Green tides in the Yellow Sea have besieged the city of Qingdao every summer over the past decade. The blooms are usually formed by Ulva prolifera algae. A recent study confirmed that the increase in green algae was caused by seaweed farming in neighboring Jiangsu Province. Known as zicai in Chinese, gim in Korean, and nori in Japanese, Porphyra is an edible seaweed that plays an important part in the diets of East Asian countries, e. g., in sushi roles. Farmers on Jiangsu’s northern coast use rafts floating in shallow waters to grow Porphyra. In spring, the sunshine and warmer water temperatures are ideal for U. prolifera to grow on the edges of rafts. After farmers have harvested Porphyra, the boats and attached U. prolifera are left at sea. The algae grow very fast and join together to form huge floating masses which winds and currents push to the north. Having identified the source of the algae blooms, authorities have introduced a simple and effective intervention: Porphyra farmers must bring the algae-covered rafts ashore instead of leaving them in the water after the harvest.

CAS news release, June 21, 2017