By 
Estonia’s freshwater researchers are adding a molecular tool to the country’s efforts to protect native crayfish. A doctoral study defended at the Estonian University of Life Sciences on 9 September shows that environmental DNA, or eDNA, can help identify crayfish species and crayfish plague from water samples, including when populations are still difficult to find through traditional trapping.
The research by Michael Oliewo Aluma examined invasive crayfish in Estonian inland waters and assessed whether eDNA could complement existing monitoring programmes. The approach does not require researchers to catch the animals themselves. Instead, laboratories analyse traces of genetic material left behind in the water.
Looking for traces in the water
Every aquatic organism releases small amounts of genetic material into its surroundings. These traces can come from skin, mucus, waste or other biological material. By collecting and analysing a water sample, researchers can determine whether the DNA of a particular species or pathogen is present.
For conservation work, the method is especially useful when an invasive population is newly established, widely dispersed or present at a low density. Conventional trapping remains important, but it can miss animals that are difficult to capture or that occupy a large and complex water system.
Aluma’s thesis tested eDNA surveillance for native noble crayfish, invasive signal crayfish and spiny-cheek crayfish, as well as the pathogen that causes crayfish plague. The study found that the method successfully detected the target organisms in Estonian freshwater environments. The thesis reports a detection accuracy of 100 per cent for noble crayfish and 87.5 per cent for signal crayfish in the relevant field testing.
A complement, not a replacement
The study does not present eDNA as a substitute for field biology. Its main practical conclusion is that molecular testing should be combined with traditional methods, including trapping and direct observation. Each method answers slightly different questions: water samples can reveal whether a species is present, while field surveys can provide information about abundance, condition and habitat.
That combination could make monitoring more responsive. A positive eDNA result might encourage specialists to carry out targeted trapping or additional sampling before an invasive population spreads further. Repeated sampling could also help authorities track changes across seasons and identify waterways that deserve closer attention.
The Estonian University of Life Sciences says the eDNA analyses used in the study were also tested in an international interlaboratory comparison. The results were considered reliable and comparable with analyses performed by other European laboratories, supporting the possibility of wider use.
Why early detection matters
Estonia’s native noble crayfish is an important part of freshwater ecosystems and is vulnerable to competition, habitat change and crayfish plague. Invasive crayfish can carry the pathogen without suffering the same consequences, allowing the disease to reach native populations. The doctoral study found that signal crayfish had become established in at least five new Estonian locations since 2008, while native crayfish populations had disappeared from several sites, including Riksu Stream and the mouth of the Pärnu River.
Those findings describe an environmental management challenge, but the value of the new research lies in improving the information available to conservation teams. Better information can support earlier intervention, more targeted use of resources and more consistent national monitoring.
From doctoral research to public policy
The thesis proposes that eDNA-based surveillance could eventually be integrated into national monitoring programmes. That would require decisions about sampling frequency, laboratory capacity, quality control and how molecular results are combined with field observations. It would also require continued testing in different water bodies and under changing environmental conditions.
For Estonia, the work is an example of how university research can address a concrete environmental question close to home. It also illustrates the growing role of molecular methods in biodiversity monitoring: instead of relying only on what can be seen or caught, researchers can use biological traces to build a faster picture of life in rivers and lakes.
The broader lesson is practical rather than dramatic. Protecting native species often depends on detecting change early, before it becomes expensive or impossible to reverse. In that effort, a small water sample may provide conservationists with information that would otherwise take much longer to obtain.
Comments