Uncovering the potential effect of microplastics on Alexandrium pacificum: From the perspective of cyst formation and toxin production

Toxigenic dinoflagellate blooms and microplastics pollution are significant ecological concerns in coastal waters. Alexandrium spp. can produce paralytic shellfish toxins (PSTs), posing a serious threat to marine ecological security. Cysts can serve as the source of Alexandrium algal blooms. The formation of cysts and the toxin production capacity of algal cells are both easily influenced by external environmental factors. However, the impact of microplastics on these processes remains poorly understood. Therefore, the effects of microplastics on the growth, cyst formation, and toxin production of A. pacificum were investigated in this study. The results showed that cell growth was inhibited, while the proportion of cysts increased under polystyrene (PS) microplastics treatment. On the 8th day, the proportion of cysts in the 100 mg/L PS-treated groups was (47.70 ± 3.84)%, which was significantly higher than that of the control (p < 0.01). Meanwhile, after 8 days of PS treatment, the relative proportion of extracellular toxins to total toxin content increased significantly. On the 8th and 16th days, the toxins cell quotas in the PS-treated groups were all significantly higher than that in the control group (p < 0.05). This suggested that PS microplastics did not stimulate an increase in total toxin production, but promoted the release of PSTs to some extent. This study would provide theoretical reference for assessing and predicting the ecological risks of the coexistence of microplastics and toxigenic dinoflagellates in coastal waters.