Feasibility of estimating phytoplankton size and biomass in fresh and preserved samples from the Benguela Current with a Coulter counter

Abstract

Counting phytoplankton with a Coulter counter gave a higher degree of reproducibility than the inverted microscope method. Certain recommendations as to counting procedures are made. Repeating the count in the same sample resulted in underestimates of particle volume of up to 19 per cent. Replicates should be decanted into different beakers and counted separately so as to prevent any conductivity effects on the phytoplankton. In order to obtain representative particle volumes, samples should not exceed 25 mℓ at a concentration index (CI) of 5 per cent and not be less than 50 mℓ at a CI of 1 per cent. The counting of preserved samples is not recommended, because of the introduction of artefacts, resulting in a reduction of 77 per cent in particle volume after a year of preservation. Correlations of particle volume with chlorophyll a, carbon and nitrogen were calculated, with highest correlations occurring between particle volume and chlorophyll a. Total particle volume represents biomass as accurately as any other method. © 1985 Taylor & Francis Group, LLC.