Diversity and Key Organisms in the Biocrust of a Tropical Granite-Gneiss Rocky Outcrop

Rocky outcrops are harsh habitats that support specialized organisms and communities, including biocrusts, which play roles in soil stabilization, water retention, and nutrient cycling. Despite their importance, tropical biocrusts, particularly in granite-gneiss formations, remain underexplored. This study examines biocrust composition in a granite-gneiss outcrop in a rural landscape in Southeastern Brazil, identifying microhabitats and analyzing co-occurrence patterns and community structure. We recorded eleven bryophyte species and one diatom species, while six cyanobacteria, three charophytes, and two chlorophytes were identified at the genus level. They were found in shallow depressions, though termite mounds also served as an important microhabitat. The cyanobacterium <i>Scytonema</i> was the most prevalent taxon. The liverwort <i>Riccia weinionis</i> had the highest number of positive co-occurrences, associating with cyanobacteria and algae. Network analysis based on co-occurrence revealed that <i>Scytonema</i> and the mosses <i>Anomobryum conicum</i> and <i>Bryum argenteum</i> were the most connected taxa, crucial for ecological network stability. The moss <i>Bryum atenense</i> acted as a key intermediary, with the highest betweenness centrality-a measure of its role in linking taxa. These findings provide insights into tropical rocky outcrop biocrusts, shedding light on their composition and interactions. Furthermore, the co-occurrence patterns and key taxa connectivity uncovered provide insights into ecosystem stability and can guide ecological restoration strategies.