Impact of chlorpyrifos on growth and community structure of diatoms and dinoflagellates in the Bohai Sea, China.

The diatom/dinoflagellate ratio in the Bohai Sea is influenced by various environmental factors, potentially including the increasing input of agricultural pesticides. This study investigated the effects of chlorpyrifos (CPF) on phytoplankton growth and community structure through field-based culture experiments. The results showed that at a concentration of 30.0 μg L^-1 CPF had a stimulatory effect on algal growth, whereas a concentration of 50.0 μg L^-1 exhibited an inhibitory effect under low-temperature conditions (<24.0 °C). Continuous low-dose exposure to CPF prolonged and amplified the phytoplankton growth plateau. CPF exposure also drove a shift in the phytoplankton community structure from diatom-dominated to dinoflagellate-dominated, with Prorocentrum minimum and Karenia mikimotoi emerging as dominant species. Kinetic analysis revealed that CPF's impact on phytoplankton growth was primarily regulated by nitrogen uptake rates. These findings supplement and clarify a potential regime shift from diatom to dinoflagellate dominance associated with CPF in the Bohai Sea. Future coastal management strategies should account for the ecological risks of residual insecticides to ensure ecosystem stability.