When the inflow of nutrient salts from land becomes excessive, non-diatom phytoplankton in place of diatoms and micro zooplankton that feed on it increase and unfastidious jellyfish that feed on micro zooplankton multiply. Including the Seto Inland Sea, the seas of the world is confronted with this problem. In a sea of jellyfish, fish production scales down. It will take a great deal of effort to improve eutrophication and bring the Seto Inland Sea back into a sea of anchovies.