Aquatic phytoplankton are in charge of the majority of photosynthesis on earth, and serve as the main contributors to primary productivity. Cells of these species carry molecular systems that specialize in funneling radiative energy for performing photosynthesis-related charge separation, and subsequently respiration. These systems include photosystems embedded in membranes, and light harvesting complexes on top of photosystems to optimize the funneling of radiative energy. Such well-controlled highly-efficient use of light is driven by the spatial organization of specific pigments and by the excitation energy transfer between them at different coupling regimes. As such, the autofluorescence of unicellular phytoplankton species is meaningful and therefore can be used for identifying different species and their metabolic responses to certain environmental changes. As for the control over the photosynthesis efficiency, time-resolved fluorescence can also be used.

In this work I will showcase the single-cell time-resolved multiparameter fluorescence spectroscopy approach we used with our confocal-based setup, to extract multiple autofluorescence parameters, and use them to track photo-physiological changes that different phytoplankton species (i.e., cyanobacteria, dinoflagellates and red algae) undergo in response to changes in light intensity that mimic day/night cycles, as well as abrupt vertical mixing. Based on our results, we show how different species alter the function of their photosynthetic apparati differently in response to light intensity changes.

In the next part of the talk, I will present some preliminary results from an experimental mimic of algal bloom rise of the Kinneret-Blooming Microcystis phytoplankton, in which we characterize the earliest stages in algal blooms before cells start to re-proliferate.
In the final part of my talk, I will discuss some exotic excited-state dynamics, which suggest a unique energy trapping mechanism that exists in species of cyanobacteria with depopulation times that do not distribute exponentially.