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The Great Big Unknown: Studying Freshwater Mussels in Central America

“The chance of discovering a new species is highly likely,” said Shedd Research Biologist Kentaro Inoue, Ph.D., as he prepared for a trip to El Salvador. “We have no idea what species are there and what we could find.”

Inoue and Chuck Knapp, Ph.D., Vice President of Conservation Research, were on their way to a biodiversity hotspot in Central America, yet little research had been done in nearly 100 years on the animals they were preparing to study.

As part of Shedd’s designation as a Center for Species Survival: Freshwater by the International Union for the Conservation of Nature’s Species Survival Commission (IUCN SSC), Inoue and Knapp were eager to better understand the distribution of freshwater mussels in Central America, build relationships and provide training to local collaborators.

A single mussel sits on a sandy coast close to the water and surrounded by thin stalks of seaweed

A mussel buried in the sand in El Salvador.

Freshwater mussels are nature’s water filtration system. The curious creatures anchor themselves deep in river bottoms with a muscular “foot.” Staying mostly sedentary for decades, they remove harmful algae and bacteria from water, as well as protect streambeds from erosion and serve as food for other animals.

Freshwater mussels are considered an indicator species, meaning that if their health is declining, the health and function of the ecosystems they live in could also be impaired. Freshwater mussels are highly sensitive to habitat degradation, invasive species and pollution, and have steadily become one of the most endangered animals in the world due to these human-caused problems.

Dr Ken Inoue in waist-deep water holding up a small mussel and smiling during a research trip in El Salvador

Research Biologist Kentaro Inoue, Ph.D., after finding a freshwater mussel in El Salvador.

Six small mussels in a person's hand near the water

A handful of freshwater mussels found at a research site.

In Central America, the true biodiversity of freshwater habitats and the mussels within them is a mystery. Currently, 971 species of freshwater mussels are listed worldwide, with 94 species in Central America. But, that number was based on one study published in 1927, and for a century the region has received considerably less attention for conservation research efforts than other parts of the world.

The concern is that unrecognized species may be disappearing from Central America before scientists can find and describe them. Inoue and Knapp’s voyage to El Salvador in March was the first of many trips and ongoing work in El Salvador, Costa Rica and Guatemala to address this problem and fill in the gaps with data on these critical freshwater animals. These data could be used to support future protections of the region and the mussel species found there.

A large mussel rests in a hand above a shoreline on a research trip in El Salvador

A freshwater mussel and its "foot" used to anchor into a streambed.

On the ground in El Salvador, Inoue and Knapp were welcomed with enthusiasm and led throughout their trip by members of the El Salvador Ministry of Environment and Natural Resources.

“The Ministry was very excited about this collaborative opportunity to better understand freshwater biodiversity in their country and build capacity for future work,” Knapp said.

The group visited nine sites from one border of the small country to the other to find freshwater mussels and collect small clips of tissue — genetic samples — from each animal that will be analyzed back in Shedd’s molecular laboratory.

Once that analysis is complete, it will reveal if, in fact, Inoue and Knapp have discovered a new freshwater mussel species in the area.

“It’s difficult to identify which species of mussel it is by looking at it,” Inoue said. “The molecular sequencing we’ll do at Shedd completely opens the door to answer questions we have about freshwater biodiversity in El Salvador.”

Dr. Ken Inoue shows a mussel to two people in El Salvador on a mussel research trip

Inoue teaches local collaborators how to take a sample from a freshwater mussel.

Partner from Ministry holding a mussel in a boat with mountain in background on a research trip in El Salvador

A collaborator pulls up a mussel from the water.

Two kids in the water in El Salvador, each holding a mussel.

Two of the local children who helped Inoue and Knapp find freshwater mussels.

Dr. Ken Inoue observing a small mussel while a man looks on during a research trip in El Salvador

Inoue shows a local collaborator a mussel.

The vast, muddy brown waters in the rivers and lagoons were familiar to local fishermen and their children, who were eager to shuttle the scientists in their boats and dive to the bottom to help the team pull up each animal stuck deep in the sediment.

One of the most exciting moments, Inoue said, was finding a live freshwater mussel at a site where only a shell had been found previously. “Now, after genetic analysis, we can update the old description of what species are found there,” Inoue said.

At several sites, the team also helped to identify invasive species that could be competing with native mussels. One invasive mussel Inoue documented likely came to the area through the Tilapia aquaculture trade. As miniscule juveniles, mussels can attach to freshwater fish like parasites to move into new waterways.

“There’s really a need to document the spread of this invasive freshwater mussel,” Inoue said.

Much different from the freshwater mussels he surveys in the Great Lakes region, Inoue said it was thrilling for him to encounter two mussel species unique to Central America that inhabit lagoons, and one that lives in a completely different habitat than those in the Midwest.

“Most mussels in the United States don’t live in lagoons,” he said. “Usually in the U.S. mussels live in a gravelly habitat, whereas one species in El Salvador can live in a very compacted clay habitat.”

Landscape image of a coast in El Salvador during a conservation research trip.

The beautiful lanscape of El Salvador.

A small motor boat rests on the shoreline of a shallow body of water in El Salvador.

One of the nine sites Inoue and Knapp surveyed for freshwater mussels.

Inoue and Knapp also spent time working and interacting with interested local stakeholders. Inoue gave presentations about freshwater mussels in packed rooms at the Ministry of the Environment, and the University of El Salvador. Plans for additional training include involving an undergraduate student from the university to assist the Ministry with mussel research and inviting interested people to Chicago for more holistic training workshops.

Concurrently, Caleb McMahan, Ph.D., integrative tropical biologist at the Field Museum, and long-term collaborators in Central America will conduct complementary freshwater fish assessments that will lead to a better understanding of fish biodiversity as it relates to mussels.

“We’re not expecting these efforts to be ephemeral,” Knapp said. “Through additional support from Shedd, donors and grant funding, we intend to continue this work, build trust and help develop the next generation of ecology experts within the region to carry the torch.”

Dr. Ken Inoue walks through a body of water in El Salvador, looking for mussels.

Inoue serches for freshwater mussels.