As a part of a study on the primary production in the Seto Inland Sea, the photosynthesis (by 14C method) and the chlorophyll a content were measured at 21 stations in 1963. The measurement were carried out in the western half in June, and in the eastern half in September. (Text-fig. 1).
In the measurement of photosynthesis, the sample sea water was impregnated with Na214C03 (5μc/cc) and incubated in a tank at the temperature of surface water for 3 hours, being illuminated at about 12,000 lux with daylight-type fluorescent lamps. Chlorophyll a was measured by CREITZ and RICHARDS method with slight modification. In both measurements, filters of average pore size of 0.8p (Millipore AA) were used.
1) In the months when the measurements were carried out, the hydrographic conditions of the Seto Inland Sea exhibited a strong inshore character, especially in central rogion. (Text-figs. 2 and 4, Tables 1 and 2).
2) The photosynthesis (at a certain depth at a certain station) varied within the range of 0.96-9.63 C mg/m8 /h in the western half in June, and 1.60-13.83 C mg/m3 /h in the eastern half in September. Chlorophyll a content varied within the ranges of 0.21-1.38 mg/m3 and 1.60-13.83 mg/m3 respectively. And the photosynthesis per mg of chlorophyll a was within the range of 2.98-11.14 C mg/h and 1.98-11.68 C mg/h. These three variables varied from station to another over wide ranges. (Text- figs. 3 and 5, Tables 1 and 2).
3) These values are comparable in magnitude with the values obtained in 9 bays on the coasts of Japan in the corresponding months. When compared with the data reported from Kuroshio and Oyashio regions, however, they are mostly very much higher, although a few of them are of the same order. (Text-fig. 6).
4) A negative correlation is found between the chlorophyll a content and the photosynthesis per chlorophyll a in about two thirds of the measurement; namely, the ratio of photosynthesis to chlorophyll a tends to decrease as chlorophyll a content increases. (Text-fig. 8).