Here we perform a set of microcosm experiments to evaluate the impact of changing predator and prey concentrations on a marine protist community. We combine an estimate of taxonomic diversity through analysis of SSU-rDNA amplicons with metatranscriptomics, a proxy for function. We assess changes in the community sampled from New England waters with varying concentrations of predators (copepods) and prey (phytoplankton less than 10µm in size).