Phytoplankton cells can no longer be considered as passive particles and they can modulate impacts of selection factors (light, turbidity and mixing) through a wide range of adaptations . Cell shape and/or chain length modulation is one of these processes, but it still mainly studied as an adaptation or an acclimatation to a specific stress (light, nutrients, predation, etc.). This study showed that cell shape and size may have a greater role than previously known in phytoplankton ecology and species adaptation by permitting synchronous processes to be set up. Through microscale biophysical interactions leading to specific cell reorientation processes, we show that cell geometry not only modulates their sinking rate but can also provide a fast sensor response for their environment. Gyrotaxis has already been described in detail for motile phytoplankton cells, but the reorientation process described here can occur in the environment without motile capacity. An additional consistent behaviour was also recently described for a diatom species (Pseudo- nitzschia delicatessima) and with this study, and we extend this observation to Pseudo-nitzschia Pungens and Pseudo-nitzschia Fraudulenta. Our observation emphasizes the generality of this process which adds a new level of complexity with regards to cellular interactions and their network of sensors. Data : Data set is divided in three parts. 1- Labels per strain are provided in the ods file. 2- Flowcytometer raw files (.cyz) and exported files (.csv) for 19 phytoplankton strains are provided in the zip files.  Three replicates were made over the time (three subdirectories).  Flowcytometer analyses were made with and without images acquisition as indicated in each filename. Clusters available in the exported files were made manually and according to the number of cell per particle.  Mean abundances per cluster are provided in the csv files. 3- Processed LISST data. Temporal evolution of cell’s aspect ratio R, defined as the ratio between the cross-sectional (r1) and the transapical cell axis (r2) of Pseudo-nitzschia fraudulenta strains in ligth and dark conditions.