Giving the Eastern Canadian Diatom Index (IDEC) a makeover using metabarcoding: first considerations and challenges

The Eastern Canada Diatom Index (Indice Diatomées de l’Est du Canada; IDEC) was developed to assess stream biological integrity from diatoms. Since the first version of the IDEC in 2006, the number of sites monitored with this bioassessment tool has increased steadily in the province of Quebec. This resulted in an increase in samples, which in turn resulted in an increased need for highly qualified personnel to carry out microscopic diatom identification. There is thus a necessity to develop a more rapid tool for diatom assemblage analysis to maintain high-quality diatom-based stream monitoring in the province of Quebec. DNA-metabarcoding targeting diatoms represents an interesting avenue in overcoming the limitations associated with traditional taxonomic analyses by microscopy (time constraints, costs and the need for qualified diatom analysts). This preliminary study was conducted to investigate the potential use of diatom DNA metabarcoding for assessing stream biological integrity in Quebec. Overall, we observed a good fit between diatom assemblages obtained from microscopy observations and from metabarcoding. IDEC scores calculated from microscopy- and DNA-derived diatom assemblages were also comparable.