Harmful algal bloom (HAB) in the East Sea identified by the Geostationary Ocean Color Imager (GOCI)

•GOCI can be effectively applied to the monitoring of short-term and long-term movements of red tides.•The GOCI Rrs spectrum displayed marked peaks at band 4 (centered at 555nm) and band 6 (centered at 680nm), a typical radiometric characteristic of HABs.•We were able to identify the vertical migration of Cochlodinium polykrikoides through the hourly GOCI images.•C. polykrikoides bloom in GOCI images was revealed to be associated to cold water mass in its formation and propagation to offshore. Harmful Cochlodinium polykrikoides blooms have frequently appeared and caused fatal harm to aquaculture in Korean coastal waters since 1995. We investigated the applicability of GOCI, the world's first Geostationary Ocean Color Imager, in monitoring the distribution and temporal movement of a harmful algal bloom (HAB) that was discovered in the East Sea near the Korean peninsula in August 2013. We identified the existence of C. polykrikoides at a maximum cell abundance of over 6000cells/mL and a chlorophyll a concentration of over 400mg/m3. In areas of C. polykrikoides blooms, GOCI remote sensing reflectance (Rrs) spectra demonstrated the typical radiometric features of a HAB, and from the diurnal variations using GOCI-derived chlorophyll concentration images, we were able to identify the vertical migration of the red tide species. We also found that the formation and propagation of the HAB had relations with cold water mass in the coastal region. GOCI can be effectively applied to the monitoring of short-term and long-term movements of red tides.