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

本研究的目的是探讨沉积物中甲藻孢囊组合是否能够反映富营养化环境的变化。为了这项研究，从西九州的大村湾和Nagdsaki湾采集了五个岩心样品。1968<210>年前后，小柳海峡重新填海，长崎湾的甲藻孢囊组合由以Spiniferites、Lingulodinium为主的自养类群，转变为以同形类和部分裸甲藻为主的异养类群。这种变化可能是由于小柳海峡的消失改变了长崎湾的水循环模式，导致了富营养化。在大村湾，只有Pheopolykrikos hartmannii逐渐向水面增加。这可能表明，自20世纪70年代以来，该湾的富营养化程度并没有像长崎湾那样发生明显的变化，而只是在逐渐加剧。Lingulodinium和Operculodinium以及全等和复叶类等异养类群是了解该类群的良好标志之一封闭海域的富营养化。

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.