Fisheries and Marine Technology Center, Hiroshima Prefectual Technology and Research Institute, Kure-city, Hiroshima 737-1207, Japan
The dynamics of dissolved inorganic nitrogen (DIN) were investigated along the eastern coast of Hiroshima Prefecture facing the Seto Inland Sea from April 2004 to March 2007 to find the reason for the discoloration (January to March) of cultivated Porphyra yezoensis. Along the coast, salinity gradually increased from west to east from December. Low-salinity water appeared in the east but never reached the west. The salinity pattern (inverse to DIN pattern, except in 2007) and evaluation of thallus color suggested that the discoloration of P. yezoensis was caused by the decrease of river flow and migration of water mass from west to east, which disturb the extension of DIN to the culture field.