“…However, after the discovery of photoautotrophers smaller than 1 µm, such as cyanobacteria (Waterbury et al, 1979) and picoeukaryotes (Johnson & Sieburth, 1982), membrane filters of varied composition and smaller nominal pore size (0.22 or 0.10 µm) have been suggested in order to retain these organisms (Li et al, 1983;Platt et al, 1983). Many comparisons between glass fiber and membrane filters for several kinds of analyses, such as seston, POC, primary production by 14 C method and also pigments have been carried out (Sheldon, 1972;Holm-Hansen & Reimann, 1978;Phinney & Yentsch, 1985;Morán et al, 1999;Ashimoto & Hiomoto, 2000). Morán et al (1999) compared the filters GF/C (1.2 µm), GF/F (0.7 µm), polycarbonate (0.2 µm) and cellulose esters (0.22 µm) using natural samples and verified no significant differences among these filters in terms of Chl-a retention, since flow cytometry analyses showed that most cells were larger than 1 µm.…”