Effects of intrusion and retreat of deep cold waters on the causative species of red tides offshore in the South Sea of Korea

To explore the effects of eutrophic deep waters offshore on red-tide outbreaks, were collected from 0, 20, and 40 m depths at an station in South Sea Korea, growth rate each major dinoflagellate Prorocentrum donghaiense, Tripos furca, Alexandrium fraterculus, Margalefidinium polykrikoides was measured. No species grew dissolved inorganic nitrogen concentrations (DIN) < 7.0–8.4 µM, but rates all four rapidly increased became saturated 12–15 µM DIN. On July 31, 2020, DIN 4.1–4.6 0–10 depth 8.9–18.4 20–50 waters. Under these circumstances, considering that calculated reachable P. T. A. M. 10, 15, 24, 52 m, respectively, fraterculus can reach grow, donghaiense furca cannot. However, if intrude ascend by 10–20 relative to whereas retreat descend only grow. Red-tide outbreaks 2014 occurred after water retreat. Thus, position waters, affected their intrusion solar insolation, affect harmful red tides.