ABSTRACT
The diurnal vertical migration of Cochlodinium polykrikoides (C. polykrikoides), which caused a red tide in the Korean coastal waters of the East Sea/Sea of Japan in September 2003, was examined by determining the time-dependent changes in the density of living cells in relation to the depth of the water column. The ascent of this species into the surface layer (depth of water, 2 m) occurred during 1400- 1500. The descent started at 1600 and a high distribution rate (86%) at 15-20 m was observed at 0300. During the ascent, the cells were widely distributed at each depth level from 0600 hr and at 0800-1100, the cells were primarily distributed in the middle layer (0-6 m). The concentration of dissolved inorganic nitrogen was generally <2.86 μmol l -1, but at 1400-1500, the concentration in the surface layer reduced to <0.14 μmol l -1. Moreover, the concentration gradually increased as the depth increased to > 5 m. These results showed that the nutrientconsumption rate associated with the proliferation of C. polykrikoides during a red tide is more influenced by the inorganic-nitrogen resources rather than the inorganic-phosphorus compounds.