The distribution and diversity of diatoms in a coastal upwelling biome

Coastal upwelling at eastern boundary currents produces intense phytoplankton blooms often dominated by large chain-forming diatoms. Thus, diatoms play an important ecological role in supporting higher tropic levels and driving biogeochemical cycling in these regions. Here we explore spatial, temporal, and environmentally-driven variability in diatom diversity in the southern California Current Ecosystem from over 800 photic zone samples [near-surface (10 m) or deep chlorophyll maximum (DCM)] from five years (2014-2018) of quarterly California Cooperative Oceanic Fisheries Investigations (CalCOFI) surveys. Diatom-assigned 18Sv9 sequences approached saturation at 486 amplicon sequence variants comprising 32 unique genera. The top diatom genera were Chaetoceros, Pseudo-nitzschia, and Thalassiosira which are generally large chain-forming diatoms; however, high relative abundances of other genera belonging to both centric and pennate lineages were also found. Overall, these results will provide insights into the abundance and diversity of diatoms in the California Current ecosystem under different physicochemical conditions and temporal cycles.