TY - JOUR T1 - Species invasions shift microbial phenology in a two-decade freshwater time series JF - bioRxiv DO - 10.1101/2022.08.04.502871 SP - 2022.08.04.502871 AU - Robin R. Rohwer AU - Riley J. Hale AU - Todd R. Miller AU - Katherine D. McMahon Y1 - 2022/01/01 UR - http://biorxiv.org/content/early/2022/08/05/2022.08.04.502871.abstract N2 - Invasive species impart abrupt changes on ecosystems, but their impacts on microbial communities are often overlooked. We paired a 20-year freshwater microbial community time series with zooplankton and phytoplankton counts, rich environmental data, and a 6-year cyanotoxin time series. We observed strong microbial phenological patterns that were disrupted by the invasions of spiny water flea (Bythotrephes longimanus) and zebra mussels (Dreissena polymorpha). First, we detected shifts in Cyanobacteria phenology. After the spiny water flea invasion, Cyanobacteria dominance crept earlier into clearwater; and after the zebra mussel invasion, Cyanobacteria abundance crept even earlier into the diatom-dominated spring. During summer, the spiny water flea invasion sparked a cascade of shifting diversity where zooplankton diversity decreased and Cyanobacteria diversity increased. Second, we detected shifts in cyanotoxin phenology. After the zebra mussel invasion, microcystin increased in early summer and the duration of toxin production increased by over a month. Third, we observed shifts in heterotrophic bacteria phenology. After both invasions, heterotrophic bacteria with putative cyanobacterial associations increased. The Bacteroidota phylum and members of the acI Nanopelagicales lineage were differentially more abundant. The diverse summer bacterial community was most resistant to change from the zebra mussel invasion despite the observed shifts in diversity and toxicity during the summer; but the spring and clearwater bacterial communities changed most from the spiny water flea invasion, which lessened clearwater duration and intensity. These long-term invasion-mediated shifts in microbial phenology demonstrate the interconnectedness of microbes with the broader food web, and their susceptibility to long-term environmental change.Significance Statement Microbial communities are typically studied as part of the microbial loop, separately from the broader food web. Using a two-decade freshwater time series, we explored whether two species invasions that shifted the metazoan food web also impacted the microbial community. We looked for seasonal responses because of strong seasonal patterns within the microbial community. We discovered that Cyanobacteria increased in the clearwater and spring seasons, and that Cyanobacteria diversity increased in the summer. Cyanotoxins also increased in early summer, and the duration of toxin production increased. In the heterotrophic bacterial community, many organisms that putatively interact with Cyanobacteria increased. These findings represent direct observations of long-term bacterial change, and of the interconnectedness of bacteria with the broader food web.Competing Interest StatementThe authors have declared no competing interest. ER -