In 2020 we sampled a complete spring bloom in the German Bight over a 90-day period. Bacterioplankton metagenomes from 30 time-points allowed reconstruction of 251 metagenome-assembled genomes (MAGs). Corresponding metatranscriptomes highlighted 50 particularly active MAGs of the most abundant clades. Saccharide measurements together with bacterial polysaccharide utilization loci (PUL) expression data identified β-glucans (diatom laminarin) and α-glucans as the most prominent dissolved polysaccharide substrates metabolized by the bacterioplankton. Here we are depositing all supporting environmental data for the analyzed 2020 Helgoland spring algal bloom. This includes physicochemical data, data on algal abundances and biovolumes, data on copepod and flagellate abundances, data on monosaccharide and antibody-based polysaccharide measurements, and 16S rRNA-based bacterial diversity data. The corresponding metagenome, metatranscriptome and MAG sequence data of this project are available from the European Nucleotide Archive (accession PRJEB52999).

This study was funded by the Max Planck Society and supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the research unit FOR2406 'Proteogenomics of Marine Polysaccharide Utilization (POMPU)' by grants of Hanno Teeling (TE 813/2-2), Rudolf Amann (AM 73/9-2), Bernhard Fuchs (FU 627/2-2), Jan-Hendrik Hehemann (HE 7217/2-2), and Thomas Schweder (SCHW 595/10-2 & 11-2). The Helgoland Time Series of the Alfred-Wegener-Institute is supported by the Helmholtz Association as an LK-II performance category program.