Dynamics of a fish-killing dinoflagellate Karenia mikimotoi red-tide captured by composite data sources

Abstract

Bloom dynamics of K. mikimotoi during summer 2015 in the Yatsushiro Sea, Japan, which caused fish mortality was studied using field survey data and satellite data. The bloom initially formed in the western area, subsequently appeared in the southern area, and finally expanded to the central area. The field-survey detected the horizontal displacement of the bloom which was also assessed by satellite data. Acoustic backscattering intensity of the current meter captured the modulation of the diurnal vertical migration of K. mikimotoi. After the modulation, K. mikimotoi distributed at a shallower depth in the nighttime than the period prior to the modulation. Factors affecting the modulation are suggested to be the continuous low nutrient conditions. Synchronization between the shallowed distribution during the nighttime and the wind driven surface northeastward current enabled a sudden horizontal transport toward the central area. Satellite and acoustic backscattering data are beneficial subsidiary tools for detecting blooms.