Effects of experimental thinning on the growth and maturation of the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) cultivated in Matsushima Bay, northern Japan

摘要

In northern Japan, massive production of high-quality specimens of the kelp Undaria pinnatifida prior to the traditional harvest season is strongly needed to meet commercial demand. To address this need, we tested the effects of controlled thinning by cutting small plants on the growth and maturation of sporophytes cultivated in Matsushima Bay, northern Japan. In early December 2009, the stocking densities of cultivated kelps were thinned to 10 and 5 plants per 4 cm thread section in two experimental groups. In contrast, no thinning was conducted during cultivation until March 2010 in the control group (about 16-20 plants per 4 cm thread section). Morphological features, photosynthesis, and carbon and nitrogen contents were compared among the three groups. Compared to kelps of control group, total length, stipe width, the length and width of sporophyll, and dry weights of blade and sporophyll showed significantly higher values in kelps of the two experimental groups. However, stipe length of kelps of control group was significantly greater than those of the two experimental groups. The photosynthetic rates and nitrogen contents of kelps of the two experimental groups were significantly greater than those of the control from January to March. No significant differences occurred in all these parameters between kelps of the two experimental groups. Based on these results, the growth and maturation of U. pinnatifida sporophytes can be promoted greatly by experimental thinning, and this will improve production of high-quality specimens of kelps and increase economic returns before the traditional harvest season.