ABSTRACT
Indoor’s phototrophic biofilms from 21 of the 24 catacombs located in St. Paul and St. Paul and St. Agatha Catacombs (Malta) were studied. Species richness is represented by 50 taxa. Cyanobacteria are the most diversified with 24 species; among them, the most frequent are Chroococcidiopsis sp. and Leptolyngbya nostocorum. Chlorophyta are represented by 13 species, with Desmococcus olivaceus, Chlorella minutissima and Muriella sp. as the most frequent. Bacillariophyta has 5 species; with Diadesmis contenta and Hantzschia amphyoxis being the most common. Rhodophyta are represented by 2 species, growing only in areas with natural light. There are also 5 species of Bryophyta and protonemata of mosses, and one lichenized ascomycetes. Cyanobacteria seem to prevail in the photoautotrophic communities. However, Chlorophyta increase their abundance in areas with natural light, mainly entrances, where they compete with cyanobacteria. Light is the main factor driving phototrophic biofilms; however water availability and substrate characteristics can also determine changes in diversity and abundance of species.
