Metabarcoding for use in Nordic routine aquatic biomonitoring - a validation study
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Over 75% of all lakes and 40% of all rivers in the EU are found in the Nordic countries. Freshwater biomonitoring according to the EU Water Framework Directive (WFD) has been adopted by all Nordic countries and forms an integral part of management efforts to preserve and restore the ecological quality of freshwaters and their ecosystem services. Current identifications of organisms used in WFD biomonitoring are based on expert morphological identification; an approach that is time consuming and prone to errors. Molecular identification methods could alleviate many problems but thus far have not been rigorously tested for use in routine monitoring. Using a questionnaire, we consulted Nordic experts to assess opinions on the applicability of these methods in routine biomonitoring. Further, we validated the practical use of molecular metabarcoding identification for use in freshwater aquatic macroinvertebrate monitoring in all Nordic countries. A total of 297 waterbodies including both lakes and streams were sampled which constitutes the single largest validation test of the method so far. Experts in each country sampled macroinvertebrates according to their national protocols with only minor modifications and samples were analyzed using a standardized laboratory protocol. The results of this study indicate that in most cases identifications using molecular DNA-based methods were highly congruent with traditional expert-based identifications. However, the study also revealed the importance of using unified guidance documents. Several samples showed signs of DNA degradation, affecting reliability of the method. Nordic experts generally recognized molecular identification methods as playing a major role in future biomonitoring, if issues associated with the current lack of unified methodology are resolved. Based on this study, we suggest that concerted Nordic or European efforts towards implementation and standardization of DNA-based methodology should be undertaken to swiftly ensure the use of this promising tool into WFD compliant monitoring.