Arctic waders and the capital‐income continuum: Further tests using isotopic contrasts of egg components

Birds migrating annually to high‐latitude breeding grounds may benefit from the transport of endogenous nutrient reserves that ultimately contribute to reproduction. Shorebirds represent a diverse group of Arctic breeders that typically arrive on the breeding grounds with body reserves enriched in ¹³C and ¹⁵N due to wintering and staging in marine or estuarine habitats. Such isotopic differences between endogenous macronutrient reserves and local foodwebs allow the use of stable isotopes to test for the source of nutrient allocations to eggs. We examined δ¹³C and δ¹⁵N values in lipid‐free yolk and albumen and δ¹³C values in yolk lipid of first clutches of ten species of sandpiper and plover breeding near Churchill, Manitoba, Canada in 2003. Most birds had egg isotope values indicating a C3 terrestrial biome, which fits primarily an income (exogenous) breeding strategy. Two exceptions were single sandpiper and plover with strong marine isotope values. Among species, strong positive relationships for each isotope between egg tissue components suggest that egg proteins and lipids tended to be derived from the same isotopic source. Correlations of egg δ¹³C values for lipids and proteins approached theoretical relationships expected for exogenous breeding strategies, based on captive studies. Significant positive correlations between clutch initiation date and δ¹³C values of egg lipids and albumen suggest some endogenous nutrient contributions to later laid eggs but the circumstances under which this may occur are unstudied. Where possible, we recommend that researchers use blood and fat biopsies from laying females as a means of anchoring endogenous and exogenous endpoints for modeling of each reproductive event. We encourage the isotopic analysis of egg albumen, yolk and yolk lipids among individuals and species and tests of correlations among these components as a means of inferring origins of nutrients to eggs.     

Relative contribution of lipid sources to eggs of lesser scaup

Studies of how birds mobilize nutrients to eggs have traditionally considered a continuum of possible allocation strategies ranging from income breeding (rely on food sources found on the breeding grounds) to capital breeding (rely on body reserves stored prior to the breeding season). For capital breeding, stored body reserves can be acquired either on or away from the breeding grounds, but it has been difficult to quantify the relative contribution of each, precluding identification of key habitats for acquiring nutrients for clutch formation. During 2006–2009, we explored the importance of spring‐staging habitats versus breeding‐area habitats for egg‐lipid formation in female lesser scaup Aythya affinis using stable carbon (δ¹³C) isotope analyses. Although δ¹³C values for abdominal lipid reserves brought to the breeding grounds overlapped those of local amphipods, we were able to quantify the importance of local plant carbohydrates (seeds of emergent wetland plants) to the production of eggs. We compared the importance of local wetland seeds (overall δ¹³C: ?29.1 ± 0.9‰ SD) to combined lipid stores and lipids from local amphipods (overall δ¹³C: ?23.8 ± 2.2‰). Local seeds and stored body lipids contributed equally to egg lipid formation across years but we found evidence of annual variation in their relative importance. Wetland seeds contributed 39% (SE = 10%) to egg lipid production, and the importance of this source varied by year (90% CI = 47–75% in 2006, 13–42% in 2007, 29–65% in 2008, and 7–30% in 2009). In contrast to earlier studies that suggest lesser scaup predominantly employ a capital breeding strategy, our results suggest that in some years females may attain half of their energy for clutch formation from foods on the breeding grounds.     

The Altitudinal Patterns of Leaf C∶N∶P Stoichiometry Are Regulated by Plant Growth Form,Climate and Soil on Changbai Mountain,China

Understanding the geographic patterns and potential drivers of leaf stoichiometry is critical for modelling the nutrient fluxes of ecosystems and to predict the responses of ecosystems to global changes. This study aimed to explore the altitudinal patterns and potential drivers of leaf C∶N∶P stoichiometry. We measured the concentrations of leaf C, N and P in 175 plant species as well as soil nutrient concentrations along an altitudinal transect (500–2300 m) on the northern slope of Changbai Mountain, China to explore the response of leaf C∶N∶P stoichiometry to plant growth form (PGF), climate and soil. Leaf C, N, P and C∶N∶P ratios showed significant altitudinal trends. In general, leaf C and C∶N∶P ratios increased while leaf N and P decreased with elevation. Woody and herbaceous species showed different responses to altitudinal gradients. Trees had the largest variation in leaf C, C∶N and C∶P ratios, while herbs showed the largest variation in leaf N, P and N∶P ratio. PGF, climate and soil jointly regulated leaf stoichiometry, explaining 17.6% to 52.1% of the variation in the six leaf stoichiometric traits. PGF was more important in explaining leaf stoichiometry variation than soil and climate. Our findings will help to elucidate the altitudinal patterns of leaf stoichiometry and to model ecosystem nutrient cycling.     

Ontogenetic changes in biochemical composition during larval and early postlarval development of Lepidophthalmus louisianensis, a ghost shrimp with abbreviated development

Changes in growth and biochemical composition during the transition from egg through zoea to decapodid in the ghost shrimp, Lepidophthalmus louisianensis (Schmitt, 1935), were documented in terms of dry weight, lipid classes, fatty acid composition, and carbon to nitrogen (C:N) ratios. Larvae of the ghost shrimp were mass-reared in the laboratory (28°C; 20‰ S) from hatching to the decapodid stage. Iatroscan lipid class analysis revealed that major lipid classes in recently produced eggs were phospholipids (80.8±1.3%) and triglycerides (16.0±1.1%), which decreased during the incubation period. Polar lipids (zoea I: 77.4±1.7%; zoea II: 77.5±2.1%; decapodid: 80.0±1.7%) and neutral lipids, of which free fatty acids (zoea I: 10.5±2.7%; zoea II: 13.1±5.2%; decapodid: 7.8±2.1%) were dominant, represented the major lipid classes in the zoeal and decapodid stages. Triglycerides were present in small amounts. The predominant fatty acids of L. louisianensis eggs, zoeae and decapodids were palmitic (16:0), stearic (18:0), eicosapentaenoic (20:5ω3), oleic (18:1ω9), and arachidonic (20:4ω6). Elemental composition of eggs, larvae, and the decapodid stage revealed conspicuous changes in the C:N ratio, with N being relatively stable during larval development but C decreasing during the decapodid stage. These data suggest independence of newly hatched L. louisianensis on external energy resources. This combined with the ability to incorporate saturated fatty acids into polar lipids provides a selective advantage for fast development of new tissue and growth, characteristic of decapod crustacean larvae with lecithotrophic development.     

脂类抽提对北太平洋柔鱼肌肉碳、氮稳定同位素测定结果的影响

稳定同位素技术可深层次地分析头足类的摄食习性和栖息地等方面的重要信息.稳定同位素分析多选取动物肌肉为研究组织,然而,肌肉中的脂类含量会影响对其稳定同位素信息的准确解析.北太平洋柔鱼是重要的大洋经济性头足类,在海洋生态系统中具有重要的生态地位.本研究选取了53尾北太平洋柔鱼,通过分析脂类抽提对胴体肌肉稳定同位素比值的影响,探讨脂类物质对稳定同位素比值的干扰机制,对比不同碳稳定同位素比值校正模型的适用性,并提出适用于北太平洋柔鱼胴体肌肉δ¹³-C校正模型.结果表明： 北太平洋柔鱼肌肉的脂类抽提会引起稳定同位素测定结果的显著变化,δ¹³-C和δ¹⁵-N分别平均升高0.71‰和0.47‰,在分析组织碳稳定同位素比值时,脂类抽提在样品预处理过程中十分必要,其能消除脂类对样品稳定同位素分析的干扰,从而更加准确地分析研究对象食性与栖息地的变化.在单独进行氮稳定同位素比值分析时,则不需要进行脂类抽提.     

Differential Nutrient Limitation of Soil Microbial Biomass and Metabolic Quotients (qCO2): Is There a Biological Stoichiometry of Soil Microbes?

Background

Variation in microbial metabolism poses one of the greatest current uncertainties in models of global carbon cycling, and is particularly poorly understood in soils. Biological Stoichiometry theory describes biochemical mechanisms linking metabolic rates with variation in the elemental composition of cells and organisms, and has been widely observed in animals, plants, and plankton. However, this theory has not been widely tested in microbes, which are considered to have fixed ratios of major elements in soils.

Methodology/Principal Findings

To determine whether Biological Stoichiometry underlies patterns of soil microbial metabolism, we compiled published data on microbial biomass carbon (C), nitrogen (N), and phosphorus (P) pools in soils spanning the global range of climate, vegetation, and land use types. We compared element ratios in microbial biomass pools to the metabolic quotient qCO₂ (respiration per unit biomass), where soil C mineralization was simultaneously measured in controlled incubations. Although microbial C, N, and P stoichiometry appeared to follow somewhat constrained allometric relationships at the global scale, we found significant variation in the C∶N∶P ratios of soil microbes across land use and habitat types, and size-dependent scaling of microbial C∶N and C∶P (but not N∶P) ratios. Microbial stoichiometry and metabolic quotients were also weakly correlated as suggested by Biological Stoichiometry theory. Importantly, we found that while soil microbial biomass appeared constrained by soil N availability, microbial metabolic rates (qCO₂) were most strongly associated with inorganic P availability.

Conclusions/Significance

Our findings appear consistent with the model of cellular metabolism described by Biological Stoichiometry theory, where biomass is limited by N needed to build proteins, but rates of protein synthesis are limited by the high P demands of ribosomes. Incorporation of these physiological processes may improve models of carbon cycling and understanding of the effects of nutrient availability on soil C turnover across terrestrial and wetland habitats.     

Stable Isotope Ratios as a Tool for Assessing Changes in Carbon and Nutrient Sources in Antarctic Terrestrial Ecosystems

Samples of an angiosperm species, nine lichen species and a terrestrial alga, were collected from a variety of Antarctic terrestrial habitats, and were analysed for C and N stable isotope composition. Collections were made along natural gradients, the marine gradient, running from the sea coast inland and the moisture gradient, determined by melt water and precipitation runoff, and running towards the sea coast. Considerable variation in stable isotope ratios was found; δ¹³C values ranged between −16 and −32‰ and δ¹⁵N values between −23 and +23‰ The variation in stable carbon isotope ratios could be attributed in part to species specific differences, but differences in water availability also played a role, as was shown for the terrestrial alga Prasiola crispa and the lichen species Usnea antarctica. The differences in the isotope ratios of nitrogen could be retraced to the origin of nitrogen: marine or terrestrial. The nitrogen stable isotope ratios were influenced by both the marine gradient from the sea inland and the melt water and precipitation flow running in the opposite direction, towards the sea. This was shown for the lichen species Turgidosculum complicatulum and the angiosperm species Deschampsia antarctica. The variation in the C and N stable isotope ratios can be used to determine sources and pathways of N and changes in the water availability in Antarctic terrestrial ecosystems. Contrary to earlier reports the use of stable N isotope ratios is possible in this case because of the relative simplicity of the structure of the Antarctic terrestrial ecosystems.     

An assessment of sample processing methods for stable isotope analyses of marine food webs

Carbon and nitrogen stable isotope ratios are commonly used in the study of marine food webs. However, different sample processing methods can influence the measurement of these stable isotope ratios. The purpose of this study is to define an adequate methodology to be used in the construction of whole food webs. It is demonstrated that acidification of the samples results in a decrease in carbon stable isotope values for sedimentary organic matter, suspended particulate organic matter, plankton and invertebrates with carbonated structures. The response was variable for nitrogen isotope ratios. Based on our results we recommend sample acidification for carbon analysis in these compartments where effects of this treatment were observed. We observed a decrease in δ¹³C values after washing with distilled water, so we do not recommend washing with water after acidification. For nitrogen analysis, acidification should be avoided. The various dehydration treatments studied caused significant differences only in nitrogen isotope ratios.     

Atlantic walrus signal latitudinal differences in the long-term decline of sea ice-derived carbon to benthic fauna in the Canadian Arctic

Climate change is altering the biogeochemical and physical characteristics of the Arctic marine environment, which impacts sea ice algal and phytoplankton bloom dynamics and the vertical transport of these carbon sources to benthic communities. Little is known about whether the contribution of sea ice-derived carbon to benthic fauna and nitrogen cycling has changed over multiple decades in concert with receding sea ice. We combined compound-specific stable isotope analysis of amino acids with highly branched isoprenoid diatom lipid biomarkers using archived (1982–2016) tissue of benthivorous Atlantic walrus to examine temporal trends of sea ice-derived carbon, nitrogen isotope baseline and trophic position of Atlantic walrus at high- and mid-latitudes in the Canadian Arctic. Associated with an 18% sea ice decline in the mid-Arctic, sea ice-derived carbon contribution to Atlantic walrus decreased by 75% suggesting a strong decoupling of sea ice-benthic habitats. By contrast, a nearly exclusive amount of sea ice-derived carbon was maintained in high-Arctic Atlantic walrus (98% in 1996 and 89% in 2006) despite a similar percentage in sea ice reduction. Nitrogen isotope baseline or the trophic position of Atlantic walrus did not change over time at either location. These findings indicate latitudinal differences in the restructuring of carbon energy sources used by Atlantic walrus and their benthic prey, and in turn a change in Arctic marine ecosystem functioning between sea ice–pelagic–benthic habitats.     

Changes in the intramolecular stable carbon isotope ratios with age of the European cave bear (Ursus spelaeus)

Changes with age in the diet and metabolism of the extinct European cave bear (Ursus spelaeus) from the Divje Babe archaeological site in northwestern Slovenia were investigated by comparing the stable carbon isotope ratio of whole bone collagen with that of the peptide-bonded carboxyl carbons in collagen. These carboxyl carbons were selectively released by decarboxylation of the collagen hydrolysate with ninhydrin (2,2-dihydroxy-1,3-indanedione). The stable carbon isotope ratio increased with age for both the peptide-bonded and other carbons. Although only one-third of the carbon atoms in collagen are peptide-bonded, they account for most of the observed change with age of the stable carbon isotope ratio of the whole collagen. Stable nitrogen isotope ratios decreased with age and were negatively correlated with changes in the stable carbon isotope ratios. These observations support previous investigations on the unique metabolism of hibernating bears.     

Isotope alteration caused by changes in biochemical composition of sedimentary organic matter

Stable carbon (C) and nitrogen (N) isotope ratios of sedimentary organic matter (OM) can reflect the biogeochemical history of aquatic ecosystems. However, diagenetic processes in sediments may alter isotope records of OM via microbial activity and preferential degradation of isotopically distinct organic components. This study investigated the isotope alteration caused by preferential degradation in surface sediments sampled from a eutrophic reservoir in Germany. Sediments were treated sequentially with hot water extraction, hydrochloric acid hydrolysis, hydrogen peroxide oxidation and di-sodium peroxodisulfate oxidation to chemically simulate preferential degradation pathways of sedimentary OM. Residue and extracts from each extraction step were analyzed using elemental analyzer-isotope ratio mass spectrometry and solid-state ¹³C nuclear magnetic resonance spectroscopy. Our results show that stable C and N isotope ratios reacted differently to changes in the biochemical composition of sedimentary OM. Preferential degradation of proteins and carbohydrates resulted in a 1.2‰ depletion of ¹³C, while the isotope composition of ¹⁵N remained nearly the same. Sedimentary δ¹⁵N values were notably altered when lignins and lipids were oxidized from residual sediments. Throughout the sequential fractionation procedure, δ¹³C was linearly correlated with the C:N of residual sediments. This finding demonstrates that changes in biochemical composition caused by preferential degradation altered δ¹³C values of sedimentary OM, while this trend was not observed for δ¹⁵N values. Our study identifies the influence of preferential degradation on stable C isotope ratios and provide additional insight into the isotope alteration caused by post-depositional processes.

     

Gas chromatography–combustion–isotope ratio mass spectrometry analysis of 19-norsteroids: application to the detection of a nandrolone metabolite in urine

Determination of whether the major metabolite of nandrolone in urine, 19-norandrosterone (19-NA), is exogenous or endogenous in origin is one of the most exciting challenges for antidoping laboratories. Gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS) can be used to differentiate these two origins by carbon isotopic ratio analysis. A complete method for purification of 19-NA in urine has been established. Acetylated ketosteroids, and in particular 19-NA, are isolated from the urine matrix before analysis after hydrolysis and purification of urine by reversed-phase and normal solid-phase extraction. The limit of detection for 19-NA was about 60 ng with recoveries of 54–60%. Evidence of exogenous administration of 19-NA may be established from isotope ratio determination from the ¹³C/¹²C ratios of several synthetic 19-norsteroids compared to those obtained for endogenous steroids.     

Linking Stoichiometric Homeostasis of Microorganisms with Soil Phosphorus Dynamics in Wetlands Subjected to Microcosm Warming

Soil biogeochemical processes and the ecological stability of wetland ecosystems under global warming scenarios have gained increasing attention worldwide. Changes in the capacity of microorganisms to maintain stoichiometric homeostasis, or relatively stable internal concentrations of elements, may serve as an indicator of alterations to soil biogeochemical processes and their associated ecological feedbacks. In this study, an outdoor computerized microcosm was set up to simulate a warmed (+5°C) climate scenario, using novel, minute-scale temperature manipulation technology. The principle of stoichiometric homeostasis was adopted to illustrate phosphorus (P) biogeochemical cycling coupled with carbon (C) dynamics within the soil-microorganism complex. We hypothesized that enhancing the flux of P from soil to water under warming scenarios is tightly coupled with a decrease in homeostatic regulation ability in wetland ecosystems. Results indicate that experimental warming impaired the ability of stoichiometric homeostasis (H) to regulate biogeochemical processes, enhancing the ecological role of wetland soil as an ecological source for both P and C. The potential P flux from soil to water ranged from 0.11 to 34.51 mg m⁻² d⁻¹ in the control and 0.07 to 61.26 mg m⁻² d⁻¹ in the warmed treatment. The synergistic function of C-P acquisition is an important mechanism underlying C∶P stoichiometric balance for soil microorganisms under warming. For both treatment groups, strongly significant (p<0.001) relationships fitting a negative allometric power model with a fractional exponent were found between n-H_C∶P (the specialized homeostatic regulation ability as a ratio of soil highly labile organic carbon to dissolved reactive phosphorus in porewater) and potential P flux. Although many factors may affect soil P dynamics, the n-H_C∶P term fundamentally reflects the stoichiometric balance or interactions between the energy landscape (i.e., C) and flow of resources (e.g., N and P), and can be a useful ecological tool for assessing potential P flux in ecosystems.     

Use of carbon and nitrogen isotope ratios in termite research

In this paper, I review carbon and nitrogen isotopic (natural abundance levels) studies of termites. The carbon isotope ratio of CH₄ emitted from termites, together with the emission rates of CO₂, CH₄ and H₂, showed several trends corresponding to the kinds of symbiotic microbes and feeding habits. The fraction of methane oxidized in the nest structure was estimated by comparing carbon isotope ratio of CH₄ emitted from the nest with that produced by termites in the nest. Symbiotic nitrogen fixation in the gut of termites has been shown to have a significant contribution to the nitrogen economy in some wood-feeding termites. The carbon isotope ratio distinguishes between C4 from C3 plants, and the fractional contribution of grass in the diet can thereby be estimated. The carbon and nitrogen isotope ratios in termites are discernible among soil-feeders, fungus cultivators and wood-feeders. Wood/soil-interface feeders have intermediate values between wood- and soil-feeders, and thus carbon and nitrogen stable isotope ratios are assumed to characterize the degree of humification of the material consumed by termites. It is suggested that carbon and nitrogen isotope ratios are useful indicators of the functional position of termites in the decomposition process. A similar isotope pattern has been obtained in earthworms, suggesting that isotope signatures might be useful parameters in investigating detritivorous animals in general.     

不同产地三疣梭子蟹的稳定同位素比值特征及原产地溯源

探索稳定同位素对三疣梭子蟹产地溯源的可行性,可为保护地理标志产品、追溯原产地来源提供理论依据。本研究以黄海、渤海和东海3个主产区海域的三疣梭子蟹为对象,分析了其碳、氮稳定同位素值差异性和不同组织中稳定同位素比值的相关性。结果表明: 不同产地的碳、氮稳定同位素比值有显著性差异,不同组织之间有明显的同位素分馏效应。利用建立的判别分析模型,通过三疣梭子蟹不同组织稳定同位素比值进行产地判别分析,采用肌肉和腮中碳、氮稳定同位素的产地判别正确率(>95%)明显高于肝胰性腺,说明肌肉和腮稳定同位素比值可以对不同海域的三疣梭子蟹进行有效区分。本研究填补了目前三疣梭子蟹稳定同位素溯源技术的研究空白。     

Stable nitrogen and carbon isotope ratios in wild native honeybees: the influence of land use and climate

The eastern hive bee Apis cerana is a major honeybee species in Asia providing numerous ecosystem services. Understanding how much the honeybees depend on natural and human-influenced plants and landscapes in different climates is important could contribute to evaluate how wild honeybees use food resources and to measure the ecosystem services. We investigated the effects of land use and climate changes on stable nitrogen and carbon isotope ratios in wild populations of A. cerana. In populations from 139 individual sites throughout Japan, we measured nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotope ratios and analyzed the effects of land use and climate. Our results showed that forested areas and annual precipitation had significant effects on δ¹⁵N, and that paddy fields and urban areas had significant effects on δ¹³C. These results suggest that A. cerana sensibly uses available food resources in the various environments and that stable nitrogen and carbon isotope ratios clearly reflect the effects of land use and climate changes on the populations of A. cerana. Thus, stable nitrogen and carbon isotope ratios in A. cerana, which widely distributes in Asia, can be used as indicators of the environments, such as land use and climate, of an area within its foraging range.     

Estimation of growth and food consumption in juvenile Japanese flounder Paralichthys olivaceus using carbon stable isotope ratio δC under laboratory conditions

To estimate the accumulated food consumption and growth of juvenile Japanese flounder Paralichthys olivaceus, we investigated the relationships between individual food consumption and growth, and the change in the stable carbon isotope ratio (δ¹³C). Japanese flounder juveniles were individually reared and their diet was switched from one formulated feed EP1 (δ¹³C = − 19.47‰) to another EP3 (δ¹³C = − 17.21‰) and fed at different feeding regimes. After the switch, the δ¹³C content of the dorsal muscle was exponentially shifted to a different level in proportion to the feeding and growth rates. Therefore, measuring the carbon stable isotope ratio is a useful tool for estimating the food consumption and growth rate of juveniles. In addition, since the velocity of change and the asymptotic value of the carbon stable isotope ratio varied in muscle, caudal fin and liver tissue, different tissues can be used for different time scale estimations.     

The reliance on distant resources for egg formation in high Arctic breeding barnacle geese Branta leucopsis

Breeding in the high Arctic is time constrained and animals should therefore start with their annual reproduction as early as possible. To allow for such early reproduction in migratory birds, females arrive at the breeding grounds either with body stores or they try to rapidly develop their eggs after arrival using local resources. Svalbard breeding barnacle geese Branta leucopsis have to fly non‐stop for about 1100 km from their last continental staging site to the archipelago making the transport of body stores costly. However, environmental conditions at the breeding grounds are highly unpredictable favouring residual body stores allowing for egg production after arrival on the breeding grounds. We estimated the reliance on southern continental resources, i.e. body stores for egg formation, in barnacle geese using stable isotope ratios in the geese's forage along the flyway and in their eggs. Females adopted mixed breeding strategies by using southern resources as well as local resources to varying extents for egg formation. Southern capital in lipid‐free yolk averaged 41% (range: 23–65%), early laid eggs containing more southern capital than eggs laid late in the season. Yolk lipids and albumen did not vary over time and averaged a southern capital proportion of 54% (range: 32–73%) and 47% (range: 25–88%), respectively. Our findings indicate that female geese vary the use of southern resources when synthesising their eggs and this allocation also varies among egg tissues. Their mixed and flexible use of distant and local resources potentially allows for adaptive adjustments to environmental conditions encountered at the archipelago just before breeding.     

Biosignatures present in a hydrothermal massive sulfide from the Mid-Atlantic Ridge

Mid‐ocean spreading and accompanying hydrothermal activities result in huge areas with exposure of minerals rich in reduced chemicals – basaltic and peridotitic rocks as well as metal sulfide precipitates – to the oxygenated seawater. Oxidation of Fe and S present in these rocks provides an extensive long‐term source of energy to lithotrophs. Investigation of lipid biomarkers and their carbon isotope ratios from a massive iron sulfide of an inactive sulfide mound or inactive chimney sampled at the western flank of the Turtle‐Pits hydrothermal field (Mid‐Atlantic Ridge, 5°S) revealed a unique lipid distribution. The bacterial fauna appears to be dominated by chemolithotrophs with a distinct lipid composition mainly comprising of iso‐branched fatty acids and nonisoprenoidal dialkyl glycerol diethers partially including the very rare macrocyclic cores with 30–35 carbon atoms (including 13,16‐dimethyloctacosane and 5,13,16‐trimethyloctacosane). The Bacteria are accompanied by most likely hydrogen/CO₂‐dependent methanogenic Archaea (e.g. Methanococcus) as well as other Archaea with a different life style (e.g. Ferroplasma). Alike some of the bacterial lipids the archaeal lipids predominantly consist of macrocyclic diethers including one C₄₀ and one C₄₁ isoprenoid. Structural homologues of the latter are so far only reported from a methanogenic archaeum and a Pleistocene sulfur deposit. Compound‐specific analyses of the stable isotope ratios revealed δ¹³C values for the majority of bacterial and archaeal lipid components of about 0‰ (vs. VPDB), indicative for chemolithoautotrophically fixed carbon which is, for distinct pathways, accompanied by only negligible fractionations. However, the presence of methanogenic Archaea is indicated by ¹³C‐depleted isoprenoidal lipids (δ¹³C ~ –50‰) characteristic for certain CO₂‐reducing methanogens synthesizing lipids via acetyl CoA.     

Natural distinction of carbon and nitrogen isotopic niches in common fish species across marine biotopes in the Yellow River estuary

Stable isotope analysis is a universally recognized and efficient method of indicating trophic relationships that is widely applied in research. However, variation in stable isotope ratios may lead to inaccuracies due to the effects of complex environmental conditions. This research compared the carbon and nitrogen isotopic niches of fish communities between diverse biotopes around the Yellow River estuary and adjacent sea areas, with the aim of revealing distinctions in stable isotopic niche metrics, trophic positions, and feeding preferences. Our analysis of the food source contribution indicated that allochthonous sources were considered major energy sources in estuarine areas directly affected by Yellow River‐diluted water, while autochthonous benthic and pelagic producers dominated carbon input into the food web in Laizhou Bay and the open water. A significant variation in the fish δ¹⁵N characteristic was found within estuarine adjacent regions, so, together with the results from previous studies, we deemed the local high concentration of dissolved inorganic nitrogen as the original trigger of the abnormal δ¹⁵N characteristic in fishes via a transport process along food chains. These results provide a new perspective on the natural distinction of carbon and nitrogen isotopic niches. The detailed data reported here enhance our understanding of variations in fish communities in estuarine ecosystems.