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Winter conditions in the NW Mediterranean cause instability of the water column and non-geostrophic dynamics, such as vertical mixing and convection are significant. These events involve nutrient supply to the photic zone that can sustain high productivity. In this study, we aim to investigate the role of winter hydrodynamics on the spawning strategies of Sardina pilchardus and Micromesistius poutassou. Data were obtained on two oceanographic cruises (February 2017 and 2018) off the Catalan coast. The occurrence of S. pilchardus eggs very close to the coast indicated a clear preference of the species for spawning in coastal areas. Preflexion and postflexion larvae exhibited a slightly wider distribution showing a clear association with the cold, less saline and more productive coastal waters. Preflexion larvae of M. poutassou were found on the upper slope and over the shelf, being offshore limited by the shelf/slope front present all along the slope. The front would act as a barrier preventing their dispersion towards the open sea. M. poutassou larvae in advanced developmental stages were located close to the coast in the productive shelf waters, with instabilities of the front contributing to larval transport from offshore waters to the coast. The vertical distribution of both species showed high variability, not only related with the daily cycle or developmental stage, but also with the vertical structure of the water column. Overall, the results provide some clues on how the spawning strategies of both species may evolve under future scenarios of higher winter-stratification, because of the global warming

Myctophids, commonly vertical migrators, and partial and non-migrant stomiiforms constitute most of the mesopelagic biomass, and transport organic matter throughout the food web from the surface to the ocean’s depths. Both the diet and trophic structure of twenty-nine species of mesopelagic fish collected around the Iberian Peninsula were studied through the analysis of stomach contents, quantifying food items with a high taxonomic resolution. The investigation covered oligotrophic to productive habitats, with sampling stations distributed in five discrete zones of the western Mediterranean Sea and the northeastern Atlantic Ocean. The geographic environmental conditions, migratory behavior, and species-specific body sizes allowed for the identification of some major feeding patterns for these fish communities. The trophic niche of migrant myctophids showed a high overlap, with copepods as the primary prey category. The diet composition of generalist myctophids (e.g., Ceratoscopelus maderensis and Hygophum benoiti) reflected the distinct zooplanktonic communities between zones. Large stomiiforms (Chauliodus spp., Sigmops elongatus) preferred feeding on micronekton, while the smallest stomiiforms (e.g., Argyropelecus spp., Cyclothone spp., Vinciguerria spp.) preyed on copepods and ostracods. Given the relevance of the mesopelagic fish communities for commercially exploited species and, therefore, for maintaining the sustainability of the fisheries’ activity in the zones analyzed, the information provided in the present study is essential for a better understanding of the biology and ecology of these species

Mesopelagic fishes play a central role in marine food webs linking primary consumers to top predators. In this study, measures of direct calorimetry were used to analyse the energy density (ED) of 34 mesopelagic species collected at 12 stations in the equatorial and tropical Atlantic. Mean ED ranged from 2.7 kJ g−1 wet weight (WW) for the lanterfish Lampanyctus nobilis to 8.7 kJ g−1 WW for the lanterfish Benthosema glaciale. This study includes species of the orders Myctophiformes and Stomiiformes and represents migrants, non-migrants and partial-migrants species. The majority of the species were grouped into the medium-energy quality category (ED from 4 to 6 kJ g−1); Myctophiformes showed higher energetic values than the Stomiiformes. For the different species, the ED values were discussed in relation to spawning period and energy allocation strategies for reproduction and growth and feeding and migratory behaviour, as well as the ecoregion of study. These values will be useful for future assessment of energetic transfer between trophic levels and energetic modelling of Atlantic ecosystems

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.

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

Dietary and predator–prey studies are more frequently relying on DNA metabarcoding methods, typically achieving results that have a better taxonomic resolution (e.g., species-level) than previous methods. With the continuous advancement in sequencing technology, what was previously accessible only as a large, fixed structure in a laboratory, which had a limited number of users, has now advanced to a small and readily usable device. In this study, we used the gut (content and lining) from juvenile lanternfish (Hygophum) specimens to compare the short-read sequencing capability of the portable Nanopore MinION with the Illumina MiSeq. Primers common in dietary DNA metabarcoding work (COI “Leray primers” and 18S rRNA V4 “Zhan primers”) were used, with an additional comparison of cost-effective COI “Lobo primers” (targeting the same COI fragment) for the proficiency in species detection of a broad range of taxa. Our results indicate high congruency between sequencing machines for, not only taxonomic assignments, but also relative read abundance of the main dietary items. We also identified that Nanopore sequencing is more cost-effective. The Lobo primers are comparable to that of Leray, but substantially reduce the primer set price without compromising detection of taxa. Using both COI and 18S broadened the taxonomic scope, providing greater prey detection. Overall, this preliminary study was successful in creating a foundation for future dietary work involving larvae and transformation stage fishes whereby the content of the gut need not be separated from the gut lining to detect prey. The Hygophum diet detected here aligns with previous research that suggests the main dietary items to be calanoid copepods, but using molecular methods, soft prey was more readily identified compared to studies using visual methods of identification of dietary items. Overall, this study found that Nanopore sequencing is suitable for short-read DNA metabarcoding and can provide rapid acces

This thesis presents novel results on carbon remineralization by the most abundant nonmigrator meso- and bathypelagic fishes on the earth (Cyclothone spp.), on the seasonality of migrant micronekton active flux, on the swimbladder properties of six Cyclothone species inhabiting the meso- and bathypelagic layers in the North Atlantic Ocean and Mediterranean Sea, and on the use of acoustic scattering as a proxy for mesopelagic abundance/biomass. Micronekton is mainly composed of cephalopods, crustaceans and fishes. These organisms represent an important resource for higher trophic levels and are a key component of the biological carbon pump, contributing through diel vertical migrations (DVM) in the case of migrants, and through remineralization in the case of non-migrants. The vertical migrators feed at shallow ocean layers and release carbon at depth through respiration, defecation, excretion, moulting, and mortality. 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, and the seasonality of migrant micronekton active flux. In order to understand the contribution of carbon flux by non-migratory bristlemouth fishes (Cyclothone spp.) and partial migrator (Argyropelecus hemigymnus) we provide the first account of remineralisation by this community in the meso and bathypelagic zones from the oceanic upwelling off Northwest Africa to the south of Iceland (North Atlantic Ocean). We estimated that total carbon remineralisation in the meso and bathypelagic zone by these organisms was about 1%. We also studied the seasonal variability (June and October) of migrant biomass and respiratory carbon flux of numerically dominant pelagic crustaceans and mesopelagic fishes in the Gulf of California, a semi-enclosed sea (North East Pacific). Although this study included a fairly small fraction of

This thesis presents novel results on carbon remineralization by the most abundant nonmigrator meso- and bathypelagic fishes on the earth (Cyclothone spp.), on the seasonality of migrant micronekton active flux, on the swimbladder properties of six Cyclothone species inhabiting the meso- and bathypelagic layers in the North Atlantic Ocean and Mediterranean Sea, and on the use of acoustic scattering as a proxy for mesopelagic abundance/biomass. Micronekton is mainly composed of cephalopods, crustaceans and fishes. These organisms represent an important resource for higher trophic levels and are a key component of the biological carbon pump, contributing through diel vertical migrations (DVM) in the case of migrants, and through remineralization in the case of non-migrants. The vertical migrators feed at shallow ocean layers and release carbon at depth through respiration, defecation, excretion, moulting, and mortality. 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, and the seasonality of migrant micronekton active flux. In order to understand the contribution of carbon flux by non-migratory bristlemouth fishes (Cyclothone spp.) and partial migrator (Argyropelecus hemigymnus) we provide the first account of remineralisation by this community in the meso and bathypelagic zones from the oceanic upwelling off Northwest Africa to the south of Iceland (North Atlantic Ocean). We estimated that total carbon remineralisation in the meso and bathypelagic zone by these organisms was about 1%. We also studied the seasonal variability (June and October) of migrant biomass and respiratory carbon flux of numerically dominant pelagic crustaceans and mesopelagic fishes in the Gulf of California, a semi-enclosed sea (North East Pacific). Although this study included a fairly small fraction of

This file provides a list of mesopelagic species of cephalopods, decapods and teleostean fish, likely to occur in the northeastern Atlantic Ocean (central and north) and Mediterranean Sea, according to literature

Mesopelagic organisms play a crucial role in marine food webs, channelling energy across the predator-prey network and connecting depth strata through their diel vertical migrations. The information available to assess mesopelagic feeding interactions and energy transfer has increased substantially in recent years, owing to the growing interest and research activity in the mesopelagic realm. However, such data have not been systematically collated and are difficult to access, hampering estimation of the contribution of mesopelagic organisms to marine ecosystems. Here we present MesopTroph, a georeferenced database of diet, trophic markers, and energy content of mesopelagic and other marine taxa compiled from 203 published and non-published sources. MesopTroph currently includes data on stomach contents, carbon and nitrogen stable isotopes, major and trace elements, energy density, fatty acids, trophic positions, and diet proportion estimates for 498 species/genera. MesopTroph will be expanded with new data emerging from ongoing studies. MesopTroph provides a unique tool to investigate trophic interactions and energy flow mediated by mesopelagic organisms, and to evaluate the ecosystem services of this community.

Mesopelagic organisms play a crucial role in marine food webs, channelling energy across the predator-prey network and connecting depth strata through their diel vertical migrations. The information available to assess mesopelagic feeding interactions and energy transfer has increased substantially in recent years, owing to the growing interest and research activity in the mesopelagic realm. However, such data have not been systematically collated and are difficult to access, hampering estimation of the contribution of mesopelagic organisms to marine ecosystems. Here we present MesopTroph, a georeferenced database of diet, trophic markers, and energy content of mesopelagic and other marine taxa compiled from 203 published and non-published sources. MesopTroph currently includes data on stomach contents, carbon and nitrogen stable isotopes, major and trace elements, energy density, fatty acids, trophic positions, and diet proportion estimates for 498 species/genera. MesopTroph will be expanded with new data emerging from ongoing studies. MesopTroph provides a unique tool to investigate trophic interactions and energy flow mediated by mesopelagic organisms, and to evaluate the ecosystem services of this community.

The Marine Biological Reference Collections (CBMR) are specialized mainly in Chordata (fish), Arthropoda and Mollusca, mostly from the Mediterranean Sea, but also with important contributions from the Atlantic Ocean and the rest of the world’s oceans

Most mesopelagic fishes perform large diel vertical migrations from the deep-sea zone to the surface. Although there is a trade-off between a higher food availability at the upper layers and an energy cost and predation risk, incursion towards the surface also implies a transport by currents, where the fish are exposed to a stranding risk on the coast. Here, we reported the first documented stranding of mesopelagic fishes along the southeast shore of Gran Canaria Island. Our study hypothesized that (1) the influence of the Canary Current, (2) the dominant incidence of the Trade Winds during summer, and (3) the presence of an upwelling filament coupled with an anticyclonic eddy south of Gran Canaria Island were the causative mechanisms of the strandings. Diaphus dumerilii (Myctophidae family) was the main species found as observed from an external morphological analysis using traditional taxonomy. The otolith contour analysis suggested the presence of other Diaphus spp. and Lobianchia dofleini. Nevertheless, the otolith morphological features described in the literature suggested that all the specimens were actually D. dumerelii. Errors in the identification were mainly due to the high intraspecific variability found in the otolith morphology. Even so, two patterns of oval and elliptic shapes were described with significant differences in its morphometry

Mesopelagic organisms play a crucial role in marine food webs, channelling energy across the predator-prey network and connecting depth strata through their diel vertical migrations. The information available to assess mesopelagic feeding interactions and energy transfer has increased substantially in recent years, owing to the growing interest and research activity in the mesopelagic realm. However, such data have not been systematically collated and are difficult to access, hampering estimation of the contribution of mesopelagic organisms to marine ecosystems. Here we present MesopTroph, a georeferenced database of diet, trophic markers, and energy content of mesopelagic and other marine taxa compiled from 203 published and non-published sources. MesopTroph currently includes data on stomach contents, carbon and nitrogen stable isotopes, major and trace elements, energy density, fatty acids, trophic positions, and diet proportion estimates for 498 species/genera. MesopTroph will be expanded with new data emerging from ongoing studies. MesopTroph provides a unique tool to investigate trophic interactions and energy flow mediated by mesopelagic organisms, and to evaluate the ecosystem services of this community

Sota les onades de l’oceà es belluguen una immensitat d’organismes. Molts els coneixem però, t’has imaginat mai que alguns arribin a ser tan petits que no poden ser vistos a ull nu? Submergeix-te en el mar d’espècies que es deixen portar pel vaivé de les onades. Descobriràs el plàncton, un món fascinant!

The oceanic mesopelagic or twilight zone (from 200 to 1000 m depth) is inhabited by a huge variety of organisms represented by several zoological groups, both vertebrates and invertebrates. These mesopelagic species play an important role in oceanic predator-prey interactions. They all constitute the most important food elements for larger top predators, fish and mammals, and they are themselves also predators of primary consumers (small zooplankton). Thus, mesopelagic ecological communities are generally composed by small-sized organisms present in high abundances. Concerning size, the most numerous and diverse taxa are named as macrozooplankton, (which prey on smaller zooplankton, and micronekton comprising small fish, shrimps, and cephalopods (which prey on macroplankton). Other organisms, less abundant but with higher biomass, such as for example some eels, oar fish, and even some cartilaginous fish, as well of some large cephalopods, also are part of the mesopelagic fauna. [...]

Lanternfishes are the dominant component of mesopelagic fishes living in the ocean between 200 and 1000 m depth, playing a key role in the food web of oceanic ecosystems (Catul et al., 2011). Most mesopelagic fishes perform large diel vertical migrations from the deep-sea zone, where they stay during the day, to the surface where they feed at night, thereby transporting the ingested carbon in the upper productive waters to deep layers. Although there is a trade off between higher food availability at the upper layers and energy cost and predation risk, the incursions towards the surface also implies a transport by currents where they are exposed to stranding risk on the coast. This is especially important in the narrow shelves of oceanic islands where the shelf slope is nearshore. In the present study, we report the stranding of numerous myctophids along the shore of the southeast of Gran Canaria Island during June 2021. In previous studies (Battaglia et al., 2017), mesopelagic fishes strandings were frequently reported at the Sicilian coast (Strait of Messina, central Mediterranean Sea). However, this phenomenon has never been recorded in the Canary Islands coast (Central-East Atlantic). This study provides biological information on the species found, as well as the oceanographic conditions promoting the strandings. A subsample of the better-preserved specimens was used to identify the species, and morphometrics of the body (standard length, SL in mm) and of the sagittae otoliths. The remaining specimens, due to their bad conservation status, were identified through otoliths using the online AFORO web (Lombarte et al., 2006). Temperature, salinity, dissolved oxygen, and net primary production were obtained from Copernicus Marine Environment Monitoring Service (CMEMS) with the aim to understand the oceanographic conditions and discuss the causes of the stranding

Mesopelagic organisms play a crucial role in marine food webs, channelling energy across the predator-prey network and connecting depth strata through their diel vertical migrations. The information available to assess mesopelagic feeding interactions and energy transfer has increased substantially in recent years, owing to the growing interest and research activity in the mesopelagic realm. However, such data have not been systematically collated and are difficult to access, hampering estimation of the contribution of mesopelagic organisms to marine ecosystems. Here we present MesopTroph, a georeferenced database of diet, trophic markers, and energy content of mesopelagic and other marine taxa compiled from 203 published and non-published sources. MesopTroph currently includes data on stomach contents, carbon and nitrogen stable isotopes, major and trace elements, energy density, fatty acids, trophic positions, and diet proportion estimates for 498 species/genera. MesopTroph will be expanded with new data emerging from ongoing studies. MesopTroph provides a unique tool to investigate trophic interactions and energy flow mediated by mesopelagic organisms, and to evaluate the ecosystem services of this community.

This study examines vertical distribution of the early stages of mesopelagic fishes in the south-eastern Indian Ocean and oceanographic factors that may affect it. This investigation along the 110 °E transect formed part of the second International Indian Ocean Expedition (IIOE-2). Depth-stratified samples to 500 m depth of early stages of mesopelagic fishes were obtained by means a multinet EZ-1 m2. This net captured larvae and transforming stages, but juveniles and adults were also caught, particularly at night. Diel vertical patterns of the different species and stages were analysed relative to the oceanographic conditions encountered at the 20 stations along the transect. This paper provides the ranges of vertical occurrence and weighted mean depth for larvae (135 taxa), and post-metamorphic stages (75 taxa) of fishes caught during the survey. Despite the varying vertical profiles of oceanographic parameters encountered, there were consistent patterns within species and families along the transect, with broader vertical distribution of larvae at the southern stations, where the upper mixed layer was deeper. During both day and night, larval stages of all the species were concentrated in the epipelagic zone, with some differences in terms of weighted mean depth (WMD) between taxa, but with no significant differences in vertical location between day and night. Transforming and juvenile-adult stages, however, presented a wider vertical distribution range than larval stages, and showed important differences among families and species. For example, Myctophidae and Phosichthyidae species presented the highest concentrations in the upper 50–100 m at night, and a much deeper distribution during the day, thereby indicating night vertical migration behaviour of transforming and juvenile-adult stages. By contrast, during these stages the Gonostomatidae Cyclothone spp. and the Sternoptychidae Argyropelecus spp. occurred deeper than the epipelagic layer during both day and n

As part of the second International Indian Ocean Expedition, an oceanic transect from 39.5°S to 11.5°S along 110°E in the south-eastern Indian Ocean enabled concurrent oceanographic measurements and sampling of early stages of mesopelagic fishes within the upper 500 m of the water column. Notable oceanographic features along the generally oligotrophic transect included an increase in surface water temperature from 12 to 28 °C from south to north and low salinities at both ends of the transect. High salinity Subtropical Surface Water was evident over the central part of the transect and low dissolved oxygen occurred at depth at the northern end where tropical waters were influenced by the Indonesian Throughflow. Throughout the study region larval fish stages were generally concentrated in the epipelagic zone. Species richness, abundance and diversity of fishes (n = 166 species) increased towards the tropical waters. The families Myctophidae (lanternfishes; 60 species), Phosichthyidae (lightfishes; 2 species) and Gonostomatidae (bristlemouths; 5 species) were numerically dominant. Clustering of integrated abundance data (0–500 m depth) revealed four major fish assemblages along the transect. When linked to oceanographic variables, multivariate multiple regression indicated that surface temperature, surface salinity and dissolved oxygen at 400 m depth provided the best fitting model explaining fish distribution patterns. Where possible, comparisons have been made with early data collected along this 110° E line in the 1960s during the first International Indian Ocean Expedition

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).

Un relat que ens apropa a la ciència per generar consciència. Escoltem, compartim, descobrim i creem!

Mesopelagic fish populations are characterised by high species richness and abundance, and have been identified as important contributors to the active carbon fluxes in the open ocean. We report variability in communities of mesopelagic fish between five zones around the Iberian Peninsula, i.e. Balears and Alboran in the Mediterranean, and Cadiz, Lisboa and Galicia in the Atlantic. Day and night samples were collected from 7 layers of the water column with a midwater trawl fitted with a multisampler. Temperature and salinity regimes were very different on the Mediterranean and Atlantic sides of the peninsula, with much higher values through the entire water column in the Mediterranean, characterized by a strong pycnocline. The highest productivity was observed off Lisboa, where Chlorophyll a concentrations were two orders of magnitude higher than in any other zone. Samples from the western Mediterranean held 22 fish species, while 67 were found in the Atlantic. The lowest diversity and the highest dominance were observed in Balears, and the highest diversity in Cadiz zone. In all zones, but particularly in those in the Mediterranean, mesopelagic populations were dominated by a high number of small fish with low individual biomasses. The species Benthosema glaciale, Cyclothone pygmaea and Ceratoscopelus maderensis were common in the Mediterranean populations, whereas in the Atlantic, Cyclothone microdon/livida, Valenciennellus tripunctulatus, Ceratoscopelus warmingii and Benthosema suborbitale were the most common species. Temperature and salinity (both at surface and in the mesopelagic zone) were the main environmental factors explaining variability in assemblage composition. A persistent (day-night) deep scattering layer was observed using the vessel-based echosounder in all zones, and was comprised primarily of the gonostomatid Cyclothone spp. Night-time echosounder observations of scattering layers near the surface were observed in Balears, Alboran, Cadiz and Lis

The biological carbon pump is the process that transports carbon vertically out of the mixed layer in the ocean. Besides the sinking flux of organic particles, active flux due to the daily vertical migration of zooplankton and micronekton promotes a significant carbon transport not fully accounted for or understood in the world’s oceans. The diversity and abundance of epipelagic and mesopelagic species in the Gulf of California has been extensively studied, but the role of micronekton in carbon export has not yet been investigated. We studied the carbon flux promoted by juvenile and adult mesopelagic fishes and crustaceans (Decapoda and Euphausiidae) during the transition from the cold to warm period (June) and the onset of the warm season (October) in 2018. We provide the first estimation of migrant biomass and respiratory flux of the most abundant migratory species of mesopelagic fishes, decapods and euphausiids in the Gulf of California. The micronekton species collected accounted for a large biomass of mesopelagic fishes and pelagic crustaceans. The average migrant biomass estimates were 151.5 ± 101.2 mg C·m−2 during June and 90.9 ± 75.3 mg C·m−2 during October. The enzymatic activity of the electron transfer system (ETS) was measured as an estimate of their respiratory rates. Average specific ETS activity was significantly different between fishes and decapods, and between fishes and euphausiids (p < 0.05). The respiratory flux of fishes was predominant in the Gulf of California, followed by pelagic decapods and euphausiids. Seasonal changes in respiratory flux were observed for fishes (June: 6.1 ± 1.5 mg C·m−2·d−1; October: 3.2 ± 1.8 mg C·m−2·d−1) and decapods (June: 0.4 mg C·m−2·d−1; October: 0.7 ± 0.05 mg C·m−2·d−1). Respiratory flux estimation by crustaceans (decapods and euphausiids) and fishes together was 6.86 mg C·m−2·d−1 during June, and 4.21 mg C·m−2·d−1 during October 2018, suggesting a functional role of this large micronektonic fauna in the biologi

[EN] The early life history of fish is the period that elapses from spawning to recruitment into the adult population (Figure 1). These early stages –eggs and larvae– are a key component in the fish life cycle because their survival success determines both short- and long-term variations in population abundance. Most marine fishes produce thousands to millions of pelagic eggs, which in a few days hatch into larvae that spend weeks to months in the plankton. Fish larvae are characterized by their small size (a few mm to ca. 2 cm), transparency and limited swimming skills, and they display amazing shapes that differ greatly from those of adults (Figure 2). During the planktonic period, fish larvae interact with other planktonic organisms as both predators and prey (Figure 1): feeding upon small prey such as juvenile stages of copepods and, in turn, being preyed on by larger nektonic and planktonic organisms such as jellyfish. […], [ES] Las primeras etapas del ciclo vital de los peces comprenden el periodo desde la puesta hasta el reclutamiento a la población adulta (figura 1). La supervivencia de estos estadios tempranos del desarrollo, los huevos y las larvas, determina las variaciones, a corto y largo plazo, en la abundancia de sus poblaciones. La mayoría de peces marinos producen entre miles y millones de huevos pelágicos que en pocos días eclosionan dando lugar a larvas que pasan desde semanas a unos pocos meses en la comunidad planctónica. Las larvas de peces se caracterizan por su pequeño tamaño (entre pocos mm y unos 2 cm), su transparencia, una limitada capacidad natatoria, y una morfología, en ocasiones sorprendente, que difiere notablemente de la de los adultos (figura 2). Durante el periodo planctónico, las larvas interactúan con otros organismos del plancton, siendo tanto depredadores como presas (figura 1). Las larvas de peces se alimentan de organismos de pequeño tamaño, como estadios juveniles de copépodos (pequeños crustáceos), y, a su vez, son presa de otras especies más grandes que viven también en el medio pelágico, como las medusas. […], [CAT] Les primeres etapes del cicle vital dels peixos comprenen el període des de la posta fins al reclutament a la població adulta (figura 1). La supervivència d’aquests estadis inicials del desenvolupament, els ous i les larves, determina les variacions, a curt i llarg termini, en l’abundància de les seves poblacions. La majoria de peixos marins produeixen entre milers i milions d’ous pelàgics que en pocs dies eclosionen i donen lloc a larves que passen des d’unes setmanes fins a uns pocs mesos en la comunitat planctònica. Les larves de peixos es caracteritzen per tenir una mida petita (de pocs mm a 2 cm), la seva transparència, una limitada capacitat natatòria, i una morfologia, a vegades sorprenent, que difereix notablement de la dels adults (figura 2). Durant el període planctònic, les larves interactuen amb altres organismes del plàncton, sent tant depredadors com preses (figura 1). Les larves de peixos s’alimenten d’organismes de mida petita, com per exemple estadis juvenils de copèpodes (petits crustacis), i, al seu torn, són presa d’altres espècies més grans que viuen també en el medi pelàgic, com les meduses. […]

Microbial trophic steps were largely ignored in the estimations of trophic position of consumers. Recent developments in compound-specific stable isotope studies showed that the microbial exchanges may no longer be invisible. Using 24 species of mesopelagic and bathypelagic fishes collected in the North Atlantic, this study applied the analysis of nitrogen isotopes in amino acids to the estimation of their trophic position and of the contribution of microbial and metazoan trophic steps across depth layers. Isotope-based estimates agreed well with diet-based literature values, but the consideration of microbial steps reduced the mismatch between 0.5 and 0.8 trophic positions observed when only the metazoan food web is considered. Microbial trophic steps contributed between 6 to 21% to the overall trophic position of individual species. Body size was positively correlated with trophic position but not with the relative contribution of microbial trophic steps, except in the mesopelagic layer where the microbial contribution decreased with size. These results suggest that current isotope-based estimates of trophic position for marine consumers underestimate true trophic positions because they are based on metazoan-only trophic steps

[EN] The age and growth patterns of the mesopelagic fish Ceratoscopelus maderensis (family Myctophidae) of the western Mediterranean Sea were described throughout its entire life cycle (from larvae to adult stages) using the sagittae otoliths of 59 individuals collected in December 2009. Three characteristic zones were identified along the cross-section of the sagittae (larval, metamorphic and juvenile-adult zones). Assuming growth rings as daily increments, the age of the analysed individuals (from 3.5 to 64 mm standard length [SL]) would range from 7 to 332 days. The relationship between the number of increments and the fish SL was fitted to a von Bertalanffy growth model (SL=70.5899×(1–exp(–0.0501(t+2.6705))). The growth pattern of C. maderensis in the western Mediterranean Sea was similar to that reported for this species in the northeast Atlantic Ocean. Though from a body size of 40-45 mm SL, growth rates declined more slowly in individuals from the western Mediterranean Sea, growth differences between these individuals and those from the northeast Atlantic Ocean were not statistically significant. This study provides new insights into the age and growth patterns of one of the most abundant mesopelagic fish species in the Mediterranean Sea that have clear implications for the study and management of marine ecosystems, [ES] En el presente trabajo se describen la edad y los patrones de crecimiento desde la fase larvaria hasta la fase adulta del pez mesopelágico Ceratoscopelus maderensis (familia Myctophidae) del Mediterráneo occidental. Para ello, se analizó el otolito sagitta de 59 individuos capturados en diciembre de 2009. Se identificaron tres zonas en la sagitta, cada una de las cuales se corresponde con una fase del desarrollo ontogenético del pez: larvaria, metamórfica y juvenil-adulta. Asumiendo que los anillos de crecimiento son diarios, la edad de los individuos analizados (de 3.5 a 64 mm de longitud estándar [SL]) oscilaría entre 7 y 332 días. La relación entre el número de incrementos y la SL de los peces se ajustó al modelo de crecimiento de von Bertalanffy (SL=70.5899×(1–exp(–0.0501(t+2.6705))). El patrón de crecimiento de C. maderensisen el Mediterráneo occidental fue similar al previamente descrito para esta especie en el Noreste del Océano Atlántico. A pesar de que, a partir de 40-45 mm SL, las tasas de crecimiento disminuyeron más lentamente en los individuos del Medi-terráneo occidental, las diferencias de crecimiento entre estos individuos y los del Noreste del Océano Atlántico no fueron estadísticamente significativas. Los resultados de este estudio aportan nuevos conocimientos sobre la edad y el crecimiento de una de las especies más abundantes del Mar Mediterráneo, lo cual tiene claras implicaciones de cara al estudio y la gestión de los ecosistemas marinos

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

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

The sustainable management of marine life is essential for the well-being of present and future human generations as it plays a crucial role in the Earth’s climate and biogeochemical cycles regulation, food security and coastal protection and provides many other goods and services of socio-economic and cultural value to humans. We identify the key scientific challenges where major research advances are needed to ensure well managed resilient living oceans in the coming decades from deep to coastal ecosystems.

Oceans cover 71% of the Earth’s surface. Most of the solar radiation is absorbed by the oceans. The way the oceans use and distribute this radiation affects the Earth’s weather and climate. Advances in our knowledge of the interplay between air-sea interactions, mechanical turbulent mixing and the biological carbon pump remain key to understanding the past, present and future climate scenarios of Earth

This document presents the State of Fisheries in Catalonia between October 2019 and December 2020, both inclusive. It was produced by the Catalan Institute for Ocean Governance Research (ICATMAR), which is a cooperation organism between the Directorate-General of Maritime Policy & sustainable fisheries of the Government of Catalonia and the Institute of Marine Sciences (ICM) of the Spanish National Research Council (CSIC)

This document presents the State of Fisheries in Catalonia between October 2019 and December 2020, both inclusive. It was produced by the Catalan Institute for Ocean Governance Research (ICATMAR), which is a cooperation organism between the Directorate-General of Maritime Policy & Sustainable Fisheries of the Government of Catalonia and the Institute of Marine Sciences (ICM) of the Spanish National Research Council (CSIC)

SUMMER “Sustainable Management of Mesopelagic Resources". The project is part of the H2020 Program of "Food security, sustainable agriculture, marine and maritime research and bioeconomy" and covers ecological aspects of mesopelagic communities. A fundamental part of this research lies in obtaining samples of plankton and micronekton from the mesopelagic zone to the epipelagic layers, acoustic records in the same places, and information on the hydrographic parameters throughout the water column. The survey will have 2 main study sites in eastern Iberia- western Mediterranean sea (oligotrophic region), and 2 more in western Iberia (productive region). In each of the 4 sites repeated samples will be performed day and night during 3 journeys. From Cape San Vicente to Lisbon latitude, the work will focus on the location of Eddies of Mediterranean water (MEDIS), therefore CTDs will be the priority. To study the influence on these MEDIS on mesopelagic populations, plankton hauls will be also performed in particular locations. We foresee to spend at least 3 days per study site. Two days (day and night) will be devoted to sample micronekton (small fishes, crustaceans, cephalopods etc) and mesozooplankton in the water column (from the mesopelagic to the epipelagic zone). Then, to obtain more accurate view of the migratory populations, one of the journeys will focus on the study of surface layer

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

Mesopelagic fishes of the southeastern Indian Ocean are represented by a high number of lanternfish species (Myctophidae). The horizontal distribution patterns of their larvae have been previously studied; however, research on larval feeding habits is non-existent. The goal of this study was to describe the diet and trophic-based strategies of the most abundant myctophid larvae off Western Australia through stomach content analysis. Samples were collected in autumn 2007 off southwestern Australia when this oligotrophic area was under the influence of the seasonal Leeuwin Current, and in autumn 2010 on the tropical continental shelf of northwestern Australia. The species investigated during these periods were Benthosema fibulatum, B. pterotum, B. suborbitale, Dasyscopelus asper, Diaphus “deep” and “slender” morphotypes, Hygophum hygomii, Lampadena luminosa, Lampanyctus alatus, Lampanyctus spp. and Myctophum sp. Generally, myctophid larvae showed a diurnal feeding pattern. Only postflexion stages in L. alatus, L. luminosa, B. pterotum, Diaphus “slender”, and Myctophum sp. preyed at dawn or during the night. The highest feeding incidence was found in L. luminosa and the Diaphus “deep” morphotype, while the lowest, in H. hygomii. Generally, larvae were zooplankton feeders with nauplii and copepodites being the most abundant dietary groups, except for B. suborbitale and Myctophum sp. where the small non-calanoid genus Oncaea was dominant. Soft organisms such as appendicularians were frequent items in most fish diets throughout their entire larval phase, and highly abundant in Diaphus “deep” morphotype. The wide prey-size spectrum indicates that the majority of the fish species were not size-specific feeders for most of their larval life. Nevertheless, B. suborbitale, B. fibulatum, and L. alatus preferred larger prey, ignoring the smaller items as they grew. Larval feeding patterns of similar genera from other ecosystems are discussed and compared with those in Western Au

Adult and juvenile myctophids feed at night in the epipelagic zone (<200 m) and are more dispersed in the mesopelagic zone (200-1000 m) during the daylight hours. In contrast, larvae inhabit the upper 200 m throughout a 24 h period and have daylight feeding patterns. Transforming stages occur both at the surface and in the mesopelagic zone and show less-defined feeding patterns. In this study, we analysed the trophic ecology of transforming and juvenile stages of 4 myctophids that occupy the neustonic layers (first 0-20 cm of the water column) during their nightly vertical migrations: Dasyscopelus asper, Gonichthys cocco, Myctophum affine, and M. nitidulum. Day and night neuston samples were collected across the equatorial and tropical Atlantic in April 2015. Transforming and juvenile stages occurred at night in the neuston, where they fed, but were absent from this layer during the day. The highest prey ingestion was observed between 01:00 and 04:00 h (UTC). Feeding incidence and the number of prey ingested increased from transformation stages to juvenile stages. Although the maximum prey size increased with fish body length, there was no significant increasing trend in mean prey sizes, but a great variability in the sizes of consumed prey. Diets of the 4 species mainly comprised a variety of copepod genera, usually dominated by Oncaea species. There was no evidence of resource partitioning among the 4 myctophid species. Estimates of daily feeding rations, based on the relationship between carbon content per gut and carbon content of fish body, throughout the night feeding period, showed that these species in these early stages ingested between 0.43 and 5.78% of their body carbon weight daily. We suggest that the occurrence and feeding of these early stages in the neuston may contribute to reducing trophic competition between migrating myctophids by space segregation

En aquest informe es presenta l’Estat de les Pesqueres a Catalunya entre novembre del 2018 i setembre del 2019 ambdós inclosos i ha estat realitzat per l’Institut Català de Recerca per a la Governança del Mar (ICATMAR), un òrgan de cooperació entre la Direcció General de Pesca i Afers Marítims del Departament d’Agricultura, Ramaderia, Pesca i Alimentació (DARP) de la Generalitat de Catalunya i l’Institut de Ciències del Mar (ICM) del Consejo Superior de Investigaciones Científicas (CSIC)

Length–weight relationships (LWRs) were estimated for 36 mesopelagic fish species collected from the equatorial and tropical Atlantic encompassing several oceanographic regions: oligotrophic, equatorial, Cape Blanc, Cape Verde and the Canary Islands. The sample was composed of myctophids (25 species), gonostomatids (5), sternoptychids (3), stomiids (2) and phosichthyids (1). The species were clustered according to body shape: “short‐deep” (sternoptychids), “elongate” (gonostomatids, stomiids and some phosichthyids) and “fusiform” (myctophids and some phosichthyids). Three types of weight and LWRs were considered: wet weight (WW ), eviscerated wet weight (eWW ) and eviscerated dry weight (eDW ). The study demonstrated that most species present a positive allometric growth, independent of the weight used. However, the allometric value varied in 40–50% of species depending on the type of weight considered. Significant variations linked to fish morphology were found in the relationship between the slope and intercept of the LWR equation. Significant differences were also noted in the water content linked to fish body shape. Based on the distributions of several species we compare their fitness between oceanographic regions using the relative condition factor (K rel). Except for Diaphus brachycephalus (oligotrophic vs. equatorial waters) and Lampanyctus alatus (equatorial, Cape Blanc, Cape Verde and the Canary Islands), no regional significant differences were observed in the species analysed

The mesopelagic layer is one of the least understood ecosystems on Earth. Recent research suggests that the fish biomass in the mesopelagic ecosystem might be 10 times higher than previously thought. However, this estimate is subject to a high degree of uncertainty in the fraction of the community that is fish. The potential high biomass has raised interest in its exploitation. Nevertheless, if the biomass is as high as estimated, mesopelagic fish may play a key role in ecosystem services, such as sustaining other commercially relevant species, and on carbon sequestration. Combining trawls, in situ acoustics and eDNA, SUMMER seeks to obtain an accurate assessment of the composition and biomass of the mesopelagic community. Gut content analysis, molecular markers and stable isotopes will allow quantification of the vertically integrated trophic network, linking to commercial and charismatic species. Models will be used to estimate the impact of fishing scenarios on trophic network stability and carbon sequestration. Mesopelagic organisms will be tested for their potential as fish meal, nutra and pharmaceuticals. The project will develop a decision support tool to enable accounting for trade-offs between services in when considering sustainable use of mesopelagic resources

In the eastern Indian Ocean, the Kimberley region off north-western Australia is characterised by a wide continental shelf, complex coastal topography and very large tides (>10 m). Diversity of fishes is high although little is known about the distribution of their larvae in this dynamic region. This study investigated spatial variation in ichthyoplankton assemblages along four coastal-oceanic transects and related the results to tidal cycles and other environmental variables. Larvae representing 92 neritic and 21 mesopelagic teleost families were collected; this far exceeds the diversity described for other comparable tropical continental shelf and oceanic systems. Distinct ichthyoplankton assemblages characterised inner shelf (Engraulidae and Gobiidae were dominant families), outer shelf / slope (mixed neritic and mesopelagic taxa) and oceanic waters (mesopelagic taxa, particularly Myctophidae, Gonostomatidae and Phosichthyidae), and were correlated with changes in environmental variables (water depth, seawater density, mixed layer depth and zooplankton). The spring-neap tidal cycle and subsequent tides (same stations sampled 12 h apart) had no significant influence on larval fish assemblages. Coastal waters were delineated by a density front and larval fish assemblages were significantly different from offshore assemblages. This study provides new insights into the pelagic ecosystem in the tropical eastern Indian Ocean and contributes to the understanding of the role of environmental variables and physical forcing in the structuring of larval fish assemblages

[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

In the eastern Indian Ocean, the Kimberley region off north-western Australia is characterised by a wide continental shelf, complex coastal topography and very large tides (>10 m). Diversity of fishes is high although little is known about the distribution of their larvae in this dynamic region. This study investigated spatial variation in ichthyoplankton assemblages along four coastal-oceanic transects and related the results to tidal cycles and other environmental variables. Larvae representing 92 neritic and 21 mesopelagic teleost families were collected; this far exceeds the diversity described for other comparable tropical continental shelf and oceanic systems. Distinct ichthyoplankton assemblages characterised inner shelf (Engraulidae and Gobiidae were dominant families), outer shelf / slope (mixed neritic and mesopelagic taxa) and oceanic waters (mesopelagic taxa, particularly Myctophidae, Gonostomatidae and Phosichthyidae), and were correlated with changes in environmental variables (water depth, seawater density, mixed layer depth and zooplankton). The spring-neap tidal cycle and subsequent tides (same stations sampled 12 h apart) had no significant influence on larval fish assemblages. Coastal waters were delineated by a density front and larval fish assemblages were significantly different from offshore assemblages. This study provides new insights into the pelagic ecosystem in the tropical eastern Indian Ocean and contributes to the understanding of the role of environmental variables and physical forcing in the structuring of larval fish assemblages

Mesopelagic fish of the eastern Indian Ocean are represented by a high number of myctophid species. The horizontal distribution patterns of their larvae have been previously studied; however research on larval feeding habits is non-existent. The main goal of this study is the description of the diet for the most abundant myctophid larvae off Western Australia: Benthosema suborbitale; B. fibulatum; B. pterotum, Lampadena luminosa, Hygophum hygomii, Lampanyctus alatus, Myctophum asperum, M. obtusirostre, M. selenops, and Diaphus spp. >deep> and >slender> morphotypes. The study region is an oligotrophic area under the influence of the Leeuwin Current for part of the year, such as in the period of study, autumn 2007. Myctophid larvae were diurnal feeders, and only a few postflexion individuals prey at dawn or night-time. Feeding incidence was higher in postflexion than earlier stages, and in larvae with saccular guts than in those with straight guts. The highest feeding incidence was found in L. luminosa and Diaphus spp. >deep-morphotype>, and the lowest in H. hygomii. Larvae were zooplankton feeders, with nauplii and copepodites being the most important groups in their diet. In general, the species with straight guts fed mainly on nauplii and those with saccular guts had a wider variety of prey categories. Some species such as B. pterotum and M. obtusirostre fed also over larval-stage euphausiids and on small amphipods. Presence of soft prey such as larvaceans was also observed in the guts of Diaphus >slender morphotype>. The wide prey size spectrum observed in larvae of many species indicated that they are generalist for most of their larval life e.g., M. obstusirostre, others such as L. alatus and Diaphus spp., preferred larger prey items, disregarding the small ones as they growth. Comparisons with larval feeding patterns of similar species from other ecosystems were discussed on the light of the environmental features of the region

Blue whiting, Micromesistius poutassou, is a gadoid widely distributed in the North-Atlantic Ocean and Mediterranean Sea. The Mediterranean population is considered isolated from the Atlantic Ocean, and in the northern Catalan coast (NW Mediterranean Sea) it is a species of high commercial interest. In this area, fluctuations in the abundance of blue whiting have been related to interannual variations in winter hydrodynamics. These, in turn, lead to fluctuations in primary production that, may then determine changes the survival of early life stages. For this reason, understanding food web interactions during the larval stage is pivotal to predict the success of recruitment to adult fish populations. In order to approach this subject, we studied the trophic ecology of blue whiting larvae by combining stomach content and stable isotopic analyses, in the Catalan coast, during two consecutive winters of contrasted environmental conditions. The specific aims were: (1) to analyse the diet composition of blue whiting larvae; (2) to assess the likely interannual differences in diet in relation to winter conditions and (3) to examine the trophic structure and relationships among blue whiting larvae and the biomass-dominant plankton items. The stomach content of blue whiting larvae (2-34 mm SL), collected day and night, was analysed and prey were measured and identified to the lowest taxon possible. Prey carbon content was estimated from size data using taxon-specific allometric equations. The stable isotope analyses were conducted in blue whiting larvae at different ages (preflexion, flexion and postflexion stages), in fractionated plankton samples, and in the most abundant planktonic groups

The species composition, distribution and abundance of meso- and bathypelagic species from oceanic waters of the NE Atlantic have been analysed to investigate the modifications in vertical distribution patterns from larvae to adult stages. Plankton and micronekton samples from surface to 1800 m depth, were taken in May 2018 in 8 stations placed in a transect from 20°N to 55°N. The transect crossed intense productivity, thermal and salinity gradients, from the North Atlantic Subtropical Gyral Province (NASGP) to the north Atlantic Artic Province (NAAP). Hydrographical boundaries were evident in the species composition and abundance, with lower diversity in the northernmost station in the NAAP. Larvae and transforming stages of myctophiforms and stomiiforms dominated all over the region. Although the Brunt-Väisälä frequency indicates higher water column stability in the NASGP stations than in the north, vertical distributions were similar along the region. Myctophid larvae were always concentrated in the first 100 m, irrespective of the time of the day. Their transforming stages occurred from surface to 1200 m at night (with no clear migration), and from 400-700 during the day. Stomiiform larvae appeared in the upper 200 m, while transforming showed a wide distribution from surface to 1000 m both day and night. The distribution of the gonostomatid Cyctothone (7 species) is an interesting case of study with larvae always in the upper 100 m, and non-migrating juvenile and adults located in the mesopelagic zone (even reaching the bathypelagic layers in the case of C. microdon). As in previous investigations, it was globally observed that the deepening in the water column is an ontogenetic process related with development that starts when ventral groups of photophores become formed. The wider vertical distribution of this transition stages compared to both larva and adult indicates that they have not developed yet the vertical displacement characteristic of adult stages

Winter conditions in the NW Mediterranean cause instability of the water column and non geostrophic dynamics, such as vertical mixing and convection, are significant. These events contribute to renew nutrients at the photic zone thus providing conditions for phytoplankton blooms at shallow shelves. Interestingly, besides the high productivity in winter, only few fish species reproduce (~20 %): those characteristic of relatively cold water of north Atlantic biogeographic affinity. This study aims to elucidate how the winter hydrodynamics off the Catalan coast determine the spawning strategies of Micromesistius poutassou and Sardina pilchardus in February 2017 and 2018. In 2017, a surface strip of low salinity, due to heavy rain, was found in a wide area along the northern coastal area. Besides this situation played against vertical mixing, these surface waters were rich in nutrients. By contrast, 2018 was dry thus with higher surface salinity and lower vertical stability involving subduction and cascading events. In both years, the shelf-slope front was evident through the epipelagic layers. The spawning and larval distribution of S. pilchardus were associated with the coastal productive waters. The spawning of M. poutassou took place along the upper slope and even over the shelf, also at the submarine canyons, but offshore limited by the front. Larger larvae were mainly found over the highly productive shelf. The larval vertical distribution of both species showed high variability, not only related with the daily cycle or developmental stage, but also with the vertical instability. The well known hydrodynamic structures, such as anticyclonic eddies that use to retain larvae during the stratified season, become less important in winter. In that case, the shelf-slope front appears to be a key factor retaining M. poutassou larvae avoiding their offshore dispersion, even though the species is commonly considered as oceanic

Lanternfish of the family Myctophidae are one of the most abundant fish in the open ocean. Adult myctophids have a wide vertical distribution through the water column; with conspicuous differences in their day and night location, feeding at night in the epipelagic zone and being more disperse in the mesopelagic region during the day. Contrasting, larval stages are restricted to the upper 200 m, both day and night, performing restricted vertical displacements. Transforming stages show a less defined diel vertical and feeding pattern, while juveniles behave like adults. In this study we analysed the trophic ecology of transforming and juvenile stages of a particular group of myctophids known for reaching the neustonic layers in their adult night migration: Myctophum affine, M. asperun, M. nitidulum and Gonichthys cocco. Neuston samples were collected across the tropical and equatorial Atlantic, in 12 stations sampled day and night. Transforming and juvenile stages occurred at night in in the neuston, where they fed, and were absent from this layer during the day. The highest prey ingestion was observed for individuals collected mainly between 1-4 am. The incidence of feeding in the stages of transformation (60%) was lower than in the juveniles (66-100%). The number of prey ingested and their sizes did not show any increasing trend between stages, but there was great variability among individuals. Diet of the four species was mainly composed by a variety of genus of copepods, generally dominated by Oncaea spp species. For M. asperum there was almost no other type of prey in the stomachs. The high carbon content of preys like hyperiids made that the total carbon content per stomach was higher when these prey occur in the diet, such as in juveniles of M. nitidulum

[EN] The studies that determine the trophic biology of the species and the knowledge of their food patterns provide basic and necessary information to understand the biological and ecological role of an organism within the ecosystem. Food is one of the most important factors in the biology of organisms because it regulates or affects growth and reproduction, as well as the way in which their life cycle develops. Likewise, the knowledge of the feeding habits of the species allows to evaluate their status in the community, i.e., their trophic level, relationships with other species or groups and to provide an approximate idea of their environment. This thesis provides information about the distribution patterns and the trophic ecology of early life stages of mesopelagic fishes in the western Mediterranean Sea and the equatorial and tropical Atlantic Ocean. We studied the vertical distribution and feeding patterns of some of the most abundant and most frequent mesopelagic fish species of these regions. Changes in the diet are described throughout its ontogenetic development. These aspects have been studied mainly in juveniles and adults of mesopelagic fish; however they are much scarcer for the early stages of development of these species. The importance of mesopelagic fishes is due to their high biomass in all the oceans. They are key elements in marine trophic networks, as they are part of the diet of pelagic fish, birds and marine mammals. Migratory mesopelagic species, such as myctophids, make extensive daily vertical migrations, between the mesopelagic zone (daytime habitat) andepipelagic zone (where they feed at night); thus contributing to the transport of carbon from the photic zone to deeper waters. […], [ES] Los estudios que determinan la biología trófica de las especies y el conocimiento de sus hábitos alimenticios, aportan información básica y necesaria para comprender el papel biológico y ecológico que desempeña un organismo dentro del ecosistema. La alimentación constituye uno de los factores más importantes en la biología de los organismos porque regula o afecta al crecimiento y reproducción, así como la forma en que se desarrolla su ciclo de vida. Asimismo, el conocimiento de los hábitos alimenticios de las especies permite evaluar su estatus en la comunidad, es decir su nivel trófico, sus posibles relaciones con otras especies o grupos y proporcionar una idea aproximada de su entorno. Esta tesis aporta información sobre las pautas de distribución y la ecología trófica de los primeros estados de desarrollo de los peces mesopelágicos del Mediterráneo occidental y el océano Atlántico ecuatorial y tropical. Se ha estudiado la distribución vertical y la alimentación de algunas de las especies de peces mesopelágicos más abundantes y más frecuentes de estas regiones. Se describen los cambios en la dieta a lo largo de su desarrollo ontogénico. Estos aspectos han sido estudiados principalmente en juveniles y adultos de peces mesopelágicos, en cambio son mucho más escasos para los estados tempranos de desarrollo de estas especies. La importancia de los peces mesopelágicos se debe a su elevada biomasa en todos los océanos. Son elementos clave en las redes tróficas marinas, pues son parte de la dieta de peces pelágicos, aves y mamíferos marinos. Las especies mesopelágicas migradoras, como los mictófidos, efectúan extensas migraciones verticales diarias, entre la zona mesopelágica (hábitat diurno) y epipelágica (donde se alimentan por la noche); contribuyendo así al transporte de carbono desde la zona fótica hacia aguas más profundas. […], [CAT] Els estudis que determinen la biologia tròfica de les espècies i el coneixement dels seus hàbits alimentaris, aporten informació bàsica i necessària per a comprendre el paper biològic i ecològic que té un organisme dins de l'ecosistema. L'alimentació constitueix un dels factors més importants en la biologia dels organismes perquè regula o afecta el creixement i reproducció, així com la forma en què es desenvolupa el seu cicle de vida. Així mateix, el coneixement dels hàbits alimentaris de les espècies permet avaluar el seu estatus dins la comunitat, és a dir el seu nivell tròfic, les seves possibles relacions amb altres espècies o grups i proporcionar una idea aproximada del seu entorn. Aquesta tesi aporta informació sobre les pautes de distribució i l'ecologia tròfica dels primers estats de desenvolupament dels peixos mesopelágicos de la Mediterrània occidental i l'oceà Atlàntic equatorial i tropical. S ha estudiat la distribució vertical i l'alimentació d'algunes de les espècies de peixos mesopelàgics més abundants i freqüents d'aquestes regions. Es descriuen els canvis en la dieta al llarg del seu desenvolupament ontogènic. Aquests aspectes han estat estudiats principalment en peixos mesopelàgics juvenils i adults de, en canvi són molt més escassos per als estats primerencs de desenvolupament d'aquestes espècies. La importància dels peixos mesopelàgics es deu a la seva elevada biomassa en tots els oceans. Són elements clau en les xarxes tròfiques marines, ja que són part de la dieta de peixos pelàgics, aus i mamífers marins. Les espècies mesopelágicas migradores, com els mictófids, efectuenextenses migracions verticals diàries, entre la zona mesopelàgica (hàbitat diürn) i epipelàgica (on s'alimenten a la nit); contribuint així al transport de carboni des de la zona fòtica cap a aigües més profundes. […]