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To identify a novel optimized strategy for preventing fraudulent substitutions of squid species and origins, forty European squids (Loligo vulgaris) and forty flying squids (Todarodes sagittatus) from the Mediterranean Sea and Atlantic Ocean were analyzed for δ 13 C, δ 15 N, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu using isotope ratio mass spectrometry and inductively coupled plasma-mass spectrometry. While δ 13 C and δ 15 N variations were mainly species-related, they alone could not reliably distinguish samples. To address this issue, decision rules were developed using Classification and Regression Tree analysis. Threshold values for δ 13 C (-19.91‰), δ 15 N (14.87‰), and Pr (0.49 μg kg -1 ) enabled successful discrimination among Mediterranean European squids, Atlantic European squids, Mediterranean flying squids, and Atlantic flying squids, achieving over 90% accuracy, 81% precision, 80% sensitivity, and 93% specificity. This method holds promise for enhancing traceability and safety in the seafood industry, ensuring product integrity and consumer trust., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Nitrate (NO 3 - ) is an important contributor to PM 2.5 which can adversely affect the environment and human health. A noticeable decrease in NO x concentrations has been reported due to the lockdown measures implemented to curb the spread of Corona Virus Disease 2019 (COVID-19). However, questions remain, regarding the nonlinear relationship between NO x and NO 3 - . Here, we collected PM 2.5 samples in two periods, before and during the lockdown of COVID-19 in Shanghai. Dual isotopes (δ 18 O-NO 3 - and δ 15 N-NO 3 - ) of NO 3 - were measured to investigate the formation pathways and potential sources of NO 3 - . The results showed that the concentration of NO 3 - decreased significantly during the lockdown period compared to the period before the lockdown. Additionally, the hydroxyl pathway was the dominant contributor to NO 3 - production during the lockdown period, while N 2 O 5 hydrolyses dominated the formation of NO 3 - before the lockdown. This change is largely attributable to alterations in the oxidative potential of the environment. In comparison to the period preceding the lockdown, the relative contributions of each NO x source remained largely unchanged throughout the lockdown periods. Nevertheless, the concentration of NO 3 - contributed by each NO x source exhibited a notable decline, particularly the mobile sources and coal combustion. Furthermore, the reduction extent of NO 3 - due to the lockdown period was also greater than the reduction during the Clean Air Actions (2013-2017). Our findings provide evidence that the COVID-19 lockdown led to a decrease in NO 3 - concentration due to changes in the formation pathway and reductions in NO x emissions from various sources., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In order to evaluate mercury (Hg) accumulation patterns in Southern Ocean penguins, we measured Hg concentrations and carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope ratios in body feathers of adult Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins living near Anvers Island, West Antarctic Peninsula (WAP) collected in the 2010/2011 austral summer. With these and data from Pygoscelis and other penguin genera (Eudyptes and Aptenodytes) throughout the Southern Ocean, we modelled Hg variation using δ 13 C and δ 15 N values. Mean concentrations of Hg in feathers of Adélie (0.09 ± 0.05 μg g -1 ) and gentoo (0.16 ± 0.08 μg g -1 ) penguins from Anvers Island were among the lowest ever reported for the Southern Ocean. However, Hg concentrations in chinstrap penguins (0.80 ± 0.20 μg g -1 ), which undertake relatively broad longitudinal winter migrations north of expanding sea ice, were significantly higher (P < 0.001) than those in gentoo or Adélie penguins. δ 13 C and δ 15 N values for feathers from all three Anvers Island populations were also the lowest among those previously reported for Southern Ocean penguins foraging within Antarctic and subantarctic waters. These observations, along with size distributions of WAP krill, suggest foraging during non-breeding seasons as a primary contributor to higher Hg accumulation in chinstraps relative to other sympatric Pygoscelis along the WAP. δ 13 C values for all Southern Ocean penguin populations, alone best explained feather Hg concentrations among possible generalized linear models (GLMs) for populations grouped by either breeding site (AICc = 36.9, w i  = 0.0590) or Antarctic Frontal Zone (AICc = 36.9, w i  = 0.0537). Although Hg feather concentrations can vary locally by species, there was an insignificant species-level effect (w i  < 0.001) across the full latitudinal range examined. Therefore, feeding ecology at breeding locations, as tracked by δ 13 C, control Hg accumulation in penguin populations across the Southern Ocean., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Background and Aims: Freshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants of the genus Utricularia are hypothesized to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic Utricularia requires improvement., Methods: We developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three Utricularia species, Utricularia australis, U. gibba and U. uliginosa, in 11 wetlands across a 794-km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural-abundance nitrogen isotope composition (δ15N) of Utricularia spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources., Key Results: Carnivory supplied 40-100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon., Conclusions: Our findings suggest that Utricularia populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

The Atlantic bluefin tuna (ABFT) population ranges throughout the Atlantic Ocean and Mediterranean Sea, and consists of multiple contingents that use diverse habitats and show different movement patterns over the life cycle. Based on body size, elemental and isotopic data of C and N in muscle and liver, we analysed eastern-stock ABFT by comparing mid-sized individuals caught by hook-and-line gears with larger individuals harvested from traps in the Strait of Gibraltar (SoG). Our results show that trophic-related chemical markers have potential for separating temporarily sympatric contingents throughout the ABFT population range, reflecting size-dependent spatial distribution and differential patterns of residency and migration. We present evidence of long-term residency of ABFT in the SoG that persists until the estimated age of ∼5 years (size of ∼140 cm in straight fork length). This age apparently marks a turning point in the life history, where there occurs an ontogenetic switch in the migratory behaviour and distributional pattern. This study contributes new insight into our knowledge about size structure and residency-movement patterns in eastern ABFT. It shows distinct size-dependent migratory and spatial dynamics. The present results encourage further investigation on poorly studied ABFT contingents for a better understanding of the population dynamics towards more comprehensive management plans., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

We investigated trophic structures in rocky subtidal ecosystems transitioning from canopy-forming to barren states across coastlines with varying oceanographic conditions. We examined stable isotopes and functional traits of common invertebrate and fish taxa to understand the food-web consequences. We hypothesized that resource exploitation patterns of functional guilds would result in distinct isotopic niches, defining trophic diversity and niche. δ 13 C and δ 15 N ranges of invertebrate functional groups differentiated pelagic from benthic trophic pathways, reflecting flexible dietary use in the absence of macroalgae. Fish production relied on prey using pelagic and benthic basal resources. Trophic redundancy among consumers within functional guilds contributed to intrinsic trophic structure in barren ecosystems. The resulting community-wide trophic diversity has led to consistent niche widths and overlapping niche space. Overall, our findings highlight the crucial roles of consumers that persist with diverse functional guilds in conferring the adaptability of barren rocky ecosystems following habitat disturbance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

We employed Fourier infrared spectroscopy, laser infrared technology, and stable isotope analysis to investigate the relationships between characteristics of ingested plastics and size-related feeding ecology of a mesopelagic predator, longnose lancetfish Alepisaurus ferox. Plastics were detected in 81.48 % of specimens, up to 8.81 ± 8.29 items/individual and 0.59 ± 0.66 items/g wet weight of intestine, and were sized 20.00 μm to 6.50 cm. The majority were granules and fragments in shape, and polystyrene and acrylate copolymer in polymer type. The diversity indices exhibited a correlation with trophic position and body size groups, emphasizing that the ontogenetic dietary shift of A. ferox may influence the diversity of plastics ingested. This study provides new insights into the plastic pathways linking epipelagic and mesopelagic food webs and demonstrates that biochemical ecological tracers can effectively indicate the bioavailability of plastic correlated with growth in mesopelagic predator., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Spatial differences in the isotope values of widely distributed marine apex consumers may reflect geographical differences in the isotopic composition of basal resources (e.g., phytoplankton) fueling food webs (bottom-up effects) or spatial differences in the trophic ecology of the taxon of interest (top-down effects). We examined spatial variation in δ 13 C and δ 15 N values from 264 South American sea lions (SASL, Otaria flavescens) of different age classes (adults, subadults and juveniles), their putative prey consisting of pelagic and benthic coastal fishes, and particulate organic matter (POM) measured from locations situated across >2300 km of the Chilean coast (between 18°42' and 39°17' S). We used generalized least squares (GLS) models to compare the form of the relationship between δ 13 C and δ 15 N and latitude between the three functional groups. Our results show that SASL from northern, central, and southern areas were isotopically distinct, with individuals from the north having lower δ 13 C and higher δ 15 N values in comparison to individuals from the south. When the relationship for each functional group was modelled individually using GLS, results indicated that for each degree of increasing latitude δ 15 N decreased on average by 0.12‰ (POM), 0.15‰ (prey), and 0.14‰ (SASL), while δ 13 C increased by 0.06‰ (POM) and 0.05‰ in both prey and SASL. We suggest that the latitudinal differences observed in SASL δ 13 C and δ 15 N values reflect baseline isotopic variation rather than marked differences in trophic ecology of these widely distributed consumers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Few studies have examined the N kinetics of individual feeds with stable isotope tracing. We hypothesized that N partitioning to milk and excreta pools as well as the rates of the processes that drive this partitioning would differ for alfalfa silage, corn silage, corn grain, and soybean meal. Feed ingredients were endogenously labeled with 15 N and included in 4 diets to create treatments with the same dietary composition and different labeled feed. Diets were fed to 12 late-lactation dairy cows for 4 d (96 h) and feces, urine, and milk collection proceeded during the 4 d of 15 N enrichment and for 3 d (80 h) after cessation of label feeding. Nonlinear models of 15 N enrichment and decay were fit to milk (MN), urine (UN), and fecal N (FN) in R with the nlme package, and feed-specific parameter estimates were compared. The estimated proportions of feed N that were excreted in feces supported our understanding that N from soybean meal and corn grain is more digestible than N from alfalfa and corn silage. Estimates for the N partitioning between milk and urine from the 2 concentrate feeds (soybean meal and corn grain) indicated that UN/MN ratios were less than or equal to 1:1, indicating either more or equal nitrogen partitioning to milk compared with urine. It is important to maintain factual accuracy in representing the results rather than implying a desired outcome unsupported by the data. In contrast, UN/MN ratios for forage feeds (corn and alfalfa silage) were >1:1, indicating more N partitioning to urine than milk. The modeled proportion of total FN that originated from feed N was 82.2%, which is in line with previous research using a similar 15 N measurement timeframe. However, the proportion of urinary and MN originating from feed N was much lower (60.5% for urine, 57.9% for milk), suggesting that approximately 40% of urinary and MN directly originate from body N sources related to protein turnover., (The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).)

Patterns of mother-embryo fractionation of 13 C and 15 N were assessed for their predictability across three species of batoids caught as by-catch in south-eastern Australia. Stable isotope analysis of 24 mothers and their litters revealed that isotope ratios of embryos were significantly different from their corresponding mothers and that the scale and direction of the difference varied within and across species. The range of variation across species was 3.5‰ for δ 13 C and 4‰ for δ 15 N, equivalent to a difference in trophic level. In one species (Urolophus paucimaculatus) litters could be significantly enriched or depleted in 13 C and 15 N relative to their mothers' isotope signatures. These results suggest that patterns of mother-embryo isotope fractionation vary within and between species and that these patterns may not be explained only by developmental mode. Contrasting patterns of fractionation between and within species make it difficult to adjust mother-embryo fractionation with broad-scale correction factors., (© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Silver nanoparticles (AgNPs) are added as antibacterial and anti-odor agents to a wide range of textiles, with high potential for release into aquatic environments via domestic wastewater. Previous work demonstrating the negative impacts of AgNP exposure on periphyton production suggests benthic primary production could be reduced in aquatic ecosystems impacted by AgNP discharge. To evaluate the potential for AgNPs to alter benthic-pelagic coupling in aquatic ecosystems, tissue-stable isotope ratios of carbon and nitrogen from northern pike (Esox lucius) and yellow perch (Perca flavescens) were measured before, during, and after the addition of AgNPs to a whole-lake ecosystem, and compared to those collected from a nearby reference lake. A shift in carbon isotope ratios toward more negative values was observed in both P. flavescens and E. lucius collected from the lake where AgNPs were added, with no shift in similar magnitude observed in E. lucius from the reference lake. Consequently, Bayesian estimates of benthic energy consumed decreased by 32% for P. flavescens and by 40% for E. lucius collected after AgNP additions relative to pre-addition estimates, greater in magnitude or opposite in direction of trends observed in our reference lake. Analyses suggest no changes in fish nitrogen isotope ratios related to AgNP additions. We hypothesize that the observed reduction in littoral energy use of fish reported here is a response to AgNP settling in littoral benthic habitats-the main habitat in lakes supporting periphyton-as AgNP has been shown elsewhere to significantly reduce the rates of periphyton production. Further, our study highlights the need to broaden the scope of risk assessments for AgNPs and other emerging contaminants prone to settling to consider habitat-specific impacts on resource utilization by organisms after their release into aquatic ecosystems., (© 2023 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Stable isotope analysis of fish muscle tissue has been used to quantify fish migratory behavior in many systems, and these chemical tracers are especially useful for euryhaline fishes that traverse significant salinities and gradients in baseline signatures. However, the removal of muscle tissues often requires lethal sampling. Fish scales may be removed non-lethally and offer potential alternatives to stable isotope ratios from muscle to indicate recent feeding histories. For this study, red drum Sciaenops ocellatus were collected in subtropical estuaries in the northwestern Gulf of Mexico and analyzed for stable isotope (𝛿 13 C and 𝛿 15 N) compositions of scale exteriors. Decalcification of scale samples was deemed unnecessary given the preservation of linearity and minimal offsets between paired decalcified and untreated scale samples. Stable isotope signatures of muscle tissue and scales were closely matched and indicated high degrees of residence within bays at fine spatial scales. This study also surveyed the existing body of literature comparing scale and muscle isotope values from the same individuals and found that the majority reports linear relationships with slopes close to unity, although species-specific offsets and intercepts vary. This work expands the body of literature indicating that scales are a viable non-lethal alternative for stable isotope assessments of dietary and habitat use histories for mobile fishes., (© 2023 Fisheries Society of the British Isles.)

Reef ecosystems are characterized by highly heterogenous habitats and functionally diverse fish communities. Few studies have examined how functional diversity differs among habitats within these communities, i.e., species associated with a specific habitat may have similar trophic ecologies meaning that the functional diversity within the community is driven by habitat diversity or, conversely, high functional diversity within each habitat would indicate that resource segregation also occurs at the habitat level. We used stable isotope ratios of carbon and nitrogen to estimate trophic position, resource use and ontogenetic niche shifts of 15 reef fishes associated with four distinct habitat types (cryptobenthic, epibenthic sand, epibenthic rock and hyperbenthic) on the Croatian coast of the Adriatic Sea. Trophic ecology was quite similar across fish assemblages, but there was strong evidence of niche segregation among fish species within each assemblage showing high functional diversity within each microhabitat. The sampled fish community contained benthic and pelagic resource users, along with multiple intermediate generalists. Consumer stable isotope ratios revealed considerable interspecific variation in resource use among fishes within each habitat type. The cryptobenthic fishes were a notable exception to this trend with the narrow range of resource use values, indicating reliance of these species on a single resource. The greatest diversity of trophic positions within a guild was observed in cryptobenthic and rock-associated epibenthic fishes. The majority of observed ontogenetic variation in studied fish species reflected an increase in benthic resource use and trophic position. However, the degree of ontogenetic variation in trophic ecology of studied species, if present, was generally low, showing no dramatic change in the ecology of any species. The size structuring among guilds was considerable, with cryptobenthic fishes the smallest on average and hyperbenthic fishes the largest, despite guilds having similar ranges of trophic positions., (© 2022 Fisheries Society of the British Isles.)

The combined use of otolith chemistry and tissue isotopes has the potential to reveal movements, habitat associations and food web interactions at a variety of spatial and temporal scales. Here, a combination of otolith Ba:Ca life-history transects with muscle tissue δ 13 C and δ 15 N values has been used to assess habitat use and oligohaline residence in red drum Sciaenops ocellatus in subtropical estuaries in the north-western Gulf of Mexico. Tissue isotopes were distinct among capture locations, particularly between bays with differing proximities to freshwater inflow sources. Otolith edge Ba:Ca values and tissue δ 13 C values were not correlated. These results indicated that fish were neither residing in nor feeding in oligohaline waters for significant periods of time within the tissue turnover window of several months prior to capture. Nonetheless, spatial differences in tissue isotope values indicated limited mixing among bays and relatively high site fidelity during estuarine occupancy. Lifetime otolith Ba:Ca transects revealed individual variability in the magnitude of residence in oligohaline waters. Using a mean oligohaline occupancy threshold, an estimated 82% of individuals used oligohaline waters at some point in their life. Nonetheless, 66% of individuals spent <20% of their life histories in oligohaline waters, suggesting intermittent and infrequent excursions into low salinity waters. Finally, a literature survey identified 56 peer-reviewed publications using combinations of otolith chemistry and tissue stable isotope ratios with a wide range of marker pairings and study aims. The diversity of ecological questions that can be asked with the combined use of these two approaches will provide valuable insight into fish ecology., (© 2022 Fisheries Society of the British Isles.)

Seasonal differences in the availability of resources potentially result in the food web architecture also varying through time. Stable isotope analyses are a logistically simple but powerful tool for inferring trophic interactions and food web structure, but relatively few studies quantify seasonal variations in the food web structure or nutrient flux across multiple trophic levels. We determined the temporal dynamics in stable isotope compositions (carbon, nitrogen and sulphur) of a fish community from a highly seasonal, temperate estuary sampled monthly over a full annual cycle. Sulphur isotope values in fish tissues discriminated among consumers exploiting pelagic and benthic resources but showed no seasonal variation. This implied limited change in the relative consumption of pelagic and benthic resources by the fish community over the study period despite major seasonal changes in phytoplankton biomass. Conversely, carbon and nitrogen isotope values exhibited seasonality marked by the commencement of the spring phytoplankton bloom and peak chlorophyll concentration, with δ 13 C values following expected trends in phytoplankton growth physiology and variation in δ 15 N values coinciding with changes in major nitrogen sources to plankton between nitrate and ammonium. Isotope shifts in fish muscle were detected within 2 weeks of the peak spring phytoplankton bloom, suggesting a rapid trophic transfer of carbon and nitrogen along food chains within the estuarine food web during periods of high production. Therefore we caution against the assumption that temporal averaging effectively dampens isotopic variability in tissues of higher trophic-level animals in highly dynamic ecosystems, such as temperate estuaries. This work highlights how stable isotope analyses can be combined with environmental data to gain a broader understanding of ecosystem functioning, while emphasising the need for temporally appropriate sampling in stable isotope-based studies., (© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Although considered a hallmark in early ontogeny, weaning from breastmilk is difficult to monitor in wild primates and weaning ages remain unknown for wild bonobos (Pan Paniscus). Here, we calculated inter-birth intervals from demographic data and measured the isotopic offsets (Δ 15 N and Δ 13 C) between mother (n = 17) and offspring (n = 28) fecal sample pairs (n = 131, total n = 246) in the LuiKotale bonobos to assess nutritional weaning for the first time. We tested the effects of infant age, female parity, and sibling competition on Δ 15 N and Δ 13 C values. We found bonobo inter-birth intervals ranging from 2.2 to 7.3 years (x̄ = 4.7 ± 1.3 years) at LuiKotale. The Δ 15 N and Δ 13 C values suggested nutritional weaning on average by 6.6 and 7.0 years of age respectively, considerably exceeding weaning ages reported for chimpanzees (P. troglodytes) using the same approach. Our Δ 13 C data suggested that the number of offspring present affected nursing, with first-time mothers nursing more and possibly longer. The Δ 15 N and Δ 13 C values decreased with the arrival of the next sibling, suggesting sibling competition reduces milk access. Nevertheless, offspring may continue nursing 2.5-3 years after the birth of the next sibling, corresponding well with observations on low infant mortality. In conclusion, bonobo mothers provide remarkably enduring materna l support in the form of nursing concurrently to several offspring., (© 2024 Wiley Periodicals LLC.)

Trophic niche is the result of the long-term evolution of species and can reflect the pressures they experience in habitats. The whole-genome sequencing of giant pandas (Ailuropoda melanoleuca) has indicated that populations distributed in Qinling (QIN) and non-QIN probably diverged 300 ky ago. Although many studies regarding foraging strategy, habitat preference, and niche partition have been conducted on these populations, there is still a lack of precise quantification of trophic niches. Here, we calculated and compared isotopic trophic niche widths of giant pandas from Sichuan (SC) and QIN populations by measuring carbon and nitrogen isotopes of their hairs; combined with data from sympatric mammals, we explored the relative trophic positions of giant pandas in the ecosystem, respectively. The Stable Isotope Bayesian Ellipses in R (SIBER) model results showed the trophic niche width of QIN pandas was 3.44‰ 2 , which was significantly bigger than those of the SC population (2.03‰ 2 ), with an overlapping about 1.45‰ 2 ; and they both occupied a unique position in the context, almost one trophic level lower than herbivores. Then, we determined the isotopic ratios of the main foods from the habitats of these pandas; the results suggested that the isotopic difference between bamboo shoots and other parts plus the various feeding selections of pandas on them accounted for pandas' trophic niche widths. We considered the higher nutrition availability and digestible food resources giving QIN pandas a wider trophic niche than pandas from SC. This conclusion provides a new insight into the resource use and trophic ecology of giant pandas and is important to develop refined management plans for the two populations., (© 2023 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

Patterns of feeding and growth of Atlantic salmon Salmo salar L. in the marine environment are critical to understanding how observed declines in recruitment may reflect warming or other oceanic drivers. The isotopic composition of scales can provide insight into differences in marine feeding location and possibly temperature regime. The authors used archived scale samples to measure δ 13 C and δ 15 N deposited in the scales of one sea-winter (1SW) salmon during their last season of growth at sea before they returned to five Irish rivers. δ 13 C values were related statistically to observed salmon body condition (Fulton's K), and fish with higher δ 13 C values tended to show significantly better condition. In contrast, δ 15 N values were negatively related to body condition. There was no important effect on condition of length at smolt migration, and the effect of duration of marine residence varied among rivers. It is likely that δ 13 C values partly reflected ambient ocean temperature and recent marine feeding environment before return migration, such that the observed relationship between higher δ 13 C values and increased body condition may express an advantage for adult fish feeding in warmer, potentially closer, waters. If greater body condition influences fitness, then a changing temperature regime in the Northeast Atlantic may drive shifts in salmon survival and reproduction. This study provides evidence that there is spatial and trophic variation at sea between salmon from rivers of origin that are located relatively close to each other, with potential consequences for body condition and, consequently, fitness and life history; this suggests that salmon populations from geographically proximate rivers within regions may exhibit differential responses to ocean-scale climatic changes across the Northeast Atlantic., (© 2021 Fisheries Society of the British Isles.)

Pulsed flows following heavy monsoon rain events alter riverine food webs, but their impact on headwater stream food webs across the continuum from forested canopy to open agricultural land use remains unclear. We investigated carbon and nitrogen stable isotopes in macroinvertebrates and fish in two tributaries of the Suyeung River, Korea, before and after heavy monsoon rains to assess changes in community trophic niches. Basal resources (leaf litter and biofilms) exhibited consistent δ 13 C and δ 15 N values across seasons, with biofilms showing higher δ 13 C values. δ 15 N values increased from forested to agricultural reaches, indicating varied nutrient inputs. Consumer isotope values remained stable over time but varied longitudinally, reflecting reliance on local resources. Trophic niches differed between watershed locations but overlapped seasonally. Despite a decrease in consumer δ 13 C ranges after heavy rainfalls, variations in their δ 15 N ranges and the ellipse centroid (SEAc) of isotopic niches between sites resulted in broadly consistent SEAc across locations and seasons. This indicates limited evidence for directional reshaping of food-web properties across channel reaches following monsoon rains. Downstream isotopic shifts suggest substantial agricultural influences on food webs. Overall, our findings highlight that monsoon rains may have minimal effects on the community trophic niches of stream food webs., (© 2024. The Author(s).)

Biological N 2 fixation (BNF) is traced to the Archean. The nitrogen isotopic fractionation composition (δ 15 N) of sedimentary rocks is commonly used to reconstruct the presence of ancient diazotrophic ecosystems. While δ 15 N has been validated mostly using organisms grown under present-day conditions; it has not under the pre-Cambrian conditions, when atmospheric p O 2 was lower and p CO 2 was higher. Here, we explore δ 15 N signatures under three atmospheres with (i) elevated CO 2 and no O 2 (Archean), (ii) present-day CO 2 , and O 2 and (iii) future elevated CO 2 , in marine and freshwater, heterocytous cyanobacteria. Additionally, we augment our data set from literature for more generalized dependencies of δ 15 N and the associated fractionation factor epsilon ( ε = δ 15 N biomass - δ 15 N N2 ) during BNF in Archaea and Bacteria, including cyanobacteria, and habitats. The ε ranges between 3.70‰ and -4.96‰ with a mean ε value of -1.38 ± 0.95‰, for all bacteria, including cyanobacteria, across all tested conditions. The expanded data set revealed correlations of isotopic fractionation of BNF with CO 2 concentrations, toxin production, and light, although within 1‰. Moreover, correlation showed significant dependency of ε to species type, C/N ratios and toxin production in cyanobacteria, albeit it within a small range (-1.44 ± 0.89‰). We therefore conclude that δ 15 N is likely robust when applied to the pre-Cambrian-like atmosphere, stressing the strong cyanobacterial bias. Interestingly, the increased fractionation (lower ε ) observed in the toxin-producing Nodularia and Nostoc spp. suggests a heretofore unknown role of toxins in modulating nitrogen isotopic signals that warrants further investigation.IMPORTANCENitrogen is an essential element of life on Earth; however, despite its abundance, it is not biologically accessible. Biological nitrogen fixation is an essential process whereby microbes fix N 2 into biologically usable NH 3 . During this process, the enzyme nitrogenase preferentially uses light 14 N, resulting in 15 N depleted biomass. This signature can be traced back in time in sediments on Earth, and possibly other planets. In this paper, we explore the influence of p O 2 and p CO 2 on this fractionation signal. We find the signal is stable, especially for the primary producers, cyanobacteria, with correlations to CO 2 , light, and toxin-producing status, within a small range. Unexpectedly, we identified higher fractionation signals in toxin-producing Nodularia and Nostoc species that offer insight into why some organisms produce these N-rich toxic secondary metabolites., Competing Interests: The authors declare no conflict of interest.

Deep-pelagic species are central to marine ecosystems and increasingly vulnerable to global change and human exploitation. To date, our understanding of these communities remains limited mainly due to the difficulty of observations, calling for complementary innovative tools to better characterize their ecology. We used mercury (Δ 199 Hg, δ 202 Hg, Δ 201 Hg, and Δ 200 Hg), carbon (δ 13 C), and nitrogen (δ 15 N) stable isotope compositions to segregate deep-pelagic species caught on the continental slope of the Bay of Biscay (NE Atlantic) according to their foraging depth and trophic ecology. Decreasing fish Δ 199 Hg values with corresponding depth estimates from the surface to down to 1,800 m confirmed that mercury isotopes are able to segregate deep species over a large vertical gradient according to their foraging depth. Results from isotopic compositions also identified different mercury sources, likely reflecting different trophic assemblages over the continental slope, in particular, the demersal influence for some species, compared to purely oceanic species. Overall, our results demonstrate how mercury stable isotopes can inform the vertical foraging habitat of little-known species and communities feeding in the deep.

Rationale: Natural variations in the abundance of the stable isotopes of nitrogen (δ 15 N) and carbon (δ 13 C) offer valuable insights into metabolic fluxes. In the wake of strong interest in cancer metabolism, recent research has revealed δ 15 N and δ 13 C variations in cancerous compared to non-cancerous tissues and cell lines. However, our understanding of natural isotopic variations in cultured mammalian cells, particularly in relation to metabolism, remains limited. This study aims to start addressing this gap using metabolic modulations in cells cultured under controlled conditions., Methods: Prostate cancer cells (PC3) were cultured in different conditions and their δ 15 N and δ 13 C were measured using isotope ratio mass spectrometry. Isotopic variations during successive cell culture passages were assessed and two widely used cell culture media (RPMI and DMEM) were compared. Metabolism was modulated through glutamine deprivation and hypoxia., Results: Successive cell culture passages generally resulted in reproducible δ 15 N and δ 13 C values. The impact of culture medium composition on δ 15 N and δ 13 C of the cells highlights the importance of maintaining a consistent medium composition across conditions whenever possible. Glutamine deprivation and hypoxia induced a lower δ 13 C in bulk cell samples, with only the former affecting δ 15 N. Gaps between theory and experiments were bridged and the lessons learned throughout the process are provided., Conclusions: Exposing cultured cancer cells to hypoxia allowed us to further investigate the relation between metabolic modulations and natural isotopic variations, while mitigating the confounding impact of changing culture medium composition. This study highlights the potential of natural δ 13 C variations for studying substrate fluxes and nutrient allocation in reproducible culture conditions. Considering cell yield and culture medium composition is pivotal to the success of this approach., (© 2024 The Author(s). Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)

In recent years, it has become evident that human activities have significantly disrupted the nitrogen cycle surpassing acceptable environmental thresholds. In this study, chemical and isotopic tracers were combined with a mathematical mass balance model (EMMA), PHREEQC inverse mixing model, and statistical analyses to evaluate groundwater quality, across an area experiencing substantial human activities, with a specific focus on tracing the origin of nitrate (NO 3 - ) with potential water mixing processes. This multi-technique approach was applied to an unconfined aquifer underlying an agricultural area setting in an inter-mountain depression (i.e., the "Pampa de Pocho Plain" in Argentina). Here, the primary identified geochemical processes occurring in the investigated groundwater system include the dissolution of carbonate salts, cation exchange, and hydrolysis of alumino-silicates along with incorporating ions from precipitation. It was observed that the chemistry of groundwater, predominantly of sodium bicarbonate with sulfate water types, is controlled by the area's geology, recharge from precipitation, and stream water infiltration originating from the surrounding hills. Chemical results reveal that 60% of groundwater samples have NO 3 - concentrations exceeding the regional natural background level, confirming the impact of human activities on groundwater quality. The dual plot of δ 15 N NO3 versus δ 18 O NO3 values indicates that groundwater is affected by NO 3 - sources overlapping manure/sewage with organic-rich soil. The mathematical EMMA model and PHREEQC inverse modeling, suggest organic-rich soil as an important source of nitrogen in the aquifer. Here, 64 % of samples exhibit a main mixture of organic-rich soil with manure, whereas 36 % of samples are affected mainly by a mixture of manure and fertilizer. This study demonstrates the utility of combining isotope tracers with mathematical modeling and statistical analyses for a better understanding of groundwater quality deterioration in situations where isotopic signatures of contamination sources overlap., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Rationale: Stable isotope analysis of bone provides insight into animal foraging and allows for ecological reconstructions over time, however pre-treatment is required to isolate collagen. Pre-treatments typically consist of demineralization to remove inorganic components and/or lipid extraction to remove fats, but these protocols can differentially affect stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope values depending on the chemicals, tissues, and/or species involved. Species-specific methodologies create a standard for comparability across studies and enhance understanding of collagen isolation from modern cetacean bone., Methods: Elemental analyzers coupled to isotope ratio mass spectrometers were used to measure the δ 13 C and δ 15 N values of powdered killer whale (Orcinus orca) bone that was intact (control) or subjected to one of three experimental conditions: demineralized, lipid-extracted, and both demineralized and lipid-extracted. Additionally, C:N ratios were evaluated as a proxy for collagen purity. Lastly, correlations were examined between control C:N ratios vs. historical age and control C:N ratios vs. sample characteristics., Results: No significant differences in the δ 15 N values were observed for any of the experimental protocols. However, the δ 13 C values were significantly increased by all three experimental protocols: demineralization, lipid extraction, and both treatments combined. The most influential protocol was both demineralization and lipid extraction. Measures of the C:N ratios were also significantly lowered by demineralization and both treatments combined, indicating the material was closer to pure collagen after the treatments. Collagen purity as indicated via C:N ratio was not correlated with historical age nor sample characteristics., Conclusions: If only the δ 15 N values from killer whale bone are of interest for analysis, no pre-treatment seems necessary. If the δ 13 C values are of interest, samples should be both demineralized and lipid-extracted. As historical age and specimen characteristics are not correlated with sample contamination, all samples can be treated equally., (© 2024 The Author(s). Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)

The economic, socio-political, and cultural significance of camelids in the Andean region is well-recognized, yet an understanding of their management evolution over pre-historical periods remains limited. This study aims to fill this gap by conducting the first cross-regional assessment of camelid pastoralism in Peru from 900 BCE to 1470 CE, using stable carbon and nitrogen isotopic compositions from the bone collagen and fibers of 577archaeological camelids across 21 sites. This research investigates the spatio-temporal shifts in camelid dietary habits, focusing on how the rise of intensive agriculture may have influenced change and led to the evolution of distinct roles for camelids in coastal versus non-coastal Andean economies. Our analysis indicates an increase in δ13C values over time on the coast, suggesting a shift towards maize-based camelid diets. Conversely, δ13C values decrease over time in highland environments, suggesting camelids consumed relatively more wild C3 forage and/or cultivated crops such as tubers. The study also reveals a significant positive relationship between latitude and δ15N values, suggesting increasing environmental aridity enriches δ15N in bone collagen. After controlling for this latitudinal effect, we observe a rise in δ15N values in both coastal and non-coastal camelids, suggesting that in later periods camelids may have been foddered in agricultural fields that were enriched with guano or dung fertilizer used to intensify production. Importantly, this research uncovers a distinct dietary divergence between coastal and inland camelids. The observed divergence in diets suggests contrasting socio-economic uses of camelids, where coastal camelids were predominantly involved in ceremonial and political activities, while those in non-coastal areas were crucial to the subsistence economy., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Noe et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Uniform enrichment of 15 N and 13 C in proteins is commonly employed for 2D heteronuclear NMR measurements of the three-dimensional protein structure. Achieving a high degree of enrichment of both elements is important for obtaining high quality data. Uniform labeling of proteins and glycoproteins expressed in higher organisms (yeast or mammalian cell lines) is more challenging than expression in Escherichia coli , a prokaryote that grows on simple, chemically defined media but does not provide appropriate eukaryotic modifications. It is difficult to achieve complete incorporation of both heavy isotopes, and quality control measures are important for quantitating the level of their enrichment. Mass spectrometry measurements of the isotopic distribution of the intact protein or its proteolytic fragments provide the means to assess the enrichment level. A mass accuracy of 1 ppm or better is shown to be required to distinguish the correct combination of 13 C and 15 N enrichment due to subtle shifts in peak centroids with differences in the underlying, but unresolved, isotopic fine structure. A simple computer program was developed to optimize the fitting of experimental isotope patterns to statistically derived distributions. This method can determine the isotopic abundance from isotope patterns and isotopologue masses in conventional MS data for peptides, intact proteins, and glycans. For this purpose, MATLAB's isotope simulator, isotopicdist, has been modified to permit the variation of 15 N and 13 C enrichment levels and to perform a two-dimensional grid search of enrichment levels of both isotopes. We also incorporated an alternate isotope simulator, js-emass, into MATLAB for use in the same fitting program. Herein we benchmark this technique on natural abundance ubiquitin and uniformly [ 15 N, 13 C]-labeled ubiquitin at both the intact and peptide level, outline considerations for data quality and mass accuracy, and report several improvements we have made to the previously reported analysis of the [ 15 N, 13 C]-enriched human IgG Fc domain, a glycoprotein that has been expressed in Saccharomyces cerevisiae .

In recent years, the arctic tundra has been subject to more frequent stochastic biotic or extreme weather events (causing plant dieback) and warmer summer air temperatures. However, the combined effects of these perturbations on the tundra ecosystem remain uninvestigated. We experimentally simulated plant dieback by cutting vegetation and increased summer air temperatures (ca. +2°C) by using open-top chambers (OTCs) in an arctic heath tundra, West Greenland. We quantified surface greenhouse gas fluxes, measured soil gross N transformation rates, and investigated all ecosystem compartments (plants, soils, microbial biomass) to utilize or retain nitrogen (N) upon application of stable N-15 isotope tracer. Measurements from three growing seasons showed an immediate increase in surface CH 4 and N 2 O uptake after the plant dieback. With time, surface N 2 O fluxes alternated between emission and uptake, and rates in both directions were occasionally affected, which was primarily driven by soil temperatures and soil moisture conditions. Four years after plant dieback, deciduous shrubs recovered their biomass but retained significantly lower amounts of 15 N, suggesting the reduced capacity of deciduous shrubs to utilize and retain N. Among four plant functional groups, summer warming only increased the biomass of deciduous shrubs and their 15 N retention, while following plant dieback deciduous shrubs showed no response to warming. This suggests that deciduous shrubs may not always benefit from climate warming over other functional groups when considering plant dieback events. Soil gross N mineralization (~ -50%) and nitrification rates (~ -70%) significantly decreased under both ambient and warmed conditions, while only under warmed conditions immobilization of NO 3 - significantly increased (~ +1900%). This explains that plant dieback enhanced N retention in microbial biomass and thus bulk soils under warmed conditions. This study underscores the need to consider plant dieback events alongside summer warming to better predict future ecosystem-climate feedback., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Rapid coagulation of reptile blood often hinders its use in studies in remote and difficult-to-access areas, necessitating chemical preservation. Therefore, understanding the potential effects of anticoagulants on the isotopic compositions of blood is essential to avoid issues in interpreting the results for ecological studies. In this study we aimed to verify whether the storage time of the blood tissue in anticoagulants can influence its isotopic compositions of the broad-snouted caiman ( Caiman latirostris ), an ectothermic top predator from eastern South America. Blood samples were obtained from ten adult females of C. latirostris from a commercial breeding facility in 2015. Samples were stored in vials containing ethylenediaminetetraacetic acid (EDTA) and sodium heparin (SH) and centrifuged after 2 and 8 h to separate red blood cells and plasma. No effect of time was found on the δ 13 C and δ 15 N of whole blood, plasma, and red blood cells in contact with the two types of anticoagulants, EDTA and SH. The findings have practical implications for researchers in this field, as they suggest that anticoagulants can be used effectively for at least eight hours under refrigeration.

Estuaries exhibit high physicochemical variability and the properties of estuaries and the constituent segments are not yet systematically understood. This study aims to reveal the spatial heterogeneity of predominant organic sources using carbon and nitrogen stable isotope ratios (δ 13 C and δ 15 N, respectively) of Japanese eels (Anguilla japonica), one of the ideal natural samplers. In the Miyakoda River, Japan, our study site, the effectiveness of eel δ 13 C and δ 15 N values as standard indices of predominant organic sources was tested by employing the River Continuum Concept. This study then extended the application of these indices to the estuary, i.e., the Hamana Lake system, into which the Miyakoda River flows. Once in the upper estuary, eel δ 13 C and δ 15 N values became high, with the latter peaking in this river-estuary continuum, indicating that artificial labile subsidies (nutrients and organic matter) with high δ 15 N values were rapidly assimilated into the food web. Eel δ 15 N values decreased again in the middle estuary. Nevertheless, the influence of terrestrial organic subsidies extended into this segment, as evidenced by the low δ 13 C values of eels. These results suggest that refractory organic matter with low δ 15 N values, such as plant-derived ones, is slowly assimilated into the food web in the downstream estuarine segments. The higher δ 13 C values in the lower estuary suggested that the contribution of eelgrass or macroalgae occurred in addition to benthic microalgae. Thus, our results emphasize the need to consider the multiple energy flows to understand the estuary as a continuum., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The addition of Navicula sp. to shrimp nurseries can improve the growth of Penaeus vannamei reared in biofloc systems. However, the contribution of microalgae to the biofloc formation and the effective contribution to shrimp nutrition remain unknown. In this study, Navicula sp. was added to biofloc nursery systems of P. vannamei at distinct time frequencies for evaluating its nutritional contribution to shrimp growth. Nursery rearing was carried out in bioflocs for 35 days at a stocking density of 3000 post-larvae m -3 . Shrimp were fed using a commercial feed plus fresh culture of Navicula sp. at different frequencies: no addition of Navicula sp. (WN - control), the addition of 10 × 10 4 cells mL -1 of the diatom every 5, 10 and 15 days (N5, N10 and N15, respectively). Food sources relative contribution to P. vannamei development was estimated using a Bayesian mixture model. The isotopic discrimination factor (Δ 15 N and Δ 13 C) for each food source was determined experimentally. After 35 days of culture, survival (∼93 %) was similar across all treatments but there was a significant difference in weight gain and feed conversion ratio. The N10 treatment (0.50 ± 0.05 g, 0.99 ± 0.01) exhibited better growth parameters when compared to the WN treatment (0.33 ± 0.07 g, 11.46 ± 0.30). Biofloc was the food source most assimilated by shrimp followed by Navicula sp. and commercial feed. Contribution of Navicula sp. was higher in the N5 treatment. In the treatments with diatom addition, an inverse correlation was observed between the relative contributions of biofloc and Navicula sp., indicating that Navicula sp. is not in the biofloc composition, but it is directly consumed by P. vannamei post-larvae. Biofloc and Navicula sp. exhibited larger contributions to the growth of shrimp, reinforcing the importance of natural food sources to the aquaculture of P. vannamei post-larvae.

Agricultural nitrogen (N) contributes a dominant percentage to global N pollution in the coastal zone. Emerging research on N isotopes in bivalve shells has shown value for reconstructing historical increases in estuarine wastewater inputs. However, applications for fertilizer N are understudied. Here, we integrate the study of organic N isotopes, in concert with δ 18 O and δ 13 C, in estuarine bivalve shells to investigate spatial and long-term changes in nitrogen inputs and sources. Modern, museum-collected, and subfossil specimens of the genera Mytilus and Ostrea were profiled in a California estuary with an intensely agricultural watershed. Spatial patterns in bivalve isotopic composition reflected gradients in watershed nutrient inputs and productivity parameters. Furthermore, a comparison between modern and historical periods revealed changes in nutrient source or processing over the last 1,000 years. The N isotope values from shells offer perspective on agricultural pollution in estuaries., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Macroalgal nitrogen isotope analysis (δ 15 N) is a reliable method for the identification of nitrogen pollutant sources. Understanding δ 15 N geospatial variation within small bays and/or harbour environments can help identify point sources of nitrogen pollution. This study sampled over 300 Fucus vesiculosus and Ulva sp. specimens in September 2022 and May 2023 from Staithes Harbour, North Yorkshire, England. δ 15 N values for Staithes Beck were elevated when compared to sites in Staithes Harbour and the North Sea: this is attributed to sewage effluent and/or agricultural manure. Few sites within Staithes Harbour were significantly different from one another in terms of δ 15 N, suggesting a relatively homogenous nitrogen isotope record of the harbour. Simple harbour environments like Staithes may be relatively well mixed, and thus, sampling one harbour site may be enough to represent the entire harbour. Of course, more complex harbours may require more sample locations to ascertain point sources and mixing in the harbour., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Knowledge of predator-prey interactions is key in ecological studies and understanding ecosystem function, yet this is still poorly explored in the deep-sea environment. Carbon (δ 13 C: 13 C/ 12 C) and nitrogen (δ 15 N: 15 N/ 14 N) stable isotope ratios of a deep-diving species, the short-finned pilot whale (Globicephala macrorhynchus), were used to explore knowledge gaps on its ecological niche and foraging habitats in the Webbnesia marine ecoregion (Tenerife Island, n = 27 animals vs. Madeira, n = 31; 500 km apart) where animals display distinct levels of site fidelity. Specifically, we tested whether intraspecific isotopic variation results from differences between geographic areas (due to possible foraging plasticity between regions), sexes, and/or years (2015-2020) using Generalized Linear Models. In general, significant differences (p < 0.05) were found in the stable isotope profiles of pilot whales between the two archipelagos, which were also reflected in their isotopic niche. The higher mean and wider range of δ 15 N values in Tenerife suggest that pilot whales consume prey of higher trophic levels and more diverse than Madeira. The higher mean and wider range of δ 13 C values in Madeira suggest that in that island, pilot whales rely on prey from more diverse habitats. There was significant variation between some years, but not between sexes. Finally, we discuss pilot whales' foraging strategies worldwide and infer the reliance on benthic or benthopelagic food sources in the Webbnesia., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objectives: Nitrogen isotopes (δ 15 N) are widely used to study human nursing and weaning ages. Conventional methods involve sampling 1-mm thick sections of tooth dentine-producing an averaging effect that integrates months of formation. We introduce a novel protocol for measuring δ 15 N by multicollector secondary ion mass spectrometry (SIMS)., Materials and Methods: We sampled dentine δ 15 N on a weekly to monthly basis along the developmental axis in two first molars of healthy children from Australia and New Zealand (n = 217 measurements). Nitrogen isotope ratios were determined from measurements of CN - secondary molecular ions in ~35 μm spots. By relating spot position to enamel formation, we identified prenatal dentine, as well as sampling ages over more than 3 years. We also created calcium-normalized barium and strontium maps with laser ablation-inductively coupled plasma-mass spectrometry., Results: We found rapid postnatal δ 15 N increases of ~2‰-3‰, during which time the children were exclusively breastfed, followed by declines as the breastfeeding frequency decreased. After weaning, δ 15 N values remained stable for several months, coinciding with diets that did not include meat or cow's milk; values then varied by ~2‰ starting in the third year of life. Barium did not show an immediate postnatal increase, rising after a few months until ~1-1.5 years of age, and falling until or shortly after the cessation of suckling. Initial strontium trends varied but both individuals peaked months after weaning., Discussion: Developmentally informed SIMS measurements of δ 15 N minimize time averaging and can be precisely related to an individual's early dietary history., (© 2024 The Author(s). American Journal of Biological Anthropology published by Wiley Periodicals LLC.)

Objective: To evaluate the potential of compound-specific isotope analysis of amino acids (CSIA-AA) for investigating infant feeding practices, we conducted a long-term study that compared infant and maternal amino acid (AA) nitrogen isotope ratios., Materials and Methods: Fingernail samples were collected from a single mother-infant dyad over 19 months postpartum. Carbon and nitrogen stable isotope ratios were measured in the bulk keratin of the fingernail samples. Selected samples were then hydrolyzed and derivatized for compound-specific nitrogen isotope analysis of keratin AAs., Results: As in previous studies, infant bulk keratin nitrogen isotope values increased during exclusive breastfeeding and fell with the introduction of complementary foods and eventual cessation of breastfeeding. Infant trophic AAs had elevated nitrogen isotope values relative to the mother, while the source AAs were similar between the mother and infant. Proline and threonine appeared to track the presence of human milk in the infant's diet as the isotopic composition of these AAs remained offset from maternal isotope values until the cessation of breastfeeding., Discussion: Although CSIA-AA is costly and labor intensive, it appears to hold potential for estimating the duration of breastfeeding, even after the introduction of complementary foods. Through the analysis of a full suite of AAs, it may also yield insights into infant physiology and AA synthesis., (© 2024 The Author(s). American Journal of Biological Anthropology published by Wiley Periodicals LLC.)

Golden cuttlefish play a significant role in the food web of the East and Yellow Seas and are a valuable fishery resource in Chinese coastal waters. Samples of golden cuttlefish were obtained from the northern East China Sea between September 2021 and March 2022, and stable isotope methods were utilized in this study to examine the variations in the forage ecology of golden cuttlefish. Our findings reveal dynamic shifts in carbon and nitrogen stable isotopes (δ 13 C and δ 15 N), highlighting intricate foraging strategies tailored to growth and environmental changes. A notable trend emerges: an initial growth-linked rise in δ 13 C and δ 15 N enrichment, followed by seasonal fluctuations mirroring seasonal food availability. The ontogenetic niche evolution displays striking habitat shifts and trophic level escalation in small mantle length stages, transitioning to niche overlap and subtle trophic shifts later on. Sex-specific differences emerge, with females occupying higher trophic levels than males in most samples. This comprehensive study underscores the complexity and adaptability of golden cuttlefish feeding ecology, inviting further inquiry into their intricate relationships within the marine ecosystem., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Understanding the relationship between suspended particulate matter (SPM), sediment organic C, N stable isotopes, and lake trophic state index (TSI) is essential for managing lake pollution and eutrophication. According to the δ 13 C, δ 15 N, and C/N we found that the organic C in SPM and sediment of Caohai Lake primarily originated from macrophytes, while N was sourced from chemical fertilizers, phytoplankton, and aquatic plants. Total nitrogen, total phosphorus, NO3 - -N, oxidation reduction potential, and Chl.a were identified as key factors influencing the sources and variations of SPM and sediment organic C and N stable isotopes in Caohai Lake, with a significant linear correlation observed between C, N stable isotopes, and TSI in sediments. To mitigate eutrophication in Caohai Lake, it is recommended that farmers apply fertilizers judiciously to minimize nutrient loss and that aquatic plants be regularly harvested to reduce N release from plant residues., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Limpets are a key taxon regulating the benthic community structure and serving as prey for various predators in rocky shores, however, their role in food web dynamics is still unclear. To determine environmental factors influencing the limpet diet, carbon and nitrogen stable isotopes in limpets and food sources were analyzed on three different coastal habitats. Sediment organic matter contributed the most (86 %) to the limpet diet in bedrocks around tidal flats with abundant sediment supply from the terrestrial matter inflow and the sediment resuspension. Microphytobenthos and macroalgae were the main food sources (57 % and 20 %, respectively) for the limpets around beaches, where benthic flora was abundant. Limpets in bedrocks, erosional habitat, primarily consumed relatively abundant phytoplankton (33 %) and microphytobenthos (28 %). Contrary to previous studies, habitat type, rather than latitude or seawater characteristics, was the most important factor determining the limpet diet. This result also suggests that limpets are non-selective scraper that consume abundant food sources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Rationale: Understanding the migration of marine animals is hindered by the limitations of traditional tracking methods. It is therefore crucial to develop alternative methods. Stable isotope-based tracking has proven useful for this task, although it requires detailed isoscapes in the focal area. Here, we present predator-based isoscapes of the coastal zone of the Patagonian Shelf Large Marine Ecosystem (PSLME), which offers a novel tool for geolocation., Methods: Whole-blood samples from breeding Magellanic penguins nesting at 11 colonies were used to create δ 15 N and δ 13 C isoscapes. Isotopic values were assigned to random positions inside their corresponding foraging area. Spatial analysis and data interpolation resulted in δ 15 N and δ 13 C isoscapes for the coastal zone of the PSLME, which were validated through cross-validation., Results: The isoscapes mean standard error ranged from 0.05 to 0.41 for δ 15 N and from 0.07 to 0.3 for δ 13 C, similar to the error range of the mass spectrometer used for measuring isotope ratios. Predictive surfaces reflected the latitudinal trends, with δ 13 C and δ 15 N values increasing northwards. δ 13 C values showed a strong latitudinal gradient, while δ 15 N values had two distinct domains, with higher values in the north. The error surface indicated the highest certainty within 130 km from the shore and within the reported Magellanic penguin foraging areas., Conclusions: Both isoscapes revealed strong spatial variation. The δ 13 C isoscape showed a latitudinal gradient, consistent with patterns in other oceans. The δ 15 N isoscape clearly separated northern and southern colonies, likely influenced by nitrogen sources. The error obtained fell within the measurement error ranges, adding credibility to the models., (© 2024 John Wiley & Sons Ltd.)

Since the Industrial Revolution, human activities have led to a rapid and sustained increase in reactive nitrogen production, resulting in nitrogen enrichment at the Earth's surface and triggering many ecological and environmental issues. Stable isotopes are effective tools for tracing the sources and mechanisms of environmental processes. The nitrogen isotope values in surface environments integrate the isotope signatures of different nitrogen sources and the isotope fractionation effects of transformation processes. The composition of nitrogen isotopes can thus be utilized to trace the sources and cycling of nitrogen at the surface, aiding the development of strategies to reduce reactive nitrogen emissions, and assess the ecological effects of nitrogen enrichment. We reviewed the research progress on nitrogen isotope in the sources of reactive nitrogen in atmospheric systems, plant nitrogen utilization, and tracking of nitrogen processes in forest ecosystems. We further discussed how to gain a more systematic and accurate understanding of nitrogen cycle within and between the various spheres of the surface environment.

Wheat-based products are staples in diets worldwide. Organic food frauds continuously threaten consumer trust in the agri-food system. A multi-method approach was conducted for the organic authentication and safety assessment of pasta and bakery products along their production chain. Bulk and Compound-Specific (CS) Isotope Ratio Mass Spectrometry (IRMS) suggested the δ 15 N bulk , δ 15 N leucine and δ 15 N proline as promising organic markers, with CS able to distinguish between pairs which bulk analysis could not. Processing significantly affected the values of δ 15 N leucine , δ 13 C proline and δ 13 C leucine . Multi-mycotoxin analysis (HT-2, T-2, DON, ZEN, OTA, AFB1) revealed higher contamination in conventional than organic samples, while both milling and baking significantly reduced mycotoxin content. Lastly, from the evaluation of 400 residues, isopyrazam was present at the highest concentration (0.12 mg/kg) in conventional wheat, exhibiting a 0.12 Processing Factor (PF), while tebuconazole levels remained unchanged in pasta production (90 °C) and reduced below LOQ in biscuits and crackers (180-250 °C)., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Zoe Giannioti reports financial support was provided by European Commission Marie Sklodowska-Curie Actions. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Fishing has significant trophodynamic impacts on marine communities, including reductions in the mean trophic position (TP) of the ecosystem resulting from a decrease in the abundance and size of species and individuals with high TPs. This study demonstrates the erosion of fish TP, an additional process that results in lower TP of individuals of a given size, which may exacerbate the effects of fishing on the food web. A stable isotope approach based on the tRophicPosition Bayesian method was used to quantify the TP of 12 target marine species at a given length, and compare their TP between fishery-restricted areas and trawled areas. The results show a difference in the TP of six benthic and apical nekto-benthic predators, which feed in the median at about 0.5 TP lower in trawled areas. It appears that current 'fishing down marine food webs' analyses may underestimate the trophic effects of fishing. Accounting for changes in trophodynamics of individuals at a given size is important to detect indirect effects through food web interactions. The application of a trawling ban may lead to the restoration of lost trophic structure; however, trophic changes may occur more slowly than changes in biomass. This article is part of the theme issue 'Connected interactions: enriching food web research by spatial and social interactions'.

Atmospheric nitrogen (N) deposition has notably increased since the industrial revolution, doubling N inputs to terrestrial ecosystems. This could mitigate N limitations in forests, potentially enhancing productivity and carbon sequestration. However, excessive N can lead to forest N saturation, causing issues like soil acidification, nutrient imbalances, biodiversity loss, increased tree mortality and a potential net greenhouse gas emission. Traditional experiments often overlook the canopy's role in N fate, focusing instead on direct N addition to the forest floor. In our study, we applied 20 kg N ha y-1 of labeled 15NH415NO3 solution (δ15N = 30‰) both above and below the canopy, maintaining also control plots. We assessed ecosystem components before and after treatment, calculated N stocks, and used mass balance for fertilizer recovery analysis. Findings revealed that the above-canopy N addition intercepted up to 31 ± 4% of added N in foliage, a significant contrast to the negligible recovery in leaves with below-canopy treatment. Overall plant recovery was higher in the above-canopy treatment (43 ± 11%) compared with below (9 ± 24%). Post-vegetative season, about 15 ± 1% of above-canopy added N was transferred to soil via litterfall, indicating substantial N reabsorption or loss through volatilization, stemflow or throughfall. In contrast, the below-canopy approach resulted in just 4.0 ± 0.6% recovery via litterfall. These results highlight a significant difference in N fate based on the application method. Nitrogen applied to the canopy showed distinct recovery in transient compartments like foliage. However, over a few months, there was no noticeable change in N recovery in long-lived tissues across treatments. This implies that N application strategy does not significantly alter the distribution of simulated wet N deposition in high Carbon/N tissues, underscoring the complex dynamics of forest N cycling., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The fruticose lichen Stereocaulon vesuvianum is among the most abundant and widespread lichens in upland Britain. It typically produces cephalodia (nodules) that contain the cyanobacterium Stigonema, which can fix atmospheric nitrogen. However, over much of England, Wales, and southern Scotland S. vesuvianum no longer produces cephalodia and does not fix nitrogen, a morphological change linked to elevated atmospheric nitrogen deposition. This provided a unique opportunity to compare the 15 N natural abundance signatures in N 2 -fixing and non-N 2 -fixing lichen populations, keeping in mind that fixed nitrogen has a 15 N content close to that of atmospheric N 2 while, in comparison, several components of atmospheric combined N (e.g. nitrate and ammonium in precipitation) tend to be 15 N depleted. We found that in N 2 -fixing samples, there was a steep gradient in 15 N relative abundance in the terminal 15 mm of thallus branches (pseudopodetia), changing from 15 N depleted tissues at 10-15 mm below the tips to values close to that of atmospheric N 2 at the apices while in non-N 2 -fixing samples thallus branches were uniformly 15 N depleted. The 15 N gradient in N 2 -fixing material could not be explained by the presence of cephalodia since these are more abundant towards branch bases. The data provide the first evidence in lichens of translocation of recently fixed N to sink regions of active growth and production of asexual reproductive propagules, bringing lichens into line with N source-sink relationships in N 2 -fixing plant symbioses., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

The mercury pollution status in the northwestern Sea of Okhotsk remains largely unexplored. In this study, hair samples were collected from 40 bearded seals harvested between August and October 2021 in the region. Total mercury (THg) concentrations in the samples exhibited a wide range from 137 to 1885 ng/g (median: 407 ng/g). While no significant differences in THg concentrations were found between male and female seals, distinctions were observed between young and potentially mature seals. Stable nitrogen isotope analysis indicated that juveniles and mature adults did not differ, although sample sizes were limiting. The higher THg concentrations in juveniles were attributed to variations in the seals' diets and/or variations in foraging locations during the juvenile stage which likely contribute to THg differences due to greater seasonal migration to offshore habitats. Notably, THg levels in bearded seals from the northwestern Sea of Okhotsk were lower in comparison to other pinniped species in the North Pacific. These findings, representing the first dataset for this pinniped species in the Russian segment of its habitat, contribute insights into mercury exposure in the Sea of Okhotsk mammalian population., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Within the complex world of disaster victim identification, or DVI, forensic science practitioners use a variety of investigative techniques to work toward a common goal: identification of the decedents, bringing closure to the affected communities. Identification is a complex undertaking; the event (disaster) also can be extraordinarily complex, as it may be an acute event, or one that spans months or years. Compounding this time issue, remains may be heavily fragmented, dispersed, commingled, or otherwise disrupted by either the perpetrators or the disaster itself. To help solve these complexities, we explore the use of stable isotope analysis (SIA) in DVI events. SIA can be used with a variety of body tissues (hair, nail, bone, and teeth), and each represents different time depths in a decedent's life. Bone collagen and tooth enamel carbonate are useful to reconstruct an individual's diet and source water intakes, respectively, leading to likely population or geographic origin determinations. Additionally, the carbon and nitrogen isotopic signatures of bone collagen have calculated intraperson ranges. These facts allow investigators to determine likely origin of remains using isotopic data and can be used to link skeletal elements (to an individual), or perhaps more importantly, show that remains are not linked. Application of SIA can thus speed remains identification by eliminating individuals from short lists for identification, linking or decoupling remains, and reducing the need for some DNA testing. These strategies and hypothesis tests should commence early in the DVI process to achieve maximum effectiveness., (© 2024 American Academy of Forensic Sciences.)

Reservoir construction promotes many environmental impacts, including the enhancement of mercury concentrations in fish. The processes that can influence mercury concentrations in fish in Amazonian reservoirs are still little explored in depth, especially when we consider the possible particularities of the ecosystems in question. This study aims to investigate how mercury concentrations in fish could be influenced by the Tucuruí dam, considering possible changes in their feeding and trophic position according to the dam position (up or downstream). Fish were sampled upstream and downstream of the Tucuruí reservoir, and total mercury (THg) and stable isotopes of carbon and nitrogen (δ 15 N and δ 13 C) were measured in muscles. We observed three different Hg bioaccumulation patterns influenced by the dam. These differences occurred due to species trophic niche changes corroborated by the isotope analysis. Higher THg concentrations downstream compared to those upstream ones were only observed for Geophagus proximus. On the contrary, Plagioscion squamosissimus, from downstream, presented lower concentrations than upstream ones. The isotopic niche of these two species presented different changes according to the sampled site. THg biomagnification was higher upstream compared to downstream, considering that the regression slope was approximately two times higher upstream versus downstream. THg concentrations in fish were explained by the differences in their feeding habits according to their location in relation to the dam. The difference in THg biomagnification was able to reflect differences in structure of the food web chain in ecosystems under the dam's influence., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Anthropogenic activities pose significant challenges to the accumulation of coastal nitrogen (N). Accurate identification of nitrate (NO 3 - ) sources is thus essential for mitigating excessive N in many marginal seas. We investigated the dual isotopes of NO 3 - in the central Yellow Sea to elucidate the sources and cycling processes of NO 3 - . The results revealed significant spatial variability in NO 3 - concentrations among the Yellow Sea Surface Water (YSSW), Changjiang Diluted Water (CDW), Yellow Sea Cold Water Mass (YSCWM), and Taiwan Warm Current Water (TWCW). Stratification played a crucial role in restricting vertical nutrient transport, leading to distinct nutrient sources and concentrations in different water masses. The dual NO 3 - isotopic signature indicated that atmospheric deposition was the primary source of surface NO 3 - , contributing approximately 30 % to the NO 3 - in the YSSW. In the NO 3 - -rich CDW, the heavier δ 15 N-NO 3 - and δ 18 O-NO 3 - suggested incomplete NO 3 - assimilation. Organic matter mineralization and water stratification played crucial roles in the accumulation of nutrients within the YSCWM and TWCW. Notably, regenerated NO 3 - accounted for approximately half of the NO 3 - stored in the YSCWM. A synthesis of NO 3 - dual isotope data across the coastal China seas revealed significant spatial and seasonal variations in the N source. The study emphasized the dynamics of coastal NO 3 - supply, which are shaped by the complex interconnections among marine, terrestrial, and atmospheric processes. Our approach is a feasible method for exploring the origins of N amidst the escalating pressures of anthropogenic nutrient pollution in coastal waters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Understanding the mechanism by which non-native fish species integrate into native communities is crucial for evaluating the possibility of their establishment success. The genus Pangasianodon, comprising Pangasianodon gigas and Pangasianodon hypophthalmus, has been introduced into reservoirs, which are non-native habitats, for fishery stock enhancement. P. gigas and P. hypophthalmus often successfully establish and co-occur in several Thai reservoirs, but there is little information on differences in food resource use between the two species. To investigate the trophic niche width of P. gigas and P. hypophthalmus in a Thai reservoir, we conducted stable carbon and nitrogen ratio (δ 13 C and δ 15 N) analyses. We examined the degree of individual specialization in both species using the δ 13 C and δ 15 N values of muscle and liver tissues, which provides long- and short-term diet information. The isotopic niches did not overlap between P. gigas and P. hypophthalmus. The δ 15 N value of P. gigas was significantly higher than that of P. hypophthalmus, whereas the δ 13 C value did not significantly differ between the two species. The isotopic niche sizes were larger in P. hypophthalmus than in P. gigas. Individual specialization was observed in P. hypophthalmus but not in P. gigas, indicating that intraspecific variation in food resource use was larger in P. hypophthalmus compared to P. gigas. These findings suggest that trophic niche partitioning was one of the factors facilitating the establishment success of P. gigas and P. hypophthalmus in a reservoir, but the establishment process may differ between the two species., (© 2024 Fisheries Society of the British Isles.)

The nitrogen isotopic composition of sedimentary rocks (δ 15 N) can trace redox-dependent biological pathways and early Earth oxygenation 1,2 . However, there is no substantial change in the sedimentary δ 15 N record across the Great Oxidation Event about 2.45 billion years ago (Ga) 3 , a prominent redox change. This argues for a temporal decoupling between the emergence of the first oxygen-based oxidative pathways of the nitrogen cycle and the accumulation of atmospheric oxygen after 2.45 Ga (ref.  3 ). The transition between both states shows strongly positive δ 15 N values (10-50‰) in rocks deposited between 2.8 Ga and 2.6 Ga, but their origin and spatial extent remain uncertain 4,5 . Here we report strongly positive δ 15 N values (>30‰) in the 2.68-Gyr-old shallow to deep marine sedimentary deposit of the Serra Sul Formation 6 , Amazonian Craton, Brazil. Our findings are best explained by regionally variable extents of ammonium oxidation to N 2 or N 2 O tied to a cryptic oxygen cycle, implying that oxygenic photosynthesis was operating at 2.7 Ga. Molecular oxygen production probably shifted the redox potential so that an intermediate N cycle based on ammonium oxidation developed before nitrate accumulation in surface waters. We propose to name this period, when strongly positive nitrogen isotopic compositions are superimposed on the usual range of Precambrian δ 15 N values, the Nitrogen Isotope Event. We suggest that it marks the earliest steps of the biogeochemical reorganizations that led to the Great Oxidation Event., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)