Evidence of the Modern Oncoids in Salgada Lagoon, North of Rio de Janeiro State, Southeast Brazil.

Abstract

Salgada Lagoon, a hypersaline natural aquatic body (21o54’’10”S - 41o00’30”W), occupies an area about 16 km2, near the coastal town of Cape São Tome between the municipalities of Campos dos Goytacazes and São João da Barra. The lagoon has a connection with the ocean through the Açu River and its main feature is the presence of biogenic carbonate structures. The object this study was to characterize the oncoids and cyanobacterial composition present in this construction. The first collect from Salgada Lagoon occurred in 1999 and subsequently other four campaigns occurred between 2000 and 2001. During the period were retreated samples of oncoids, through the manual extraction, in southwest edge, in infratidal zone. The material was selected in agreement with the integrity, size and colour. To verify the cyanobacteria was applied HCL N/10 solution, a followed by treatment H2O2 a 20%. Fresh and permanent laminas was make. The analysis allowed the identification of the several sizes of oncoids They are minute, examples with variation between 9,50 a 23,50 mm, with diameter average to 14,90 mm and colour is varying among the white and grey. They have spherical, oval, elliptical e irregular forms, are still, associated with smooth microbial mats and show thin concentric lamination. The study of samples enables the identification of 15 species of cyanobacteria in oncoids. The family most representative is Chroococcaceae Nägeli 1849 (53,38%), followed by the families Nostocaceae Kützing 1843 and Schizothricaceae Elenkin 1934 (6,66%), Synechococcaceae Komárek & Anagnostidis 1995 (13,32%), Phormidiaceae Anagnostidis & Komárek 1988 (19,98%). Chroococcus Nägeli 1849 is the genus most representative (46,66%). These bacteria are responsible by CaCO3 precipitation and by lamination structure. The oncoids are distributed on few deep region, accented energy, rise oxygenation, rise luminous incidence, site environmental factors.