• Korean Journal of Ecology and Environment
• /
• v.36 no.1 s.102
• /
• pp.1-8
• /
• 2003

Growth, colony formation and microcystin production of 'low-toxic' Microcysits aeruginosa $K{\"{u}}tzing$ were examined in relation to the 'info-chemicals' released by zooplankton. Algae were cultured in a medium with or without filtered water taken from cultures of Daphnia magna Straus (300 ind./L) or Moina macrocopa Straus (500 ind./L), The growth of M. aeruginosa, based on cell number, was also significantly different from populations cultured in the media with and without filtered zooplankton water from the exponential growth phase. In the 6-day experiment, the growth pattern of M. aeruginosa cultured with ZCMF was clearly different to control with-out ZCMF. Mean number of cells/particle and particle bio-volume of M. aeruginosa increased significantly from the day 2 for the Daphnia-CMF or Moina-CMF treat-ments. Microcystin production was promoted showing from 18.7 to 55 ${\mu}g/g$-dry cell in the zooplankton treatments relative to the controls. At peaked level on day 4, the highest level of up to $70.5{\pm}16.8\;{\mu}g/g$-dry cell was observed in the D. magna treatment. This study suggested that 'info-chemicals' from zooplankton might induce the increase of algal growth rates, colony formation and microcystin production, these seem to be advantageous to the alga and thus as a grazing defense mechanism.

• Korean Journal of Ecology and Environment
• /
• v.39 no.2 s.116
• /
• pp.209-218
• /
• 2006

This study was to evaluate microcystin production by two strains of cyanobacteria (Microcystis aeruginosa and Planktothrix agardhii) in response to three different levels of direct (0,4,8 inds.) or indirect (0,25, 50% of zooplankton culture media filtrate) exposures to zooplankton (Daphnia magna and Moina macrocopa). The cell biomass and intracellular microcystin (MC) were measured everyday. The survival rates of zooplankton were evaluated for daily intervals for the direct exposure. The intracellular MC produced peaked on the day 3 or 4, and then decreased over the both exposure experiment. In the direct experiment, the MC values were significantly different among the control and zooplankton treatments (ZT; repeated measures-ANOVA: P< 0.039). The MC contents of P. agardhii strain (No.204) were significantly higher (Tukey test, P< 0.082) in ZT2 (8 inds.) than in ZT2 (4 inds.). On the peak day, the intracellular MC exposed to both zooplanktons was significantly higher than the control (One-way ANOVA, P< 0.021). Higher zooplankton survivals were observed in the M. aeruginosa strain (No. 111) rather than in high toxic P. agardhii strain. In the indirect experiment, the intracellular MC of the M. aeruginosa strain was significantly different among the control and zooplankton culture media filtrate (ZCMF)treatments (rm-ANOVA: P<0.004), The MC exposed ZCMF2 (50%) were significantly higher than in ZCMFI (25%: Tukey test, P< 0.025) for both strains. This study strongly supports the induced-defensive MC production of potentially toxic cyanobacteria in response to the presence of zooplankton.