Comparison of bacterioplankton communities between before and after inoculation with an algicidal material, Ca-aminoclay, to mitigate Cochlodinium polykrikoides blooms: assessment using microcosm experiments

We investigated the ecological responses with a focus on the diversity of bacterioplankton communities with regard to the effects of artificial clay (Ca-aminoclay) on suppressing harmful algal bloom species (HABs) of Cochlodinium polykrikoides in indoor microcosms. The Ca-aminoclay induced cell lysis in the HABs within a few minutes, but had negligible impact on the non-harmful phytoplankton. However, the findings showed that applying Ca-aminoclay could have negative environmental effects. Specifically, it increased nutrient and dissolved organic carbon concentrations and caused anoxic conditions to emerge. The bacterioplankton abundance increased and the dominant species changed from alpha-proteobacteria and Bacteroidetes to gamma-proteobacteria. It was noted that Phaeobacter caeruleus (alpha-proteobacteria) was strongly associated with the blooming stage of C. polykrikoides, suggesting that the alpha-proteobacteria are intimately linked to the development of C. polykrikoides blooms. In contrast, Alteromonas macleodii (gamma-proteobacteria) was associated with the termination of HABs and hypertrophic environmental conditions due to the algicidal material. The abundance of heterotrophic flagellates and ciliates increased rapidly with the increase in bacterioplankton. The information obtained in this study should be important when incorporated into our understanding of the interactions between bacterioplankton communities and environmental changes due to algicidal materials.