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Spring neap variations in stratification and chlorophyll fluorescence were studied during the summers of 2011–2014 in a tidal sea (Yatsushiro Sea, Japan) using monitoring data and hydrodynamic models. Vertical profiles of salinity, temperature and chlorophyll fluorescence were collected nearly weekly from nine stations in this sea during the same period. Composite analysis using vertical profiles of density clearly indicated enhancement of the stratification during the neap tide and a vertically mixed water column during the spring tide in the tidal area. Interregional differences were revealed in the variation of chlorophyll fluorescence with the spring neap tidal cycle. More notable increases in chlorophyll fluorescence were observed during the neap tide in the tidal area around the narrow strait than in the inner area. Temporal stratification led to an increase in the chlorophyll fluorescence in the tidal strait during the neap tide. [ABSTRACT FROM AUTHOR]

Mass mortality of Seriola quinqueradiata was caused by a Chattonella bloom in summer 2010 in the southern area of the Yatsushiro Sea. We analyzed the diurnal records of the mortality occurrence and cell density of C. marina to examine the short-term mortality dynamics. In addition, a hydrodynamic model and Lagrangian particle tracking method were used to examine interregional differences in the mortalities. Mortalities were concentrated along the southern coast of Shishi Island and western coast of Nagashima Island in early July. In late July, mortalities occurred along the southern coast of Shishi Island and eastern coast of Nagashima Island. Severe mortalities occurred where the bloom (>100 cells ml of Chattonella marina) appeared in both early and late July. Model results show that interregional difference of the bloom was controlled by the advection system in the Yatsushiro Sea. The consistent spatio-temporal pattern between fish mortalities and bloom dynamics indicates the potential benefits of real-time monitoring of harmful algae and assessing factors controlling hydrographic conditions to mitigate mortalities. [ABSTRACT FROM AUTHOR]

The relationship between harmful blooms of raphidophycean flagellate Chattonella spp. and preceding meteorological conditions was investigated in the Yatsushiro Sea, Japan, using data over a 25-year period from 1988 to 2012. The occurrence date of Chattonella blooms was significantly correlated with the average air temperature from February through April and with the onset date of Baiu, the Japanese name for the rainy season in early summer. These two meteorological factors showed significant differences between occurrence and non-occurrence years of Chattonella blooms in the Yatsushiro Sea. The Chattonella blooms tended to occur in years that were relatively warm from winter to spring and had a relatively late onset of Baiu. The duration of Chattonella blooms was significantly correlated with the interval between the closing date of Baiu and the occurrence date of the Chattonella blooms, suggesting an important role of Baiu as nutrient input affecting the magnitude of the bloom event. The East Asian monsoon, which controls local meteorological conditions, is likely involved in the population dynamics of Chattonella through its life cycle and physiological characteristics. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Chattonella antiqua blooms initially formed in the northern area of the Yatsushiro Sea. [•] The blooms were triggered in the riverine water advection in the southern area. [•] The southward advection was determined by the wind stress and pressure gradient. [ABSTRACT FROM AUTHOR]

Abstract: A harmful bloom due to the raphidophycean flagellate, Chattonella antiqua, was found in the Yatsushiro Sea, western Kyushu, Japan, from the end of July to the beginning of August 2009. The bloom resulted in enormous economic damage to cultured finfish production in aquaculture farms concentrated in the southwestern area. To investigate the factors controlling the spatio-temporal distribution of the bloom, data analysis and numerical simulations were conducted using field monitoring data and a three-dimensional hydrodynamic model coupled to a Lagrangian particle-tracking model. Results of the monitoring data analysis showed that the initial development of the C. antiqua bloom occurred in Kusuura Bay and the northeastern area near the mouth of the Kuma River, and subsequently the bloom expanded rapidly to the whole area. The simulation results indicated that the source region of the widespread bloom was not Kusuura Bay but the northeastern area. The southwestward evolution of the bloom was primarily controlled by the passive transport due to the surface residual current driven by fresh water discharge from the Kuma River and northeasterly winds. On the favorable conditions of river discharge and wind, the massive bloom of C. antiqua that formed in the northeastern area was quickly transported southwestward within a few days. [Copyright &y& Elsevier]