ABSTRACT

Dilution of natural microbial plankton communities with particle-free water from the same source can be used, under appropriate conditions, to estimate instantaneous rates of growth and grazing mortality of phytoplankton. The analytical framework for the method uses differences in measured net growth rates at different dilution levels to uncouple average growth and mortality rates over a defined incubation period. The major advantages of the dilution approach are: it provides rate estimates for both growth and grazing mortality of phytoplankton in a single experiment, it involves minimal handling and physical disruption of the organisms and it allows simultaneous analysis of the dynamics of different components of the phytoplankton community. The objective of the filtration step is to produce, as efficiently as possible, a desired volume of water, free of the populations of interest and free of contaminants that might either enhance or depress growth rates relative to ambient water.