Ecological roles of heterotrophic dinoflagellates in coastal ecosystems

通过室内培养、野外观察和野外试验，研究了异养甲藻的生态学作用。在实验室培养条件下，建立了优势旋甲藻（Gyrodiniumdominans）的培养体系，并对该藻在18种浮游植物中的生长和摄食进行了研究，结果表明，优势旋甲藻对ESD为15 μ m的颗粒物比ESD为约5 μ m的颗粒物的摄食能力强。1995年夏季，在濑户内海对优势藻和米氏裸甲藻的数量进行了每日监测。米氏裸藻赤潮爆发后，米氏裸藻的丰度迅速增加，并通过摄食赤潮细胞而增加。暴发后优势种的原位生长速率也迅速增加。这些结果与实验室培养结果表明，异养甲藻在富营养化海区赤潮消失和控制浮游植物生产中起着重要作用。

Ecological roles of heterotrophic dinoflagellates (h-dinos) were investigated based on laboratory culture experiments, field observations and field experiments. In laboratory culture experiments, culture of a h-dinos, Gyrodinium dominans was established and growth and grazing of this species fed 18 species of phytoplankton were examined.G.dominans ingests particles with ESD of 15 um more effectively than those with ESD of ca.5 um. These results also suggested that G.dominans can play a major role in the disappearance of red tides by Gymnodinium mikimotoi (ESD = 15 um).In the summer of 1995, population of G.dominans and a red tide flagellate, G.mikimotoi was monitored daily in the Seto Inland Sea. Following the outbreak of G.mikimotoi red tide, the abundance of G.mikimotoi increased rapidly by ingesting the red tide cells. In situ growth rate of G.dominans also increased drasticlaay just after the outbreak. These results, together with those obtained in laboratory cultures indicated that heterotrophic dinoflagellates playd major roles in the disappearance of the red tide and in controlling phytoplankton production in eutrophicated coastal area.