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Microbial mats are organo-sedimentary ecosystems formed by autotrophic and heterotrophic bacterias. Cyanobacteria contribute to the formation of these structures from the entrapment and engulfment of sediments contributing to the formation of carbonate rocks found in the geological record from the Precambrian to the Recent. In this research we identified the living cyanobacteria mats type 1 (gelatinous) and type 2 (cohesives) present in Brejo do Espinho and Araruama saline, east Fluminense, Rio de Janeiro state. The microbial mats type 1, were found in compartiment A and B of Brejo do Espinho and the Araruama saline in the tank with a depth of 10 cm. The mats type 2 were only found in compartiment A and in tank with 15 cm depth. In the microbial mats of compartiments A and B predominated the spherical forms of genres Chroococcus Nägeli 1948 and Aphanothece Nägeli 1948. In the tanks predominated filamentous forms of the Leptolyngbya Anagnostidis and Komárek 1988 genre. In mats type 1, the diversity indices (H') were 1.95 and 2.24 and in type 2 of 2.16 and 2.14 for the Brejo do Espinho and Araruama saline, respectively. The highest values of diversity indices found in saline tanks occurred by stable salinity conditions.

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