish movement. Above the dam, there is a relic population of aging spectaclecase mussels with no young to take their place. Below the dam, spectaclecase are reproducing. “So, I got a list of fish [that currently occur] above and below the dam and a list of which ones existed historically above and below the dam, and I looked at the ones that no longer occur above St. Croix Falls,” Sietman explained.
American eels were on that list, and when Sietman and Davis saw that, they thought the snaky fish might be a good guess because both eels and spectaclecase live among rocks. “We tried them two years in a row, got zero,” Davis said.
Two fish species from the same family were also on Sietman’s list: mooneye and goldeye. They are both flattened, silvery fish that migrate up and down the Mississippi basin, get to be about a foot long, and have big, bug eyes. “Both of those species were gone above the falls, so I thought, ‘Well, we’ve got to try these guys,’” Sietman said. There was just one problem: keeping the fish alive. “They’re extraordinarily fragile,” Davis said. “You look at them, they die.”
Some animals just do not do well in captivity, and mooneye and goldeye fish are definitely on that list. They get stressed out and have disease problems, the CAMP team said. For some reason, they always swim around the edge of their tanks and wind up rubbing their bulging eyes against the glass. Their eyes get scratched. They get infections. They die.
The first time the CAMP team tried mooneye, they could not keep the fish alive long enough to complete the experiment. It takes glochidae two to four weeks to mature. However, the mooneye did stay alive long enough for the spectaclecase larvae to grow just a little bit. Sietman knew they were onto something, if only he could keep mooneye alive.
The CAMP team members focused on upgrading their aquarium technology and called in the Minnesota Zoo for help. The zookeepers showed them how to keep fish in circular tanks with aerators all around the edge to produce a curtain of bubbles that discourages the fish from touching the sides. The CAMP team switched to goldeye, which do slightly better in captivity, and on June 7, Sietman and his colleagues got spectaclecase glochidae to fully transform into juvenile mussels in the lab. To double-check the finding, Hove electrocuted some goldeye and mooneye in the wild, examined their gills, and found spectaclecase glochidae. “Finally,” Sietman said.
The CAMP team got so many juvenile spectaclecase mussels from their experiments that they shipped thousands off to Eckert and the FWS National Fish Hatchery in Genoa, Wis., and down to Chris Barnhart’s lab at Missouri State University, to see who can come up with the best system for fattening them.“This one was a big mystery for a long time,” the FWS' lead biologist for the endangered species, Tamara Smith, stated. “Bernard and his crew were finally able to crack the code and make that discovery.”
Now that the spectaclecase’s host has been discovered, Smith plans to talk with experts this winter and draw up a plan for how to propagate spectaclecase and where to reintroduce them. “Hopefully we’ll be able to go to rivers where the species was once naturally occurring and produce self-sustaining populations there. So basically, that’s a huge step for recovery of the species,” Smith stated.
“I told my mom and dad, and they were like, ‘Neat,’ but in the mussel world that’s the Holy Grail,” Secrist said.
This is just the beginning for spectaclecase conservation efforts, Sietman stressed. For the mussel to really make a comeback, Sietman said, conservationists need to reverse the problems that pushed it toward extinction in the first place. The spectaclecase needs habitat, and it needs goldeye and mooneye to be able to move freely through rivers — both things that dams inhibit. In Wisconsin, goldeye themselves are endangered. Virtually all native mussels would benefit from more freedom of fish movement, less erosion and pollution, and fewer invasive zebra mussels.
The spectaclecase and North America’s 296 other species of mussels matter because they help create healthy river and lake ecosystems and are among the first species to show signs of bigger environmental problems, mussel biologist say. “The presence of a good [mussel] bed indicates a healthy system from the bottom up,” CAMP Propogation Biologist Madeline Pletta explained.
Barnhart said of the spectaclecase discovery, “It is a big deal, and yet there are 88 federally endangered species [of mussels] and this is just one of them.”
Native mussels face big challenges, but progress is possible. Davis has seen it. As a kid growing up in Southeast Minnesota, Davis trapped beaver in streams where dairy plants dumped waste whey. He had to scrub the pelts to get the stink off. After dropping out of college in 1971 and buying a farm near Plainview, the CAMP founder spent a decade as a commercial fisherman on the Mississippi River. For years, he harvested native mussels for the pearl industry. “We could get 10 cents per pound of live clams, and we could only get seven cents for the carp,” Davis explained. He started diving for clams with a hose attached to a beer keg that he had converted into an air tank. He took that set up and down the river in a busted up truck; the local police had a lot of questions, Davis said. The mussels Davis and other clammers dug up were shipped to Japan, where oyster farmers would insert a piece of mussel shell into each oyster. Those “seeds” would grow pearls, and nothing else worked like mussel shells. As North American mussel populations dwindled, the oyster farmers would pay more and more to get them. It was a classic tragedy of the commons, Davis said.
Motivated by a growing appreciation for mussels and a desire to find any way to make a living on the river, Davis went from harvesting clams to conserving them. “I saw what was going on and learned more about what was going on in North America,” Davis said of the decline and extinction of mussels. He went back to school at Winona State University and started doing mussel survey dives for the DNR. Over the next three decades, he stitched together a patchwork of funding for mussel conservation. Science only recently became his main source of income.
Davis said that for most of the 20th century, the Mississippi River from Minneapolis to Lake Pepin was a dead zone, with sewage from the Twin Cities zapping dissolved oxygen, depositing a layer of toxic sludge, killing fish and mussels, and sickening swimmers. That changed, however, as local people demanded action in the 1970s and ‘80s, and the Clean Water Act was gradually enforced, Davis stated. The metro area cleaned up its wastewater treatment plants and overhauled its sewer system to keep raw waste from flowing into the river during storms. By the 2000s, Davis was working on a project to release federally endangered Higgin’s eye mussels into the Mississippi River in downtown St. Paul. “The dead zone became a refuge for endangered species — kind of a twist of fate,” he said.
While native mussels now face new challenges like zebra mussels and pharmaceuticals, pesticides, and road salt in the river, Davis has seen native mussels come back in places. “The water quality is much, much better than it was 50 years ago,” he said.
Davis’ life spans from an era when humans saw the river and its wildlife as resources too vast to be depleted or despoiled to an era when people have recognized environmental problems and made some changes. “That’s a piece of history we don’t want to forget,” he said.
This story was part two in a two-part series on Mississippi River mussels and mussel divers. Find part one here.