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This study examined the diet and assimilation of basal resources by the redeye piranha, Serrasalmus rhombeus, in a low-flow section of the Xingu River, Brazil. Samples of both individuals and basal resources were collected monthly from December 2020 to November 2021, encompassing a complete hydrological cycle. The stomach contents of the individuals and tissue samples of the species were submitted to stable isotope analysis for δ13C and δ15N. The species exhibited a predominantly piscivorous diet, with no observed variation in diet composition or feeding intensity across different hydrological periods. However, δ15N levels in the species varied between periods, indicating potential shifts in the availability and assimilation of basal resources during controlled flood pulses. The trophic position of the species was higher during flood periods and lower during low-water periods. Mixing models revealed the assimilation of different basal sources in each period, with the significance of terrestrial producers evident in almost all periods except during ascending. These findings are crucial for understanding the trophic dynamics of predators in flooded forests with reduced flow, highlighting the reliance of S. rhombeus on piscivory while being supported by terrestrial basal sources in its trophic chain. [ABSTRACT FROM AUTHOR]

Providing novel food subsidies to wildlife can influence behavior, resource use, disease dynamics, and food web interactions. Studies examining impacts of anthropogenic food have primarily occurred in urban landscapes where anthropogenic resources are consistently accessible. National parks, however, experience similar issues regarding wildlife exploiting anthropogenic food, but access to anthropogenic food is contingent on human visitation, which can fluctuate dramatically between seasons. We evaluated how fluctuating availability of anthropogenic food and demographic factors influenced the isotopic niche of Rocky Mountain Red Fox (Vulpes vulpes macroura) at the population and individual level in Grand Teton National Park, Wyoming. From 2016 to 2021, we assessed diet-related questions by collecting 55 whisker samples and 52 hair samples from 40 unique individuals and analyzed them using stable isotope analysis (δ13C and δ15N). We discovered that Rocky Mountain red foxes have a broad isotopic niche, with seasonal differences in their consumption of anthropogenic food. Contrary to our expectations, foxes demonstrated increased reliance on anthropogenic food (higher δ13C values) during winter months, whereas natural food consumption or dietary mixing was more prominent in summer months. Natural food scarcity could be driving foxes to seek out more anthropogenic food in the winter, whereas the increased abundance of natural food items in the summer could result in a lower need for foxes to supplement their diet with anthropogenic food. Adults had consistently higher δ13C values relative to juveniles, indicating either intraspecific variation in boldness or dominance leading to increased exploitation of anthropogenic food, which could be a learned behavior coinciding with habituation. Finally, we observed that increasing densities of human features within the home range of a fox was a strong predictor of anthropogenic food reliance at the individual level. Our work provided a deeper understanding of the trophic ecology of Rocky Mountain Red Fox in relation to human activity in a nature preserve, and equipped managers with insight into potential patterns associated with food-conditioned foxes. [ABSTRACT FROM AUTHOR]

We assessed the impact of a modified flood pulse on the trophic ecology of Ilisha amazonica by analyzing diet and resource assimilation through stable isotope analysis (δ13C and δ15N). Collections were conducted monthly between December 2020 and November 2021 in the Xingu River, Amazon. Stomach and muscle tissue were extracted for analysis, and both allochthonous and autochthonous resources were collected. Stomach contents of 247 specimens were analyzed and identified. The water flow regime influenced the consumption of aquatic insects, as well as the trophic niche breadth and feeding intensity of I. amazonica. Based on isotopic composition, the primary carbon sources in the species' diet originated autochthonous items, and the species exhibited a higher trophic position during the flood period. These results highlight the influence of the flood pulse, in a reduced flow environment, on the trophic dynamics of I. amazonia. Our results emphasize the importance of comprehending the interplay between consumers and resources, in areas with human influence, where impacts are practically unknown. [ABSTRACT FROM AUTHOR]

Calcite plays a pivotal role in regulating the mobility and fate of zinc (Zn) in natural environments. Despite its significance, the mechanism of Zn sorption on calcite surfaces, particularly the transitional dynamics from surface adsorption to precipitation, remains unclear. This research studied the sorption behavior of Zn on calcite across a wide range of reaction times, pH values, and Zn concentrations. The underlying sorption mechanisms were examined through a combination of Zn stable isotope measurements and X-ray absorption fine structure (XAFS) spectroscopy. At pH 6.5 and a low Zn concentration of 5 μM, the surface coverage reached 0.9 μmol/m2, accompanied by a pronounced Δ66Zn sorbed-aqueous of + 0.40 ‰, which is indicative of a tetrahedral inner-sphere surface complexation mechanism. Conversely, at pH ≥ 7.5 and a higher Zn concentration (100 μM), the surface coverage surpassed 57.6 μmol/m2, resulting in diminished Zn isotope fractionation (+0.20 ‰), suggesting the formation of hydrozincite precipitates. These results, integrated with the XAFS analysis, revealed a continuous transition from inner-sphere tetrahedral surface complexes to hydrozincite precipitates as the pH and/or Zn concentration increased. Notably, the sensitivity of Zn isotope fractionation to distinct Zn sorption mechanisms was supported by an inverse linear relationship between Zn isotope fractionation and the Zn-O bond distance. This study significantly advances our understanding of Zn sorption mechanisms on calcite by demonstrating that the surface of calcite may have catalyzed hydrozincite precipitation when the bulk solution was undersaturated with respect to hydrozincite. The synergistic application of Zn stable isotopes and XAFS spectroscopy provides a robust framework for probing metal-mineral interactions under environmentally relevant conditions. [ABSTRACT FROM AUTHOR]

The southern oceans are home to a large variety of organisms, including many endemic species. High levels of endemism are due in part to non-physical barriers limiting gene flow in marine species. The sooty albatross Phoebetria fusca is an endangered seabird breeding on seven island groups in Atlantic and Indian Oceans. We sequenced the mitochondrial control region (55 birds) and genotyped 10 microsatellite markers (88 birds) to examine the population genetics of sooty albatrosses from Tristan da Cunha and Gough Island (Atlantic Ocean), and Marion Island, Île de la Possession (Crozet) and Amsterdam Island (Indian Ocean), which together support > 99% of the global population. We also analysed the bill sulcus colouration and quantified stable isotope composition of body feathers of breeding adults from Gough and Marion Islands. Both genetic markers identified two clusters separating sooty albatrosses breeding in the Atlantic and Indian Ocean basins. Standardized colour analysis also separated populations in the two ocean basins and revealed the sulcus of sooty albatrosses on Gough Island is significantly more yellow than individuals on Marion Island. Stable isotope analysis of body feathers showed significantly higher δ13C values from Marion sooty albatrosses compared to Gough conspecifics, indicating different moulting areas. Sooty albatrosses breeding on islands in the two ocean basins differ from each other in their genetics, morphology and ecological preferences. Accordingly, it is recommended that separate conservation management plans be implemented for sooty albatrosses breeding in each ocean basin to prevent the loss of evolutionarily significant units. [ABSTRACT FROM AUTHOR]

Compound-specific stable carbon isotope analysis of amino acids (CSIA-AA) is widely used in ecological studies to analyze food-webs and is gaining use in archaeology for investigating past diets. However, its use in reconstructing breastfeeding and weaning practices is not fully understood. This study evaluates the efficacy of stable carbon isotope analysis of amino acids in early life diet reconstruction by analyzing keratin from fingernail samples of three mother-infant pairs during late gestation and early postpartum periods. Our results show that stable carbon isotope ratios (δ13C) of glycine, and to a lesser extent glutamate, effectively trace the onset of exclusive breastfeeding and the end of weaning in infants. We propose that glycine's 'conditionally essential' metabolic pathway during infancy allows it to reflect maternal glycine δ13C, indicating breastmilk consumption. Subtle changes in glutamate δ13C likely result from its 'non-essential' status. Additionally, δ13C values of glycine and glutamate indicate maternal physiological and pathological stress due to catabolic effects such as gluconeogenesis. These findings have significant implications for ecological and archaeological research using CSIA-AA for dietary reconstructions. They highlight the need to understand how metabolic pathways affecting δ13C of amino acids may change over an individual's lifespan or be altered due to various forms of stress. [ABSTRACT FROM AUTHOR]

Lake restoration by biomanipulation or phosphorus fixation has been commonly applied methods to improve the ecological status of lakes. However, the effects of lake restoration on food-web dynamics are still poorly understood, especially when biomanipulation and nutrient fixation are used simultaneously. This study investigated the combined effects of a 70% fish removal (mainly roach (Rutilus rutilus Linnaeus, 1758) and bream (Abramis brama Linnaeus, 1758) and Phoslock® treatment on fish trophic ecology in Lyngsø (area: 9.6 ha, mean depth: 2.6 m), Denmark. The lake restoration resulted in decreased nutrient levels, increased water clarity, and increased coverage of more structurally complex submerged macrophytes. Following lake restoration, significant changes in diets of the dominant fish species were observed. Stomach content analyses of roach and perch (Perca fluviatilis Linnaeus, 1758) revealed significantly reduced detritus utilization and increased foraging on macrophytes and macrophyte living invertebrates. Results from stable isotope mixing models indicated a shift from littoral benthic to more pelagic food resources by the dominant fish species. Our findings provide further evidence that lake restorations can lead to substantial changes in lake food webs and fish communities, thereby potentially facilitating a shift toward an ecological state resembling the pristine reference state, less influenced by anthropogenic factors. [ABSTRACT FROM AUTHOR]

Much has been learned about Mars through data returned from space missions and analyses of martian meteorites. There are, however, many questions still outstanding which cannot currently be answered--including the issue of whether there is, or was, life on Mars. The return of a cache of samples--including of the atmosphere--from separate locations in Jezero Crater and with differing petrogeneses will provide the international community with the opportunity to explore part of the evolutionary history of Mars in great detail. Specifically, measurements of the isotopic compositions of the light elements H, C, N, O, Cl, and S can be used to follow how volatile species cycle through the different martian volatile reservoirs (atmosphere, lithosphere, cryosphere, and hydrosphere). Measurement of isotopic fractionation enables inference of the environmental conditions (e.g., temperature, water/rock ratio) under which fractionation occurred. Knowing the contextual relationship of the materials to their geological settings, coupled with precise compositional measurements will enable a more thorough understanding of martian volatile history and allow a picture to be constructed of water and climate on Mars as represented at Jezero Crater. [ABSTRACT FROM AUTHOR]

Stable isotope analysis (SIA) is a useful tool to assess the health and foraging habits of large marine predators, metabolic stress, pregnancy, and migration patterns. This study provides baseline SIA data for four Gulf of Maine mysticete species and serves as a benchmark for future assessments. SIA was conducted on skin biopsies collected in two time periods: 1988 to 1992 (n = 15) and 1999 to 2005 (n = 187). Samples were collected from humpback whales (Megaptera novaeangliae; n = 116), fin whales (Balaenoptera physalus; n = 74), minke whales (Balaenoptera acutorostrata; n = 6), and North Atlantic right whales (Eubalaena glacialis; n = 6). There were statistically significant differences in isotopic value among species, years, and regions sampled. By species, North Atlantic right whale δ13C and δ15N levels were significantly different than the other species analyzed. Additionally, humpback whales had a δ15N value that was significantly higher than the value found in fin whales. By date, humpback whales showed significant difference in δ13C in 2002 from the two previous years. For fin whales, 2002 showed significant difference in δ13C for all other years' samples (2000 to 2003). By region, two regions that were the greatest distance apart (Bay of Fundy and Great South Channel) showed significant differences in d13C for humpback whales. Demographic analyses for humpback and fin whales found a significant difference between calves versus other age classes, presumably due to nursing. A decadal comparison of humpback whales at one site (Stellwagen Bank) found no significant difference between decades. This dataset provides a benchmark for stable isotope measurements in large baleen whales for this regional ecosystem. [ABSTRACT FROM AUTHOR]

Black sea bass (Centropristis striata) feed on epibenthic prey, particularly decapods, and become more piscivorous as they grow larger, a trend that has energetic consequences for growth. In the coming decades, construction of wind energy systems will expose black sea bass to a large-scale manipulation of continental shelf habitats in the northeastern United States. In this study, we tested the effects of habitat type (natural versus artificial reef habitats) on size, age, growth, diet, and trophic dynamics of black sea bass, using 407 specimens collected with rod-and-reel gear near Ocean City, Maryland, in 2016 and 2018. No significant differences in fish length, age, size at age, or diet are attributable to habitat. The stable isotope composition (δ13C and δ15N) in samples of 3 tissue types (liver, muscle, and mucus) vary significantly by habitat except for δ15N values in mucus samples. Across tissue type, δ13C values are higher for fish at artificial habitats, indicating more littoral than pelagic feeding. We conclude that, although both types of reef habitats are ecologically equivalent as a source of growth and diet for black sea bass, the differences in stable isotope signatures indicate functional differences in system energy flow that should be investigated further in this and other marine species that will be affected by offshore wind energy development. [ABSTRACT FROM AUTHOR]

Simple Summary: Hongze Lake, a key storage lake in China's South-to-North Water Diversion project, experiences off-seasonal water level regulation that disrupts native fish and others. This study explored the trophic dynamics of three fish species—Parabramis pekinensis, Carassius auratus, and Toxabramis swinhonis—using stable isotope analysis during high-, mid-, and low-water periods. Results showed that all three fish species generally occupied similar mid-level trophic positions across different water periods. The SEAc values of P. pekinensis and T. swinhonis were highest during high-water periods and lowest during low-water periods, whereas C. auratus exhibited the opposite trend. These findings suggest that P. pekinensis and T. swinhonis function as optimal foragers, while C. auratus adopts a generalist strategy, consistent with classical competition theory. Niche overlap analysis demonstrated that dynamic resource partitioning during high-water periods and resource sharing during low-water periods promote the coexistence of these species. This coexistence strategy is further influenced by shifts in dietary composition, as although POM was the main dietary component, its contribution decreased over time as SOM and macrophytes became increasingly significant, highlighting the adaptability of these species to fluctuating environments. This study emphasizes the role of water level fluctuations in shaping interspecific interactions, providing insights into coexistence mechanisms of euryphagous fish species and ecological dynamics in Hongze Lake. Off-seasonal water level regulations disrupt the biological traits and phenological rhythms of native fish species, yet their impacts on interspecific trophic interactions remain understudied. This study employed stable isotope analysis to assess the trophic dynamics of three fish species (Parabramis pekinensis, Carassius auratus, and Toxabramis swinhonis) across different water periods in Hongze Lake. The findings revealed that all three species occupied similar mid-level trophic positions, with no significant difference among water periods (p > 0.05). During high-water periods, P. pekinensis and T. swinhonis exploited broader niches, while C. auratus relied on a narrower diet. In contrast, during low-water periods, C. auratus expanded its niche, while P. pekinensis and T. swinhonis reduced their isotopic niche widths. Niche overlap analysis showed minimal trophic overlap among the three species during high-water periods, with increased overlap during low-water periods, except for the highest overlap between C. auratus and T. swinhonis during mid-water periods. This variation in niche overlap aligns with shifts in dietary reliance, as POM was the predominant dietary component for all three species, but its contribution varied significantly across different water periods. These findings indicated that adaptive trophic niche facilitated the coexistence of these fish species, while off-seasonal water level regulation may intensify interspecific competition. These insights are essential for refining water management policies and developing sustainable fishery management strategies of Hongze Lake and other water-level-regulated systems. [ABSTRACT FROM AUTHOR]

Opsariichthys uncirostris uncirostris (Hasu fish), a vulnerable potamodromous fish, is the only piscivorous cyprinid fish in Japan and endemic as a subspecies to Lake Biwa. The species population is on a continued decline for the past 70 years. This study aimed at developing a portfolio on the species during its reproductive migration to Shiotsuo River, a Lake Biwa tributary, by using a combination of biometric measurements and stable isotope ratios in its tissues. Hasu fish were collected monthly, from May to September 2019, using cast nets. The biometric measurements: wet weight, standard length, gonad weight and gut content were collected and used to calculate the gonado-somatic index (GSI) and Fulton's condition constant (K) and determine the feeding habits of Hasu fish. Carbon and nitrogen isotope ratios (δ13C and δ15N) in slow-changing muscle and fast-changing mucus tissues of Hasu fish were also used to determine recent diet change. At the beginning of the reproductive season, fewer females than males were caught; however, the number of females increased as the season progressed. On average, males were larger than females. Migrating individuals were healthy (K > 1) and over 37% larger in length than those in the 1960s. Gut content analysis revealed, for the first time, Hasu fish feeding in the rivers, primarily on Ayu fish, during the reproductive migration. δ13C and δ15N in muscle and mucus indicated a recent change in diet, i.e., from Lake Biwa to Shiotsuo River, with differences in the onset of feeding (and consequently upstream migration) between sexes and individuals. For the effective conservation of Hasu fish in the other tributaries where Ayu fish traps block other fishes' migration, we recommend having the rivers open from June to September to cover its variable timing in the recruitment of reproductive individuals. [ABSTRACT FROM AUTHOR]

According to European reports, the population of Anguilla anguilla has declined to unsafe biological limits in most areas and current fisheries are unsustainable. Indeed, the European eel has been listed as a critically endangered species since the 1970s and has been on the IUCN Red List of Threatened Species since 2010. Glass eel fisheries in Europe are very limited, but illegal catches and international parallel trade are major threats to eel stocks due to their high commercial value. The main hypothesis of this study is that glass eels from each estuary have unique chemical profiles according to the ecological quality of the habitat. These unique chemical fingerprints were assessed using Chemical Integrating Approaches (CIA) based on multi-element (macro, trace and ultra-trace metals), global metabolome and stable isotope analyses. Thus, CIA are intended to be an effective chemical "weapon" to (i) fingerprint wild glass eels; (ii) fingerprint captive glass eels; (iii) authenticate and trace glass eels; and (iv) combat the illegal trade in juvenile European eels. The results of this study showed that Zn and Ni can fingerprint the chemical profiles of wild and captive glass eels and their geographical origin. In the same vein, metabolomes such as Butyric acid 4-vinylphenyl ester, N-(3-carboxypropanoyl)-Met, 2-(4-Methylphenyl)acetamide, N-formyl-glutamic acid, 3-Hydroxy-2-(3-methylbutanoylamino)propanoic acid, 4-Dodecylbenzenesulfonic Acid, Arginine and Pyrazole and the stable isotope 15N show potential as a chemical tools for glass eel traceability. [ABSTRACT FROM AUTHOR]

This study is based on stable isotope analysis of a rich ammonite assemblage from the Sogukcam Formation, which is widely exposed in Yesilbaglar (Olur‐Erzurum, NE Türkiye). The presence of ammonid, planktic, and benthic foraminifers in the marine sediments suggests that they are from the early Cretaceous period. The late Valanginian‐early Aptian‐rich ammonite assemblage includes the following genera and species: Acrioceras sp., Barremites difficilis, Barremites sp., Crioceratites duvalii, Crioceratites sp., Deshayesites aff. dechyi, Deshayesites sp.1, Deshayesites sp.2, Deshayesites sp.3, Deshayesites sp., Dufrenoyia cf. dufrenoyi, Dufrenoyia cf. furcata, Dufrenoyia sp., Hemihoplites sp., Heteroceras sp., Neocomites sp., Phyllopachyceras infundibulum, Protetragonites cf. quadrisulcatus, Protetragonites sp., Ptychoceras sp., Turkmeniceras cf. geokerense, and Turkmeniceras sp. This assemblage suggests that the Sogukcam Formation's deeper facies formed in the late Valanginian to early Aptian period. Fossils and δ18O data show normal paleosalinity levels. During the late Valanginian‐early Aptian period, δ18O values ranged from −3.67‰ to −2.24‰, with paleotemperatures ranging from 21.3°C to 27.9°C. δ13C positive values range from +0.65‰ to +2.86‰. δ13C isotope data show the oxygen minimum zone (OMZ) and changes in sea level and productivity. The presence of planktonic foraminifera and the ammonite assemblage indicates that the formation was deposited in warm subtropical waters ranging from the outer shelf to the open sea. [ABSTRACT FROM AUTHOR]

Controversy exists as to whether the Pleistocene vegetation in northern Sundaland was dominated by lowland tropical grasslands or rainforests, due to limited palaeoecological evidence recorded from the region. We describe a new Pleistocene large mammal fauna from Tham Kra Duk, a cave in the Tham Phedan mountain, Nakhon Si Thammarat Province in Peninsular Thailand, with emphasis on its palaeoecological and palaeoenvironmental investigations using the stable isotope analysis of mammalian tooth enamel. The fossil site has yielded at least nine mammalian taxa almost comparable to late middle to latest Pleistocene faunas in the mainland, thus suggesting the same biogeographic mammal elements with a range extension south of the Kra Isthmus. The stable isotope results indicate that mixed woodland to grassland ecosystems were dominated by C4 vegetation in the area. This supports the assumption that the expansion of Pleistocene tropical savanna ecosystems might have held the key to facilitating the southward distribution range of grazing mammals such as gaurs and Himalayan gorals into the Thai-Malay Peninsula. The presence of the Tham Kra Duk fauna was probably linked to some major biogeographic events of Pleistocene hominin and mammal migration through the land-bridge peninsula into the islands of Southeast Asia during a period of glaciation. [ABSTRACT FROM AUTHOR]

The analysis of carbon and nitrogen stable isotopes (δ13C and δ15N) has been widely used in ecology since it allows to identify the circulation of energy in a trophic network. The anchialine ecosystem is one of the less explored aquatic ecosystems in the world and stable isotope analysis represents a useful tool to identify the routes through which energy flows and to define the trophic niches of species. Sampling and data recording was conducted in one anchialine cave, Cenote Vaca Ha, near the town of Tulum, Quintana Roo, Mexico, where seven stygobitic species endemic to the anchialine caves of the Yucatan Peninsula, plus sediment, water and vegetation samples were analyzed to determine what the main nutrient sources are. We compared our results with two previous studies, one conducted in the same cave and another one from a cave in the same area, both based on the same seven species which are widely distributed in the area. Our study revealed: a) that despite a certain amount of variation in the δ13C and δ15N values of the species through time, both seasonally and interannually, the anchialine isotopic niche is much conserved; b) through contribution models we propose what are the most probable food sources for the studied species and the results confirm previous trophic classifications; and c) that the shrimp Typhlatya pearsei presents very negative δ13C values, suggesting their consumption of bacterial sources consistent with a chemosynthetic origin of organic matter. The implications of the new findings show a very stable ecosystem with the shrimp Typhlatya pearsei, as the key species to link chemosynthetic microbial production of organic matter to the anchialine trophic web. [ABSTRACT FROM AUTHOR]

This article presents data from the stable isotope analysis of marble from five fragments of sculpture and a massive base that together are said to comprise the remains of the statue on Delos known as the Naxian Colossus. This key work in the early history of monumental Greek marble sculpture has attracted the attention of travelers since the 15th century (Buondelmonti, Cyriacus of Ancona). Plutarch's testimony that the great andrias of the Naxians was knocked down by the bronze palm tree of Nicias in a storm promoted the belief that all or some of the pieces identified with the colossus belonged to a later replacement for the original Archaic-period statue (dated ca. 600 BCE). The data from stable isotope analyses, in combination with the evidence from a recent analysis of style and proportions, now points to the conclusion that the fragments and base likely belong to at least three different archaic colossal statues. We explore the present limits in our interpretation of marble isotope analyses. We argue that this evidence is currently the best available means of understanding the highly debated inscription on the east side of the base: "I am of the same stone, statue and base." 1 [ABSTRACT FROM AUTHOR]

In British Columbia, Canada, unidentified skeletal human remains are often recovered by law enforcement or civilians and there is a question if they are modern and of medicolegal significance, or historical or archaeological. We used relatively fast and inexpensive carbon and nitrogen stable isotope analysis of human bone collagen from a selection of these remains (n = 48) combined with a logistic regression model to classify remains as modern, historical, or archaeological. We then confirmed our temporal classification through directly radiocarbon dating each individual and found that we could predict the temporal group with 93% accuracy. In regions where archaeological remains have dietary isotope values distinct from living people, dietary stable isotope analysis can provide a time‐, and resource‐efficient method to screen cases of unidentified human remains early in death investigation. [ABSTRACT FROM AUTHOR]

Stable isotope analysis of museum specimens presents an opportunity to evaluate trophic relationships from historical surveys. After testing the effects of preservation methods on archived specimens, we analyzed beak tissue from 69 Northern shortfin squid (Illex illecebrosus) collected between 1873 and 1987 from the Northeast U.S. Continental Shelf Large Marine Ecosystem. Stable nitrogen (δ15N) and carbon (δ13C) isotopes were used to infer ecological changes in I. illecebrosus across historical periods spanning the pre-industrial era (late 1800s), subsequent periods of industrial fishing (1930–1960; 1960–1976), and widespread industry regulation (1985–1995). δ15N values for samples collected in the 1900s were significantly depleted compared to values in the 1800s, with the highest δ15N values occurring between 1985 and 1995. There was also a significant shift over time to more depleted δ13C values. Illex illecebrosus occupied completely distinct isotopic spaces during the pre-industrial (1800s) and industrial (1930–1995) periods, suggesting a change in food-web linkages and habitat use over the last century. Changes in δ15N indicated a shift to lower trophic-level foraging habits in the 1900's, while shifts in δ13C may be associated with mechanisms such as the Suess effect and increased reliance on more pelagic resources. Isotopic niche breadth and diversity increased in I. illecebrosus over time, potentially indicating expanded resource use associated with anthropogenic impacts on regional trophic guild structure. Our results are the first to examine isotopic changes of I. illecebrosus over multi-decadal periods using museum collections, and among the first to track long-term changes in the trophic role of cephalopods in marine ecosystems. [ABSTRACT FROM AUTHOR]

Antarctic krill (Euphausia superba) is a keystone species in the Antarctic marine ecosystem. The pelagic tunicate (Salpa thompsoni) interacts with krill in diverse aspects, which imposes krill distribution and even survival, especially under the context of changing climate. Understanding the diet of both species during autumn—a season with shifting food composition and availability—is critically understudied. Therefore, this study aims to investigate the diet composition and trophic ecological niches of krill and salps in the Bransfield Strait during autumn in 2022 using stomach content, fatty acid (FA), and stable isotope analyses. Stomach content analysis revealed that krill primarily consumed copepods, while salps primarily consumed diatoms. FA analysis confirmed significant differences between the FA markers of diatoms and copepods for each species, aligning with stomach content analyses. Stable isotope analysis also indicated low overlap of trophic niches. By consuming more copepods, krill may reduce direct dietary competition with the less prevalent salps during autumn. Although the feeding strategy (active or passive) exerted by krill is warranted to further investigate, the differentiated feeding pattern occupied by two species promotes their coexistence. [ABSTRACT FROM AUTHOR]

Aims: Roux‐en‐Y gastric bypass (RYGB) surgery alters postprandial glucose profiles, causing post‐bariatric hypoglycaemia (PBH) in some individuals. Due to the liver's central role in glucose homeostasis, hepatic glucose handling might differ in RYGB‐operated patients with PBH compared to non‐operated healthy controls (HC). Materials and Methods: We enrolled RYGB‐operated adults with PBH and HCs (n = 10 each). Participants ingested 60 g of [6,6′‐2H2]‐glucose (d‐glucose) after an overnight fast. Deuterium metabolic imaging (DMI) with interleaved 13C magnetic resonance spectroscopy was performed before and until 150 min post‐d‐glucose intake, with frequent blood sampling to quantify glucose enrichment and gluco‐regulatory hormones until 180 min. Glucose fluxes were assessed by mathematical modelling. Outcome trajectories were described using generalized additive models. Results: In RYGB subjects, the hepatic d‐glucose signal increased early, followed by a decrease, whereas HCs exhibited a gradual increase and consecutive stabilization. Postprandial hepatic glycogen accumulation and the suppression of endogenous glucose production were lower in RYGB patients than in HCs, despite higher insulin exposure, indicating lower hepatic insulin sensitivity. The systemic rate of ingested d‐glucose was faster in RYGB, leading to a higher, earlier plasma glucose peak and increased insulin secretion. Postprandial glucose disposal increased in RYGB patients, without between‐group differences in peripheral insulin sensitivity. Conclusions: Exploiting DMI with stable isotope flux analysis, we observed distinct postprandial hepatic glucose trajectories and parameters of glucose–insulin homeostasis in RYGB patients with PBH versus HCs. Despite altered postprandial glucose kinetics and higher insulin exposure, there was no evidence of impaired hepatic glucose uptake or output predisposing to PBH in RYGB patients. [ABSTRACT FROM AUTHOR]

American black bear (Ursus americanus) populations are increasing throughout much of North America. Use of multiple harvest methods, including hunting over bait, is intended to increase harvest success rates to meet harvest and population management objectives. However, black bear population growth can be influenced by food availability, and some speculate the use of bait may inadvertently increase bear abundance through food resource supplementation. We collected hair from black bears captured from 2005–2019 and a selection of potential food items, including those used as bait from 3 study areas in Maine, USA, with different levels of human influence. We used stable isotope analysis of the black bear hair and food item samples to evaluate the contribution of different identified food groups to the diet of individual bears. We found no evidence that greater contribution of human food resources, including bait, increased the number of cubs per litter for reproductive females or that human foods comprised a greater part of the diet in years when natural food resources were less abundant. Approximately 69% of black bear harvest occurred over bait. We found the probability of reproductive‐age females to be harvested increased with average representation of human foods with high carbon enrichment (including bait) in their diet, but the relationship was weak, likely because of sampling constraints. Additionally, the probability of being harvested was greater in years when natural food resources were scarce. We conclude that bait is not available on the landscape in large enough amounts or for a sufficient amount of time in Maine to substantially influence female reproduction. Our results indicate hunting over bait is an effective tool in a state that is attempting to maintain a stable bear population via harvest, and dispels conjecture that hunting over bait may increase cub production and offset the intention of harvest. [ABSTRACT FROM AUTHOR]

Most Sub-Saharan Africa countries including Nigeria rely heavily on groundwater resource for their domestic, agricultural and industrial uses because of its ease of development, naturally great quality and growing demand arising from rapid population growth. Understanding the evolution and recharge of groundwater is mandatory for preserving and effective use of water resources. This study employed hydrochemical and stable isotope analyses to assess groundwater recharge and evolution of the Egbako aquifer in the Northern Bida Basin, Central Nigeria. Thirty-five (35) water samples from boreholes, hand-dug wells and springs were collected in the study area for this purpose. Results revealed that about 50% of the water are mixed Ca – Na – HCO3 and mixed Ca – Na – HCO3 and mixed Ca – Mg – Cl; while Ca – HCO3 type accounts for 36%. Ionic loading is in the order Ca2+ > K+ > Na+> Mg2+ for the cations while it is HCO3ˉ> Cl-> SO42-> NO3-> NO2- for the anions, with Ca, Mg, K, SO4, Cl playing leading roles in the groundwater mineralization. Groundwater quality is generally within the WHO drinking water guideline, with elevated nitrate (> 50 mg/L) in 11% of the samples pointing to some anthropogenic influence. Bivariate plots showed that silicate weathering, cation exchange and evaporite dissolution are the major hydrochemical processes controlling groundwater chemistry. Results of stable Isotope shows a depletion of δ18O (-2.87 to -4.81‰ VSMOW) signifying that the Egbako aquifer is recharged largely from meteoric sources through rapid infiltration of rainwater with low imprint of kinetic evaporation. [ABSTRACT FROM AUTHOR]

Although biological invasions are becoming more frequent, their underlying ecological mechanisms often remain unknown. One of the most poorly understood aspects is the relationship between ontogenesis and the trophic role of alien species in invaded ecosystems. The aim of this study was to investigate the role of littoral habitat complexity in the shift from benthivory to piscivory of Micropterus salmoides, one of the most widely introduced and invasive fish species. Specifically, populations from two habitats differing in terms of aquatic vegetation cover within the same ecosystem were studied. Specimens of M. salmoides and its potential prey collected in both habitats were analyzed for C and N stable isotopes. The consumption of macroinvertebrates decreased with body size, but in the less complex habitat, M. salmoides shifted its diet to piscivory at an earlier stage of its life cycle. In this habitat, the size-based food web appears highly connected, as largemouth bass have diffuse weak interactions with multiple prey species occupying a range of trophic levels. This may lead bass to threaten the native fish not only by competition but also by predation. Large piscivorous individuals preferred conspecific fry as prey, on which they concentrated particularly in the more complex habitats, where diet specialization was marked. Since preying on conspecifics is energetically costly, according to Optimal Foraging Theory it only becomes advantageous when competition for other food items is intense. This evident trophic plasticity may favor the success of bass in invaded ecosystems and should be considered when deciding management policy, which should also include the preservation of habitat complexity. [ABSTRACT FROM AUTHOR]

The use of biological samples from museum and/or archive collections is common in stable isotope research, particularly for marine mammals. Yet, the temporal stability of isotopic values across various tissue types and the influence of different preservatives on these values are not fully understood, posing significant challenges for accurate data interpretation. Here we examine the impact of three different tissue preservation methods (DMSO, ethanol, freezing), on seven different tissues (blubber, heart, kidney, lung, liver, muscle, and skin) from both a harbor porpoise (Phocoena phocoena) and a gray seal (Halichoerus grypus) for stable isotope analysis in a 1‐year period. Our results demonstrate that storage in DMSO generates greater temporal variability in δ13C and δ15N for all tissue types, particularly in the first six months of storage. Furthermore, tissues stored in DMSO often exhibited lower δ13C and δ15N values compared to those stored frozen or in ethanol. This finding highlights a significant issue for studies utilizing tissues stored in DMSO, regardless of the storage duration. These results underscore the critical need for careful consideration of preservation methods in studies involving stored tissues, providing valuable insights for experimental design and management of tissue archives. [ABSTRACT FROM AUTHOR]

Intertidal environments receive energy from marine ecosystems in the form of marine wrack, which makes up the base of a food web that includes both intertidal and terrestrial consumers. Consumption of wrack by terrestrial consumers can elevate their abundance and alter how they interact with organisms in adjacent terrestrial environments. Although rarely documented, terrestrial invaders may exploit marine wrack subsides and potentially disrupt intertidal and terrestrial food webs. Here, we examine consumption of marine wrack resources by the introduced Argentine ant (Linepithema humile), which occurs commonly on beaches in southern California. In controlled trials the Argentine ant readily scavenged arthropod detritivores (amphipods and flies) abundant in wrack. In spite of obvious risks (e.g., exposure to tides, desiccation, thermal stress) associated with intertidal foraging, Argentine ant activity on beaches was comparable to that in spatially-paired, scrub environments. Foraging on beaches allowed ants to access higher densities of arthropod prey and carrion compared to those found in scrub environments. Stable isotope analyses provide evidence for extensive assimilation of marine-derived resources. Values of δ15N and δ13C for the Argentine ant were higher at beach sites than at scrub sites, and Argentine ant δ15N values broadly overlapped those of intertidal consumers at beach sites. Although ants are known to forage in intertidal environments, this study provides a novel example of an introduced ant species exploiting a cross-boundary subsidy. [ABSTRACT FROM AUTHOR]

The recognition of individual variation has fundamental implications for ecological, evolutionary and biodiversity conservation. There is increasing theoretical interest in how spatial and temporal variation in the environment can create differences in the demographic contribution of individuals over space and time. However, empirical information about the characteristics of the environmental drivers of key vital rates and their spatiotemporal variation is still scarce. Here, we used data generated by a monitoring scheme (1990–2015) of a population of a long‐lived territorial avian predator, Bonelli's Eagle Aquila fasciata, which included estimations of individuals' diet through stable isotope analysis (2008–15), to evaluate whether temporal consistency in spatially structured dietary patterns affects key demographic parameters, namely productivity and survival, at territory scales. We found strong within‐population heterogeneity in survival and reproduction rates associated with Eagle territories, with territory average values ranging, respectively, from 0.58 to 1.00 and from 0 to 1.71 for the overall study period. Reproduction and survival were predictable over, respectively, 4‐ and 3‐year periods for the bulk of the population, which suggests that the environmental drivers of these vital rates changed at these temporal scales. Interestingly, the characteristics of and the temporal variation in the diets of territorial individuals during these periods were associated with their survival and reproduction. Based on these findings, we suggest that spatial and temporal variations in trophic scenarios potentially act as meaningful drivers of intrapopulation demographic heterogeneity. [ABSTRACT FROM AUTHOR]

Opportunistic species, including some gulls (Laridae), can benefit from urbanization and increased anthropogenic food resources. Knowledge of the level of exploitation of anthropogenic resources by gulls is crucial to understand how changes in food availability might affect their populations, which in turn may impact other species. The Kelp Gull Larus dominicanus is widely distributed in the southern hemisphere and consumes a wide variety of resources, from waste in landfills to seabirds. We assessed if proximity to landfills influenced the diet and trophic ecology of Kelp Gull incubating adults and chicks using a combination of conventional diet sampling (stomach contents, regurgitated pellets), and carbon and nitrogen stable isotope analysis of blood plasma in seven colonies over two consecutive years in South Africa. Kelp Gulls consumed a variety of resources, including marine (e.g. fish), coastal (e.g. molluscs), terrestrial natural (e.g. insects, mammals), or terrestrial anthropogenic (e.g. chicken, bread) items. Inter‐annual differences were most apparent among gulls breeding next to a seabird colony, whereas gulls breeding at other colonies were more consistent in diet and trophic ecology. At most colonies, chicks were fed more natural and higher trophic level food items than were consumed by incubating adults. Overall, distance to landfill did not strongly affect the diet and trophic ecology and our results suggest that the Kelp Gull's broad feeding ecology allows it to buffer changes in food availability by switching among food resources. However, such dietary changes triggered by human actions may impact other species, including threatened seabirds. [ABSTRACT FROM AUTHOR]

Rationale: Carbon (δ13C) and nitrogen (δ15N) stable isotope analysis is a powerful tool to investigate diverse questions in fish ecology, such as their trophic position or migration strategies. These questions appear particularly important to protect endangered European eel. However, elevated lipid content in eel muscle can bias δ13C values, as lipids are 13C‐depleted compared to proteins and carbohydrates. Methods: We measured δ13C and δ15N values of bulk and lipid‐free samples of eel muscle. Lipid‐free samples were obtained after the extraction of lipids with cyclohexane. Lipid‐corrected δ13C values, using five different mathematical equations based on bulk δ13C values, were compared to lipid‐free δ13C values. We also evaluated the effect of lipid extraction on δ15N values. The analyses were based on linear regression performed on 333 individuals captured in nine lagoons and four rivers. Results: Independently to the capture site or habitat (river or lagoon), the predicted lipid‐corrected δ13C values were highly consistent with the measured lipid‐free δ13C values (R2 > 0.90). The application of specific equations for each habitat or capture site only slightly increases these R2 (1.5% or less). The lipid extraction treatment significantly decreased by 0.2‰ the δ15N values compared to bulk samples. Conclusions: Given the excellent prediction of mathematical equations and the small decrease of δ15N values after lipids extraction, we propose to use mathematical correction to estimate δ13C values of eel muscle. As the habitats or sites did not strongly influence the results, the coefficients from our study can be applied to other studies on European eel. [ABSTRACT FROM AUTHOR]

ABSTRACT The investigation of wildlife trade and crime has benefitted from advances in technology and scientific development in a variety of fields. Stable isotope analysis (SIA) represents one rapidly developing approach that has considerable potential to contribute to wildlife trade investigation, especially in complementing other methods including morphological, genetic, and elemental approaches. Here, we review recent progress in the application of SIA in wildlife trade research to highlight strengths, shortcomings, and areas for development in the future. SIA has shown success in species identification, determination of geographic provenance, and differentiating between captive‐bred and wild individuals. There are also emerging applications of SIA in wildlife trade research including the use of labelling for traceability, more in‐depth analyses such as compound specific isotope analysis (CSIA), the use of trace metal isotopes, and monitoring the health of individuals (e.g. dietary history and nutritional status). While these applications have shown the utility of SIA in wildlife trade investigations, there are a number of limitations and issues where standardisation of analytical procedures would improve the comparability and interpretation of results. First, there is high variation within many stable isotopes geographically and within tissues – this variation presents opportunities for tracking and monitoring but can also challenge detection of patterns when variation is high. Second, the choice of isotopes and tissues within an organism (and ideally, multiple isotopes and tissues) should be considered carefully as different isotopes and tissue types have variable strengths and weaknesses depending on the research question. Third, validation of SIA methods remains underutilised in the field but is critical for applying SIA broadly to wildlife trade investigations and, particularly, for applications in forensics and in court. Fourth, standards are essential for comparisons across studies. Fifth, while some reference databases exist for the use of SIA in wildlife trade research (e.g. ivory), there are still few comprehensive reference databases available. Development of robust reference databases should be a priority for advancing the use of SIA in wildlife trade research, and ecological study more broadly. Ultimately, further recognition of these primary challenges (and development of solutions) within wildlife SIA research will improve the potential for this technique in tackling the threat of overexploitation to global biodiversity – particularly in concert with the application of other investigative techniques such as genetics and elemental analysis. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents and discusses isotopic data on breastfeeding, weaning, and complementary diet during early childhood in Middle Holocene southeastern Brazil. The study focuses on human individuals from two contemporaneous shell mounds, Piaçaguera (7151–5668 yBP) and Moraes (6791–5590 yBP), which show distinct patterns of infant mortality. We conducted δ15N and δ13C analyses on collagen extracted from subadult bones (Piaçaguera: n = 13; Moraes: n = 13) and sequential dentine slices from permanent (Piaçaguera: n = 7; Moraes: n = 11) and deciduous teeth (Moraes: n = 5). Our findings indicate that weaning ended between 2 and 4 years old in Piaçaguera, with complementary foods similar to the adults. At Moraes, weaning ended between 2 and 5 years old, with a higher consumption of freshwater fish during early childhood and by pregnant women. The weaning ages at Piaçaguera and Moraes align with those documented in other precolonial South American groups. However, our study suggests different dietary preferences and strategies within each group, possibly linked to distinct patterns of infant mortality, particularly evident in the Moraes group. [ABSTRACT FROM AUTHOR]

AbstractThe growing demand for food, coupled with climate change risks, highlights the need to enhance agricultural productivity while reducing environmental impacts. Tropical and subtropical regions, although offering potential for increased production, are highly vulnerable to climate variability. This study evaluated the nitrogen use efficiency (NUE) of Marandu Palisadegrass (Urochloa brizantha, syn. Brachiaria brizantha) under water stress, considering agronomic (biomass production) and environmental parameters (N losses). NUE was assessed using 15 N-labeled fertilizer, and the Nitrogen Nutrition Index (NNI) was tested as a tool for nitrogen management. Climatic conditions significantly influenced NUE and biomass production. For the 100 kg N ha−1 treatment, biomass decreased from 17.51 tons ha−1 in 2020 to 10.38 tons ha−1 in 2021, while nitrogen losses were reduced from 70.48 to 48.29 kg N ha−1. Similarly, for the 50 kg N ha−1 treatment, biomass dropped from 16.08 to 6.94 tons ha−1, and N losses decreased from 21.38 to 15.93 kg N ha−1. These reductions highlight the role of climatic variation, with reduced precipitation and increased temperature fluctuations impacting productivity. The NNI proved effective in monitoring critical nitrogen levels and guiding fertilizer management. These findings support the adoption of proper fertilization practices to enhance NUE, reduce environmental impacts, and aid in the recovery of degraded pastures in tropical and subtropical agroecosystems. [ABSTRACT FROM AUTHOR]

With rapid urbanization, intensified agricultural activities, and industrialization, groundwater resources are increasingly threatened by pollution. Industrial wastewater discharge and the extensive use of agricultural fertilizers in particular, have had substantial impacts on groundwater quality. This study examines 18 groundwater samples collected from the main urban area of Yibin City to assess hydrochemical characteristics, spatial distribution, source attribution, water quality, and human health risks. Statistical analysis reveals significant exceedances in TDS, NO3−, Mn, and As levels in groundwater, with elevated concentrations of B as well. Isotopic analysis identifies atmospheric rainfall as the primary recharge source for groundwater in the area, with water–rock interactions and limestone dissolution playing key roles in shaping its chemical composition. Applying the Entropy-Weighted Water Quality Index (EWQI) for a comprehensive water quality assessment, the study found that 94.44% of groundwater samples were rated as "good", indicating relatively high overall water quality. Deterministic health risk assessments indicate that 72.22% of the groundwater samples have non-carcinogenic health risks below the threshold of 1, while 66.67% have carcinogenic health risks below 1.00 × 10−4. Monte Carlo simulations produced similar results, reinforcing the reliability of the health risk assessment. Although the study area's groundwater quality is generally good, a significant human health risk persists, underscoring the need to ensure the safety of drinking and household water for local residents. This study provides a valuable reference for the rational management and remediation of groundwater resources. [ABSTRACT FROM AUTHOR]

Investigating how multiple invasive fish species with similar ecological traits respond to different environmental conditions is crucial to understanding their successful invasion and coexistence. Here, we used stomach content analysis and stable isotope analysis to analyse the effects of water level fluctuation on the trophic niche plasticity of three dominant co‐occurring invasive tilapia species (Coptodon zillii, Sarotherodon galilaeus, and Oreochromis niloticus) in the Shanmei Reservoir, southern China. We found that the tilapia species exhibited an iliophagous habit with dietary variations between the high‐water (HW) and low‐water (LW) level periods. During the LW period, tilapia fishes primarily fed on periphytic algae, whereas during the HW period, they reduced their consumption of epiphytic algae and increased their intake of plant remains. Biofilms were the most assimilated resource by the species during the LW period, whereas riparian plants dominated during the HW period. The niche width and niche overlap of the three tilapia species were significantly greater in the HW period than in the LW period. However, their trophic positions were not significantly affected by water level fluctuations. Our findings indicate that temporal variation in diet composition and trophic niche, driven by water level fluctuations, may favor food resource partitioning and facilitate the coexistence of these invasive tilapia species. [ABSTRACT FROM AUTHOR]

Ancient Native American ancestors (Clovis) have been interpreted as either specialized megafauna hunters or generalist foragers. Supporting data are typically indirect (toolkits, associated fauna) or speculative (models, actualistic experiments). Here, we present stable isotope analyses of the only known Clovis individual, the 18-month-old Anzick child, to directly infer maternal protein diet. Using comparative fauna from this region and period, we find that mammoth was the largest contributor to Clovis diet, followed by elk and bison/camel, while the contribution of small mammals was negligible, broadly consistent with the Clovis zooarchaeological record. When compared with second-order consumers, the Anzick-1 maternal diet is closest to that of scimitar cat, a mammoth specialist. Our findings are consistent with the Clovis megafaunal specialist model, using sophisticated technology and high residential mobility to subsist on the highest ranked prey, an adaptation allowing them to rapidly expand across the Americas south of the Pleistocene ice sheets. [ABSTRACT FROM AUTHOR]

Current climate change, particularly ocean warming, will induce shifts in marine species distribution and composition, affecting the marine food web and, thus, trophic interactions. Analyses of the stable isotopes 13C and 15N are commonly used to detect trophic markers for food web analyses. With the current standard methods used in food web ecology, it is still challenging to identify potential changes in the uptake and utilization of trophic markers. In this work, we present a 13C-enrichment analysis by NMR spectroscopy to track the uptake and utilization of dietary carbon in a simple laboratory experiment of a primary producer and its consumer (algae and bivalve). In particular, we tested the hypothesis of a temperature-dependent use of dietary carbon by tracing the incorporation of 13C-atoms. Unicellular phytoplankton, Phaeodactilum tricornutum , was reared in a medium containing 13C-labeled bicarbonate. The accompanying 13C-NMR spectra of labeled P. tricornutum showed a specific profile of 13C-labeled compounds, including typical trophic markers such as the polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA). Afterwards, 13C-labeled P. tricornutum was fed to King scallops, Pecten maximus , kept at two different temperatures (15°C and 20°C). Tissue-specific NMR spectra of P. maximus revealed elevated 13C-NMR signals, particularly of the fatty acid EPA in the digestive gland, which was not evident in muscle tissue. The comparison between the two temperatures indicated a change in trophic markers. At the higher temperature, less unsaturated fatty acids were detected in the digested gland, but increased 13C-labels in sugars were detected in the adductor muscle. This might indicate a change in the uptake and utilization of the trophic marker EPA in P. maximus due to a shift in energy conversion from favored beta-oxidation at colder temperatures to conversion from carbohydrates in the warmth. Our approach indicates that besides the accumulation of trophic markers, their incorporation and conversion are additional important factors for the reliable interpretation of trophic linkages under climate change. [ABSTRACT FROM AUTHOR]

Seahorses (Hippocampus spp.; Family Syngnathidae) are mainly targeted by Traditional Chinese Medicine, curio and ornamental trade, as dried or live specimens. Traceability tools may help fill the gaps on supply chains, securing information on geographic origin and identification of traded specimens. Fin-clipping, a non-lethal and well-established method in seahorse research, offers a potential approach to trace the geographic origin and certify the aquaculture of these flagship species. As such, this study aimed to investigate the existence of differences in isotopic profiles of four seahorse species cultured at research centers located in southern Portugal and northern Spain, as well as between cultured Hippocampus guttulatus sourced from two research centers, and between wild and cultured specimens of this species. This research also evaluated the potential of combining isotopic and elemental fingerprints for seahorse species discrimination, through inductively continuous-flow isotope ratio mass spectrometry (IR-MS) and plasma mass spectrometry (ICP-MS). Species cultured at the same research centers exhibited similar stable isotope composition (δ13C and δ15N), except in the case of temperate H. guttulatus from northern Spain, which differed significantly from tropical species H. kuda and H. reidi. These differences could be due to phylogenetic dissimilarities and differences in seawater temperature. The δ15N composition allowed to discriminate between cultured H. guttulatus from the two research centers and between cultured and wild specimens. While dorsal fin isotopes alone did not prove to be a reliable tool for the discrimination of different cultured species, combining them with elemental profiles from seahorses' whole-body allowed to successfully discriminate between H. kuda and H. reidi. This preliminary research demonstrates the potential of stable isotope and elemental analyses for tracing seahorses' geographic origin and species identification. However, further research should be performed to validate these findings for wild specimens, particularly those from illegal, unreported and unregulated (IUU) fisheries and trade. [ABSTRACT FROM AUTHOR]

Historical plankton samples from the St. Lawrence Great Lakes were subjected to taxon-specific 15N analysis to test the hypothesis that the changes recorded in zooplankton communities during the 21st Century are related to changes in the trophic positions of large-bodied carnivorous copepods. Daphnia mendotae was used as the reference herbivore for trophic-level comparisons. The results were that Limnocalanus macrurus, Diaptomus (Leptodiaptomus) sicilis as well as the cladoceran Bythotrephes cederstroemi show evidence of elevated carnivory compared to data from the 20th Century. The large diaptomid Diaptomus (Leptodiaptomus) sicilis has a stable isotope signature that is significantly more carnivorous in Lake Superior than in Lakes Michigan and Huron by approximately one-half trophic level. Differences were found in 10 cases out of 15 for Limnocalanus (Huron, Michigan Superior), 6 cases out of 15 for Diaptomus (Huron, Michigan) and in 1 out of 1 for Senecella (Superior). We did not find evidence to support the theory that large-bodied calanoid copepods may have improved their representation in the food webs of the upper Great Lakes by shifting their trophic position downward. Instead, large-bodied Calanoida have increased their trophic positions in parallel with their increased relative abundance. More research is thus needed to explain the driving forces for changing food web dynamics in the Great Lakes. [ABSTRACT FROM AUTHOR]