Lower pH limit for the existence of blue-green algae: evolutionary and ecological implications.

Observations on a wide variety of acidic environments, both natural and man-made, reveal that blue-green algae (Cyanophyta) are completely absent from habitats in which the pH is less than 4 or 5, whereas eukaryotic algae flourish. By using enrichment cultures with inocula from habitats of various pH values, the absence of blue-green algae at low pH was confirmed.