Dataset: Abundances of mixotrophic, phototrophic, and heterotrophic nanoflagellates, and associated environmental data, synthesized from the scientific literature.

 Data were compiled from 130 experiments in 11 publications that use fluorescently labeled bacteria or beads to estimate the abundance of bacterivorous mixotrophic nanoflagellates (MNF), defined as nanoflagellates with both ingested labeled prey and chlorophyll autofluorescence.These experiments simultaneously counted heterotrophic nanoflagellates (nanoflagellates with no chlorophyll autofluorescence, HNF) and total phototrophic nanoflagellates (all nanoflagellates with chlorophyll autofluorescence, PNF). In some cases researchers also estimated bulk ingestion rate by MNF and HNF, and these data were also extracted.

To ask whether MNF, HNF, and PNF shift in relative abundance across environmental gradients, data on environmental conditions were extracted from the same studies: temperature, chlorophyll-a concentration, nitrate concentration, and bacterial abundance. Although some samples were taken from below the mixed layer, mixed layer Chl-a and nitrate were used as predictors for all analyses, intended as proxies of total productivity or nutrient supply at that location. For two studies Chl-a was not reported and climatological values were used. To capture the light environment, climatological photosynthetically active radiation data (PAR) were used, because in situ PAR data were reported in few studies. Monthly climatological mean PAR from the SeaWiFS mission for each location was extracted from the NASA Giovanni portal (https://giovanni.gsfc.nasa.gov/giovanni/).

For samples taken within the mixed layer the light environment was characterized as the median mixed layer PAR, defined as PARin * e^(−(0.121*Chlmix^0.428)*MLD/2), where PARin is incident PAR (mole photons per square meter per day), Chlmix is mixed layer Chl-a (micrograms per liter), and MLD is mixed layer depth (meters). For samples taken below the mixed layer the light environment was characterized as PAR at the sample depth, defined as PARin * e^(-(0.121*Chlmix^0.428)*MLD)

For four studies mixed layer depth could not be estimated from data in the study and was taken from a climatology (http://www.ifremer.fr/cerweb/deboyer/mld/Surface_Mixed_Layer_Depth.php).