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

本研究的目的是探索保存在表层沉积物中的甲藻孢囊组合是否能反映富营养化的环境变化。在这项研究中，从西九州的大村湾和长崎湾采集了五个岩心样本。在确认这些岩样没有受到干扰的基础上，计算了每个岩心的沉积速率。1968年小柳海峡恢复时，长崎湾岩芯中发现的甲鞭毛孢子组合从主要由刺藻、Lingulodina组成的自养群转变为同种异养群和部分裸藻。甲藻包囊的这种变化可能是由于小柳海峡消失，改变了长崎湾的水循环格局而造成的富营养化。在大村湾，只有Pheopolykrikos hartmannii向表层逐渐增加。这可能表明，自20世纪70年代以来，长崎湾并没有发生类似长崎湾那样的明显变化，而是富营养化程度逐渐加剧。基于这些观察，甲藻孢囊组合的变化，特别是以棘藻、钩吻藻属和角藻为主要成分的自养类群与同余、复盐类等异养类群之间的比率，是了解封闭海域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.