2.3.1. Growth curves
The cells were counted, after fixation with Lugol solution,
by an inverted microscope (Leitz Labovert F8) at 400× magnification
using Kolkwitz chambers and by applying the
method of Lund et al. (1958). The cell concentrations were
determined in three replicate sub-samples (3 × 1 ml). Cell
count data were used to define the growth curve for each
species, by plotting the natural logarithm of the number of
cells per milliliter against age culture (days).