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17 pages, 7 figures, 5 tables.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) ; Estuarine environments are highly heterogeneous habitats where numerous organisms interact with each other. Aquaculture systems encompass such interactions, and the eventual yields depend on how the cultivated species respond to the environmental heterogeneity. Marine mussels are calcifying organisms that rely on calcium carbonate shell and byssus filaments secreted during their lifetime to protect soft vital tissues against aggressive (abiotic and biotic) environments. Nevertheless, these protective structures can be energetically costly, depending on the environment, thus affecting the energy allocation patterns in the organism. Consequently, other important fitness parameters for the aquaculture industry, such as soft tissue condition and market value, may also be affected. Here, we present a spatial and temporal analysis of the protective and soft tissues responses in the mussel Mytilus galloprovincialis with the aim of obtaining a better understanding of the inter-location variability in individual's performance and the corresponding main environmental drivers. Local environment with regard to food availability and hydrodynamics impact very distinctly mussel tenacity and shell thickening, e.g., higher-energy environments at the outer exposed zones caused individuals secreted stronger byssus and thicker shells. By contrast, the state of soft tissues (condition index) was similar between very distinct and distant outer exposed and inner sheltered zones due to differences in both environmental drivers. A novel, intuitive ecological index that measures the impact of both protective and soft tissues was developed and is discussed in relation to cultivation timing. The data presented provides the basis for understanding the natural variability in energetic requirements for different vital tissues in bivalve mollusk that support survival and growth. We report the scientific basis for management actions aimed to shortening the cultivation cycle in the aquaculture sector. These actions are based on the combined use of the PROFIT index and other aquaculture practices (e.g., modifying density). PROFIT helps to identify when the quality of the product, understood as PROtection and FITness strategies, would be best suited for the market ; This study was funded by the Spanish Government through the Ministerio de Economía y Competitividad through European FEDER funds (projects Ref. AGL-2013-45945-R, CTM2016-76146-C3-2-R/CTM2016-76146-C3-1-R) ; Peer reviewed

6 pages, 5 figures, 1 table.-- This is an open access article under the CC BY-NC-ND license ; We describe the valve-opening behavior of raft-cultivated mussels (Mytilus galloprovincialis) in the Ría de Arousa (Arousa estuary), Spain. Eight rope-grown mussels [mean ± standard error (SEM), shell length 61.6 ± 2.1 mm] were connected to a non-invasive valvometry apparatus that monitored (one measurement min−1) the magnitude of valve openness systematically over a 10 day period. It was found that valves were open 97.5 ± 1.3% percent of the time. Valve closures were not synchronized among the eight monitored mussels, suggesting that feeding cessation was physiologically-regulated rather than environmentally-mediated. The opening amplitudes that were most frequently observed were in the range of 60–90%, indicating that, when open, valves are usually opened relatively close to their maximum possible extent. The majority (7/8) of mussels displayed a circadian rhythm (τ = 24.0 h) in valve opening amplitude. They tended to exhibit maximum valve opening during nighttime and minimum opening during daytime. It is possible that the light:dark cycle represents an environmental zeitgeber entraining an endogenous gaping rhythm in this bivalve ; This study was funded by the Spanish government through the Ministerio de Economía y Competitividad (project Mytiga AGL2013- 45945-R) ; Peer reviewed

9 páginas, 1 tabla, 2 figuras.-- Proyecto Carbochange.-- The OVIDE data analyzed in this study are available at the CLIVAR and Carbon Hydrographic Data Office (http://cchdo.ucsd.edu/search?q=Ovide) and at the Carbon Dioxide Information Analysis Center (http://cdiac.ornl.gov/oceans/RepeatSections/clivar_ovide.html). The climatology of Takahashi et al. was downloaded from http://www.ldeo.columbia.edu/res/pi/CO2/carbondioxide/pages/air_sea_flux_2000.html ; The subpolar North Atlantic (SPNA) is important in the global carbon cycle because of the deep water ventilation processes that lead to both high uptake of atmospheric CO2 and large inventories of anthropogenic CO2 (Cant). Thus, it is crucial to understand its response to increasing anthropogenic pressures. In this work, the budgets of dissolved inorganic carbon (DIC), Cant and natural DIC (DICnat) in the eastern SPNA in the 2000s, are jointly analyzed using in situ data. The DICnat budget is found to be in steady state, confirming a long-standing hypothesis from in situ data for the first time. The biological activity is driving the uptake of natural CO2 from the atmosphere. The Cant increase in the ocean is solely responsible of the DIC storage rate which is explained by advection of Cant from the subtropics (65%) and Cant air-sea flux (35%). These results demonstrate that the Cant is accumulating in the SPNA without affecting the natural carbon cycle ; This work is a contribution to the EU FP7 CARBOCHANGE project (264879) and the ANR GEOVIDE project (http://www.agence-nationale-recherche.fr/?Project=ANR-13-BS06-0014). For this work P. Zunino was funded by CARBOCHANGE and GEOVIDE projects as well as by IFREMER. The Tricontinental Atlantic Campus funded a 6 months contract for the first author at the Universidad de Las Palmas de Gran Canaria where part of this paper was written. P. Lherminier was supported by IFREMER, H. Mercier by the CNRS and the ATLANTOS GA 633211 H2020 project, and A. Padin by the Consejo Superior de Investigaciones Científicas (CSIC). A.F. Ríos and F.F. Pérez were supported by BOCATS (CTM2013-41048-P) project cofounded by the Spanish Government and the Fondo Europeo de Desarrollo Regional (FEDER) ; Peer reviewed

16 pages, 4 figures, 2 tables.-- This is an Open Access article distributed under the terms of the Creative Commons Attribution License ; The impact of simulated seawater acidification and warming conditions on specimens of the mussel Mytilus galloprovincialis locally adapted to very distinct, widely separated sites in the Mediterranean Sea (Tunisia) and Atlantic Sea (Galicia, NW Spain) was evaluated in relation to key behavioural and eco-physiological parameters. Over the 2-month exposure to the experimental conditions, mussels were fed optimally to ensure that there are no synergistic interactions between climate change drivers and energetic status of the individuals. In general, regardless of origin (Atlantic or Mediterranean), the mussels were rather resilient to acidification for most of the parameters considered and they were able to grow in strongly acidified seawater through an increased feeding activity. However, shell strength decreased (40%) consistently in both mussel populations held in moderately and highly acidified seawater. The observed reduction in shell strength was not explained by slight alterations in organic matter, shell thickness or aragonite:calcite ratio. The combined effects of high acidification and warming on the key response of byssus strength caused a strong decline in mussel performance, although only in Galician mussels, in which the valve opening time decreased sharply as well as condition index (soft tissue state) and shell growth. By contrast, the observed negative effect of highly acidified scenario on the strength of Tunisian mussel shells was (partly but not totally) counterbalanced by the higher seawater temperature. Eco-physiological and behavioural interactions in mussels in relation to climate change are complex, and future scenarios for the ecology of the species and also the feasibility of cultivating them in Atlantic and Mediterranean zones are discussed ; This work was supported by the Spanish government through the Ministerio de Economía y Competitividad and European FEDER funds (AGL-2013-45945-R, CTM2016-76146-C3-2-R/CTM2016-76146-C3-1-R) and the Spanish National Research Council (CSIC) through the program I-COOP+ 2016 (ICOOPA20147 to J.L.) ; Peer reviewed

The carbon dioxide taken up by the ocean is increasing as levels of atmospheric carbon dioxide increase, thus lowering the ocean pH and altering the carbonate system. In this laboratory study, we evaluated the physiological responses of juvenile mussels Mytilus galloprovincialis from Galician waters (NW Iberian Peninsula) exposed to control (500 µatm) and elevated (800 or 1200 µatm) seawater pCO2 conditions under 2 different feeding regimes (optimal and suboptimal). Shell properties such as compressive strength and composition (organic matter and aragonite:calcite ratio) were negatively affected by high seawater pCO2, regardless of food availability. This result suggests that water chemistry is a main driver for shell development. Under the optimal feeding regime, mussel feeding rates increased in response to elevated pCO2, presumably as a strategy to maintain a high strength of attachment. In contrast, mussels on the suboptimal diet showed weak attachment and narrow valve opening at the highest pCO2 condition. Thus, our results suggest that with optimal food availability, mussels were resilient to water acidification with respect to feeding activity, valve opening and attachment strength. Under a suboptimal diet, however, the ability of mussels to respond to acidification was compromised. These results highlight complex ecophysiological interactions for calcifying organisms subjected to climate change ; This study was funded by the Spanish government through the Ministerio de Economía y Competitividad that included European FEDER funds (projects Ref. AGL-2013-45945-R, CTM2016-76146-C3-2-R/ CTM2016- 76146-C3-1-R). J.L. acknowledges funding from the Spanish National Research Council (CSIC) through the Program ICOOP+ 2016 (Ref. ICOOPA20147) ; Peer reviewed

10 pages, 6 figures, 1 table.-- This article is licensed under a Creative Commons Attribution 4.0 International License ; The oceanic uptake of atmospheric carbon dioxide (CO 2) emitted by human activities alters the seawater carbonate system. Here, the chemical status of the Northeast Atlantic is examined by means of a high-quality database of carbon variables based on the GO-SHIP A25 section (1997–2018). The increase of atmospheric CO 2 leads to an increase in ocean anthropogenic carbon (Cant) and a decrease in carbonate that is unequivocal in the upper and mid-layers (0–2,500 m depth). In the mid-layer, the carbonate content in the Northeast Atlantic is maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate and the arrival of subpolar-origin waters close to carbonate undersaturation. In this study we show a progression to undersaturation with respect to aragonite that could compromise the conservation of the habitats and ecosystem services developed by benthic marine calcifiers inhabiting that depth-range, such as the cold-water corals (CWC) communities. For each additional ppm in atmospheric pCO2 the waters surrounding CWC communities lose carbonate at a rate of − 0.17 ± 0.02 μmol kg−1 ppm−1. The accomplishment of global climate policies to limit global warming below 1.5–2 ℃ will avoid the exhaustion of excess carbonate in the Northeast Atlantic. ; For this work M. Fontela was funded by the Spanish Ministry of Economy and Competitiveness (BES-2014-070449) supported by the Spanish Government and co-funded by the Fondo Europeo de Desarrollo Regional 2007–2012 (FEDER) and by Portuguese national funds from FCT Foundation for Science and Technology through project UID/Multi/04326/2019 and CEECINST/00114/2018. F.F. Pérez was supported by the BOCATS Project (CTM2013-41048-P) and ARIOS project (CTM2016-76146-C3-1-R) both co-funded by the Spanish Government and the Fondo Europeo de Desarrollo Regional (FEDER). This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 820989 (COMFORT, Our common future ocean in the Earth system—quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points). ; Peer reviewed

20 pages, 11 figures, 2 tables.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) ; Estuarine exchange flow plays an important role in the biogeochemical properties exchange between the coastal ocean and the estuaries. Circulation patterns inside the Rias Baixas (NW Iberian Peninsula) have been widely studied, while the Ría de Pontevedra has received less attention. A high-resolution ROMS-AGRIF system configuration with three online two-way nesting domains was used and validated to enhance the knowledge about the circulation patterns of this Ría. Two representative estuarine circulation patterns were studied: a coastal upwelling event and a downwelling event associated with a maximum river runoff of 84 m3/s. An analysis using Empirical Orthogonal Functions (EOF) was applied to the horizontal subtidal velocity fields at the surface layer and at 20 m depth and to the subtidal normal velocity across vertical cross-sections. Upwelling events are characterized by a reinforcement of the positive estuarine circulation, in which the surface waters outflow and deep waters inflow at the main sill of the Ría, whilst full water column inflow (outflow) is observed at the northern (southern) openings. Conversely, downwelling events induce an opposite behavior, consisting of a negative estuarine circulation with the surface (deep) inflow (outflow) at the main sill of the Ría and outflow (inflow) at the northern (southern) openings. Evidences of a front splitting two vertical clockwise circulation cells were found. These cells are associated with the ocean water subduction that enters through the surface layer under downwelling favorable winds and this surface inflow opposes to the direction of the inner estuarine circulation. The EOF study confirms that shelf wind forcing has an important contribution to the variability of the velocity field, inducing positive or negative estuarine like circulation. The temporal principal components (PC) of EOF analysis present correlations of 0.92 between the meridional wind component and the first mode, and 0.77 between the zonal wind component and the second mode. Third EOF mode represents the circulation during transitional winds when some vorticity structures are visible. The realistic high-resolution simulation of the physical conditions at the Ría de Pontevedra provides new insights into the ocean-estuarine water exchanges and allow the visualization of recirculation processes and characteristic structures that have consequences in the marine ecosystem and in their productivity ; This study was performed in the framework of MYTIGA project (AGL2013-45945-R) supported by the Spanish government through the Ministerio de Economía y Competitividad. This work contributes to HABWAVE project (LISBOA-01-0145-FEDER-031265), and CESAM_LA (UIDP/50017/2020 + UIDB/50017/2020), funded by FCT/MEC through national funds, and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. This work also contributes to MarRisk project (0262_MARRISK_1_E) co-funded by European Regional Development Fund (FEDER) in the framework of Interreg V A España – Portugal (POCTEP) 2014-2020 ; Peer reviewed

6 páginas, 5 figuras, 1 tabla.-- Proyecto Carbochange.-- Open access ; Global ocean acidification is caused primarily by the ocean's uptake of CO2 as a consequence of increasing atmospheric CO2 levels. We present observations of the oceanic decrease in pH at the basin scale (50°S–36°N) for the Atlantic Ocean over two decades (1993–2013). Changes in pH associated with the uptake of anthropogenic CO2 (ΔpHCant) and with variations caused by biological activity and ocean circulation (ΔpHNat) are evaluated for different water masses. Output from an Institut Pierre Simon Laplace climate model is used to place the results into a longer-term perspective and to elucidate the mechanisms responsible for pH change. The largest decreases in pH (∆pH) were observed in central, mode, and intermediate waters, with a maximum ΔpH value in South Atlantic Central Waters of −0.042 ± 0.003. The ΔpH trended toward zero in deep and bottom waters. Observations and model results show that pH changes generally are dominated by the anthropogenic component, which accounts for rates between −0.0015 and −0.0020/y in the central waters. The anthropogenic and natural components are of the same order of magnitude and reinforce one another in mode and intermediate waters over the time period. Large negative ΔpHNat values observed in mode and intermediate waters are driven primarily by changes in CO2 content and are consistent with (i) a poleward shift of the formation region during the positive phase of the Southern Annular Mode in the South Atlantic and (ii) an increase in the rate of the water mass formation in the North Atlantic ; This research was supported by the Spanish Ministry of Sciences and Innovation and was cofunded by the European Regional Development Fund 2007–2012 (FEDER) through the Carbon Transport and Acidification Rates in the North Atlantic Project (CTM2010-17141/MAR), by the European Union Seventh Framework Programme CARBOCHANGE project under Grant Agreement 264879, and by the Office of Atmospheric and Oceanic Research of the NOAA ; Peer reviewed

15 pages, 3 tables, 9 figures ; Since the Industrial Revolution, the North Atlantic Ocean has been accumulating anthropogenic carbon dioxide (CO2) and experiencing ocean acidification1, that is, an increase in the concentration of hydrogen ions (a reduction in pH) and a reduction in the concentration of carbonate ions. The latter causes the 'aragonite saturation horizon'—below which waters are undersaturated with respect to a particular calcium carbonate, aragonite—to move to shallower depths (to shoal), exposing corals to corrosive waters2,3. Here we use a database analysis to show that the present rate of supply of acidified waters to the deep Atlantic could cause the aragonite saturation horizon to shoal by 1,000–1,700 metres in the subpolar North Atlantic within the next three decades. We find that, during 1991–2016, a decrease in the concentration of carbonate ions in the Irminger Sea caused the aragonite saturation horizon to shoal by about 10–15 metres per year, and the volume of aragonite-saturated waters to reduce concomitantly. Our determination of the transport of the excess of carbonate over aragonite saturation (xc[CO32−])—an indicator of the availability of aragonite to organisms—by the Atlantic meridional overturning circulation shows that the present-day transport of carbonate ions towards the deep ocean is about 44 per cent lower than it was in preindustrial times. We infer that a doubling of atmospheric anthropogenic CO2 levels—which could occur within three decades according to a 'business-as-usual scenario' for climate change4—could reduce the transport of xc[CO32−] by 64–79 per cent of that in preindustrial times, which could severely endanger cold-water coral habitats. The Atlantic meridional overturning circulation would also export this acidified deep water southwards, spreading corrosive waters to the world ocean ; The OVIDE research project was co-funded by the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) and CNRS/Institut National des Sciences de l'Univers (INSU)/Les Enveloppes Fluides et l'Environnement (LEFE). H.M. was supported by CNRS. This is a contribution to the AtlantOS project funded by the European Union's Horizon 2020 research and innovation programme under grant agreement 633211. This study is also a contribution to the BOCATS project (CTM2013-41048-P) supported by the Spanish Ministry of Economy and Competitiveness and co-funded by the Fondo Europeo de Desarrollo Regional 2014–2020 (FEDER) ; Peer reviewed

54 páginas, 19 figuras, 3 anexos ; The FICARAM-15 is the fifteenth repetition of a section conducted in 1994. This section is part of the international program GOSHIP (http://www.go-ship.org/CruisePlans.html) to develop a globally coordinated network of sustained hydrographic sections as part of the global ocean/climate observing system. The objective of the FICARAM-15 cruise is to investigate the temporal evolution of the anthropogenic carbon and evaluate the CO2 absorption capacity of the South Atlantic region, the Equatorial zone, and the subtropical region of Azores-Gibraltar in the North Atlantic. This cruise is supported by the CATARINA project funded by the Ministry of Economy and Competitiveness (CTM2010-17141) and is part of the European Union FP7 project CARBOCHANGE (http://carbochange.b.uib.no/). The objective of FICARAM-15 cruise is framed in the CATARINA project conducted by the tasks I.2.1 (air-sea CO2 exchange) I.3 (ventilation of water masses), I.4.1 (zonal variability of N2O and CH4), I.4.2 (anthropogenic carbon storage), I.4.4 (saturation horizon of calcium carbonate along the section) and I.5.4 (evolution of the acidification rates). Another component of the FICARAM-15 cruise aims to examine the biological and biogeochemical mechanisms that hinder total dissolved organic carbon (DOC) remineralisation in marine systems, taking a multidisciplinary perspective and applying many different approaches. This is the global objective of the Spanish project DOREMI (CTM2012-34294) that joins this FICARAM-15 cruise. ; During the FICARAM cruise the physical oceanography group was responsible for collecting the following data sets: CTD and XBT data; vessel-mounted ADCP and lowered ADCP; continuous thermosalinograph. Physical oceanographers participated in the cruise financed through Project "Tipping Corners in the Meridional Overturning Circulation" (TIC-MOC), CTM2011-28867. The FICARAM-15 cruise was organized in two phases with a common sampling. LEG 1: From Punta Arenas (Chile) to Recife (Brazil): 62 stations. Chief Scientist: Aida F. Ríos, PI of CATARINA project LEG 2: From Recife (Brazil) to Cartagena (Spain): 46 stations Chief Scientist: Celia Marrasé, PI of DOREMI project This report contains the sampling of all the variables at each station along the FICARAM section, as well as the analysis of the biogeochemical variables and the preliminary results. The principal investigator of the DOREMI project produced another report with the common sampling section, showing the analysis and results of the experiments on dissolved organic matter carried out on board. ; This cruise is supported by the CATARINA project funded by the Ministry of Economy and Competitiveness (CTM2010-17141) and is part of the European Union FP7 project CARBOCHANGE (http://carbochange.b.uib.no/) ; Peer reviewed