The seaweed P. yezoensis was obtained from a seaweed farm in Lianyungang, Jiangsu Province, China in January, 2013. The average length of P. yezoensis used in the study was 13 ± 2 cm. At the laboratory, the seaweed was washed using clean seawater (filtered with 0.45 μm Millipore filters) and then cultured in 50 l of clean seawater for 3 days in a transparent plastic box. As the optimised growth temperature for P. yezoensis in natural environment is about 0.5–10 °C, the seaweed was cultured at 5 ± 1 °C, with a light intensity of 50 μmol m−2 s−1 and a photoperiod of 12/12 h.