A Comparative Analysis of DNA Metabarcoding and Morphological Identification in Diatoms Reveals Similar Patterns of Environmental Response

Diatoms are widely used as environmental sentinels and are commonly studied through morphological identification. However, this method requires specialist knowledge, which is becoming increasingly scarce, resulting in species identification becoming costly, time-consuming, and difficult. DNA metabarcoding offers an alternative method to semiautomate some identification processes to circumvent these difficulties, thus minimizing identification costs while providing objective and reliable information. However, discrepancies between marker genes and morphological identification remain unsolved. This study investigated the 66 diatom communities on 26 high mountain mires in the Pyrenees by identifying morphological species and sequencing the Cytochrome c oxidase I (COI) and 18S rRNA markers. We assessed whether morphological and molecular approaches reveal the same patterns of alpha and beta diversity. Our results showed a strong correlation between beta diversity patterns of diatoms obtained by morphological identification and genetic markers. In contrast, alpha diversity calculated through molecular studies underestimated species richness and the Shannon index. The diatom community was chiefly driven by pH, Mg, and temperature, reflecting these patterns in morphological and molecular data. DNA metabarcoding also proved to represent diatom community patterns and the roles of the environmental drivers as clearly as in morphological identifications in high mountain mire diatom communities.