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 repro ducibility of the most probable number (MPN) technique for estimating conce ntrations of viable planktonic diatoms from sediment samples. Two contrasti ng species were used to inoculate sterilised sediments: Ditylum brightwelli i (large single-celled species) and Skeletonema costatum (small chain-formi ng species). MPN estimates were carried out on sediment samples that had be en inoculated with known numbers of cells to produce three different cell c oncentrations for each species. The results obtained for these samples were predominantly underestimates of cell concentration for both species. The m ethod was insensitive to low cell concentrations (less than or equal to 50 ml(-1)). Results at higher concentrations indicate that the technique is be st treated as a semiquantitative method for determining relative abundance. (C) 1998 Elsevier Science B.V. All rights reserved.