A model experiment on discoloration and recovery of Pyropia suborbiculata

Abstract Low nutrient levels have been shown to cause deterioration in the quality of Pyropia , resulting in discoloration and detachment of the frond. In this study, we investigated the critical concentration of nitrogen that causes discoloration of P. suborbiculata , the effective period, and the appropriate nutrient concentration for the recovery of the discolored thalli. To calculate the critical nutrient concentration that causes the discoloration of the thalli, a culture experiment was conducted at 5 DIN concentrations (30, 50, 70, 90, 110 µg L − 1 ) for 14 days. To test recovery of discolored thalli, a culture experiment was conducted at 4 NH 4 -N concentrations (10, 20, 40, 60 mg L − 1 ) for 96 hours. After 8 days culture, discoloration of thalli occured at nutrient concentrations between 70 and 90 µg L − 1 of dissolved inorganic nitrogen. When exposure to low nutrient levels lasted for less than 10 days, discoloured thalli recovered their colour within 72 hours when supplied with NH 4 -N at 20 ~ 40 mg L − 1 . In this study, we revealed that the discoloration of Pyropia caused by low nitrogen concentrations on seaweed farms can be restored by supplying nitrogen at an appropriate concentration.