Journal de biologie marine et d'océanographie

Physical Factors Involved in the Isoyake (Seaweed Forest Depletion) at Mio, Pacific Coast of Central Japan

Hisayuki Arakawa, Kazuhiro Shinoda, Akira Matsumoto, Hikaru Endo and Yukio Agatsuma

 Physical Factors Involved in the Isoyake (Seaweed Forest Depletion) at Mio, Pacific Coast of Central Japan

In Japan, seaweed forest depletion is known as isoyake. We conducted a study on the marine environment to clarify the cause and the persistence of the isoyake in the sea area at Mio, on the west coast of the Kii Peninsula, central Japan. In the sea area at Mio, a layer of high-turbidity seawater formed on the sea surface (lowest Secchi disc depth: 1m) during and after precipitation. The average accumulation of sediment on the bedrock was 6.7 mg/ cm2. This value was approximately four times that recorded in the sea area at Noshima, where seaweed communities were present. These results imply that the large amounts of suspended particles in the seawater and sediment particles that settled on the bedrock were the major factors contributing to the continuation of the isoyake at Mio.