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.

Size structure of populations (shell length in mm) and oocyte size (in µm) distribution of three hydrothermal vent gastropod species (Lepetodrilus schrolli, L. fijiensis and Shinkailepas tollmanni) of the South West Pacific back-arc basins. Individuals were collected in Bathymodiolus spp. and Ifremeria nautilei habitats at several vent sites in the Manus, North Fiji, Futuna and Lau back-arc basins during the CHUBACARC cruise in 2019. These data were collected through stereoscopic microscope observations and hostological analyses on several individuals of each species. 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.

List of macroinvertebrate taxa found in Sacharina latissima and Alaria esculenta cultivated on longlines. Objectives within WP6 of GENIALG: assessing the biodiversity associated with cultivated seaweed. Location of seaweed farm: Ventry Harbour, Ireland. Dataset consists of macroinvertebrate taxa identified and enumerated from 25 cm replicate seaweed samples removed from the longlines. The samples were collected at seven different time points along the growing season in 2018 and 2019. Samples collected as part of the GENIALG project (project ID: 727892, GENIALG - GENetic diversity exploitation for Innovative Macro-ALGal biorefinery, http://genialgproject.eu/). GENIALG was funded by the European Union Horizon2020 programme. The remit of the work was assessing the environmental footprint and ecosystem services provided by seaweed aquaculture in Europe to provide best practice advice to industry.

List of macroinvertebrate taxa associated with experimental dropper replicates. Collected at two test seaweed farms in The Netherlands. Samples collected as part of the GENIALG project (project ID: 727892, GENIALG - GENetic diversity exploitation for Innovative Macro-ALGal biorefinery, http://genialgproject.eu/). GENIALG was funded by the European Union Horizon2020 programme. The remit of the work was assessing the environmental footprint and ecosystem services provided by seaweed aquaculture in Europe to provide best practice advice to industry. A total of twelve seaweed lines (droppers of 2m length) were deployed in the farm at November 21st 2018. Six lines were located on the outer edge of the farm and six lines were located in the middle of the farm. At both locations three lines were seeded with seaweed and three lines were left empty. The ropes were collected on the 24th of April by gently removing the ropes from the water and directly transferring them into plastic bags. On May 14th 2020 droppers were randomly selected and cut from the longlines and processed following the same protocols.