Mudsnails are keepers of historical secrets

Study lead author Elizabeth Watson examines historically collected mudsnails under a dissecting microscope. “I was looking to see if snail bodies are preserved inside the shells,” she said. “Also many of the snails have a lot of mud and algae attached. That would need to be removed before they could possibly be analyzed for stable isotopes.”  |  Roger Thomas/Drexel University photo

If a 50-year-old snail could talk, it would probably have plenty of tall tales to tell. Now, thanks to modern isotope testing technology, those snails can tell us stories without speaking.

Researchers at the Academy of Natural Sciences of Drexel University in Philadelphia have found that oceanic mudsnails preserve information about nitrogen levels in the water where they are captured. Comparing isotope analysis of 2018 mudsnails to isotope analysis of dead snails captured more than a century ago lets scientists chart nitrogen levels down to a specific decade. It’s the snail version of counting rings on a newly felled giant redwood tree.

The tiny mudsnails being studied are found along the eastern Atlantic coast from Nova Scotia to Georgia. In many of these areas, human activities have brought large amounts of nitrogen to coastal habitats, according to Elizabeth Watson, lead author of the study.

“Mudsnails are convenient organisms to use as water quality indicators. They’re small, usually less than an inch in length. They’re abundant with up to 1,500 mudsnails per sq. metre. They’re pretty easy to catch and some of them live for more than 50 years,” says Watson.

Nitrogen is an important nutrient on land, but high levels in water severely affect aquatic ecosystems. Large amounts of nitrogen cause dense blooms of algae that consume a lot of oxygen. These low-oxygen dead zones make it difficult for aquatic organisms to survive. The Philadelphia researchers have proven that eastern mudsnails can serve as canaries to indicate how much nitrogen is in an ecosystem. That information is key to identifying and remedying ecosystems where water quality has been compromised.

“This is perhaps the first study to highlight the use of these snails as water quality indicators. I think scientists will now be much more confident in applying this approach.

“We measured levels of two different nitrogen isotopes in mudsnail tissue. The proportions of heavier and lighter versions of nitrogen show how much nitrogen is available in that ecosystem. Higher levels of the heavier version in mudsnail tissues signal higher overall levels of nitrogen in the environment.”

Researchers collected mudsnails from 40 muddy study sites, spread across Long Island.

They found that the heavier version of nitrogen was enriched in mudsnail tissue in several study sites.

“These sites were near areas with high population densities or where land use is more urbanized. We also had similar results from sites next to waste-water treatment plant discharges. Some of the study sites are extremely nutrient-polluted. An example is areas that experienced the discharge of untreated sewage during heavy rains.

“Nitrogen pollution is also a concern in more pristine coastal areas such as eastern Long Island and Barnegat Bay. In these areas, the goal is to detect and undo human impacts.

We want to preserve coastal wildlife. We also want to protect human activities such as fishing, clamming and other recreational activities. Mudsnails can help researchers do that.

“A water sample reflects just one instant in time. A mudsnail sample reflects an entire lifespan. Researchers can get an idea of conditions over a much broader period of time.”

Watson is now trying to establish water quality base lines for New York and New Jersey based on analysis of older material. The Academy of Natural Sciences in Philadelphia has collections of mudsnails that are at least a 100 years old.

“We can analyze recently collected mudsnail shells and compare them with shells from a century ago. That can help researchers detect how much nitrogen levels in coastal areas have changed over the last 100 years.”

Watson says using mudsnails as indicators of water quality can engage local populations. Citizen scientists and organizations can help collect and prepare mudsnails for isotopic analyses.

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