EU directives (e.g. MSFD, Habitats Directive), along with OSPAR guidelines, mandate sustainable marine resource management across national borders. Benthic organisms are crucial for assessing marine ecosystem health, but their morphological identification is time-consuming and costly. High-throughput sequencing, particularly DNA metabarcoding, offers an alternative. However, DNA-based monitoring requires substantial investment in high-quality DNA reference libraries. The GEANS project (Genetic Tools for Ecosystem Health Assessment in the North Sea Region) aimed to develop efficient DNA-based tools for benthic biomonitoring. GEANS created a curated DNA reference library (COI) for species relevant to North Sea macrobenthos monitoring, using new sequences, non-public barcode sequences, and mined sequences from GenBank and BOLD. The library, stored in a dedicated BOLD project with photographs and metadata, includes DNA barcodes for 4005 specimens from 715 species, representing over 29% of North Sea macrobenthos species. Arthropoda is the most represented, while Bryozoa and Annelida have the lowest coverage. This DNA library is expected to facilitate fast, cost-effective environmental health assessments in the North Sea for public authorities and academics.