Distribution: Recent Stromatolites
Recent stromatolites occur primarily in supratidal, intertidal, and shallow subtidal zones.  Because of this occurrence, it had been thought that ancient stromatolites occurred only in shallow-water environments as well.
Geologist studying stromatolite underwater at lee Stocking Island, Bahamas

This assumption was disproved by Playford and Cockbain (1969) with the discovery of widespread columnar stromatolites in Devonian fore-reef facies in Western Australia that developed in water at least 45m deep.  It is likely that ancient stromatolites formed in low-latitude environments, not because of ecological restrictions, but that these areas at that time were marine, shallow-water environments where carbonate deposition was predominant.  At present, microbial mats are restricted to areas where the photosynthetic production rates exceeds the grazing stress.  These areas are generally found to be hypersaline, where many grazing organisms can not thrive.