Bloom Potential of Toxic Dinoflagellate Alexandrium spp. in Jinhae Bay, Korea

Abstract

Harmful algal blooms (HABs) are phenomenon which shows serious impacts on the marine ecosystem and aquaculture productivity in many areas of the world. In Korea, Jinhae Bay is a highly developed coastal area in aquaculture productivity, where mussels, oysters and fish farms are widely distributed. however, the occurrences of HABs and paralytic shellfish poisoning (PSP) caused by the genus Alexandrium which has frequently bloomed around Jinhae Bay are imposing serious damage to public health as well as shellfish farming. To examine bloom potential and development of the toxic dinoflagellate Alexandrium spp., 182 sediment samples collected from 14 stations in Jinhae Bay from December 2011 to December 2012 by National Fisheries Research and Development Institute (NFRDI) were analysed, and the occurrence of vegetative cells and abundance of resting cysts of Alexandrium spp. at two periodic stations (CCSt. 1 and CCSt. 2) in Jinhae Bay were monthly surveyed from from February to May 2013. Water temperature (°C) averaged on the periodic sampling stations in Jinhae Bay from Dec 2011 to Dec 2012 shows a clear seasonal variation pattern with lower ranges in winter and higher in summer. Also on the physical factors such as pH and DO (mg/L) observed at the stations near Chilcheon Island in Jinhae Bay from Feb to May 2013 indicated for the highest mean in the summer season and the lowest in the winter, while the salinity ranges high in winter and low during spring season. Alexandrium spp. cysts were found in 182 sediment samples received from National Fisheries Research and Development Institute (NFRDI) at 14 stations in Jinhae Bay from Dec 2011 to Dec 2012, but the abundance was highly variable in a concentration range of 14-250 cysts/cm3 by showing spatio-temporal distribution patterns. Also the abundance of Alexandrium cysts varied horizontally among the sampling stations, where the highest concentration was found in St.11 (141.5±51.9 cysts/ cm3) and relatively higher distribution pattern showed around Jindong Bay stations. When a relationship between motile cells occurrence and cysts abundance was focused on the periodic stations near Chilcheon Island during vernal warming period, vegetative cells and cysts of Alexandrium spp. were also present at two stations of CCSt. 1 and CCSt. 2. moreover, there was a close relationship between the occurrence of vegetative cells and the abundance of cysts. vegetative cells of Alexandrium spp. appeared at all the stations in February, and reached maximum concentration (13.6±2.8 cells/L) in April. In contrast, Alexandrium cysts showed in maximum abundance in February, and the highest concentration of vegetative cells was followed by a sharp decrease in the cysts abundance, adversely both with temperature elevation and with the increase of motile cells. Motile cells recurrent in the cold season could result from the germination of their cysts which have been controlled largely by the environmental and biological regimes. Considering the extensive occurrence of toxic algal species with the same seasonality as a cysts germination, it is suggested that monitoring for the prediction of regional impacts should be undertaken based on the life cycle strategies of causative organisms.