Microbial responses to physical variations in coastal Southern California: Changes in community structure and ecosystem function assessed via an 18 month twice-weekly time-series at the Scripps Ecological Observatory

Nearshore chemical and physical processes impact the structure of marine microbial processes and their resulting ecosystem functions. To investigate the relationship between physical processes and microbial ecosystem function we initiated the Scripps Ecological Observatory (SEO); a time-series off the Scripps Pier in La Jolla, CA. The SEO adds sequencing, flow cytometry, and dissolved gas components to several historical Scripps Pier datasets. Our analysis of SEO data involves two different approaches to link microbial community structure with function: 1) Self Organizing Maps, which aggregate samples into like “modes”; 2) Weighted Gene Correlation Network Analysis, which finds subnetworks within the larger community that co-occur. Data from the past year reveal that temperature, wind, and tidal height all have strong effects on prokaryotic and eukaryotic microbial community structure. Notably, internal waves were more prevalent during the spring-summer period and (from a Eulerian, fixed-depth perspective) changed the eukaryotic community to become more winter-like during the height of summer. We also observed distinct changes in O2/Ar under different microbial regimes. Network analysis allowed us to find specific groups of microbial taxa whose populations most correlated with environmental variables/rates. For example, a prokaryotic subnetwork dominated by many different Alpha- and Gamma-proteobacteria was prevalent in the summer when daily wind direction tended to be from the West (P<0.001, r=0.29) and temperatures were warmer (P<0.001, r=0.75); while a eukaryotic subnetwork dominated by Prymnesium polylepis and Dinophyceae was more prevalent when temperatures were cooler (P<0.001, r=0.32) and was associated with higher periods of maximum wave energy (P<0.001, r=0.34). Together these data demonstrate how the microbial community responds to coastal physical forcing, with implications for forecasting carbon and energy flow in coastal ecosystems.