Since Zuiken Kawamura (1617-1699) discovered the westward and eastern sailing routes in the middle of 17th century, large quantities of marine products from the land of the Ainu people (Hokkaido) was carried to Edo (Tokyo)and Osaka. At the end of 18th century, Satsuma merchants exchanged kelp, which was transported to Osaka from Hokkaido through the Japan Sea, for sugar. They also took advantage of Ryukyu's tribute and trading with China and to export kelp to China. And they purchased materials such as raw silk, fabrics and Chinese medicine from China in exchange.
Kelp occupied 70-90 % of the freight from Ryukyu to China after the 1820's. This was about 10 % of the gross weight produced in Japan. Even an office of the "Kelp Magistrate" was established in Naha in the middle of 19th century. Kelp was a very important export product for the Ryukyu Kingdom until tribute and trading with China was severed by dissolution of the kingdom. Kelp became not only an export product but also largely influenced to the cuisine of the Ryukyuan people. It became a quintessential part of their diet, as is pork. Even today the per capita consumption of kelp is the greatest in Japan. Okinawans credit kelp with helping to make them as long-lived as they are.