Growth rate of macroalgae is affected by water flow. However, few experimental works have been conducted for the species distributed in Japan. In this study, we set up a siphon-pipe system which maintains water flow velocity, to examine the effect of water flow on the growth rate of the kelp Saccharina japonica. Seawater, which was taken from the sea and filtered with sand, flowed only once through the experimental pipe. The seawater was not adjusted for temperature and nutrients so that the nitrate concentration of the seawater remained below the detection limit (less than 0.1 mg L^-1). Flow rates in the experiments were set at three steps in a range of 0.2 to 8.1 cm s^-1 and the growth rate of the kelp significantly increased with water flow. For the experiments set at five steps in a range of 2.0 to 20.4cm s^-1, the growth rate of the kelp increased with water flow below 13-14cm s^-1 and it was relatively stable in water flow higher than 13-14 cm s^-1. For the experiments with 0.2 to 29.4 cm s^-1, the growth rate increased with water flow below 10.2 cm s^-1 and it was not significantly different between 10.2 cm s^-1 and 29.4 cm s^-1. Photosynthetic oxygen evolution rate of the kelp, which was measured at three steps of the water flow of 0.6-3.0 cm s^-1, increased in higher flow rates. These results suggest that the growth rate of the kelp could be dependent on water flow velocity below 10 cm s^-1.

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Stabilization of seedling production is an urgent issue in the land-based cultivation of Ulva prolifera. In this study, we established a new seedling production method, in which branching formation from ground fragments is stimulated by addition of the Solution Extracted from Homogenized Thalli (SHET) of U. prolifera. The cells in the fragments cultured with SHET differentiated into six types of cells: swelled cells, branch cells, rhizoid cells, matured cells, empty cells, or dead cells. As the amount of the added SHET increased, the proportion of the fragments with branch cells increased. The branch cells grew normally, forming leaves after 7 days of culture period. Within the tested settings, the rate of branch formation increased accordingly to the extension of storage period and increase in culture temperature. We recommend storage period of 6 weeks and incubation temperature of 25℃ for seedling production, as the increase of maturing cells at 30℃ makes seedling production unstable, especially after extended storage period.

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The Sakhalin kelp Saccharina latissima have been collected in Wakkanai, Northern Hokkaido, Japan, in 1973 and 1983, also obtained in Southern Sakhalim, Russia. Diving researches were conducted from 2013 to 2015 in Koetoi and Hourai, Wakkanai, also Yabloney, Bogdanovitch Krilion, Korsakov, and Lesnoye, southern Sakhalin, August 2013. Saccharina latissima was not found in the present sampling fields. However, S. japonica, Alaria crassifolia and A. sp. were observed in these sites. Water temperature and light intensity from 2016 to 2017, change of water temperature of past thirty years, recent situation of kelp community in Wakkanai is shown. Also, change of water temperature in Yanloney and Boddanovitch from 2008-2009, in Korsakov from 2012-2013 were shown. Our study examined this change of flora in Wakkanai and Southern Sakhalin.

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