Seasonal morphological plasticity of phytoplankton in Lago Maggiore (N. Italy)

During the year 2002, the size variability of most of the species found in Lago Maggiore was analysed in detail, measuring through image analysis the main morphological parameters (maximum linear dimension, surface, volume) of the algal cells. Many individuals belonging to the same species were measured sampling by sampling, collecting about 28,000 data. This data set allowed us to evaluate the morphological plasticity of many species across the seasonal succession: through multivariate statistical analysis we compared the changes of cell volume, cell surface, maximum linear dimension and surface-to-volume ratio to the fluctuations of the main physical and chemical parameters. The responses we observed were variable, depending on the different taxonomic groups or species as well as on the morphometric parameter considered. As a general pattern, a strong seasonality of the size changes was observed, mainly dependent on the gradients of nutrients and temperature.