The estimation of cell numbers of flagellate and coccoid Chlorophyta in natural populations

Abstract

Methods for the quantitative estimation of the small coccoid and flagellate Chlorophyta in natural algal communities are outlined. Experiments to demonstrate the precision of these methods are discussed and the components of variance are calculated for several experimental procedures, both for phytoplanktonic and benthic associations. The smallest overall variance for phytoplankton estimations is 27% where a large number of samples were collected and bulked to reduce the sampling error. The precision in counting epipelic algae by this method is only 12%. This result suggests that the inclusion of a short period of ultrasonication may reduce the overall variance in estimation by randomising the distribution of the algae prior to plate inoculation. Close agreement exists between direct counts and plate counts. It is realised that the cultural approach has limitations, but comparison with results obtained from other methods indicates the advantages of cultural techniques, particularly when estimating small or motile algae.