[pp.65-72]

Allelopathic Effect of the Cyanobacterium Microcystis aeruginosa and the Diatom Cyclotella sp. on Interspecific Algal Co

Yoshimasa AMANO, Satomi SEKI, Motoi MACHIDA and Fumio IMAZEKI （Graduate School of Engineering, Chiba University / Safety and Health Organization, Chiba University / Faculty of Enginee）

Abstract:
This study examined a possibility of the allelopathic interaction in the interspecific algal competition between the cyanobacterium Microcystis aeruginosa and the diatom Cyclotella sp. through a monoculture experiment at 20ºC assuming spring and/or early summer period. The growth characteristics of M. aeruginosa and Cyclotella sp. were investigated using culture medium of each species obtained in different growth phases to reveal the intensity of their allelopathic sucstances, and a possibility of the dominant species transition from M. aeruginosa to Cyclotella sp. was discussed from a viewpoint of the allelopathic effect. The results showed that the allelopathic effect was varied depending on the growth phase of M. aeruginosa and Cyclotella sp. The allelopathic substances produced by M. aeruginosa in the stationary growth phase caused a positive effect for Cyclotella sp. leading to the growth promotion, while a negative effect by Cyclotella sp. was found for M. aeruginosa. The growth promotion of Cyclotella sp., which plays an important role for the dominant species transition from M. aeruginosa to Cyclotella sp., could be one of the ways to inhibit cyanobacterial blooms implying that creating the diatoms rich condition is important to control of cyanobacterial blooms.

Key Word:
allelopathic effect, dominant species transition, Cyclotella sp., Microcystis aeruginosa

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