Four seasons of the phototrophic biofilms at the cave entrance zone of Petnica Cave

This study investigated seasonal variations in phototrophic biofilm communities at the entrance zone of Petnica Cave. Biofilm samples were collected from seven sampling sites over four seasons. Several parameters were measured at each site, including air temperature, relative humidity, light intensity, substrate temperature, and moisture content of both biofilm-covered and bare substrates, to assess their influence on species composition. Cyanobacteria were the dominant group. According to the redundancy analysis (RDA), coccoid and simple trichal Cyanobacteria predominated in winter, while heterocytous Cyanobacteria were more abundant in summer. Chlorophyta exhibited a relatively even distribution across all seasons. Principal component analysis (PCA) revealed that Cyanobacteria occurrence showed a positive correlation with the moisture content of both the biofilm and the substrate, whereas Chlorophyta demonstrated a negative correlation with these parameters. Despite the presence of core taxa in all seasons, additional taxa appeared seasonally, contributing to increased diversity. These findings highlight the importance of moisture for the composition and resilience of the biofilm and provide insights into the seasonal adaptations of microorganisms in the cave entrance zone ecosystem.