Subaerial cyanobacteria

Abstract

Summary: Subaerial cyanobacterial communities are conspicuous on the surfaces of many environments subject to considerable water stress, though the communities are increasingly likely to be endolithic the greater the water stress. In temperate regions the communities tend to be best developed on calcareous surfaces, especially in the case of strict epiliths. However, the contrast with non-calcareous surfaces is less obvious in the tropics, where many examples of well developed cyanobacterial communities have been reported from non-calcareous surfaces. Detailed floristic lists often include species of Gloeocapsa, Pseudocapsa, Phormidium, Microcoleus, Tolypothrix, Scytonema, Dichothrix and Stigonema, and also Nostoc from the more horizontal surfaces. Almost all taxa have a well developed extracellular matrix, which includes scytonemin or other coloured UV-protective pigments in all except the most shaded environments. Although the general effects of differences in environmental factors such as temperature, light, UV stress, pH, CO 2 and mineral nutrients are understood quite well, relatively little is known about the detailed responses to different combinations and periodicities of these factors.