The calculation of in situ growth rates of phytoplankton populations from fractions of cells undergoing mitosis: A clarification1

Abstract

A review of existing approaches used to calculate phytoplankton population growth rates from fractions of cells undergoing mitosis (mitotic index) has revealed inconsistencies in their content and underlying assumptions. The appropriate expressions are derived for populations in exponential growth and those which exhibit phased cell division. Growth rate estimates calculated from the maximum mitotic index in phased populations are shown to be accurate when the duration of the mitotic stage is greater than the interval during which the increase in cell number occurs. This characteristic is manifested in a plateau‐shaped curve of mitotic index vs. time. The alternative approach of averaging sequential observations is also considered, and the conditions for which one can obtain exact results are defined. The magnitude of uncertainties is examined as a function of the frequency of sampling.