Towards standardization of DNA metabarcoding for marine environmental monitoring
A European scale monitoring method has been identified as a science priority need to support benthic ecosystem assessments (Van Hoey et al., 2019). Biotic indexes inferred from DNA based taxonomic assignments are comparable to indexes derived from morphological identifications (Aylagas et al., 2018; Elbrecht, Vamos, et al., 2017; Lobo et al., 2017). When using DNA metabarcoding for monitoring, a standardized method that compares best with traditional morphological analyses in order not to break up the existing traditional monitoring time series is preferable. Our results show that bulk samples with use of the Leray primer set would be the method of choice for benthic monitoring in the North Sea. The next step is now to show case the repeatability and robustness of DNA metabarcoding for European legislation such as the Marine Strategy Framework Directive which may be achieved through the organization of a ring test in which the same samples are processed by different laboratories. Finally, our results show that complete reference sequence databases will not be the holy grail to come to 100% comparability with morpho-taxonomic datasets, but at this point the reference databases are our only link with the ecological and biological information imbedded in the Linnean system. As such, collaboration with taxonomic experts to further populate the reference database remain highly recommended (Porter & Hajibabaei, 2018) to benefit as much as possible from the inclusion of DNA metabarcoding in monitoring studies.