Community stability on built and natural intertidal habitats: Implications for coastal urban management

Coastal built structures often support benthic communities that differ in species diversity and composition from those found in natural reference habitats. However, most research has been conducted over short periods, limiting comprehensive analysis of long-term community trajectories and the potential for temporal convergence with natural habitats. Whether impoverished communities in novel habitats experience large fluctuations or maintain stability over time remains largely unexplored. Community composition and species abundances were studied annually over a 20-year period following the construction of a wave-exposed breakwater and compared with two adjacent natural rocky habitats in northern Chile (20° S) to determine whether the built structure develops a more variable community or converges with natural communities. Our long-term analysis of mid-intertidal community fluctuations using stability metrics, alongside short-term field experiments, revealed persistent differences in community composition between the built structure and natural rocky platforms, with transient convergence in the abundance and identity of key functional groups around 11-13 years post-construction. Due to lower abundances of foundation species, especially the absence of mussels, the built structure exhibited significantly lower species richness, greater community variability, and higher species synchrony than natural rocky platforms. Our findings suggest that communities in novel coastal habitats undergo distinct successional stages during the initial decades, indicating that the efficacy of ecological interventions is time-dependent. Supporting the rehabilitation of built structures through eco-engineering, specifically targeted early during succession or at transient saturation points, provides a strategic framework for urban coastal management. This approach is crucial for mitigating the ecological footprint of escalating coastal urbanization and successfully rehabilitating community functioning.