Abstract

Environmental DNA (eDNA) offers a powerful, non-invasive means of assessing biodiversity in marine ecosystems, yet the spatial resolution of eDNA remains poorly understood. We investigated the vertical and horizontal dispersion of eDNA from an isolated mesophotic coral reef (Bright Bank) in the stratified offshore waters of the northern Gulf of Mexicos shelf edge. We conducted comprehensive vertical and horizontal water column eDNA sampling across multiple radial directions and depths. We characterized invertebrate communities using a paired metabarcoding approach targeting broad (18S) and taxon-specific (28S) markers. We found that vertical transport of benthic eDNA was limited by water column stratification, with distinct benthic community signals confined to the near-bottom layers. In contrast, horizontal dispersal of eDNA extended beyond at least 1.5 km, though the prevalence of eDNA from benthic invertebrates declined with increasing distance from the bank. Taxon-specific primers showed greater detection sensitivity and dispersal range, particularly for benthic corals, than primers that are used to broadly assess eukaryotic biodiversity. These findings demonstrate that water column structure and marker selection critically influence the spatial interpretation of marine eDNA data. The study represents a snapshot of late-summer conditions. Seasonal variability should be considered in future studies. Our results provide a realistic framework for integrating eDNA into offshore environmental surveillance, biodiversity monitoring, and spatial management.