Regional variation of phytoplankton diversity in the subtropical Indian Ocean

Here, we used a high-resolution spatial and temporal analysis of cyanobacteria in the Eastern Indian Ocean to determine whether ecotypes and microdiverse taxa can be used to identify fine-scale biogeochemical regimes in this under-studied region. A total of 245 DNA samples were collected every 4-6 hours in April 2016 on GO-SHIP cruise IO9N, which transected gyre, equatorial, and monsoonal ecosystems between Western Australia and the Bay of Bengal. Using amplicon sequencing of the highly variable cyanobacteria-specific rpoC1 marker, we found that surface waters were largely dominated by the Prochlorococcus HL-II clade. Microdiverse Prochlorococcus populations also showed regional patterns of relative abundance that were significantly correlated with environmental conditions. Overall, this work demonstrates how the integration of a large ‘omics dataset into a biogeochemical framework can reveal a more nuanced understanding of a complex ocean basin.