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In the context of climate change, the European budget for marine data collection is up to €1.4 billion p.a., both for satellite data and for in-situ observations. In the latter case, the resort to vessel-based data-gathering remains associated to elevated costs. Meanwhile, burgeoning technology made it possible to create complexes of distributed, autonomous, real-time sensor systems called “observatories” which allow to obtain a huge amount of data covering large area at a reasonable cost. However, research and decision-making policies at transnational level require those data to be reliable and comparable in order to be used for any user-group requirements purposes. The instruments which produce these data are required to measure within known specifications, at any time despite the harsh conditions in which they operate, so that the measurement results will be metrologically sound. Supporting the development of the operational oceanography in Europe, a metrology community dedicated to oceanography has been collaborating from the very early days in order to sustain and promote the quality of measurements made in marine environments. However, up to now, this quality insurance relies on ten or so metrology laboratories all over Europe, and the number of metrology laboratory creations is scarce despite an important increase of metrology needs. Responding to the need, 10 years ago, in the framework of EU projects (JERICO, FixO3), several metrology laboratories from oceanographic institutes (HCMR, OGS, IFREMER, SYKE) initiated discussions on possible ways to structure the community, enhancing collaboration, promoting integration and adopting best practices. Parallel to this, national metrology institutes (LNE, PTB, INRIM, IPQ, YMPARISTO, …) started to address the oceanographic metrology topic through dedicated metrology calls (EURAMET). This dispersion of effort was rapidly identified as the main cause of lack of progress in the thematic and laboratories decided to engage in a sustained effort for collaboration. This paper illustrates how metrology is a key player in the current environmental and political context, why it is so important to agree quickly about solutions to build a European sustainable structure and what are the different collaborative opportunities afforded by Europe.

Coastal observing systems are typically nationally funded and built around national priorities. As a result, there are presently significant differences between countries in terms of sustainability, observing capacity and technologies, as well as methods and research priorities. Ocean observing systems in coastal areas must now move toward an integrated, multidisciplinary and multiscale system of systems, where heterogeneity should be exploited to deliver fit-for-purpose products that answer the diversity and complexity of the requirements from stakeholders and end-users. Essential elements of such distributed observation systems are the use of machine-to-machine communication, data fusion and processing applying recent technological developments for the Internet of Things (IoT) toward a common cyberinfrastructure. This perspective paper illustrates some of the challenges for sustained coastal observations and provides details on how to address present gaps. We discuss the role of collaborative robotics between unmanned platforms in coastal areas and the methods to benefit from IoT technologies. Given present trends in cost-effective solutions in ocean sensors and electronics, and methods for marine automation and communication, we consider that a distributed observation system can effectively provide timely information in coastal regions around the world, including those areas that are today poorly observed (e.g., developing countries). Adaptation in space and time of the sensing nodes, and the flexibility in handling different sensing platforms can provide to the system the ability to quickly respond to the rapid changes in oceanic and climatic processes, as well as to promptly respond to evolving stakeholder and end-user requirements.

International audience; EMSO is a distributed Research Infrastructure currently comprising nine Regional Facilities (RFs) and three shallow water test sites, strategically located all the way from the southern entrance of the Arctic Ocean across to the North Atlantic through the Mediterranean to the Black Sea. Since the beginning of 2021 Norway has been integrated as a new EMSO ERIC member, extending the geographical coverage to the Nordic Sea and the Arctic. EMSO’s extension will benefi t from an experienced team managing moored observatories, ocean gliders and the Mohn Ridge Seafl oor and Water Column Observatory.

39 pages, 6 figures, 2 tables, This paper presents major gaps and challenges for implementing the UN Decade of Ocean Science for Sustainable Development (2021-2030) in the Mediterranean region. The authors make recommendations on the scientific knowledge needs and co-design actions identified during two consultations, part of the Decade preparatory-phase, framing them in the Mediterranean Sea’s unique environmental and socio-economic perspectives. According to the ‘Mediterranean State of the Environment and Development Report 2020’ by the United Nations Environment Programme Mediterranean Action Plan and despite notable progress, the Mediterranean region is not on track to achieve and fully implement the Sustainable Development Goals of Agenda 2030. Key factors are the cumulative effect of multiple human-induced pressures that threaten the ecosystem resources and services in the global change scenario. The basin, identified as a climate change vulnerability hotspot, is exposed to pollution and rising impacts of climate change. This affects mainly the coastal zones, at increasing risk of extreme events and their negative effects of unsustainable management of key economic assets. Transitioning to a sustainable blue economy is the key for the marine environment’s health and the nourishment of future generations. This challenging context, offering the opportunity of enhancing the knowledge to define science-based measures as well as narrowing the gaps between the Northen and Southern shores, calls for a joint (re)action. The paper reviews the state of the art of Mediterranean Sea science knowledge, sets of trends, capacity development needs, specific challenges, and recommendations for each Decade’s societal outcome. In the conclusions, the proposal for a Mediterranean regional programme in the framework of the Ocean Decade is addressed. The core objective relies on integrating and improving the existing ocean-knowledge, Ocean Literacy, and ocean observing capacities building on international cooperation to reach the “Mediterranean Sea that we want”, With the institutional support of the ‘Severo OchoaCentre of Excellence’ accreditation (CEX2019-000928-S)

Report on assessment of the EuroSea observational (and thematic) networks coordination This Deliverable serves to present the initial situation, in terms of coordination, of the observation and thematic networks in EuroSea represented in work package 3 (WP3). The networks include the networks represented in EuroGOOS and additional ones. The study is based on a comprehensive questionnaire that was answered by all EuroSea WP3 tasks. In addition, information from the Global Observing Networks of GOOS was considered. An important basis for the questionnaire was the list of "Network Attributes, Commitment and Benefits -What it means to be an OPA network" which was compiled by the Observation coordination group (OCG) of GOOS. This deliverable is linked to the deliverable D3.10 that will repeat the assessment at the end of the EuroSea project to assess the evolution of the coordination over the period of the EuroSea project. The present study shows that the observation and thematic networks in EuroSea all have highly developed coordination mechanism elements, except for task 3.7 - ASV, which represents a new network to be established. Given the spectrum of coordination themes and envisioned targets significant heterogeneity across the networks is also evident. The coordination of ship-based observations is not fully represented in EuroSea (and thus in EuroGOOS) and ideally this task should have been divided into research vessels and commercial vessels (container ships, ferries) but as it stands currently is dominated by one technology only (Ferrybox). This reflects the situation in EuroGOOS. For the thematic networks it is interesting to note that the observatories that are operated in task 3.8 (Augmented observatories) are not represented in the observational networks (task 3.1-3.7). The assessment presented in this deliverable has its focus on the status quo. It does not question or analyze the necessity for individuals, institutions and countries to be represented in a network - “Why should individuals, institutions or countries feel a need or a motivation to engage with the networks?”. It seems logical that networks are only founded, maintained and developed when individuals see an advantage in their involvement in a network – for themselves, their institution or a country. The "characteristics" of the apparent advantage of contributing to a network is likely of central importance. For example, if the advantage is only that there are no disadvantages (e.g. fines), a further development and improvement of the network is questionable. This important investigation of the motivation of individuals will be part of final assessment prepared in D3.10.

The European Copernicus programme ensures long-term delivery of high-quality, global satellite ocean colour radiometry (OCR) observations from its Sentinel-3 (S3) satellite series carrying the ocean and land colour instrument (OLCI). In particular, the S3/OLCI provides marine water leaving reflectance and derived products to the Copernicus marine environment monitoring service, CMEMS, for which data quality is of paramount importance. This is why OCR system vicarious calibration (OC-SVC), which allows uncertainties of these products to stay within required specifications, is crucial. The European organisation for the exploitation of meteorological satellites (EUMETSAT) operates the S3/OLCI marine ground segment, and envisions having an SVC infrastructure deployed and operated for the long-term. This paper describes a design for such an SVC infrastructure, named radiometry for ocean colour satellites calibration and community engagement (ROSACE), which has been submitted to Copernicus by a consortium made of three European research institutions, a National Metrology Institute, and two small- to medium-sized enterprises (SMEs). ROSACE proposes a 2-site infrastructure deployed in the Eastern and Western Mediterranean Seas, capable of delivering up to about 80 high quality matchups per year for OC-SVC of the S3/OLCI missions.

Microplastics (MPs) are a contaminant of growing concern due to their widespread distribution and interactions with marine species, such as filter feeders. To investigate the MPs accumulation by wild and cultured mussels, a Dynamic Energy Budget (DEB) model was developed and validated with the available field data of Mytilus edulis (wild) from the North Sea and Mytilus galloprovincialis (cultured) from the North Ionian Sea. Towards a generic DEB model, the site-specific model parameter, half saturation coefficient (Xk) was applied as a power function of food density for the cultured mussel, while for the wild it was calibrated to a constant value. The DEB-accumulation model simulated the uptake and excretion rate of MPs, taking into account environmental characteristics (temperature and chlorophyll-a). An accumulation of MPs equal to 0.64 particles individual−1 (fresh tissue mass 1.9 g) and 0.91 particles individual−1 (fresh tissue mass 3.4 g) was found for the wild and cultured mussel respectively, in agreement with the field data. The inverse experiments investigating the depuration time of the wild and cultured mussel in a clean from MPs environment showed a 90 % removal of MPs load after 3 and 14 days, respectively. Furthermore, sensitivity tests on model parameters and forcing functions highlighted that besides MPs concentration, the accumulation is highly depended on temperature and chlorophyll-a of the surrounding environment. For this reason, an empirical equation was found relating directly the concentration of MPs in seawater, with MPs accumulation in mussel’s soft tissue, temperature and chlorophyll-a.

A dynamic energy budget (DEB) model was developed to investigate the growth and reproduction of cultured bivalve species raised under different environmental conditions (varying phytoplankton carbon biomass [Phyto-C], particulate organic carbon [POC] and temperature) and tuned against field data for Mytilus galloprovincialis from the Maliakos and Thermaikos Gulfs (Aegean Sea, Greece). Values of most DEB model parameters were adopted from the literature, while half saturation constant (Xk) and initial values of energy reserves (E) and reproductive buffer (R) were calibrated. Different values have been found for Xk in the 2 areas (Maliakos: Xk = 36 mg C m-3; Thermaikos: Xk = 28 mg C m-3), suggesting that Xk should be treated as a site-specific parameter. Food density (X) was adapted to include not only Phyto-C but also POC in the diet of M. galloprovincialis and only when Phyto-C density was low compared to POC density. Results showed a small contribution of POC during spring in the Maliakos Gulf and almost none at Thermaikos Gulf. The simulated mussel growth showed good agreement with field data. Sensitivity tests on the calibrated parameters (E, R and Xk) were performed to investigate model uncertainty. The standard deviation of simulations with perturbed parameter/initial values remained relatively small and appeared to increase as the modeled mussel grew, in agreement with observations.

A hybrid ensemble data assimilation scheme (HYBRID), combining a flow-dependent with a static background covariance, was developed and implemented for assimilating satellite (SeaWiFS) Chl-a data into a marine ecosystem model of the Mediterranean. The performance of HYBRID was assessed against a model free-run, the ensemble-based singular evolutive interpolated Kalman (SEIK) and its variant with static covariance (SFEK), with regard to the assimilated variable (Chl-a) and non-assimilated variables (dissolved inorganic nutrients). HYBRID was found more efficient than both SEIK and SFEK, reducing the Chl-a error by more than 40% in most areas, as compared to the free-run. Data assimilation had a positive overall impact on nutrients, except for a deterioration of nitrates simulation by SEIK in the most productive area (Adriatic). This was related to SEIK pronounced update in this area and the phytoplankton limitation on phosphate that lead to a built up of excess nitrates. SEIK was found more efficient in productive and variable areas, where its ensemble exhibited important spread. SFEK had an effect mostly on Chl-a, performing better than SEIK in less dynamic areas, adequately described by the dominant modes of its static covariance. HYBRID performed well in all areas, due to its “blended” covariance. Its flow-dependent component appears to track changes in the system dynamics, while its static covariance helps maintaining sufficient spread in the forecast. HYBRID sensitivity experiments showed that an increased contribution from the flow-dependent covariance results in a deterioration of nitrates, similar to SEIK, while the improvement of HYBRID with increasing flow-dependent ensemble size quickly levels off.

The oceans play a key role in global issues such as climate change, food security, and human health. Given their vast dimensions and internal complexity, efficient monitoring and predicting of the planet’s ocean must be a collaborative effort of both regional and global scale. A first and foremost requirement for such collaborative ocean observing is the need to follow well-defined and reproducible methods across activities: from strategies for structuring observing systems, sensor deployment and usage, and the generation of data and information products, to ethical and governance aspects when executing ocean observing. To meet the urgent, planet-wide challenges we face, methods across all aspects of ocean observing should be broadly adopted by the ocean community and, where appropriate, should evolve into “Ocean Best Practices.” While many groups have created best practices, they are scattered across the Web or buried in local repositories and many have yet to be digitized. To reduce this fragmentation, we introduce a new open access, permanent, digital repository of best practices documentation (oceanbestpractices.org) that is part of the Ocean Best Practices System (OBPS). The new OBPS provides an opportunity space for the centralized and coordinated improvement of ocean observing methods. The OBPS repository employs user-friendly software to significantly improve discovery and access to methods. The software includes advanced semantic technologies for search capabilities to enhance repository operations. In addition to the repository, the OBPS also includes a peer reviewed journal research topic, a forum for community discussion and a training activity for use of best practices. Together, these components serve to realize a core objective of the OBPS, which is to enable the ocean community to create superior methods for every activity in ocean observing from research to operations to applications that are agreed upon and broadly adopted across communities. Using selected ocean observing examples, we show how the OBPS supports this objective. This paper lays out a future vision of ocean best practices and how OBPS will contribute to improving ocean observing in the decade to come.

The POSEIDON system is a comprehensive marine monitoring and forecasting system that progressively fills the gaps of observing facilities in the eastern part of the Mediterranean Sea. This system is expanding its various open and coastal sea infrastructure that includes fixed platforms, a cabled deep-ocean observatory, a FerryBox system, high-frequency (HF) radars, gliders, a calibration lab and Argos floats. Besides offering information to science and society, the POSEIDON system via its various platforms is also being used as a technology test-bed for numerous applications. The fields of technological test span from industrial application as material aging, advanced positioning systems, fuel cells technology, new sensor testing, to multiple scientific uses as carbonate system and fluorescence sensors, microplastics and pollutants sampling. These applications are summarized and selected examples are presented. The demand for access to POSEIDON infrastructures for technological tests has increased over the last years thanks to the transnational access activities coordinated by EU projects and is expected to further increase via a national research marine observing infrastructure initiated in 2018. The addition of new infrastructures planned for the near future will further enhance the technological test-bed possibilities and thus the interaction with other research institutions and the industry.

Maritime economy, ecosystem-based management and climate change adaptation and mitigation raise emerging needs on coastal ocean and biological observations. Integrated ocean observing aims at optimizing sampling strategies and cost-efficiency, sharing data and best practices, and maximizing the value of the observations for multiple purposes. Recently developed cost-effective, near real time technology such as gliders, radars, ferrybox, and shallow water Argo floats, should be used operationally to generate operational coastal sea observations and analysis. Furthermore, value of disparate coastal ocean observations can be unlocked with multi-dimensional integration on fitness-for-the-purpose, parameter and instrumental. Integration of operational monitoring with offline monitoring programs, such as those for research, ecosystem-based management and commercial purposes, is necessary to fill the gaps. Such integration should lead to a system of networks which can deliver data for all kinds of purposes. Detailed integration activities are identified which should enhance the coastal ocean and biological observing capacity. Ultimately a program is required which integrates physical, biogeochemical and biological observation of the ocean, from coastal to deep-sea environments, bringing together global, regional, and local observation efforts.

Este artículo contiene 30 páginas, 14 figuras., The Mediterranean community represented in this paper is the result of more than 30 years of EU and nationally funded coordination, which has led to key contributions in science concepts and operational initiatives. Together with the establishment of operational services, the community has coordinated with universities, research centers, research infrastructures and private companies to implement advanced multi-platform and integrated observing and forecasting systems that facilitate the advancement of operational services, scientific achievements and mission-oriented innovation. Thus, the community can respond to societal challenges and stakeholders needs, developing a variety of fit-for-purpose services such as the Copernicus Marine Service. The combination of state-of-the-art observations and forecasting provides new opportunities for downstreamservices in response to the needs of the heavily populatedMediterranean coastal areas and to climate change. The challenge over the next decade is to sustain ocean observations within the research community, to monitor the variability at small scales, e.g., the mesoscale/submesoscale, to resolve the sub-basin/seasonal and inter-annual variability in the circulation, and thus establish the decadal variability, understand and correct the model-associated biases and to enhance model-data integration and ensemble forecasting for uncertainty estimation. Better knowledge and understanding of the level ofMediterranean variability will enable a subsequent evaluation of the impacts and mitigation of the effect of human activities and climate change on the biodiversity and the ecosystem, which will support environmental assessments and decisions. Further challenges include extending the science-based added-value products into societal relevant downstream services and engaging with communities to build initiatives that will contribute to the 2030 Agenda and more specifically to SDG14 and the UN’s Decade of Ocean Science for sustainable development, by this contributing to bridge the science-policy gap. The Mediterranean observing and forecasting capacity was built on the basis of community best practices in monitoring and modeling, and can serve as a basis for the development of an integrated global ocean observing system.

In this work, the hydrodynamic picture of the South Aegean Sea is examined through an analysis of recent measurements in its sub-basins, the Myrtoan and Cretan Sea. Both sub-basins play an important role in the water circulation, exchange, and formation processes that affect the dynamics of the whole Eastern Mediterranean. For the first time, Bio-Argo floats were deployed in the area under the Greek Argo Research Infrastructure coordination. The acquired profiles cover an almost 2-year period (November 2013–July 2015) and are compared with previous Argo profiles and the re-processed time-series data recorded from the E1-M3A POSEIDON observatory operating in the area since 2007. The spatio-temporal distribution of the physical and chemical properties in each sub-basin is examined. Dense water formation events are revealed in the northern part (Myrtoan), while the wider area can be characterized as pre-conditioned. In the Cretan basin, a strong inter-annual variability of the salinity field at intermediate and deep layers is observed that is associated with water exchange from its open boundaries. Furthermore, comparison of the dissolved oxygen (DO) distribution with physical water properties within both the mixed layer, and at greater depths, indicated that relatively high but still under-saturated DO values are more likely to be associated with convection events. Finally, an updated picture of the physical properties and the DO distribution is presented based on the last 5 years of measurements and the recent introduction of Bio-Argo floats with DO sensors in the area.

A new approach for processing the remote sensing chlorophyll-α (Chl-α) before assimilating into an ecosystem model is applied in two contrasting, regarding productivity and nutrients availability, Mediterranean sites: the DYFAMED and POSEIDON E1-M3A fixed point open ocean observatories. The new approach derives optically weighted depth-distributed Chl-α profiles from satellite data based on the model simulated Chl-α vertical distribution and light attenuation coefficient. We use the 1D version of the operational ecological 3D POSEIDON model, based on the European Regional Seas Ecosystem Model (ERSEM). The required hydrodynamic properties are obtained (off-line) from the POSEIDON operational 3D hydrodynamic Mediterranean basin scale model. The data assimilation scheme is the singular evolutive interpolated Kalman (SEIK) filter, the ensemble variant of the singular evolutive extended Kalman (SEEK) filter. The performance of the proposed assimilation approach was evaluated against the Chl-α satellite data and the seasonal averages of available in situ data for nitrate, phosphate and Chl-α. An improvement of the model simulated near-surface and subsurface maximum Chl-α concentrations is obtained, especially at the DYFAMED site. Model nitrate is improved with assimilation, particularly with the new approach assimilating depth-distributed Chl-α, while model phosphate is slightly worse after assimilation. Additional sensitivity experiments were performed, showing a better performance of the new approach under different scenarios of model Chl-α deviation from pseudo-observations of surface Chl-α.

The historical and future impacts of atmospheric deposition of inorganic nitrogen (N) and phosphorus (P) on the marine ecosystem in the east Mediterranean Sea are investigated by using a 1D coupled physical– biogeochemical model, set up for the Cretan Sea as a representative area of the basin. For the present-day simulation (2010), the model is forced by observations of atmospheric deposition fluxes at Crete, while for the hindcast (1860) and forecast (2030) simulations, the changes in atmospheric deposition calculated by global chemistry–transport models are applied to the present-day observed fluxes. The impact of the atmospheric deposition on the fluxes of carbon in the food chain is calculated together with the contribution of human activities to these impacts. The results show that total phytoplanktonic biomass increased by 16% over the past 1.5 centuries. Small fractional changes in carbon fluxes and planktonic biomasses are predicted for the near future. Simulations show that atmospheric deposition of N and P may be the main mechanism responsible for the anomalous N:P ratio observed in the Mediterranean Sea.

In this essay we briefly describe climate change in the Mediterranean Sea Large Marine Ecosystem (LME) using different indices. We further describe the evolution of yearly catches and species composition of the catches in the West (W), Central (C), and East (E) Mediterranean LME during 1970–2010 and the exploitation status of the fisheries resources and review various signals of climate on Mediterranean fisheries. In addition, we explore the mean temperature of the catch in the W, C and E Mediterranean under a scenario considering the catches of species migrating through the Suez Canal. We further review the existing habitat modeling studies at the Mediterranean scale of various species and discuss their response to climate change. Finally, we present the development of a 3-D full life cycle population model and the respective model forecasts of European anchovy ( Engraulis encrasicolus ) biomass at the Mediterranean Sea LME scale.

In the field of ocean observing, the term of ‘observatory’ is often used without a unique meaning. A clear and unified definition of observatory is needed in order to facilitate the communication in a multidisciplinary community, to capitalize on future technological innovations and to support the observatory design based on societal needs. In this paper, we present a general framework to define the next generation Marine OBservatory (MOB), its capabilities and functionalities in an operational context. The MOB structure has four components (observatory infrastructure, cyberinfrastructure, human capacity and knowledge generation engine) that are constantly and adaptively interacting with each other. Therefore, MOB is a complex infrastructure focused on a specific geographic area with the primary scope to generate knowledge via data and information thus addressing scientific, societal and economical challenges. MOB long-term sustainability, is a key feature that should be guaranteed by strategic planning that incorporates governance feedbacks. Innovations and the overall reduced-cost of equipment and operations will allow the development in quality and quantity of the MOBs globally. Thanks to the desirable MOB’s proliferation, a deeper biological understanding of the marine ecosystem should be reached thus contributing to effective conservation of ecosystems and management of humankind activities in the oceans. In sum, we provide an actionable blue-print for the upgrade and development of a sustained marine observatory producing knowledge to support science-based economical and societal decisions.

The lack of knowledge of the mesopelagic layer inhabitants, especially of those performing strong vertical migration, is an acknowledged challenge as its incomplete representation leads to the exclusion of an active carbon and nutrient pathway from the surface to the deeper layers and reversely. The vertical migration of mesopelagic inhabitants (macro-planktonic and micro-nektonic) was observed by acoustical means in the epi- and mesopelagic layer of the open oligotrophic Cretan Sea (Eastern Mediterranean) for almost 2.5 years at the site of an operational fixed-point observatory located at 1500 m depth. The observed organisms were categorized in four groups according to their migration patterns. The variability of the migration patterns was inspected in relation to the physical and biological environmental conditions of the study area. The stratification of the water column does not act as a barrier for the vertical motion of the strongest migrants, moving up to 400 m every day. Instead, changes of light intensity (lunar cycle, daylight duration, cloudiness) and the presence of prey and predators seem to explain the observed daily, monthly and seasonal variability. The continuous presence of these organisms, yet capable of vertical motion and despite the profound seasonal circulation variability at the site of the observatory, implies their presence in the broader study area. The fundamental implications of the above for biogeochemical processing in oligotrophic seas due to the intimate link of the C and nutrient cycles, are discussed.

During the second phase (2003–2006) of the Mediterranean ocean Forecasting System Project (MFS) named Toward Environmental Predictions (MFSTEP) one of the three major aims was the development of numerical forecasting systems. In this context a generic Biogeochemical Flux Model (BFM) was developed and coupled with hydrodynamic models already operating at basin scale as well as in regional areas. In the Eastern Mediterranean basin the BFM was coupled with the Aegean Levantine Eddy Resolving MOdel (ALERMO). The BFM is a generic highly complex model based on ERSEM and although a detailed description of the model and its components is beyond the scope of this work, a short overview of the main processes, laying emphasis on the parameter values used is presented. In addition the performance of the model is evaluated with some preliminary results being qualitatively compared against field observations. The model in its present form is rather promising and reproduces all important major features although there are some slight inefficiencies mostly related to primary and bacterial productivity rates.

A 3-D full life cycle population model for the North Aegean Sea (NAS) anchovy stock is presented. The model is two-way coupled with a hydrodynamic–biogeochemical model (POM–ERSEM). The anchovy life span is divided into seven life stages/age classes. Embryos and early larvae are passive particles, but subsequent stages exhibit active horizontal movements based on specific rules. A bioenergetics model simulates the growth in both the larval and juvenile/adult stages, while the microzooplankton and mesozooplankton fields of the biogeochemical model provide the food for fish consumption. The super-individual approach is adopted for the representation of the anchovy population. A dynamic egg production module, with an energy allocation algorithm, is embedded in the bioenergetics equation and produces eggs based on a new conceptual model for anchovy vitellogenesis. A model simulation for the period 2003–2006 with realistic initial conditions reproduced well the magnitude of population biomass and daily egg production estimated from acoustic and daily egg production method (DEPM) surveys, carried out in the NAS during June 2003–2006. Model simulated adult and egg habitats were also in good agreement with observed spatial distributions of acoustic biomass and egg abundance in June. Sensitivity simulations were performed to investigate the effect of different formulations adopted for key processes, such as reproduction and movement. The effect of the anchovy population on plankton dynamics was also investigated, by comparing simulations adopting a two-way or a one-way coupling of the fish with the biogeochemical model.

In this work, we examine the complex hydrology of the Cretan Sea, an important area which affects the dynamics of the Eastern Mediterranean basin. We use T/S profile data derived from the first Argo float deployed in the area during June 2010 within the framework of the Greek Argo program. Temperature and salinity profiles were measured over a 2-year period, analyzed, and combined with time series data recorded from the POSEIDON E1-M3A multi-parametric instrumentation platform operating in the area since 2007. The acquired datasets have been enriched with available CTD profiles taken on the mooring site during cruise maintenance surveys. The combined research activities resulted in a large dataset of physical properties allowing extended geographical coverage and an in-depth analysis of the Cretan Sea dynamics during this 2-year period. Data analysis shows significant variability of water masses of different origin at subsurface and deep layers. This confirms previous findings describing the area as transitional with water masses of different origin meeting and interacting. Furthermore, additional features of the area are described combining information from satellite altimetry. In this study, new circulation systems are identified at intermediate and subsurface layers affecting both the dynamic behavior of the basin’s upper thermocline and the intermediate/deep water mass tempo-spatial variability. We further investigate the physical properties of the water column and suggest an updated mesoscale circulation picture based on the dynamics of the variable hydrological regimes of the Cretan Sea basin.

Operational monitoring and forecasting of marine environmental conditions is a necessary tool for the effective management and protection of the marine ecosystem. It requires the use of multi-variable real-time measurements combined with advanced physical and ecological numerical models. Towards this, a FerryBox system was originally installed and operated in the route Piraeus–Heraklion in 2003 for one year. Early 2012 the system was upgraded and moved to a new high-speed ferry traveling daily in the same route as before. This route is by large traversing the Cretan Sea being the largest and deepest basin (2500 m) in the south Aegean Sea. The HCMR Ferry Box is today the only one in the Mediterranean and thus it can be considered as a pilot case. The analysis of FerryBox SST and SSS in situ data revealed the presence of important regional and sub-basin scale physical phenomena, such as wind-driven coastal upwelling and the presence of a mesoscale cyclone to the north of Crete. In order to assess the impact of the FerryBox SST data in constraining the Aegean Sea hydrodynamic model which is part of the POSEIDON forecasting system, the in situ data were assimilated using an advanced multivariate assimilation scheme based on the Singular Evolutive Extended Kalman (SEEK) filter, a simplified square-root extended Kalman filter that operates with low-rank error covariance matrices as a way to reduce the computational burden. Thus during the period mid-August 2012–mid January 2013 in addition to the standard assimilating parameters, daily SST data along the ferryboat route from Piraeus to Heraklion were assimilated into the model. Inter-comparisons between the control run of the system (model run that uses only the standard data set of observations) and the experiment where the observational data set is augmented with the FerryBox SST data produce interesting results. Apart from the improvement of the SST error, the additional assimilation of daily of FerryBox SST observations is found to have a significant impact on the correct representation of the dynamical dipole in the central Cretan Sea and other dynamic features of the South Aegean Sea, which is then depicted in the decrease of the basin wide SSH RMS error.