A model experiment on discoloration and recovery of Pyropia suborbiculata

Abstract

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 NH4-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 NH4-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.