2.2. Data collection and analysis
Samples were collected at quarterly intervals over two years, from December 2007 to September 2009, at 12 stations located along the longitudinal axis of each reservoir (Figure 1, Table 1). Samples were obtained by vertical hauls of the net along the euphotic zone, determined by a digital quantometer (Licor-250), using conical-cylindrical plankton nets with a 25μm mesh size. The material was preserved in 4% formaldehyde and then examined using an optical microscope and photographed with the aid of a microscope (Zeiss/Axioskop) coupled to a Samsung SCC833, Japan camera, using the software Imagelab (Softium, Brazil).
Figure 1.