Study on the outbreak/ extinction mechanisms of marine harmful microalga Cochlodinium polykrikoides in Korean coastal waters

Abstract

In Korea, red tide events by dinoflagellate Cochlodinium occur every year and affect serious economic losses to fisheries. In particular, the chain form of Cochlodinium is known to cause fish death by gill-clogging when its abundance exceeds approximately 1000 cells ml-1. The study aims to clarify the outbreak/extinction mechanisms of marine harmful microalga Cochlodinium polykrikoides blooms based on the physical, chemical and biological environments (i.e., vertical structure of sea water, nutritional characteristics and biological interaction etc.). At near coast of St. 22, there was no significant difference between temperature of upper and bottom layers, and high nutrient was kept in surface layer. These suggest that wind driven coastal upwelling have supplied nutrients to the euphotic zone. In August, low salinity water (below 30 psu) at offshore front station was constantly observed, which may have originated from Changjiang River discharge in China. Such events of upwelling and introduction of Changjiang Diluted Water can lead to nutrient-rich environmental condition, indicating that the diatom species respond to pulsed nutrient loading and dominate in Tongyeong coastal area. For these reasons, red tide of dinoflagellate Cochlodinium in 2016 did not occur in late July and early August normally. In late August of 2016, however, the Cochlodinium bloom occurred in Goheung area partly, which was delayed about a mos approximately 1000 cells ml-1. The study aims to clarify the outbreak/extinction mechanisms of marine harmful microalga Cochlodinium polykrikoides blooms based on the physical, chemical and biological environments (i.e., vertical structure of sea water, nutritional characteristics and biological interaction etc.). At near coast of St. 22, there was no significant difference between temperature of upper and bottom layers, and high nutrient was kept in surface layer. These suggest that wind driven coastal upwelling have supplied nutrients to the euphotic zone. In August, low salinity water (below 30 psu) at offshore front station was constantly observed, which may have originated from Changjiang River discharge in China. Such events of upwelling and introduction of Changjiang Diluted Water can lead to nutrient-rich environmental condition, indicating that the diatom species respond to pulsed nutrient loading and dominate in Tongyeong coastal area. For these reasons, red tide of dinoflagellate Cochlodinium in 2016 did not occur in late July and early August normally. In late August of 2016, however, the Cochlodinium bloom occurred in Goheung area partly, which was delayed about a mo