真鶴・勝浦・八丈島におけるミクロプランクトン量の季節的変化

抄録

During the years from 1951 to 1957, microplankton were collected at three coastal stations: one being near an offshore set-net at Manazuru, Kanagawa Prefecture, and the others, one nautical mile off the coast of either Katsuura, Chiba Prefecture, or Kanminato, Hachijo Island. Fifty-meter vertical hauls of a quantitative net (conical net of Hensen type, 22.5cm in diameter at the month, 1m long, made of bolting silk of 128 meshes per linear inch) were carried out 1-3 times per mouth at those stations.
Each sample was preserved in formalin solution, shaken and left standing for 24 hours to measure the settled volume for observing seasonal changes in the quantity. The main re-sults obtained are as follows:
1) In addition to the outbursts of phytoplankton in spring (around March) and in autumn (September), summer vegetation of diatoms was commonly observed at Manazuru. The settled volume, usually less than 10cc, was found greater than 100cc in the flowering periods. Slight multiplication of microplankton in winter (January) and great flowering in summer were found in some years (Fig. 1).
2) At Katsuura, increment and decrease of microplankton were repeated from March to June. Then prominent outbursts commonly took place in summer (July). Autumnal incre-ment in September was also considerably great. The settled volume, though it was frequently less than 20cc, all at once attained to 200cc in summer (Fig. 2).
3) Excluding special cases, microplankton quantity was very small at Hachijo Island every year. The settled volume was usually less than 5cc, did not exceed 20cc even at the maximum (Fig. 3). Diatoms increased sporadically in all the seasons except the warmest pe-riod of water temperature.
Conclusively, though there were different patterns of seasonal changes of microplankton quantity depending on years and stations, summer flowering of phytoplankton around July was remarkable at all the stations, and was sometimes greater than the vernal outburst in the same year.