Life finds its way in seaports: environmental DNA monitoring in the Grand Port Maritime de Guadeloupe shows vertebrate richness but reduced phylogenetic diversity

Ports are increasingly recognized as distinct urban marine ecosystems (UME) shaped by intense human activities, yet their biodiversity remains poorly documented, particularly in tropical regions. Environmental DNA (eDNA) metabarcoding offers a powerful, non-invasive approach to assessing biodiversity in these complex and highly modified environments. In this study, we conducted, to our knowledge, the first eDNA-based inventory of marine vertebrates within the Grand Port Maritime de la Guadeloupe, a semi-enclosed coastal system embedded in a mosaic of coral reefs, seagrass beds, mangroves and restored habitats. Using a standardized sampling and taxonomic assignment protocol, we characterized vertebrate communities across four sites and compared them with a reference transect outside the port area. We detected 140 teleost taxa, representing more than one-third of the known regional diversity, including several species of management concern. Despite their proximity, sites exhibited compositional and phylogenetic contrasts, revealing fine-scale spatial structuring of eDNA signals within the port. Restored mangrove and seagrass areas combined high taxonomic richness with unexpectedly low phylogenetic diversity, suggesting colonization by closely related opportunistic species. By integrating taxonomic and phylogenetic metrics, our study highlights the unique biodiversity assemblages found in port ecosystems and demonstrates the value of eDNA-derived metrics for future biodiversity monitoring and marine spatial planning in UME.