Study on Areal Expansion of Harmful Plankton

用TU-1型活塞式取样器采集了和歌山县塔纳部湾和岩手县大船渡湾的表层沉积物，通过比较沉积物中的包囊分布和浮游生物记录，研究了该地区有毒甲藻是否在首次发现之前很久就出现了。每隔1或2 cm切割一次沉积物岩心，分析亚历山大藻包囊浓度、沉积物年龄和各部分的压实率。在包括KK和Frager重力取样器在内的三种取样器中，TU-1取样器在收集沉淀量和避免分层混合方面是最好的。对于沉积物年龄的测定，利用钚210的α发射分析了铅210的垂直分布，并测量了该组分的含水率。在塔纳部湾，从表层到30 cm深的所有组分中都发现了亚历山大藻包囊，在3-4 cm处的最大浓度为175个/cm~3。考虑到沉积速率为0.98 cm/年和压实率，1945年前后积累了28-30 cm的最深层，考虑到沉积速率为0.98 cm/年和压实率。作为第一次发现浮游亚历山大藻是在1980年，这种生物已经出现在第一次观测的大约35年前亚历山大藻包囊分布于表层至14厘米深处，最大密度为1,620个/cm~3，深度为2~3 cm。考虑到沉积物的沉积速率为0.23 cm/年和压实速率，亚历山大藻包囊最深处为12~14 cm。1963年首次发现浮游亚历山大藻，表明亚历山大藻在首次发现之前已存在50~60年。这些发现表明亚历山大藻在首次发现之前就已经存在很长一段时间了，该物种的入侵可能不会发生在最近。

Surface sediments were collected by using TU-1 piston corer at Tanabe Bay, Wakayama Prefecture, and Ofunato Bay, Iwate Prefecture, to investigate whether toxic dinoflagellates of the areas occurred long time before the first finding, by comparing cyst distribution in the sediment with plankton record.The sediment core was cut every 1 or 2 cm interval.Alexandrium cyst concentration, age of sediment, and compaction rate of each fraction were analyzed.The TU-1 corer was evaluated as the best among three types of corers including KK and Frager gravity corers regarding the amount of sediment collected and avoidance of mixture of layrs.For measurement of sediment age, the vertical distribution of lead 210 was analyzed by using alpha emission from polonium 210, in addition to the measurement of water contents of the fraction.In Tanabe Bay, Alexandrium cysts were found in all fractions from surface to 30cm deep, having maximum concentration of 175 cysts/cm^3 at3-4cm deep.The deepest layr of 28-30cm in which Alexandrium cysts were detected accumulated around 1945, taking into account of the sedimentation rate as 0.98 cm/y and the compaction rate.As the first finding of planktonic Alexandrium was made in 1980, the organism has already occurred about 35 years before the first observation.In Ofunato Bay, Alexandrium cysts were found in all fractions from surface to 14cm deep, having maximum consentration of 1,620 cysts/cm^3at2-3cm deep.The deepest layr of 12-14cm in which Alexandrium cysts were detected deposited between 1898 and 1914, taking into account of the sedimentation rate as 0.23cm/y and the compaction rate.As the first finding of planktonic Alexandrium was reported in 1963, the organism has already occurred about 50 to 60 years before the first observation.These findings indicate that Alexandrium has occurred a long time before the first observation, and invasion of the species might not occur recently.