Status of diatom barcode databases for improved assessments in DNA metabarcoding for WFD phytobenthos reporting in Luxembourg
Diatoms are widely recognized as powerful bioindicators for assessing aquatic ecosystem health due to their species-specific responses to environmental stressors. They play a central role in European monitoring frameworks such as the Water Framework Directive, where accurate ecological status assessments depend on reliable species identification.
Traditionally, diatom identification has relied on morphological analysis using light microscopy. However, this approach is time-consuming and highly expertise-dependent, as diatoms exhibit remarkable morphological plasticity throughout their life cycles. At the same time, Luxembourg faces a critical environmental challenge, with none of its surface waters currently achieving “good” ecological status, reinforcing the need for more precise and scalable freshwater monitoring tools.
DNA metabarcoding has emerged as a promising alternative, enabling rapid and large-scale biodiversity assessments. Yet, its effectiveness is severely constrained by a major bottleneck: the lack of comprehensive DNA barcode reference libraries, with less than 20% of European diatom species currently represented. This knowledge gap limits the accuracy of ecological assessments and risks underestimating biodiversity, particularly within rare and cryptic species.
The DIACODE project addresses the taxonomic gap by improving the DNA barcode reference library for freshwater diatoms in Luxembourg, a flora that has not yet been systematically characterized at the genetic level.
The project adopts an integrated approach by establishing clonal cultures of diatoms, enabling both:
By linking genotypes (genetic data) with phenotypes (morphological traits), the project will refine species delimitation and improve taxonomic resolution. This approach goes beyond standard metabarcoding workflows and strengthens the connection between traditional microscopy and molecular methods.
Importantly, the project contributes to a “dual-pipeline” monitoring framework, combining DNA metabarcoding with expert-driven morphological validation. This will ensure that high-throughput genetic data can be translated into robust and ecologically meaningful indicators, supported by taxonomic expertise.
The project will significantly enhance the accuracy and reliability of freshwater monitoring in Luxembourg and beyond. By expanding diatom barcode reference libraries, it directly improves the taxonomic assignment of environmental DNA sequences used in metabarcoding studies.
Key expected impacts include:
Beyond applied monitoring, the project will contribute to fundamental biodiversity knowledge by uncovering hidden diatom diversity and documenting the freshwater flora of Luxembourg.
Ultimately, it reinforces the need for an “expert-in-the-loop” approach, where taxonomic expertise and molecular tools work in synergy to transform raw genetic data into actionable ecological intelligence for supporting environmental management and policy.
