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Many marine fish species are widely distributed over large areas. Failing to acknowledge that such species may be composed of distinct populations may result in overestimation of the stock's true harvest potential. To avoid overexploitation, ways to identify population structuring are therefore needed. In this study, we developed and applied a statistical approach to identify biologically relevant population boundaries for a widely distributed marine fish species, European sprat (Sprattus sprattus). Specifically, we compiled and standardized multiple trawl-survey data sets and used a range of statistical tools to assess whether the current management boundaries adequately account for potential population structuring. Our results demonstrate regional differences in spatial abundance patterns, temporal dynamics and population demographics. These findings are in line with recent genetic studies of sprat, indicating reproductive isolation between the Baltic Sea/Kattegat and a larger cluster containing the North-, Irish-, Celtic Sea, and Bay of Biscay. Since relying on routinely collected survey data, our statistical approach can be a cost-effective complement to population genetic methods for detecting population structuring. These can be used to guide spatial management efforts and ensure sustainable exploitation, especially under climate change and the expected changes in species distributions across current management borders.

1. The concept of biodiversity-ecosystem functioning (BEF) has been studied over the last three decades using experiments, theoretical models, and more recently observational data. While theoretical models revealed that species richness is the best metric summarizing ecosystem functioning, it is clear that ecosystem function is explained by other variables besides species richness. Additionally, theoretical models rarely focus on more than one ecosystem function, limiting ecosystem functioning to biomass or production. There is a lack of theoretical background to verify how other components of biodiversity and species interactions support ecosystem functioning.2. Here, using simulations from a food web model based on a community assembly process and a trait-based approach, we test how species biodiversity, food web structure and predator-prey interactions determine several ecosystem functions (biomass, metabolism, production, and productivity).3. Our results demonstrate that the relationship between species richness and ecosystem functioning depends on the type of ecosystem function considered and the importance of diversity and food web structure differs across functions. Particularly, we show that dominance plays a major role in determining the level of biomass, and is at least as important as the number of species. We find that dominance occurs in the food web when species do not experience strong predation.4. By manipulating the structure of the food web, we show that species using a wider trait space (generalist communities) result in more connected food webs, and generally reach the same level of functioning with less species. The model shows the importance of generalist versus specialist communities on biodiversity-ecosystem functioning relationships, and as such, empirical studies should focus on quantifying the importance of diet/habitat use on ecosystem functioning.5. Our study provides a better understanding of BEF underlying mechanisms, and generates research hypotheses that can be considered and tested in observational studies. We recommend that studies investigating links between biodiversity and ecosystem functions should include metrics of dominance, species composition, trophic structure and possibly environmental trait space. We also advise that more effort should be made into calculating several ecosystem functions and properties with data from natural multi-trophic systems.

International audience; Sea water temperature affects all biological and ecological processes that ultimately impact ecosystem functioning. In this study, we examine the influence of temperature on global biomass transfers from marine secondary production to fish stocks. By combining fisheries catches in all coastal ocean areas and life history traits of exploited marine species, we provide global estimates of two trophic transfer parameters which determine biomass flows in coastal marine food web: the trophic transfer efficiency and the biomass residence time in the food web. We find that biomass transfers in tropical ecosystems are less efficient and faster than in areas with cooler waters. In contrast, biomass transfers through the food web became faster and more efficient between 1950 and 2010. Using simulated changes in sea water temperature from three Earth system models, we project that the mean trophic transfer efficiency in coastal waters would decrease from 7.7% to 7.2% between 2010 and 2,100 under the ‘no effective mitigation’ Representative Concentration Pathway (RCP 8.5), while biomass residence time between trophic level 2 and 4 is projected to decrease from 2.7 to 2.3 year on average. Beyond the global trends, we show that the trophic transfer efficiencies and biomass residence times may vary substantially among ecosystem types and that the polar ecosystems may be the most impacted ecosystems. The detected and projected changes in mean trophic transfer efficiency and biomass residence time will undermine food web functioning. Our study provides quantitative understanding of temperature effects on trophodynamic of marine ecosystems under climate change.

A fundamental challenge in ecology is to understand why species are found where they are and predict where they are likely to occur in the future. Trait-based approaches may provide such understanding, because it is the traits and adaptations of species that determine which environments they can inhabit. It is therefore important to identify key traits that determine species distributions and investigate how these traits relate to the environment. Based on scientific bottom-trawl surveys of marine fish abundances and traits of >1,200 species, we investigate trait-environment relationships and project the trait composition of marine fish communities across the continental shelf seas of the Northern hemisphere. We show that traits related to growth, maturation and lifespan respond most strongly to the environment. This is reflected by a pronounced “fast-slow continuum” of fish life-histories, revealing that traits vary with temperature at large spatial scales, but also with depth and seasonality at more local scales. Our findings provide insight into the structure of marine fish communities and suggest that global warming will favour an expansion of fast-living species. Knowledge of the global and local drivers of trait distributions can thus be used to predict future responses of fish communities to environmental change., SI

Marine biota are redistributing at a rapid pace in response to climate change and shifting seascapes. While changes in fish populations and community structure threaten the sustainability of fisheries, our capacity to adapt by tracking and projecting marine species remains a challenge due to data discontinuities in biological observations, lack of data availability, and mismatch between data and real species distributions. To assess the extent of this challenge, we review the global status and accessibility of ongoing scientific bottom trawl surveys. In total, we gathered metadata for 283,925 samples from 95 surveys conducted regularly from 2001 to 2019. We identified that 59% of the metadata collected are not publicly available, highlighting that the availability of data is the most important challenge to assess species redistributions under global climate change. Given that the primary purpose of surveys is to provide independent data to inform stock assessment of commercially important populations, we further highlight that single surveys do not cover the full range of the main commercial demersal fish species. An average of 18 surveys is needed to cover at least 50% of species ranges, demonstrating the importance of combining multiple surveys to evaluate species range shifts. We assess the potential for combining surveys to track transboundary species redistributions and show that differences in sampling schemes and inconsistency in sampling can be overcome with spatio‐temporal modeling to follow species density redistributions. In light of our global assessment, we establish a framework for improving the management and conservation of transboundary and migrating marine demersal species. We provide directions to improve data availability and encourage countries to share survey data, to assess species vulnerabilities, and to support management adaptation in a time of climate‐driven ocean changes., While many species are changing their spatial distributions rapidly with climate change, the global capacity to track these changes and then adapt management and policy has been limited. To build this capacity for demersal fishes, we compiled the largest worldwide collection of bottom trawl survey metadata and demonstrate how surveys can be combined to follow species across national and survey boundaries. Open data and transparent scientific assessment can be a key step towards improved management of redistributing transboundary species and stocks.

The relationship between biodiversity and ecosystem functioning (BEF) is a topic of considerable interest to scientists and managers because a better understanding of its underlying mechanisms may help us mitigate the consequences of biodiversity loss on ecosystems. Our current knowledge of BEF relies heavily on theoretical and experimental studies, typically conducted on a narrow range of spatio-temporal scales, environmental conditions, and trophic levels. Hence, whether a relationship holds in the natural environment is poorly understood, especially in exploited marine ecosystems. Using large-scale observations of marine fish communities, we applied a structural equation modelling framework to investigate the existence and significance of BEF relationships across northwestern European seas. We find that ecosystem functioning, here represented by spatial patterns in total fish biomass, is unrelated to species richness—the most commonly used diversity metric in BEF studies. Instead, community evenness, differences in species composition, and abiotic variables are significant drivers. In particular, we find that high fish biomass is associated with fish assemblages dominated by a few generalist species of a high trophic level, who are able to exploit both the benthic and pelagic energy pathway. Our study provides a better understanding of the mechanisms behind marine ecosystem functioning and allows for the integration of biodiversity into management considerations.

For AM, the present work was conducted while a master thesis at UMR 985 Ecology and ecosystem health, funded by Agrocampus Ouest (http//www.agrocampus-ouest.fr/). The work has been done in collaboration with the Institute for the Oceans and Fisheries at the University of British Columbia. This collaboration was funded by the Nippon Foundation-UBC Nereus Program (http.//www.nippon-foundation.or.jp/; http://www.nereusprogram.org/). MC, HDP and WWLC acknowledge funding support from the Nippon Foundation-UBC Nereus Program. DP, MLDP and MC acknowledge funding support from the Sea Around Us (http://www.seaaronndns.org/), funded by the Paul G. Allen Family Foundation (ham;// www.pgafamilyfoundation.orgi) and the Oak Foundation (http://oakfnd.org/). The funders had no role to play in study design, data collection and analysis, decision to publish, or preparation of the manuscript.; We wish to thank the Nippon Foundation-UBC Nereus program and Yoshitaka Ota for supporting the collaboration between Agrocampus Ouest, Rennes, and the University of British Columbia, Vancouver. Mathieu Colleter, Hubert Du Pontavice and William W.L. Cheung acknowledge funding supporting from the Nippon Foundation-UBC Nereus Program. Daniel Pauly, Maria L.D Palomares and Mathieu Colleter acknowledge support from the Sea Around Us, funded by the Paul G. Allen Family Foundation, and the Oak Foundation. We acknowledge assistance from the FishBase and EcoBase consortia, from Gabriel Reygondeau, Francois Gouffier and Maxime Olmos for sharing data and ideas.; International audience; The development of fisheries in the oceans, and other human drivers such as climate warming, have led to changes in species abundance, assemblages, trophic interactions, and ultimately in the functioning of marine food webs. Here, using a trophodynamic approach and global databases of catches and life history traits of marine species, we tested the hypothesis that anthropogenic ecological impacts may have led to changes in the global parameters defining the transfers of biomass within the food web. First, we developed two indicators to assess such changes: the Time Cumulated Indicator (TCI) measuring the residence time of biomass within the food web, and the Efficiency Cumulated Indicator (ECI) quantifying the fraction of secondary production reaching the top of the trophic chain. Then, we assessed, at the large marine ecosystem scale, the worldwide change of these two indicators over the 1950–2010 time-periods. Global trends were identified and cluster analyses were used to characterize the variability of trends between ecosystems. Results showed that the most common pattern over the study period is a global decrease in TCI, while the ECI indicator tends to increase. Thus, changes in species assemblages would induce faster and apparently more efficient biomass transfers in marine food webs. Results also suggested that the main driver of change over that period had been the large increase in fishing pressure. The largest changes occurred in ecosystems where ‘fishing down the marine food web’ are most intensive.