Mesozooplankton size structure in the Canary Current System

Changes in plankton composition influences the dynamics of marine food webs and carbon sinking rates. Understanding the core structure and function of the plankton distribution is of paramount importance to know their role in trophic transfer and efficiency. Here, we studied the zooplankton distribution, abundance, composition, and size spectra for the characterization of the community under different oceanographic conditions in the Canaries-African Transition Zone (C-ATZ). This region is a transition zone between the coastal upwelling and the open ocean showing a high variability because of the physical, chemical, and biological changes between eutrophic and oligotrophic conditions through the annual cycle. During the late winter bloom (LWB), chlorophyll a and primary production were higher compared to that of the stratified season (SS), especially in the upwelling influenced area. Abundance distribution analysis clustered stations into two main groups according to the season (productive versus stratified season), and one group sampled in the upwelling influenced area. Size-spectra analysis showed steeper slopes during daytime in the SS, suggesting a less structured community and a higher trophic efficiency during the LWB due to the favorable oceanographic conditions. We also observed a significant difference between day and nighttime size spectra due to community change during diel vertical migration. Cladocera were the key taxa differentiating an Upwelling-group, from a LWB- and SS-group. These two latter groups were differentiated by Salpidae and Appendicularia mainly. Data obtained in this study suggested that abundance composition might be useful when describing community taxonomic changes, while size-spectra gives an idea of the ecosystem structure, predatory interactions with higher trophic levels and shifts in size structure

Swimbladder properties of Cyclothone spp. in the northeast Atlantic Ocean and the Western Mediterranean Sea

Non-migratory bristlemouth fishes (Cyclothone spp.) are the most abundant vertebrates on Earth and play an important role in the biological carbon pump by remineralizing organic carbon in deep ecosystems. Acoustic data and net sampling are often used in combination to estimate fish and zooplankton biomass, but this procedure may be subject to several sources of error when applied to mesopelagic species. For instance, the allocation of echoes to species has often been biased by not considering Cyclothone spp. due to the use of nets targeting larger fish. Furthermore, the acoustic properties of the target organisms must be well understood to convert acoustic density into numerical density. The characteristics of a fish’s swimbladder are the most relevant features necessary to assess its acoustic properties. This study provides information on the swimbladder properties of six Cyclothone species inhabiting the meso- and bathypelagic layers in the North Atlantic Ocean and Mediterranean Sea, including swimbladder location within the body, fat tissue content, morphology, morphometry (only available for C. braueri and C. pseudopallida), and fish body-mass density (only available for C. braueri, C. pseudopallida, C. pallida, and C. pygmaea). The studied species showed a functional physoclistous swimbladder, with well-developed gas glands and rete mirabile and numerous capillaries in the case of the shallower species C. braueri and C. pseudopallida (mainly distributed from 400 to 600 m depth), and a fat-invested swimbladder in species with deeper vertical distribution (C. livida, C. microdon, C. pallida, and C. pygmaea). The fat content in the swimbladder (C. pallida and C. microdon) increased with depth and latitude, reducing the space in the swimbladder that could contain gas. Changes in swimbladder size and volume during growth were analyzed for shallower species, where swimbladder volume and equivalent radius followed negative allometric growth in relation to body length. Finally, values of body-mass density (ρ) and gas content required for neutral buoyancy (VG) were estimated for C. braueri and C. pygmaea collected between 350 and 550 m (ρ = 1.052–1.072 g·cm−3, VG = 2%–4%; ρ = 1.052–1.062 g·cm−3, VG = 3.6%), and for C. pallida and C. pseudopallida sampled in the 450–700 m layer (ρ = 1.052–1.062 g·cm−3, VG = 2.6–3.1%; ρ = 1.052–1.062 g·cm−3, VG = 2.8%–3.25%). Results in this study highlight the change in scattering behavior of Cyclothone species from gas-bearing organisms (those that contain gas in their swimbladder) in the upper mesopelagic zone to the fluid-like scattering (with fat-filled swimbladders) of the deeper and northern individuals. The data presented in this manuscript are important for parametrizing acoustic backscattering models built to estimate the echo of Cyclothone species, although further work is needed, particularly for individuals with partially invested swimbladders with an irregular fat-free shape

Análisis de las propiedades acústicas y patrones de distribución vertical de los peces meso- y batipelágicos, y su contribución a la bomba biológica

Tesis Doctoral presentada por D. Airam Nauzet Sarmiento Lezcano dentro del Programa de doctorado en Oceanografía y Cambio Global (Universidad de Las Palmas de Gran Canaria), dirigida por la Dra. Marian Peña Sáenz y Codirigida por la Dra. María Pilar Olivar Buera. - Se sube resumen al no estar disponible hasta el 30 de junio de 2025.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 marine life present in that zone, biomass and migrant fluxes values were similar or higher than in other regions. Acoustic and net sampling data are often used in combination to estimate fish and zooplankton biomass in the shelfs, but this technique is subject to several sources of errors when applied to mesopelagic species. The allocation of echoes to species for instance has often been biased by not considering Cyclothone spp. due to the use of nets targeting larger fishes. As expected, direct relationships between scattering and net sampling data were not significant. Comparisons made on depth-stratified data was only significant for the main non-migrant deep-scattering layer and Cyclothone braueri abundance as previously described in the literature. A significant correlation was also found for migrant fishes by manually selecting their contribution to the echogram based on previous knowledge. The acoustic properties of the target organisms must be well understood in order to allocate species to acoustic data and to convert acoustic density into numerical density. The gas content in swimbladdered fishes greatly determines their acoustic signature and thus it is of most importance to know the swimbladder morphology and gas properties. Cyclothone spp. vary in vertical distribution and thus in swimbladder strategies for buoyancy purposes. Our studies highlight the change in scattering properties of Cyclothone species from gas-bearing organisms (those that contain gas in their swimbladder) in the upper mesopelagic zone to the fluid-like scattering (with fat-filled swimbladders) of the deeper individuals. However, it also points out the necessity to further know about the regression process and to build more complex models that include swimbladders with both gas and lipids for intermediate lengths. Our results suggest the importance of the non-migratory bristlemouth fishes in the deep ocean according to their role in the biological carbon pump, the significance values of the seasonality active flux by migrant micronekton, and the importance of gaining knowledge on the acoustic properties of meso- and bathypelagic fishes for parametrizing acoustic backscattering models and inferring information from the combination of acoustic and net-sampling data.Peer reviewe

Análisis de las propiedades acústicas y pautas de distribución vertical de los peces meso y batipelágicos y su contribución a la bomba biológica

Memoria de tesis doctoral presentada por Airam Nauzet Sarmiento Lezcano para obtener el título de Doctor en Oceanografía y Cambio Global por la Universidad de Las Palmas de Gran Canaria (ULPGC), realizada bajo la dirección de la Dra. María Angeles Peña Sáenz del Instituto Español de Oceanografía (IEO) y de la Dra. Pilar Olivar Buera del Institut de Ciències del Mar (ICM-CSIC)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 marine life present in that zone, biomass and migrant fluxes values were similar or higher than in other regions. Acoustic and net sampling data are often used in combination to estimate fish and zooplankton biomass in the shelfs, but this technique is subject to several sources of errors when applied to mesopelagic species. The allocation of echoes to species for instance has often been biased by not considering Cyclothone spp. due to the use of nets targeting larger fishes. As expected, direct relationships between scattering and net sampling data were not significant. Comparisons made on depth-stratified data was only significant for the main non-migrant deep-scattering layer and Cyclothone braueri abundance as previously described in the literature. A significant correlation was also found for migrant fishes by manually selecting their contribution to the echogram based on previous knowledge. The acoustic properties of the target organisms must be well understood in order to allocate species to acoustic data and to convert acoustic density into numerical density. The gas content in swimbladdered fishes greatly determines their acoustic signature and thus it is of most importance to know the swimbladder morphology and gas properties. Cyclothone spp. vary in vertical distribution and thus in swimbladder strategies for buoyancy purposes. Our studies highlight the change in scattering properties of Cyclothone species from gas-bearing organisms (those that contain gas in their swimbladder) in the upper mesopelagic zone to the fluid-like scattering (with fat-filled swimbladders) of the deeper individuals. However, it also points out the necessity to further know about the regression process and to build more complex models that include swimbladders with both gas and lipids for intermediate lengths. Our results suggest the importance of the non-migratory bristlemouth fishes in the deep ocean according to their role in the biological carbon pump, the significance values of the seasonality active flux by migrant micronekton, and the importance of gaining knowledge on the acoustic properties of meso- and bathypelagic fishes for parametrizing acoustic backscattering models and inferring information from the combination of acoustic and net-sampling dataPeer reviewe

First record and new size record for the oceanic species Psenes sio (Actinopterygii: Scombriformes: Nomeidae) in the northern Gulf of California, Mexico

The biological information for many species of the family Nomeidae is scarce, given the difficulty of capturing these species in the oceanic environment. A specimen of the twospine driftfish, Psenes sio Haedrich, 1970, was collected in the northern Gulf of California with a bottom trawl net at the depth of more than 250 m. This specimen represents the northernmost record of this species to date, and provides valuable information on this fish, such as maximum weight and height recorded, vertical distribution and latitudinal range, in addition to meristic counts and body morphometry

Changes in vertical location in the water column of meso- and bathypelagic species through development: Behaviour vs hydrography

43 Annual Larval Fish Conference, 21-24 May 2019, Palma, Balearic IslandsThe 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 stagesPeer Reviewe

Mesozooplankton size structure in the Canary Current System

Changes in plankton composition influences the dynamics of marine food webs and carbon sinking rates. Understanding the core structure and function of the plankton distribution is of paramount importance to know their role in trophic transfer and efficiency. Here, we studied the zooplankton distribution, abundance, composition, and size spectra for the characterization of the community under different oceanographic conditions in the Canaries-African Transition Zone (C-ATZ). This region is a transition zone between the coastal upwelling and the open ocean showing a high variability because of the physical, chemical, and biological changes between eutrophic and oligotrophic conditions through the annual cycle. During the late winter bloom (LWB), chlorophyll a and primary production were higher compared to that of the stratified season (SS), especially in the upwelling influenced area. Abundance distribution analysis clustered stations into two main groups according to the season (productive versus stratified season), and one group sampled in the upwelling influenced area. Size-spectra analysis showed steeper slopes during daytime in the SS, suggesting a less structured community and a higher trophic efficiency during the LWB due to the favorable oceanographic conditions. We also observed a significant difference between day and nighttime size spectra due to community change during diel vertical migration. Cladocera were the key taxa differentiating an Upwelling-group, from a LWB- and SS-group. These two latter groups were differentiated by Salpidae and Appendicularia mainly. Data obtained in this study suggested that abundance composition might be useful when describing community taxonomic changes, while size-spectra gives an idea of the ecosystem structure, predatory interactions with higher trophic levels and shifts in size structure.The authors would like to thank Emilio Marañón for his useful comments on the manuscript. This study was partially funded by the Spanish Ministry project DESAFÍO (PID 2020- 118118RB-100), TRIATLAS (Grant Agreement 817578), and SUMMER (Grant Agreement 817806). María Couret was supported by a postgraduate grant (TESIS2022010116) from the Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI). Airam Sarmiento-Lezcano was supported by a postgraduate grant from the Spanish Ministry of Science and Innovation (BES-2017-082540). José Landeira was supported by the Beatriz Galindo individual grant BEAGAL 18/00172

First Record of Stranded Mesopelagic Fishes in the Canary Islands

VIII International Symposium on Marine Sciences, 6-8 July 2022, Las Palmas de Gran Canaria, EspañaLanternfishes 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 strandingPeer reviewe

Stranding of Mesopelagic Fishes in the Canary Islands

Special issue Trophic Web and Predator–Prey Dynamics in Marine Environment.-- 13 pages, 6 figures.-- Data Availability Statement: The raw data supporting the conclusions of this article are publicly available through AFORO website (http://aforo.cmima.csic.es/ (accessed on 12 August 2022)) and PANGEA platform: Sarmiento-Lezcano, Airam Nauzet; Couret, María; Lombarte, Antoni; Olivar, M Pilar; Landeira, José María; Hernández-León, Santiago; Tuset, Victor M (2022): Otolith morphological measures of stranding mesopelagic fishes in the Canary Islands during June 2021. PANGAEA, https://doi.org/10.1594/PANGAEA.951480 (accessed on 12 August 2022)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 morphometryThis research was funded by the Spanish Government through the Project Desafío (PID2020-118118RB-I00). Additional funding for this research came from the European Union (Horizon 2020 Research and Innovation Programme) through the projects SUMMER (Grant Agreement 817806) and TRIATLAS (Grant Agreement 817578). Airam Sarmiento was supported by a postgraduate grant (BES-2017-082540) and José M Landeira by the “Beatriz Galindo” grant (BEAGAL 18/00172) both from the Spanish Ministry of Science and Innovation. María Couret was supported by a postgraduate grant (TESIS2022010116) from the Agencia Canaria de Investigación, Innovación y Sociedad de la Información (ACIISI)With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Peer reviewe

Variation in mesopelagic fish community composition and structure between Mediterranean and Atlantic waters around the Iberian Peninsula

22 pages, 9 figures, 2 tables, supplementary material https://www.frontiersin.org/articles/10.3389/fmars.2022.1028717/full#supplementary-material.-- Data availability statement: The raw data supporting the conclusions of this article are publicly available through PANGEA platform: Olivar et al. (2022) https://doi.org/10.1594/PANGAEA.947631, and Yang et al. (2021) https://doi.pangaea.de/10.1594/PANGAEA.938688Mesopelagic 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 Lisboa, where night surface net collections indicated that Myctophidae, Stomiidae and Phosichthyidae migration extended to the upper 100 m. Sternoptychids and the gonostomatid Sigmops elongatus seldom reached the upper 100 m in their night vertical migrations. Night stratified hauls of 30 m resolution carried out in the epipelagic zone showed that abundances maxima of migratory fish coincided with the location of the Chlorophyll a maximaThis work was a component of the European Union Project ‘Sustainable Management of Mesopelagic Resources’ (SUMMER, Grant Agreement 817806) as funded by the Horizon 2020 Research and Innovation Programme. [...] AS-L was supported by a postgraduate grant (BES-2017-082540) from the Spanish Ministry of Science and Innovation. We acknowledge the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S)Peer reviewe