Impact of combined seawater warming and triazine-type herbicide pollution on the physiology and potential toxicity of the dinoflagellate Alexandrium minutum

Coastal phytoplankton communities are often exposed to multiple anthropogenic stressors simultaneously. Here, we experimentally examined how temperature increase (20–26 °C) and triazine-type herbicides pollution (500 ng terbutryn L⁻¹), both recognized as emerging stressors, affect the abundance, physiology and selected saxitoxin gene expression in the toxic dinoflagellate Alexandrium minutum. The results show that A. minutum is more susceptible to terbutryn pollution with increasing temperatures, resulting in a significant decline in its abundance (∼80 %) and photosynthetic activity (∼40 %), while saxitoxin gene expression increased (1.5–2.5-fold). This suggests that in warming polluted coastal areas where A. minutum is often found, saxitoxin poisoning may occur even in the absence of a massive bloom. Our results recommend the development of science-based monitoring practices for algal dissolved toxins in coastal waters and estuaries, supporting environmental policies under warming and contaminated coastal regions.