Ocean Targeted Locus (Loci)

The cyanobacteria Prochlorococcus and Synechococcus are important marine primary producers. We explored their distributions and co-variance along a physico-chemical gradient from coastal to open ocean waters in the Northeastern Pacific Ocean. Based on 16S rRNA gene sequencing we identified two new clades of Synechococcus, EPC1 and EPC2, and delineated an interannual pattern in a dynamic transition zone where upwelled and eastern boundary current waters mix. In years when more oligotrophic water intrudes further inshore Prochlorococcus HLI and LLI are more abundant, while under stronger upwelling Synechococcus I and IV dominate. However, contributions of some cyanobacterial clades are proportionally relatively constant, e.g., Synechococcus EPC2. In addition to supporting observations that Prochlorococcus LLI thrive at higher irradiances than other LL taxa, the results suggest LLI tolerate lower temperatures than reported. The phylogenetic precision of our analytical approach and depth of barcoded pyrosequencing also allowed us to detect clades at low abundance in unexpected places. For example, Prochlorococcus at the coast, and sequences related to freshwater Cyanobium spp. in the open ocean, although it remains unclear whether these come from resident or advected cells. Our study enhances understanding of cyanobacterial distributions by applying state-of-the-art phylogenetic analysis tools to an ecologically important eastern boundary system.