Abstract
The so-called yakumizu, a form of red sea-water phenomena, was observed in the upper 25-meter layer at a station in the Oyashio water 95 nautical miles east of Miyako on May 27, 1955. The hydrographical conditions are almost the same as in previous reports concerning such phenomena. The number of diatom cells is 120, 000 to 190, 000 per liter in the said upper layer, and Rhizosolenia hebetata f. semispina constitutes the major part in volume of the community. Considering from the phosphorus contents of the sea-water and from the vertical distribution of diatoms, it seems that the yakumizu water is notin its early stage of production.
