A quick and effective estimation of algal density by turbidimetry developed with Chlorella vulgaris cultures

The use of Chlorella vulgaris Beijerinck as a food source for zooplankton requires the optimization of algal-culture conditions for prolonged growth maintenance. In this study, we developed a method that relates algal density to culture turbidity to estimate culture biomass. This method was improved by applying digital analysis for algal counting, which promotes accuracy, low culture disturbance, easy repetition and the rapid acquisition of results. Two 3-L cultures of C. vulgaris, maintained for two weeks with continuous lighting (eight light-emitting diodes at 50 [mu]mol photons m-2 [middot]s super(-1), at 660 nm) and aerators to prevent algal sedimentation, reached turbidities of 214 and 280 NTUs, respectively. Sample counting was performed using digital images obtained with an inverted microscope. Aliquot sedimentation was compared with or without previous homogenization through photographs taken in the central, middle, and peripheral sectors of the Utermohl settling chambers. For each procedure, we counted between 17 and 404 individuals image-1, requiring, on average, one minute image super(-1). At low turbidity (