Understanding and protecting aquatic ecosystems has always been a formidable challenge for aquatic biologists and environmental scientists. Invasive species monitoring, threatened and endangered species surveys and biodiversity monitoring are important components of the environmental review process and ecosystem restoration.
Traditional methods like trapping, netting, electrofishing, and diving surveys have long been an effective means of characterizing the presence or absence of a species in a given area. However, these procedures often require significant time, effort and expenditures of financial resources, in addition to having a relatively low success rate for some elusive species.
Enter eDNA Sampling
Environmental DNA (eDNA) is DNA shed by organisms into their environment. In aquatic environments, a water sample is taken and sent through a specialized filter that isolates and preserves any DNA present within the water sample. These isolated DNA samples are then placed in a preservative and sent to a lab for sequencing. Sequencing allows the surveyor to determine whether the target species is present in the survey area without the need to capture or otherwise disturb the target species itself.
As sampling and sequencing technology evolves, eDNA methods are decreasing in cost while also becoming increasingly more effective in detecting species, even when they are in low abundance. Furthermore, researchers continue to develop resources for listed species, including developing markers for identifying a broader range of species. As the technology supporting eDNA surveys improves, environmental review documents required under the National Environmental Policy Act (NEPA) have increasingly incorporated eDNA to complement traditional survey results.
Time and Cost Savings
Traditional methods of monitoring and analysis often require extensive fieldwork utilizing specially trained and certified staff and expensive equipment. In contrast, eDNA methods require relatively little training and equipment to conduct the field sampling protocol, which helps deliver significant time and cost savings. For projects where monitoring biodiversity is a central goal, these advantages enable broader and more frequent monitoring, delivering a more accurate picture of what may be happening below the water’s surface.
An increasing number of case studies demonstrate the potential for eDNA surveys as a more accurate and cost-friendly alternative to traditional sampling methods. For example, eDNA was shown to be 18.7% less expensive than traditional trapping methods while returning a 5.5 times higher detection rate during surveys for the proposed federally-threatened alligator snapping turtle (Macrochelys temminckii). Numerous studies have also shown cost savings and increased accuracy for projects that monitor aquatic communities in both marine and freshwater environments.
Challenges to Implementation
While eDNA sampling offers numerous benefits, it also presents challenges. Samples may degrade over time, meaning that eDNA may yield only a one-time snapshot of the species that were present when the sample was taken. Additionally, contamination and improper methodology can lead to false positives or negatives, necessitating stringent protocols and controls. Many regulatory agencies remain cautious about relying solely on eDNA for presence/absence determination due to varying degrees of demonstrated success across species and aquatic systems. These factors, at present, limit the implementation of eDNA surveys to a complementary tool rather than a standalone solution.
Immense Potential
The potential for eDNA sampling in aquatic surveys is immense. This technique transforms how we monitor and understand aquatic environments, offering a noninvasive, cost-effective, and highly sensitive method to detect species presence. Genetic resources for threatened and endangered species are rapidly growing, which allows the application of this technology to an increasing number of species and projects. Additionally, as the cost of sequencing technology continues to decrease and new sampling methods are refined, eDNA methods will become increasingly cost-effective and provide more accurate results.
By augmenting traditional methods, eDNA provides a comprehensive approach to aquatic ecosystem monitoring. As technology advances and acceptance grows, eDNA will undoubtedly become an even more valuable tool in aquatic biology and ecology, helping us protect and preserve the incredible diversity of aquatic life.
Working to protect threatened and endangered species requires extensive working knowledge of the many variables that come into play under provisions of the U.S. Endangered Species Act.