Integrating geomorphological and ecological indicators to assess coastal dune vulnerability in southern Brazil

Abstract

Coastal dunes play a vital role in protecting human communities and ecosystems by acting as natural barriers against erosion, storm surges, and sea-level rise. However, these systems are increasingly degraded by urban expansion and climate change. In this study, we reassessed coastal vulnerability to erosion in the municipality of Imbé, southern Brazil—one of the fastest-growing coastal areas in the state of Rio Grande do Sul—12 years after the implementation of a local Dune Management Plan. We applied a geomorphological checklist method across 44 coastal segments (each 250 m long), scoring 25 variables grouped into four parameters: dune morphology, beach condition, adjacent land use, and anthropogenic pressure. Relative Vulnerability Index (RVI) values ranged from 28.0% to 69.6%, with 36% of the segments experiencing an increase in vulnerability classification compared to the 2012 baseline. Cluster analyses revealed distinct spatial patterns between seasons, with winter clusters better reflecting structural vulnerability and summer clusters influenced by tourism-related pressures. Concurrently, we recorded 30 active nests from three bird species - Athene cunicularia (n = 15), Vanellus chilensis (n = 13), and Haematopus palliatus (n = 2) - georeferenced along the 11 km coastline. Nest abundance negatively correlated with dune width and area (Pearson’s r = –0.40 and –0.35, respectively), indicating that more degraded dune units supported fewer nesting birds. A. cunicularia emerged as a promising bioindicator due to its fidelity to nesting sites and preference for less fragmented dunes. These findings highlight the value of integrating physical and biological indicators to assess coastal vulnerability and suggest a cost-effective and ecologically informed framework for monitoring and managing sandy coasts under increasing environmental pressures.