Multiple environmental stressors mediate cyanobacteria recruitment in microcosms simulating spring conditions from two Midwest US hypereutrophic reservoirs.

Cyanobacteria harmful algal blooms (cyanoHABs) are a complex threat to water quality. Most research to date on the drivers of cyanoHABs focuses on environmental factors in the typical "growing season" despite evidence that cyanobacteria overwintering dynamics may have substantial effects on cyanobacteria seasonal succession and bloom formation. Additionally, the growing season is now beginning earlier and ending later in many parts of the world. Here, we examine the impacts of light, temperature and nutrients on the magnitude and timing of cyanobacteria recruitment from sediments in two hypereutrophic reservoirs in the Midwestern USA in the early spring season via microcosm recruitment experiments. We observed that recruitment was greatest at the first sampling point (Day 3), then declined throughout the rest of the 18-day experiment for both reservoirs. Further, increasing light and temperature significantly promoted recruitment in both systems, while nutrient additions were only a significant driver of recruitment in one lake. The recruited cyanobacteria community identity was similar in both lakes, with Planktothrix, Raphidiopsis and Pseudanabaena being most abundant. This study highlights the complex, interactive effects of environmental variables on cyanobacteria recruitment.