Michael Oliewo Aluma’s doctoral thesis: eDNA helps detect invasive crayfish early

The thesis contributes to improving the early detection of invasive crayfish species and crayfish plague and supports the conservation of Estonia’s native noble crayfish. The thesis was supervised by Assistant Professor Katrin Kaldre and Dr Lilian Pukk from the Estonian University of Life Sciences. The opponent was Associate Professor Sandra Hudina from the University of Zagreb.

Signal crayfish is spreading to new areas

The study revealed that since 2008, signal crayfish has become established in at least five new locations in Estonia and is spreading beyond its previously known range. At the same time, noble crayfish populations have disappeared from several locations, including the Riksu Stream and the mouth of the Pärnu River. The results indicate that the spread of invasive alien crayfish species has probably contributed to the decline or disappearance of native noble crayfish populations.

The doctoral thesis also assessed the effectiveness of the catch-based monitoring currently in use. The results showed that although trial trapping is an important monitoring tool, its impact on reducing the abundance of invasive alien crayfish is limited. Trapping methods may also fail to detect populations that are still small or have only recently begun to spread.

DNA in water reveals the presence of species

As an important innovation, the eDNA method was applied in Estonia to monitor crayfish and crayfish plague. The method analyses genetic material found in water, enabling species to be detected without capturing them. Using eDNA, the study successfully detected the presence of noble crayfish, signal crayfish, spiny-cheek crayfish and the crayfish plague pathogen (Aphanomyces astaci). The detection accuracy was 100% for noble crayfish and 87.5% for signal crayfish.

The Estonian University of Life Sciences research group also participated in an extensive interlaboratory trial comparing the performance of eDNA analyses conducted by different European laboratories. The results confirmed that the methodology used in Estonia is reliable and comparable to that of other European laboratories, supporting the wider adoption of eDNA-based monitoring. “Environmental DNA does not completely replace traditional monitoring methods, but it can significantly complement them. It helps us detect invasive species and pathogens earlier, thereby providing better opportunities to protect the noble crayfish,” said Michael Oliewo Aluma, the author of the thesis and a junior researcher at the Chair of Aquaculture at the Estonian University of Life Sciences.

Effective monitoring requires a combination of methods

The doctoral thesis concludes that preserving the biodiversity of Estonia’s freshwater ecosystems requires an integrated approach combining traditional monitoring with new molecular methods. eDNA-based monitoring provides a strong foundation for the early detection of invasive alien crayfish species and crayfish plague and could also be incorporated into national monitoring programmes in the future.

The full text of the doctoral thesis is available in the Estonian University of Life Sciences digital repository, EMÜ DSpacelink opens in new page.