Stable Carbon Isotope Analysis Research Articles

Controls of carbon isotope fractionation during gas desorption in overmature marine shales

Carbon isotope fractionation serves as a crucial tool for assessing gas-in-place content and the gas-adsorbed ratio of shale gas during production. However, a significant gap exists in the understanding of the mechanism and impacts of diverse composition and organic matter on carbon isotope fractionation. To address this gap, this study conducted adsorption and desorption experiments on ten shale samples from the Longmaxi Formation. Various integrated analytical techniques were employed, encompassing X-ray diffraction, bitumen reflectance measurement, total organic carbon (TOC) content analysis, stable carbon isotope analysis, low-pressure gas adsorption tests, and field emission scanning electron microscopic observations. The results reveal that methane dominates the shale gas, with the carbon isotopes exhibiting a distinctive full reversal, attributed to the redox reaction between the ethane and water or transition metals. Differential adsorption capacities of shale led to varied carbon isotope distribution during desorption experiments. Increased micropore quantity in shale is anticipated to augment its adsorption capacity, while elevated feldspar content constrains adsorption due to the absence of intraparticle pores. Consequently, a negative correlation is observed between feldspar content and shale gas fractionation. Although intraparticle pores exist in carbon minerals, their connectivity and low carbonate content limit adsorption capacity in clay-rich shale. Deep burial depletes slit pores in clay minerals, resulting in a low adsorption capacity in clay-rich shale. Notably, the over-mature stage exhibits a substantial increase in micropores within organic matter, positively correlating with carbon isotope fractionation. The positive correlation between quartz content and TOC content is attributed to the positive relationship between the quartz content and carbon isotope fractionation. Additionally, the isotopic values of desorbed gas exhibit significant variability when TOC content exceeds 2.0%, remaining stable when TOC content is less than 2.0%.

Food web structures of irrigated rice fields estimated from carbon and nitrogen stable isotopes: Special reference to the role of filamentous green algae as a food resource of aquatic consumers

AbstractRice fields are characterized by high algal production and dense mats of filamentous green algae, and they function as habitats for various aquatic organisms. However, how algal production supports the secondary production of aquatic consumers in rice fields has not been assessed. Herein, aquatic food web structures in two adjacent rice fields in northeastern Japan were examined using carbon and nitrogen stable isotope analyses. Filamentous algae often showed higher δ13C values (mean, −23.1‰ to −21.4‰) than other organic matter sources, including particulate organic matter, benthic microalgae, and soil organic matter (−30.1‰ to −25.4‰). A δ13C‐based isotopic mixing model estimated that among 19 taxa of herbivores and omnivores, most taxa depended on filamentous algae‐derived carbon (ca. >30%). Particularly, Peltodytes intermedius larvae, a specialist feeder for filamentous algae, showed the highest reliance (mean, 66.7%–80.0%). The microcrustacean, Ostracoda sp. also utilized a diet consisting of a substantial proportion of filamentous algae‐derived carbon (57.6%). Seven out of 10 carnivorous taxa showed reliance on filamentous algae‐derived carbon by >30%. Particularly, larvae of beetles (Berosus sp., Enochrus sp., and Hydrochara affinis) showed the highest reliance (40.2%–44.3%). They could assimilate filamentous algae‐based carbon by consuming herbivores, such as P. intermedius. Because fresh filamentous green algae were eaten less by aquatic consumers, the herbivores could consume decomposed filamentous algae rather than fresh ones. Our results suggest that filamentous algae are one of the major organic matter sources supporting secondary production in rice field food webs.

Stable isotope analyses of carbon and nitrogen in hair keratin of suspected man-eating wolves from 1880s

The so-called man-eating wolves of Turku, a pack of three wolves, reportedly killed 22 children in South-Western Finland in 1880–1881. Enormous efforts were carried out to eradicate them. In January 1882 the last remaining wolf was killed. Since then, there has been considerable debate regarding the validity and extent of the man-eating behaviour. This study aims to clarify whether man-eating behaviour can be observed from the remains of these wolves. One of the wolves was mounted in 1882 and is on display at St. Olaf’s school in Turku, enabling us to collect hair keratin samples. Additionally, hair keratin was collected from two other suspected man-eaters. We analysed carbon (δ13C) and nitrogen (δ15N) stable isotope values to study the wolf’s diet during the last months of its life. Samples from seven temporally concurrent wolves were used to construct reference values. Our analyses indicated that δ15N values of suspected man-eaters were relatively low compared to the reference sample. We could not detect clear trends in isotope ratios associated with potential man-eating behavior. We believe that this lack of distinctive patterns can be explained by the relatively minor role that man-eating played in their overall diet.

Paleoenvironmental reconstruction of the Berriasian organic-rich interval of the Vaca Muerta Formation (Neuquén Basin, Argentina): Insights for the characterization of unconventional hydrocarbon shale reservoirs

The 50 m-thick Berriasian organic-rich interval (BORI) of the Vaca Muerta Formation (Neuquén Basin, Argentina) represents one of the most attractive stratigraphic intervals for unconventional hydrocarbon exploration in the unit. Nevertheless, little is known about the environmental conditions prevailing during the accumulation of the sediments. To unravel the causes that favored the preservation of the organic matter (OM) in the BORI, a detailed multiproxy sedimentological approach was conducted. The study included the analyses of microfacies, palynological content, calpionellid-calcisphere dinocysts, mineralogy, spectral gamma-ray, inorganic geochemistry, Rock-Eval pyrolysis and stable carbon isotopes of whole rock carbonate (δ13Ccarb), and associated OM (δ13Corg). The BORI presents a late Early to early Late Berriasian age and is subdivided into a lower and upper interval. The lower interval (25.6 m-thick) is primarily formed by radiolaritic wackestones and presents higher total organic carbon (TOC) content (4.2 wt% on average), mainly in the form of amorphous OM (AOM), with variable contribution of phytoclasts. The geochemical analyses (Si, Ni, Cu, Mo, U, V) indicate high productivity of the water column and overall sea bottom anoxia. Oppositely, the upper interval (24.4 m-thick) is mostly constituted by peloidal packstones/grainstones and presents a lower TOC content (1.5 wt% on average) mainly constituted by phytoclasts, with variable contribution of AOM. A decrease of the productivity and an increase of sea bottom oxygenation is recorded based on the geochemical analyses. The high OM content of the BORI responds to the combination of high productivity of the water column and sea bottom anoxia in response to the Berriasian transgression and a worldwide paleoclimatic change towards more humid conditions. The results of our study position the BORI as an attractive interval for unconventional hydrocarbon production due to its high TOC, low bulk clay mineral and high biogenic quartz content, granting an adequate geomechanical behavior.

Spatial distribution, environmental behavior, and health risk assessment of PAHs in soils at prototype coking plants in Shanxi, China: Stable carbon isotope and molecular composition analyses

To investigate the environmental behavior of and carcinogenic risk posed by 16 priority-controlled polycyclic aromatic hydrocarbons (PAHs), soil samples and air samples from the coke oven top were collected in two prototype coking plants (named PF and JD). The PF soils contained more PAHs than the JD soils because the PF plant employed the side-charging technique and had a lower coke oven height. The soils from both plants contained enough PAHs to pose a carcinogenic risk, and this risk was higher in the PF plant. Data were collected on the source characteristic spectrum of stable carbon isotopic composition (δ13C) of PAHs emitted from the coke oven top (δ13C values of −36.02‰ to −32.05‰ for gaseous PAHs and −34.09‰ to −25.28‰ for particulate PAHs), and these data fill a research gap and may be referenced for isotopic-technology-based source apportionment. Diagnostic ratios and isotopic technology revealed that the coking plant soils were mainly influenced by the coking process, followed by vehicle exhaust; the soils near the boundary of each plant were slightly affected by C3 plant burning. For most PAHs [excluding fluoranthene, benzo(k)fluoranthene, indeno(1,2,3-c,d)pyrene, and dibenzo(a,h)anthracene], the dominant migration process was the net volatilization of PAHs from soil to air. In the PF plant, 13C was depleted in gaseous PAHs during volatilization.

Effects of thinning and understory removal on water use efficiency of Pinus massoniana: evidence from photosynthetic capacity and stable carbon isotope analyses

Effects of thinning and understory removal on water use efficiency of Pinus massoniana: evidence from photosynthetic capacity and stable carbon isotope analyses

Impacts of anthropogenic eutrophication on the carbon transfers in lacustrine food webs: A paleolimnological assessment in four mountain lakes

Over the last decades, the intensification of anthropogenic activities and associated disturbances on lake watersheds have led to major changes in lakes trophic functioning through accelerated eutrophication. In many lakes, these changes are characterized by an unprecedented increase in organic carbon fluxes, potentially leading to a shift in biogeochemical cycles and in the balance between carbon sequestration and greenhouse gas emissions. Understanding the response of the carbon cycle to natural and anthropogenic environmental changes is becoming a crucial challenge in the context of increasing global pressures. In this study, we reconstructed the changes in the trophic functioning of the benthic and pelagic food web, in response to accelerated eutrophication in four lakes over the last millenium. Changes in carbon pathways in food webs were assessed using stable carbon isotope analysis of chitinous subfossil remains of Daphnia, Bosmina, and Chironomini archived in sedimentary records. Changes in the trophic state were inferred from sedimentary geochemical analysis, including carbon accumulation rates, Chl a accumulation rates and carbon-to-nitrogen ratios. Agro-pastoral activities were tracked by analysis of coprophilous ascospores. Results provided by this multi-proxy approach highlight recent disruptions in carbon sources and transfer pathways in lakes food webs. In particular, changes in the carbon isotopic signature of pelagic consumers suggest a recent increase in the use of 13C-depleted carbon sources such as methanogenic or respiration-derived carbon linked to recent changes in trophic state under the intensification of anthropogenic pressures.

Disclosing phototransformation mechanisms of decabromodiphenyl ether (BDE-209) in different media by simulated sunlight: Implication by compound-specific stable isotope analysis.

As one of the typical brominated flame retardants, decabromodiphenyl ether (BDE-209) has been widely detected in environment. However, scarce information was available on BDE-209 phototransformation mechanisms in various media. In this study, compound-specific stable isotope analysis was first applied to investigate BDE-209 phototransformation in n-hexane, MeOH:H2O (v:v, 8:2), and simulated seawater by simulated sunlight. BDE-209 transformation followed pseudo-first-order kinetic, with degradation rate in the following of n-hexane (2.66 × 10-3min-1) > simulated seawater (1.83 × 10-3min-1) > MeOH:H2O (1.41 × 10-3min-1). Pronounced carbon isotope fractionation was first observed for BDE-209 phototransformation, with carbon isotope enrichment factors (εC) of -1.01 ± 0.14‰, -1.77 ± 0.26‰, -2.94 ± 0.38‰ in n-hexane, MeOH:H2O and simulated seawater, respectively. Combination analysis of products and stable carbon isotope, debromination with cleavage of C-Br bonds as rate-limiting step was the main mechanism for BDE-209 phototransformation in n-hexane, debromination and hydroxylation with cleavage of C-Br bonds as rate-limiting steps in MeOH:H2O, and debromination, hydroxylation and chlorination in simulated seawater. This present study confirmed that stable carbon isotope analysis was a robust method to discovery the underlying phototransformation mechanisms of BDE-209 in various solutions.

Organic geochemical heterogeneity of cretaceous mudrocks and reassessment of oil sources in the Tano Basin, Ghana

The Tano Basin in Ghana, situated within the South Atlantic margin, is a significant area for petroleum exploration. Previous studies have recognized the presence of source rocks rich in organic matter from the Cretaceous period in this basin. However, the specific origins of this organic matter, as well as the thermal maturity and depositional environment of the Cretaceous source strata, are not well characterized in existing literature. Here, geochemical data are reported on the bulk geochemical composition of 45 Maastrichtian to Albian-aged rock cuttings via pyrolysis and total organic carbon (TOC) analysis. Out of these samples, 29 were selected for further biomarker and stable carbon isotope (δ13C) analysis. The biomarker and isotopic signatures of the 29 rock extracts and 6 crude oils from the basin's productive Jubilee and TEN oil fields were compared to establish oil-oil and oil-source correlations. The Cenomanian and Turonian source rocks showed the greatest oil generation potential based on current bulk geochemical analysis. These rocks are dominated by oil-prone organic matter and are at a more favorable maturity stage compared to the Maastrichtian, Santonian, and Coniacian (M-S-C) rock suites. In contrast, the Albian rock samples, characterized by mixed Type II/III and Type III kerogen, and their high thermal maturity, indicate a high potential for the generation of gaseous hydrocarbons. The biomarker and isotope data from the Cenomanian, Turonian, and Albian (T-C-A) source rocks suggest that they were deposited in a Transitional Marine-Lacustrine environment characterized by reducing redox conditions. This environment effectively preserved organic matter from diverse sources such as bacteria, algae, and higher plants. Furthermore, biomarker ratios indicated that the T-C-A source rocks are in the early-peak mature window. On the other hand, the M-S-C source rocks appear to have been deposited under suboxic conditions in a Coastal Marine environment. Lower aquatic organisms dominate these rocks, which have an immature to marginally mature level. The analysis of lower molecular weight hydrocarbons (≤C20), characterized by an unresolved complex mixture, did not reveal any obvious correlation between the oils and the Cretaceous source rocks. However, the analysis of higher molecular weight hydrocarbons (≥C20) and isotopic ratios indicated that the commercial discoveries in the Jubilee and TEN fields share a genetic similarity and are primarily sourced from the T-C-A source rocks. Furthermore, the molecular and isotopic characteristics suggest that the M-S-C source rocks do not appear to have contributed to the oils found in the Jubilee and TEN fields. These new geochemical findings shed light on the paleoenvironmental conditions and source rock characteristics of the region, significantly contributing to our understanding of the petroleum evolution and potential of the Tano Basin.

Neolithisation through bone: Stable isotope analysis of human and faunal remains from Syltholm II, Lolland, Denmark

Despite an increasing number of studies, the application of stable sulfur (δ34S) isotope analysis to prehistoric bone collagen remains in its infancy. Conventionally, stable sulfur isotope compositions reflect coastal proximity and the interaction between humans and animals. Here, we undertook stable carbon (δ13C), nitrogen (δ15N) and sulfur (δ34S) isotope analysis of human and faunal bone collagen. To understand the local environmental conditions as well as the husbandry regime employed by the first farmers, and investigate where the animals were raised or hunted in non-specific terms, we sampled 50 faunal, including wild and domestic taxa, and human remains from the Late Mesolithic to Early-Middle Neolithic (c. 4860–2310 cal BC) site of Syltholm II on the island of Lolland, Denmark. We show that the wild animals were obtained from multiple locations surrounding the prehistoric Syltholm Fjord, including forested and open landscapes, areas impacted by sea spray and saltmarshes. In contrast, the domestic taxa, especially cattle, were tightly managed for the majority of their lives based on their δ13C and δ15N isotope compositions, though were likely raised in multiple locations, including sea spray-affected areas, saltmarshes and wetlands, based on their δ34S values. The domestic dogs had a broad range of δ13C, δ15N and δ34S values, reflecting the consumption of varying degrees of marine foodstuffs, including animals that were sulfide-derived. Overall, our results contribute to a growing body of evidence for possible cultural and animal husbandry duality during the earliest Neolithic in southern Scandinavia.

Implications of dietary carbon incorporation in fish carbonates for the global carbon cycle

Marine bony fish are important participants in Earth's carbon cycle through their contributions to the biological pump and the marine inorganic carbon cycle. However, uncertainties in the composition and magnitude of fish contributions preclude their integration into fully coupled carbon-climate models. Here, we consider recent upwards revisions to global fish biomass estimates (2.7–9.5×) and provide new stable carbon isotope measurements that show marine fish are prodigious producers of carbonate with unique composition. Assuming the median increase (4.17×) in fish biomass estimates is linearly reflected in fish carbonate (ichthyocarbonate) production rate, marine fish are estimated to produce between 1.43 and 3.99 Pg CaCO3 yr−1, but potentially as much as 9.03 Pg CaCO3 yr−1. Thus, marine fish carbonate production is equivalent to or potentially higher than contributions by coccolithophores or pelagic foraminifera. New stable carbon isotope analyses indicate that a significant proportion of ichthyocarbonate is derived from dietary carbon, rather than seawater dissolved inorganic carbon. Using a statistical mixing model to derive source contributions, we estimate ichthyocarbonate contains up to 81 % dietary carbon, with average compositions of 28–56 %, standing in contrast to contents <10 % in other biogenic carbonate minerals. Results also indicate ichthyocarbonate contains 5.5–40.4 % total organic carbon. When scaled to the median revised global production of ichthyocarbonate, an additional 0.08 to 1.61 Pg C yr−1 can potentially be added to estimates of fish contributions to the biological pump, significantly increasing marine fish contributions to total surface carbon export. Our integration of geochemical and physiological analyses identifies an overlooked link between carbonate production and the biological pump. Since ichthyocarbonate production is anticipated to increase with climate change scenarios, due to ocean warming and acidification, these results emphasize the importance of quantitative understanding of the multifaceted role of marine fish in the global carbon cycle.

13C dicarboxylic acid signatures indicate temporal shifts in catchment sediment sources in response to extreme winter rainfall

Rainfall and land-use interactions drive temporal shifts in suspended sediment sources, yet the magnitude of such changes remains poorly understood due to the lack of land-use specific source tracers. We investigated α,ω-dicarboxylic fatty acid root-specific biomarkers, as diagnostic tracers for apportioning sources of time-integrated suspended sediment samples collected from a grassland dominated agricultural catchment in the southwest of England during the wet winter period. Applying fatty acids-specific stable carbon isotope analysis and a Bayesian isotope mixing model, we show that stream banks contributed most of the sediment in the early winter, i.e. October–December, while winter cereal-dominated arable land contributed more than half of the sediment during the late winter, i.e. January–March. The dominant sediment source shifted in conjunction with a period of prolonged consecutive rainfall days in the later period suggesting that intervention required to mitigate soil erosion and sediment delivery should adapt to changing rainfall patterns. Our novel findings demonstrate that isotopic signatures of α,ω-dicarboxylic fatty acids are promising tracers for understanding the resistance of agricultural soils to water erosion and quantifying the interactive effects of extreme rainfall and land use on catchment sediment source dynamics.

Assessment of nursery areas for the scalloped hammerhead shark (Sphyrna lewini) across the Eastern Tropical Pacific using a stable isotopes approach

The scalloped hammerhead shark (Sphyrna lewini) is one of the most iconic marine species across the Eastern Tropical Pacific (ETP), yet little is still known about its reproductive biology and the origin of their nursery areas, despite a continuous global decline in their populations. Understanding the origin of shark nurseries is a complex task; however, it is known that the obtention of resources in the first stages of life of placental sharks occurs through maternal reminiscence, thus it is possible to infer the origin of the energy that neonates accumulate during their gestation. In this study we assessed the ecological connectivity and nursery ground use by undertaking a stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) in skin samples of neonates S. lewini across much of their distribution in the ETP, including the Galapagos Marine Reserve (GMR). Our isotopic mixing models revealed that the S. lewini neonates found in the GMR, have isotopic information similar to adult females inhabit in the Galapagos archipelago, suggesting that they are direct descendants of the females that inhabit the GMR. While neonates found off the continental coasts of Ecuador and Panama have isotopic signatures like those of adult females inhabiting several locations across the ETP. This work provides insight into the origin of nursery areas used by adult S. lewini that aggregate in large numbers across oceanic islands of the ETP, highlighting the value of isotopic models to generate useful information for the conservation of sharks.

Sustained use of marine subsidies promotes niche expansion in a wild felid

The use of marine subsidies by terrestrial predators can facilitate substantial transfer of nutrients between marine and terrestrial ecosystems. Marine resource subsidies may have profound effects on predator ecology, influencing population and niche dynamics. Expanding niches of top consumers can impact ecosystem resilience and interspecific interactions, affecting predator-prey dynamics and competition. We investigate the occurrence, importance, and impact of marine resources on trophic ecology and niche dynamics in a highly generalist predator, the caracal (Caracal caracal), on the Cape Peninsula, South Africa. Caracals have flexible diets, feeding across a wide range of terrestrial and aquatic prey. We use carbon and nitrogen stable isotope analysis of fur samples (n = 75) to understand trophic position and niche shifts in coastal and inland foragers, as well as the implications of a diet rich in marine resources. We found significant differences in isotope signatures between these groups, with higher δ13C (P < 0.05) and δ15N values (P < 0.01) in coastal foragers. Isotope mixing models reveal that these elevated signatures were due to non-terrestrial food subsidies, where approximately a third of coastal foraging caracal diet comprised marine prey. The addition of marine prey species to diet increased both the trophic level and isotope niche size of coastal foraging caracals, with potential impacts on prey populations and competition. Our results suggest that marine prey are an important dietary resource for coastal foraging caracals, where seabirds, including two endangered species, are a major component of their diet. However, there are likely risks associated with these resource benefits, as routine consumption of seabirds is linked with higher pollutant burdens, particularly metals. Increased encounters between this terrestrial predator and seabirds may be a result of increased mainland colonies due to changes in habitat availability and the highly opportunistic and generalist foraging behaviour of a native predator.

A novel ontogeny-related sampling of dental tissues for stable isotopes interpretation of the paleobiology of the cave bear

In cave bear studies, stable isotope analysis of carbon and nitrogen is typically conducted on bone collagen. However, challenges arise due to biases in the classification of bones into age groups, which can be influenced by various factors that affect bone size. To overcome such issues, we present and evaluate a novel approach that involves sampling dental collagen from different ontogenetic stages of 45 fossil teeth, where only a portion of each tooth formed during the periods of interest was sampled. This approach enabled us to obtain a carbon and nitrogen fingerprint specific to a particular period in a cave bear’s life without interference from earlier stages. Stable isotopic analysis revealed a rapid decrease in δ15N values from 3 to 15 months of age. After that, the δ15N values remain stable. Based on the nitrogen isotope composition (15N/14N), cubs aged 0–3 months exclusively consumed milk, while the gradual introduction of solid plant food occurs at 5–10 months, resulting in a shift in δ15N values. Based on similar δ15N values in older age groups, it can be assumed that juveniles did not resume milk suckling after the first hibernation. The δ13C values increase until 15 months, followed by a gradual decrease until adulthood, potentially attributable to hibernation. The δ13C values also seems to indicate isotopic differences between yearlings with low δ13C values that successfully established hibernation and those with high δ13C values that failed to hibernate and starved. This novel observation, i.e., decreasing δ13C values from the second year of life onward, agrees with predicted isotopic skeletal collagen δ13C values calculated from modern brown bear blood plasma. In summary, the ontogenetic sampling strategy facilitated the acquisition of further paleobiological insights into the distinct life periods of cave bears.

Effects of large dams on the aquatic food web along a coastal stream with high sediment loads

The contribution of two basal energy sources – detrital organic matter and primary producers – as part of aquatic food webs varies typically along river continua. A host of barriers to river flow increase the water residence time and sediment and nutrient retention in reservoirs worldwide, and potentially alter the balance between detritus-based and algae-based energy pathways in the downstream food webs. We explored this issue on the Sélune River (Normandy, France), a small coastal stream that drains an agricultural catchment with high sediment runoff. Seasonal measurements of the following parameters were compared upstream and downstream of the reservoirs of two large dams (16 m and 36 m high): sediment fluxes, nutrient and chlorophyll a concentrations, algal communities in the epilithic biofilm (taxonomic composition, biomass and growth), and benthic invertebrate communities (abundance and trophic guild structure). As anticipated, annual sediment fluxes were much lower downstream of the reservoirs, where significant decreases in water turbidity, phosphate and silicate concentrations were recorded. A higher chlorophyll a concentration in water and a higher contribution of pelagic algae taxa to the photosynthetic biofilm suggested drifting and deposition of reservoir-borne phytoplankton downriver. Photosynthetic biofilm growth was higher downstream of the reservoirs in spring and fall, and so was the abundance of herbivores in the invertebrate community, notably scrapers and algae eaters. Energy pathways within riverine food webs were traced using stable isotope analyses of carbon (C) and nitrogen in the tissues of aquatic consumers (invertebrates and fish). Mixing models revealed a discontinuity in the origin of the C entering the food webs along the river continuum, confirming a greater contribution of algal C to aquatic consumers downstream of the reservoirs. These results illustrate mechanisms whereby large reservoirs can modulate C flow in food webs along a small coastal river with high sediment loads, and make it possible to anticipate the effects of dam removal on the future river ecosystem.

Identifying the foraging grounds of the new loggerhead turtle nesters in the western Mediterranean

Abstract The western Mediterranean Sea has traditionally served as a primary foraging ground for juvenile loggerhead turtles from three distinct regional management units: the North‐western Atlantic, the Mediterranean and Cape Verde. Nesting activities were sporadic. Recently, nesting activity on the beaches of eastern Spain has increased, due to warmer sand and water temperatures during the summer months. The study has integrated stable isotope analysis of carbon (C), nitrogen (N) and sulphur (S) with satellite telemetry to identify the foraging grounds of these new colonizers nesting on Spanish beaches. Results indicate that the majority of these adult females forage oceanically in the Algerian Basin, with a few exhibiting distinct stable isotope signals, tentatively associated with foraging in shallow coastal areas in the central Mediterranean Sea. The dominance of oceanic foragers in this new population is noteworthy, given the Algerian Basin's oligotrophic nature. This contrasts with the prevalence of neritic foraging in adult females nesting in the central and eastern Mediterranean Sea. The use of the Algerian Basin as a foraging ground for adult loggerhead turtles exposes them to bycatch from drifting longlines. The authorities should refrain from increasing bluefin quotas imposed on longliners in the Algerian Basin unless the fishery avoids using squid as bait and agrees to deploy hooks deeper than 25 m to reduce loggerhead turtle bycatch.

Stable Isotope Analysis of Antipatharian Diets from the Northwestern Gulf of Mexico

Antipatharians, or black corals, form a key component of the benthic fauna found throughout the Gulf of Mexico (GOM). In the northwestern GOM, they are a common member of the communities found on the natural relic coral—algal banks known as the South Texas Banks as well as on artificial reefs. They are known to provide important habitat for many ecologically and economically important species in the area but are relatively understudied. Here we present a study on their trophic ecology using stable isotope analysis of carbon and nitrogen from 2 species, Antipathes atlantica and Stichopathes luetkeni from a mesophotic artificial reef in close proximity to the South Texas Banks. We observed that a large proportion of the 2 coral’s diets was composed of detrital matter, likely driven by the continuous disturbance of the benthos by high velocity benthic currents common to the region that support a persistent nepheloid layer below 30 m. Both species also show a reliance on different members of the planktonic community, with A. atlantica consuming more micro and mesozooplankton compared to S. luetkeni. Comparative analysis between soft tissue and skeletal material also indicates that A. atlantica may change its diet on a seasonal basis, while S. luetkeni appears to rely on detrital matter consistently. This study represents the first assessment of the diets of these organisms and provides valuable insight on the trophic ecology of 2 common antipatharian corals in the GOM on natural and artificial reef ecosystems.

Trophic positions of soil microarthropods in forests increase with elevation, but energy channels remain unchanged

AbstractMountain forests are at risk as the consequences of climate change will likely lead to altered tree species boundaries. Characterizing food webs along elevation gradients in primary forests may help to predict the potential consequences of such changes, for example with regard to the decomposition of dead organic matter. Here, for the first time, we studied trophic variations in two species‐rich microarthropod taxa, Collembola and Oribatida, along an elevation gradient of primary forest at Changbai Mountain, China. Samples were taken at seven elevations of 150‐m elevational difference between 800 and 1700 m. At each elevation, Collembola and Oribatida were extracted from litter samples of eight subplots. We applied three state‐of‐the‐art methods to elucidate trophic positions and basal resource use at community level: Bulk stable isotope analysis of nitrogen (Δ15Nbulk) and carbon (Δ13Cbulk), compound‐specific stable isotope analysis of amino acids (CSIA‐AA), and dietary routing of neutral lipid fatty acids (NLFAs). Trophic positions calculated using Δ15Nbulk and CSIA‐AA (TPCSIA) in both taxa increased similarly with elevation by about half and one third of a trophic position, respectively. Stable isotope mixing models and linear discriminant analysis bootstrapping using δ13C of essential amino acids indicated fungi as the most important resource at all elevations for both taxa. Also, proportions of marker NLFAs changed little across elevations in both taxa; overall high proportions of linoleic acid indicated high fungal contributions, but in Collembola the contribution of bacterial markers was generally higher than in Oribatida. Δ13Cbulk did not respond linearly to the elevation gradient; however, changes in elevation differed between Collembola and Oribatida. A strong linear relationship between δ15N of phenylalanine and δ15N of litter indicated litter as the basis of energy channels in both taxa. Overall, food web functioning likely changes with changing forest types along elevation gradients, with microarthropods switching from feeding closer to the base of the food web at lower elevations to feeding at higher trophic levels at higher elevations, potentially compromising their role in litter decomposition and nutrient cycling.

Dealing with biases introduced by lipids in stable carbon and nitrogen isotope analyses: a solution based on 28 marine invertebrate, fish, and mammal species

Dealing with biases introduced by lipids in stable carbon and nitrogen isotope analyses: a solution based on 28 marine invertebrate, fish, and mammal species