The Spatio-Temporal Analysis of Cochlodinium polykrikoides Blooms Occurrence in the South Sea of Korea

Abstract

Cochlodinium polykrikoides Margalef is a marine ichthyotoxic dinoflagellate, one of several taxa responsible for the ecologically and economically important event known as harmful algal blooms (HABs), commonly referred to as “Red Tide”. HABs caused by C. polykrikoides has been first recorded in the estuary of Nak-dong River close to Busan city of Korea in 1982. According to the observed in-situ data, the frequency of this phenomenon has been increased every year. The prevalent bloom season was from July to October with a peak in August. This HABs has caused major impacts on aquaculture and socioeconomic in Korean waters, especially in the South Sea of Korea since 1982 until nowadays. The purpose of this study was to elucidate a statistical and spatio-temporal analysis of the progress of the red tide caused by this dinoflagellate species in the South Sea of Korea from 2000 to 2015. This analysis helped us to determine the progress and the most concentrated and frequented areas year after year. The data were obtained from the National Institute of Fisheries Science (NIFS) from July to October which encompassed cell density of C. polykrikoides (cells/ml) and seawater temperature (°C). The study area was divided into three zones; Wando, Yeosu and Tongyeong. Then, we applied a comparative statistical analysis with each area data. Thus, a spatial analysis tool of GIS was adopted; Kernel Density, by using ArcGIS 10.5. The results were shown that the most frequented area by the occurrence of C. polykrikoides during the study period was Yeosu followed by Tongyeong and Wando, with a number of 61, 50 and 31 occurrences, respectively. Comparing with previous studies, we conclude that these studied periods shown the longest time duration of Cochlodinium polykrikoides occurrence which reached 29 days (4 weeks). It was recorded in Yeosu. Thus, the most important widespread occurrence was reported in 2008, 2014 and 2015, respectively.