Allelopathic effects induced by Cylindrotheca closterium on the toxic dinoflagellate Prorocentrum donghaiense under varying nutrient conditions

The allelopathic effects of the diatom Cylindrotheca closterium on the dinoflagellate Prorocentrum donghaiense were investigated under varying nutrient conditions (standard and modified f/2 media) and initial cell densities. Results revealed that C. closterium culture filtrates significantly inhibited the growth of P. donghaiense across all experimental conditions, with stronger effects observed at higher filtrate concentrations and lower initial cell densities. The inhibitory effects were dose-dependent and more pronounced under nutrient-limited conditions, indicating that allelopathy serves as a competitive mechanism regardless of nutrient availability. Interestingly, P. donghaiense filtrates did not affect the growth of C. closterium, underscoring species-specific resistance mechanisms. Biochemical analyses indicated substantial disruptions in P. donghaiense cellular metabolism, including reduced protein synthesis, increased oxidative stress and membrane damage. These findings underscore the ecological role of C. closterium in shaping phytoplankton community dynamics, particularly in nutrient-depleted environments, where allelochemical production may intensify as a competitive strategy. This research provides insights into the mechanism of allelopathic interactions and their potential implications for managing harmful algal blooms in coastal ecosystems.