# Identifying and addressing the anthropogenic drivers of global change in the North Sea: a systematic map

Alexandra M Blöcker, Dominik Auch, Helene M Gutte, Johanna Biederbick, Rémy Asselot, Leonie Färber, Gregor Börner, Elvis Kamberi, Frane Madiraca, Claudia Ofelio, et al.

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## To cite this version:

Alexandra M Blöcker, Dominik Auch, Helene M Gutte, Johanna Biederbick, Rémy Asselot, et al. "Identifying and addressing the anthropogenic drivers of global change in the North Sea: a systematic map." Environmental Evidence, 2025, 14 (1), pp.24. 10.1186/s13750-025-00377-2. hal-05408353

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# Identifying and addressing the anthropogenic drivers of global change in the North Sea: a systematic map

Alexandra M. Blöcker¹*, Dominik Auch¹, Helene M. Gutte¹, Johanna Biederbick¹,², Rémy Asselot³, Leonie Färber¹, Gregor Börner¹,⁴, Elvis Kamberi¹,⁵, Frane Madiraca¹, Claudia Ofelio¹,⁶, Laurin Steidle¹ and Fabien Moullec⁷

**Abstract**

**Background** Marine ecosystems worldwide face extreme stress from human activities, with the North Sea being particularly affected and experiencing altered processes. To assess anthropogenic drivers for sustainable management, the Millenium Ecosystem Assessment (MEA) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) distinguished five main anthropogenic drivers: direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species. However, evidence of the drivers' relevance and their potential effects on species and the environment over time remains scarce. This systematic map provides knowledge on the five main anthropogenic drivers in the North Sea from 1945 to 2020 and identifies potential knowledge gaps in terms of management implications.

**Methods** To identify relevant articles we used our published systematic map protocol. We conducted systematic searches of academic and grey literature in English, German, and French in online databases (Web of Science, Scopus, PubMed, AquaDocs). The search followed a Population-Exposure-Comparison-Outcome framework and included the period January 1945 to December 2020. A total of 22,511 articles were deduplicated and screened by title and abstract, the remaining 5795 were screened full-text to provide a widely integrated evidence base. A set of 3356 articles were retained following eligibility criteria and were included in the final database. We extracted information on drivers in detail and their effects on study populations within different areas in the North Sea. Knowledge clusters and gaps were identified from the scientific effort and are synthesized narratively.

**Results** Out of the 3356 articles, the majority focused on pollution throughout the entire period of 75 years. Research interest has increased in climate change and biological invasion only in the most recent decades. We identified knowledge clusters in the southern North Sea, especially in ICES standard species areas 6 and 7, which has the most articles overall, mainly emphasizing pollution. Northern areas were in contrast studied the least. The effects of pollution were mainly linked to changes in chemical water properties and to contamination levels for benthos and fish. The other drivers were rather associated with changes in biomass or abundance, with a strong focus on fish and benthos populations. A key knowledge gap was on the effects of global change, herein defined as simultaneous assessment of all five drivers, at different organizational levels and therein on different populations.

<footnote>*Correspondence:
Alexandra M. Blöcker
alexandra.bloecker@uni-hamburg.de</footnote>

<footnote>Full list of author information is available at the end of the article</footnote>
**Conclusions** This systematic map reveals substantial peer-reviewed evidence on the five main anthropogenic drivers in the North Sea. The map uncovers a strong increase in research interest regarding these drivers over the years, with a strong focus towards pollution and southern North Sea areas. Despite the increasing importance of climate change effects, this map highlights limited research effort on it. As ecosystem management nowadays strives for sustainable use of marine systems, it is more important than ever to understand linkages between drivers, potential cumulative effects and possible repercussions. The map revealed a strong knowledge gap regarding these linkages due to global change. On this basis, further systematic reviews can acknowledge these gaps, identifying the drivers' impacts and their quick evolvement to support management decision-making at various governance levels.

**Keywords** Climate change, Direct exploitation, Pollution, Biological invasions, Sea-use change, Anthropocene, Marine ecosystem, Research gap, Research trend, Evidence-based

## Background

Marine ecosystems worldwide are heavily impacted and largely altered by human activities [1–4]. Continuously increasing anthropogenic pressures, especially due to demographic pressures in coastal areas, cause direct (e.g. fishing exploitation) and indirect (e.g. bioaccumulation) effects specifically on the oceans’ functionality, resilience and biodiversity leading to severe repercussions in human well-being and ecosystem services [4–8]. In the last decades, close to 66% of the ocean’s surface has experienced cumulative impacts, for example due to invasive species or nutrient enrichment [1, 9–11].

For marine systems, the Millennium Ecosystem Assessment (MEA) [12] and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) [13] identified five main anthropogenic drivers, which directly affect ecosystem processes: direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species. Global change is considered to include the impacts of all these five drivers at once. Whereas direct exploitation was considered as the prime driver affecting marine ecosystems and biodiversity for several decades, the latter four are considered as recently increasing threats with the possibility to be the major drivers leading to biodiversity loss in the future [13–15]. Given these rapid changes in anthropogenic drivers, marine ecosystems are already severely impacted and are expected to be further affected in the near future [16–20].

Among all oceans worldwide, the North Sea is a paradigm for being one of the most human-influenced marine ecosystems in the Northeast Atlantic Ocean [10, 21]. The North Sea experiences strong effects of multiple anthropogenic pressures with increasing tendency given about 184 million inhabitants surrounding the sea and over 500 inhabitants per km² in coastal areas [22, 23]. The European Green Deal implying EU’s climate neutrality by 2050, for instance, strengthens the construction of offshore renewable energy in the North Sea (300 GW by 2050). The transition of vast North Sea areas into “a green power plant” is setting a new dimension of industrial sea use change [24, 25]. However, specifically climate change

is predicted to be the key player in the future, outpacing the other drivers [13, 16, 26, 27]. As the North Sea is considered already as a hot spot of climate change due to strong water temperature increases [28], severe impacts can be expected on its ecosystem functioning and biodiversity [29, 30].

Due to the increasing pressure of the five drivers on marine ecosystems, there is an urgent need to achieve the Sustainable Development Goal (SDG 14) established by the United Nations (conserve and sustainably use oceans, seas and marine resources for sustainable development) [31]. Additionally, there is a need to reach the new biodiversity goals and targets of the post-2020 global biodiversity framework [15], and to progress towards an effective science-based and integrated ocean management system [32]. Understanding how anthropogenic drivers affect marine ecosystems in space and time can promote the achievement of these goals and support the maintenance and restoration of key ecosystem functions [33, 34]. Also, the ongoing UN Decade of Ocean Science for Sustainable Development 2021–2030 and its 2030 Agenda can be supported by a retrospective evaluation of climate change by clearly identifying knowledge gaps and clusters of the main anthropogenic drivers in marine research [35–38]. Along with their distinct relevance in impacting marine ecosystems, the five main anthropogenic drivers appear to be studied unequally. As an example, climate change is globally the most studied driver of biodiversity loss in the last decade, whereas studies on pollution and habitat change were rather rare [39].

Due to extensive monitoring by several countries organized in the International Council for the Exploration of the Sea (ICES) and the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR), the North Sea is a well-studied and data-rich system [28, 40, 41]. Despite this robust scientific foundation, only few studies analyze or synthesize research on global change, and how this research is connected and correlated with the magnitude and trends of the five anthropogenic drivers.

Here, we present a systematic map that focuses on academic and grey literature and highlights the effects of the
five main anthropogenic drivers on the North Sea ecosystem. Our study aims to examine and provide an overview of the scientific research on these drivers across various study populations and geographical areas, in order to identify knowledge gaps and to connect scientific knowledge generated over the last 75 years (1945–2020). Following our previously published systematic map protocol [42], the present systematic map shows the state of scientific research on the five anthropogenic drivers, and provides an asset towards reaching the UN Decade of Ocean Science for Sustainable Development.

## Objective of the review

The main objective of the systematic map is to give a thorough overview of the knowledge and methods used to assess the impacts of the five main drivers (direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species) on the marine ecosystem in the North Sea since the 1940s by focusing on the ecological, physical and chemical components using an ecosystem approach. In addition to these five drivers, global change was included as another category, representing the existence of all five main drivers simultaneously. Socio-economic impacts and indirect anthropogenic drivers (e.g., governance, economic, demographic drivers) were out of scope. A detailed description of the objectives is available in our protocol [42].

The primary overarching research question this study addresses is:

How did the research interest in anthropogenic drivers of marine ecosystem changes develop over the past 75 years (1945–2020) regarding the North Sea?

This research question was subsequently complemented by the following set of secondary research questions:

1. Which direct drivers have been neglected by "modern" (since 1940's) marine science? (Knowledge gaps)

2. What is the proportion of research dedicated towards testing responses to observed or anticipated impacts?

3. Facing global change, which changes in nature's contribution to people are least studied?

4. Is there a relationship among advances in applied methodologies, conceptual frameworks and acknowledged gaps in knowledge?

5. Are ecological shifts in the North Sea reflected in funded research programs and topics?

6. What are the main future avenues of research in marine science?

To answer these questions, we created a systematic map, using the following components:

- Population: any biotic and abiotic component of the North Sea marine ecosystem, e.g. plant and animal species (excluding humans) and e.g. seawater and sediment properties, respectively. Geographical scope: ICES divisions IVa, IVb and IVc; ICES standard species areas 1–7 [43, 44], Norwegian coast.

- Exposure(s)/intervention(s): the five anthropogenic drivers (direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species) will be considered as the exposures. Also, global change representing the impacts of all five main drivers at the same time is considered as a holistic exposure. Hence, studies that include all five drivers simultaneously will be labeled as global change, instead of labeling all five drivers separately. Management, conservation and protection, and restoration will be considered as interventions.

- Comparator: studies will not be required stricto sensu to have a comparator.

- Outcome(s): changes in the five anthropogenic drivers and their relation to populations studied (No outcomes were predefined, i.e., all possible outcomes).

## Methods

This systematic map was performed in accordance with the previously published protocol [42] and followed as precisely as possible the Collaboration for Environmental Evidence (CEE) Guidelines and Standards for Evidence Synthesis in Environmental Management [45]. The map complies with the RepOrting standards for Systematic Evidence Syntheses (ROSES) [46] (Additional file 1). Updates in the process of study screening and coding are listed in the following section.

### Deviations from the protocol

The systematic map was conducted following the methods described in the published protocol [42], including deviations described as followed: in contrast to the protocol, information to answer secondary questions 2 was not retrieved consistently. The label was located last in the overview, which might be a reason for overlooking answering the solution investigated (not tested, management, conservation and protection, restoration). The responses given are not sufficient to provide a good and comprehensive answer for secondary question 2. Also, information about funding was not extracted during the coding stage as the funding information gained was little during the test periods, i.e., excluding information to answer secondary question 5. Metadata on the countries and lab of authors (bibliographic information) was not extracted in the end, as the original idea to link publications to authors' countries and funding was not
## Geographical scope

AND TS = ("North Sea" OR "Brent Group" OR "Sleipner Vest Field" OR "Sleipner Field" OR "Maar Bank" OR "Pobie Bank" OR "Forty Mile Ground" OR "Viking Bank" OR "Viking Graben" OR "Little Halibut Bank" OR "Smith Bank" OR "Moray Firth" OR "Buchan Deep" OR "Fladen Ground" OR "Utsira high" OR "Utsira Formation" OR "Ling Bank" OR "Revet" OR "Norwegian Trench" OR "Eigersunds Bank" OR "Little Fisher Bank" OR "Great Fisher Bank" OR "Fisher Banks" OR "Jutland Bank" OR "Jutland Coastal Current" OR "Horns Rev" OR "Long Forties" OR "Scalp Bank" OR "Devil's Hole" OR "Firth of Forth" OR "Farn Deeps" OR "Dogger Bank" OR "Silverpit Crater" OR "Outer Silver Pit" OR "Inner Silver-Pit" OR "Silver Pit" OR "Norfolk Banks" OR "The Wash" OR "Southern Bight" OR "Broad Fourteens" OR "Frisian Front" OR "Cleaver Bank" OR "Oyster Ground" OR "German Bight" OR "German Bight Water" OR "Heligoland Bight" OR "Wadden Sea" OR "Strait of Dover" OR "Central Graben" OR "Snorre Field" OR "Wee Bankie" OR "North Sea Canal" OR "Fair Isle Current" OR "Norwegian Trench" OR "Hild Field" OR "Tern Field" OR "Middelkerke Bank" OR "Fulmar Formation" OR "Ninian Field" OR "Frigg Field" OR "Statfjord Field" OR "Statfjord Formation" OR "Gullfaks Field" OR "Pomeranian Bight" OR "Norwegian Deep" OR "Broad Fourteens Basin" OR "North Sea Flemish Banks" OR "Norwegian Channel" OR "Ekofisk Field" OR "North West Hutton Field" OR "Leman Field" OR "Aberdeen Bank" OR "Plaice Box" OR "Troll Field" OR "Mellum I.").

## Search limitations and sources

The search was conducted for studies published from January 1945 to December 2020 and no further updates were made due to the limited number of researchers involved (lack of manpower) and the great number of articles already reviewed. The search term focused on English studies. Studies published in French and German language were nonetheless reviewed by those reviewers being fluent in the respective language. Studies in other languages were excluded. The limitation to these languages is expected to be of minor importance as English is largely accepted as the scientific language in coastal states of the North Sea. In addition, the ultimate combination of search terms encompasses the five main anthropogenic drivers and several geographic areas. However, it might have missed other potential emerging threats in the North Sea in specific areas that are not covered.

Published literature was searched using Web of Science Core Collection on the Web of Science platform (Clarivate), Scopus (Elsevier) PubMed (https://pubmed.ncbi.nlm.nih.gov/) and AquaDocs (see Additional File 2 for all search results). Additional grey literature was extracted via BASE (Bielefeld Academic Search Engine; https://www base search net/) and CORE (https://core.ac.uk/)

extracting the first 300 results over the entire period of interest, following Haddaway et al. [46]. Additionally, 300 results per driver and decade were extracted from Google Scholar (https://scholar.google.com/) using simplified search terms per individual anthropogenic driver and the 'Advanced Search' option. Furthermore, organizational websites were searched for one of the five major direct anthropogenic drivers ('climate change'; 'overexploitation'; 'invasive species'; 'habitat change'; 'pollution') in conjunction with the term 'North Sea'. The literature search was completed by references cited in the benchmark articles. Literature from all searches was compiled in SysRev, an online platform for collaborative document reviews and automated data extraction (https://sysrev.com/ [47]). Duplicates coming from different platforms were removed.

## Article screening and study eligibility criteria

### Screening process

The screening was conducted in two consecutive steps, starting with a title and abstract screening and a subsequent full-text screening. While the first screening was conducted by six reviewers, 10 reviewers (the authors) were involved in the full text screening process. Prior to both screenings multiple training sessions were performed, discussing and clarifying all issues of disagreement in the group. A detailed coding guide was prepared and used consistently. The start of both screening stages was determined after reaching a good level of consistency concerning inclusion/exclusion decisions, using the Fleiss' kappa (K) parameter > 0.6. To ensure impartiality, reviewers skipped any studies which they were authoring themselves. During both screening steps, each study was screened by two reviewers. During the phase of title and abstract screening, decisions were made conservatively, meaning that studies were included at this step when being in doubt. Two additional reviewers screened all studies with conflicting screening results. During the full text screening the same process was conducted, including two reviewers per study and four reviewers for papers with conflicting coding results.

## Eligibility criteria

Articles found with the search strategy had to meet a set of eligibility criteria described in our protocol [42]:

Relevant spatial and temporal focus: literature was included when it included ICES subdivisions IVa, IVb and/or IVc (ICES standard species areas 1–7, Norwegian coast [43, 44]), including fjords, estuaries and temporarily flooded areas such as marshlands or beaches. Literature with a broader focus (Northeast Atlantic, global perspective) had to explicitly include the North Sea. Studies from adjacent areas alone (English Channel, Kattegat,
Skagerrak) were excluded from the analysis. Only literature dealing with anthropogenic drivers in the period from January 1945 to December 2020 was considered as relevant.

Relevant populations: studies with a focus on anthropogenic effects on the abiotic (chemical, physical) or biotic components (plants, animals) of the North Sea (water column, sediment/substrate) including temporarily relevant components such as sea birds were included. Effects on humans were considered irrelevant. Literature solely investigating atmospheric effects was excluded likewise.

Relevant exposure: literature was required to explicitly focus on the effect of one of the five major anthropogenic impacts (direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species). Literature dealing with respective management/mitigation actions was included if analyzing their effects. Socio-economic or political papers were, on the contrary, excluded if they were not explicitly linked to anthropogenic effects on the North Sea ecosystem. Literature on climate variability that was not explicitly linked to climate change was excluded as well. Management actions related to climate change mitigation, such as engineering solutions for carbon capture and storage (CCS) were considered as irrelevant if lacking any analysis of direct impacts on the North Sea ecosystem (e.g., leakage of CO₂ from a storage site).

Relevant study design: a broad variety of studies was included, covering primary research articles, book chapters, reviews, conference papers, meta-analyses, reports, theses, and others to assess potential changes in how anthropogenic effect analyses are approached. Therefore, our dataset covers a broad methodological variety analyzing historic, current, and future impacts of anthropogenic drivers. Methodological papers without an

application of these methods to the North Sea ecosystem were considered as irrelevant. Scientific studies where only an abstract was found were removed.

## Study validity assessment

A validity assessment was not conducted. The huge variety of literature types and the wide temporal period of publication provide information on study design and approach, which will facilitate an eventual quality assessment for specific research questions later on.

## Data coding strategy

During the data coding step, a comprehensive set of meta-data was extracted including bibliographic information, information concerning the drivers on two detail levels, insights into the effect assessed, the methodological approach (Table 1), and the analyzed impacts (Table 2, see Additional file 3 for all labels and their explanations). Bibliographic information on authors were only obtained for author names and therefore number of authors too. Countries and labs of authors were no included during the extraction process, as they were meant to be linked to funding information (not retrievable). If a study analyzed more than three impacts simultaneously, the label 'multiple impacts' was applied. The labels 'not specified' for ICES locations and 'not applicable' for organizational level (e.g., individual or community) were used to indicate that no specific area in the North Sea was mentioned in the article (e.g., only North-east Atlantic) and none living organizational level applied (e.g., chemical or metal substances). SysRev was used as the platform for coding. Before starting the coding, 12 rounds of training were conducted during which categories and their labels were discussed, and thresholds defined. During the coding process, each study was reviewed twice and in case of conflicts a third person carried out the conflict solving decision.

## Data mapping method

The detected evidence base was compiled into a Microsoft Excel database, which was explored and cleaned for duplicates using the package tidyverse [48, 49] in R [50, 51]. Plots, Sankey diagrams, and maps were created using the R packages ggplot [7, 52], network3D [53, 54] and mapplets [55], respectively. To highlight knowledge gaps and clusters, we summarized the data accordingly to the five main anthropogenic drivers, ICES standard species areas, precision of drivers (the driver in detail), analyzed impacts (Table 2), nature of the study population, organizational level (individual, population, community and ecosystem level), and the main methodology used. Based on the outcomes, we show how research regarding the five main anthropogenic drivers (direct exploitation of fish and seafood, sea use change, human-driven

<table><caption>**Table 1** Categories used for coding studies</caption><thead><tr><td>Category</td><td>Type of data</td></tr></thead><tbody><tr><td>Bibliographic information</td><td>Author names<br>Numbers of authors<br>Publication type<br>Publication source<br>Publication year<br>Number of citations<br>Current impact factor of the journal</td></tr><tr><td>Subject of investigation</td><td>Type of driver and precision of driver<br>Analyzed impact (Table 2)<br>Affected population (incl. biotic and abiotic pop.)<br>Organizational level (e.g., species, population)<br>ICES major (IVa-c) and medium (ICES standard species areas 1–7, Norwegian coast) areas<br>Habitat type</td></tr><tr><td>Methodological approach</td><td>Main methodology<br>Spatial and temporal dimension<br>Solution investigated</td></tr></tbody></table>
<table><caption>**Table 2** Impacts extracted from coding studies</caption><thead><tr><td>Analyzed impacts</td><td>Comment</td></tr></thead><tbody><tr><td>Change in biomass/abundance</td><td>Abundance/Density/includes catch volumes as well</td></tr><tr><td>Change in demographic structure</td><td>Age/size/sex ratio etc. size spectrum</td></tr><tr><td>Change in life history traits</td><td>Number of generations, rates of reproduction, mortality/ survival/development, age and size at maturity, size at birth, longevity</td></tr><tr><td>Change in spatial distribution</td><td>Latitudinal, longitudinal, vertical</td></tr><tr><td>Degradation of habitat</td><td>Degradation/destruction of a habitat</td></tr><tr><td>Change in diversity</td><td>Species richness, other biodiversity indicators (e.g., functional diversity)</td></tr><tr><td>Change in physiology</td><td>Metabolic processes, energetics, stress, regulation processes, sexual inversion</td></tr><tr><td>Change in contamination level</td><td>Pollutant concentration in (organs/tissues of) living organisms</td></tr><tr><td>Change in phenology</td><td>Timing of seasonal activities (bloom formation, breeding, migration etc.)</td></tr><tr><td>Change in genetic</td><td>Changes in genes/alleles</td></tr><tr><td>Bioaccumulation in food web</td><td>Gradual accumulation of substances through trophic interactions</td></tr><tr><td>Change in trophic functioning</td><td>Change in trophic levels, food web structures (e.g., bottom-up/top-down), trophic efficiency, predation/grazing pressures</td></tr><tr><td>Change in biochemical fluxes</td><td>Phosphorus, Carbon, Nitrogen, ratios (e.g. Cd:Ca,Cd:PO4)</td></tr><tr><td>Change in harmful algal blooms</td><td>Increase/decrease of harmful algal blooms</td></tr><tr><td>Change in extreme events</td><td>Marine heat waves, storm surges, floods, etc</td></tr><tr><td>Change in physical water properties</td><td>Stratification, currents, warming</td></tr><tr><td>Change in physical sediment properties</td><td>Grain density, grain size structure, porosity, seafloor structure, geomorphological changes</td></tr><tr><td>Change in chemical water properties</td><td>pH, salinity, oxygen concentration, concentration of pollutants</td></tr><tr><td>Change in chemical sediment properties</td><td>pH, salinity, oxygen concentrations, concentration of pollutants; includes particulate organic matter in the water column</td></tr><tr><td>Coastal in erosion and sedimentation</td><td>Geomorphological changes of coastlines</td></tr><tr><td>Change in toxins</td><td>Biological toxins (e.g., Paralytic shellfish poisoning)</td></tr><tr><td>Quantification of the driver</td><td>If the driver was only quantified and assessed (e.g., fishing effort, plastic litter)</td></tr></tbody></table>

climate change, pollution, and invasive alien species) in the North Sea has changed over 75 years, and make suggestions on the importance of future research regarding these drivers.

## Review findings

The initial database search revealed a total of 31,016 articles from searches across WoS, Scopus, AquaDocs and Pubmed (in total n = 26,131), and through other sources (n = 6491) (Fig. 1).

Out of the total number of records retrieved, 10,111 duplicates and 15,071 articles were removed at the title and abstract screening stage, leaving 7440 articles. At the stage of retrieving full texts, 1645 articles were unretrievable (Additional file 4), leaving 5795 articles for the full-text screening process. An additional 2439 articles were excluded after the full-text screening due to duplication (n = 1056), non-fitting populations and comparators (n = 1379) (e.g., studies not within our North Sea domain) and not available (NAs = 4; no anthropogenic driver was selected during full text screening process). The latter compromised insufficient labeling by reviewers, leading to no information retrievable. Ultimately, a total of 3356 articles were included in the systematic map (Additional files 5, 6).

## Anthropogenic drivers over time and space

The analyzed time period of our study spans over 75 years (January 1945–December 2020). However, the first article meeting all criteria was found in 1950. The total number of published articles per year addressing the five main anthropogenic drivers increased strongly from the 1980s onwards (Fig. 2a). After a peak in 2014 (n = 180 articles), the number of publications per year decreased slightly until 2020 (n = 123). The first four articles in 1950, 1959, 1964 and 1967 were the only ones published in the respective years, and all of them were related to direct exploitation (Fig. 2b). From 1968 until the late 2000s, the focus of articles was mainly on the field of pollution, representing 85% (n = 6) and 94% (n = 32) in 1968 and 1988, respectively.

Articles on sea use change became more dominant in the 1970s, followed by a strong decrease in 1990 (0%). The number of articles in sea use change slightly increased again until 2020. Publications focusing on climate change increased each year from 1989 (4%, n = 2) until 2020 (24%, n = 16). Articles regarding biological invasion appeared consistently from 1997 (4%, n = 3) until 2020 (7%, n = 9), staying rather constant in numbers. Global change publications, that considered all five main drivers simultaneously, were mainly published last in the period, showing only a small number of publications from 1989 to 2020 (ranging between 0 and 8%). Over the 75 years analyzed, knowledge on pollution and direct
<figure><img src="image_4.png" /><figcaption>**Fig. 1** ROSES flow diagram showing the systematic mapping process [46]</figcaption></figure>

exploitation was dominant throughout, whereas knowledge gaps were identified for drivers such as biological invasion and global change.

The number of articles of anthropogenic drivers over space, using the 'Whole North Sea', the 'ICES standard species areas (1–7)', the 'Norwegian coast' and 'not specified' (studies where no specific location in the North Sea was mentioned) as categories, shows a similar pattern within the ICES areas (Fig. 3). Pollution represented the major proportion of articles in all ICES areas, followed by direct exploitation, climate change, sea use change,

biological invasion, and lastly global change. It is apparent that most articles focused on ICES area 6 (n = 1858), whereas the least number of studies were carried out in the Norwegian coast area (n = 167). The distribution of articles per anthropogenic driver that focused on areas 1, 2, 3, and 7 (n = 338, n = 340, n = 422, n = 351, respectively) was similar but comparatively low to area 6. Areas 4 and 5 also showed similar patterns regarding the anthropogenic drivers, having a higher number of publications (n = 512 and n = 471, respectively) compared to 1, 2, 3 and 7. A different picture is seen for the categories 'Whole
<figure><img src="image_5.png" /><figcaption>**Fig. 2** Number of articles per anthropogenic driver published over time (1945–2020). **a** total number of articles published per year over time; **b** proportion of anthropogenic driver published per year. Global change articles studied all five main drivers simultaneously</figcaption></figure>

North Sea' and 'not specified'. For the 'Whole North Sea', the strongest focus laid on climate change (34%, n = 157) and pollution (32%, n = 149). For 'not specified', the focus was highest for direct exploitation (42%, n = 272) and pollution (36%, n = 236). The majority of articles focusing on global change (4%, n = 642) were in the 'not specified' category and were not related to a specific area in the North Sea. Hence, there appear to be strong knowledge clusters regarding the southern North Sea regions, whereas less studies were conducted in northern regions, or considered the 'Whole North Sea'.

**Distribution of anthropogenic drivers by drivers' precision and study population**

Articles showed differences in the 'analyzed impacts', the 'precision of the drivers' (more detail on the driver itself) and their relation to the 'study population', depending on the 'anthropogenic driver' investigated (Figs. 4, 5, Additional files 2). For biological invasion, climate change, direct exploitation and sea use change, the most analysed effect was change in biomass abundance. In contrast, for pollution, the dominant effects studied were changes in chemical water properties or changes in contamination

level (Fig. 4). In third place, multiple impacts (more than three impacts) were analyzed with the pollution driver, whereas changes in biomass abundance were only fourth for this driver in the number of articles. The precision of the drivers regarding pollution were strongly focusing on chemical substances, such as hazardous substances, metal substances, eutrophication (nutrient input of nitrogen and phosphorous in the environment), as well as oil and hydrocarbon related substances. The effects of these precise drivers and changes in chemical water properties were mainly studied on the chemical environment, benthos and fish.

Regarding pollution, knowledge clusters exist for studies that focus on changes in the chemical water properties (e.g., chemicals in dissolved water) and to a lesser extent on changes in contamination level in benthos and fish. Even fewer studies included analyses on other study populations like seabirds, zooplankton or, to an even lesser extent cephalopods or bacteria, highlighting clear knowledge gaps for these trophic groups.

Literature focusing on global change included all five drivers and had a strong tendency towards analyzing multiple impacts (more than three impacts) and their
<figure><img src="image_6.png" /><figcaption>**Fig. 3** Number of anthropogenic drivers published in ICES (International Council for the Exploration of the Sea) standard species areas and the Norwegian coast. Global change articles studied all five main drivers simultaneously. Articles without any specific study area mentioned in the North Sea were categorized as 'not specified' while articles including study areas in the whole North Sea (areas IVa, b and c) were defined as 'Whole North Sea'</figcaption></figure>

effects on all study populations (Fig. 5). These articles included to a high share reports, which provide a broad overview of drivers affecting ecosystems and their populations. Even though individual species were mentioned, our screening method allows for the category 'all' only if all study populations are represented. This way, distinct study populations were also, to a varying degree, included in the 'all' label. Notably, articles focusing on global change, along with climate change (temperature), were the only ones with a strong focus on phytoplankton and seabirds. Fish were mainly studied in articles related to direct exploitation. Sea use change, on the other hand, had the highest variability in study populations investigated. The major precise drivers were civil engineering works and coastal development (e.g., construction of offshore wind farms), which contributed most to changes in biomass. Knowledge clusters are still visible for the abiotic (chemical, physical) levels, fish, higher trophic levels (seabirds, marine mammals), and benthos. The strongest

analyzed impacts on benthos were through changes in biomass and abundance that occurred through the introduction of non-native species. Also, macrophytes were most frequently studied within the context of biological invasion, compared to the other anthropogenic drivers. The analyses of the anthropogenic drivers, analyzed impacts, the precision of these drivers and the study population investigated revealed clear knowledge clusters and knowledge gaps. In general, a lot of knowledge is provided for changes in impacts on biomass and abundance and on multiple impacts on benthos and fish, highlighting knowledge clusters. Still, the analyses revealed knowledge gaps for macrophytes, zooplankton, especially cephalopods and bacteria and other microorganisms.

### Distribution of anthropogenic drivers by organizational level

We distinguished four organizational levels: individual (only a single individual considered), population (e.g., fish
<figure><img src="image_7.png" /><figcaption>**Fig. 4** Sankey diagram for the anthropogenic driver pollution by analyzed impacts (middle row), divided into precision of driver (left row) and study population (right row). The nodes represent the respective entities, colored links show the flow between these, colors are accordingly to the entities in the middle row. The links' width is proportional to the size of the flow to allow for comparison of contributions. Here, the reading direction is from the central entities towards the left and right, showing in how many driver precisions (left) the impacts (middle) are divided and which study population (right) the impacts affect</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 5** Sankey diagram for the anthropogenic driver global change by analyzed impacts (middle row), divided into precision of driver (left row) and study population (right row). Global change articles studied all five main drivers simultaneously. The nodes represent the respective entities, colored links show the flow between these, colors are accordingly to the entities in the middle row. The links' width is proportional to the size of the flow to allow for comparison of contributions. Here, the reading direction is from the central entities towards the left and right, showing in how many driver precisions (left) the impacts (middle) are divided and which study population (right) the impacts affect</figcaption></figure>

stock), community (e.g., fish community) and ecosystem level (e.g., Wadden Sea and all its compartments, meaning living organisms and abiotic factors). The distribution of organizational levels among the anthropogenic

drivers varied greatly (Fig. 6a). Most studies lacking a specified organizational level were related to pollution (39%, n = 692/1742) mostly focusing on chemical and metal substances, whereas there was only one article with
<figure><img src="image_9.png" /><figcaption>**Fig. 6** Total number of articles per organizational level per anthropogenic driver over time (1945–2020). **a** Published articles per organizational level; **b** number of articles published per organizational level per year. Global change articles studied all five main drivers simultaneously</figcaption></figure>

no organizational level for biological invasion (0.04%, n = 1/211). On an individual level, most articles were also published within pollution (34%, n = 600/1742), and the least within climate change topics (7%, n = 37/507).

However, on a population level, pollution had the lowest share (9%, n = 162/1742) and direct exploitation the highest (56%, n = 457/805). Communities were mostly studied in the context of sea use change (25%, n = 80/312) and
the least in the context of pollution (12%, n = 214/1742). Global change, where all five drivers are considered at once, had the highest proportion in ecosystems (43%, n = 30/69), whereas biological invasion had the lowest (2%, n = 6/211). Physical and chemical pollutions were mainly studied through the assessment of the abiotic components (chemical and physical water properties) of the North Sea ecosystem (Fig. 4). Hence, knowledge regarding pollution was not as available at population and community levels. These were rather explored for sea use change and global change, respectively. Global change included many reports that highlight all anthropogenic drivers and their effects on multiple dimensions and study populations (Fig. 5). This way, ecosystems, demonstrating a strong interaction between the abiotic (physical, chemical) and biotic compartments, included the full holistic dynamics driven by global change. Populations mainly studied in direct exploitation articles relate to fishing exploitation on fish populations.

The amount of articles differed strongly between
anthropogenic drivers and organizational level over the

study period (Fig. 6b). While the number of articles on global change remained almost constant, there were slight increases in the late 2000s for biological invasion, sea use change and climate change. Direct exploitation articles increased strongly at a ‘population’ level in the 1990s, and to a lesser extent at a community level since the 2000s. The ‘not applicable’ and ‘individual’ levels had the highest records in pollution articles, both raised intensively since the 1980s. Overall, there is a knowledge gap regarding global change at all organizational levels. Studies on ecosystems in general were comparatively low in contrast to individual and population levels for pollution and direct exploitation (knowledge clusters).

Distribution of methodologies among anthropogenic
drivers

The methodologies used in the articles change in propor-
tion over time (Fig. 7). Sometimes more than one meth-
odology was used in the same article, e.g., the article in
1959 includes field observations measurement and mod-
elling (Fig. 7b). Across the whole time period, the biggest

<figure><img src="image_10.png" /><figcaption>**Fig. 7** Number of main methodologies used in the published articles over time (1945–2020). **a** total number of articles published per year over time; **b** proportion of methodology used published per year. Global change articles studied all five main drivers simultaneously</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Fig. 8** Number of articles per anthropogenic driver and main methodology. Global change articles studied all five main drivers simultaneously</figcaption></figure>

proportion was made up of field observations measurement, being continuously implemented each year in our study period (1950: 100%, n = 1, and 2020: 51%, n = 65). However, the share of field observations measurement decreased over time, whereas modelling increased. Articles involving experiments and reviews had lower proportions and only appeared consistently each year from 1982 onwards, at which point the overall number of papers published per year increased steadily (Fig. 2). Meta-analyses occurred the least (0 – 1%, n = 2 in 2014).

Differences in the methodologies applied in the articles were evident across anthropogenic drivers (Fig. 8). All five methodologies were used only in articles focusing on pollution, direct exploitation, and sea use change. No meta-analyses studies related to climate change, biological invasion and global change were found, with the latter also lacking experimental studies. On the other hand, global change articles had the highest overall proportion of reviews (68%, n = 47/69). Field observations measurements was the method applied most for the other anthropogenic drivers, followed by modelling, reviews and experiments. Only climate change articles included field observations measurements (38%, n = 201/572) and modelling (36%, n = 194/572) to an almost equal share.

In contrast, meta-analyses were by far the least represented (up to 0.08% maximum). In total, 13 NAs were included in the analyses, were no labeling occurred for the method during the full-text screening process. In general, it is obvious that knowledge clusters exist around articles applying field observations measurements. The proportion of field observations measurement, modelling and review was almost evenly distributed among the anthropogenic drivers, showing that meta-analyses and experiments were not the preferred methodologies. With the increasing threat of climate change to ecosystems in mind, it would be expected that modelling represents a comparatively high share in the future due to forecasting models.

## Limitations of the map

While the search strategy used to create this systematic map was designed to encompass a wide range of anthropogenic drivers in the North Sea, it is not comprehensive, and we recognize potential for limitations. We have included a wide range of areas in our search string, but probably missed locally performed studies at certain locations. Also, the search terms focus strongly on the five main anthropogenic drivers, leaving space for
undetected impacts that are not covered in detail, such as e.g., tourism and landscape changes causing loss of coastal protection. Furthermore, based on the broad taxonomic resolution this study is not able to highlight important threats for certain species that play a key role in the North Sea. For example, jellyfish were categorized as zooplankton, just like copepods. With these limitations, we may have missed important threats for certain species that play a key role in North Sea areas. Nevertheless, we are confident that our search terms cover all threats that emerges out of the five main anthropogenic drivers.

Although our map provides evidence on the whole North Sea, several articles were excluded due to language barriers, e.g., Dutch, Italian, Spanish publications. In this way, especially nationally published reports on North Sea research were missed. Also, we see a steep increase of articles over time, especially since the 1980s. The low number of papers at the beginning of the time series could be a bias due to lacking digitalization. Articles found in the earlier decades (1950s to ~1980s) were often a scanned version of formerly printed articles. Hence, the results of our study are strongly dependent on the number of articles being available electronically over time. Although the participating reviewers screened the full texts throughout, the final data set contained 17 NAs where no information was added to certain labels during the screening. Still, given the large number of texts screened, we do not expect any major effects on the results of our study. Furthermore, we did not update our search to the most recent years due to the lack of time and manpower. However, given our 75-year span (January 1945–December 2020), we believe that the exclusion of the last four years would not strongly affect our results, particularly as this represents the most extensive systematic map to date. This is especially relevant considering the global slowdown in research activities during that period due to the COVID-19 pandemic, which limited research activities worldwide (e.g., the conduction of experiments and field observations) [49, 51, 56, 57]. Given the detailed description of our map in our protocol [42] and in the methods section of the current paper, the search for more recent years can be updated in the future. These updates can thus benefit this systematic map.

## Conclusions

This systematic map provides the first comprehensive overview of research trends over 75 years (January 1945–December 2020) concerning the top five anthropogenic drivers affecting marine ecosystem changes in the North Sea: direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species. We found that there were a high number of studies in the field of pollution and

an increasing interest in direct exploitation and climate change topics, and in their effects, on fish and benthos biomass especially. However, sea use changes and biological invasion drew less research interest during the study period. We also identified knowledge gaps for global change studies that considered all five main anthropogenic drivers at once and in spatial coverage in the studies, with a higher proportion of studies being performed in the southern North Sea areas. Studies were mainly performed through field observations measurements, whereas meta-analyses for a holistic approach are scarce.

## Implications for policy/management

Effective management of marine anthropogenic drivers is becoming more important than ever due to increasing threats to ecosystem resilience and biodiversity [4–8, 8–59, 59–68]. The need to understand, assess and mitigate anthropogenic drivers is increasing in EU member states, especially in the context of global goals like the SDG goals of the United Nations (SDG 14—Life below water) [31], and the UN Decade of Ocean Science [35–38], as well as within the EU level context implementing ICES advices and OSPAR [28, 40, 41]. Given the changes in the strength of the drivers studied in the North Sea over time, EU management is required to adapt quickly to differences in drivers’ importance. While direct exploitation through fishing, for instance, has historically led to substantial declines in the North Sea fish populations over five decades [7, 8], the effects of climate change prevent population recovery despite current fishing pressure reductions [54, 58, 60, 61]. Knowing that climate change is expected to outpace the other drivers [13–15], a flexible and adaptable management approach is needed. Rapid changes in populations, so-called regime shifts, are well known in the North Sea for lower trophic levels, caused by climate change [56, 57, 59, 62, 64], and in fish populations, as a result of the interplay between direct exploitation and climate change induced water temperature increases [21, 54, 58, 60, 61, 65]. Climate change also causes changes in species distribution due to changes in thermal habitats [28, 62, 65, 66, 69], which could not be determined with our systematic map showing knowledge clusters in the southern North Sea regions while the northern North Sea is less considered. Changes in species distribution make it difficult to transfer knowledge between different areas due to changes in ecosystem structures [21, 70]. Decision-makers should therefore be aware of this and take caution when transferring and generalizing results from one spatial area to another [66, 71].

An ecosystem-based management to reach sustainable (development) goals requires us to understand linkages between different systems. Our map allows decision-makers to understand system changes within the field of a certain anthropogenic driver. However, our map
also revealed the lack of information on global changes, including the impacts of all drivers at the same time, and their coherent effects at an ecosystem level thus diminishing the opportunity for decision-makers to include cascading effects and possible repercussions that pass through several systems (e.g., study population level: trophic levels; ecosystem level: different habitats vertically and horizontally). Such lack of evidence hinders a holistic ecosystem management approach, as required by OSPAR [23, 53, 67]. Furthermore, offshore wind farms (OWF), among other energy infrastructure, are currently implying the most structural change due to the EU's Green Deal. Our map has identified a knowledge gap regarding the novelty of OWF development and their impacts on the environment [24, 25]. Hence, the change in importance of the drivers for the North Sea ecosystems in the future should be taken into account by decision-makers for a sustainable management. Decision-makers should commission further systematic maps and reviews in the rapidly evolving field of climate change to better determine its impacts on study populations. It would prevent missing out rapid developments and allow to assess cascading effects and repercussions for humans and their well-being [68, 69, 72, 73]. Especially given the currently on-going 7th assessment cycle (AR7) by IPCC, further climate change and marine research is demanded to inform decision-makers and provide decision-support tools about climate change variables, ocean processes, and potential adaptation strategies, as outlined by their working groups [70, 74].

Our systematic map represents a useful resource to understand (i) the effects of the five main anthropogenic drivers on the North Sea system (complementing to the knowledge gaps identified by [71, 75]); taking chemical and biological effects of man-made structures into account), (ii) knowledge clusters which can be helpful for decision-making to implement appropriate measures, (iii) knowledge gaps for potential further research, and (iv) potential developments of methodologies applied to study the drivers.

## Implications for research

This systematic map has uncovered a disproportional research focus in understanding the top five anthropogenic drivers (direct exploitation of fish and seafood, sea use change, human-driven climate change, pollution, and invasive alien species) and their environmental effects in the North Sea from 1945 to 2020. High research investment has been put into understanding pollution, even though climate change appears to be the driver that will become most important in future [13–15]. Often, chemical water properties were studied in the southern North Sea, neglecting detailed information regarding pollution of oil platforms located in the northern North Sea.

In general, evidence on the drivers is unevenly distributed across the North Sea. Clear knowledge gaps exist in the northern parts, where more research is required to gain a comprehensive assessment of drivers' effects on ecosystems. Additionally, the species studied were clearly disproportionate, with macrophytes, zooplankton, cephalopods, and bacteria and other microorganisms being studied the least. This might have strong implications, especially because microorganisms are essential for underlying biogeochemical processes. They provide high catalytic capacities, building the basis for higher trophic life [72]. Hence, more research at other population levels is needed for understanding linkages between trophic levels, either positive or negative and causing system changes if they diminish and if new ones establish their populations. Studies on specific drivers were mainly performed through field measurements and modelling methodologies. Often, studies focus only on single drivers without inter-relations, cumulative effects or feedback mechanisms of drivers. Studies linking the results of already published work, e.g., using reviews and meta-analyses are comparatively low, but are needed to understand system linkages.

The distribution in knowledge clusters revealed in this strong evidence based systematic map align with the results of areas worldwide. Given the increasing impact of climate change, the field is rapidly evolving, filling knowledge gaps worldwide [68, 69, 72, 73, 76]. Also the number in published articles in biological invasions generally expanded over the past decades, showing a strong research interest in this field. However, in the case of adjacent North Sea areas, the strength of studied impacts might slightly differ at regional scales—as for local differences within the North Sea. In the Norwegian region, aquaculture around salmon is steadily increasing, being the worldwide second biggest aquaculture industry nowadays. Hence, increased research on direct exploitation of fish and seafood (aquaculture) can be expected here [74–79]. In the Baltic Sea, research largely directs towards fishing, climate change and pollution (eutrophication). Here, these drivers are interlinked through the strong exploitation of fish stocks that determine coastal inhabitants' livelihood. Key species were overfished until depletion and are not recovering due to rising climate change and eutrophication effects [79–85]. Even though regional and local areas might have different outcomes in the strength of emergent of fields, climate change appears still to be the major driver being studied in the future [68, 72]. Continuously incorporating recent studies in this map can further prove these findings, as well as address further affected ecosystems compartments that were not determined yet.

In general, future research and systematic maps can evolve on this basis. On the one hand, identified
knowledge gaps provide key opportunities for future research to take studies at different spatial scales into account. Since this systematic map highlights ecological effects of anthropogenic drivers, future research could include a multidisciplinary team to analyze interlinkages between ecological, social and economic dimensions to further support the Sustainable Development Goals. The evidence base also provides possibilities to draw linkages between anthropogenic drivers and their effects on study population, as many studies included several impacts simultaneously. Researchers can also deepen knowledge clusters, such as analyzing drivers' impacts on species and at local levels of the North Sea and adjacent seas for comparison reasons. Future research can focus on which areas are impacted most and whether management implications are necessary for restoration.

In a world facing escalating threats from anthropogenic drivers on ecosystems, understanding interactions between the human activities and natural systems is more crucial than ever [84, 85]. To meet the goals of sustainable use of marine ecosystems, it is important to study feedback mechanisms between drivers, as well as their synergistic and antagonistic effects. Only a holistic perspective, with articles assessing global changes, allows us to understand, adapt, and mitigate anthropogenic drivers in the future.

## Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s13750-025-00377-2.

Additional File 1: ROSES form, description: filled in ROSES form

Additional File 2: Complete Search Results

Additional File 3: Label description of the map, description: the file shows explicit descriptionsof all labels that were used during the coding phase.

Additional File 4: Unobtainable full texts, description: the file contains a list with all full textsthat were unretrievable

Additional File 5: List of articles included and answers of screening process, description: thefile provides an overview of all answers that were provided during the screening process. Thisfile was used for the final analyses.

Additional File 6: List of articles excluded after full text screening, description: the fileprovides an overview of all articles that were excluded during the screening process and showstheir exclusion criteria.

## Acknowledgements

The authors would like to thank Sahed Ahmed Palash and Jan Conradt for their additional help retrieving the metadata of the articles for this study, Hannah Russel for supporting the full text coding, and Jöran Paap for manually retrieving papers that could not be downloaded with automated method.

## Author contributions

AMB, DA, RA, GB, LF, CO, LS and FMo conceived the study. AMB and FMo led the development of the systematic map's scope, design, and implementation, with input of DA, RA, GB, LF, CO, and LS. HMG and LS downloaded all articles and extracted their metadata. All authors conducted the full-text screening for article inclusion and labeling. AMB, JB, HMG and FMo did the conflict solving. AMB, JB and HMG conceptualized the data presentation. HMG and AMB performed all data analyses and data presentation. AMB wrote the

main manuscript, DA contributed to writing, and all authors reviewed the manuscript. All authors read and approved the final manuscript. The authors between this systematic map differ from the previously published protocol, given changes in authors' affiliations and time availability. Hence, newly involved authors (HMG, JB, EK, FMa) were trained along with previous authors (AMB, DA, RA, GB, LF, CO, LS, FMo).

## Funding

Open Access funding enabled and organized by Projekt DEAL. AMB is funded by the SeaUseTip (Spatial and temporal analysis of tipping points of the socio-ecological system of the German North Sea under different management scenarios) project, German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) grant 01LC1825 and the MarEEchange project, German Federal Ministry of Education and Research grant 01LC2326B. DA and CO are funded by the German Federal Ministry of Education and Research project CUSCO (FKZ: 03F0813B). HMG is funded by the Mission Atlantic project, EU H2020 Comfort grant 862428. JB is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the Research Training Group 2530: "Biota-mediated effects on Carbon cycling in Estuaries" (project number 407270017; contribution to Universität Hamburg and Leibniz-Institut für Gewässerökologie und Binnenfischerei im Forschungsverbund Berlin e.V.). RA is supported by the Bureau de Recherches Géologiques et Minières (BRGM). FMa is funded by the balt_ADAPT (Adaptation of the Western Baltic Coastal Fishery to Climate Change) project, German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung, BMBF) grant 03F0863. GB is funded by the German Research Foundation (DFG) under the THRESHOLDS project (Disentangling the effects of climate-driven processes on North Sea herring recruitment through physiological thresholds, MO 2873-3-1). LF is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy—EXC 2037 'CLICCS—Climate, Climatic Change, and Society'—Project Number: 390683824, contribution to the Center for Earth System Research and Sustainability (CEN) of Universität Hamburg. LS is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within Research Training Group 2530: "Biota-mediated effects on carbon cycling in estuaries" (project number 407270017), contribution to Universität Hamburg and Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) im Forschungsverbund Berlin e.V. FMo acknowledges funding support from the Biodiversa and Belmont Forum project SOMBEE (BiodivScen ERA-Net COFUND program, ANR contract no. ANR-18-EBI4-0003-01) and the European Union's Horizon 2020 research and innovation program under grant agreement no. 101059823 (B-USEFUL).

## Data availability

The coding guide, datasets generated and analyzed during the current study, as well as the R codes for analyses and figures are freely available in the "north_sea_review" repository, https://github.com/HeleneGutte/north_sea_review.

## Declarations

### Ethics approval and consent to participate

Not applicable.

### Consent for publication

Not applicable.

### Competing interests

The authors declare that they have no competing interests.

### Author details

¹Institute for Marine Ecosystem and Fisheries Science (IMF), Center for Earth System Research and Sustainability (CEN), University of Hamburg, 22767 Hamburg, Germany

²Institute of Carbon Cycles, Helmholtz-Centre Hereon, Max-Planck-Strasse 1, 21502 Geesthacht, Germany

³BRGM, French Geological Survey, 24 Avenue Léonard de Vinci, 33600 Pessac, France

⁴GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3
Geb. 4/325, 24148 Kiel, Germany
⁵Department of Aquaculture and Fisheries, Agricultural University of Tirana, St. Paisi Vodica 1025, Tirana, Albania

⁶Valencian International University, C/ Pintor Sorolla 21, 46002 Valencia, Spain

⁷MARBEC, Univ Montpellier, CNRS, Ifremer, IRD, Montpellier, France

Received: 18 July 2024 / Accepted: 23 September 2025

Published online: 02 December 2025

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