Mind the gap-analysis! – How complete are DNA barcode reference libraries for monitoring-relevant aquatic species in Europe?

Molecular species identification with DNA metabarcoding can potentially accelerate, streamline and standardise biomonitoring routines. Currently, it is tested how this new technique be implemented for the European Water Framework Directive (WFD) Marine Strategy (MSFD). To connect results from current monitoring routines, an extensive, high-quality barcode reference database required. Hence, a gap-analysis of Barcode Life Data Systems (BOLD) was performed as part EU-COST Action DNAqua-Net (Weigand et al. 2019), which updated in 2021. It aimed to analyse completeness BOLD on national WFD lists marine ERMS (European Register Species) AMBI (AZTI Biotic Index) lists. The data were supplemented by MitoFish freshwater fish Diat.barcode diatoms. Several thousands included gap-analysis, although not all countries currently apply species-level biological quality elements. coverage different taxonomic groups varied strongly, high levels (> 80%) vascular plants, low diatoms plathelminths (< 15%). As general pattern, monitored several had higher compared those only single country. focused additionally availability metadata (e.g., geographical origin specimen or determiner name) barcodes. we analysed if stored public (with access metadata) private (without mined GenBank (metadata are available but easy access). Although many (43% macroinvertebrates 21% species), proportion without neglectable (22% 22% species). Another issue that emerged deposited barcodes identified reverse taxonomy (RT), i.e., specimens molecularly via its itself associated name. This problematic originally misidentified samples lead false RT-identifications, making appear more trustworthy than actually is. For macroinvertebrates, 39% 65% originated RT, impacting 11% species. information about RT publicly data, real impact might even higher.