A layered community of cyanobacteria and purple bacteria that developed within a gypsum crust on the bottom of a hypersaline saltern pond was characterized in Eilat, Israel. The upper 1 to 2 cm of the 4 to 5 cm thick gypsum crust is inhabited by carotenoid-rich unicellular cyanobacteria (Aphanothece sp. and others), imparting an orange-brown color to the gypsum. Under the brown layer, a green layer dominated by unicellular cyanobacteria of the genus Synechococcus is found, with filamentous Phormidium-type cyanobacteria as a minor component. Below these layers of oxygenic phototrophs is a red layer of purple bacteria. -from Authors