Occurrence and Fluctuation in Photosynthetic Biocoenoses Dwelling on Stone Monuments

This research deals with the occurrence and fluctuation of phototrophic microbial communities dwelling on stone monuments. We examined many photosynthetic biocoenoses of several Italian monuments. The most widespread and recurring taxa occurring in the epilithic communities were among the cyanobacteria Chroococcidiopsis, Pleurocapsa, Leptolyngbya and Plectonema, and among the chlorophytes were Coccomyxa, Apatococcus, Chlorococcum and Stichococcus. The community composition was subjected to small seasonal changes affecting the amounts of the different components more than the qualitative biocoenosis structure. The number of phototrophic microorganisms increased slightly from late spring to autumn, in accordance with the improvement of climatic conditions. In winter and early spring, we found the lowest amount of phototrophic microorganisms. A detailed study, carried out on marble statues in the Boboli Garden (Florence, Italy), showed that the first coloniser was the green alga Coccomyxa. We observed that stone colonisation started about one year after restoration. The success of Coccomyxa in marble stone colonisation could be attributed to its specific growth strategy and features.