Influence of cell equivalent spherical diameter on the growth rate and cell density of marine phytoplankton

The maximal growth rates (μmax) of 8 species of marine phytoplankton were studied in detail. A Logistic growth model was used to describe the growth process of phytoplankton and the averaged plotting correlation coefficient was 1.00 ± 0.01 (mean ± standard deviation). The size distribution of phytoplankton could be well represented by single or combined Gaussian distribution functions. The size distribution of phytoplankton was investigated by daily analysis, and the variation of the median equivalent spherical diameter (MESD) was recorded. The size of algal cells varied throughout the process of population growth, and the size distribution characteristic of the two species of pyrrophytes investigated also changed during the growth process. The relation between maximum growth rate and MESD could be expressed by the equation μmax = a * MESDb (where μmax is the maximum specific growth rate, MESD is the median equivalent spherical diameter, and a and b are constants equal to 2.10 × 105 and − 1.15, respectively), estimated by nonlinear regression analysis with the allometric function. The dependence of maximum cell density on algal MESD was also investigated and the relationship Bf = 1.56 × 107 MESD− 1.20 was obtained (where Bf is the maximum cell density).