Our understanding of the relative contribution of genetic and epigenetic mechanisms to organismal response to stress is largely biased towards specific taxonomic groups (e.g. seed plants) and environmental stresses (e.g. drought and salinity). In previous work, we found intraspecific differences in heavy metal (HM) uptake capacity in the brown macroalgae Fucus vesiculosus. The molecular mechanisms underlying these differences, however, remained unknown. Here, we evaluated the concentrations of HMs, and characterized the genetic (single nucleotide polymorphisms) and epigenetic (cytosine DNA methylation) variability in reciprocal transplants of F. vesiculosus between two polluted and two unpolluted sites on the NW Spanish coast after 90 days. Genetic and epigenetic differentiation did not explain the phenotypic differentiation observed, possibly due to the combined effect of multiple environmental factors acting on the algae in their natural habitats. Nonetheless, we provide further evidence of intraspecific genetic differentiation in F. vesiculosus at short spatial scales, as well as first evidence of population-specific epigenetic changes in brown macroalgae in response to changes in environmental conditions (i.e. transplantation ex situ). We propose that both genetic and, to some extent, epigenetic mechanisms might impinge upon the adaptive potential of this species to environmental change, but this needs to be further addressed., The authors are members of the Galician Competitive Research Group GRC/GPC2016-002 and to the CRETUS Strategic Partnership (AGRUP2015/02), which are co-funded by FEDER (EU). This research has received funding from the Spanish Ministry of Science, Innovation and Universities, through the “Proyectos de Generación del Conocimiento 2022” program under the project ID “PID2022–142802NB-I00, CoastProtect”. Dr. R. García Seoane is grateful to the Spanish Ministerio de Educación, Cultura y Deporte for a grant awarded within the Programa de Formación de Profesorado Universitario “FPU Estancias” (Ref. EST16/00109). She is currently supported by the European Union’s Horizon Europe research and innovation programme under a Marie Skłodowska-Curie Postdoctoral Fellowship 2023 (Grant Agreement No 101150001, PelCon). Dr. M. Teresa Boquete is currently supported by the Maria Zambrano program from the Spanish Ministry of Science, Innovation and Universities., Peer reviewed

The complete dataset named: “[Article dataset] Establishing a comprehensive host-parasite stable isotope database to unravel trophic relationships”18 (https://doi.org/10.6084/m9.figshare.28087397) is readily available on Figshare and on ISOBANK19 (https://isobank.tacc.utexas.edu/). Our data-gathering template is comprehensive and designed to encompass as much useful information about the parasite-host system as possible. There are 60 required metadata fields, all of which can also be found in the same Figshare repository, as “ParaSITE project_Legend key”. Collaborators were asked to fill in this template as accurately as possible. When some information was not known or was inaccessible, default or “n/a” parameters were selectable., Over the past decades, stable isotopes have been infrequently used to characterise host-parasite trophic relationships. This is because we have not yet identified consistent patterns in stable isotope values between parasites and their host tissues across species, which are crucial for understanding host-parasite dynamics. To address this, we initiated a worldwide collaboration to establish a unique database of stable isotope values of novel host-parasite pairs, effectively doubling the existing data in published literature. This database includes nitrogen, carbon, and sulphur stable isotope values. We present 3213 stable isotope data entries, representing 586 previously unpublished host-parasite pairs. Additionally, while existing literature was particularly limited in sulphur isotope values, we tripled information on this crucial element. By publishing unreported host-parasite pairs from previously unsampled areas of the world and using appropriate host tissues, our dataset stands unparalleled. We anticipate that end-users will utilise our database to uncover generalisable patterns, deepening our understanding of the complexities of parasite-host relationships and driving future research efforts in stable isotope parasitology., We would like to thank the IsoEcol 2021/2022 team for allowing us to run this project and for waiving our conference fees when we presented the preliminary results of this work. We are also very grateful to Isotrace, the IRMS Unit in Dunedin, New Zealand, for running part of these samples free of charge. This research was supported by the Royal Society Te Apārangi Marsden Fund (19-UOO-212) awarded to AJMS, which allowed her to study host-parasite interactions using stable isotopes for four years. JB was supported through a New Zealand Ministry of Business, Innovation and Employment Endeavor Grant (no CAWX2207). RGS was supported by a Juan de la Cierva-Formación post-doctoral research grant (FJC2019-040921-I) from MCIN/AEI/10.13039/501100011033 (Spain) and EU NextGenerationEU/PRTR programmes. RGS is currently supported by the European Union’s Horizon Europe research and innovation programme under a Marie Skłodowska-Curie Postdoctoral Fellowship 2023 (grant agreement No 101150001-PelCon). IGV was supported by a Juan de la Cierva-Incorporación post-doctoral research grant (IJC2019-040554-I) from MCIN/AEI/10.13039/501100011033 (Spain). TJW received support from the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.4 – Call for tender No. 3138 of 16 December 2021, rectified by Decree No. 3175 of 18 December 2021 of the Italian Ministry of University and Research funded by the European Union – NextGenerationEU; Award Number: Project code CN_00000033, Concession Decree No. 1034 of 17 June 2022 adopted by the Italian Ministry of University and Research, CUP C63C22000520001, Project title ‘National Biodiversity Future Center – NBFC., Peer reviewed

Understanding the trophic ecology of herbivorous and detritivorous fishes is essential for evaluating their ecological roles in coral reef ecosystems. In this study, we combined bulk stable isotope (δ15N and δ13C) and fatty acid analyses to investigate trophic partitioning and dietary resource use among herbivorous and detritivorous fishes from the Great Barrier Reef, Australia. Isotopic niches and fatty acid profiles confirmed significant trophic partitioning among algivores, detritivorous surgeonfishes, and parrotfishes. We also applied mixing models based on these ecological tracers to quantify the contributions of basal dietary sources to the fish. Our findings further support previous dietary knowledge for several species, including algivorous acanthurids, kyphosid chubs, and the rabbitfish Siganus doliatus. However, they also highlight trophic niche specializations within these groups, particularly in Naso unicornis, which assimilates substantial dietary protein from epiphytic cyanobacteria despite a macroalgal diet, and in the detritivorous Ctenochaetus striatus, which exhibited isotopic similarities to parrotfishes but differed in fatty acid composition, likely due to a higher intake of diatoms. Additionally, our analyses reinforce the distinctive dietary composition of parrotfishes, emphasizing the complexity of their feeding biology, in which microscopic photoautotrophs such as cyanobacteria and dinoflagellates play a key dietary role that has often been overlooked in previous studies on their nutritional ecology. Furthermore, these findings underscore the usefulness of multi-tracer approaches in refining our understanding of coral reef fish trophic ecology., This research was funded by the University of Auckland School of Biological Sciences PBRF Research Fund. RGS was supported by a postdoctoral research grant Juan de la Cierva-Formación (FJC2019-040921-I), funded by MCIN/AEI/10.13039/501100011033 (Spain) and EU NextGenerationEU/PRTR programmes, and is currently supported by the European Union’s Horizon Europe research and innovation programme under a Marie Skłodowska-Curie Postdoctoral Fellowship 2023 (grant agreement No 101150001- PelCon). We also acknowledge the CSIC Open Access Publication Support Program, through its unit of Information Resources for Research (URICI), for covering the publication fees. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript., Peer reviewed

[Data Availability]:
Upwelling index values are available at http://www.indicedeafloramiento.ieo.es. Hydrographic data are available at https://doi.org/10.1594/PANGAEA.919087 and at https://cdi.seadatanet.org/csr/ (project RADIALES). Stable isotope data are available at https://doi.org/10.1594/PANGAEA.974186 and https://doi.org/10.1594/PANGAEA.974299, Upwelling is one of the major mechanisms responsible for the input of nutrients sustaining high levels of marine primary production. As a consequence of global change, variations in upwelling intensity may affect nutrient supply thus impacting marine food webs. In this study, we examine the effects of decadal variability of upwelling strength on nitrate supply and its influence on the nitrogen stable isotope composition at the base of the marine food web at the northern boundary of the Canary Current upwelling system (NW Spain) between 1989 and 2023. The study focused on the early upwelling season each year (March-June) to minimize the effects of nitrogen remineralization. Intertidal macroalgae (Phaeophyceae) and mussels (Mytilus galloprovincialis) were used as proxies for temporally integrated isotopic signals of nitrogen sources (δ15N). While no significant temporal trends for either upwelling strength, nitrate concentrations, or stable isotopes were found, three periods with characteristic upwelling and nutrient regimes were identified. A linear increase in δ15N, particularly in Fucus spp., associated with a decreasing contribution of upwelling-derived nitrogen suggest the influence of additional sources, likely of anthropogenic origin. Thus, no net change in productivity would be expected in this region despite quasi-decadal shifts in upwelling dynamics. Further insights on the origin and relevance of these sources can be gained through the investigation of river and runoff inputs and the use of more sensitive tracers, such as amino acid δ15N analysis in mussels., This research was supported by Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033 Spain) through project QLOCKS (PID2020-115620RB-100), and additional funds by the Consellería de Medio Ambiente (Galicia, Spain) through the 3rd phase of the Environmental Specimen Bank (2000–2004), the Competitive Reference Group GRC GI-1252/GPC2020-23 (ED431C 2020/19), co-funded by the Xunta de Galicia (Spain) and the European Regional Development Fund (ERDF, EU), and postdoctoral research grants Juan de la Cierva-Incorporación to I.G.V. (IJC2019-040554-I), Juan de la Cierva-Formación to R.G.S. (FJC2019-040921-I), and María Zambrano Programme of the Spanish Ministry of Universities to Z.V. R.G.S also received funds from the European Union NextGenerationEU/PRTR programmes and is currently supported by the Horizon Europe research and innovation programme under a Marie Skłodowska-Curie Postdoctoral Fellowship 2023 (101150001-PelCon). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript., Peer reviewed

[Data availability statement]
The datasets presented in this study can be found in online repositories. The raw data on upwelling strength computed by the Instituto Español de Oceanografı́a (IEO-CSIC) is available at http://www.indicedeafloramiento.ieo.es. Satellite sea surface temperature and chlorophyll-a concentrations were obtained from the NOAA Earth System Research Laboratory (https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html) and from the GlobColour Project (https://hermes.acri.fr/), respectively. Stable isotope data is available at the PANGAEA repository (https://doi.pangaea.de/10.1594/PANGAEA.985234)., Correction: Trophic niche characterization of zooplankton and planktivorous fish: a comparative approach using stable isotopes in bulk and amino acid samples, https://doi.org/10.3389/fmars.2026.1799156, Quantification of the size and overlap of trophic niches of species with similar diets is crucial to understand food web dynamics. However, there are difficulties in determining all food resources used by each species over time and resolving competition suggested by niche overlap. In this study, we compare niche estimations in zooplankton and four species of planktivorous fish using stable carbon and nitrogen isotopes analyzed in bulk tissue samples with those using stable nitrogen isotopes in amino acids. Samples were collected in spring 2021 and 2022 in two areas of the northwestern Iberian shelf (Galicia) and southern Bay of Biscay (mar Cantábrico) with different influence of the seasonal upwelling. Estimations of trophic niches using both methods were complementary, revealing interspecific differences among fish species in the exploitation of food web resources. For instance, marked differences in the sources of carbon and nitrogen and low niche overlap indicated local feeding for zooplankton and some fish species (sardine and chub mackerel), while other species showed large variability in sources and niche overlap across zones (anchovy and mackerel). The apparent competition of fish species for resources suggested by these results can be explained by differences in their mobility, particularly in mackerel and anchovy, when the isotopic signal is not equilibrated with the new diet., The author(s) declared that financial support was received for this work and/or its publication. PELACUS surveys (Spanish Institute of Oceanography, Spain) are co-funded by the European Union through the Data Collection Framework. This research was supported by MCIN/AEI/10.13039/501100011033 (Spain) through the QLOCKS (PID2020-115620RB-100) and MTL-FISH (PID2023-147149NB100) projects. RG-S. received funding from a Juan de la Cierva-Formación postdoctoral grant (FJC2019-040921-I) from MCIN/AEI and the EU NextGeneration/PRTR programs, as well as from the Spanish Ministry of Science, Innovation and Universities through the José Castillejo mobility program (CAS21/00543). She is currently supported by the European Union’s Horizon Europe research and innovation program under a Marie Skłodowska-Curie Postdoctoral Fellowship 2023 (grant agreement No 101150001-PelCon). IV was supported by a Juan de la Cierva-Incorporación postdoctoral grant (IJC2019-040554-I) from MCIN/AEI. NM was supported by a predoctoral grant (PREP2023-001364) from MCIN/AEI., Peer reviewed

This dataset contains the values of natural abundance of stable carbon and nitrogen isotopes in bulk muscle and gut contents, and nitrogen isotopes in muscle amino acids measured in 1801 samples of 10 small pelagic fish species sampled during the PELACUS spring cruises in the northwestern Iberian shelf and in adjacent waters of the southern Bay of Biscay. Length, weight, sex and maturity stage data for each individual analyzed are also provided. Fishes were collected by midwater trawls of ca. 30 m2 pelagic net equipped with a graded-mesh netting (starting with 30 mm and ending with 4 mm). The duration of each trawl was between 25 and 40 min. Different species occurred in the same trawls. Samples of muscle tissue and gut contents were preserved dried (50°C, 48 h) or freeze-dried. No treatments for lipid removal were used prior to carbon analyses. Stable isotope determinations in bulk samples (also carbon and nitrogen contents) were made by isotope-ratio mass spectrometry coupled to an elemental analyzer (Bode et al. 2018). Stable nitrogen isotopes in amino acids were determined by isotope-ratio mass spectrometry couples to a gas chromatograph (Bode et al., 2021)., Agencia Estatal de Investigación (AEI), grant/award no. MCIN/AEI/10.13039/501100011033 FJC2019-040921-I: Postdoctoral research grant Juan de la Cierva-Formación
Agencia Estatal de Investigación (AEI), grant/award no. MCIN/AEI/10.13039/501100011033 IJC2019-040554-I: Postdoctoral research grant Juan de la Cierva-Formación
Agencia Estatal de Investigación (AEI), grant/award no. PID2020-115620RB-100: QLOCKS project
Agencia Estatal de Investigación (AEI), grant/award no. PID2023-147149NB-100: MTL-FISH
Fifth Framework Programme (FP5), grant/award no. QLRT-2001-00818: SARDYN (2002-2005)
Horizon Europe (HorizonEU), grant/award no. 101150001: A new approach to deciphering inshore-offshore connectivity of pelagic food webs
Instituto Español de Oceanografía (IEO), grant/award no. ECOPEL: ECOPEL (2006-2008)
Sixth Framework Programme of the European Commission (FP6), grant/award no. 8120-09-9: Understanding recruitment processes using coupled biophysical models of the pelagic ecosystem (REPROdUCE), Peer reviewed

Coastal eutrophication driven by anthropogenic nitrogen (N) is a major pressure on estuarine ecosystems. Here, we analyzed stable N isotopes (δ15N) and tissue N content (%N) in the brown algae Fucus spp., collected in 171 sampling stations along the NW Spanish coastline (ca. 1500 km) between 1990 and 2023, to investigate long-term and spatial N enrichment patterns. We further related these indicators to seawater nutrients, land cover, and anthropogenic pressure proxies. Macroalgal δ15N ranged from 2.98 to 16.8‰ (median = 7.6‰) and was often above regional baseline thresholds for unimpacted systems (≤6‰), indicating widespread anthropogenic influence. Strong spatial gradients occurred, with higher δ15N in inner estuarine areas (Fucus ceranoides) and lower values at exposed sites (F. vesiculosus – F. spiralis). δ15N declined significantly since 1990, consistent with wastewater treatment improvements. However, the following stabilization in recent years, indicate continuing N pressures. Seawater nitrate and phosphate, agriculture land cover and, to a lesser extent, artificial surfaces were significantly associated with macroalgal N indicators, although effects were moderate, highlighting multiple interacting environmental drivers. Highest δ15N values in inner areas were consistent with sewage effluent and manure fertilization, whereas lower values at exposed areas likely reflected upwelling. Overall, macroalgal δ15N was a robust indicator of N enrichment across coastal gradients. However, source attribution remains limited by overlapping isotopic signatures and the limited spatial resolution of available datasets. These results support macroalgae as cost-effective biomonitors for long-term monitoring and underscore the need for integrated approaches to improve N source discrimination and management