Biological soil crusts (biocrusts) fulfil key ecological functions in arid ecosystems, yet their microbiome composition remains insufficiently resolved. Here, we characterise the microbial communities of the fog-dependent grit crust in the Pan de Az & uacute;car National Park (Atacama Desert, Chile) using multi-marker metabarcoding (16S rRNA, 18S rRNA, ITS2) across 11 coastal-inland sites. Chlorophylla+b concentrations reached up to 900 mg m-2, ranking among the highest reported for arid biocrusts and reflecting exceptional fog-sustained productivity. Bacterial assemblages were dominated by Proteobacteria and Actinobacteria, fungal communities by lichenized Ascomycota (Caliciaceae), and eukaryotic diversity by the green algal photobiont genus Trebouxia. Black-pigmented crusts with dense colonisation exhibited higher biomass but lower taxonomic richness, consistent with later-successional, lichen-dominated stages, whereas lighter, less colonised crusts were taxonomically richer yet functionally less integrated, indicative of earlier succession. The prevalence of Trebouxia, lichenized fungi, and lichen-associated bacterial taxa demonstrates that the grit crust microbiome is structured around symbiotic photobiont-mycobiont interactions rather than typical edaphic microbial assemblages. These findings redefine biocrust paradigms by documenting a fog-driven, chlorolichen-based system that bridges the ecological spectrum between lithic lichen communities and conventional soil crusts, establishing a critical baseline for assessing dryland microbial resilience under climate change.