Cyanobacteria and other components in the smooth microbial mats from Pitanguinha lagoon, Lagos Region, Rio de Janeiro, Brazil

Abstract

Pitanguinha Laggon is part of a set of small hipersaline lagoons known as Lagos region, placed in the northern Rio de Janeiro littoral, near Araruama city. They are genetically related to the last Quaternary glacial events and the sea level changes. The microbial mats formed around their margins are being affected by the advance of urbanisation and by salting exploration and are now threatened. The climatic conditions, with a semi-arid climate and warm temperatures stimulate the high evaporation rate. Many kinds of algalic mats growing up in their bottoms, associated with bioclastics and the lithified substrate of the lagoon. The composition of the smooth microbial mats and the associated organic rests are analyzed in this work. The study was carried out monthly on five sampling stations. The mats are stratified and filamentous forms dominante in the upper layer. Thirty seven species of cyanobacteria were identified, being Lyngbya aestuarii Liebman ex Gomont (1892) the more frequent. Specimens of Synechococcaceae Komárek and Anagnostidis, 1995 are the most abundant. Shells of bivalves, gastropods, foraminifers and ostracods occur together as associated bioclasts and have a critical role in the structure of the mats, being the source of calcium carbonate resulting from the chemically and physical action of the cyanobacteria over their skeletal remains. It attests that the cyanobacteria are the primary producers, located at the basis of the microbial food web in the microbial mats.

Key words: Cyanobacteria, smooth microbial mats, hipersaline lagoon, Brazil.