Cyanophyta-3 
Terrestrial
Surface Crusts which appear lifeless, are revived following significant rains. These dry to a brittle crust as the substrate looses water.
These can be ecologically significant because they add Biomass and Nitrogen to barren areas. This is a long-term process, however. These crusts can be seen in places like Arches National Park (Utah) where it is very dry & there is little ground cover or litter.
These can also be seen locally on abandoned,
dry lots. Heavy rains allow desiccated Cyanobacteria to revive. They form undulating
to round hydrated masses. These gradually shrink and crack as the substrate dries.
Some Cyanobacteria (CBs) are also found in "green snow" which appears in the springtime on semi-permanent snowfields and glaciers.
Endolithic (Inside Rocks)
Cyanobacteria have recently found in the most barren area of Antarctica where no other life has been found. Similar observations have been made in the high Arctic. They can live just below the surface of rocks. This sounds unbelievable but it is true. They may also survive in the cold dry soil of Antarctica. They become active when melt water appears.
Cyanobacteria can also inhabit carbonatic substrates like Limestone. (http://bio.bu.edu/~golubic/marine-cyano.html).
Some species inhabit the Calcium Carbonate secreted by Coralline Algae.
Hyella stella: a Cyanobacterium that lives in Marine Limestone
Scytonema endolithicumOrganisms like this can live in Coral Rubble which rolls about as "sand". Consequently, they inhabit a reef zone that would otherwise be unavailable to them, due to the absence of a stable substrate and the presence of vigorous wave action which would be unfavorable for Planktonic algae. These areas are often turbid due to wave & wind action and from soil runoff.
"Ooid" sand grain containing Endolithic Cyanobacterium (CB). The presence of these organisms in limestone & coral reefs can lead to erosion. This is caused by grazing animals who eat the Cyanobacteria and consequently decrease the amount of limestone present. The effect of this is illustrated below.
Erosion caused by Endolithic Cyanobacteria
This can sometimes produce fantastic "Biocarst" shapes.
