The diatom flora in Conceição Lagoon, Florianópolis, SC, Brazil

Abstract

“Lagoa da Conceição” is a small lagoon located at Santa Catarina Island, Santa Catarina State, Brazil (27º 34`S; 48º 27`W). In recent decades, their characteristics have been changed mainly due to the increase in average salinity caused by permanent opening of the canal, in 1982, that connects the lagoon to the sea and the growing urbanization impact of the surrounding areas. The only study on the lagoon phytoplankton was conducted in 1988, showing that diatoms were the most diverse group and were dominant at some periods. This study aimed to make a floristic survey of the Conceição Lagoon diatom community, analyzing its variation over a sampled period. The samples were obtained in 1979, 1980, 1982, and 1994 at six stations and in 2002 at ten stations with a phytoplankton net. One hundred and eight specific and infraspecific taxa were identified belonging to Coscinodiscophyceae, (32), Fragilariophyceae (14) and Bacillariophyceae (62). Six taxa were present in all sampling periods and fifteen at 80% sampled years. The Conceição lagoon diatom flora showed 41% of taxa in common with the Santa Catarina Southern Lagoon Complex. Scanning electron microscopy studies confirmed the presence of the Cyclotella litoralis Lange et Syvertsen and Paralia fenestrata Sawai et Naguno in the lagoon which probably had been misidentified as Cyclotella striata (Kützing) Grunow and Paralia sulcata (Ehrenberg) Cleve respectively in a former survey. Available data are insufficient to explain the distribution of diatom species related to salinity at the Conceição lagoon.