The Harmful Cyanobacterium <i>Microcystis aeruginosa</i> Differently Affects the Growth Rate and Photosynthetic Efficiency of Several Species of Marine Phytoplankton

Microcystis aeruginosa is a major cyanobacterium that can secrete toxins, such as microcystin, and causes harmful algal blooms. Despite extensive research on the effects of microcystins on other organisms, research on how introduced M. aeruginosa into estuaries affects marine phytoplankton is scarce. In this study, the effect of M. aeruginosa on the growth of seven representative marine phytoplankton species that inhabit estuaries was determined. The marine phytoplankton species differed in their responses to M. aeruginosa; of the seven species, the growth rate of Akashiwo sanguinea was the most affected by M. aeruginosa cells and filtrate. Moreover, our results revealed that M. aeruginosa affected the growth rate and photosynthetic efficiency of A. sanguinea in a density- and time-dependent manner. Our findings suggest that M. aeruginosa may alter the phytoplankton community structure in estuarine ecosystems.