Morphospecies-dependent disaggregation of colonies of the cyanobacterium Microcystis under high turbulent mixing

Abstract

Preventing formation of large colonies and reducing colony size of the cyanobacterium Microcystis may lead to reductions in bloom formation. Here we investigated the effects of artificial mixing on morphology and disaggregation dynamics of Microcystis colonies in vivo, using a stirring device and a laser particle analyzer. The turbulent dissipation rate (ε) was varied from 0.020 to 0.364 m2 s−3. We hypothesized that colonies of M. aeruginosa and M. ichthyoblabe would be more susceptible to disaggregation from turbulent mixing than colonies of M. wesenbergii. Our results showed that colony size of M. aeruginosa and M. ichthyoblabe decreased with increased turbulence intensity and duration of stirring for ε > 0.094 m2 s−3, while M. wesenbergii showed less obvious changes in colony size with mixing. Spherical M. wesenbergii colonies exposed to high turbulence intensities for 30 min gradually transitioned to colony morphologies similar to M. ichthyoblabe and M. aeruginosa-like colonies (irregular, elongated or lobed, with distinct holes). Our results suggest that turbulent mixing is an important factor driving morphological changes of Microcystis colonies, and artificial mixing may effectively reduce colony size of Microcystis, thereby preventing bloom formation.