砂浜海岸に設置した人工リーフへのカジメ移植と群落の拡大

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Here we discuss the establishment of the brown macroalgae, Ecklonia cava, on a submerged breakwater in Sagami Bay along the Miyuki-no-Hama coast. The small number of available spores for E. cava was the principal factor underlying the localized distribution of this alga. In an attempt to promote the establishment and subsequent transfer of E. cava, the following transplantation technique was employed: during the maturation period of E. cava, 14 40-ton concrete blocks were temporally placed on a natural E. cava community off Nebukawa, 3km west of the coast in October 1993. The E. cava colonized the concrete blocks within a year. All of the concrete blocks were then transferred to the submerged breakwater in December 1994. The same procedure was conducted from November 1994 using an additional 14 concrete blocks, which were transferred to the submerged breakwater in January 1996. No reduction in the E. cava population was observed on the concrete blocks during transplantation. The number of E. cava sporophytes transplanted in this way was estimated at 11,805 in December 1994 and 15,042 in January 1996. While several other seaweed taxa were observed after transplantation, E. cava was dominant and was observed to have colonized the submerged breakwater at depths of 3〜9m in the areas adjacent to the two transplanted zones. High recruitment of juvenile E. cava was observed from 1996 to 1997 in response to lower than average water temperatures, which contributed to range expansion in E. cava. Grazing pressure by herbivores such as sea urchins and fish was low. The climax phase of the E. cava community was reached in March 2001, when the colony occupied an area covering 8000m2. Density and expansion rates of the E. cava community were 16〜34 indiv./m^2 in November 1997, and 20〜48m/yr from 1997 to 2001, respectively. These rates are comparable with those of a neighboring endemic E. cava community. Distribution of E. cava on the crest of the submerged breakwater was limited by the shallow water depth (D.L. 1m). The E. cava community on the eastern section of the submerged breakwater was washed away when the powerful Typhoon 0115 hit Sagami Bay in September 2001. It is suggested that kelp forest creation on submerged breakwaters should be planned with respect to strong wave activity.
日本水産工学会の論文
2006-11-15

砂浜海岸に設置した人工リーフへのカジメ移植と群落の拡大

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