Résumé
The coastal oceans can be highly variable, especially near ocean fronts. The Ushant Front is the dominant oceanographic feature in the Iroise Sea (NE Atlantic) during summer, separating warm stratified offshore waters from cool vertically-mixed nearshore waters. Mesozooplankton community structurewas investigated over an annual cycle to examine relationshipswith oceanographic conditions. DNAmetabarcoding of COI and 18S genes was used in communities from six sites along two cross-shelf transects. Taxonomic assignments of 380 and 296 OTUs (COI and 18S, respectively) identified 21 classes across 13 phyla. Meroplankton relative abundances peaked in spring and summer, particularly for polychaete and decapod larvae, respectively, corresponding to the reproductive periods of these taxa. Meroplankton was most affected by season, while holoplankton variedmost by shelf position. Copepodswith amixed feeding strategywere associated with themostoffshore sites, especially in the presence of the front, while filter-feeding or carnivorous copepods were associated with nearshore sites. In sum, mesozooplankton communities in well-mixed coastal waters were distinct from those found in the Ushant Front (high thermal stratification and chlorophyll-a). Furthermore, the benthic compartment, through its partial life cycle in the water column, contributed to high heterogeneity in planktonic communities over short temporal and spatial scales.This is the raw sequence data produced by a Illumina MiSeq used for the metabarcoding analyses in the article published in ICES Journal of Marine Science.https://doi.org/10.1093/icesjms/fsab127Sampling took place as part of the PNMIR monitoring program from the Iroise Natural Marine Park (Parc Naturel Marine de l'Iroise), and consisted in sampling vertical plankton tows along two parallel cross-shelf transects, in front of the bays of Brest (seven stations) and Douarnenez (six stations). For the present study, zooplankton was sampled in six stations, three in each transect, in spring (23 May 2019), summer (11 July 2019), and fall (22–24 October 2019).