Species diversity gradient to darkness stress in blue-green algae/cyanobacteria: A microscale test in a prehistoric cave, Mount Carmel, Israel

Species diversity of epilithic cyanobacteria was studied in a 90 m deep pre historic el-Wad cave eroded in Cenomanian limestones of Mount Carmel, Israe l. The degree of illumination is the most variable index throughout the cav e, whereas humidity and temperature vary moderately. In a number of sites i nside the cave dripping water occurs due to filtration of rain water. In el -Wad cave 42 species from 20 genera of blue-green algae were found. The sha re of coccoid forms decreased and filamentous (especially oscillatorial) on es increased from the entrance to the end of the cave. Intensity of Light w as the governing factor for distribution of cyanobacteria in el-Wad cave; t he availability of dripping affected it to a lesser extent due to the const antly high humidity of the air. Diversity of species composition and taxono mic spectrum of cyanophytes was reduced from the entrance to the end of the cave, covarying positively with darkness stress.