Frequently Asked Questions

Below is a list of frequently asked questions. If you have any other questions, please send them in.

  • Does the eDNA technique also detect species that occurred in a water body in the past?
    • No. Experiments have shown that eDNA persists in water for up to 3 weeks. For longer ago than that, no eDNA is detected. Detection of the DNA of a target species therefore indicates the recent presence of that species (click here for publication). Please not that in sediments or soil eDNA can persist for long periods of time, this has to be taken in account when interpreting results. 
  • Can the eDNA approach be used for detecting species in large water bodies, such as rivers or lakes?
    • Yes we carried out succesful studies using eDNA-metabarcoding in large rivers like the Rhine, Meuse and Rhone and in large lakes in the Netherlands. Sampling strategy has to be adjusted to those large waterbodies by sampling long transects and high volumes of water.  
  • Can the eDNA approach be used to detect a species in fast-flowing water?
    • Yes. The eDNA technique also works well in fast-flowing water. One thing to take into account is the downstream transport of eDNA in those systems. Local species will be dominant in the eDNA samples, however eDNA from (far) upstream can be detected to. This should be taken into account when interpreting results. 
  • How powerful is the environmental DNA method?
    • During our large studies on eDNA-metabarcoding fish in parallel to conventional Waterframework directive (WFD) monitoring we found that eDNA detected on average 60% more species per sampled transect and 15% to 20% more species per waterbody. 
    • During a pilot study carried out by RAVON and SPYGEN on the Pond Loach (Misgurnus fossilis) an eDNA sample was taken in the Rijnstrangen, a vast wetland near Zevenaar. Earlier, only one juvenile had been captured from this location despite considerable sampling effort using both electro-fishing and dipnets. The eDNA sample confirmed the presence of the species, the amount of DNA in the sample even suggesting that there must be a significant population (click here for publication (in Dutch!)).
    • In a study carried out by SPYGEN in France, traditional inventory methods were compared to the environmental DNA technique for the detection of the American Bullfrog (Lithobates catesbeianus). With traditional methods, the bullfrog was only found in 7 out of 49 sampled waters, while eDNA technique established the presence of the bullfrog in 38 of the 49 waters.
    • However, the environmental DNA approach is, just like traditional methods, not flawless: during an a large-scale inventory of Misgurnus fossilis carried out by RAVON in 2012, the technique failed to detect the species at a few locations where traditional sampling had revealed its presence. The eDNA approach needs to be further perfected. It is clear that ecological knowledge is needed on when and where to sample. Moreover, to be able to interpret the results, experience with the analysis and awareness of the limitations of the primers are crucial. 
  • Is it possible to determine the density of a species with the eDNA technique?
    • eDNA-metabarcoding provides the proportion in eDNA-sequences per species in the samples. With techniques like qPCR and ddPCR it is possible to absolutely quantify the amount of eDNA in a sample, but only when concentrations are high enough. In practise we see that the concentration of eDNA of rare species is often below the limit of quantification, meaning it cannot be quantified reliably. Furthermore research has shown that small individuals release more eDNA compared to their biomass then large individuals (due to a higher surface in relation to their biomass).  In addition, more research is needed into the persistence and breakdown of DNA in various environments, that is environments differing in their microbial communities and abiotic conditions. To summarize: there are possibilities to see which species are most common and which species are rare (compared to each other) and for some common species absolute quantification of the amounts of eDNA in the water samples is possible. However more knowledge is needed on factors influencing the amounts of eDNA per species and the relation between the eDNA and biomass/numbers. 

If you have other questions, please feel free to contact RAVON.

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