10:00 AM - 10:15 AM
[ACG40-05] The relationship between the timing and scale of Karenia mikimotoi bloom and environmental factors in the western Bungo Channel of Seto Inland Sea, Japan
Keywords:Karenia mikimotoi, Bungo Channel, open ocean water intrusion, weather condition, marine condition
In recent years, harmful algae bloom of Karenia mikimotoi has caused serious damage for aquaculture in the eastern part of the Bungo Channel in the Seto Inland Sea, and the damage of aquaculture has been more than a billion yen per year. To reduce the fisheries damage, we try to predict the dynamics of HAB of K.mikimotoi such as timing of the appearance and scale of HAB using the easily-obtainable environmental data. Previous studies suggested that intrusions of oceanic water from the Kuroshio affected the HAB (Kamada et al., 2010), and weather condition also affected the HAB (Onitsuka et al., 2021). However, these studies usually focused on the sporadic HAB events, and did not comprehensively analyze using the long-term HAB data in this region. We investigated the relationships among the HAB dynamics, the oceanic water intrusions and the weather conditions from 1997 to 2020, and considered whether the environmental factors can be used for the prediction of HAB dynamics.
We estimated the strength of the two types of the oceanic water intrusions (surface water intrusion: Kyucho, bottom water intrusion: Bottom intrusion) based on Takeoka et al., (2000) using the variabilities of the surface and bottom water temperatures at the Shiokojima monitoring station every ten days from April to September. For weather conditions, we used the daily hours of daylight and precipitation at the Uwajima AMEDAS station of Japan Meteorological Agency. For dynamics of HAB, we extracted the first appearance date and the maximum cell density of the year using the HAB report of the Seto Inland Sea, Fisheries Agency.
From the statistical analysis between the oceanic water intrusions and HAB dynamics, there was a significant correlation between the strength of Kyucyo in early May and the timing of appearance of HAB (r = 0.60, p < 0.01), while the strength of Bottom intrusion did not have any significant correlations. Focusing on the relationships between the weather condition and HAB dynamics, there was significant correlation between the precipitation in the early Jun and the maximum cell density of the year (r = 0.58, p < 0.05). However there was no clear relationship between the hours of daylight and the dynamics of HAB. From the view point of the growth condition for phytoplankton such as water temperature, the timing of water temperature rising in the spring has been getting faster from 2002 to 2016, and the timing of HAB also has become faster in this period. It was found the significant correlation between the arrival date of 20°C at the surface water and the first appearance date (r = 0.52, p < 0.05), and the arrival date of 20°C usually observed in May in this region. These results suggested that the strength of Kyucho in the early May and the arrival date of 20°C at the surface water in May controlled the timing of appearance of HAB, and precipitation in early Jun affected the scale of HAB.
In this study, we found three important environment factors that can be used for prediction of the dynamics of HAB. First was the strength of Kyucho in early May, second was the arrival date 20°C at the surface water in May, and third was precipitation in early Jun. These environmental factors are easily obtained from the website of Japan Meteorological Agency and the Uwa-Sea water temperature information system “You see U-Sea”. We suggest the step-by-step prediction of the dynamics of HAB of K. mikimotoi using the easily-obtainable environmental data from 1-2 months before the appearance of HAB.
We estimated the strength of the two types of the oceanic water intrusions (surface water intrusion: Kyucho, bottom water intrusion: Bottom intrusion) based on Takeoka et al., (2000) using the variabilities of the surface and bottom water temperatures at the Shiokojima monitoring station every ten days from April to September. For weather conditions, we used the daily hours of daylight and precipitation at the Uwajima AMEDAS station of Japan Meteorological Agency. For dynamics of HAB, we extracted the first appearance date and the maximum cell density of the year using the HAB report of the Seto Inland Sea, Fisheries Agency.
From the statistical analysis between the oceanic water intrusions and HAB dynamics, there was a significant correlation between the strength of Kyucyo in early May and the timing of appearance of HAB (r = 0.60, p < 0.01), while the strength of Bottom intrusion did not have any significant correlations. Focusing on the relationships between the weather condition and HAB dynamics, there was significant correlation between the precipitation in the early Jun and the maximum cell density of the year (r = 0.58, p < 0.05). However there was no clear relationship between the hours of daylight and the dynamics of HAB. From the view point of the growth condition for phytoplankton such as water temperature, the timing of water temperature rising in the spring has been getting faster from 2002 to 2016, and the timing of HAB also has become faster in this period. It was found the significant correlation between the arrival date of 20°C at the surface water and the first appearance date (r = 0.52, p < 0.05), and the arrival date of 20°C usually observed in May in this region. These results suggested that the strength of Kyucho in the early May and the arrival date of 20°C at the surface water in May controlled the timing of appearance of HAB, and precipitation in early Jun affected the scale of HAB.
In this study, we found three important environment factors that can be used for prediction of the dynamics of HAB. First was the strength of Kyucho in early May, second was the arrival date 20°C at the surface water in May, and third was precipitation in early Jun. These environmental factors are easily obtained from the website of Japan Meteorological Agency and the Uwa-Sea water temperature information system “You see U-Sea”. We suggest the step-by-step prediction of the dynamics of HAB of K. mikimotoi using the easily-obtainable environmental data from 1-2 months before the appearance of HAB.