Seasonal variations of photo-acclimation in the phytoplankton assemblages of the Tuscan Tyrrhenian Sea.

The photo-acclimation responses of natural phytoplankton from the Tuscan Tyrrhenian Sea were assessed in different seasons through the measurements of Photosynthesis-Irradiance curves (PEc) by pulse amplitude modulated (PAM, Walz) variable fluorescence. The analysis of photosynthetic parameter variations allowed distinguishing between low-light (shade-acclimation) and high-light (sun-acclimation) responses. The relationship between phytoplankton response to light and the structure of the water column (mixed or stratified) is discussed, together with the taxonomic composition. Variable fluorescence PEc measurement turned out to be particularly suitable in these low chlorophyll a concentration conditions, finally allowing the assessment of photosynthetic parameters as a valid alternative to more traditional gas exchange techniques.