20 pages, 11 figures, 3 tables, supplemental material https://doi.org/10.3389/fmars.2019.00535, Quantification of the actual amount of carbon export to the mesopelagic layer by both zooplankton and micronekton is at present a gap in the knowledge of the biological pump. These organisms perform diel vertical migrations exporting carbon through respiration, excretion, mortality, and egestion during their residence at depth. The role of zooplankton in active flux is nowadays partially assessed. However, micronekton active flux is scarcely known and only a few studies addressed this downward transport. Even less is known about the capacity of both communities to export carbon in the ocean. Here, we show the results of zooplankton and micronekton active flux across a productivity gradient in the tropical and subtropical Atlantic Ocean. Biomass vertical distribution from the surface up to 800 m depth by day and night was studied during April 2015 in a transect from 9°S to 25°N, covering from the quite oligotrophic zone off Brazil to the meso- and eutrophic areas of the equator, Guinea Dome, and the oceanic upwelling off Northwest Africa. Zooplankton and micronekton migrant biomass was estimated from day and night catches at different layers of the water column using MOCNESS-1 (1 m2 mouth area) and Mesopelagos (35 m2) nets, respectively. Respiratory flux was assessed by measuring the enzymatic activity of the electron transfer system (ETS) of organisms at depth. Results showed a close relationship between migrant biomass and respiratory flux in zooplankton and micronekton as expected. Using a rather conservative 50% of efficiency for the net used to capture micronekton, respiratory flux resulted in similar values for both communities. Gravitational (passive) flux measured using sediment traps increased from the oligotrophic toward the meso- and eutrophic zones. Total active flux (including respiration and estimated mortality, excretion, and gut flux) by zooplankton and micronekton accounted for about 25% of total flux (passive plus active) in oligotrophic zones. Total active flux also increased toward meso- and eutrophic zones, reaching about 80% of total flux and being at least twofold higher than passive flux. These results alert about an important underestimation of the ocean biological pump using only passive flux measurements, This work was supported by projects “Migrants and Active Flux in the Atlantic Ocean” (MAFIA, CTM2012-39587-C04), and “Biomass and Active Flux in the Bathypelagic Zone” (Bathypelagic, CTM2016-78853-R) from the Spanish Ministry of Economy and Competitiveness, Peer Reviewed

8 pages, 4 figures, 1 table, supplementary information https://doi.org/10.1038/s41467-020-19875-7.-- Data sets generated during and/or analyzed during the current study are available at PANGAEA (http://www.pangaea.de). The zooplankton biomass from the Malaspina cruise is available in https://doi.org/10.1594/PANGAEA.922974, the deep-sea zooplankton biomass reviewed is available in https://doi.org/10.1594/PANGAEA.923149, the reviewed carbon flux and respiration are available in https://doi.org/10.1594/PANGAEA.923832, the acoustic backscatter is available in https://doi.org/10.1594/PANGAEA.922619, and the stable isotope data in https://doi.org/10.1594/PANGAEA.919314, The biological pump transports organic carbon produced by photosynthesis to the meso- and bathypelagic zones, the latter removing carbon from exchanging with the atmosphere over centennial time scales. Organisms living in both zones are supported by a passive flux of particles, and carbon transported to the deep-sea through vertical zooplankton migrations. Here we report globally-coherent positive relationships between zooplankton biomass in the epi-, meso-, and bathypelagic layers and average net primary production (NPP). We do so based on a global assessment of available deep-sea zooplankton biomass data and large-scale estimates of average NPP. The relationships obtained imply that increased NPP leads to enhanced transference of organic carbon to the deep ocean. Estimated remineralization from respiration rates by deep-sea zooplankton requires a minimum supply of 0.44 Pg C y−1 transported into the bathypelagic ocean, comparable to the passive carbon sequestration. We suggest that the global coupling between NPP and bathypelagic zooplankton biomass must be also supported by an active transport mechanism associated to vertical zooplankton migration, This study was funded by projects Malaspina (CSD2008-00077), Bathypelagic (CTM2016-78853-R) from the Spanish Ministry of Economy and Competitiveness, and to projects SUMMER (Grant Agreement 817806) and TRIATLAS (Grant Agreement 817578) from the European Union (Horizon 2020 Research and Innovation Programme), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

Trabajo final presentado por Mar Llaberia Robledillo para el grado de Ciencias del Mar de la Universitat de Barcelona (UB), realizado bajo la dirección del profesor Alejandro Aguilar de la Universitat de Barcelona (UB) y de la Dra. Mª Pilar Olivar del Institut de Ciències del Mar (ICM-CSIC).-- 48 pages, 16 figures, 9 figures, 5 tables, 2 annexes, [EN] In the present study were analyzed the differences between the patterns of energy density and the allometric growth of 11 species from the Atlantic. The analysis showed differences between some of the species which were discussed in terms of migration behavior (realization or not of diel vertical migrations -DVM-). It was based on the hypothesis that migratory species should have a greater muscular development, which would result in higher growth in weight and probably, in energy density.
The allometric growth of two myctophids, Benthosema glaciale and Lobianchia dofleini, and two stomiids, Argyropelecus hemigymnus and Cyclothone microdon were determined. Most cases showed isometry, while C.microdon showed a positive allometry, an opposed result to the initial hypothesis, since it is non-migratory species.
The energy density was determined in mesopelagic (mostly migratory) and batipelagic species (mostly non-migratory species), where mesopelagics showed higher caloric density compared to batipelagics. However, some energy values were similar between both, which indicates that energy density also depends on the oceanographic conditions of the area and the availability of food, different from the stations where the individuals were collected.
Only the results of the non-migratory species C.microdon were opposed to the two hypotheses mentioned, where it showed positive allometry and the highest range of energy density, which is interpreted as a result of lipid accumulation and the decrease in energy rates due to the low temperatures where it lives.
The body water content was related to the minimum depth of occurrence (MDO), where there was a directly proportional relationship between MDO and water content of individuals, explained by the buoyancy strategy they present. The results are discussed comparing the present data in the study with bibliographic data of phylogenetically close species, [CAT] En el present estudi es van analitzar les diferències entre les pautes de densitat energètica i de creixement al·lomètric d’11 espècies procedents de l’Atlàntic. Els anàlisis mostraven diferències entre algunes de les espècies que es va discutir en termes de comportament migrador (realització o no de migracions verticals diàries –MVD-). Es partia de la hipòtesis que les espècies migradores haurien de tenir un major desenvolupament muscular, que es traduiria a un major creixement en pes i probablement, en densitat energètica.
Es va determinar el creixement al·lomètric de dos mictòfids, Benthosema glaciale i Lobianchia dofleini, i de dos estòmids, Argyropelecus hemigymnus i Cyclothone microdon. La majoria dels casos mostraven isometria, mentre que C.microdon mostrava una al·lometria positiva, resultat contrari a la hipòtesi inicial, ja què és no-migradora.
Es va determinar la densitat energètica en espècies mesopelàgiques (majoritàriament migradores) i batipelàgiques (majoritàriament no-migradores), on les mesopelàgiques van presentar uns resultats superiors de densitat calòrica respecte les batipelàgiques. Tanmateix, alguns valors energètics eren similars entre ambdues, el què indica que la densitat energètica també depèn de les condicions oceanogràfiques de la zona i de la disponibilitat d’aliment, diferent en les estacions on els individus van ser recol·lectats.
Només els resultats de l’espècie no-migradora C.microdon van ser contraris a les dues hipòtesis esmentades, on presentava al·lometria positiva i el rang més elevat de densitat energètica, que s’interpreta com a resultat de l’acumulació lipídica i la disminució en les taxes energètiques per les baixes temperatures on habita.
El contingut d’aigua corporal es va relacionar amb la profunditat mínima d’ocurrència (MDO) dels individus, on es va presentar una relació directament proporcional, explicat per l’estratègia de flotabilitat que presenten. Els resultats es discuteixen comparant les dades presents en l’estudi i dades bibliogràfiques d’espècies filogenèticament pròximes, En primer lloc, agrair al projecte "CTM2016-78853-R Bathypelagos” per haver-me cedit les mostres necessàries pel present estudi

10 pages, 4 figures, supplementary information https://doi.org/10.1038/s41598-021-87767-x.-- The original data on sample location, individual fish characteristics and stable isotope composition, including amino acids, can be accessed through the PANGAEA repository (https://doi.org/10.1594/PANGAEA.930111).-- Data Availability: DIGITAL.CSIC https://doi.org/10.20350/digitalCSIC/18157, The importance of microbes for the functioning of oceanic food webs is well established, but their relevance for top consumers is still poorly appreciated. Large differences in individual size, and consequently in growth rates and the relevant spatial and temporal scales involved, make the integration of microorganisms and large metazoans in a common food web framework difficult. Using stable isotopes, this study estimated the trophic position of 13 species of micronektonic fishes to examine the microbial and metazoan contribution to mid trophic level consumers. Vertically migrant species displayed higher trophic positions than non-migrant species in all depth layers. The estimated trophic positions agreed well with those from the literature, but all species displayed mean increases between 0.5 and 0.8 trophic positions when taking into account microbial trophic steps. Trophic position, but not the relative importance of the microbial food web, increased with individual size, suggesting that current estimates of the trophic position of top consumers and of the length of oceanic food webs are too low because they are based only on metazoan trophic steps. This finding calls for a review of trophic position estimates and of the efficiency of trophic transfers along oceanic food webs, This research was funded by projects BATHYPELAGIC (CTM2016-78853-R) from the Plan Estatal de I+D+I (Spain), SUMMER (Grant Agreement 817806) and TRIATLAS (Grant Agreement 817578), from the European Union (Horizon 2020 Research and Innovation Programme), and Grant Number IN607A2018/2 from the Axencia Galega de Innovación (GAIN, Xunta de Galicia, Spain), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

9 pages, 3 figures, 1 table, supplementary data https://doi.org/10.1093/icesjms/fsab189.-- Data availability statement: The original data on sample location, individual fish characteristics and stable isotope composition, including amino acids, can be accessed through the PANGAEA repository (Bode et al., 2021b). Similarly, the original data for copepods can be found in Bode et al. (2018b), The trophic position (TP) of fishes determines their importance in terms of energy flows within food webs. However, accurate estimations of TP are often prevented because of the difficulties in tracing all food sources. This is particularly challenging for omnivorous fishes, such as those from the Order Stomiiformes. In this study, we applied recent developments in stable isotope analysis of amino acids to untangle the contributions of microbial vs. metazoan food webs in 13 species of Stomiiformes. The inclusion of the microbial food web reduced the differences between TP estimates using stable isotopes and those derived from stomach content analysis. In addition, the new estimates allowed to quantify the relative contribution of the microbial food web to each species (6–21%), highlighting the importance of detritus consumption even in piscivorous species (e.g. Stomias boa and Chauliodus danae). The comparison of TP estimates obtained with selected amino acids in fish muscle allowed for the detection of the microbial influence integrated at time scales relevant for net fish growth, even when trophic exchanges in the microbial food web occur at much shorter time scales. The assessment of TP considering the differential contribution of microbial and metazoan food webs challenges our current understanding of marine food webs; yet provides a new quantitative tool for the analysis of their structure and function, This research was funded by projects MAFIA (CTM2012-39587-C04), BATHYPELAGIC (CTM2016-78853-R), and QLOCKS (PID2020-115620RB-100) from the Plan Estatal de I+D+I (Spain), projects SUMMER (grant agreement number 817806) and TRIATLAS (grant agreement number 817578), from the European Union (Horizon 2020 Research and Innovation Programme), and the support through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

24 pages, 4 figures, 1 table.-- Data availability: The data underlying this article are available in the GenBank Nucleotide Database at https://www.ncbi.nlm.nih.gov/genbank/ and can be accessed with the GenBank accession numbers MW233711–MW233782 and MW255551–MW255585. The FastQ files can be accessed within the GenBank Nucleotide Database with the BioProject accession number PRJNA716134, Oceanic squids of the order Oegopsida are ecologically and economically important members of the pelagic environment. They are the most diverse group of cephalopods, with 24 families that are divergent morphologically. Despite their importance, knowledge of phylogenetic relationships among oegopsids is less than that among neritic cephalopods. Here, we provide the complete mitogenomes and the nuclear 18S and 28S ribosomal genes for 35 selected oceanic squids, which were generated using genome skimming. We performed maximum likelihood and Bayesian inference analyses that included 21 of the 24 oegopsid families. In our analyses, the architeuthid, chiroteuthid and enoploteuthid family groups, which have been proposed previously based on morphological and natural history characteristics, were retrieved as monophyletic. The morphologically divergent Cranchiidae formed a well-supported clade with families Ommastrephidae and Thysanoteuthidae, with a unique mitochondrial gene order. The family Lycoteuthidae was revealed as paraphyletic and contained Pyroteuthidae. Thus, the two lycoteuthid subfamilies are herein elevated to family level, increasing the number of oegopsid squid families to 25. In order to describe the diversity and evolutionary trends of oegopsid squids accurately, the superfamilies Architeuthoidea, Chiroteuthoidea, Cranchioidea and Enoploteuthoidea are resurrected from the literature, and the superfamilies Cycloteuthoidea, Octopoteuthoidea and Pholidoteuthoidea are proposed. The phylogenetic positions of Gonatidae, Histioteuthidae and Onychoteuthidae were not stable in our phylogenetic analyses and are not assigned to a superfamily. This study supports the utility of genome skimming to solve the phylogenetic relationships of oceanic squids, Specimens were collected primarily during the research project MAFIA (CTM2012-39587-C04-03) and BATHYPELAGIC (CTM2016-78853-R), funded by the Spanish Ministry of Economy and Competitiveness (MINECO/ FEDER/EU). F.Á.F.-Á. was supported by an Irish Research Council–Government of Ireland Postdoctoral Fellowship Award (ref. GOIPD/2019/460). M.T. is funded by a PhD fellowship from the Irish Research Council and is supported by the Dr Tony Ryan Research Fund. Support to R.V. was provided by the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S) and the European Commission (SUMMER project, GA-817806), Peer reviewed

14 pages 11 figures, 3 tables, supplementary data https://doi.org/10.1016/j.pocean.2022.102787.-- Data Availability: DIGITAL.CSIC https://doi.org/10.20350/digitalCSIC/18162, The organic carbon resulting from photosynthesis in the upper ocean is transferred downward through the passive sinking of organic particles, physical mixing of particulate and dissolved organic carbon as well as active flux transported by zooplanktonic and micronektonic migrants. Several meso- and bathypelagic organisms feed in shallower layers during the nighttime and respire, defecate, excrete and die at depth. Recent studies suggest that migrant micronekton transport similar amounts of carbon to migrant zooplankton. However, there is scarce information about biomass and carbon flux by non-migratory species in the mesopelagic and bathypelagic zones. The non-migratory bristlemouth fishes (Cyclothone spp.) and partial migrator (A. hemigymnus) remineralise organic carbon at depth, and knowledge about this process by this fauna is lacking despite them having been referred to as the most abundant vertebrates on Earth. Here we show the vertical distribution of biomass and respiration of non-migratory mesopelagic fishes, during day and night, using the enzymatic activity of the electron transfer system (ETS) as a proxy for respiration rates. The study is focused on five Cyclothone species (C. braueri, C. pseudopallida, C. pallida, C. livida and C. microdon) and Argyropelecus hemigymnus. The samples were taken on a transect from the oceanic upwelling off Northwest Africa (20° N, 20° W) to the south of Iceland (60° N, 20° W). Cyclothone spp. showed, by far, the largest biomass (126.90 ± 86.20 mg C·m−2) compared to A. hemigymnus (0.54 ± 0.44 mg C·m−2). The highest concentrations of Cyclothone spp. in the water column were observed between 400 and 600 m and from 1000 to 1500 m depths, both during day and night. For the different species analysed, ETS activity did not show significant differences between diurnal and nocturnal periods. The total average specific respiration of Cyclothone spp. (0.02 ± 0.01 d-1) was lower than that observed for A. hemigymnus (0.05 ± 0.02 d-1). The average carbon respiration of Cyclothone spp. was 2.22 ± 0.81 mg C·m−2·d-1, while it was much lower for A. hemigymnus (0.04 ± 0.03 mg C·m−2·d-1). The respiration of Cyclothone spp. was lower in the bathypelagic than in the mesopelagic zone (0.84 ± 0.48 vs 1.36 ± 1.01 mg C·m−2·d-1, respectively). These results, to our knowledge, provide the first account of remineralisation by this community in the meso and bathypelagic zones of the ocean, This work was funded by the Spanish Government through the project Bathypelagic (CTM2016-78853-R), and by the European Union (Horizon 2020 Research and Innovation Programme) through projects SUMMER (Grant Agreement 817806), TRIATLAS (Grant Agreement 817578) and the Spanish Government through the Project Desafío (PID2020-118118RB-I00). Airam Sarmiento-Lezcano was supported by a postgraduate grant (BES-2017-082540) and José María Landeira by the “Beatriz Galindo” grant (BEAGAL 18/ 00172) both from the Spanish Ministry of Science and Innovation. Laia Armengol was funded with a postdoctoral fellowship from “Unidad de Océano y Clima” of R&D&I Consejo Superior de Investigaciones Científicas and IOCAG, and a postdoctoral fellowship from project South and Tropical Atlantic Climate-Based Marine Ecosystem Prediction for Sustainable Management (TRIATLAS, 817578; European Commission) and Ione Medina-Suárez by project MAC-CLIMA (MAC2/3.5b/254) from the European Union. MPO acknowledges the institutional support of the AEI ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

Special issue Technological Oceanography.-- 10 pages, 6 figures, 1 table.-- Data Availability Statement: No new data were created or analyzed in this study. Data sharing is not applicable to this article, Different types and systems to discriminate plankton samples at different strata in the water column have been developed in recent decades. For sampling at sufficient depth, opening and closing zooplankton multinets are ideal because there is no contamination of one sample with organisms of the previous one. However, for bigger nets, such as those used to collect micronektonic organism, it is difficult to use multiple net units, and multiple cod ends are preferred because of their simplicity, but with the problem of sample contamination from having a common net passageway. We present here a cod-end Multisampler design, VERDA, that uses a carrousel-like system. Similar to some sediment traps, the system works like a revolver with six or eight compartments whose turning mechanism is triggered when the net arrives to a programmed depth level. This prototype was built with inexpensive and recycled components and electronics similar to Arduino® and Teensy PCB to carry out electronic control. The net we used for testing the equipment was a mid-size midwater trawl of ca. 30 m2 and total length of 58 m that works with a single towing cable and no doors. The overall system is useful for all type of ships, due to the relatively easy deployment operations and because the Multisampler does not need electrical cable or acoustics. In our case, we used a Marport® (Reykjavik Iceland) and Scanmar (Åsgårdstrand, Norway) sensors for real-time depth monitoring and opening distance, This research was funded by the projects “Migrants and Active Flux in the Atlantic Ocean” (MAFIA, CTM2012-39587-C04) and “Biomass and Active Flux in the Bathypelagic Zone” (Bathypelagic, CTM2016-78853-R) from the Spanish Ministry of Economy and Competitiveness, and SUMMER (grant agreement number 817806) from the European Union (Horizon 2020 Research and Innovation Programme), and the support through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), Peer reviewed

22 pages, 11 figures, 7 tables.-- Data availability statement: Publicly available datasets were analyzed in this study. This data can be found here: Olivar et al. (2022) https://doi.org/10.1594/PANGAEA.947631 and Sarmiento-Lezcano et al. (2023) https://doi.org/10.1594/PANGAEA.95494.-- Data Availability: DIGITAL.CSIC https://doi.org/10.20350/digitalCSIC/18162, Non-migratory bristlemouth fishes (Cyclothone spp.) are the most abundant vertebrates on Earth and play an important role in the biological carbon pump by remineralizing organic carbon in deep ecosystems. Acoustic data and net sampling are often used in combination to estimate fish and zooplankton biomass, but this procedure may be subject to several sources of error when applied to mesopelagic species. For instance, the allocation of echoes to species has often been biased by not considering Cyclothone spp. due to the use of nets targeting larger fish. Furthermore, the acoustic properties of the target organisms must be well understood to convert acoustic density into numerical density. The characteristics of a fish’s swimbladder are the most relevant features necessary to assess its acoustic properties. This study provides information on the swimbladder properties of six Cyclothone species inhabiting the meso- and bathypelagic layers in the North Atlantic Ocean and Mediterranean Sea, including swimbladder location within the body, fat tissue content, morphology, morphometry (only available for C. braueri and C. pseudopallida), and fish body-mass density (only available for C. braueri, C. pseudopallida, C. pallida, and C. pygmaea). The studied species showed a functional physoclistous swimbladder, with well-developed gas glands and rete mirabile and numerous capillaries in the case of the shallower species C. braueri and C. pseudopallida (mainly distributed from 400 to 600 m depth), and a fat-invested swimbladder in species with deeper vertical distribution (C. livida, C. microdon, C. pallida, and C. pygmaea). The fat content in the swimbladder (C. pallida and C. microdon) increased with depth and latitude, reducing the space in the swimbladder that could contain gas. Changes in swimbladder size and volume during growth were analyzed for shallower species, where swimbladder volume and equivalent radius followed negative allometric growth in relation to body length. Finally, values of body-mass density (ρ) and gas content required for neutral buoyancy (VG) were estimated for C. braueri and C. pygmaea collected between 350 and 550 m (ρ = 1.052–1.072 g·cm−3, VG = 2%–4%; ρ = 1.052–1.062 g·cm−3, VG = 3.6%), and for C. pallida and C. pseudopallida sampled in the 450–700 m layer (ρ = 1.052–1.062 g·cm−3, VG = 2.6–3.1%; ρ = 1.052–1.062 g·cm−3, VG = 2.8%–3.25%). Results in this study highlight the change in scattering behavior of Cyclothone species from gas-bearing organisms (those that contain gas in their swimbladder) in the upper mesopelagic zone to the fluid-like scattering (with fat-filled swimbladders) of the deeper and northern individuals. The data presented in this manuscript are important for parametrizing acoustic backscattering models built to estimate the echo of Cyclothone species, although further work is needed, particularly for individuals with partially invested swimbladders with an irregular fat-free shape, This research was funded by projects Bathypelagic (CTM2016-78853-R), Ideados (CTM2007-65844-C02-01-02-03), and Desafío (PID2020-118118RB-I00) from the Spanish Ministry of Science and Technology, “Sustainable Management of Mesopelagic Resources” (SUMMER, 817806) from European Union Horizon 2020 Research and Innovation Programme, and the “South and Tropical Atlantic Climate-Based Marine Ecosystem Prediction for Sustainable Management” (TRIATLAS, 817578) from European Commission. AS-L was supported by a postgraduate grant (BES-2017-082540) from the Spanish Ministry of Science and Innovation, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

12 pages, 1 figure, 1 table, supplementary data https://doi.org/10.1093/icb/icad116, Cryptic species complexes represent an important challenge for the adequate characterization of Earth's biodiversity. Oceanic organisms tend to have greater unrecognized cryptic biodiversity since the marine realm was often considered to lack hard barriers to genetic exchange. Here, we tested the effect of several Atlantic and Mediterranean oceanic barriers on 16 morphospecies of oceanic squids of the orders Oegopsida and Bathyteuthida using three mitochondrial and one nuclear molecular marker and five species delimitation methods. Number of species recognized within each morphospecies differed among different markers and analyses, but we found strong evidence of cryptic biodiversity in at least four of the studied species (Chtenopteryx sicula, Chtenopteryx canariensis, Ancistrocheirus lesueurii and Galiteuthis armata). There were highly geographically-structured units within Helicocranchia navossae that could either represent recently diverged species or population structure. Although the species studied here can be considered relatively passive with respect to oceanic currents, cryptic speciation patterns showed few signs of being related to oceanic currents. We hypothesize that bathymetry of the egg masses and duration of the paralarval stage might influence the geographic distribution of oceanic squids. Because the results of different markers and different species delimitation methods are inconsistent, and because molecular data encompassing broad geographic sampling areas for oceanic squids are scarce and finding morphological diagnostic characters for early life stages is difficult, it is challenging to assess the species boundaries for many of these species. Thus, we consider many to be in the “grey speciation zone.” As many oceanic squids have cosmopolitan distributions, new studies combining genomic and morphological information from specimens collected worldwide are needed to correctly assess actual oceanic squid biodiversity, Samples were collected as part of the research projects MAFIA (Ref. CTM2012-39587-C04-03, Spanish Ministry of Economy and Competitiveness, MINECO/FEDER/EU), BATHYPELAGIC (Ref. CTM2016-78853-R MINECO/FEDER/EU) and SUMMER (Ref. GA-817806, European Commission). FÁF-Á was supported by a JdC-I Postdoctoral Fellowship Grant (ref. IJC2020-043170-I) awarded by MCIN/AEI /10.13039/501100011033 and by a Beatriu de Pinós fellowship from Secretaria d´Universitats i Recerca del Departament de Recerca i Universitats of the Generalitat de Catalunya (Ref. BP 2021 00035). GS was supported by the 22K15085 Grant-in-Aid for Early-Career Scientists (KAKENHI). MT was funded by a Tony Ryan Fellowship and Irish Research Council postgraduate scholarship GOIPG/2017/1740. This research was supported by the project ECOPHYN (Ref. PID2021-126824NB-C32, Ministerio de Ciencia e Innovación, Gobierno de España) and the European Union and the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

Plankton communities underpin marine ecosystem functioning, yet the mechanisms driving the onset and termination of spring phytoplankton blooms are not fully understood. In particular, the role of microzooplankton grazing and the impact of mixotrophic versus heterotrophic ciliates on phytoplankton dynamics. This study aimed to quantify ciliate grazing and phytoplankton growth rates throughout a spring bloom in Roskilde Fjord, Denmark; and determine whether nutrient depletion or microzooplankton grazing was the primary driver of bloom culmination. Surface water was collected during March 2017, and multiple dilution experiments were conducted to estimate phytoplankton growth and grazing mortality rates. Phytoplankton community structure was assessed by flow cytometry, while ciliate morphotypes and nutritional modes were identified using FlowCam imaging. Despite initially high nutrient concentrations, a marked decrease in DIN and DIP occurred over the study period. Phytoplankton biomass, dominated by cryptophytes, reached its peak by mid-March before declining. Concurrently, ciliate assemblages shifted from mixotrophic to heterotrophic dominance. Grazing rates frequently exceeded phytoplankton growth rates after the first experimental day, indicating strong top-down control. The lack of significant differences in growth between nutrient-amended and unamended treatments suggested grazing, rather than nutrient depletion, predominantly constrained phytoplankton accumulation. These findings highlight how ciliate grazing can exert a critical influence on spring bloom dynamics, even under moderate nutrient conditions. Understanding these trophic interactions is essential for predicting the resilience and stability of coastal marine ecosystems in the face of changing environmental conditions., This research was funded by the project “Biomass and Active Flux in the Bathypelagic Zone" (Bathypelagic, CTM2016-78853-R) from the Spanish Ministry of Economy and Competitiveness (MINECO) to SHL. LA was funded with a doctoral fellowship (BES-2013-063148) from the MINECO of Spain, and with a postdoctoral fellowship “Margarita Salas" from Spanish Ministry of University. LH was supported by a grant from the Brazilian program Science without Borders/CAPES (Grant No. 13581-13-9). HHJ received funding from the Innovation Found Denmark; SeaStatus – Innovative Technologies for Quantification of Sea Status (Seastatus 6154-00005B)., Peer reviewed

This dataset presents information on the vertical distribution and abundance of juvenile and adult myctophids (F. Myctophidae) throughout the daily cycle in the Northeast Atlantic Ocean. The survey extended from south of the Canary Islands to south of Iceland and was carried out in May 2018. Results evidenced the diel vertical migration pattern to the upper 200 m of the water column, during night-time, and the return to the mesopelagic layers during the day, This research was funded by project "Biomasa y flujo activo en la zona batipelagica. BATHYPELAGIC. (CTM2016-78853-R), Peer reviewed

This dataset gives information on the vertical distribution and abundance of early stages of meso and bathypelagic fishes throughout the daily cycle in the Northeast Atlantic Ocean. The larvae of the majority of species were found in the upper 100 m of the water column, both day and night. Transforming stages of myctophiforms and stomiiforms tend to be located at deeper depths during the day than at night. The most abundant specimens collected with the MOCNESS plankton net were the adults and juveniles of Cyclothone species, which do not show significant differences in vertical distributions between day and night, This research was funded by project "Biomasa y flujo activo en la zona batipelagica. BATHYPELAGIC. (CTM2016-78853-R), Peer reviewed

Mesozooplankton is a key component of the ocean, regulating global processes such as the carbon pump, and ensuring energy transfer from lower to higher trophic levels. Yet, knowledge on mesozooplankton diversity, distribution and connectivity at global scale is still fragmented. To fill this gap, we applied DNA metabarcoding to mesozooplankton samples collected during the Malaspina-2010 circumnavigation expedition across the Atlantic, Indian and Pacific oceans from the surface to bathypelagic depths. We highlight the still scarce knowledge on global mesozooplankton diversity and identify the Indian Ocean and the deep sea as the oceanic regions with the highest proportion of hidden diversity. We report no consistent alpha-diversity patterns for mesozooplankton at a global scale, neither across vertical nor horizontal gradients. However, beta-diversity analysis suggests horizontal and vertical structuring of mesozooplankton communities mostly attributed to turnover and reveals an increase in mesozooplankton beta-diversity with depth, indicating reduced connectivity at deeper layers. Additionally, we identify a water mass type-mediated structuring of mesozooplankton bathypelagic communities instead of an oceanic basin-mediated as observed at upper layers. This suggests limited dispersal at deep ocean layers, most likely due to weaker currents and lower mixing of water mass types, thus reinforcing the importance of oceanic currents and barriers to dispersal in shaping global plankton communities.