Alejandro Martinez^a, Sude Cakir^b, Marta García-Cobo^a,c, Diego Fontaneto^a, Michael Lemke^b, Maximilian Pichler^d, Nuria Sánchez^c, Thom Stoppelenburg^b, Jan-Berend Stuut^e,f, Willem Renema^b,g, Jan-Niklas Macher^b,h *

^{a: National Research Council of Italy (CNR), Italy b: Naturalis Biodiversity Center, Netherlands c: Complutense University of Madrid, Spain d: University of Regensburg, Germany e: NIOZ Royal Netherlands Institute for Sea Research, Netherlands f: Vrije Universiteit Amsterdam, Netherlands g: University of Amsterdam, Netherlands h: Institute of Environmental Sciences (CML), Leiden University, Netherlands}

^* Corresponding author: jan.macher@naturalis.nl

Introduction

Coastal urbanisation is accelerating globally, yet we lack habitat-specific understanding of where along the beach–dune gradient animal communities respond most strongly to urban pressures such as trampling, beach grooming, and infrastructure. It also remains unclear whether observed biodiversity change is driven mainly by community reassembly (turnover/replacement of taxa) or biodiversity loss (reduced richness and occurrence). Identifying the most sensitive habitats along the beach–dune ecotone, and the dominant type of impact, is essential for targeted coastal management and restoration.

Objective and Methods

We studied how urban proximity shapes animal communities across a beach–dune ecotone along the Dutch North Sea coast. We collected environmental DNA from 660 sediment cores across 55 transects between Scheveningen and Zandvoort, spanning landward stabilised dunes, seaward foredunes (the zeereep), and upper and lower intertidal habitats. Using eDNA metabarcoding and habitat-specific scalable joint species distribution models (sJSDMs), we tested relationships between urban proximity and (i) community differentiation, (ii) Operational Taxonomic Unit (OTU) richness, and (iii) OTU occurrence probability, and identified potential “winner” and “loser” taxa associated with urbanisation.

Results

Urban proximity was most strongly linked to compositional change in dune habitats. In embryonal and established dunes, community similarity declined as transect pairs differed more in distance to the nearest city, indicating stronger community differentiation along the urban gradient, whereas intertidal habitats showed weaker patterns. Across all habitats, transects far from cities hosted more consistently similar communities, while near-city transects were more compositionally variable, suggesting increased heterogeneity near urban areas. Richness and OTU-level responses generally indicated lower diversity near cities, but embryonal dunes were an exception: despite strong compositional shifts, they showed no clear richness or occurrence decline, consistent with community replacement rather than simple impoverishment. Overall, embryonal dunes emerge as a management priority, and habitat-specific eDNA assessment can localise urban-associated biodiversity change across coastal gradients.