Although zooplankton was extensively studied in the North Sea, knowledge about winter zooplankton assemblages is still scarce, despite potential influence of zooplankton overwintering stocks on seasonal plankton succession and productivity. Furthermore, several economically and ecologically important fish species reproduce during winter contributing to the zooplankton community as passive members (eggs) or predators (larvae). To shed some light on winter zooplankton distribution, abundance and composition in the Southern North Sea and Eastern English Channel, we defined assemblages based on mesozoo- and ichthyoplankton data sampled between January and February 2008 using fuzzy-clustering and indicator species. Mesozoo- and ichthyoplankton (eggs+larvae) were integrated in a common analysis by using a spatial grid adapted to the datasets and defined by means of a geostatistical method developed in agronomics. Potential environmental drivers of assemblage distribution were evaluated by means of GLMM and comparison with data from 2022 facilitated insight about the inter-annual representativeness of the assemblages. Five zooplankton assemblages were found varying with regard to total zooplankton abundance, dominant and indicator taxa. Spatial variability of abiotic (dissolved nutrients, salinity, depth, temperature, organic matter in suspension, chlorophyll a), biotic variables (phyto- and microplankton composition), water masses and fish spawning grounds were revealed as potential drivers of assemblage distribution. Assemblages off the Rhine-Scheldt estuary and in the German Bight harbored the biggest zooplankton overwintering stocks that might influence the grazing pressure on phytoplankton spring production. Assemblages off the Rhine-Scheldt estuary and covering the English Channel and the Southern Bight were found to be of high importance for herring and plaice larvae. Although further analyses suggested inter-annual representativeness of the assemblages found (2008 vs 2022), the assessment of further years would be necessary to account for potential inter-annual variability. Future studies could profit from the assessment of microzooplankton facilitating insight in fish larvae feeding potential and zooplankton overwintering strategies. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

The California Current system (CCS) comprise two large regions, one subarctic from central California to British Columbia, and other subtropical from Point Conception, California to the tip of Baja California peninsula. To progress in the knowledge of the subtropical part of the CCS, was created the IMECOCAL program, which means “Mexican Research of the California Current”. The data base presented here is a product of the zooplankton collection during ten IMECOCAL cruises. Zooplankton samples were collected with oblique net tows in the upper 200 m (or from 10 m above the sea floor in shallow stations), using a Bongo net of 500 µm mesh width and mouth diameter of 0.7 m. Four cruises correspond to the four seasons of 2005 and the rest are summer cruises preformed during 2002-2008. Hyperiid amphipods were identified using mainly the taxonomic key for Hyperiidea of the world oceans (Vinogradov et al., 1996). The total number of samples analyzed were 482 but hyperiids were absent in 18. The positive samples were 75% of the oceanic stations collected during nighttime, and the rest were from neritic stations (11% nighttime and 14% daytime). The total number of species found are 125, with strong dominance of Vibilia armata, Lestrigonus schizogeneios, Primno brevidens, and Eupronoe minuta. The abundances of these and other common species changes seasonally as described by Lavaniegos & Hereu (2009), and interannually as observed in summer of the period 2002-2008 for the northern Baja California region (Lavaniegos, 2017) and the Gulf of Ulloa and offshore region (Lavaniegos, under review). Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.