PRESERVATION OF DINOFLAGELLATE CYSTS IN SURFACE SEDIMENTS OF INNER BAYS

为了澄清水生环境中营养物质的变化，硅藻和鞭毛藻等浮游植物群落是非常有用的。在鞭毛藻中，营养细胞群落比囊胞群落更有用，特别是富营养化。不幸的是，并非所有现代鞭毛藻都能产生保存在沉积物中的静止囊肿。因此，当我们使用囊肿群落时，我们必须理解沉积物中保存的鞭毛藻囊肿的偏见。不幸的是，目前关于这个问题的研究很少。本研究在长崎县三村湾Matoya湾采集了浮游生物和囊样，该湾保存了近30年甲藻营养细胞的历史记录。在Matoya湾的2个测点和0村湾的1个测点，采用简易活塞式岩心采集了3个岩心沉积物，沉积物扰动较小。经210Pb测量，这些岩心的平均沉积速率分别为0.55cm/年（Matoya Bay St.1）、0.41cm/年（Matoya Bay St. 2）和0.31cm/年（0mura Bay St.5）。根据这些沉积速率，沉积物中的记录可能分别追溯到120年前、125年前和145年前。Matoya湾St.1鞭毛藻囊群落包括至少18属34种，其中包括一些无法确定的物种。类群中以扁针虫（Lingulodinium machaerophorum, = L. polydrum）、大泡棘虫（Spiniferites bulloideus, = Gonyaulax scrippsae）、细刺虫（Spiniferites belerius, = Gonyaulax scrippsae）为主；类群中有丰富的Brigantedinium spp. （= Protoperidinium spp）。共鉴定浮游生物32属134种。其中，只有9属和17种囊状生物与浮游生物种类相对应。特别是，从沉积物中没有发现前中部和双中部的囊肿。这强烈表明，与浮游生物群落相比，来自囊孢群落的信息非常有限。

For clarifying a change such as nutrients in aquatic environments, such phytoplankton communities as diatoms and dinoflagellates are very useful. In dinoflagellates the vegetative cell community is more useful than the cyst community, especially the eutrophication. Unfortunately all modern dinoflagellates can not produce a resting cyst which is preserved in sediments. Therefore, when we employ the cyst community, we have to understand a bias of dinoflagellate cyst preserved in sediments. Unfortunately there are only a few study on this subject for the moment.In this study, we collected plankton and cyst samples from Matoya Bay in Mie the 0mura Bay in Nagasaki Prefecture, where historical record of dinoflagellate vegetative cells has been kept throughout over past 30 years. In 2 sites of Matoya Bay and 1 site 0mura Bay, three core sediments were collected with a handy piston core with out serious disturbance of sediments. After measurement of 210Pb, the average sedimentation rates of these cores are estimated as 0.55cm/year (Matoya Bay St.1), 0.41cm/year (Matoya Bay St. 2) and 0.31cm/year (0mura Bay St.5). According to these sedimentation rates, the record in sediments may be back to 120, 125 and 145 years ago respectively.Dinoflagellate cyst community of St.1 in Matoya Bay consists of at least 18 genera and 34 species including several undeterminable species. In gonyaulacoid group, Lingulodinium machaerophorum (= L. polyedrum), Spiniferites bulloideus (= Gonyaulax scrippsae), Spiniferites belerius were dominated and Brigantedinium spp. (= Protoperidinium spp.) were abundant in protoperidinioid group. 32 genera and 134 species of plankton form were identified. Among them, only 9 genera and 17 species in cyst forms were corresponding with plankton species. In particular, no cysts of prorocentlales and dinophysales were recovered from the sediments. This strongly suggests that the information from cyst community is very limited in comparison with plankton community.