Cyanobacterial distributions along a physico‐chemical gradient in the Northeastern Pacific Ocean

Abstract

SummaryThe cyanobacteria Prochlorococcus and Synechococcus are important marine primary producers. We explored their distributions and covariance along a physico-chemical gradient from coastal to open ocean waters in the Northeastern Pacific Ocean. An inter-annual pattern was delineated in the dynamic transition zone where upwelled and eastern boundary current waters mix, and two new Synechococcus clades, Eastern Pacific Clade (EPC) 1 and EPC2, were identified. By applying state-of-the-art phylogenetic analysis tools to bar-coded 16S amplicon datasets, we observed higher abundance of Prochlorococcus high-light I (HLI) and low-light I (LLI) in years when more oligotrophic water intruded farther inshore, while under stronger upwelling Synechococcus I and IV dominated. However, contributions of some cyanobacterial clades were 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 previously reported. The phylogenetic precision of our 16S rRNA gene analytical approach and depth of bar-coded sequencing also facilitated detection of clades at low abundance in unexpected places. These include Prochlorococcus at the coast and Cyanobium-related sequences offshore, although it remains unclear whether these came from resident or potentially advected cells. Our study enhances understanding of cyanobacterial distributions in an ecologically important eastern boundary system.

Abundance and Biogeography of Picoprasinophyte Ecotypes and Other Phytoplankton in the Eastern North Pacific Ocean

“…During the Transect survey, Prochlorococcus HLI and LLI ecotypes dominated the OO and TZ samples based on a previous report (32). Clade IV dominated Synechococcus in the OO, and clades I, V/VI/VII, EPC1, and EPC2 were present at 3% to 10% of TZ cyanobacterial 16S amplicons (32).…”

“…The Transect study sampled three ecological regimes along California Cooperative Oceanic Fisheries Investigations (CalCOFI) line 67: the coastal ocean (CO), a mesotrophic/transition zone (TZ), and the oligotrophic ocean (OO) (Fig. 1B) (cruise WFAD09) (32). Along line 67, surface waters at coastal stations are typically colder and more nutrient rich, reflecting coastal upwelling (19,50), while sea surface temperatures increase and nutrient concentrations decrease offshore (see Data Set S1 in the supplemental material).…”

“…Clade IV dominated Synechococcus in the OO, and clades I, V/VI/VII, EPC1, and EPC2 were present at 3% to 10% of TZ cyanobacterial 16S amplicons (32). However, knowledge on the abundance of small eukaryotic taxa is limited to Ostreococcus (10) in this region.…”

Genomic differentiation among wild cyanophages despite widespread horizontal gene transfer

“…To deeply evaluate isolate genomes in the environment, the 142 isolates were sourced from only two water samples such that 77 isolates were derived from a coastal water sample and 65 isolates were derived from an offshore, mesotrophic water sample. Both sites are part of the well-described California Cooperative Oceanic Fisheries Investigations Line 67 oceanographic transect, and represent ecologically distinct environments based on physical-chemical parameters (Additional file 1: Table S1) and proportions of host clades (Additional file 1: Figure S1), despite strong interconnecting currents [18]. All 142 genomes were sequenced and annotated and found to be myoviruses using transmission electron microscopy of representative isolates from each lineage (Additional file 2: Figure S2).…”

“…These were then used in a second Phyloassigner run to assign them to a validated cyanobacterial 16S rRNA gene reference tree [18]. A total of 477 sequences from the coastal sample were assigned to Synechococcus clades.…”