Characteristics of Harmful Algal Blooms in the Southern Coast of Korea using In situ and Multi-Satellite Data

Abstract

Harmful Algal Blooms (HAB) due to C. polykrikoides species has caused impact on aquaculture and socioeconomic in Korean waters since 1982 until nowadays. The HAB annually present on summer. Therefore, HAB can be called as ‥seasonal disaster…. Many studies on HAB have been carried out using either in situ data that restricted local area or laboratory study or satellite data. Even though the studies using satellite data seemingly are still done partially. Therefore, comprehensive study of HAB using in situ and multi？Vsatellite data was an interesting object and actual. That is the reason choosing object as a topic in this study. The purpose of this study was to elucidate the characteristics of HAB that caused by C. polykrikoides species in the Southern Coast of Korea using in situ and multi？Vsatellite data. The data which used as the analytical object was obtained from July to September 2002~2008. The characteristics in this study mean the favorable conditions of HAB, which was influenced on environment parameters such as water and air temperature, precipitation, wind speed and direction, and sunshine duration. In situ data involved oceanic parameters (cell density of C. polykrikoides and seawater temperature) and meteorological parameters (air temperature, precipitation, wind speed and direction, and sunshine duration). The oceanic data were obtained from National Fisheries Research and Development Institute (NFRDI) and meteorological data were obtained from Korea Meteorological Administration (KMA). The environment parameters of HAB also were depicted by using some satellite data such as ocean color images, sea surface temperature, sea surface height anomaly, sea surface wind, and precipitation. Because of used some satellite data with different application, here was mentioned as multi？Vsatellite. Ocean color images from SeaWiFS that use Ocean Color 4 (OC4) (O…Reilly et al., 1998, 2000) and Red tide Index Algorithms (RCA) (Ahn and Shanmugam, 2006) methods were used to detect and estimate the area of HAB in term chlorophyll a. Ocean color images from MODIS also was used to support the information of HAB. Sea surface temperature data was used to depict seawater temperature in surface and detect the warm current that passed through in the Southern Coast of Korea. Sea surface height anomaly data were used to depict the elevation of sea surface and depicted the geostrophic surface currents in the sea. Sea surface wind data was used to depict wind speed and direction on the sea surface. Geostrophics currents and sea surface wind influenced on the blooming, spreading and migration of HAB. Precipitation data was used to estimate precipitation that occurred in the Southern Coast of Korea. In this research, the Southern Coast of Korea was used as study area. The study area was divided into 4 inshore areas namely south west (SW), south middle (SM), south east (SE), and east south (ES), where these regions are vicinity with Wando, Yeosu, Tongyeong, and Pohang, respectively. The results of this study are as followings. The in situ data have shown the greatest number of HAB occurred in Yeosu, followed by Tongyeong, Wando, and Pohang. The highest total numbers of blooms were occurred on August. When the HAB occurred, seawater temperature have ranged 20.1~31？aC, 19.4~30.2？aC, 20~28？aC, and 14~27.5？aC, in Wando, Yeosu, Tongyeong, and Pohang, respectively. The time duration of the HAB was ranged 1~29 days (1~4 weeks). Typhoons that passed over or near the sea resulted in high precipitation and strong winds in inshore areas. A high density of HAB outbreak often occurred a day after typhoon. The time duration of HAB increased if a precipitation event occurred during the occurrences of HAB. The high precipitation and the runoff from land brought some nutrients and triggered the HAB in the coastal area. Precipitation data from satellite and meteorological data from in situ show the same trend and were positively correlated. The correlation coefficients ranged from 0.422 to 0.826. Mean sea surface wind data from satellite indicated that southeasterly, southerly, and southwesterly winds blew from July to mid August, and that wind direction then changed to northeasterly in late August to September. The strong southeasterly and southerly winds drove rich nutrient in the surface waters from the Changjiang Dilute Water (CDW) to the Southern Coast of Korea, especially in July in the SW region. The light southwesterly (2~6 m s-1) are favorable condition for the occurrences. The multi？Vsatellite image obviously shows the CDW, sea surface current, and Tsushima Warm Current (TWC) in the Southern Coast of Korea. The CDW flowed eastward to northern Jeju Island, merged with TWC and moved to the East Sea. The bathymetry, OC4, RCA, SST, and SSH data from the 127.55？aE transect showed that the steep gradients of SST near Naro Island indicated a mixture of inshore and offshore waters.