Abstract:In the 1990s, kelp (Laminaria japonica) aquaculture was over capacity in Sanggou Bay; however, the area used for kelp aquaculture has almost doubled since then. Consequently, the levels and proportion of nutrients has changed since the end of last century. In order to address this problem, we previously established standard long line culture to reduce kelp density. After two years, profit had increased significantly; however, the reasons why kelp growth improved in the standard long line culture area compared to the traditional area remained unknown. This study was carried out to elucidate the advantages of standard kelp long line culture in Sanggou Bay. There were two 40 hm2 experimental areas: a standard kelp long line culture area and a traditional long line culture area. The distance between the two areas was approximately 50 m. The growth and composition of kelp, light density, and current in both areas were measured throughout the experiment. The length, width, average thickness, wet weight, projected area, and specific growth rate of kelp were higher in the standard long line culture area than in the traditional long line culture area, with kelp weight significantly higher in the standard area. The carbon, nitrogen, and protein content of the kelp in the standard long line culture area was significantly higher than that in the traditional culture area, and the quality of the kelp product was greatly improved. During the later stages of cultivation, the ratio of the sum of the projection area of cultured kelp in the standard culture area to the corresponding cultured sea area was 6.33, while that of the traditional area was 9.15. The light density of the water layer beneath the kelp in the standard area was significantly higher than that in the traditional area, and the current speed was also higher in the standard area than in the traditional culture area. Our results showed that kelp overlap decreased in the standard area and that total light density was higher in the standard area than in the traditional area. Moreover, the increased current in the standard area carried more nutrients to the kelp. These may be the factors resulting in differences between the two methods of kelp culture.
