Inhibition of Cochlodinium polykrikoides related with abnormal high temperature by large among of Changjiang River discharge along the southern coastal water, Korea

Abstract

Dinoflagellate Cochlodinium polykrikoides bloom during the past 20 years have been consistently present along the southern coastal water, whereas they abruptly disappeared in 2016. So, to understand these phenomena, physico-chemical and biological data were collected along the Tongyeong coast through a biweekly field survey from June to September. In 2016, the amount of Changjiang River discharge from China, which can affect coastal environments via ocean currents, was relatively larger than in the past four years, reducing the salinity in August. As a result, the environmental differences between 2016 and previous years (2012-2015) were investigated. In particular, the water temperatures (c.a.,30°C) and the salinity (c.a., 30) in August were outside the optimum ranges for C. polykrikoides growth in the study area. Moreover, the averages of these factors were significantly different from previous years (p<0.001). Increased stratification and diatom dominance, both negatively associated with C. polykrikoides growth, were consistently observed during the study period. In the Goheung area, which is the western part of the southern Korean coastal waters (KCW), C. polykrikoides bloomswere observed, but they did not expand to the entire southern KCW, unlike in previous years. At that time, the strong winds from the Malakas typhoon may have terminated the bloom. In addition, westward winds may have inhibited the spread oflogical data were collected along the Tongyeong coast through a biweekly field survey from June to September. In 2016, the amount of Changjiang River discharge from China, which can affect coastal environments via ocean currents, was relatively larger than in the past four years, reducing the salinity in August. As a result, the environmental differences between 2016 and previous years (2012-2015) were investigated. In particular, the water temperatures (c.a.,30°C) and the salinity (c.a., 30) in August were outside the optimum ranges for C. polykrikoides growth in the study area. Moreover, the averages of these factors were significantly different from previous years (p<0.001). Increased stratification and diatom dominance, both negatively associated with C. polykrikoides growth, were consistently observed during the study period. In the Goheung area, which is the western part of the southern Korean coastal waters (KCW), C. polykrikoides bloomswere observed, but they did not expand to the entire southern KCW, unlike in previous years. At that time, the strong winds from the Malakas typhoon may have terminated the bloom. In addition, westward winds may have inhibited the spread of