Bottom trawling is one of the most destructive fishing methods currently in use, with acute impacts on benthic ecosystems and chronic impacts on macrofauna communities. However, the long-term effects of chronic bottom trawling on smaller components of benthic communities and on sediment biogeochemistry are less well understood. To address this knowledge gap, we examined the effects of bottom trawling and environmental variables (bottom water and sediment properties) on alpha diversity and community structure of prokaryotes, meiofauna (including metazoans and foraminifera), and macrofauna over a spatial gradient of commercial bottom trawling, including a marine protected area which has been unfished for 12 years after >100 years of chronic trawling. Our results showed that chronic trawling affected the four organism groups in different ways. Prokaryote and foraminifera diversities were slightly higher at sites with higher trawling intensities, due to a greater number of rare species. Community composition was affected by trawling in all groups except meiofaunal metazoans. Sedimentary carbon played a significant role in shaping all four communities, as well as carbon degradation rates, but was not itself affected by trawling. Our results highlight that the complex interactions between environmental variables and disturbances from bottom trawling affect different components of the benthic fauna in different ways. Differences in organism size, population turnover rates, metabolic and ecological plasticity, feeding traits, and sensitivity to physical disturbance probably explain these differences.

Objective: This position paper results from an International Union of Radioecology symposium aimed at identifying challenges to develop eco-centric and holistic approaches to understanding ionizing radiation impacts on ecosystems. An ecosystem approach is particularly relevant today not only because of the triple planetary crisis of climate change, biodiversity loss, and pollution, which make single-stressor approaches unrealistic, but because of renewed interest in nuclear power as a potential solution to transition away from fossil fuels. For example, there are proposals to site small modular reactors in remote and pristine areas. The focus of the symposium was to expand the boundaries of existing approaches in radioecology and look at issues like ecosystem complexity and multiple stressors, which complicate single-stressor approaches.

Conclusions: Discussion centered around existing tools for radiation protection e.g. Adverse Outcome Pathway (AOP) analysis, biomarkers, use of microcosms and mesocosms and modeling approaches. These approaches were discussed with emphasis on identifying gaps, boundaries, and where leaps into the unknown might be beneficial. Identified challenges with biomarker and AOP approaches were that the individual level is generally addressed while interrelatedness of ecosystem components is difficult to capture. Novel ideas suggested were to construct multiple-stressor AOPs which capture key interactions and consider time as a critical component, or to exploit ‘ecological network analysis’ metrics which have been extensively used in ecological science. Other discussions centered on complexity and chaos modeling. The use of microcosms, focused field studies, and harnessing ecosystem information and communication systems were suggested to bridge the gap between individual and population-level responses.

The understanding of the depletion of species and communities and recovery following the reduction of pressures is fundamental in conservation biology. The impact of bottom trawl fisheries on benthic communities has been well studied, but there are few studies of the long-term recovery after the cessation of bottom trawling. Here we followed the recovery of the benthic macrofaunal community over 12 years in a large (426 km2) no-take zone (NTZ) area in the south Kattegat after demersal trawling was stopped and compared it to a nearby area where trawling continued. Using multivariate analyses, we found shifts in the community composition. Two species of burrowing brittle stars, Amphiura filiformis and Amphiura chiajei, dominated abundance and biomass and decreased in the closed area (abundance effect size A. filiformis 48%; A. chiajei 45%). In parallel, there was an increase in benthivore flatfish. Stomach contents of the dominating flatfishes matched the availability of benthic prey taxa, and brittle stars were the staple food. Food web effects thus appear to override the decrease in mortality of the dominant macrofauna caused by the cessation of trawling in the NTZ. The recovery response in the species community in the NTZ correlated with the pattern in community composition along a chronic bottom trawling intensity gradient in the same area. This indicates that the recovery of the benthic community is not random but follows a successional pattern that can also be observed in chronic states of disturbance from bottom trawling. This is important information from the perspective of management efforts to restore marine ecosystems from the impact of bottom trawl fisheries, as it indicates that reduced effort may lead to predictable recovery.

Deep soft bottoms are of vital importance for the functioning of the whole marine ecosystem and for long-term carbon storage. These functions may be reduced when the bottoms are trawled for commercial fishing and during seabed mining. Still, these habitats are often overlooked when outlining marine protected areas and restricting fisheries and exploitation. EU Member States must better protect deep soft bottoms in the Baltic and North Sea.

Djupa mjukbottnar är viktiga för hela det marina ekosystemets funktion och för långsiktig kolinlagring. Dessa funktioner riskerar att försämras när bottnarna trålas vid kommersiellt fiske och vid gruvdrift på havsbotten. Ändå förbises dessa livsmiljöer ofta när man fastställer marina skyddsområden och begränsar fiske och exploatering. EU:s medlemsländer måste skydda djupa mjukbottnar i Östersjön och Nordsjön bättre.

Marine sediments are among the largest carbon reservoirs on the planet and play a key role in the global cycling of organic matter. Bottom fisheries are the most widespread anthropogenic physical disturbance to seabed habitats, prompting NGOs and governments to act on regulating mobile bottom-contacting fishing gear. However, the scientific evidence of the effects of bottom trawling on sediment biogeochemistry is highly diverse and presents contrasting results. Here we present a global harmonized dataset of 71 independent studies that assess the effects of demersal fisheries on sedimentological (i.e. grain size, porosity) and biogeochemical (i.e. organic carbon, phytopigments, nutrient fluxes) properties: the Demersal fishery Impacts on Sedimentary Organic Matter (DISOM) database (Paradis, 2023; 10.3929/ethz-b-000634336). We identify considerable gaps, namely in the geographical extension of the data; coverage of environmental predictors (i.e. seasons); fishing descriptors such as the availability of true controls, quantification of fishing effort, and distribution of fishing gear types; and biogeochemical variables that study the remineralization of organic matter. Future studies should address these data gaps to enhance the comprehensiveness of the dataset. With this harmonized database, we aim to allow researchers to explore the effects of demersal fisheries in variable environmental settings to disentangle the effects of this disturbance and provide efficient management strategies.

Hydrophobic organic contaminants (HOCs) affect phytoplankton at cellular to population levels, ultimately impacting communities and ecosystems. Baseline toxicants, such as some HOCs, predominantly partition to biological membranes and storage lipids. Predicting their toxic effects on phytoplankton populations therefore requires consideration beyond cell uptake and diffusion. Functional traits like lipid content and profile can offer insights into the diverse responses of phytoplankton populations exposed to HOCs. Our study investigated the vulnerability of five phytoplankton species populations to varying chemical activities of a mixture of polycyclic aromatic hydrocarbons (PAHs). Population vulnerability was assessed based on intrinsic sensitivities (toxicokinetic and toxicodynamic), and demography. Despite similar chemical activities in biota within the exposed algae, effects varied significantly. According to the chemical activity causing 50% of the growth inhibition (Ea₅₀), we found that the diatom Phaeodactylum tricornutum (Ea₅₀ = 0.203) was the least affected by the chemical exposure and was also a species with low lipid content. In contrast, Prymnesium parvum (Ea₅₀ = 0.072) and Rhodomonas salina (Ea₅₀ = 0.08), both with high lipid content and high diversity of fatty acids in non-exposed samples, were more vulnerable to the chemical mixture. Moreover, the species P. parvum, P. tricornutum, and Nannochloris sp., displayed increased lipid production, evidenced as 5–10% increase in lipid fluorescence, after exposure to the chemical mixture. This lipid increase has the potential to alter the intrinsic sensitivity of the populations because storage lipids facilitate membrane repair, reconstitution and may, in the short-term, dilute contaminants within cells. Our study integrated principles of thermodynamics through the assessment of membrane saturation (i.e. chemical activity), and a lipid trait-based assessment to elucidate the differences in population vulnerability among phytoplankton species exposed to HOC mixtures.

Soft sediment marine benthic ecosystems comprise a diverse community of bacteria, meiofauna and macrofauna, which together support a range of ecosystem processes such as biogeochemical cycling. These ecosystems are also fishing grounds for demersal species that are often caught using bottom trawling. This fishing method can have deleterious effects on benthic communities by causing injury or mortality, and through alteration of sediment properties that in turn influence community structure. Although the impacts of bottom trawling on macrofauna are relatively well studied, less is known about the responses of meiofauna and bacteria to such disturbances, or how bottom trawling impacts benthic ecosystem processes. Quantifying trawling impacts against a background of natural environmental variability is also a challenge. To address these questions, we examined effects of bottom trawling and a range of environmental variables (e. g. water chemistry and physical and biochemical surface sediment properties) on a) bacterial, meiofaunal and macrofaunal community structure and b) benthic ecosystem processes (nutrient fluxes, extracellular enzyme activities and carbon turnover and degradation rates). We also investigated the link between the benthic macrofauna community and the same ecosystem processes. While there was a significant effect of bottom trawling intensity on macrofaunal community structure, the same was not seen for bacterial or meiofaunal community composition, which were more affected by environmental factors, such as surface sediment properties. The labile component of the surface sediment carbon pool was higher at highly trawled sites. Carbon degradation rates, extracellular enzyme activities, oxygen fluxes and some nutrient fluxes were significantly affected by trawling, but ecosystem processes were also strongly linked to the abundance of key bioturbators (Macoma balthica, Halicryptus spinulosus, Scoloplos armiger and Pontoporeia femorata). Although benthic ecosystems were affected by a combination of trawling and natural variability, disentangling these showed that the anthropogenic effects were clearest on the larger component of the community, i.e. macrofauna composition, and on ecosystem processes related to sedimentary carbon.

The potential threat of fisheries on seabed carbon is a topic of growing concern, yet existing literature presents inconsistencies leaving experts divided on the topic. We conducted a global meta-analysis to synthesize the current knowledge and quantify how demersal fishing impacts various biogeochemical properties. Direct impact studies revealed overall reductions in chlorophyll-a (Chl-a, 17%), phaeopigments (24%), and proteins (32%). Effects on these reactive compounds were more pronounced on surface sediment (0–2 cm), where the impact on total organic carbon (TOC) also became significant, demonstrating the effect of gear penetration, and highlighting that sampling strategies combining sediment layers can mask observed effects. Current velocity and primary productivity significantly influenced the direction and magnitude of fishing impacts. Trawling-induced subsurface reductions of TOC in low-energy habitats may affect carbon sequestration due to the preferential removal of semi-reactive carbon. Intriguingly, fishing intensity gradient studies showed an average increase in TOC in chronically fished areas, possibly reflecting fishing preferences for meso-eutrophic grounds. We estimate a ~300-day recovery period post-fishing for Chl-a, though values for other parameters are less certain. Limited data on seasonality, gear types, and an under-representation of studies in tropical and deep-sea areas pose challenges to quantifying global scale geochemical impacts of demersal fisheries. Knowledge gaps persist in understanding the fate of disturbed organic matter including its mineralization, transport, and sequestration. Nonetheless, our insights and estimates provide foundational knowledge that can contribute to science-based approaches for spatial fisheries management while preserving natural carbon dynamics on the seabed.

This study investigates six areas in a historically heavily trawled region of the southern Baltic Sea. Using acoustic geophysical mapping data and sediment cores from three field campaigns (2019, 2020, 2023), we evaluate and quantify the cumulative physical impacts from bottom trawling and the influence of seabed geology on mapped trawl tracks. The results are compared with fishing intensity data over three periods; 2012–2016, 2017–2019 and after the fishery closed. A correlation between fishing intensity and density of mapped trawl tracks exists in the soft sediments of the northern part of the area, while this link is weak in the less trawled southern part, where the seabed is characterized by more consolidated glacial clays and the high density of mapped trawl tracks reflects the preservation of tracks >8 years old. Four years after the closure of the fishery there were no signs of trawl-track degradation in any of the areas. In summary, mapped track densities alone are not a suitable measure of trawling intensity, considering the influence of seabed geology and the persistence of trawl tracks over time. Sediment deformation, observed by CT-scanning, indicates extensive remoulding and coarsening of the upper 20–40 cm of sediments in the trawled areas.