Guest blog by Maria Kahlert
Diatom DNA metabarcoding holds great potential for biodiversity monitoring and ecological assessment, particularly within the EU Water Framework Directive (WFD) and the recently introduced EU Nature Restoration Law (NRL). However, several challenges remain, among which gaps in reference databases have been identified as a major obstacle, especially for understudied habitats and ecoregions.
In this context, we present results from the national barcoding project (FRESHBAR), conducted between 2019 and 2023 and focusing on benthic freshwater diatoms of Sweden, a key organism group for both ecology and environmental assessment. The study was recently published in the open-access Metabarcoding and Metagenomics journal. A primary goal of the project was the publication and vouchering of all data, materials, and results to support further research.
The project established a total of 312 diatom cultures, with a focus on oligotrophic and acidic habitats. The cultures were sequenced for two barcodes (rbcL and 18SV4) and identified using light microscopy, while selected strains were additionally examined by scanning electron microscopy. All data, including sampling metadata, barcode sequences, images, and voucher material, were published in accordance with the FAIR principles, and a subset of cultures was archived in diatom culture collections.
Nearly all strains were successfully sequenced, identifying 51 taxa across 17 genera. A notable highlight was the relatively high proportion of Eunotia taxa, a genus poorly represented in diatom databases yet frequently encountered in Swedish freshwaters. Beyond molecular and morphological data, we also captured images of colony formation and sexual reproduction stages from living cultures, information that is only rarely documented.
FRESHBAR represents the first large-scale effort to generate barcode reference sequences for Nordic benthic freshwater diatoms. As all data are publicly available, we are confident that the added sequences and morphological information will contribute to more accurate species-level identification, help resolve taxonomic relationships within diatoms, and improve reference databases for environmental monitoring and research.
Original source:
Kahlert M, Mora D, Kusber W-H, Abarca N, Zimmermann J (2026) New DNA barcode reference data of freshwater diatoms (Bacillariophyceae) from Sweden: old acquaintances and new taxa. Metabarcoding and Metagenomics 10: e186778. https://doi.org/10.3897/mbmg.10.186778