Germlings of Sargassum horneri and S. yezoense were maintained for one year at 1μmol m^-2s^-1 in order to clarify their tolerance to low photon irradiance. All germlings of S. horneri maintained for one year showed viable growth after transfer to 27μmol m^-2s^-1. The percentage of S. yezoense germlings that retained their ability to grow viably began to decrease after 28 weeks, but 17% still showed a capacity for viable growth after one year of maintenance. These results indicate that germlings produced in a particular season can be maintained throughout the year by keeping them at a low photon irradiance. They would thus always be available for laboratory culture to investigate the effects of environmental factors on their growth and survival, bioassays, and artificial establishment of Sargassum beds. The decrease of viable germlings of S. yezoense may have been caused by a difference in the initial quantity of stored photosynthates used under conditions of very low photon irradiance, because the germlings of S. horneri are bigger than those of S. yezoense.

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Water temperature, food density, and salinity are among the factors that may influence the growth of barnacles. In this study the influences affecting the growth of early juveniles of the barnacle Balanus amphitrite were investigated by means of three experiments, and growth rates under experimental conditions were compared with those under field conditions. The three experiments were conducted under the following conditions: salinity, 34.54‰; water temperature, 13.0°C or 24.0°C; and different concentrations of food (Skeletonema costatum, Brachionus plicatilis, Artemia nauplii) provided for different lengths of time (4, 5 or 20, and 15days, respectively). At 13.0°C, A growth was reduced to 8.3% of that at 24.0°C. Growth diminished much less, to 41.7%, when food density was lowered by 90%. These results demonstrate that low water temperature has a stronger influence than low food density in inhibiting the growth of these barnacles.

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