Assessing change of environmental dynamics by legislation in Japan, using red tide occurrence in Ise Bay as an indicator

•It is necessary to understand what factors cause red tides in semi-closed systems.•I investigated the relationship between the dynamics of the red tide and NP reduction.•By selecting a suitable objective variable and applying it in a multiple regression model•The total pollution load control has influenced the dynamics of red tide blooms in Ise Bay.

Tokyo Bay, Ise Bay, and the Seto Inland Sea are the total pollutant load control target areas in Japan. A significant correlation between the incidence of red tides and water quality has been observed in the Seto Inland Sea (Honjo, 1991). However, while red tides also occur in Ise Bay and Tokyo Bay, similar correlations have not been observed. Hence, it is necessary to understand what factors cause red tides to effectively manage these semi-closed systems. This study aims to investigate the relationship between the dynamics of the Red Tide Index and nitrogen regulation as well as phosphorus regulation, even in Ise Bay where, unlike Tokyo Bay, there are few observation items, by selecting a suitable objective variable. The introduction of a new technique that uses the Red Tide Index has revealed a possibility that the total pollution load control has influenced the dynamics of red tide blooms in Ise Bay.