Persistent El Nino driven shifts in marine cyanobacteria populations

<p>From 2014 through 2016, a significant El Ni&#241;o event and the North Pacific warm anomaly (a.k.a., &#8220;the blob&#8221;) resulted in a marine heatwave across the Eastern North Pacific Ocean. To develop a deeper understanding of the impacts of El Ni&#241;o on the Southern California Bight (SCB), we used coastal cyanobacteria populations in order to &#8220;bi-directionally&#8221; link shifts in microbial diversity and biogeochemical conditions. We sequenced the <em>rpo</em>C1 gene from the ecologically important picocyanobacteria <em>Prochlorococcus</em> and <em>Synechococcus</em> at 434 time points from 2009&#8211;2018 in the MICRO time series at Newport Beach, CA. Across the time series, we observed an increase in the abundance of <em>Prochlorococcus</em> relative to <em>Synechococcus</em> as well as elevated frequencies of clades commonly associated with low-nutrient and high-temperature conditions. The relationships between environmental and diversity trends appeared to operate on differing temporal scales. In addition, microdiverse populations from the <em>Prochlorococcous</em> HLI clade as well as <em>Synechococcus</em> Clade II that shifted in response to the 2015 El Ni&#241;o did not return to their pre-heatwave composition by the end of this study. This research demonstrates that El Ni&#241;o-driven warming in the SCB can result in persistent changes in key microbial populations.</p>