Invasive Snail Populations Tracked Using a New Technique Called eDNA

A new method of identifying and tracking organisms based on their biological leavings appears to be a significant step forward in the management of invasive species.

Biologists led by the University of Iowa used a special technique called eDNA to discover an invasive species of tiny snails in streams in central Pennsylvania where the snails’ presence had been unknown. The invasive New Zealand mud snail has spread to the Eastern Seaboard after arriving in the western United States decades ago. (Edward Levri, Pennsylvania State University-Altoona)

(CN) — Tiny rice-sized snails from New Zealand have been taking over North American waterways for decades, blanketing riverbeds and crowding out native species. A new method of identifying these miniscule creatures may provide hope for other as-of-yet untainted ecosystems.

Spread far and wide by fisherman and unwary beach-goers, invasive species like the mud snail are often hard to detect early on and can cause untold harm to vulnerable habitats. A single female mudsnail can spawn a colony of 40 million in a single year.

Using a novel technique developed less than a decade ago called eDNA analysis, biologists can now identify these and other invasive species before they get a stranglehold on a new environment. Researchers from the University of Iowa were able to detect populations of mud snails without ever seeing the creatures, merely by testing the water these snails were presumed to be hiding in. The team published their results in a new study Monday in the journal Biological Invasions.

“It’s the first successful application of using this eDNA technique to discover a new invasive population of these snails,” said author Maurine Neiman, associate professor at the University of Iowa, in a telephone interview. “The procedure had been developed and worked successfully when the researchers knew what they were looking for — what’s cool here is we tried it out in the wild and found a new population. These are destructive invasive snails, and by using a technique like eDNA that can discover invasive populations early in the process, we can deploy containment early enough to be effective.”

eDNA stands for “environmental DNA,” which is DNA such as skin and hair that animals shed into their surroundings. Dust, composed largely of human skin cells, is one example of this. With samples taken from employees, scientists could swab a company conference table and determine exactly who met there recently, or whether someone brought their dog in for show-and-tell last week.

That same concept is now being applied to the search for invasive species. By testing samples taken from waterways, researchers can determine exactly which species reside there, even if they’re barely visible, such as the case with the pesky New Zealand mud snail.

“Traditional techniques rely on physically finding organisms, which can be easy with something big and obvious, like rabbits in Australia, but a lot of invasive organisms are tiny. The snails are the size of a grain of rice,” Neiman said. “Early in the process the chances of finding them in a visual survey is pretty low, but with eDNA you don’t have to find anything — you just sample the environment.”

By lowering the threshold for observation, scientists must no longer wait idly by until a troublesome organism reaches high population density to identify a looming problem. Early identification significantly increases the likelihood that an invasive species can be eradicated from a vulnerable ecosystem before they’re able to inflict serious damage.

Neiman and her team collected samples from multiple sites across six rivers in the Susquehanna River and Mid-Atlantic River watersheds in central Pennsylvania. They determined these snails were just getting a foothold in waterways which were previously believed to be snail-free based on visual inspections. Because eDNA degrades rapidly in the environment, finding an organism’s DNA means that species was recently present nearby, even if it left no other discernable traces.

The authors plan to revisit these sites, as well as sites where they detected DNA but found no snails, to track population densities over time. By continuing to monitor these locations they say they can track population growth and locate dispersal events to head off future snail incursions. As eDNA disperses throughout connected waterways, they believe it may also be possible to rapidly survey large regions by monitoring watersheds near the mouth and moving upstream.

“You know in principle these techniques are supposed to work but to see them work in practice is pretty neat,” Neiman said. “The point of doing eDNA is you don’t need to find these organisms to know that they’re there, to say ‘Hey this really does work.’ Now this affords the possibility of alerting conservation agencies and fisheries that they have to clean their equipment very carefully and know that these invasive snails are around and they’re spreading.”

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