Evolution of the microbial community within a westward propagating coastal filament in the California Current Ecosystem

Mesoscale features are prominent in the California Current Ecosystem (CCE) and their frequency and magnitude are linked to local climatological conditions. One such feature, westward propagating coastal filaments, can mediate the lateral transport of nutrients and organic matter from eutrophic nearshore to oligotrophic offshore regions. Heterotrophic bacteria, as dominant recyclers of organic matter, play a critical role in modulating this transport by transforming dissolved and particulate organic carbon (DOC and POC). Here we present results from a study of a coastal filament that developed near Morro Bay, CA in June of 2017. Several parameters related to the microbial community were measured including chlorophyll a concentration, bacterial abundance, bacterial production, microzooplankton grazing rates, and organic carbon stocks. Overall, these data are consistent with the hypothesis that a eutrophic nearshore environment can be net autotrophic before shifting to a net heterotrophic state in the oligotrophic offshore environment in the CCE. Additionally, community composition was examined using 16S and 18S rRNA transcripts. Interactions between members were identified and visualized via microbial correlation networks. These relationships were further evaluated in the context of regional chemotypes as detected by environmental metabolomics. The integration of biogeochemical measurements with community composition enabled us to examine how relationships between primary and secondary producers shifted across gradients in nutrient status and carbon production as the filament was propagated offshore.