Vitamin B12 Contents in Sea Water along the Coast of Fukuyama in 1970 and 1971

赤潮が頻発する福山周辺海域に8定点を設け,1970-1971年の間,冬期を除きほぼ毎月海水中のビタミンB12含量を測定した.採水は2m層から行ない,メンブランフィルターで沪過後,沪液についてLactobacillus leichmaniiを用いてビタミンB12を定量した.

結果を要約すると次の通りである.
1) この海域において,ビタミンB12は海水中からたえず検出され,その量は0.42～6.43mμg/lであった.
2) この両年にも赤潮は頻発したが,発生時に海水中のビタミンB12の含量に顕著な低下は認められなかった.季節変化は著しくはなかったが,高水温期(約18℃以上)にはビタミンB12含量は概して高く,梅雨期の塩分低下期である6-7月に最高を示し,9-10月にもやや増加の傾向を示した.
3) 河口から最も遠い(約6㎞)定点では,他の定点よりも幾分含量が低かった.なお,ビタミンB12の補給は,河水によるほか,海底泥にも由来するものと考えられた.
4) この海域においては,暖期には一般に2mμg/l以上のビタミンB12が海水中に溶存した.これはビタミンB12を要求するプランクトンが105cells/ml程度の集群を形成するに足る濃度である.従って,少なくともこの海域においては,ビタミンB12が暖期における赤潮の消長現象を制約する因子とは考えにくい.

In the nearshore region of the Seto Inland Sea off Fukuyama, where red water blooms of phytoplankton frequently occur, the vitamin B12 content of the sea water was determined at nearly monthly intervals except in winter during 1970 and 1971. Water samples were taken from a depth of 2 m. The vitamin B12 content of the sample water filtered through a membrane filter was determined by the microbiological assay depending on Lactobacillus leichmanii. The results can be summarized as follows:
1) Vitamin B12 was detected in all the samples. Its concentration varied between 0.42 and 6.43 mµg/l
2) The vitamin B12 content was not conspicuously low in the sea water samples taken within red water blooms. Though its seasonal variation was not conspicuous, it was generally high in the months of high water temperatures (ea. 18°C or above); the maximum occurred in June or July when the chlorinity of sea water dropped due to the rainy season; a secondary maximum occurred in September or October.
3) At the station most distant from the river mouth (viz., 6 km) the sea water showed somewhat lower contents of vitamin B12 than at other stations. Besides the river drainage, the bottom mud was also considered as source of vitamin B12 supply.
4) In the present waters the fluctuation and succession of phytoplankton blooms took place during warm months. It does not seem probable, however, that these phenomena were controlled by any paucity of vitamin B12, because the latter was present in these months usually in concentrations of 2 mµg/l or above, which is sufficient to grow some of the vitamin B12 requiring plankters to a population density of about 105 cells/ml