The objective of this work is to determine the spatial and temporal variation of microphytoplankton and environmental variables in Lake Azul, a permanent protected area in the town of Marechal Deodoro, Alagoas State, Brazil. Samples were collected from April to September 2008. Phytoplankton samples were obtained by surface-horizontal trawling with a 45µm mesh net. Water samples were taken with a Van Dorn bottle, during the phytoplankton collection, in order to determine physical-chemical parameters. A total of 27 taxa were identified, Chlorophyta were the most abundant taxa (63% of the sample) followed by Bacillariophyta (26%) and Cyanobacteria (11%). The dominant species were Desmidium swartzii var. quadrangulatum (Ralfs) A. Roy (62.3%) and D. cylindricum Greville (55.1%). The slightly acid pH associated with low nutrient availability favors the development of Desmidiaceae: Closterium sp., Cosmarium goniodes West & West, C. margaritiferum Meneghini ex Ralfs, C. vogeciacum Gutwinski, Desmidium cylindricum Greville, D. pseudotreplonema West & West, D. swartzii var. quadrangulatum (Ralfs) A. Roy, Euastrum brasiliense Borge var. minus G.S.West, Gymnozyga moniliformis Ehrenberg, Micrasterias denticulata Brébisson ex Ralfs, M. (Kützing) Ralfs, M. radians Turner and Tetmemorus laevis (Kuetzing) Ralfs.
phytoplankton; lakes; oligotrophic; desmidiaceae
