The inhibition and development of harmful alga Cochlodinium polykrikoides bloom related with Changjiang River discharge in Korean coastal waters

Abstract

Over the last three decades, harmful alga Cochlodinium polykrikoides bloom have been consistently present along the Korean coastal water but they abruptly disappeared in 2016. Despite extensive studies on this dinoflagellate, the cause of this abrupt decline remains largely unknown. To understand the inhibition and development of harmful alga Cochlodinium polykrikoides population related with Changjiang River discharge, physico-chemical and biological data were collected along the south-eastern area of South Sea through a biweekly field survey from June to September. The environmental differences between 2016 and previous years (2012-2015) were investigated. In August, the water temperatures (c.a.,30°C) and the salinity (c.a., 30) 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). In 2016, the amount of Changjiang River discharge, which can affect coastal environments via ocean currents, was relatively larger than in the past four years, reducing the salinity in August. Increased stratification and diatom dominance, both negatively associated with C. polykrikoides growth, were consistently observed during the study period. In the Goheung-Oenarodo area, which is the western part of the southern Korean coastal waters (KCW), C. polykrikoides blooms were observed, but they did not expand to the