Daily microbial rhythms of the surface ocean interrupted by the new moon-a lipidomic study

Lipids are essential biomolecules for cell physiology and are commonly used as biomarkers to elucidate biogeochemical processes over a large range of environments and timescales. Here, we use high-temporal-resolution lipidomic analysis to characterize the surface ocean community in the productive upwelling region overlying the Monterey Bay Canyon. We observed a strong diel signal with a drawdown of lipids at night and an increase during the day that seemed to correspond to wholesale removal of lipids from the surface ocean as opposed to internal metabolism. Individual lipid species were organized into coregulated groups that were interpreted as representing different phytoplankton guilds. Concentrations of long-chained triacylglycerols (TAGs) showed unique patterns over the course of five days. TAGs were used to estimate the amount of energy cycled through the surface ocean. These calculations revealed diurnal carbon cycling that was on scales comparable to net primary production. The diel pattern dissipated from most lipid modules on Day 3 as tidal forcing increased at our site with the advent of the new moon. Pigment analysis indicated that the community shifted from a diatom-dominated community to a more diverse assemblage, including more haptophytes, chlorophytes, and Synechococcus during the new moon. The shift in community appears to promote higher nutritional quality of biomass, with more essential fatty acids in the surface ocean during the spring tide. This analysis showcases the utility of lipidomics in characterizing community dynamics and underscores the importance of considering both diel and tidal timescales when sampling in productive coastal regions.