Marine microbial communities form the basis for the functioning of marine ecosystems and the conservation of biodiversity. With the application of metagenomics and metatranscriptomics in marine environmental studies, significant progress has been made in analysing the functioning of microbial communities as a whole. These molecular techniques are highly dependent on reliable, well-characterised, comprehensive and taxonomically diverse sequenced reference transcriptomes of microbial organisms. Here we present a set of 12 individual transcriptomes derived from 6 representative diatom species from the northern Adriatic Sea grown under 2 environmentally relevant growth conditions (Eutrophic vs. Phosphate deprived). The resulting diatom reference database for the northern Adriatic, focussing on the response to nutrient limitation as characteristic for the region and predicted for the future world oceans, provides a valuable resource for analysing environmental metatranscriptome and metagenome data. At the same time, the established diatom reference database for the northern Adriatic is a reference and supporting tool for transcriptomics of further diatom and diatom-containing communities.