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Data relative to the article Low-density plastic debris dispersion beneath the Mediterranean Sea surface (Baudena et al., 2023; DOI: https://doi.org/10.1021/acs.est.2c08873). The dataset contains all the data necessary to produce the main figures of this publication(e.g. Fig2.nc file contains all the data used to produce Figure 2). In particular the available data are: - the concentration of Low-Density Plastic (LDP) on the Mediterranean virtual seafloor at 1000 m (defined as the Mediterranean seafloor, with the difference that the locations deeper than 1000 m were set to 1000 m depth due to computational constraints). A deeper virtual seafloor was used (at 2000 m) with the exception of Scenario 4 (Fig3BCDE.nc). - the lateral distance traveled by simulated LDP debris during their sinking from the sea surface until they reach the virtual seafloor (Fig3F.nc) - the concentration of LDP particles deposited less than 20 km from the coast (called the coastal strip) for each country; in addition, we provide the percentage of these particles which were released from the country's own land sources, other countries, or shipping lanes (Fig4.nc and Coastal_Stat_Scenario1_4.txt) - the relationship relationship between the sinking speed from the drag model (SS_DM) and the difference of the densities of LDP particles and seawater (Fig2.nc) - the surface sinking rate used as initial condition to release particles at the Mediterranean Sea surface (Fig3A.nc; also available at 10.5281/zenodo.5931213) For further information, or report any eventual issue, please feel free to contact alberto.baudena@gmail.com

Main objective of this study was to describe chemical composition of MP collected in surface waters of Mediterranean Sea. Samples were collected by manta net during Tara Mediterranean expedition (June–Nov.2014). Our results pointed to certain homogeneity at Mediterranean Sea scale. Main polymers collected were polyethylene (PE) (67.3±2.4%), polypropylene (20.8±2.1%), polystyrene (3.0±0.9%). Still, discrepancies, confirmed by literature, were observed at mesoscale level. Thus, in North Tyrrhenian Sea, proportion of PE was significantly lower than average value of Mediterranean Sea (57.9±10.5%).

International audience; The Mediterranean Sea is recognized as one of the most polluted areas by floating plastics. During the Tara Mediterranean expedition, an extensive sampling of plastic debris was conducted in seven ecoregions, from Gibraltar to Lebanon with the aim of providing reliable estimates of regional differences in floating plastic loads and plastic characteristics. The abundance, size, surface, circularity and mass of 75,030 pieces were analyzed and classified in a standardized multi-parameter database. Their average abundance was 2.60 × 105 items km−2 (2.25 × 103 to 8.50 × 106 km−2) resulting in an estimate of about 650 billion plastic particles floating on the surface of the Mediterranean. This corresponds to an average of 660 metric tons of plastic, at the lower end of literature estimates. High concentrations of plastic were observed in the northwestern coastal regions, north of the Tyrrhenian Sea, but also off the western and central Mediterranean basins. The Levantine basin south of Cyprus had the lowest concentrations. A Lagrangian Plastic Pollution Index (LPPI) predicting the concentration of plastic debris was validated using the spatial resolution of the data. The advanced state of plastic degradation detected in the analyses led to the conclusion that stranding/fragmentation/resuspension is the key process in the dynamics of floating plastic in Mediterranean surface waters. This is supported by the significant correlation between pollution sources and areas of high plastic concentration obtained by the LPPI.

The marine weathering of microplastics is spectrally characterized by the appearance of new bands that disturb our understanding of the information carried by the spectra. Yet, no explanation has been provided on the chemical origin of these new bands. Thus, the main objective of this work was to identify the origins of these additional bands. To this end, 4042 spectra of poly (styrene), poly(ethylene) and poly(propylene) microplastics collected in the Mediterranean Sea, were analysed using principal component analysis. The results showed that the spectral variability was mainly related to only three processes: chemical ageing, organic and inorganic fouling. These processes probably differ from one polymer family to another due to surface affinities. This work has also led to the proposal of two new polymer indices that could be used to monitor the intensity of (bio)fouling. Finally, the development of advanced analyses could also provide information on the nature of the plastisphere.

A Correction to this paper has been published: https://doi.org/10.1038/s43247-021-00119-5

Anthropogenic pollution from marine microplastic particles is a growing concern, both as a source of toxic compounds, and because they can transport pathogens and other pollutants. Airborne microplastic particles were previously observed over terrestrial and coastal locations, but not in the remote ocean. Here, we collected ambient aerosol samples in the North Atlantic Ocean, including the remote marine atmosphere, during the Tara Pacific expedition in May-June 2016, and chemically characterized them using micro-Raman spectroscopy. We detected a range of airborne microplastics, including polystyrene, polyethylene, polypropylene, and poly-silicone compounds. Polyethylene and polypropylene were also found in seawater, suggesting local production of airborne microplastic particles. Terminal velocity estimations and back trajectory analysis support this conclusion. For technical reasons, only particles larger than 5 µm, at the upper end of a typical marine atmospheric size distribution, were analyzed, suggesting that our analyses underestimate the presence of airborne microplastic particles in the remote marine atmosphere. Airborne microplastic particles with a possible oceanic origin were identified in the marine atmosphere, far from the coast, using micro-Raman spectroscopy analyses of air samples, during a transect across the North Atlantic Ocean in 2016.

The Mediterranean Sea is one of the most studied regions in the world in terms of microplastic (MP) contamination. However, only a few studies have analysed the chemical composition of MPs at the Mediterranean Sea surface. In this context, this study aims to describe the chemical composition as a function of particle size, mass and number concentrations of MPs collected in the surface waters of the Mediterranean Sea. The chemical composition showed a certain homogeneity at the Mediterranean Sea scale. The main polymers identified by Fourier Transform Infra-Red (FTIR) spectroscopy were poly(ethylene) (67.3 +/- 2.4%), poly(propylene) (20.8 +/- 2.1%) and poly(styrene) (3.0 +/- 0.9%). Nevertheless, discrepancies, confirmed by the literature, were observed at a mesoscale level. Thus, in the North Tyrrhenian Sea, the proportion of poly(ethylene) was significantly lower than the average value of the Mediterranean Sea (57.9 +/- 10.5%). Anthropic sources, rivers, or polymer ageing are assumed to be responsible for the variations observed.

The dissolution of anthropogenic atmospheric CO 2 in seawater is suspected to exert a strong pressure on biological processes as well as on carbon and nutrient cycles. Transparent exopolymeric particles (TEP) are polysaccharide particles, formed by aggregation of polymers exuded by phytoplankton and strongly involved in organic matter sedimentation. A mesocosm experiment was performed from February to March 2013 in the coastal waters of the Northwestern Mediterranean Sea, a region characterised by low-nutrient low-chlorophyll (LNLC) levels. We aimed to determine the effect of ocean acidification on the organic carbon pool of TEP produced by a natural phytoplankton community. The experiment was conducted in nine mesocosms of 50 m 3 deployed for 12 days, and subjected to seven partial pressures of CO 2 ( p CO 2 ) levels: one control level in triplicate and six elevated levels between 450 and 1250 μatm. The use of different analytical methods allowed the assessment of TEP density, volume concentration and size distribution as well as both TEP and TEP precursors carbon content. TEP contributed vastly to the particulate organic carbon pool (∼62%), and were mainly produced by small-sized phytoplankton such as pico- and nanophytoplankton. TEP precursors carbon content represented three times the carbon content of particulate TEP, showing that this pool has to be considered in experiments focused on the environmental control of TEP production. There was no evidence that TEP and TEP precursors were dependent on p CO 2 . These parameters exhibited clear temporal dynamics, with tight links to community composition, nutrient availability and other environmental parameters.

International audience; The development of methods to automatically determine the chemical nature of microplastics by FTIR-ATR spectra is an important challenge. A machine learning method, named k-nearest neighbors classification, has been applied on spectra of microplastics collected during Tara Expedition in the Mediterranean Sea (2014). To realize these tests, a learning database composed of 969 microplastic spectra has been created. Results show that the machine learning process is very efficient to identify spectra of classical polymers such as poly(ethylene), but also that the learning database must be enhanced with less common microplastic spectra. Finally, this method has been applied on more than 4000 spectra of unidentified microplastics. The verification protocol showed less than 10% difference in the results between the proposed automated method and a human expertise, 75% of which can be very easily corrected. Highlights ► A machine learning algorithm was developed to determine the chemical nature of microplastics. ► This method allows a fast and reliable automated identification even when several thousand of FTIR spectra have to be studied.► This method is the first part of a software dedicated to the study of microplastics: POSEIDON.

Copyright © 2020 The Author(s). Background: Pollution – unwanted waste released to air, water, and land by human activity – is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems. Ocean pollution is an important, but insufficiently recognized and inadequately controlled component of global pollution. It poses serious threats to human health and well-being. The nature and magnitude of these impacts are only beginning to be understood. Goals: (1) Broadly examine the known and potential impacts of ocean pollution on human health. (2) Inform policy makers, government leaders, international organizations, civil society, and the global public of these threats. (3) Propose priorities for interventions to control and prevent pollution of the seas and safeguard human health. Methods: Topic-focused reviews that examine the effects of ocean pollution on human health, identify gaps in knowledge, project future trends, and offer evidence-based guidance for effective intervention. Environmental Findings: Pollution of the oceans is widespread, worsening, and in most countries poorly controlled. It is a complex mixture of toxic metals, plastics, manufactured chemicals, petroleum, urban and industrial wastes, pesticides, fertilizers, pharmaceutical chemicals, agricultural runoff, and sewage. More than 80% arises from land-based sources. It reaches the oceans through rivers, runoff, atmospheric deposition and direct discharges. It is often heaviest near the coasts and most highly concentrated along the coasts of low- and middle-income countries. Plastic is a rapidly increasing and highly visible component of ocean pollution, and an estimated 10 million metric tons of plastic waste enter the seas each year. Mercury is the metal pollutant of greatest concern in the oceans; it is released from two main sources – coal combustion and small-scale gold mining. Global spread of industrialized agriculture with increasing use of chemical fertilizer leads to extension of Harmful Algal Blooms (HABs) to previously unaffected regions. Chemical pollutants are ubiquitous and contaminate seas and marine organisms from the high Arctic to the abyssal depths. Ecosystem Findings: Ocean pollution has multiple negative impacts on marine ecosystems, and these impacts are exacerbated by global climate change. Petroleum-based pollutants reduce photosynthesis in marine microorganisms that generate oxygen. Increasing absorption of carbon dioxide into the seas causes ocean acidification, which destroys coral reefs, impairs shellfish development, dissolves calcium-containing microorganisms at the base of the marine food web, and increases the toxicity of some pollutants. Plastic pollution threatens marine mammals, fish, and seabirds and accumulates in large mid-ocean gyres. It breaks down into microplastic and nanoplastic particles containing multiple manufactured chemicals that can enter the tissues of marine organisms, including species consumed by humans. Industrial releases, runoff, and sewage increase frequency and severity of HABs, bacterial pollution, and anti-microbial resistance. Pollution and sea surface warming are triggering poleward migration of dangerous pathogens such as the Vibrio species. Industrial discharges, pharmaceutical wastes, pesticides, and sewage contribute to global declines in fish stocks. Human Health Findings: Methylmercury and PCBs are the ocean pollutants whose human health effects are best understood. Exposures of infants in utero to these pollutants through maternal consumption of contaminated seafood can damage developing brains, reduce IQ and increase children’s risks for autism, ADHD and learning disorders. Adult exposures to methylmercury increase risks for cardiovascular disease and dementia. Manufactured chemicals – phthalates, bisphenol A, flame retardants, and perfluorinated chemicals, many of them released into the seas from plastic waste – can disrupt endocrine signaling, reduce male fertility, damage the nervous system, and increase risk of cancer. HABs produce potent toxins that accumulate in fish and shellfish. When ingested, these toxins can cause severe neurological impairment and rapid death. HAB toxins can also become airborne and cause respiratory disease. Pathogenic marine bacteria cause gastrointestinal diseases and deep wound infections. With climate change and increasing pollution, risk is high that Vibrio infections, including cholera, will increase in frequency and extend to new areas. All of the health impacts of ocean pollution fall disproportionately on vulnerable populations in the Global South – environmental injustice on a planetary scale. Conclusions: Ocean pollution is a global problem. It arises from multiple sources and crosses national boundaries. It is the consequence of reckless, shortsighted, and unsustainable exploitation of the earth’s resources. It endangers marine ecosystems. It impedes the production of atmospheric oxygen. Its threats to human health are great and growing, but still incompletely understood. Its economic costs are only beginning to be counted. Ocean pollution can be prevented. Like all forms of pollution, ocean pollution can be controlled by deploying data-driven strategies based on law, policy, technology, and enforcement that target priority pollution sources. Many countries have used these tools to control air and water pollution and are now applying them to ocean pollution. Successes achieved to date demonstrate that broader control is feasible. Heavily polluted harbors have been cleaned, estuaries rejuvenated, and coral reefs restored. Prevention of ocean pollution creates many benefits. It boosts economies, increases tourism, helps restore fisheries, and improves human health and well-being. It advances the Sustainable Development Goals (SDG). These benefits will last for centuries. Recommendations: World leaders who recognize the gravity of ocean pollution, acknowledge its growing dangers, engage civil society and the global public, and take bold, evidence-based action to stop pollution at source will be critical to preventing ocean pollution and safeguarding human health. Prevention of pollution from land-based sources is key. Eliminating coal combustion and banning all uses of mercury will reduce mercury pollution. Bans on single-use plastic and better management of plastic waste reduce plastic pollution. Bans on persistent organic pollutants (POPs) have reduced pollution by PCBs and DDT. Control of industrial discharges, treatment of sewage, and reduced applications of fertilizers have mitigated coastal pollution and are reducing frequency of HABs. National, regional and international marine pollution control programs that are adequately funded and backed by strong enforcement have been shown to be effective. Robust monitoring is essential to track progress. Further interventions that hold great promise include wide-scale transition to renewable fuels; transition to a circular economy that creates little waste and focuses on equity rather than on endless growth; embracing the principles of green chemistry; and building scientific capacity in all countries. Designation of Marine Protected Areas (MPAs) will safeguard critical ecosystems, protect vulnerable fish stocks, and enhance human health and well-being. Creation of MPAs is an important manifestation of national and international commitment to protecting the health of the seas. The Centre Scientifique de Monaco, the Prince Albert II of Monaco Foundation and the Government of the Principality of Monaco John J. Stegeman is supported by U.S. Oceans and Human Health Program (NIH grant P01ES028938 and National Science Foundation grant OCE-1840381). Lora E. Fleming is supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 774567 (H2020 SOPHIE Project) and No 666773 (H2020 BlueHealth Project). Plastic toxicity research for Dimitri Deheyn is supported by the BEST Initiative (https://deheynlab.ucsd.edu/best-2/). Barbara Demeneix is supported by grants from the program H2020. Charles J. Dorman is supported by Science Foundation Ireland Investigator Award 13/IA/1875. William H. Gaze is supported by a Natural Environment Research Council Knowledge Exchange Fellowship NE/S006257/1 on the environmental dimension of antimicrobial resistance. Philippe Grandjean is supported by National Institute of Environmental Health Sciences (NIEHS) of the NIH (grant No. ES027706), a Superfund center grant for the Sources, Transport, Exposure and Effects of Perfluoroalkyl Substances (STEEP) Center. Mark E. Hahn is supported by U.S. Oceans and Human Health Program (NIH grant P01ES028938 and National Science Foundation grant OCE-1840381). Amro Hamdoun is supported by NIH and NSF Program on Oceans and Human Health Grants NIH ES030318 and NSF 1840844. Philipp Hess is supported by the IAEA Core Research Project K41014, by the European H2020 program for funding the EMERTOX project (grant number 778069), by the Atlantic Interreg (grant number Alertox-Net EAPA-317-2016) and by EFSA for the project EUROCIGUA (framework partnership agreement GP/EFSA/AFSCO/2015/03). Rachel T. Noble was supported by the US National Science Foundation Accelerating Innovations in Research #1602023 and the NOAA NERRS Science Collaborative. Maria Luiza Pedrotti is supported by Centre National de la Recherche Scientifique (CNRS). Luigi Vezzulli is supported by the following grants: European FP7 Program Grant AQUAVALENS 311846 and European Union’s Horizon 2020 Research and Innovation Program Grant VIVALDI 678589. Pál Weihe is supported by the Danish EPA programme: Danish Cooperation for Environment in the Arctic and by the Faroese Research Council.

Since the 1950s plastic production has exponentially increased. Different expeditions have sampled microplastics in all the world’s oceans in order to better know this pollution. However, a large amount of plastic particles is collected during all campaigns, such as during the Tara Mediterranean Sea campaign. And, methods developed to analyse them are time-consuming. So, how to work to chemically characterize samples from large libraries?

Within the COST action EMBOS (European Marine Biodiversity Observatory System) the degree and variation of the diversity and densities of soft-bottom communities from the lower intertidal or the shallow subtidal was measured at 28 marine sites along the European coastline (Baltic, Atlantic, Mediterranean) using jointly agreed and harmonized protocols, tools and indicators. The hypothesis tested was that the diversity for all taxonomic groups would decrease with increasing latitude. The EMBOS system delivered accurate and comparable data on the diversity and densities of the soft sediment macrozoobenthic community over a large-scale gradient along the European coastline. In contrast to general biogeographic theory, species diversity showed no linear relationship with latitude, yet a bell-shaped relation was found. The diversity and densities of benthos were mostly positively correlated with environmental factors such as temperature, salinity, mud and organic matter content in sediment, or wave height, and related with location characteristics such as system type (lagoons, estuaries, open coast) or stratum (intertidal, subtidal). For some relationships, a maximum (e.g. temperature from 15–20°C; mud content of sediment around 40%) or bimodal curve (e.g. salinity) was found. In lagoons the densities were twice higher than in other locations, and at open coasts the diversity was much lower than in other locations. We conclude that latitudinal trends and regional differences in diversity and densities are strongly influenced by, i.e. merely the result of, particular sets and ranges of environmental factors and location characteristics specific to certain areas, such as the Baltic, with typical salinity clines (favouring insects) and the Mediterranean, with higher temperatures (favouring crustaceans). Therefore, eventual trends with latitude are primarily indirect and so can be overcome by local variation of environmental factors.

The frequency of lytically infected and lysogenic cells (FLIC and FLC, respectively) was estimated during an in situ mesocosm experiment studying the impact of ocean acidification on the plankton community of a low nutrient low chlorophyll (LNLC) system in the north-western Mediterranean Sea (Bay of Villefranche, France) in February/March 2013. No direct effect of elevated partial pressure of CO2 (pCO2) on viral replication cycles could be detected. FLC variability was negatively correlated to heterotrophic bacterial and net community production as well as the ambient bacterial abundance, confirming that lysogeny is a prevailing life strategy under unfavourable-for-the-hosts conditions. Further, the phytoplankton community, assessed by chlorophyll a concentration and the release of >0.4 μm transparent exopolymeric particles, was correlated with the occurrence of lysogeny, indicating a possible link between photosynthetic processes and bacterial growth. Higher FLC was found occasionally at the highest pCO2-treated mesocosm in parallel to subtle differences in the phytoplankton community. This observation suggests that elevated pCO2 could lead to short-term alterations in lysogenic dynamics coupled to phytoplankton-derived processes. Correlation of FLIC with any environmental parameter could have been obscured by the sampling time or the synchronization of lysis to microbial processes not assessed in this experiment. Furthermore, alterations in microbial and viral assemblage composition and gene expression could be a confounding factor. Viral-induced modifications in organic matter flow affect bacterial growth and could interact with ocean acidification with unpredictable ecological consequences.

International audience; Modifications in the strength of the biological pump as a consequence of ocean acidification, whether positive or negative, have the potential to impact atmospheric CO2 and therefore climate. So far, most plankton community perturbation studies have been performed in nutrient-rich areas although there are some indications that CO2-dependent growth could differ in nutrient-replete vs. -limited regions and with different community compositions. Two in situ mesocosm experiments were performed in the NW Mediterranean Sea during two seasons with contrasted environmental conditions: summer oligotrophic stratified waters in the Bay of Calvi vs. winter mesotrophic well-mixed waters in the Bay of Villefranche. Nine mesocosms were deployed for 20 and 12 d, respectively, and subjected to seven CO2 levels (3 controls, 6 elevated levels). Both phytoplankton assemblages were dominated by pico- and nano-phytoplankton cells. Although haptophyceae and dinoflagellates benefited from short-term CO2 enrichment in summer, their response remained small with no consequences on organic matter export due to strong environmental constraints (nutrient availability). In winter, most of the plankton growth and associated nutrient consumption occurred during the 4-day acidification period (before the experimental phase). During the remaining experimental period, characterized by low nutrient availability, plankton growth was minimal and no clear CO2-dependency was found for any of the tested parameters. While there is a strong confidence on the absence of significant effect of short-term CO2 addition under oligotrophic conditions, more investigations are needed to assess the response of plankton communities in winter when vertical mixing and weather conditions are major factors controlling plankton dynamics.

The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris., Tara Oceans particularly acknowledges the commitment of the following sponsors: the CNRS (in particular Groupement de Recherche GDR3280), the European Molecular Biology Laboratory, Genoscope/CEA, French Government “Investissements d’Avenir” programs OCEANOMICS (ANR-11-BTBR-0008) and FRANCE GENOMIQUE (ANR-10-INBS-09-08), Agence Nationale de la Recherche, and European Union FP7 (Micro B3 no. 287589). We appreciate the support and commitment of agnès b. and E. Bourgois, Veolia Environment Foundation, Region Bretagne, Lorient Agglomeration, World Courier, Illumina, Eléctricité de France Foundation, Fondation pour la recherche sur la biodiversité, Prince Albert II de Monaco Foundation, Tara Foundation, its schooner, and its teams. We are also grateful to the French Ministry of Foreign Affairs for supporting the expedition and to the countries that granted sampling permissions. Tara Oceans would not exist without continuous support from 23 institutes (http://oceans.taraexpeditions.org/en/m/science/les-labos-impliques/). This article is contribution number 52 of Tara Oceans. This study is funded by Tara Oceans and the Malaspina 2010 Expedition project (Spanish Ministry of Economy and Competitiveness, CSD2008-00077) and has received additional support from the King Abdullah University of Science and Technology through baseline funding to X.I. and C.M.D., Campus de Excelencia Internacional del Mar (CEIMAR), and PLASTREND (BBVA Foundation) and MIDaS (CTM2016-77106-R, AEI/FEDER/UE) projects.

The mesopelagic ('twilight') zone of the ocean is the sandwich layer between euphotic surface waters and the deep ocean. The physical, chemical, and biological processes in this layer strongly influ- ence the marine carbon cycle, although some surpris- ing knowledge gaps remain, e.g. with respect to micro- bial communities. We therefore determined biological parameters such as microbial abundances, community respiration, and bacterial and archaeal community composition (as assessed by 16S rRNA gene PCR dena- turing gradient gel electrophoresis, DGGE) over a sea- sonal time scale (at ca. 46 d intervals for 433 d) at a coastal mesopelagic site in the NW Mediterranean Sea (Point C, 300 m depth) and related them to physico- chemical parameters. Some chemical and most biolog- ical parameters showed strong variability, thus con- firming the emerging view that this water layer is more dynamic than previously thought. Community respira- tion was likely influenced by seasonal changes as indi- cated by its indirect relationship with water density. The high detected community respiration rates (0.23� 1.65 µmol O2 l �1 d �1 ) confirm that the twilight zone plays a critical role as a hub between surface and deep water. Statistical analyses indicate that water stratifica- tion, dissolved organic carbon, and transparent exo - polymeric particles were controlling factors of bacterial community composition, whereas the archaeal com- munity was likely controlled by other mechanisms. A sequence analysis of DGGE bands and a literature comparison suggests some specificity of the mesopela- gic zone regarding bacterial and archaeal community composition, thus further confirming the peculiarity of this water layer.

International audience; The composition, size distribution, and abundance of floating plastic debris in surface waters of the Mediterranean Sea were analyzed in relation to distance to land. We combined data from previously published reports with an intensive sampling in inshore waters of the Northwestern Mediterranean. The highest plastic concentrations were found in regions distant from from land as well as in the first kilometer adjacent to the coastline. In this nearshore water strip, plastic concentrations were significantly correlated with the nearness to a coastal human population, with local areas close to large human settlements showing hundreds of thousands of plastic pieces per km2. The ratio of plastic to plankton abundance reached particularly high values for the coastal surface waters. Polyethylene, polypropylene and polyamides were the predominant plastic polymers at all distances from coast (86 to 97% of total items), although the diversity of polymers was higher in the 1-km coastal water strip due to a higher frequency of polystyrene or polyacrylic fibers. The plastic size distributions showed a gradual increase in abundance toward small sizes indicating an efficient removal of small plastics from the surface. Nevertheless, the relative abundance of small fragments (< 2 mm) was higher within the 1-km coastal water strip, suggesting a rapid fragmentation down along the shoreline, likely related with the washing ashore on the beaches. This study constitutes a first attempt to determine the impact of plastic debris in areas closest to Mediterranean coast. The presence of a high concentration of plastic including tiny plastic items could have significant environmental, health and economic impacts.

Coccolithophores, a key phytoplankton group, are one of the most studied organisms regarding their physiological response to ocean acidification/carbonation. The biogenic production of calcareous coccoliths has made coccolithophores a promising group for paleoceanographic research aiming to reconstruct past environmental conditions. Recently, geochemical and morphological analyses of fossil coccoliths have gained increased interest in regard to changes in seawater carbonate chemistry. The cosmopolitan coccolithophore Emiliania huxleyi (Lohm.) Hay and Mohler was cultured over a range of pCO2 levels in controlled laboratory experiments under nutrient replete and nitrogen limited conditions. Measurements of photosynthesis and calcification revealed, as previously published, an increase in particulate organic carbon production and a moderate decrease in calcification from ambient to elevated pCO2. The enhancement in particulate organic carbon production was accompanied by an increase in cell diameter. Changes in coccolith volume were best correlated with the coccosphere/cell diameter and no significant correlation was found between the coccolith volume and the particulate inorganic carbon production. The conducted experiments revealed that the coccolith volume of E. huxleyi is variable with aquatic CO2 concentration but its sensitivity is rather small in comparison with its sensitivity to nitrogen limitation. Comparing coccolith morphological and geometrical parameters like volume, mass and size to physiological parameters under controlled laboratory conditions is an important step to understand variations in fossil coccolith geometry.

International audience; The dynamics of dissolved inorganic nitrogen and phosphorus in seawater after a dust event were followed to better understand the impact of dust deposition in low nutrient waters of the Mediterranean Sea. Three independent abiotic experiments were performed over three seasons (winter, spring, end of summer) characterized by contrasted biogeochemical conditions. Experiments consisted of seeding evapocondensed Saharan dust at the surface of a polyethylene tank filled with filtered surface seawater. Phosphate (PO43-), nitrate (NO3-), size and number of particles and transparent exopolymeric particles production (TEP) were measured over the course of 1 week following seeding. Dust deposition was followed by a transient increase in [PO43-] during the first 3 h with a maximum input of 33, 9, and 39 nM, respectively in May, October and February. The removal of almost all the PO43- initially released suggests a scavenging process of PO43- back onto ferric oxide-rich particles leading to concentrations at the end of the experiment close to the initial values (7 nM in May and October, and 6 nM in February). NO3- released from dust was high especially in May and October (maximum input of 23 and 11 mu M, respectively) and was attributed to nitrogen dissolution from the large amount of small particles (

Kopf, Anna ... et. al.-- 5 pages, 1 figure.-- This manuscript is NOAA-GLERL contribution number 1763, Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits, This work was supported by the Micro B3 project, which is funded from the European Union’s Seventh Framework Programme (FP7; Joint Call OCEAN.2011‐2: Marine microbial diversity – new insights into marine ecosystems functioning and its biotechnological potential) under the grant agreement no 287589

Allison N. Schwier et al., © Author(s) 2015. The effect of ocean acidification and changing water conditions on primary (and secondary) marine aerosol emissions is not well understood on a regional or a global scale. To investigate this effect as well as the indirect effect on aerosol that changing biogeochemical parameters can have, ∼ 52 m3 pelagic mesocosms were deployed for several weeks in the Mediterranean Sea during both winter pre-bloom and summer oligotrophic conditions and were subjected to various levels of CO2 to simulate the conditions foreseen in this region for the coming decades. After seawater sampling, primary bubble-bursting aerosol experiments were performed using a plunging water jet system to test both chemical and physical aerosol parameters (10-400 nm). Comparing results obtained during pre-bloom and oligotrophic conditions, we find the same four log-normal modal diameters (18.5 ± 0.6, 37.5 ± 1.4, 91.5 ± 2.0, 260 ± 3.2 nm) describing the aerosol size distribution during both campaigns, yet pre-bloom conditions significantly increased the number fraction of the second (Aitken) mode, with an amplitude correlated to virus-like particles, heterotrophic prokaryotes, TEPs (transparent exopolymeric particles), chlorophyll a and other pigments. Organic fractions determined from kappa closure calculations for the diameter, Dp ∼ 50 nm, were much larger during the pre-bloom period (64 %) than during the oligotrophic period (38 %), and the organic fraction decreased as the particle size increased. Combining data from both campaigns together, strong positive correlations were found between the organic fraction of the aerosol and chlorophyll a concentrations, heterotrophic and autotrophic bacteria abundance, and dissolved organic carbon (DOC) concentrations. As a consequence of the changes in the organic fraction and the size distributions between pre-bloom and oligotrophic periods, we find that the ratio of cloud condensation nuclei (CCN) to condensation nuclei (CN) slightly decreased during the pre-bloom period. The enrichment of the seawater samples with microlayer samples did not have any effect on the size distribution, organic content or the CCN activity of the generated primary aerosol. Partial pressure of CO2, pCO2, perturbations had little effect on the physical or chemical parameters of the aerosol emissions, with larger effects observed due to the differences between a pre-bloom and oligotrophic environment., This work was supported by the MISTRALS/ChArMEx project and by the EC FP7 project “Mediterranean Sea Acidification in a changing climate” (MedSeA; grant agreement 265103).

Marine debris has been defined as any manufactured or processed solid waste material that enters the marine environment from any source. While plastics constitute a lower percentage of discarded waste, they are the most important part of marine litter, comprising sometimes up to 100 % for floating items. Plastics have been considered an environmental and pollution threat to the marine environment whose importance will increase through the 21st century. In Mediterranean Sea more than 70 % of plastic litters comes from land-based source. Once in the marine environment debris may remain for many years. The Mediterranean Sea is one of the most affected by floating plastic debris however scientific investigation on the impact of microplastics isrecent and results beginning to emerge. Here we report a study on the abundance, size and spatio-temporal distribution of microplastic and zooplakton carried out in summer 2013 in the Ligurian Sea. Surface floating microplastics abundance and area per square kilometer were calculated and compared to the size distribution and mean spatial trends of the neustonic plankton.

Marine litter in the Mediterrranean and Black Seas

The stoichiometric model of Redfield, which describes the elemental composition of marine organic matter, is generally used to link the production of new organic matter to the uptake of nitrate. The Redfield C:N molar ratio of 6.6 is a well-established value for particulate organic matter produced in surface waters. Yet recent studies have shown that the inorganic C:N uptake ratio during nitrate-limiting conditions is >14. This non-Redfield behavior during the production of new organic matter suggests that a large standing stock of organic matter, rich in carbon, should accumulate in the euphotic zone from the spring bloom to late summer. This hypothetical pool of carbon-rich organic matter and the pool of transparent exopolymeric particles (TEP) exhibit similar seasonal distributions, which suggests that TEP may indeed be this carbon-rich pool. For this scheme to work, TEP should have a high C:N ratio. TEP distribution from an open-ocean site in the northwestern Mediterranean Sea (DYFAMED) was monitored, and TEP C:N ratio was measured from TEP produced in the laboratory by bubbling dissolved organic matter collected in the field. We found that the TEP pool increases during the summer season and that the C:N ratio of TEP produced from naturally occurring dissolved organic matter, is well in excess of the Redfield ratio with an overall average C:N molar ratio of ~20. As a result, the production of TEP could be the main pathway of carbon overconsumption required of oligotrophic, nitratelimiting waters, and, thus, TEP may represent an important intermediary pool in the ocean carbon cycle.

The production of transparent exopolymeric particles (TEP) by the coccolithophores, Emiliania huxleyi, Calcidiscus leptoporus and Syracosphaera pulchra was investigated in batch cultures. The abundance, size spectra and carbon content of TEP were examined during the exponential growth phase of both haploid and diploid life stages grown under ambient (400 atm) and elevated (760 atm) CO2 partial pressure (pCO(2)) conditions. Results showed species- and life stage-specific differences in TEP production rate (day(1)) derived from abundance and carbon content of TEP. At 400 atm, TEP production rate was the highest in the diploid stage of S. pulchra and E. huxleyi, while TEP carbon content per cell was the highest in the diploid stage of C. leptoporus. At 760 atm, TEP production rate increased in almost all species and was closely related to the cell growth rates (except in the diploid stage of C. leptoporus), while the slope values of the regression lines between TEP size distribution and concentration decreased. This means that the contribution of smaller size TEP was relatively more important than larger TEP in the high pCO(2) treatment. Elevated pCO(2) is potentially able to alter TEP size distribution. TEP-C content cell(1) generally decreased with increasing pCO(2). TEP-C accounted for 124 of the cell particulate organic carbon production and was inversely related to increasing pCO(2). TEP production by C. leptoporus and S. pulchra has not previously been documented. The amount of organic carbon released as TEP by these coccolithophores is comparable to and may even exceed TEP production by some diatoms.

SUMMARYOcean acidification is predicted to have significant effects on benthic calcifying invertebrates, in particular on their early developmental stages. Echinoderm larvae could be particularly vulnerable to decreased pH, with major consequences for adult populations. The objective of this study was to understand how ocean acidification would affect the initial life stages of the sea urchin Paracentrotus lividus, a common species that is widely distributed in the Mediterranean Sea and the NE Atlantic. The effects of decreased pH (elevated PCO2) were investigated through physiological and molecular analyses on both embryonic and larval stages. Eggs and larvae were reared in Mediterranean seawater at six pH levels, i.e. pHT 8.1, 7.9, 7.7, 7.5, 7.25 and 7.0. Fertilization success, survival, growth and calcification rates were monitored over a 3 day period. The expression of genes coding for key proteins involved in development and biomineralization was also monitored. Paracentrotus lividus appears to be extremely resistant to low pH, with no effect on fertilization success or larval survival. Larval growth was slowed when exposed to low pH but with no direct impact on relative larval morphology or calcification down to pHT 7.25. Consequently, at a given time, larvae exposed to low pH were present at a normal but delayed larval stage. More surprisingly, candidate genes involved in development and biomineralization were upregulated by factors of up to 26 at low pH. Our results revealed plasticity at the gene expression level that allows a normal, but delayed, development under low pH conditions.

Summary We examined the effects of phytoplanktonic food on the survival rate, growth, development, length of larval life and competence for metamorphosis for two species of echinoids from the northeastern part of the western Mediterranean Sea. For larvae of Arbacia lixula seven diets were tested and for those of Paracentrotus lividus two. A diet of Cricosphaera elongata yielded a high survival rate (80%) and rapid larval growth; development was shorter, rudiment diameter was larger and metamorphosis rate was higher. There was a maximum feeding level beyond which no change in growth and development rate was observed. In response to a poor diet, larvae increased the larval period and the length of the larval arms; the survival rate decreased and development was slow and more variable. However, there was no change in the post-larval diameter regardless of diet history.

International audience; Nanomolar concentrations of tri-n-butyltin (TBT) from 5 x 10-10 M to 5 x 10-9 M, were assayed on sea urchin (Paracentrotus lividus) egg cleavage and on larval development. Preincubation enhanced TBT toxicity to first cleavage DNA and protein syntheses but not to intracellular calcium sequestration. Exposure to nanomolar TBT affected the larval development up to the ninth day by reducing arm length and increasing the diameter of the rudiment. Chromatographic analysis of TBT in eggs shows a dose-dependent biomagnification with a half-time of 5 min, which is much shorter than the length of preincubation necessary to provoke cytotoxicity at the same concentration (5 x 10-9 or 5 x 10-10 M). Our data suggest that nanomolar concentrations of TBT similar to those encountered in polluted waters could directly affect sea urchin egg development after fertilization and the larval cycle, these effects being independent of bioaccumulation.

Food preferences (flavor and size) by two echinoderm plutei, Paracentrotus lividus and Arbacia lixula, were studied in two experiments. These included selection between polystyrene spheres (flavored and non-flavored) of different sizes in short-term (15 min) feeding experiments and selection among food algae of varying sizes in long-term (24 h) feeding experiments. Clearance and ingestion rates change during larval ontogenesis and are dependent on the size and the quality of available particles. In general, clearance rates were higher for larvae fed on a mixture of three sizes of polystyrene spheres or algae than for those fed separate foods. Young larvae (4- and 6-arm stage) had a higher clearance rate with larger-sized spheres (18.5 mu m) and larger-sized alga Prorocentrum micans (26.0 mu m). For older larvae (8-arm stage with rudiment), the preference was divided between medium- and larger-sized particles. Retention capability of small-sized spheres (2.9 mu m) and algae (Isochrysis galbana), compared to the other sizes of particles, was very low during all experiments. When different sizes of spheres and algae were offered separately, Arbacia lixula larvae ingested larger-sized particles at great rates throughout development. Young Paracentrotus lividus larvae ingested larger-sized spheres at greater rates than other sizes of particles. During older larval stages, medium-sized spheres are ingested preferentially. In mixtures of different-sized particles, medium-sized spheres and algae are generally captured first. For young larvae clearance and ingestion rates increased when spheres were treated with a filtrate of Criscosphaera elongata algae. Young larvae select particles on the basis of their quality and size; as larvae grow, particle selection is size dependent.

Seasonal and annual variations in the distribution and abundance of echinoderm larvae (early to post-larvae of principally echinoids and ophiuroids), were determined from a series of plankton net tows taken at three stations in the Bay of Villefranche (France) and along a radial transect of 28 nautical miles (52 km), from the Bay to half-way to Corsica, between 1984 and 1988. Spatial distribution of six echinoderm species have been mapped. For the echinoids, Paracentrotus lividus and Arbacia lixula, spawning takes place twice a year and appears to be synchronous because larval cohorts were comprised of distinct age-classes both near and far from the coast. Recruitment for these species is, therefore, thought to occur at well-defined periods. In contrast, the ophiuroid species studied (Amphiura filiformis, Ophwthrix fragilis, Ophiopluteus bimaculatus and O. compressus) spawn several times per year with a relatively short period in late spring and a prolonged spawning between the end of autumn and winter. These later results are consistent with the presence of mixed size-classes of larvae either from the nearby coast or offshore. Recruitment for these ophiuroids appears to be much more variable and spread over time.

Postlarvae and competent larvae of five species of echinoids (Genoadaris metadata, Arbticia lixula, Puracentrolus lividus, Echinocyamus pusillus, and Ediinocardiurn cordulum) were found in vertical hauls taken in the upper layer of the water column (30-0 m). Competence of larvae was associated with both the extrusion of the adult rudiment and the retraction of the epidermis of the arms. Postlarvae of A. lixida were found offshore in areas where the sea floor is at a depth of more than 2(K)C.m. The occurrence of postlarvae far from their settlement grounds questions the necessity of a suitable benthic substrate to induce metamorphosis. Hypotheses dealing with the possibility of undergoing metamorphosis in midwater are discussed. Resume Des larves competentes et des post-larves de trois echinides reguliers: Arbacia lixula, Genocidaris maculata, Paracentrotus lividus et du clypeastreide Echinocyamus pusillus ont ete trouvees dans des peches verticales effectuees dans des couchesd'eaux superficielles (30-0 m). Les larves competentes montrent les caracteristiques considerees comme des phenomenes irreversibles de la metamorphose: evagination du rediment et retraction de 'epiderme des bras larvaires. Des post-larves de 'oursin A. lixula ont ete recoltees dans des peches pratiquees loin de la cote au-dessus de fonds de plus de 2000m. La presence de ces post-larves loin des sites de recrutement des juveniles pose le probleme de la necessite du choix d'un substrat benthique pour que les evenements qui caracterisent la metamorphose puissent etre induits. Ce probleme et les hypotheses sur la possibilite d'une induction en pleine eau est discute.