Limnetica 39

This study focused on the phytoplanktonic community of lake Sanabria (NW Spain) during the mixing period. We integrated the classic phytoplankton counting method and the pigment analysis via high performance liquid chromatography, to obtain a global image of the community structure, which was very similar among the study zones and unaltered despite a temporal increasing of biomass during this period. The diatom Asterionella formosa Hassall (around 80%), and consequently the fucoxanthin were the species and the secondary pigment more abundant, respectively. This dominance contrasted with the studies performed in 90´s, where the community structure was distributed among chlorophytes, cryptophytes, diatoms, dinoflagellates and cyanophytes, with no clear and persistent dominance of any of the main taxonomic groups and an occasional presence of Asterionella formosa. However, the classical variables, such as nutrients or chlorophyll a concentration, used for trophic definition have barely changed since the studies of 90’s. It is possible that other parameters, such as the residence time or the effect of the increase in the temperature since 90´s could have influenced the phytoplankton community structural changes observed.