Study on marine biological pollution of enclosed seas in dinoflagellate cyst assemblages recorded in surface sediments

本研究的目的是寻找地表沉积物中保存的鞭毛藻囊的组合是否能够反映富营养化的环境变化。本研究在西九州大村湾和长崎湾采集了5个岩心样本。在确认这些岩心样品没有受到干扰后，根据^<210>Pb测量值计算每个岩心的沉积速率。1968年前后，当小山城海峡被划为陆地时，长崎湾岩心中恢复的鞭毛藻囊群由以刺虫、梭子虫为主的自养类群转变为由同质类和部分裸子类组成的异养类群。甲藻囊的这种变化可能是由于小城海峡消失导致长崎湾水循环格局改变后水体富营养化所致。在大村湾，只有海斑蝶逐渐向海面增加。这可能说明自20世纪70年代以来，这里没有像长崎湾那样发生显著的变化，只是富营养化逐渐加剧。综上所述，鞭毛藻囊群的变化，特别是以刺虫、扁藻和包藻为主的自养类与同卵、双体等异养类的比例变化，是了解封闭海富营养化的良好标志之一。

The purpose of this study is to search for the possibility that the assemblage of dinoflagellate cysts preserved in surface sediments can reflect the environmental change of the eutrophication. For this research, five core samples were collected from Omura Bay and Nagdsaki Bay, West Kyushu. After confirming that these core samples were not disturbed, sedimentation rate on each cores was calculated on the basis of ^<210>Pb measurements.Around 1968 when the Koyagi Strait were reclimed, the dinoflagellate cyst assemblage recovered from the cores of Nagasaki Bay changed from autotrophic group mainly comprising Spiniferites, Lingulodinium to heterotrophic groups of congruentid and some of gymnodinioid. This change in dinoflagellate cysts was probably due to the eutrophication after changing water circulation pattern in Nagasaki Bay owing to disappear the Koyagi Strait. In Omura Bay, only Pheopolykrikos hartmannii gradually increase toward the surface. This probably shows that there was no remarkable change like to Nagasaki Bay, but only gradual increase of eutrophication since 1970's.Based on these observations, the change of dinoflagellate cyst assemblage, in particular a ratio between the autotrophic group mainly consisting Spiniferites, Lingulodinium and Operculodinium and the heterotrophic group such as congruentid and diplopsalid species is one of the good marker for understanding the eutrophication in the enclosed seas.