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The cruises conducted in the spring and autumn of 2008 in the frame of the European project SESAME represented the first coordinated surveys that allowed acquiring a quasi-synoptic picture of epipelagic mesozooplankton in most regions of the Mediterranean Sea. Seasonal differences were recorded in biomass, total abundance, and community composition and structure. In both seasons, it did not appear a clear west-east decreasing gradient in total standing stock, but rather regional discontinuities. However, west or east preferences were observed in the distribution of some zooplanktonic groups and copepod species. An artificial neural network analysis (SOM) identified, in both seasons, a clear mesozooplankton regionalization, which resembled the autotrophic regimes based on color remote sensing data. The correspondence between the distribution of zooplankton communities and the trophic regimes appeared more precise in spring, when the increased concentration of chlorophyll a makes the Mediterranean Sea a more heterogeneous environment, but it was still visible in the more uniform oligotrophic autumn conditions. Three distinct types of mesozooplankton communities seem to flourish in the investigated regions: the first type is the most widespread and thrives in the >non-blooming> areas, the second type occurs in the >intermittently-blooming> areas, and the third type is a characteristic of areas with recurrent and intense phytoplankton blooms. Overall, the well defined regionalization of mesozooplankton that appears from our results corroborates the view of the Mediterranean Sea as a mosaic environment, as previously emerged from the analyses of different biological compartments. © 2013 Elsevier B.V. This is a contribution of the European IP SESAME (FP6), Work Package-2 on “Coordinated acquisition of new multidisciplinary data in the Southern European Seas”. Mazzocchi, M. G. et al. Peer Reviewed

We would like to express our deepest gratitude to L. Naval, the staff from ``La Bacaladera´´ and the crew from ``Attalaya Berria´´ for sampling help in the Bay of Biscay. We also thank all the people that actively participated in sample collection across the Mediterranean Sea and the Strait of Gibraltar. The authors are indebted to the two anonymous reviewers for their many helpful insights and suggestions which improved the manuscript considerably. This work was carried out under the provision of the ICCAT Atlantic Wide Research Programme for Bluefin Tuna (GBYP), co-funded by the European Union (grant SI2/585616), by several other ICCAT CPCs, the ICCAT Secretariat and by other entities (see http://www.iccat.int/GBYP/en/Budget.htm). The contents of this paper do not necessarily reflect the point of view of ICCAT or of the other funders. This work was also supported by grant CTM2011-27505 by the Spanish Ministry of Economy and Competitiveness (MINECO), National Geographic Society (Grant W132-10) and the Basque Government (Grant 351BI20080022). This paper is contribution number 733 from AZTI-Tecnalia (Marine Research). Otoliths of Atlantic bluefin tuna (Thunnus thynnus) collected from the Mediterranean Sea and North Atlantic Ocean were analyzed to evaluate changes in the seawater isotopic composition over time. We report an annual otolith delta C-13 record that documents the magnitude of the delta C-13 depletion in the Mediterranean Sea between 1989 and 2010. Atlantic bluefin tuna in our sample (n = 632) ranged from 1 to 22 years, and otolith material corresponding to the first year of life (back-calculated birth year) was used to reconstruct seawater isotopic composition. Otolith 8180 remained relatively stable between 1989 and 2010, whereas a statistically significant decrease in delta C-13 was detected across the time interval investigated, with a rate of decline of 0.05 parts per thousand yr(-1) (-0.94 parts per thousand depletion throughout the recorded period). The depletion in otolith delta C-13 over time was associated with the oceanic uptake of anthropogenically derived CO2. (C) 2016 Elsevier B.V. All rights reserved.

A comprehensive understanding of the mechanisms that control the ctenophore Mnemiopsis blooms in the Black Sea is gained with a zero-dimensional population based model. The stage resolving model considers detailed mass and population growth dynamics of four stages of model-ctenophore. These stages include the different growth characteristics of egg, juvenile, transitional and adult stages. The dietary patterns of the different stages follow the observations given in the literature. The model is able to represent consistent development patterns, while reflecting the physiological complexity of a population of Mnemiopsis species. The model is used to analyze the influence of temperature and food variability on Mnemiopsis reproduction and outburst. Model results imply a strong temperature control on all stages of Mnemiopsis and that high growth rates at high temperatures can only be reached if food sources are not limited (i.e. 25 mg C m(-3) and 90 mg C m(-3) mesozooplankton and microplankton, respectively). A decrease of 5 degrees C can result in considerable decrease in biomass of all stages, whereas at a temperature of 25 degrees C a 40% decrease in food concentrations could result in termination of transfer between stages. Model results demonstrate the strong role of mesozooplankton in controlling the adult ctenophore biomass capable of reproduction and that different nutritional requirements of each stage can be critical for population growth. The high overall population growth rates may occur only when growth conditions are favorable for both larval and lobate stages. Current model allows the flexibility to assess the effect of changing temperature and food conditions on different ctenophore stages. Without including this structure in end-to-end models it is not possible to analyze the influence of ctenophores on different trophic levels of the ecosystem.

International audience; There is growing interest in linking marine biogeochemistry with marine ecosystems research in response to the increasing need to understand and predict the effect of global change on the marine ecosystem. Such a holistic approach combines oceanographic and biogeochemical processes and information on organisms, ranging from microbes to higher-trophic-levels. Comparative studies offer a means to improve understanding of critical mechanisms that influence marine systems by showing differences in ecosystem response to changing ocean conditions. Comparing similar biomes that differ in a particular set of physical or biological characteristics can provide insight into the susceptibility of the key features of a system to perturbation. Also, comparative studies based on long-term observations at fixed time-series stations enable the evaluation of long-term changes in the physical and biological environment, such as those driven by climate patterns. Moreover, the comparative approach provides a feasible alternative to costly and complex research programs designed to provide detailed end-to-end evaluations of marine systems. Planned and unplanned perturbations allow the investigation of the sensitivity of ecosystems and their biogeochemical processes to change at different time and space scales. In well-studied regions where sufficient data are available, models can provide comprehensive syntheses, mechanistic insights and even predictions. We present examples of successful comparative studies that incorporate both biogeochemical and ecosystems aspects. A framework for a basic approach for comparative studies is proposed that considers the interactions between biogeochemical cycles and ecosystems. This approach is based on constructing a minimalistic observational framework grounded within a conceptual model. (C) 2012 Elsevier B.V. All rights reserved.

The Black Sea, a land-locked deep basin with sulfide bearing waters below 150-200 m, has been subject to anthropogenic pressures since the 1970s. Large inputs of nutrients (nitrate - N, phosphate - P, silicate - Si) with high N/P but low Si/N ratios and subsequent development of intensive eutrophication over the basin have changed vertical distributions and inventories of nutrients and redox-sensitive metals in the oxic, suboxic and anoxic layers. Chemical data sets obtained between 1988 and 2010, and older data from before 1970 were evaluated to assess spatial/temporal variations of the dissolved oxygen (O-2), nutrients and dissolved/particulate manganese (Mn-d, Mn-p) in the water column from the lower salinity, oxygenated surface waters through the SubOxic Layer (SOL; O-2 < 20 mu M; H2S < 1 mu M) to the anoxic, sulfidic water interface. Correlations were observed between salinity and nutrients (nitrate, silicate) in the nearshore waters off the Danube delta and in the southwestern (SW) coastal waters which had low Si/N ratios. Surface waters from the western central gyre were consistently depleted in nitrate and phosphate with low N/P but higher Si/N molar ratios throughout the year. Chemical profiles obtained recently in the Rim Current and western central gyre displayed very similar vertical features through the halocline to the sulfidic water interface. However, in the SW coastal margin, lateral intrusion of O-2 and nutrients by the Bosporus Plume resulted in formation of secondary maxima of nitrate, nitrite and O-2 in the SOL, and local deepening of the first appearance of anoxic, sulfidic waters. Before the mid 1960s. nitrate-enriched major rivers fed the Black Sea with high N/P ratios (>50). The surface waters over the basin were rich in silicate (25-70 mu M), but poor in nitrate (<0.1 mu M) and phosphate (0.05-03 mu M), resulting in very high Si/N (>500) but very low N/P (<1.0) ratios. After the mid 1970s, construction of dams, especially on the Danube River, resulted in lower Si concentrations. At this time the increased loads of anthropogenic nitrate and phosphate by the major rivers resulted in lower Si/N, but still high N/P molar ratios, which enhanced eutrophication (production of particulate organic matter, POM) drastically in the coastal waters. This led to reductions in the surface Si/N ratio by up to 500-fold in the western basin while the N/P ratio increased. The enhanced POM export increased the nitrate inventory and thus N/P ratios of the NW shelf waters spreading over the whole basin. The increased export of POM decreased the Si inventory of the upper layer down to the boundary of sulfidic waters. This export also increased O-2 consumption and removal of nitrate to N-2 form by denitrification in the oxic/suboxic interface, leading to seasonal/decadal changes in the boundaries of the nitracline and main oxycline and changes in the slopes of the nitrate-phosphate and Apparent Oxygen Utilization (AOU)-nitrate regressions in the steep oxycline down to the SOL. These slopes are much smaller than those observed in the lower layer of Marmara Sea fed by the Black Sea outflow. The enlargement of SOL by similar to 15-20 m after the 1970s modified the vertical features of nitrate, phosphate and manganese (Mn-d, Mn-p) species in the redox gradient zone. (C) 2013 Elsevier B.V. All rights reserved.

Coordinated cruises conducted in the Black Sea offshore waters in spring and autumn 2008, within the framework of European project SESAME, allowed the obtainment of a quasi-synoptic picture of the mesozooplankton standing stock and community composition. A clear spatial difference in total abundance was observed in spring with higher values over the slope than over the deep basin, due to the development of the fast boundary current. In autumn, standing stock was lower than in spring weakening of the boundary current and extensive eddy formation caused small-scale variability in mesozooplankton distribution and intensification of the exchange between the different parts of the sea. In both seasons, copepods comprised the bulk (62-95%) of mesozooplankton biomass. Community composition variability was tested for the first time using data obtained from the entire basin; the application of neural network analysis (Self-organizing Maps) revealed a rather homogenous picture of community composition. The development of cladocerans in autumn resulted in the differentiation of the slope areas from the deep basin. Mass development of the heterotrophic dinoflagellate Noctiluca scintillans was observed in the western and north-western areas in autumn. No change in standing stock values and community composition seem to have occurred since 2000 in the north-eastern region. © 2013 Elsevier B.V.

Abstract Four Ecopath mass-balance models were implemented for evaluating the structure and function of the Black Sea ecosystem using several ecological indicators during four distinctive periods (1960s, 1980–1987, 1988–1994 and 1995–2000). The results exemplify how the Black Sea ecosystem structure started to change after the 1960s as a result of a series of trophic transformations, i.e., shifts in the energy flow pathways through the food web. These transformations were initiated by anthropogenic factors, such as eutrophication and overfishing, that led to the transfer of large quantities of energy to the trophic dead-end species, which had no natural predators in the ecosystem, i.e., jellyfish whose biomass increased from 0.03 g C m − 2 in 1960–1969 to 0.933 g C m − 2 in 1988–1994. Concurrently, an alternative short pathway for energy transfer was formed that converted significant amounts of system production back to detritus. This decreased the transfer efficiency of energy flow from the primary producers to the higher trophic levels from 9% in the 1960s to 3% between 1980 and 1987. We conclude that the anchovy stock collapse and successful establishment of the alien comb-jelly Mnemiopsis in 1989 were rooted in the trophic interactions in the food web, all of which were exacerbated because of the long-term establishment of a combination of anthropogenic stressors.