The complicated, no good, multifaceted and confusing reasons for Microcystis blooms.

Blooms of toxic cyanobacteria have become a global problem and dramatically affect human interactions with coastal systems. Intrinsic within this problem are two issues: 1) the exacerbated growth of all phytoplankton associated with nutrient loads and 2) the proliferation of specific populations that are often deemed harmful. Within the later context are the broad-scale bloom events of Microcystis that are currently proliferating around the planet. Yet while many researchers focus on specific nutrients (N or P) and ask questions about biomass formation, there are important and significant questions to be answered regarding why Microcystis is a dominant bloom former. For the last two decades we have focused on this question, teasing apart the multiple drivers of the proliferation of specific populations in fresh waters that had otherwise been addressed by stating “it’s complicated”. Nutrient chemistry and concentration, predation by viruses, light and temperature all play a role in the proliferation of Microcystis or its production of toxin. Metatranscriptomic and metabolomic data as well as stable isotope labeling results from lab batch cultures and chemostats have been examined in conjunction with field data from 2 continents to ask how Microcystis varies seasonally and spatially. These data are used to support the development of a molecular-level model of Microcystis growth and toxin production. In teasing apart this multivariate problem, our goal is to define a new path forward when considering how to best understand and resolve the proliferation of a specific population – Microcystis – in fresh waters impacted by eutrophication.