Phycotoxin-producing microalgae can secrete toxins into the water during their normal growth and metabolism, as well as following cell lysis, posing potential threats to marine organism health. The distribution of dissolved paralytic shellfish toxins (PSTs) in the Yellow Sea and the Bohai Sea, China, was investigated by two cruises in April and July 2023. Results showed that C1/2, GTX1/4, GTX2/3 and dcGTX2/3, were detected in seawater samples in both spring and summer, with the detection rates 100 % and 97.6 %, respectively. The total PST (ΣPSTs) concentrations ranged from 12~590 pmol/L and from not detected (nd)~188 pmol/L in surface seawater samples collected in spring and summer, respectively. Concentrations of ΣPSTs in surface waters were much lower in summer than those in spring. Dissolved GTX1-4 can be accumulated by organisms such as bivalves and mysids, posing toxic hazards. Sublethal exposure to PSTs elicited multifaceted physiological disruptionsin mysids, encompassing significant oxidative stress and complex dysregulation of neurotransmission. Concurrently, the expressions of genes associated with ABC transporters, cytochrome P450, phase II metabolic and antioxidant enzymes were significantly unregulated, while genes involved in governing synaptic function and neurotransmission showed notable dysregulation. The transcriptional response of mysids to PSTs reveals a multi-level defense strategy involving detoxification, oxidative stress mitigation, and neurobehavioral adaptation.