European Seas Research Articles

Wandering the taxonomic mine-field: the Podocotyle species complex (Digenea: Opecoelidae).

This study focuses on the opecoelid genus Podocotyle, particularly the species in the northern European seas (White, Barents and Pechora), with additional data from few isolates from the Far East. The research combines molecular analyses (28S, 5.8S+ITS2 rDNA, and cox1 mtDNA) and morphological examinations. Molecular analyses suggested that there are most likely four species of Podocotyle in the northern European seas and three more in the Far East. Morphological redescriptions are provided for three northern European species: P. atomon, P. reflexa, and P. odhneri, with the latter recognized as a valid species. The study also verified the life cycle of P. atomon and identified Lacuna vincta (Littorinidae) as the first intermediate host for P. reflexa. In the Sea of Okhotsk, L. turrita is the first intermediate host for two apparently undescribed Podocotyle species. The results also highlight the morphological variability of P. atomon, emphasizing the need for an integrative approach in the taxonomy and biodiversity studies.

National and transboundary contributions to surface ozone concentration across European countries

Tropospheric ozone impacts health, climate, and ecosystems. Effective ozone mitigation policies are challenged by limited quantitative understanding of national versus transboundary contributions to surface ozone. This study uses a chemical transport model with a source apportionment algorithm to analyze ozone contributions across Europe from 2015 to 2017 during peak ozone season. We quantify country-level ozone production and imported ozone, distinguishing contributions from 35 European countries, neighboring countries, seas, and hemispheric influences. Results show substantial contributions from outside the 35 European countries, with hemispheric contributions playing a significant role. European contributions are crucial during high ozone episodes, especially from Germany, France, Italy, the UK, Poland, and Spain. Spain, northern Italy, and northwest France are identified as areas where national precursor reductions would be more effective in improving national air quality. Furthermore, 25 of the 35 European countries studied are net importers of cumulative ozone mass, with the Netherlands, Belgium, and the UK acting as major exporters. These findings highlight the need for comprehensive air quality policies and cross-border cooperation.

Genetic Stock Identification Reveals Mismatches Between Management Areas and Population Genetic Structure in a Migratory Pelagic Fish.

Sustainable fisheries management is important for the continued harvest of the world's marine resources, especially as they are increasingly challenged by a range of climatic and anthropogenic factors. One of the pillars of sustainable fisheries management is the accurate identification of the biological units, i.e., populations. Here, we developed and implemented a genetic baseline for Atlantic herring harvested in the Norwegian offshore fisheries to investigate the validity of the current management boundaries. This was achieved by genotyping > 15,000 herring from the northern European seas, including samples of all the known populations in the region, with a panel of population-informative SNPs mined from existing genomic resources. The final genetic baseline consisted of ~1000 herring from 12 genetically distinct populations. We thereafter used the baseline to investigate mixed catches from the North and Norwegian Seas, revealing that each management area consisted of multiple populations, as previously suspected. However, substantial numbers (up to 50% or more within a sample) of herring were found outside of their expected management areas, e.g., North Sea autumn-spawning herring north of 62° N (average = 19.2%), Norwegian spring-spawning herring south of 62° N (average = 13.5%), and western Baltic spring-spawning herring outside their assumed distribution area in the North Sea (average = 20.0%). Based upon these extensive observations, we conclude that the assessment and management areas currently in place for herring in this region need adjustments to reflect the populations present. Furthermore, we suggest that for migratory species, such as herring, a paradigm shift from using static geographic stock boundaries towards spatial dynamic boundaries is needed to meet the requirements of future sustainable management regimes.

Thermal stability of sedimentary organic carbon in a large river dominated marginal sea

The thermal stability of organic carbon (OC) in marine sediments is one of the critical factors that influences its burial efficiency in marine environments. However, the distribution patterns and influencing factors of the thermal stability of OC in marginal seas remain poorly understood. In this study, we conducted the thermal gravimetric analysis (TGA) of OC in surface sediments of the Changjiang Estuary (CE) and its adjacent East China Sea (ECS) shelf. Both labile and refractory organic matter (OML and OMR) contents derived from the TGA were higher in the CE and Zhe-Min Coast (ZMC) mobile muds relative to those in the sandy areas. The average Carbon Reactivity Index (CRI) is 69.3 ± 4.2 %, ranging from 62.8 % to 85.1 %. Most of the stations in the CE and ZMC mobile muds were characterized by relatively low CRI values, while only some stations in the inner estuary and outer shelf had higher CRI values. As a result, the CRI values correlated reversely with the OC contents and positively with the median grain size, especially in sandy sediments. Despite being sandy sediments, there were significant differences in the thermal stability of OC among the three different sandy sediment areas, with the highest CRI value in the inner estuary, lower CRI values in the outer estuary and outer shelf sediments, possibly related to the sources and composition of OC in different regions as shown by the negative correlation between CRI and δ13C for sandy sediments. Compared with certain European marginal seas, the sedimentary OC (SOC) in the CE and ECS shelf exhibits greater thermal stability, which is probably linked to the reduced preservation efficiency of OC caused by the extensive sediment dynamics in this area. This study supports the notion that organo-mineral interactions and the sources are two major factors controlling the reactivity of OC.

Management of jellyfish outbreaks to achieve good environmental status

Jellyfish and gelatinous zooplankton (GZ) in general, fulfill important ecological roles with significant impacts, although they are often oversimplified or misunderstood. This paper reviews the impacts, pressures, monitoring methods and current management strategies for various GZ groups. It also introduces potentially applicable indicators for their assessment in ecosystem-based management approaches, such as the European Marine Strategy Framework Directive (MSFD). This multi-faceted review is primarily envisioned to serve as a state-of-the-art document for scientists and policymakers to foster a holistic assessment and management of GZ across European regional seas. The systematic review on global impacts of GZ shows a notable increase in the number of studies since the early 2000s. Stings were the main cause of human health impacts. Mechanisms that impact biodiversity included direct predation, modification of trophic flows or competition for resources. Several GZ taxa may be beneficial to biodiversity acting as biological regulators and provide societal ecosystem services such as food provision or medical applications. The systematic review on monitoring techniques outlined a variety of methods, such as nets (the most common technique), continuous plankton recorder (CPR), polyp and jelly-fall monitoring, acoustic methods, remote aerial and underwater imaging, molecular methods, and citizen science. Furthermore, several currently employed management strategies were enumerated, including the use of anti-jelly nets, bubble curtains, chemical compounds, or the introduction of GZ predators. This study highlights the pressing need for enhanced GZ-dedicated monitoring, assessment, and anticipatory management of GZ populations to address future GZ crises more effectively and cost-efficiently. Moreover, exploring GZ ecosystem services unveils opportunities to harness marine resources while mitigating adverse effects, thereby supporting sustainable blue economies.

Seasonal forecasting of the European North-West shelf seas: limits of winter and summer sea surface temperature predictability

The European North-West shelf seas (NWS) support economic interests and provide environmental services to adjacent countries. Expansion of offshore activities, such as renewable energy infrastructure, aquaculture, and growth of international shipping, will place increasingly complex demands on the marine environment over the coming decades. Skilful forecasting of NWS properties on seasonal timescales will help to effectively manage these activities. Here we quantify the skill of an operational large-ensemble ocean-atmosphere coupled global forecasting system (GloSea), as well as benchmark persistence forecasts, for predictions of NWS sea surface temperature (SST) at 2–4 months lead time in winter and summer. We identify sources of and limits to SST predictability, considering what additional skill may be available in the future. We find that GloSea NWS SST skill is generally high in winter and low in summer. GloSea outperforms simple persistence forecasts by adding information about atmospheric variability, but only to a modest extent as persistence of anomalies in the initial conditions contributes substantially to predictability. Where persistence is low – for example in seasonally stratified regions – GloSea forecasts show lower skill. GloSea skill can be degraded by model deficiencies in the relatively coarse global ocean component, which lacks dynamic tides and subsequently fails to robustly represent local circulation and mixing. However, “atmospheric mode matched” tests show potential for improving prediction skill of currently low performing regions if atmospheric circulation forecasts can be improved. This underlines the importance of coupled atmosphere-ocean model development for NWS seasonal forecasting applications.

Navigating the Marine Strategy Framework Directive D11: Updates on Threshold Values and Future Perspectives

The Marine Strategy Framework Directive (MSFD), enacted by the European Union in 2008, seeks to achieve a Good Environmental Status for European seas through 11 qualitative descriptors. This paper specifically examines Descriptor 11 (D11), which focuses on the impact of anthropogenic noise on marine ecosystems. Despite significant advancements and extensive work done by expert groups and researchers to establish methodologies for assessing this issue, critical gaps remain, such as the effects of anthropogenic noise on many marine species, including cetaceans. As the second MSFD cycle concludes, this paper emphasizes the need for further research on other forms of energy, such as electromagnetic fields, and advocates for standardized approaches, including a unified Level of Onset of Adverse Biological Effects (LOBE) for species and habitat.

Long-Term Sea Level Periodicities over the European Seas from Altimetry and Tide Gauge Data

This study investigates the long-term temporal patterns of sea level changes by analyzing monthly tide gauge data from 1950 to 2022 (42 to 72 years) along the European coastline and monthly altimetry data from 1992 to 2024 in the surrounding European seas. The primary focus is on signals with periods longer than 5 years. The application of wavelet-based approaches and multiresolution analysis has enabled the isolation of signals with periods of approximately 8 and 16 years. However, the latter has only been observed in tide gauge data, as the altimetry time series is not sufficiently long. The same analysis was applied to the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) indices, which enabled the detection of the same signals. The reported multiyear signals of sea level are correlated with NAO and AMO indices, particularly during the period spanning from 1975 to 2010.

Bridging Data Standards and FAIR Principles in Biodiversity Digital Twinning: Prototyping, Challenges, Lessons Learned, and Future Plans

Digital twins combine modelling, domain knowledge, computing power, and multiple datasets to offer the potential to unlock new insights into biodiversity (de Koning et al. 2023). The Biodiversity Digital Twin (BioDT) project pioneers this approach to aid in understanding biodiversity through prototyping digital twins (Golivets et al. 2024). However, working with biodiversity data presents challenges due to their dynamic and diverse nature as well as the need for having to deal with incompleteness, uncertainties (Rocchini et al. 2011), disproportionate representation patterns in global studies from wealthier economies (Hughes et al. 2024), and issues with data aggregation and integration (Wüest et al. 2020). Similar to BioDT, there are also plans for creating a Digital Twin of the Ocean (DTO). DTO-Bioflow project addresses these data challenges in the marine domain, where studies show that although European seas host 48,000 marine species (75% described), the data are not yet FAIR (Findable, Accessible, Interoperable, and Reusable) (Ramírez et al. 2022). These challenges hamper the modelling capabilities needed for effective predictions and conservation prioritisation. The adaptability of digital twins across temporal and spatial scales and their ability to model dynamic ecosystems make them ideal for biodiversity research and real-time conservation efforts. However, their success hinges on the consistent integration and alignment of data from disparate sources (Trantas et al. 2023). This integration involves standardising terms used to describe datasets, such as temporal coverage or controlled vocabularies like "Forest" for targetHabitatScope. Thus, adopting data standards is essential. Additionally, challenges such as model bias (Lewers 2023), research context, and data provenance must be considered, adding complexity to metadata capture and alignment. BioDT addresses these challenges with modular building blocks for data integration, model deployment, and workflow management. This approach facilitates the gradual adoption of data standards and FAIR principles, which need to encompass not just data, but also models and software. As automation, ease of reproducibility, and deployability are critical for digital twinning success, data integration and interoperability issues may arise due to missing or insufficient parameter descriptions in the model, incomplete information on data selection, and the unavailability of required software package details. Thus, data standardisation provides a pathway for a consistent approach that can be adopted for different use cases. Common data sources in BioDT, like species occurrences and environmental variables, benefit from standards such as Darwin Core (Wieczorek et al. 2012) and the Ecological Metadata Language (Jones et al. 2019). While valuable, these standards may not fully encompass the complexity needed for comprehensive biodiversity digital twins. Additionally, differing familiarity with these standards and FAIR principles among communities pose challenges. Continuous adoption of data standards, alongside exploring complementary approaches like schema.org or bioschemas.org for capturing diverse (meta)data, is essential. Collaboration with data providers, modellers, and various research infrastructures is also crucial (Andrew et al. 2024). We share our experience using Research Object Crate (RO-Crate), leveraging common JavaScript Object Notation for Linked Data (JSON-LD) representation for metadata profiles and workflow representation, to connect with different infrastructures. In the BioDT project, we are working with various use cases to create prototype digital twins that can serve as valuable resources for other projects. The evolving landscape of digital twin concepts, along with other European Union-funded initiatives like DTO-Bioflow and Destination Earth (DestinE), emphasises the importance of alignment within the digital twin ecosystem. BioDT is committed to aligning with and contributing to this broader context, highlighting the critical role of data standardisation and FAIR implementation.

Long‐term changes in taxonomic and functional composition of European marine fish communities

Evidence of large‐scale biodiversity degradation in marine ecosystems has been reported worldwide, yet most research has focused on few species of interest or on limited spatiotemporal scales. Here we assessed the spatial and temporal changes in the taxonomic and functional composition of fish communities in European seas over the last 25 years (1994–2019). We then explored how these community changes were linked to environmental gradients and fishing pressure. We show that the spatial variation in fish species composition is more than two times higher than the temporal variation, with a marked spatial continuum in taxonomic composition and a more homogenous pattern in functional composition. The regions warming the fastest are experiencing an increasing dominance and total abundance of r‐strategy fish species (lower age of maturity). Conversely, regions warming more slowly show an increasing dominance and total abundance of K‐strategy species (high trophic level and late reproduction). Among the considered environmental variables, sea surface temperature, surface salinity and chlorophyll‐a most consistently influenced communities' spatial patterns, while bottom temperature and oxygen had the most consistent influence on temporal patterns. Changes in communities' functional composition were more closely related to environmental conditions than taxonomic changes. Our study demonstrates the importance of integrating community‐level species traits across multi‐decadal scales and across a large region to better capture and understand ecosystem‐wide responses and provides a different lens on community dynamics that could be used to support sustainable fisheries management.

Editorial: Multi-scale variability of ecosystem functioning in European and Chinese shelf seas

Editorial: Multi-scale variability of ecosystem functioning in European and Chinese shelf seas

A Comparison between the Production of Edible Macroalgae Worldwide and in the Mediterranean Sea

Macroalgae are beneficial for consumers and producers due to their high productivity, their chemical composition and their efficient cultivation without additional feed. Asia dominates global macroalgae production, while European production is still marginal and mainly based on wild harvesting in the North Atlantic. The European Commission has launched initiatives to promote the sustainable production, safe consumption and innovative use of macroalgae products in European regional seas, including the Mediterranean Sea. A variety of coastal and seabed types and a wide range of environmental conditions make the Mediterranean a hotspot of marine biodiversity while providing good conditions for the cultivation of macroalgae. The aim of this paper is to compare the global macroalgae production and macroalgae production in the Mediterranean Sea, focussing on the cultivation of edible macroalgae. The paper also discusses the limitations and possibilities of macroalgae production in the region. Macroalgae production is one of the most promising sectors of the blue economy in the Mediterranean. The production of edible macroalgae suitable for human consumption has great potential, considering future population growth and related food security and health issues, as well as the additional ecosystem benefits of macroalgae production.

A Climatology of Convective Precipitation over Europe

Abstract The annual, seasonal, and diurnal spatiotemporal heavy convective precipitation patterns over a pan-European domain are analyzed in this study using a combination of datasets, including the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (GPM) (IMERG) precipitation rate product, E-OBS ground-based precipitation gauge data, European climatological gauge-adjusted radar precipitation dataset (EURADCLIM), Operational Programme for the Exchange of Weather Radar Information (OPERA) ground-based radar-derived precipitation rates, and fifth major global reanalysis produced by ECMWF (ERA5) total and convective precipitation products. Arrival Time Difference Network (ATDnet) lightning data are used in conjunction with IMERG and EURADCLIM precipitation rates, with an imposed threshold of 10 mm h−1 to classify precipitation as convective. Annually, the largest convective precipitation accumulations are over the European seas and coastlines. In summer, convective precipitation is more common over the European continent, though relatively large accumulations exist over the northern coastal waters and the southern seas, with a seasonal localized maximum over the northern Adriatic Sea. Activity shifts southward to the Mediterranean and its coastlines in autumn and winter, with maxima over the Ionian Sea, the eastern Adriatic Sea, and the adjacent coastline. Over the continent, 1%–10% of the total precipitation accumulated is classified as convective, increasing to 10%–40% over the surrounding seas. In contrast, 30%–50% of ERA5 precipitation accumulations over land is produced by the convective parameterization scheme and 40%–60% over the seas; however, only 1% of ERA5 convective precipitation accumulations are from rain rates exceeding 10 mm h−1. Regional analyses indicate that convective precipitation rates over the inland mountains follow diurnal heating, though little to no diurnal pattern exists in convective precipitation rates over the seas and coastal mountains.

Are we even close? Five years marine litter ingestion monitoring in loggerhead turtles along Italian coast reveals how far we are from the Good Environmental Status

The loggerhead sea turtle Caretta caretta has been chosen as bioindicator to monitor the amount of litter ingested by marine animals within the European Marine Strategy Framework Directive and the Barcelona Regional Sea Convention. European Member States and Contracting Parties are committed to achieve the Good Environmental Status (GES), which is reached when the quantity of ingested litter does not adversely affect the health of the species concerned. Although the monitoring strategy has been outlined for more than a decade, to date no threshold values have been adopted to verify GES achievement. After five years of extensive monitoring along the Italian coasts, this study evaluates the suitability of five different GES scenarios and proposes a new threshold value (i.e., “there should be less than 33% of sea turtles having more than 0.05 g of ingested plastic in the GI”) for its implementation in the European seas and the Mediterranean basin.

Nature of Hydrocarbons in Bottom Sediments of the European Arctic Seas

Nature of Hydrocarbons in Bottom Sediments of the European Arctic Seas

Investigating artisanal fishers’ support for MPAs: Evidence from the Tuscan Archipelago (Mediterranean Sea)

In order to meet the “30 by 30” target of the EU Biodiversity Strategy, efforts for establishing new marine protected areas (MPAs) in European seas will increase in the upcoming years, thus affecting an increasing number of stakeholders. However, despite widely distributed across the globe, many MPAs fail to achieve their goals due to the little weight attributed to fishers’ perception as well as their scarce involvement in the different stages of MPA, from planning to management. Using the Tuscan Archipelago as a model system, we gathered artisanal fishers perceptions of MPAs and investigated potential drivers for MPA support. Information was also collected on the level of satisfaction on and involvement into current management of coastal environments, as well as fishers management proposals. Data was gathered from a sample of 27 artisanal fishers (representing 30 % of total fishers) through semi-structured interviews based on an opportunistic+snowball sampling strategy. Several fishers express positive perceptions towards the MPA concept, as long as fishers involvement is granted. Fishers open to the MPA concept are also available to change fishing gear and areas if an MPA includes their usual fishing grounds. Our results suggest that the effectiveness of MPAs in sustaining coastal biodiversity and associated harvestable stocks could be enhanced by the involvement of artisanal fishers in MPA establishment and management.

Conceptualizing maritime spatial planning – A pilot study on viewpoints across Northern European Seas

Maritime Spatial Planning (MSP) is a complex process involving various actors with deviating viewpoints, perceptions and approaches. This study identifies and explains different viewpoints in northern European MSP processes by contextualizing the different viewpoints of national maritime spatial planners, policymakers, scientists, consultants, and representatives of intergovernmental organizations who are involved in the MSP process. The Q Methodology, a method to study the subjectivity of participants, combines qualitative and quantitative approaches to explore people’s viewpoints has been utilized to identify the different frameworks in MSP. A total of five viewpoints have been conceptualized in MSP, based on 17 participants and 39 statements, that cover the whole range of MSP. Simultaneously, respective factor loadings of participants have been identified. This research proves that there seems to be a limited set of viewpoints among the community, despite the amount of stakeholders, their different backgrounds and origin. Results of this study could help to manage different or even conflicting viewpoints in MSP in the future.

How Representative Are European AERONET-OC Sites of European Marine Waters?

Data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) have been extensively used to assess Ocean Color radiometric products from various satellite sensors. This study, focusing on Ocean Color radiometric operational products from the Sentinel-3 Ocean and Land Colour Instrument (OLCI), aims at investigating where in the European seas the results of match-up analyses at the European marine AERONET-OC sites could be applicable. Data clustering is applied to OLCI remote sensing reflectance RRS(λ) from the various sites to define different sets of optical classes, which are later used to identify class-based uncertainties. A set of fifteen classes grants medium-to-high classification levels to most European seas, with exceptions in the South-East Mediterranean Sea, the Atlantic Ocean, or the Gulf of Bothnia. In these areas, RRS(λ) spectra are very often identified as novel with respect to the generated set of classes, suggesting their under-representation in AERONET-OC data. Uncertainties are finally mapped onto European seas according to class membership. The largest uncertainty values are obtained in the blue spectral region for almost all classes. In clear waters, larger values are obtained in the blue bands. Conversely, larger values are shown in the green and red bands in coastal and turbid waters.

Callovian Marine Reptiles of European Russia

Our knowledge of marine reptiles of the Callovian age (Middle Jurassic) is majorly based on the collections from the Oxford Clay Formation of England, which yielded a diverse marine reptile fauna of plesiosaurians, ichthyosaurians, and thalattosuchians. However, outside of Western Europe, marine reptile remains of this age are poorly known. Here, we survey marine reptiles from the Callovian stage of European Russia. The fossils collected over more than a century from 28 localities are largely represented by isolated bones and teeth, although partial skeletons are also known. In addition to the previously described rhomaleosaurid and metriorhynchids, we identify pliosaurids of the genera Liopleurodon and Simolestes; cryptoclidid plesiosaurians, including Cryptoclidus eurymerus, Muraenosaurus sp., and cf. Tricleidus, and ophthalmosaurid ichthyosaurians, including the iconic Ophthalmosaurus icenicus. These findings expand the ranges of several Callovian marine reptile taxa far to the Eastern Europe, and support the exchange of marine reptile faunas between Western and Eastern European seas in the middle to late Callovian. However, some specimens from the lower Callovian of European Russia show differences from typical representatives of the middle Callovian Oxford Clay fauna, possibly representing the earlier stages of evolution of some of these marine reptiles not yet recorded in Western Europe or elsewhere.

Habitat characterization, anthropogenic impacts and conservation of rhodolith beds off southeastern Malta

Abstract Rhodolith beds, including maerl, are structurally complex perennial habitats that support a high species diversity but are threatened by numerous human activities, particularly in the Mediterranean Sea. Despite their global ecological importance, increased research efforts are needed to facilitate development of effective measures to conserve these habitats. Two areas hosting rhodolith beds are known to occur off the coast of Malta (central Mediterranean), but only one has been previously studied. Through analysis of video footage collected from 56 different stations coupled with a desk study on human activities, the present study characterized the rhodolith bed located off the southeastern coast of Malta, including its extent, rhodolith morphotype composition, associated megabiota and impacts of anthropogenic activities thereon. The bed occurred at depths of 60–95 m and covered an area of approximately 200 km2, making it the second most extensive rhodolith area reported for the Mediterranean to date. It was dominated by spherical and branched rhodoliths whose cover reached a maximum of 74% but was more often <50%, similar to other Mediterranean rhodolith beds. A total of 84 different megafaunal species were recorded, suggesting that the diversity of megafauna associated with rhodolith bed habitats has been previously underestimated. A number of human activities, including extensive vessel anchoring and officially designated areas for aquaculture, bunkering and trawling, overlap with the mapped rhodolith distribution, highlighting the risk of habitat degradation. A holistic approach to the management of all the competing activities and interests relative to the southeastern coast of Malta that gives due consideration to this newly characterized rhodolith bed and the threats it faces is therefore recommended. The legal framework and policy recommendations for better conservation of rhodolith bed habitats in the Mediterranean and European Seas are also discussed.