by Catarina Conran

February 20, 2025

In the early 2000s, scientists developed the technique of analyzing “environmental DNA,” or eDNA — the genetic material that organisms shed into their surroundings. This eDNA is collected from trace amounts of skin cells, mucus, feces, pollen, or tissue that linger in water, soil, and even air. By collecting samples from the environment scientists are able to identify what species are present in a particular environment. In practice, this means a single water sample can reveal fish, amphibians, invertebrates, and even microscopic organisms that traditional surveys might miss. This makes eDNA a powerful tool for understanding ecosystems and monitoring biodiversity from microbes to whales. eDNA is also especially useful for tracking changes in ecosystems over time, detecting elusive or rare species that might otherwise go unnoticed, or identifying invasive species before they spread.

However, eDNA does not necessarily reflect the current composition of the ecosystem, as it could contain older traces of organisms that have died or moved on. As a result, scientists are now exploring a faster and more dynamic analytical method — environmental RNA. Because RNA degrades within hours to days, eRNA is able to provide a real-time snapshot of what organisms are currently present in an area. Recent studies have also indicated that eRNA can reveal a higher diversity of species than eDNA, with samples containing a greater number of unique sequences that were able to precisely capture existing communities. Even more interestingly, eRNA is also able to detect organisms’ distinct life stages, helping to uncover population demographic information that is very valuable for guiding conservation strategies. Scientists are hopeful that this methodology will also be able to expand detection capabilities to sexes and even specific phenotypes within a species. While this methodology is still in development, it promises very exciting results.

Using eRNA and eDNA together would also allow scientists to determine the “age” of genetic material in the environment, as the ratio of eRNA to eDNA could help scientists distinguish between fresh biological activity and older activity. Using both techniques in tandem like this could provide a clearer picture of ecosystem dynamics and help target conservation actions where they are needed most.

Tools like eRNA are poised to change not just how we study ecosystems, but how we govern them. Environmental law and policy often depend on data that lags behind ecological reality, such as species surveys, impact assessments, and recovery plans that take years to compile. eDNA and eRNA could help bridge that gap, giving regulators and conservationists near real-time insight into ecosystem health and species activity. This kind of molecular monitoring could strengthen enforcement under the Endangered Species Act, improve water-quality assessments under the Clean Water Act, and make environmental review processes more responsive under NEPA.