Are well-studied marine biodiversity hotspots still blackspots for animal barcoding?

Marine biodiversity underpins ecosystem health and societal well-being. Preservation of biodiversity hotspots is a global challenge. Molecular tools, like DNA barcoding and metabarcoding, hold great potential for biodiversity monitoring, possibly outperforming more traditional taxonomic methods. However, metabarcoding-based biodiversity assessments are limited by the availability of sequences in barcoding reference databases; a lack thereof results in high percentages of unassigned sequences. In this study, we (i) present the current status of known vs. barcoded marine animal species at a global scale based on online taxonomic and genetic databases (NCBI and BOLD) and (ii) compare the current status with data from ten years ago. Then, we focused our attention on occurrence data of marine animal species from five Large Marine Ecosystems (LMEs) representing the most well studied biodiversity hotspots, to identify disparities in COI barcoding coverage between geographic regions and at phylum level. Barcoding coverage varied among LMEs (from 36.8% to 62.4% COI-barcoded species) and phyla (from 4.8% to 74.7% COI-barcoded species), with Porifera, Bryozoa and Platyhelminthes being highly underrepresented, compared to Chordata, Arthropoda and Mollusca. We demonstrate that barcoded marine species increased from 9.5% to 14.2% since the last assessment in 2011, due to new barcodes both on already described species and on newly described ones (about 15,000 new species were described from 2011 to 2021). The next ten years will thus be crucial to enroll concrete collaborative measures and long term initiatives (e.g., Horizon 2030, Ocean Decade) to boost animal barcoding libraries for the marine realm.