Vertical Diel Research Articles

Resolving abrupt frontal gradients in zooplankton community composition and marine snow fields with an autonomous Zooglider

AbstractAn autonomous Zooglider navigated across the California Current Front into low salinity, minty waters characteristic of the California Current proper in both summers of 2019 and 2021. Diving to 400 m depth, Zooglider transited another near‐surface frontal gradient somewhat inshore. These frontal gradients were generally associated with changes in intensity, size composition, and Diel Vertical Migration responses of acoustic backscatterers. They were also associated with pronounced changes in zooplankton community composition, as assessed by a shadowgraph imaging Zoocam. Zoocam detected a decline in concentrations of copepods, appendicularians, and marine snow in the offshore direction, and an overall shift in community structure to a higher proportion of carnivorous taxa (and, in 2019, of planktonic rhizaria). No taxon was consistently elevated at all the peak frontal gradients, but appendicularians, copepods, and rhizarians sometimes showed front‐related increases in concentration. Such frontal gradient regions represent relatively abrupt transitions to different communities of planktonic organisms and suspended marine snow particles, with consequences for predator–prey relationships and the dominant vectors of particle export into subsurface waters.

Diel Vertical Migrators Respond to Short‐Term Upwelling Events

AbstractPelagic organisms inhabiting coastal upwelling regions face a high risk of advection away from the nearshore productive habitat, potentially leading to mortality. We explored how animals remain in a productive yet highly advective environment in the Northern California Current System using the cabled observatory system located off the Oregon coast. Acoustic scatterers consistent with swimbladder‐bearing fish were only present during the downwelling season as these animals avoided the cold waters associated with strong upwelling conditions in summer and fall. Fish responded to short‐term upwelling events by increasing the frequency of diel vertical migration. Throughout the study, their vertical positions corresponded to the depth of minimum cross‐shelf transport, providing a mechanism for retention. The observed behavioral response highlights the importance of studying ecological processes at short timescales and the abilities of pelagic organisms to control their horizontal distributions through fine‐tuned diel vertical migration in response to upwelling.

A case study of anchovy diurnal migration patterns in Teluk Bakau, Bintan Regency, Riau Island, Indonesia

Teluk Bakau is an area of water on the shore of Bintan Regency where the people make their livelihoods through fishing. There is now a lot of data showing a decline in catches, but it is unclear why this is happening. Changes in migratory patterns are regarded to be one of the primary reasons. The daily diurnal migratory pattern of anchovies is assumed to correspond with the movement of plankton. Anchovies are a type of tiny fish larvae whose life cycle is tied to plankton. It is possible to see microorganisms by converting the mean volume backscattering strength (MVBS) value into a measure of anchovy quantity and presence. Anchovy diurnal vertical migration was discovered using Diel Vertical Migration (DVM) measurements, which also revealed that the fish were in the MVBS range of -40 dB to -60 dB (e.g. FL: 5–10 cm). The migration of anchovies seen by ADCP shows they typically move towards the surface in the afternoon and that their numbers generally expand until night. Along with this an increase of anchovies, a lot of plankton has been rising to the surface. The presence of an anchovies moves into deeper waters in the early morning, and until daytime, they are decreasingly abundant. An indication that anchovies are increasingly plentiful and more present is in the afternoon

Spatial and Temporal Characteristics of Winter Diel Vertical Migration of Zooplankton and Nekton in the East China Shelf Seas Based on Multi‐Frequency Echosounder

AbstractThe diel vertical migration (DVM) of plankton and nekton plays an important role in the energy flow and material cycling of marine ecosystems. Especially in shelf seas, seasonal environmental variations may distinguish DVM characteristics in winter mixed water from summer pattern. Therefore, to investigate the patterns and influencing factors of winter DVM in East China Shelf Seas (ECSS), we carried out comprehensive research based on high‐resolution multi‐frequency acoustic data during the winter of 2019/2020. The results showed that: (a) acoustic and zooplankton sampling data can effectively capture the widely existence of winter DVM of different biological community in ECSS and their spatio‐temporal variabilities. (b) In East China Sea, the migration was mainly dominated by the Gas‐bearing class (GB), which had fast migration speed, compared to the Yellow Sea where the migration was dominated by the Fluid‐like class (FL). In addition, GB descends earlier than FL. (c) For large scale factors, during the full moon, the GB will aggregate deeper and the FL shallower, compared to the new moon, and regional temperature is an important factor affecting the distribution of organisms at meridional direction; for small scale processes, cold and warm currents and ocean fronts can also affect migration behavior. In the muddy area with full moon and spring tide, GB and FL show different inconsistent migration compared to normal relatively consistent pattern. These results will help us to better understand the physiological, ecological and environmental elements that control winter DVM, facilitating the management of ecosystem‐based fisheries resources.

Morphological and taxonomic diversity of mesozooplankton is an important driver of carbon export fluxes in the ocean.

Mesozooplankton is a very diverse group of small animals ranging in size from 0.2 to 20 mm not able to swim against ocean currents. It is a key component of pelagic ecosystems through its roles in the trophic networks and the biological carbon pump. Traditionally studied through microscopes, recent methods have been however developed to rapidly acquire large amounts of data (morphological, molecular) at the individual scale, making it possible to study mesozooplankton using a trait-based approach. Here, combining quantitative imaging with metabarcoding time-series data obtained in the Sargasso Sea at the Bermuda Atlantic Time-series Study (BATS) site, we showed that organisms' transparency might be an important trait to also consider regarding mesozooplankton impact on carbon export, contrary to the common assumption that just size is the master trait directing most mesozooplankton-linked processes. Three distinct communities were defined based on taxonomic composition, and succeeded one another throughout the study period, with changing levels of transparency among the community. A co-occurrences' network was built from metabarcoding data revealing six groups of taxa. These were related to changes in the functioning of the ecosystem and/or in the community's morphology. The importance of Diel Vertical Migration at BATS was confirmed by the existence of a group made of taxa known to be strong migrators. Finally, we assessed if metabarcoding can provide a quantitative approach to biomass and/or abundance of certain taxa. Knowing more about mesozooplankton diversity and its impact on ecosystem functioning would allow to better represent them in biogeochemical models.

Copepod vertical diel migration on the continental shelf of South Central Vietnam

Zooplankton often migrates within the water column for different purposes but mostly to find food and avoid predators. Vertical migration over 24 hours is called diel vertical migration (DVM). However, knowledge of DVM for different zooplankton species is limited. The present study analysized DVM based on species distribution in the water column at each different times of day at two stations on the central Vietnam shelf. One station was on the shelf (LT2) and another was on the shelf slope (FK002). The results showed that 69 zooplankton species, out of 191 recorded at the two stations, having strong DVM (dz > 15 m). Among them, 38 species were nocturnal and 36 species showed reverse DVM. Species with nocturnal DVM were less on the shelf station than on the shelf slope. Moreover, detailed analysis at LT2 showed 18 species having DVM at dawn and 13 species having DVM at sunrise. This study provides important data for zooplankton ecology in Vietnam and marine tropical waters.

Diel Vertical Habitat Use Observations of a Scalloped Hammerhead and a Bigeye Thresher in the Northern Gulf of Mexico

Understanding habitat use of elasmobranchs in pelagic environments is complicated due to the mobility of these large animals and their ability to move great distances in a three-dimensional environment. The Gulf of Mexico is a region where many highly migratory pelagic shark species occur, while in close proximity to coastal, anthropogenic activity including recreational and commercial fisheries. This study provides summary information on the vertical habitat use for a single male scalloped hammerhead and a single male bigeye thresher that were each caught and tagged with an archiving satellite tag. The scalloped hammerhead occupied shallow depths (<100 m) over the continental shelf during the 90 d deployment. The bigeye thresher exhibited strong patterns of diel vertical migrations by occupying depths below the thermocline (>350 m) during the day, then occupying shallower depths (50–100 m) during the night. By providing summary information, this note urges future research to provide scientific information on pelagic, highly migratory species for management efforts in the Gulf of Mexico region.

Copepod Diel Vertical Distribution in the Open Southern Adriatic Sea (NE Mediterranean) under Two Different Environmental Conditions

Diel vertical migration of the copepod the community was investigated in the open South Adriatic, in June 2020 and February 2021, under two very different hydrographical conditions. The influence of a winter wind-induced mixing event on copepod vertical migration at the species level was determined for the first time and compared to the situation in June when pronounced thermal stratification was observed. The samples were collected during a 24 h cycle in four depth layers from the surface down to 300 m depth, using a Nansen opening–closing net with 250-µm mesh size. In winter, the bulk of the copepod population remained in the epipelagic zone (0–100 m) over the entire 24 h cycle, with calanoids remaining the dominant group. An increasing trend of copepod standing stocks from midnight to early morning in the surface layer found in June is in agreement with previous records of copepod day–night variations in the Mediterranean Sea. Day–night differences in diversity and the number of taxa of the epipelagic area were more pronounced in June, confirming the higher intensity of diel vertical migration in summer. Although the epipelagic community was composed of numerous weak diel vertical migrant species, for the majority of investigated copepod taxa, migration patterns differed between the environmentally contrasting seasons. A multivariate non-metric analysis showed that the copepod community was strongly affected by temperature, thus exhibiting a clear seasonal structure.

Diel Vertical Distribution Patterns of Pelagic Fish Larvae in Yilan Bay, Taiwan

To study the diel migration distribution of larval fish in an area adjacent to the Kuroshio Current, samples were collected from six depths by using a Motoda horizontal net at a fixed station in Yilan Bay on July 30 and 31, 2007. A total of 591 larval fish were collected and assigned to at least 34 families and 57 species. The first five dominant species were Benthosama pterotum (40.95%), Diaphus B type (12.18%), Callionymidae spp. (8.46%), Gobiidae spp. (6.60%), and Apogonidae spp. (4.0%). The density of larval fish varied across time. The maximum larval density was 1220.34 individuals/1000 m3 at 19:00, and the minimum larval density was 81.84 ind./1000 m3 at 14:00. The vertical distribution of species accounting for more than 10% of all fish caught was determined by the diurnal and nocturnal migration of the dominant species B. pterotum, which migrated from a depth of 50 m at night to 200 m in the afternoon. The distribution models for other species (e.g., Diaphus B type) were also analyzed in this study.

Acoustic correction factor estimate for compensating vertical diel migration of small pelagics

Differences in acoustic estimates of small pelagic fish biomass, due to data acquisition during daytime and nighttime surveys, have been recognized for many years as a problem in acoustic surveys. In the absence of a single rule for all species and for all locations, some expert groups identified specific time intervals for acoustic data acquisition in relation to the schooling behavior of the target species. In the Mediterranean Sea, the research groups working in the MEDIAS (Mediterranean International Acoustic Survey) agreed on the importance that acoustic sampling are conducted only during day-time. Only when available time does not permit to complete the survey during daytime, data collection might be extended. In this case, working on data collected during both daytime and nighttime, a bias may occur in the biomass estimates. In order to evaluate and correct such bias, specific experiments were performed in some geographical sub-areas of the Mediterranean Sea. The data analysis allowed the estimation of a mean correction factor for the Strait of Sicily, where five surveys were carried out in different years. The correction factor was estimated also for the Adriatic Sea, Tyrrhenian Sea and Northern Spain; the observed variability among areas highlighted the importance of the spatial and temporal coverage of the survey area in order to obtain reliable estimates of the correction factor. Further studies are necessary to improve the interpretation of the obtained estimates in relation to area-related peculiarities such as zooplankton composition and abundance along with small pelagic fish community structure.

Oceanic Diel Vertical Movement Patterns of Blue Sharks Vary With Water Temperature and Productivity to Change Vulnerability to Fishing

In the pelagic environment diel vertical movements (DVM) are widespread across taxa, from zooplankton ascending from day-time depths into surface layers at night to avoid visual predators, to apex predators following prey movements to maximise foraging opportunities. The drivers of DVM in large predators such as pelagic sharks have only recently begun to be investigated in detail with the advent of sophisticated archival tags and high-resolution oceanographic datasets. In this study, we satellite tagged adult [>180 cm fork length, (FL)] blue sharks (Prionace glauca) in the North Atlantic Ocean to examine behavioural changes in response to the encountered environment, and therefore, to determine potential risks of capture using pelagic longline fisheries data. Although blue sharks recurrently use surface waters, cyclic diel behaviours were observed, with >95% of night-time spent above 250 m depth and variable day-time depth use. Hence, three different diel behaviours were identified during the tracking period: (i) regular normal DVM (nDVM) (dawn descent – dusk ascent, with over 90% of nighttime spent above 250 m, and between 5 and 50% of the day below this threshold); (ii) surface-oriented behaviour (occupation of surface waters both day and night), and (iii) deep depth-oriented nDVM [dawn descent – dusk ascent, with the majority (>50%) of daytime spent at depth]. Importantly, diel behaviours generally occurred in different ocean regions with nDVM frequently observed in high latitudes, associated with cold, highly productive waters (e.g., North Atlantic Current/Labrador Current convergence zone, West African upwelling area), while depth-oriented nDVM was observed in warm, oligotrophic areas. Thus, day-time occupation of shallow waters significantly increased with lower water temperature at depth (100 m), and with increasing concentration (and decreasing depth) of the chlorophyll a maximum. During nights of full moon blue sharks spent significantly more time in the depth range of longline hooks, while fishing effort and catches were also higher. We demonstrate that increased occupancy of surface layers driven by highly productive, cold waters and greater lunar illumination lead to higher capture risk. Understanding habitat-specific vulnerability to fishing in a commercially important pelagic shark species is essential for improving management and conservation measures.

Integrating Diel Vertical Migrations of Bioluminescent Deep Scattering Layers Into Monitoring Programs

The deep sea (i.e., >200 m depth) is a highly dynamic environment where benthic ecosystems are functionally and ecologically connected with the overlying water column and the surface. In the aphotic deep sea, organisms rely on external signals to synchronize their biological clocks. Apart from responding to cyclic hydrodynamic patterns and periodic fluctuations of variables such as temperature, salinity, phytopigments, and oxygen concentration, the arrival of migrators at depth on a 24-h basis (described as Diel Vertical Migrations; DVMs), and from well-lit surface and shallower waters, could represent a major response to a solar-based synchronization between the photic and aphotic realms. In addition to triggering the rhythmic behavioral responses of benthic species, DVMs supply food to deep seafloor communities through the active downward transport of carbon and nutrients. Bioluminescent species of the migrating deep scattering layers play a not yet quantified (but likely important) role in the benthopelagic coupling, raising the need to integrate the efficient detection and quantification of bioluminescence into large-scale monitoring programs. Here, we provide evidence in support of the benefits for quantifying and continuously monitoring bioluminescence in the deep sea. In particular, we recommend the integration of bioluminescence studies into long-term monitoring programs facilitated by deep-sea neutrino telescopes, which offer photon counting capability. Their Photo-Multiplier Tubes and other advanced optical sensors installed in neutrino telescope infrastructures can boost the study of bioluminescent DVMs in concert with acoustic backscatter and video imagery from ultra-low-light cameras. Such integration will enhance our ability to monitor proxies for the mass and energy transfer from the upper ocean into the deep-sea Benthic Boundary Layer (BBL), a key feature of the ocean biological pump and crucial for monitoring the effects of climate-change. In addition, it will allow for investigating the role of deep scattering DVMs in the behavioral responses, abundance and structure of deep-sea benthic communities. The proposed approach may represent a new frontier for the study and discovery of new, taxon-specific bioluminescence capabilities. It will thus help to expand our knowledge of poorly described deep-sea biodiversity inventories and further elucidate the connectivity between pelagic and benthic compartments in the deep-sea.

Hormone-mediated foraging strategies in an uncertain environment: Insights into the at-sea behavior of a marine predator.

Hormones are extensively known to be physiological mediators of energy mobilization and allow animals to adjust behavioral performance in response to their environment, especially within a foraging context.Few studies, however, have narrowed focus toward the consistency of hormonal patterns and their impact on individual foraging behavior. Describing these relationships can further our understanding of how individuals cope with heterogeneous environments and exploit different ecological niches.To address this, we measured between‐ and within‐individual variation of basal cortisol (CORT), thyroid hormone T3, and testosterone (TEST) levels in wild adult female Galápagos sea lions (Zalophus wollebaeki) and analyzed how these hormones may be associated with foraging strategies. In this marine predator, females exhibit one of three spatially and temporally distinct foraging patterns (i.e., “benthic,” “pelagic,” and “night” divers) within diverse habitat types.Night divers differentiated from other strategies by having lower T3 levels. Considering metabolic costs, night divers may represent an energetically conservative strategy with shorter dive durations, depths, and descent rates to exploit prey which migrate up the water column based on vertical diel patterns.Intriguingly, CORT and TEST levels were highest in benthic divers, a strategy characterized by congregating around limited, shallow seafloors to specialize on confined yet reliable prey. This pattern may reflect hormone‐mediated behavioral responses to specific risks in these habitats, such as high competition with conspecifics, prey predictability, or greater risks of predation.Overall, our study highlights the collective effects of hormonal and ecological variation on marine foraging. In doing so, we provide insights into how mechanistic constraints and environmental pressures may facilitate individual specialization in adaptive behavior in wild populations.

Travelling Expenses: The Energy Cost of Diel Vertical Migrations of Epipelic Microphytobenthos

The physiology of the diel movements of epipelic microphytobenthic diatoms is not fully understood. As well, the evolutionary pressures that led to migratory behavior and the ecological role of vertical migrations remain unknown. The behavioral photoprotection hypothesis, according to which the diatoms move along the vertical light gradient to find their optimal light environment, is the most generally accepted. However, the motion is associated with an energy cost that has not been fully acknowledged before. To throw light on this issue, we looked at the mechanisms of diatom locomotion and reviewed their patterns of movement. Making use of published data, we estimated an energy cost of 0.12 pJ for a typical diatom cell to move upward (or downward) in a 400 µm photic zone. This amounts to 3.93x10-18 mol of ATP, which are released by the oxidation of 1.31 x10-19 mol of glucose. This represents only 0.0001% of the daily net photosynthetic production of a typical microphytobenthic diatom cell, showing that diel vertical migrations have a negligible impact on cell and ecosystem energy budget. Even though the migration energy cost of individual cells may depart almost two orders of magnitude from the central value presented for a typical diatom (depending on cell size, velocity of displacement and viscosity of the medium), the maximum value calculated is still negligible from the metabolic and ecologic point of view. Results show that behavioural photoprotection might be an energetically cheap mechanism, offering competitive advantages when compared with structural/physiological photoprotection.

Hydroacoustic evaluation of the spatial and temporal distribution of fish in the upstream proximity of a dam in a Neotropical reservoir

Background. Construction of dams alters the physical, chemical, and ecological characteristics of the aquatic environment and modifies fish behaviour and the community composition. Few studies have shown the diel and seasonal fish distribution in tropical reservoirs, mainly in the proximity of the dam, where the risk of injury and death of fishes, which try to migrate downstream, is high. Thus, the data obtained in these regions can encourage actions that may attenuate the impacts on ichthyofauna. Hydroacoustic sampling is an effective tool to study fish behaviour and their spatial distribution in water bodies. In this context, the aim of this study was to evaluate the spatial and seasonal distribution of fish in the reservoir of Três Marias (Minas Gerais, Brazil), immediately upstream of the dam, using hydroacoustic and gillnet sampling. Materials and methods. Hydroacoustics and gillnet sampling were carried out both during the day and at night, and during the rainy and dry seasons. For the acquisition of hydroacoustic data, we employed an echosounder (BioSonics DT-X Digital Scientific) with a split-beam digital transducer. For the biological data, gillnets of different mesh sizes were set. Results. Hydroacoustic data showed significant differences in fish depth between day and night surveys, with fish remaining in deeper water during the day, a phenomenon known as Diel Vertical Migration. Furthermore, hydroacoustic data showed that smaller fish (estimated by “target strength”) concentrate at smaller depths. There was no significant difference in the size of fish between seasons. Limnological and operation variables were not related to the fish  abundance. Distribution maps showed that during the day fishes were distributed in areas more distant from the dam, while at night they were closer to the dam. Gillnets sampled 127 individuals of 22 species and 57.5% of the collected specimens were migratory species. Conclusion. These results can contribute to the understanding of fish behaviour in reservoirs, as well as provide an empirical basis for the development of novel fish management measures for Neotropical dams.

Diel Vertical Variability of the Concentration of Chlorophyll a and Colored Dissolved Organic Matter in Possjet Bay, Sea of Japan

The vertical distribution of the concentration of chlorophyll a (Chl) and colored dissolved organic matter (CDOM), temperature (T), and salinity (S) were studied at two diel stations located at close coordinates and performed at a weekly interval and seven stations spaced 1 mi apart on hydrological section in the shelf zone of Possjet Bay (Sea of Japan) in the autumn of 2014. The Chl concentration was estimated from fluorescence intensity (FChl). In the surface layer of the diel stations, the Chl concentration varied within ± 10% of the mean value. In the water column, a negative correlation of FChl with T and a positive relationship of S with CDOM were established at both stations. At all stations, the maximum Chl concentration occurred under the seasonal pycnocline layer.

Diel Vertical Migrations of Hydrobionts in the Coastal Area of Lake Baikal

The nocturnal migratory complex (NMC) is formed in the coastal pelagic zone of seas and large lakes (including Lake Baikal) due to the diurnal vertical migrations of benthic animals and their mixing with pelagic hydrobionts. Studies of the structure and abundance of the NMC are performed using plankton nets and video surveillance in several areas of Lake Baikal different in abiotic conditions (water temperature, hydrodynamic state, and underwater landscapes) and thus characterized by the local specificity. When NMCs were observed with artificial lighting, the number of amphipods in the frame increased during the first several minutes and then usually slightly decreased. The expediency of applying underwater video observations of NMCs in environmental monitoring is recognized and appropriate guidelines are given.

Variations in Copepod Proteome and Respiration Rate in Association with Diel Vertical Migration and Circadian Cycle.

The diel vertical migration of zooplankton is a process during which individuals spend the night in surface waters and retreat to depth during the daytime, with substantial implications for carbon transport and the ecology of midwater ecosystems. The physiological consequences of this daily pattern have, however, been poorly studied beyond investigations of speed and the energetic cost of swimming. Many other processes are likely influenced, such as fuel use, energetic trade-offs, underlying diel (circadian) rhythms, and antioxidant responses. Using a new reference transcriptome, proteomic analyses were applied to compare the physiological state of a migratory copepod, Pleuromamma xiphias, immediately after arriving to the surface at night and six hours later. Oxygen consumption was monitored semi-continuously to explore underlying cyclical patterns in metabolic rate under dark-dark conditions. The proteomic analysis suggests a distinct shift in physiology that reflects migratory exertion and changes in metabolism. These proteomic analyses are supported by the respiration experiments, which show an underlying cycle in metabolic rate, with a peak at dawn. This project generates molecular tools (transcriptome and proteome) that will allow for more detailed understanding of the underlying physiological processes that influence and are influenced by diel vertical migration. Further, these studies suggest that P. xiphias is a tractable model for continuing investigations of circadian and diel vertical migration influences on plankton physiology. Previous studies did not account for this cyclic pattern of respiration and may therefore have unrepresented respiratory carbon fluxes from copepods by about 24%.

Application of Acoustic Doppler Current Profiler (ADCP) to Observe Diel Vertical Migration of Zooplankton

Study of zooplankton behavior was observed because of their importance as a source energy for small fish and other organisms in the food chain. The aim of this study was to investigate diel vertical migration (DVM) of zooplankton using high frequency acoustic scattering techniques from an acoustic Doppler current profiler (ADCP) instrument. The DVM was observed by utilizing mean volume backscattering strength (MVBS) from the recorded ADCP’s echo intensities. MVBS data were obtained using a bottom-moored, upward looking 750 kHz ADCP at 15 m depth in Lembeh Strait, North Sulawesi, Indonesia. In this work, we simultaneously presented ADCP quantifications, zooplankton net samples, and oceanographic data (tidal and water current). The movement of zooplankton was shallower during the night and deeper during the day with changes of MVBS and ranged between -65 and -80 dB. From laboratory analysis, it was found that crustacean had the highest abundance and biomass, dominated at different time during the observation. However, further research should be performed with specific species using measured sound speed and density of zooplankton and laboratory analysis for grazing angle measurement should be conducted in order to improve accurate results of specific zooplankton.

Zooplankton production and carbon export flux in the western Alboran Sea gyre (SW Mediterranean)

The distribution of marine productivity in the Alboran Sea responds strongly to its hydrodynamics, shaped by the influence of the Atlantic jet that enters through the Gibraltar Strait. This stream originates an oligotrophic western anticyclonic gyre (WAG) that dominates the western basin of the Alboran Sea. We studied vertical (0–900 m) diel changes in zooplankton biomass, potential respiration (electron transport system activity, ETS) and growth rates (aminoacyl-tRNA synthetases activity, AARS), to assess their variability in relation to the WAG structure. Zooplankton biomass was distributed in distinctive layers and we observed strong diel vertical migrations in the open sea. Diel vertical migrants (DVM) biomass, production and respiration rates doubled within the WAG core. The active carbon flux to mesopelagic waters mediated by DVM, estimated from respiration and mortality at depth, increased from the coast (2.0–5.7 mg C m−2 d−1) towards the gyre core (27.1–76.7 mg C m−2 d−1). The WAG enhanced the carbon export to deep waters, reinforcing the role of the Alboran Sea as sink of atmospheric carbon.