This study investigates how small-scale turbulence affects the toxin and ecdysal cyst dynamics of two harmful algal species, Alexandrium minutum and A. catenella. Turbulence was induced using an orbital shaker (ε = 27 cm² s⁻³) and a vertically oscillating grid system (ε = 0.4 cm² s⁻³). The results show that high turbulence levels significantly reduced the exponential growth rate of A. minutum and decreased final biomass yield compared to unshaken cultures. In A. catenella, turbulence did not significantly affect growth rate, but cyst production was inhibited during exposure to turbulence. Cyst abundances recovered quickly once turbulence stopped. The toxin content of A. catenella was significantly lower in cultures exposed to high turbulence. These findings suggest that small-scale turbulence can modulate harmful algal blooms by affecting toxin production and cyst formation. The study highlights the importance of turbulence in the life cycle of these species and its potential impact on harmful algal blooms in natural environments. The results indicate that turbulence can influence the physiological processes of these species, including cell division, cyst formation, and toxin production. The study also shows that turbulence can have different effects on different species, emphasizing the need for species-specific studies. The findings contribute to understanding the dynamics of harmful algal blooms and the role of turbulence in their development.This study investigates how small-scale turbulence affects the toxin and ecdysal cyst dynamics of two harmful algal species, Alexandrium minutum and A. catenella. Turbulence was induced using an orbital shaker (ε = 27 cm² s⁻³) and a vertically oscillating grid system (ε = 0.4 cm² s⁻³). The results show that high turbulence levels significantly reduced the exponential growth rate of A. minutum and decreased final biomass yield compared to unshaken cultures. In A. catenella, turbulence did not significantly affect growth rate, but cyst production was inhibited during exposure to turbulence. Cyst abundances recovered quickly once turbulence stopped. The toxin content of A. catenella was significantly lower in cultures exposed to high turbulence. These findings suggest that small-scale turbulence can modulate harmful algal blooms by affecting toxin production and cyst formation. The study highlights the importance of turbulence in the life cycle of these species and its potential impact on harmful algal blooms in natural environments. The results indicate that turbulence can influence the physiological processes of these species, including cell division, cyst formation, and toxin production. The study also shows that turbulence can have different effects on different species, emphasizing the need for species-specific studies. The findings contribute to understanding the dynamics of harmful algal blooms and the role of turbulence in their development.