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Arctic microbial communities (i.e., protists and bacteria) are increasingly subjected to an intrusion of new species via Atlantification and an uncertain degree of ocean warming. As species differ in adaptive traits, these oceanic conditions may lead to compositional changes with functional implications for the ecosystem. In June 2021, we incubated water from the western Fram Strait at three temperatures (2 °C, 6 °C, and 9 °C), mimicking the current and potential future properties of the Arctic Ocean. Our results show that increasing the temperature to 6 °C only minorly affects the community, while an increase to 9 °C significantly lowers the diversity and shifts the composition. A higher relative abundance of large hetero- and mixotrophic protists was observed at 2 °C and 6 °C compared to a higher abundance of intermediate-sized temperate diatoms at 9 °C. The compositional differences at 9 °C led to a higher chlorophyll a:POC ratio, but the C:N ratio remained similar. Our results contradict the common assumption that smaller organisms and heterotrophs are favored under warming and strongly indicate a thermal limit between 6 °C and 9 °C for many Arctic species. Consequently, the magnitude of temperature increase is a crucial factor for microbial community reorganization and the ensuing ecological consequences in the future Arctic Ocean.

Recent estimates suggest that the mesopelagic zone could contain a total fish biomass of 2-19.5 gigatonnes, roughly equivalent to 100 times the annual catch of all existing fisheries. In addition to the possibility of direct consumption of mesopelagic species, there is interest in their use for fishmeal, as a source of dietary supplements for humans, and to bio-prospect pharmaceuticals. All of this, and the demands for a global food supply that can feed an ever-growing population, has driven interest in the mesopelagic. Thus, accurate quantification of the biomass of mesopelagic resources, their nutritional and genetic composition, their links to other components of the food web, to other oceanic realms and to biological and chemical oceanographic processes and cycles, are the focus of growing research activity. This information is needed to ensure the sustainable management of these resources. In this introduction, we summarize the contributions included in this theme set and provide some “food for thought” on the state-of-the-art in research on the mesopelagic, including identifying the knowledge that must be generated to support its sustainable management (e.g. the effect that extracting significant biomass might have on the pelagic ecosystem and the flow of material and energy through it), Sí

From the southwestern termination of the Agulhas current, anticyclonic eddies are emitted and drift across the South Atlantic Ocean. This study is based on a FORSA (Following Ocean Rings in the South Atlantic) oceanographic cruise, from Cape Town (South AFRica) to Arraial do Cabo (Brazil) in June 2015, during which three eddies of different ages (E1, 7 months; E3, 11 months; E5, 24 months) from the Agulhas current were sampled for microplankton identification and determination of functional traits. The stations where sampling occurred at each eddy included a control outside the eddy and three stations inside the eddy—border, midway (between the border and center), and center (identified through satellite images of sea level anomaly—SLA). Functional traits were determined based on microscopic observations and consultation of the literature. An evident decay in the Agulhas eddies toward the west was observed, and each eddy proved to be different. E1 represented a younger and more robust structure. At the same time, the other eddies, E3 and E5, were more alike with similar physical, chemical, and ecological characteristics and almost the same indices values of functional diversity, demonstrating that although their species compositions were different, the strategies used by the species were the same. The most crucial ecological trait for microplankton was nutrition mode. The microplankton contained mainly mixotrophic dinoflagellates and cyanobacteria adapted to oligotrophic conditions. The functional strategy of microplankton did not differ among the eddies and stations, with mixotrophy being the most striking trait. Therefore, the older eddies’ microplankton community fits the neutrality theory, whereby species perform similar ecological functions, and the younger eddy fits in the niche complementarity. Even with the species composition being different in each eddy and/or within the same eddy, the functional strategy was the same, with scarce resources and species selected that best use any source of nutrients or use evolutionary advantages to live in an oligotrophic environment.

The availability of high-throughput sequencing (HTS) has transformed our understanding of the diversity of microbial eukaryotes (i.e., protists) across diverse habitats. Yet relating this biodiversity to function remains a challenge, particularly in the context of microbial food webs. Here we perform a set of microcosm experiments to evaluate the impact of changing predator and prey concentrations on a marine protist community, focusing on SAR (Stramenopila, Alveolata, and Rhizaria) lineages. We combine an estimate of taxonomic diversity through analysis of SSU-rDNA amplicons with metatranscriptomics, a proxy for function. We assess changes in a community sampled from New England waters with varying concentrations of predators (copepods) and prey (phytoplankton

Els microplàstics s’han convertit en un gran problema mediambiental. La sobreproducció i l’ús excessiu del plàstic ha dificultat el seu correcte tractament y això provoca que sigui el sector amb un major creixement en la generació de residus. Els residus plàstics, a través de diversos processos es degraden i es trenquen en partícules mes petites donant lloc als microplàstics. També es poden trobar un altre tipus de microplàstics, aquells originats i fabricats d’aquesta mida de forma intencionada. Tot i que s’han publicat diversos articles científics demostrant la presencia de microplàstics a zones mol localitzades, cap d’ells mostra una visió global sobre aquest problema mediambiental. En aquesta tesis presentem el desenvolupament d’una nova metodologia de mostreig de microplàstics a més de la retenció d’altres contaminants orgànics suspesos en l’aigua de mar. Per això, hem col·laborat amb la Fundació de Navegació Oceànica de Barcelona (FNOB), entitat organitzadora de la Barcelona World Race (BWR) y amb el grup Sailing Technologies. A través d’aquesta col·laboració, hem desenvolupat un dispositiu de mostreig instal·lat en un dels vaixells participants en la BWR 2015 que es capaç de col·lectar microplàstics i contaminants orgànics en aigua superficials en varies localitzacions del mon passant per quatre oceans (Mar Mediterrani i Oceans Atlàntic, Pacífic e Índic). Hem realitzat la caracterització dels microplàstics mostrejats durant la BWR 2015. L’anàlisi de la seva morfologia, composició i distribució ens ha permès conèixer el nivell de contaminació i l’impacte de tenir aquest tipus de micropartícules en els oceans. També hem demostrat el efecte concentrador dels microplàstics. Hem desenvolupat un mètode analític reproduïble per l’extracció i quantificació de varies famílies de contaminants orgànics de diferents tipus de micropartícules polimèriques. Per últim, es desenvolupa una metodologia per l’elució dels cartutxos SPE utilitzats durant la BWR 2015. A més, s’ha realitzat un anàlisis PCA i s’han agrupat les mostres en funció de diferents paràmetres com les corrents, la localització o la seva posició respecte l’equador. En conclusió, aquesta tesis proporciona informació sobre l’estat global dels oceans en relació als microplàstics i les seves conseqüències. L’estudi del efecte dels microplàstics en els oceans de forma global ajuda a comprendre la situació mediambiental actual. Los microplasticos se han convertido en un gran problema medioambiental. La sobreproducción y el uso excesivo del plástico ha dificultado mucho su tratamiento y esto provoca que sea el sector con un mayor crecimiento en la generación de residuos. Los desechos plásticos, a través de varios procesos se degradan o rompen en partículas más pequeñas dando lugar a los microplasticos. También se pueden encontrar otro tipo de microplasticos, esos originados y fabricados en ese tamaño de forma intencionada. Aunque ya se han publicado varios artículos científicos demostrando la presencia de microplasticos en zonas localizadas, ninguno de ellos muestra una visión global acerca de este problema medioambiental. En esta tesis presentamos el desarrollo de una nueva metodología de muestreo de microplásticos además de la retención de otros contaminantes orgánicos suspendidos en agua de mar. Para ello, hemos colaborado con la Fundación de Navegación Oceánica de Barcelona (FNOB), entidad organizadora de la Barcelona World Race (BWR) y con el Grupo Sailing Technologies. A través de esta colaboración, hemos desarrollado un nuevo dispositivo de muestreo instalado en uno de los barcos participantes en la BWR 2015 que es capaz de colectar microplasticos y contaminantes orgánicos de agua superficial en varias localizaciones del mundo pasando por cuatro océanos (Mar Mediterráneo y Océanos Atlántico, Pacífico y Índico). Hemos realizado la caracterización de los microplasticos muestreados durante la BWR 2015. El análisis de su morfología, composición y distribución nos ha permitido conocer el nivel de contaminación y el impacto de tener este tipo de micropartículas en los océanos. También hemos demostrado el efecto concentrador que poseen los microplasticos. Hemos desarrollado un método analítico reproducible para la extracción y cuantificación de varias familias de contaminantes orgánicos de distintos tipos de micropartículas poliméricas. Por último, se desarrolla una metodología para la elución de los cartuchos SPE usados en la BWR 2015. Además, se ha realizado un análisis PCA y se han agrupado las muestras en función de varios parámetros como las corrientes, la localización o su posición respecto al ecuador. En conclusión, esta tesis proporciona información sobre el estado global de los océanos en relación con los microplasticos y sus consecuencias. El estudio del efecto de los microplasticos en los océanos de forma global es de ayuda para comprender la situación medioambiental actual. Microplastics have become a huge environmental concern in recent years. The overproduction and excessive use of plastic have made difficult a proper manage and that is why it has become the fastest growing segment of the waste stream. Plastic debris, through several physical, chemical and biological processes can degrade or breakdown resulting in microplastics. In addition to these it can also find other type of microplastics which are those originally and intentionally manufactured in that size. Although several research studies have been published demonstrating the presence of microplastics in localised coastal regions, any of them show a global scenario about this environmental concern. Here we present the development of a new methodology for microplastics sampling and retention of pollutants present in seawater. In this sense, we have collaborated with the Barcelona World Race (BWR) organization and the “Fundació de Navegació Oceànica de Barcelona” (FNOB). Throughout this collaboration, we have developed a device, named COA device, installed in a racing boat of the BWR 2015 which collects microplastics and pollutants on superficial seawater from the different locations of the world going through four oceans (Mediterranean Sea and Atlantic, Pacific and Indian Oceans). Furthermore, we performed the characterization of the microparticles collected during the BWR 2015. The analysis, based on microscopic techniques, of their morphology, composition and distribution has allowed us to know better the level of pollution of the marine environment and which is the global impact of having that particles in the oceans. In addition to that, we demonstrate the microplastics concentration effect of persistent organic pollutants. We also developed a reproducible analytical methodology based on a new approach for the release and quantification of different families of pollutants from polymeric microparticles. Finally, different analytical methods have been optimized for the analysis of several pollutants solved in seawater. The elution of pollutants retained in the SPE cartridges used in the BWR 2015 has been performed. In conclusion, this thesis provides information about the overall status of the oceans in terms of microplastics and their consequences at present. The study of the role of microplastics in seawater in a global way have been helpful to understand the actual environmental situation.

Is there a mesopelagic protist fauna composed of species different from that of the overlying surface community? Does the mesopelagic community show seasonal changes in abundances and species composition? We addressed these questions by considering three distinct groups in which species identification is relatively unambiguous: tintinnid ciliates, phaeodarian radiolarians, and amphisolenid dinoflagellates. We sampled weekly at 250 m and 30 m depth from January to June a deep-water coastal site characterized by seasonal changes in water column structure; notably, in winter the mixed layer extends down into mesopelagic depths. We found a deep-water community of tintinnid ciliates comprised of forms apparently restricted to deep waters and species also found in the surface layer. This latter group was dominant during the winter mixis period when tintinnid concentrations were highest and subsequently declined with water column stratification. Phaeodarian radiolarians and the amphisolenid dinoflagellates were regularly found in deep samples but were largely absent from surface water samples and showed distinct patterns in the mesopelagic. Phaeodarian radiolarians declined with water column mixing and then increased in concentration with water column stratification whilst amphisolenid dinoflagellates concentrations showed no pattern but species composition varied. We conclude that for all three protists groups there appear to be both distinct mesopelagic forms and seasonal patterns.

Quantifying biotic feedbacks in response to environmental signals is fundamental to assess ecosystem perturbation. We analyzed the joint effects of eutrophication, derived from sewage pollution, and climate at the base of the pelagic food web in the Bahía Blanca Estuary (SW Atlantic Ocean). A two-year survey of environmental conditions and microplankton communities was conducted in two sites affected by contrasting anthropogenic eutrophication conditions. Under severe eutrophication, we found higher phytoplankton abundance consistently dominated by smaller sized, non siliceous species, while microzooplankton abundance remained lower and nutrient stoichiometry showed conspicuous deviations from the Redfield ratio. Phytoplankton growth in such conditions appeared controlled by phosphorous. In turn, microplankton biomass and phytoplankton size ratio (20 μm) displayed a saturation relationship with nutrients in the highly eutrophic area, although mean phytoplankton growth was similar in both eutrophic systems. The strength of links within the estuarine network, quantified through path analysis, showed enhanced relationships under larger anthropogenic eutrophication, which fostered the climate influence on microplankton communities. Our results show conspicuous effects of severe sewage pollution on the ecological stoichiometry, i.e., N and P excess with respect to Si, altering nutrient ratios for microplankton communities. This warns on wide consequences on food web dynamics and ultimately in ecosystem assets of coastal pelagic environments. Fil: López Abbate, María Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Molinero, Juan Carlos. Geomar-helmholtz Centre For Ocean Research Kiel; Alemania Fil: Guinder, Valeria Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Dutto, María Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Barría de Cao, M. Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Ruiz Etcheverry, Laura Agustina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pettigrosso, Rosa E.. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia. Laboratorio de Ecología Acuática; Argentina Fil: Carcedo, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Hoffmeyer, Monica Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; Argentina

Studies of annual successions and inter-annual variations in sub-Arctic and Arctic microplankton assemblages are required in order to understand the structure and function of marine ecosystems. This study depicts the microplankton (>20 μm) structure in a sub-Arctic tidewater glacial fjord system, SW Greenland. The descriptions are based on monthly net hauls collected between January 2006 and December 2010. Two blooms, with distinctive species compositions, were identified across all years: a spring bloom and a summer/autumn bloom. In addition, the winter season—with weak stratification, deep tidal mixing, and dense coastal inflows—was characterised by a separate species composition at much lower abundance. Here, the highest variety of microplankton groups was recorded and represented by diatoms (Chaetoceros spp. and Thalassiosira spp.), silicoflagellates, dinoflagellates, and ciliates. During the spring bloom, species correlated with higher light intensities, i.e. haptophytes and diatoms (Thalassiosira spp. and Fragilariopsis spp.), dominated the microplankton assemblage. Among these, diatoms were also correlated with cooler and fresher waters influenced by springtime melt. During the summer/autumn bloom, the microplankton assemblage was mainly represented by diatoms, such as Chaetoceros spp. ‘Low-saline’ chrysophytes were also present. The latter bloom coincides with elevated temperatures in the fjord and renewal of nutrients due to the onset of glacial meltwater run-off from the Greenland Ice Sheet. Our study shows a yearly recurrent succession of microplankton assemblages and that the annual succession is controlled primarily by ocean–fjord–glacier interactions.

A systematic investigation of non-phosphorus containing glycolipids (GL) was conducted in the northern Adriatic Sea during two years at two stations with different nutrient loads. GL concentration varied both spatially and temporally, with values of 1.1-21.5 g/L and 0.4-44.7 g/L in the particulate and the dissolved fraction, respectively. The highest concentrations were measured during summer in surface waters and at the more oligotrophic station, where GL yields (% of total lipids) were often higher than 20% and 50% in the particulate and dissolved fractions, respectively. To obtain more insight into factors governing GL accumulation autotrophic plankton community structure (pico-, nano- and microplankton fractions), chlorophyll a, heterotrophic bacteria and nutrient concentrations were measured together with hydrographic parameters and sunlight intensity. During the investigated period smaller autotrophic plankton cells (pico- and followed by nanoplankton) prevailed in abundance over larger cells (microplankton), which were found in large numbers in freshened surface samples. Several major findings resulted from the study. Firstly, during PO4 limitation, particularly at the oligotrophic station, enhanced glycolipid instead of phospholipid accumulation takes place, representing an effective phosphate-conserving mechanism. Secondly, results suggest that at seawater temperatures >19ºC autotrophic plankton considerably accumulate GL, probably to achieve thermal stability. Thirdly, high sunlight intensities seem to influence increased GL accumulation ; GL possibly plays a role in cell mechanisms that prevent/mitigate photooxidation. And finally, substantial accumulation of GL detected in the dissolved fraction could be related to the fact that GL do not contain biologically relevant elements, like phosphorus, which makes them an unattractive substrate for enzyme activity. Therefore, substantial portion of CO2 could be removed from the atmosphere in P-limited regions during summer via its capture by plankton and conversion to GL.

18 pages, 13 figures, 8 tables, The abundance, composition and mesoscale variability of the microplankton (53-200. μm) and the mesoplankton (0.2-2. mm) fractions in relation to oceanographic factors and phytoplankton biomass were compared off the Catalan coast (NW Mediterranean) during the summer stratification (June) and autumn mixing (November) periods in 2005. This work aims to determine whether the two plankton fractions that more contribute to fish larval diet respond to a common variable environment, and this study constitutes the first attempt to analyse, in parallel, the spatial structure of both fractions in this area. From June to November microplankton abundance increased mainly by the increase of dinoflagellates, tintinnids and radiolarians, and mesoplankton decreased due mainly to the decrease of long-horned dinoflagellates, cladocerans, doliolids and appendicularians. Plankton mesoscale variability in relation to environmental variables showed higher complexity in June, where environmental horizontal and vertical gradients were more marked than in November. In June, the major mode of variability of the microplankton was mainly accounted by the patchy distribution of several tintinnid species dominated by Rhabdonella spiralis associated to the subsurface phytoplankton biomass. The main mode of variability of the mesoplankton was related to the intrusion of the Ebro river plume and the related aggregation of doliolids and cladocerans, dominated by Evadne spinifera. In November, the major variability pattern in both fractions was a combination of inshore-offshore and eastern-western gradients in taxa distributions shaped mainly by the course of the Catalan Current along the shelf-break. Spatial differences in planktonic food pathways in each period are discussed on the basis of literature on plankton feeding habits and types, and on the diet of fish larvae of the main species from the same surveys. © 2014 Elsevier B.V., This research was funded by the CTM2004-03510-C02-01 and 02 ⁄MAR Project. The team of the UPV/EHU also received finnancial support for this work from the Basque Government (GIC10/168) and the University of the Basque Country (UFI11/37)

13 pages, 5 figures, 3 tables, We investigated ontogenetic and seasonal changes in the feeding ecology of 2 small pelagic fish species, the European anchovy Engraulis encrasicolus and the European pilchard Sardina pilchardus in the Gulf of Lions (NW Mediterranean). By analysing the stable isotopes δ13C and δ15N, we determined the seasonal variation in the food sources and in the trophic level of these species, and we examined dietary shifts during development. The results of these investigations provided estimates of the diets of both species. We compared the values observed during different seasons (summer, autumn and winter) and at different developmental stages (late-larvae, juveniles and adults) for both species, together with the values of potential groups of prey (microplankton, cladocerans, copepods and appendicularians). Late-larvae preferred to feed on microplankton, although differences in the diet appeared after metamorphosis. Cladocerans were usually the preferred prey when available (summer), and appendicularians were the preferred prey in autumn. During the winter, the diets seemed to be more heterogeneous. Different feeding behaviours between the late-larvae of the 2 species were the most likely reason for the slightly different trophic levels found in the present study. This research demonstrates that studies with stable isotopes can furnish an alternative and/or complementary method for determining the diet of small pelagic fishes over extended periods and provides comprehensive knowledge of the functioning of the pelagic ecosystem, D.C. was funded by a PhD contract within the European project SARDONE (FP6 - 44294). J.N. was supported by a postdoctoral contract of the Juan de la Cierva programme (MICINN-JDC, Spanish Ministry of Science and Innovation)

Carbon dioxide production rates (CDPR) of micro-organisms were monitored through their electron transport system (ETS) activity in thedeep Ross Sea. The depth-integrated CDPR amounted to 28,2 mg C m-2d-1in the depth range 100-1000 m. Comparing CDPR determinedin this study with that obtained by sediment traps in the Ross Sea resulted that about 63% of organic carbon remineralized by respirationderived from POC pool. Such evidence highlighted POC source as main organic fuel of biological pump in the Ross Sea.

The study of microplanktonic and continental organisms (mainly spores and pollens) from the Cretaceous of Gabon and from the Tertiary of Cameroon indicates the local conditions prevailing in their sedimentary environment. The diagrammatic scheme of the quantitative variations represents the floristic evolution during geological times and gives some informations about the position of the shore. On the basis of those observations, in Gabon, we can trace a succession of transgressive and regressive phases from the Aptian to the Maastrichtian. In the same way, in Cameroon, after a slight Maastrichtian transgression, a considerable change in the percentage of the spore-pollen spectra, up to the Lower Miocene, can be regarded as suggestive of withdrawal of the shore line. Besides these variations of the shore line, important modifications occurred in the continental vegetation, consequently to local climatological changes., Les éléments d'origine marine (microplancton) et d'origine continentale (spores et grains de pollen principalement), présents dans les palynoflores crétacées du Gabon et tertiaires du Cameroun, indiquent à quelles influences étaient soumis les milieux de dépôt lors de leur sédimentation. La représentation graphique de ces variations quantitatives reflète l'évolution floristique dans le temps et fournit des renseignements sur l'évolution des lignes de rivage. Ainsi, au Gabon, on remarque une succession de phases transgressives et régressives depuis l'Albien jusqu'au Maestrichtien : la transgression albienne est suivie d'une régression au Cénomanien ; à une transgression turonienne succède une alternance d'épisodes transgressifs et régressifs au Coniacien-Santonien ; le Campanien transgressif à la base devient graduellement régressif, le retrait de la mer étant plus marqué encore au début du Maestrichtien. Au Cameroun, à Kwa-Kwa, on peut mettre en évidence une brève transgression suivie d'une régression au sommet de cet étage ; on assiste ensuite à un retour de la mer pendant le Paléocène, suivi d'une régression plus généralisée qui se maintient jusqu'au Miocène inférieur en dépit de quelques épisodes transgressifs peu significatifs au cours de l'Oligocène. Ces variations de la ligne du rivage s'accompagnent d'importants changements de la végétation continentale engendrés par les fluctuations du climat., Boltenhagen Eugène, Salard-Cheboldaeff Marguerite. Le domaine continental et le domaine marin : bassins sédimentaires littoraux du Gabon et du Cameroun. The continental and marine realms : coastal sedimentary basins of Gabon and Cameroon. In: Sciences Géologiques. Bulletin, tome 38, n°1, 1985. Palynologie. pp. 35-44.