An assessment of the accuracy and reproducibility of the most probable number (MPN) technique in estimating numbers of nutrient stressed diatoms in sediment samples

A series of experiments was carried out to determine the accuracy and reproducibility of the most probable number (MPN) technique for estimating concentrations of viable planktonic diatoms from sediment samples. Two contrasting species were used to inoculate sterilised sediments: Ditylum brightwellii (large single-celled species) and Skeletonema costatum (small chain-forming species). MPN estimates were carried out on sediment samples that had been inoculated with known numbers of cells to produce three different cell concentrations for each species. The results obtained for these samples were predominantly underestimates of cell concentration for both species. The method was insensitive to low cell concentrations (less than or equal to 50 ml(-1)). Results at higher concentrations indicate that the technique is best treated as a semiquantitative method for determining relative abundance. (C) 1998 Elsevier Science B.V. All rights reserved.