Lin Huiling1, Hayato Usui1, Mizuki Hayashi2, Haruka Suzuki1, Masakazu N. Aoki1
1Graduate School of Agricultural Science, Tohoku University, Sendai 980-8572, Japan
2Kaneki Yoshida Store Co., Ltd., Shizugawa, Minami-sanriku 986-0725, Japan
The fishery production of Undaria pinnatifida commonly consumed seaweed in Japan is declining. Possible causes of the decline are rising water temperature and lowering nutrient concentration. Several studies indicated that additional nutrients and blue light emission had positive effects on the growth of U. pinnatifida in the lab. However, such experiments have rarely been conducted in the field. Therefore, this study aims to examine the in-situ effects of slow-release fertilizer and underwater blue LED light. We cultivated young sporophytes from Nov 2021 to March 2022 in the inner part of Shizugawa Bay, northeastern coast of Japan. Additional nutrients were slow-release fertilizer, and blue LED light was emitted from 6:00 pm to 6:00 am. Three experimental treatments were additional 100 g slow-release fertilizer group (F), 100 g fertilizer with blue light emission group (F+L), and control group (C) with no additional treatment. The average relative growth rates (RGR) of the blade length obtained by punch-hole method in C, F and F+L were 1.5, 1.8 and 1.4 cm/day, respectively. The average RGR of sporophyll length in C, F and F+L were 0.9, 0.9 and 1.2 cm/day, respectively. It is concluded that the growth of blades was accelerated by slow-release fertilizer under the condition with no blue light. On the other hand, sporophyll growth was assisted by the fertilizer with blue light emission and resulted higher yield of larger sporophyll production. We supposed that additional nutrients and blue light emission eased intraspecific competition and ensured all individuals to grow well.