A Chattonella bloom in the Yatsushiro Sea, Japan in summer 2016: environmental characteristics during the bloom and mortality of cultured yellowtail Seriola quinqueradiata

Abstract

　A harmful bloom of the raphidophycean flagellate Chattonella spp. occurred in the Yatsushiro Sea, Japan in summer 2016. The mechanism of occurrence of the bloom and the relationship to mass mortality of cultured yellowtail Seriola quinqueradiata were examined by analyzing field monitoring data. After nutrient concentration increased in the surface layer due to vertical mixing and intrusion of upwelled offshore water induced by meteorological disturbance, the population of Chattonella rapidly developed from the central to the southern area during early to mid-September when stratification formed again. The rate and timing of mortality of cultured yellowtail corresponded to cell density and the timing of increase of Chattonella spp., which were influenced by the strength of stratification in each fish farm. The present study suggests that real-time monitoring of oceanographic conditions is important for predicting short-term dynamics of Chattonella and for conducting countermeasures such as stopping feeding at appropriate times.