Unlikely relationship between rare amphibian and mussel spurs Iowa research collaboration

This is the sixth installment of Nature’s Alarm, a series about endangered and threatened species and research in Iowa.

Megan Bradley crouched on the bow of a boat on the Mississippi River. She plunged her hand into a cooler with water, where a bulging mesh bag was submerged. When she stood up, she was clutching a handful of freshwater mussels.

The creatures had called the U.S. Fish and Wildlife Service’s Genoa National Fish Hatchery home for years. Some had been slowly growing since 2017. They fit in the palm of Bradley’s hand now, but some could grow as large as her head one day.

With a flick of her wrist, she threw the mussels into the glossy Mississippi River. The aquatic creatures disappeared into the murkiness, sinking toward their new habitat. The reflection of the sky, now clear after a much-needed rain, rippled in their wake.

“I'm doing this Johnny Appleseed style,” said Bradley, the lead mussel biologist at the Genoa National Fish Hatchery. She reached into her bag for another handful. “There's so much good habitat here.”

  Buy Photo

Within five minutes, the bag was empty. She had tossed 65 mussels from at least seven species into the waterway to join their siblings on the riverbed. They were the last stragglers from a U.S. Fish and Wildlife Service project that propagates native mussels and releases them into the wild.

Freshwater mussels are among the most threatened animals in the world. Iowa lists nine species as endangered and six as threatened — accounting for about a third of the varieties found in the state.

As Bradley finished up at the front of the boat, Iowa Department of Natural Resources fisheries technician Kevin Hanson sat at the helm. He expertly navigated the watercraft to a trio of traps downriver. His research focuses on another fauna entirely: Iowa’s biggest salamander species, the mudpuppy. Although its populations are stable in Minnesota, they are listed as threatened in Iowa.

Its unique relationship with an imperiled mussel species — the salamander mussel — has made Bradley and Hanson’s research intertwine. Salamander mussels are under review for federal listing and currently listed as a species of concern by the U.S. Fish and Wildlife Service. They’re also listed as a species of greatest conservation need under the Iowa Wildlife Action Plan.

Their teamwork holds promise for research and reintroduction efforts for both at-risk species throughout Iowa waterways.

A unique relationship

Mudpuppies have bushy red gills that hang off their 14-inch bodies. They are freckled with blue-black splotches across their backs, each individual sporting unique patterns. Two small, beady eyes dot their flat heads.

The amphibians are fully aquatic, spending much of their time in the cozy cracks and crevices between rocks from Louisiana up into Canada.

They feed and breed during the winter — a unique trait among most salamander species. Female mudpuppies adhere between 60 to 100 eggs to the bottom side of woody debris or rocks around May.

“They’re a cute animal, personable,” Hanson said, “but also an important part of the ecosystem that we don't really know much about.”

  Buy Photo

Most importantly for Bradley’s research, mudpuppies are hosts for larval salamander mussels.

Female salamander mussels draw in free-floating male sperm to fertilize their eggs. Once larvae develop, they’re ejected toward mudpuppies, where they’ll attach to their gills or elsewhere on their bodies. The larvae take about 14 days to become self-sufficient before dropping off the salamanders to grow independently.

“We're talking about something that's the size of a grain of salt divided in thirds,” Bradley said about the larval salamander mussels. “They're tiny.”

Salamander mussels are found from Canada down into Missouri and over to Virginia. They only grow to about 3 inches long, their shells covered in shades of tan and brown. Like their hosts, they typically live under large boulders. They are more active than most mussels.

  Buy Photo

Knowledge about Iowa’s historic populations of salamander mussels is limited to an 1860s newsletter reporting that, after a millpond flooded, about 400 of the mussels were found under a single boulder.

“We know, just based on that, that the population was much larger than we're seeing anywhere now,” Bradley said. “There are just so many questions about what populations and historic densities looked like and what that means for the persistence of the species in the future.”

Live salamander mussels haven’t been reported in Iowa in decades. Their hosts are similarly rare in the state. Historically, mudpuppies used to be commercially harvested in Iowa. But now, most modern sightings in the state come from angler reports.

Both species need clean habitats to survive, which have become rare in Iowa’s waterways.

  Buy Photo

Mudpuppies, for instance, need silt-free habitats so they can get oxygen. But soil loss from agriculture can wash into waterways and suffocate the creatures.

Salamander mussels are filter feeders that draw bacteria, algae and other organic matter from water. Bradley called them, along with other mussel species, the “livers of our rivers.” That also makes them vulnerable to harmful contaminants in waterways. Ammonia — found in fertilizers — is the most toxic contaminant to them.

“All of those factors come together to create a perfect storm of decline,” Bradley said.

From disaster to potential

In 2008, a massive boulder fell from a bluff along the Mississippi River. It blocked the railroad at the bottom, causing four train cars to derail and crash into the river. The cars damaged the riverbed and released petroleum, oil and grease into the water.

The pileup took an ecological toll. A dead juvenile mudpuppy was found on the site, along with a relic salamander mussel shell. Canadian Pacific Railroad, the parent company of the derailed train, agreed to pay $625,000 to the Iowa DNR and the U.S. Fish and Wildlife Service in 2014 to mitigate the environmental damage.

“This was ground zero for it,” Hanson said as he navigated the boat around the boulder, which the researchers have since named Bob.

  Buy Photo

The accident had a silver lining: It helped fund Bradley’s native mussel reintroduction efforts on the river and was the impetus for Hanson’s mudpuppy research in Iowa.

For her research, Bradley snorkels or scuba dives to monitor mussel populations at large along riverbeds. She’ll snap photos with her underwater camera, make note of species present, and calculate species abundance. The resulting data sets baselines for current mussel populations and identifies good habitat for releasing more individuals.

Within the last eight years, the agency has released more than 225,000 mussels into the Mississippi River. About 30,000 are “teenage” mussels, which are more likely to survive than the 196,000-plus juveniles. Salamander mussels aren’t among the propagated batches because researchers want to confirm they’re using the most genetically appropriate parent population.

While Bradley hops in the water during the warmer months, most of Hanson’s mudpuppy research occurs in the winter when the amphibians are most active.

Between October and December, he lowers cylindrical traps with live minnow bait into rocky habitat along the Mississippi River. Any captured mudpuppies get implanted with a tracking tag and are weighed, measured and photographed. Tissue samples are taken at times to investigate the species’ gene diversity.

  Buy Photo

Hanson also creates more habitat for mudpuppies — and salamander mussels. He mimics their ideal habitat in waterways with items like concrete slabs, rocks and logs.

When the Iowa DNR first began surveying for mudpuppies back in 2015, some doubted they’d ever catch any in the state. But, as of 2021, they had caught close to 300 individuals. They’ve been a mix of male and female — a good sign for a stable, reproducing population.

“It’s a much bigger population than we ever knew that we had,” Hanson said.

More studies, more overlap

The mudpuppy and salamander mussel have a one-of-a-kind relationship. That has presented opportunity for collaboration.

The Iowa DNR is conducting targeted surveys for both salamander mussels and mudpuppies in northeast Iowa. The data will contribute to the U.S. Fish and Wildlife Service’s status assessment for salamander mussels. It also will help researchers better understand mudpuppies’ habitat preferences between the Mississippi River and Iowa’s interior rivers.

“Wherever mudpuppies hang out, we're looking for salamander mussels,” said Kelly Poole, the Iowa DNR’s threatened and endangered species coordinator. “And if we find salamander mussels where we didn't have records of mudpuppies, we would do some searches for mudpuppies in that area, too.”

  Buy Photo

As additional studies expand into the state, the researchers hope the data can breathe new life into both mudpuppy and salamander populations in Iowa.

Bradley hopes to be tossing salamander mussels into rivers one day to foster the first known populations in decades.

“(They’re) not in Iowa yet,” she said about the species as she looked at the other mussels in her bag, ready to be thrown into the Mississippi River for their new lives. “Some day.”

How we reported this series

Nature’s Alarm started as a question this spring: On the 50th anniversary of the Endangered Species Act, what do we know about threatened and endangered species in Iowa? Can we highlight some of these species and the researchers studying them?

Members of The Gazette’s newsroom have spent the last four months planning and reporting this series, which began July 16 and has been publishing weekly.

Reporter Brittney J. Miller started with background interviews in search of active research occurring for at-risk species in Iowa. Once she identified target species — each representing a different fauna group — she coordinated with researchers to accompany them into the field with photojournalist Jim Slosiarek and social video producer Bailey Cichon. Digital editor John McGlothlen built graphics to accompany the stories online.

The Gazette team clambered through vegetation in search of bumblebees, worked by the light of headlamps to spot bats, and floated along rivers to catch a glimpse of fish, amphibians and mussels to report this series.

Brittney J. Miller is the Energy & Environment Reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com