Mixotrophic abilities of dinof lagellate Gonyaulax species: compensation for low growth rates under low-light conditions

Several species within the genus Gonyaulax produce toxins and form blooms in diverse regions worldwide, necessitating further research on their eco-physiological characteristics to better understand their population dynamics. This study examined whether prey availability compensates for low-light limitation in Gonyaulax spp. by evaluating photosynthetic efficiency (Fv/Fm) and specific growth rate (μ) under two light levels and three prey concentrations. G. kunsanensis was the only species to ingest bacterium-sized particles, as evidenced by the uptake of fluorescein isothiocyanate-labeled fluorescent beads. G. kunsanensis growth rates were significantly increased under phagomixotrophic and low-light conditions. Under the same light condition without phago-mixotrophy, G. kunsanensis exhibited a low growth rate. Conversely, G. whaseongensis showed enhanced growth under low-light relative to highlight conditions. A light-shift experiment from high to low light showed that G. kunsanensis compensated for reduced light through phago-mixotrophy. These findings indicate that prey presence enhances growth in G. kunsanensis under low light, whereas changes in Fv/Fm were species-specific and did not consistently track growth responses.