This repository contains the rDNA 18S V9 OTU table, its rarefied version, and the related contextual data from Plankton Planet Pilot Project. In the file P2_TO_18SV9_otu_table.tsv.gz, each OTU, one per row, is described by the following fields: amplicon = identifier of the representative (most abundant) sequence of the swarm; total = total number of reads in the entire dataset; cloud = number of unique sequences constituting the OTU; length = length of the representative sequence; spread = number of samples in which the OTU has been found; quality = minimum expected error observed for the representative sequence, divided by sequence length; sequence = nucleic acid sequence of the representative sequence; identity = percentage of identity of the representative sequence to the closest reference sequence from PR2_V9 (https://doi.org/10.5281/zenodo.3768951); references = best hit reference sequence(s); taxonomy = taxonomic path assigned to the representative sequence; taxogroup = high-taxonomic level assignation of the representative barcode; chloroplast = yes: presence of permanent chloroplast / no: absence of permanent chloroplast / NA: undetermined; symb_small = parasite: the species is a parasite / commensal: the species is a commensal / mutualist: the species is a mutualist symbiont, most often a microalgal taxa involved in photosymbiosis / no: the species is not involved in a symbiosis as small partner / NA: undetermined; symbiont_host = photo: the host species relies on a mutualistic microalgal photosymbiont to survive (obligatory photosymbiosis) / photo_falc: same as photo, but facultative relationship / photo_klep: the host species maintains chloroplasts from microalgal prey(s) to survive / photo_klep_falc: same as photo_klep, but facultative / Nfix = the host species must interact with a mutualistic symbiont providing N2 fixation to survive / Nfix_falc = same as Nfix, but facultative / no: the species is not involved in any mutualistic symbioses; NA: undetermined; silicification = yes: the species has a silicified skeleton / no: it does not / NA: undetermined; calcification = yes: the species has a calcified skeleton / no: it does not / NA: undetermined; strontification = yes: the species has a skeleton made of strontium / no: it does not / NA: undetermined; PPXXX = number of reads in each of the 214 Plankton Planet samples; TARA_XXXXXXXXXX = number of reads in each of the 386 Tara Oceans samples. The file P2_TO_18SV9_otu_table_raref_313539.tsv.gz contains the same fields but with number of reads (total and per sample) obtained after random subsampling (313,539 reads per sample). In the file P2_TO_18SV9_context.tsv.gz, each sample is described by the following fields: sample = identifier of the sample; lower_size_fraction = lower limit of the size fraction in µm; upper_size_fraction = lower limit of the size fraction in µm; event_date = date (year-month-day); event_latitude = geographic position (latitude in DD); event_longitude = geographic position (longitude in DD); depth = depth in meters; temperature = sea water temperature in °C