Antarctic coastal ecosystems represent some of the most ecologically unique and vulnerable marine environments on Earth yet remain critically under-characterised due to logistical constraints and the scarcity of long-term benthic time series. Autonomous Reef Monitoring Structures (ARMS), standardised PVC plate assemblies developed to combine recruitment of benthic organisms with molecular characterisation of colonising pioneer communities, represent an effective, purpose-built tool for metabarcoding-based biodiversity assessment of marine sessile assemblages.
DNA metabarcoding has emerged as the method of choice for high-throughput, standardised biodiversity assessment of ARMS-associated communities, enabling comprehensive taxonomic characterisation of both macro- and microeukaryotes far beyond the resolution achievable through traditional morphological approaches. Despite their growing global adoption, ARMS deployments in polar regions remain exceptionally rare.
In this context, here we present the first 18S rRNA metabarcoding dataset generated from ARMS in the Ross Sea, deployed at Terra Nova Bay (Mario Zucchelli Station, Antarctica). Six ARMS units in Tethys Bay (25 m depth) were analysed across a three-year (2015–2018) colonisation period (two replicates per year), providing the first molecular baseline for Antarctic benthic eukaryotic communities. The 18S rRNA marker was selected to complement the existing COI dataset, capturing protistan diversity systematically underresolved. Results reveal a directional, taxonomically structured successional trajectory: early-stage communities dominated by opportunistic protists were progressively replaced by Bigyra and Bryozoa by Year III, suggesting the onset of a structurally complex, habitat-forming community. Alpha diversity peaked at Year II before declining, while beta diversity confirmed strong compositional turnover across years (PERMANOVA R² = 0.82, p = 0.001). A persistent core of 16% shared OTUs indicates community continuity despite marked successional dynamics. This study fills a critical gap in the molecular characterisation of Southern Ocean benthic communities, establishing a reference framework for future polar ARMS studies, with 18S uniquely resolving early-successional eukaryotic diversity systematically underrepresented in mitochondrial-based surveys.