Characterising rocky reef biodiversity using environmental DNA from local to national scalesBroad-scale Spatial Patterns

Dina-Leigh Simons^1,2,3, Nova Mieszkowska^1,3

¹University of Liverpool, UK - ²University of Sheffield, UK - ³The Marine Biological Association of the UK, UK

Climate change is reshaping marine ecosystems globally by affecting organism survival and altering species distributions. Efficient and scalable methods for monitoring climate-sensitive systems, such as rocky temperate reefs, are essential to address such changes amid limited resources. Environmental DNA (eDNA) metabarcoding has emerged as a promising tool for detecting coastal marine taxa, but the spatial resolution of the method (i.e., the ability to differentiate communities from different locations) remains insufficiently understood, particularly in dynamic intertidal environments. In this work, we evaluate the effectiveness and resolution of eDNA in detecting rocky intertidal taxa across three spatial scales – national, regional, and local - in the United Kingdom. We detected 1087 target taxa within 470 families and 19 phyla using two established primers targeting invertebrates (CO1) and macroalgae (18S). Moderately distinct eDNA signals were found at all spatial scales, indicating local discreteness even between vertical shore heights within the same sites. Notably, communities at shore heights with greater tidal connectivity were more similar than less connected areas. eDNA signals also aligned with established rocky shore ecological patterns, with higher diversity and more taxa observed at lower shore positions, reflecting the limiting effects of environmental extremes in harsher high shore zones. Regionally, detections of cold-water species increased with latitude, while warm-water species declined with latitude. Our work supports emerging evidence that eDNA has strong potential for multi-scale biodiversity monitoring, even in dynamic marine environments. We provide practical recommendations for tailoring eDNA sampling on rocky reefs and integrating the method alongside existing routine ecological monitoring. These insights contribute to the advancement of biodiversity monitoring in temperate marine systems under a changing climate.