"Short time-scale observations are valuable for understanding microbial influence on nutrient and energy cycles. We assessed dynamics in relative abundance and potential activities by sequencing of the small sub-unit ribosomal RNA gene (rDNA) and rRNA molecules (rRNA), of Bacteria, Archaea and Eukaryotes once to twice-daily over 1.5 months (13 March- 1 May) in the surface ocean off Catalina Island, California. Typically Ostreococcus, Braarudosphaera, Teleaulax, and Synechococcus dominated phytoplankton communities while SAR11, Sulfitobacter and Fluvicola were most represented among non-phytoplankton prokaryotes. We observed a short-lived bloom of diatoms, mostly Pseudo-nitzschia and Chaetoceros, with quickly-responding prokaryotes including Flavobacteria (Polaribacter and NS4), SAR92, Roseovarius, Euryarchaea (MGII), and Rhodobacteraceae. Additionally, we observed positive correlations of known interactions among the most abundant taxa: 1) The kleptochlorplastidic ciliate Mesodinium 18S and Teleaulax chloroplasts (16S) were correlated (Spearman r =0.83) with no significant correlation to Teleaulax nuclear 18S, nor any other taxon and 2) the photosynthetic prymnesiophyte Braarudosphaera bigelowii and 2 strains of nitrogen cycling cyanobacterium UCYN-A were correlated and each was correlated to a variety of other taxa, including Braarudosphaera to a Verrucomicrobium and a Dictyophyte phytoplankter (all r > 0.8). Additionally, we also report strong correlations (r > 0.7) between Ciliates and bacteria and phytoplankton, which are possibly mutually beneficial interactions. Overall, these data reiterate the utility of short time-series to show rapid reactions of microbes to environmental stimuli, and provide new information about the in-situ dynamics of previously recognized and hypothesized interactions."