Algal density assessed by spectrophotometry: A calibration curve for the unicellular algae Pseudokirchneriella subcapitata

The unicellular algae Pseudokirchneriella subcapitata (Korschikov) Hindák has been frequently used for ecotoxicological tests. In this paper, a calibration curve is proposed correlating absorbance values (684 nm) and cell density for routine ecotoxicological experiments. Density (cells/mL) could be estimated as follow: Cell Density = e {[ln (absorbance_684) +16.439]/1.0219} (n=130; r2=0.9998). Residual distribution revealed that the equation could be applied for algal densities under 5,000,000 cells/mL and/or absorbance values as high as 0.5. Key words: Pseudokirchneriella subcapitata, spectrophotometry, ecotoxicological tests.