Allelopathic interactions mediated by Alexandrium minutum bioactive extracellular compounds (BECs) may have consequences for the phytoplankton communities and carbon cycle. This study investigates the physiological effects of A. minutum allelochemicals across multiple microalgae species. Using PAM fluorometry, and flow cytometry, a microalgal screening assessing the photosynthetic efficiency, autofluorescence and growth rates was performed. For the sensitive species, roller-tank experiments were conducted to simulate sinking and aggregation similarly to the phenomenon happening in the natural water column. Rhodomonas salina was the microalgae that showed higher sensitivity, with decreases in Fv/Fm and autofluorescence values after exposure to allelochemicals, and with rapid aggregate formation. The aggregates had variable sizes and sinking speeds, indicating that microalgae physiology can also impact the aggregation process. This work shows that allelopathy can influence aggregation processes, by leading to cell lysis of the target species.
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