Stable Carbon Isotope Analysis Research Articles

A new technique to study nutrient flow in host-parasite systems by carbon stable isotope analysis of amino acids and glucose

Stable isotope analysis of individual compounds is emerging as a powerful tool to study nutrient origin and conversion in host-parasite systems. We measured the carbon isotope composition of amino acids and glucose in the cestode Schistocephalus solidus and in liver and muscle tissues of its second intermediate host, the three-spined stickleback (Gasterosteus aculeatus), over the course of 90 days in a controlled infection experiment. Similar linear regressions of δ13C values over time and low trophic fractionation of essential amino acids indicate that the parasite assimilates nutrients from sources closely connected to the liver metabolism of its host. Biosynthesis of glucose in the parasite might occur from the glucogenic precursors alanine, asparagine and glutamine and with an isotope fractionation of − 2 to – 3 ‰ from enzymatic reactions, while trophic fractionation of glycine, serine and threonine could be interpreted as extensive nutrient conversion to fuel parasitic growth through one-carbon metabolism. Trophic fractionation of amino acids between sticklebacks and their diets was slightly increased in infected compared to uninfected individuals, which could be caused by increased (immune-) metabolic activities due to parasitic infection. Our results show that compound-specific stable isotope analysis has unique opportunities to study host and parasite physiology.

Anomalous 13C enrichment in Mesozoic vertebrate enamel reflects environmental conditions in a “vanished world” and not a unique dietary physiology

AbstractBiogeochemical analyses of organisms’ tissues provide direct proxies for diets, behaviors, and environmental interactions that have proven invaluable for studies of extant and extinct species. Applying these to Cretaceous ecosystems has at times produced anomalous results, however, as dinosaurs preserve unusually positive stable carbon isotope compositions relative to extant C3-feeding vertebrates. This has been hypothesized to be a unique property of dinosaur dietary physiology, with potential significance for our interpretations of their paleobiology. We test that hypothesis through multi-taxic stable carbon isotope analyses of a spatiotemporally constrained locality in the Late Cretaceous of Canada, and compare the results to a modern near-analogue environment in Louisiana. The stable carbon isotope anomaly is present in all sampled fossil vertebrates, dinosaur or not. This suggests another more widespread factor is responsible. Examinations of diagenetic effects suggest that, where present, they are insufficient to explain the isotope anomaly. The isotope anomaly is therefore not primarily the result of a unique dietary physiology of dinosaurs, but rather a mix of factors impacting all taxa, such as environmental and/or source-diet differences. Our study underscores the importance of multi-taxic samples from spatiotemporally constrained localities in testing hypotheses of extinct organisms and ecosystems, and in the use of modern data to “ground truth” when evaluating analogue versus non-analogue conditions in greenhouse paleoecosystems.

Food Web Connectivity in a Mangrove–Seagrass–Patch Reef (MSP) Seascape: Lessons from a Tropical Back-Reef in Puerto Rico

Alterations to the functions and connectivity of mangrove–seagrass–patch reef (MSP) seascapes have the potential to impact the survival, foraging activities, and movement of reef-dependent invertebrates (e.g., crabs and shrimp) and fishes. In the current study, we examined carbon flow in the Guánica Biosphere Reserve in southwestern Puerto Rico using pigment analysis of particulate organic matter and stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) in flora and fauna. Several lines of evidence pointed to N2 fixers (cyanobacteria) being important for fueling primary productivity in this oligotrophic ecosystem including low (<0.7 µg L−1) chlorophyll, prevalence of cyanobacteria based on pigment signatures, and the isotope signatures of seagrass and red mangrove leaf tissue (enriched δ15N values) and consumers (depleted δ15N values). Food web mixing models based on stable isotopes (δ13C and δ15N) revealed that multiple producers (phytoplankton, benthic microalgae, seagrasses, etc.) contributed organic matter to the consumers (zooplankton, invertebrates, and fishes) in the MSP seascape at the center of the reserve. Contribution estimates for common benthic invertebrates (crabs and shrimp) were taxon-specific, and the highest input was generally linked to particulate organic matter (POM) and benthic microalgae (BMA)/seagrass producer categories, although meaningful mangrove contribution was observed for some taxa. Similarly, contribution estimates for fishes were highest for POM and BMA/seagrass, with the latter producer category being more important for species known to migrate from mangroves or patch reefs to seagrass beds at night (bluestriped grunt, French grunt, and white grunt). Although all fish investigated were observed in mangrove prop-root habitats, input of organic matter from mangroves to these consumers was typically limited for most of the species examined. Understanding these complex seascapes contributes to our understanding of the ecology of these vital ecosystems.

Post-depositional history of the lower Palaeocene interval using petrographic, CL and geochemical data in the East Tethys: Kopet-Dagh Basin, northeast Iran

AbstractThis study investigates the Danian siliciclastic successions in the East Tethys in the Kopet-Dagh Basin, NE Iran, which are composed of conglomerates, sandstones, shales and mudstones. The studied interval includes significant changes in sedimentary environments from alluvial to fluvial systems. The Danian siliciclastic formation is sandwiched between two marine carbonate sequences. The effects of the late Palaeocene sea transgression can be traced back to the precipitation of several types of carbonate cement in the studied siliciclastic formation. Several diagenetic features have been identified in the studied successions. The most observed features comprise physical and chemical compaction, cementation, alteration, dissolution, fractures and fillings. Some of the mentioned diagenetic processes, such as cementation, may be seen in a range of diagenetic environments and phases, such as early meteoric, low depth and deep burial, and late meteoric after the tectonic uplifting. The calcite cements considered in this study have been subdivided into four types. Some of the calcite cements, such as the rim, gravity pendant and meniscus, are classified as type one. They have formed around the rock grains and show no luminescence. The blocky and poikilotopic types have been grouped in type two. They are deposited between grains and exhibit dark luminescence. Type three cement consists of some of the blocky and poikilotopic cements that have formed amid grains and present a bright luminescence. Finally, type four comprises filled fractures which display a dark luminescence (blocky cement). Geochemical data revealed that the categorized cement types were precipitated in three diagenetic environments: early meteoric; burial; and late meteoric after the uplifting. The meteoric diagenetic environment is subdivided into vadose and phreatic meteoric. The burial diagenetic environment is subdivided into shallow burial and deeper burial. The qualitative petrographic method contributed to the initial recognition of the diagenetic features. The semi-quantitative cathodoluminescence method, the quantitative major and trace elements, and oxygen and carbon stable isotope analysis were utilized to evaluate the exact diagenetic processes and environments. Finally, the diagenetic sequence was reconstructed and depicted as diagenetic models and a paragenesis sequence. The data of this study can lay the foundation for future studies on the siliciclastic diagenesis in the studied basin.

Intraguild niche partitioning in granivorous birds from the late past

Niche partitioning is a widespread ecological strategy within trophic guilds, ensuring the coexistence of sympatric species by reducing interspecific competition. Stable isotope analysis of carbon and nitrogen and isotopic niche metrics (width and overlap) are used as a proxy to investigate niche partitioning among species of a guild. In our study, we investigated if niche partitioning was an ecological mechanism contributing to the coexistence of granivorous birds from the same geographic region along time, employing an isotopic approach. We sampled and isotopically analyzed (δ13C and δ15N values) wing feathers from 58 specimens of granivorous birds collected between 1900 and 1966 in southeastern Brazil. We grouped birds according to the main habitat type used by them (forest: Cyanoloxia brissonii, Leptotila rufaxilla, and Leptotila verreauxi; and grassland: Columbina squammata and Sicalis flaveola). We used the Isotopic Richness (IRic) metric to measure the isotopic niche width and the Isotopic Similarity (ISim) and Isotopic Nestedness (INes) metrics to measure the niche overlap between groups and species. The results of low isotopic niche overlap suggest that common granivorous birds had a clear niche partitioning in southeastern Brazil in the late past, especially through foraging in distinct habitat types (forest and grassland; ISim ​= ​0.1, INes ​= ​0.2). Niche overlaps in almost all species-by-species comparisons were low (ISim ≤0.3, INes ≤0.4), except between C. brissonii and L. verreauxi (ISim ​= ​0.6, INes ​= ​1.0). These results suggest that these birds, belonging to the same trophic guild, coexisted through niche and resource partitioning. Despite being considered a plastic trophic guild, the isotopic niche partitioning among granivorous birds indicates that each of these species uses a set of specific resources and habitats. This raises an ecological concern about the homogenization of landscapes across the Neotropics, oversimplifying food resources and habitats to granivorous birds.

Feeding ecology of coexisting Heermann’s gull (Larus heermanni) and elegant tern (Thalasseus elegans) chicks, based on stable isotope measurements

The Heermann’s gull and the elegant tern are considered Near Threatened by the IUCN Red List of Threatened Species and under special protection under Mexican environmental law. Close to 95% of the world populations of both species breed on Isla Rasa (Gulf of California). As both species breed on the same island, competition for trophic resources can be expected to be high. Here, the feeding ecology of chicks of both species, as well as the contribution by prey species provided by adults, was studied using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis in 3 consecutive breeding seasons (2017, 2018, and 2019). Results of the stable isotope analysis revealed that although some segregation in the δ13C and δ15N values exists between both species, isotopic mixing model outputs indicated that fishes were the most important prey group for both. However, at the prey species level, the most important prey consumed by Heermann’s gulls were northern anchovy, Pacific sardine, and Pacific mackerel, followed by pelagic crab, whereas elegant terns consumed mainly northern anchovy. The trophic width estimated with the stable isotope values during 2017 and 2019 was higher for the Heermann’s gull than for the elegant tern. In contrast, for 2018, the trophic width of the elegant tern was higher than that of the Heermann’s gull. In addition, both species showed a high degree of trophic width overlap during 2017 and 2019 (overlap probability 0.67 and 0.79, respectively). These results highlight the ability of the Heermann’s gull to redirect its food intake to what might be the most accessible prey groups, a feeding strategy that allows the coexistence.

Interspecies differences in food sources for the tropical callichirid shrimp Neocallichirus spp. on San Salvador Island, Bahamas

At least 4 species of callichirid shrimp coexist in the shallow marine settings of San Salvador Island, an isolated, small platform of the all-carbonates Bahama Archipelago, implying that interspecific competition or trophic niche segregation occurs between these shrimp species. Carbon and nitrogen stable isotope analyses were conducted on soft tissues of 3 callichirid species, Neocallichirus cacahuate, N. grandimana, and N. maryae, to determine the food sources for each species. These analyses revealed that the isotopic trophic niches for these 3 species do not overlap. The most important food source for all 3 species was manatee grass Syringodium filiforme. The second most important food source for N. cacahuate and N. grandimana was drifting seaweed Sargassum sp., whereas that for N. maryae was turtle grass Thalassia testudium. These food-source adaptations likely contribute to the high species diversity of callichirid shrimp in tropical settings such as those found on San Salvador Island.

Disentangling the impact of anthropogenic and natural processes on the environment in a subtropical subalpine lake catchment in northeastern Taiwan over the past 150 years

Human activities impose significant changes on sedimentation processes and vegetation cover within lake catchments. However, the needed time for an anthropogenically disturbed natural state to be reversed back to its natural state by environmental protection programs is still ambiguous. Here we employ a multi-proxy approach to delineate major environmental disturbances such as logging and forest fires on the catchment in Cueifong Lake, a subtropical subalpine lake in northeastern Taiwan. X-ray Fluorescence (XRF) core scanning, bulk total organic carbon (TOC), bulk total nitrogen (TN), stable carbon isotope (δ13Corg) analysis, and macro-charcoal counting were utilized to reconstruct changes in the catchment environment based on a sediment core from Cueifong Lake. The results show that the element content changed distinctly around 1975 CE, which coincided with the onset of profound deforestation in the lake vicinity recorded in historical documents and aerial photos. After the cessation of the logging event, the detrital input increased, accompanied by decreasing C/N ratios and increasing δ13Corg values. This suggests that increased terrestrial nutrient input promoted algae growth. After the deforestation phase, our results imply a gradual recovery of elemental composition in the catchment environment. By extrapolating the XRF element records, we suggest that it might take >50 years for the sedimentary regime to reach its pre-logging baseline. In contrast to the depositional system, the C/N and δ13Corg shifted significantly - potentially irreversibly - towards an algae-dominant environment instead of recovering to the pre-logging condition. This could be due to both 1) the changes in the different vegetation species used for reforestation and/or 2) anthropogenically introduced fishes in the 1980s. This study proposes the first assessment of the needed recovery time for subtropical Asian subalpine forests after large-scale logging activity and thus provides an apparent reference for policy decisions on natural resource development and environmental protection.

Millennial-scale drivers of small mammal isotopic niche dynamics in southern California

Quantifying the niche of contemporary and fossil organisms is key to identifying the primary factors driving species and community dynamics through time, in particular teasing apart abiotic and biotic drivers of change. However, niche quantification can be difficult due to short time spans (for contemporary systems), time averaging (for fossil systems), and incomplete information on different aspects of ecology and environment (for both contemporary and fossil systems). Here, we use stable isotope analyses coupled with specimen-level radiocarbon dating from the Rancho La Brea Tar Pits in Los Angeles, California to examine niche dynamics over the last >55,000 years. We sampled over 100 specimens of small and mid-sized mammals, mostly sciurids (squirrels) and leporids (rabbits), from Rancho La Brea to quantify their isotopic niche, track niche changes through time, and identify probable cause(s) of those changes. Individual specimens were radiocarbon dated and niches were quantified from stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of fossil collagen to track individual isotopic niches at precise points in time. Overall, sciurids and leporids exhibit different isotopic signals, suggesting niche variation among taxa. Comparison of animals during the Pleistocene versus the Holocene reveals overall greater δ13C values and greater δ13C and δ15N isotopic niche breadth among Holocene individuals, suggesting that small mammal resource use changed from the last glacial to current interglacial period. Evaluating the isotopic data continuously through time against a high-resolution regional paleoclimate record shows that climate contributed to small mammal niche variation over the last 55,000 years in the Los Angeles Basin. These findings reveal the complexity of long-term abiotic and biotic forcings on organismal niches and emphasize the importance of scale and data resolution when quantifying and interpreting (paleo)ecological patterns and processes.

Galápagos tortoise stable isotope ecology and the 1850s Floreana Island Chelonoidis niger niger extinction

A consequence of over 400 years of human exploitation of Galápagos tortoises (Chelonoidis niger ssp.) is the extinction of several subspecies and the decimation of others. As humans captured, killed, and/or removed tortoises for food, oil, museums, and zoos, they also colonized the archipelago resulting in the introduction of invasive plants, animals, and manipulated landscapes for farming, ranching, and infrastructure. Given current conservation and revitalization efforts for tortoises and their habitats, here we investigate nineteenth and twentieth century Galápagos tortoise dietary ecology using museum and archaeological specimens coupled with analysis of carbon (δ13Ccollagen and δ13Capatite), nitrogen (δ15N), hydrogen (δD) and oxygen (δ18Oapatite) stable isotopes and radiocarbon dating. We identify that Galápagos tortoise diets vary between and within islands over time, and that long-term anthropogenic impacts influenced change in tortoise stable isotope ecology by using 57 individual tortoises from 10 different subspecies collected between 1833 and 1967—a 134-year period. On lower elevation islands, which are often hotter and drier, tortoises tend to consume more C4 vegetation (cacti and grasses). Our research suggests human exploitation of tortoises and anthropogenic impacts on vegetation contributed to the extinction of the Floreana Island tortoise (C. n. niger) in the 1850s.

Multi-origin authigenic calcite controlled by the depositional environment and fluid−rock interactions in the Triassic siliciclastic strata, Junggar basin, NW China

Authigenic calcite records geologic fluid activities in sedimentary rocks, and its origin varies with changing sedimentary environments and fluid−rock interactions. This study investigated authigenic calcite with multiple origins in the Triassic siliciclastic strata of the petroliferous Mahu Sag, Junggar Basin, NW China. Detailed core logging was followed by lithological studies including optical, scanning electron and cathodoluminescence microscopic observations together with geochemical analyses of major elements and stable carbon and oxygen isotopes. The results show that there are three stages of calcite in the Baikouquan Formation with significantly differential MnO contents (average = 0.94%, 3.87%, 7.84%, respectively) and obviously negative δ13C values (−57.5‰ to −13.9‰, VPDB). It reflects the evaporation during deposition, and oxidation of hydrocarbon in oxidizing diagenetic environment. Extensive feldspar dissolution promotes the precipitation of late-stage calcite. There are two stages of calcite in the Karamay Formation and Baijiantan Formation. The positive correlation of their MgO and FeO contents reflects the alteration of volcanic materials in the strata. For the early-stage calcite, the low MnO contents (average = 0.50% and 0.61%) and positive δ13C values (>−10‰), demonstrate the paleo-meteoric water input. While the high MnO contents (average = 4.59%) and negative δ13C values (−25‰ to −10‰) of the late-stage calcite in the Karamay Formation indicate hydrocarbon charging and subsequent decarboxylation of organic acid, accompanied by feldspar dissolution. The late-stage recrystallization calcite of the Baijiatan Formation inherits the MnO and carbon isotopic characteristics of the early-stage calcite. This study shows that authigenic calcite is an effective recorder of sedimentary environment and fluid−rock interactions in siliciclastic strata. It enhances the heterogeneity of siliciclastic strata and is beneficial to hydrocarbon accumulation in lithological reservoirs.

Isotopic niche partitioning of co-occurring large marine vertebrates around an Indian ocean tropical oceanic island

Tropical oceans host a high diversity of species, including large marine consumers. In these oligotrophic ecosystems, oceanic islands often favour the aggregation of species and biomass as they provide feeding opportunities related to the mechanisms of island mass effect. As such, the waters surrounding La Reunion (Southwest Indian Ocean) host seabirds, large pelagic teleosts, elasmobranchs, delphinids and sea turtles. Isotopic niche partitioning and comparison of trophic levels among these species (n = 21) were investigated using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis. Overall, δ13C values were highly variable among taxa, indicating that the species exploit multiple foraging habitats along a coast-open ocean gradient. Overlap in δ15N values was limited, except for teleost species, the two species of sea turtles and two species of delphinids, the Indo-pacific bottlenose dolphin (Tursiops aduncus) and the Spinner dolphin (Stellena longirostris). Stable isotope analyses of samples collected over a 9-years period on different tissues with different integration times provide a consistent picture of the structure of the community of large marine vertebrates species around La Reunion and highlight the underlying mechanisms to limit the competition between species. The wide range of isotopic values confirms that large marine vertebrates have different trophic roles in coastal marine food webs around this oceanic island, which limits their potential of competitive interactions for resources.

Contrasting Male and Female Dietary Life Histories: A Case Study at an Ancestral Muwekma Ohlone Heritage Site in San Jose, California

ABSTRACT: Stable carbon and nitrogen isotope analyses of bones and teeth at the ancestral heritage Muwekma Ohlone site of Yakmuy ́Ooyákma-tka (“Place of the East Ridge Site”; CA-SCL-215) reveal significant differences in the dietary life history of males and females. Overall, isotope data indicate that site inhabitants were primarily dependent on low-trophic-level foods, likely plants, and minor amounts of marine food for their main source of dietary protein. From tooth dentin serial samples, we found that males and females were similar for δ13C in early childhood (age 1–9 years), but boys were elevated in δ15N by 0.6–1.0‰ relative to girls, indicating boys were accessing slightly greater amounts of higher-trophic-level foods, such as meat from game. The sex-biased difference in δ15N diminishes during the second decade of life, as female δ15N values increase and become equal to males. However, a difference in δ13C emerges during the second decade: female δ13C values are elevated relative to males. This could indicate that teenage females consumed higher amounts of low-trophic-level, marine-derived protein, such as shellfish. During later adult years the difference in δ13C disappears, while males again show an increase in δ15N relative to females. Although these differences are small, they reveal important sex-biased life history patterns during childhood and adulthood in this ancient community.

The Late Migration Period Cemetery at Drnholec (Břeclav District, Czech Republic) / Pohřebiště z konce doby stěhování národů z Drnholce (okres Břeclav, ČR)

The authors present part of a burial ground of the Late Migration Period in Drnholec - Pod sýpkou (Břeclav district, Czech Republic), where seven graves were discovered in 2016 and 2017. The grave goods were identified, by typological analysis, as Langobardian/Lombardian. The authors argue that even a small part of a cemetery with a limited number of graves can bring important new data and open strategic questions, challenging traditional interpretations. The paper aims to present the results of excavation in the light of archaeological, anthropological and zooarchaeological perspectives. Archaeological part is focused on presenting the grave units and the cemetery as a contextual unit. Stylistic and typological analysis of grave goods, radiocarbon dates and probability modeling were used to establish the chronology of the cemetery. Anthropological and palaeopathological examinations were accompanied with buccal dental microwear analysis and tooth cementum annulation (TCA) which provide information about diet and age-at-death estimation. Zooarchaeological analysis was mainly driven by the find of a mule skeleton. In addition to skeletal expertise, Nitrogen and Carbon stable isotopes analyses were also applied. The authors set out their thoughts, based on material and bibliographical study, on the problem of classifying and understanding the cultural and ethnic identity of the Migration Period populations.

From Forests to the Coast - Multidisciplinary Investigation of Human Adaptations at the Mini-athiliya Shell Midden, Sri Lanka

Over the last three decades, Sri Lanka has risen to international prominence as a key area for exploring past forager adaptations. Much of this discussion has focused on the lowland rainforests of the Wet Zone of the island, and their preservation of the earliest fossils of our species, bone tools, and microlithic technologies in the region ca. 45,000 years ago. It has been recognized that the northern and southern coasts of Sri Lanka represent crucial locales for studying human occupation and adaptation through the Pleistocene and Holocene. Here, we revisit the important shell midden site of Mini-athiliya (dating to ca. 4,000 cal. years BP), on the southern coast of Sri Lanka, which has yielded human remains alongside microlithic stone tools and animal remains. We present a comparative analysis of body size variation of the human remains belonging to the HMA 6 adult skeleton from Mini-athiliya with a wider database of foragers to investigate local adaptations. We also apply stable carbon and oxygen isotope analysis to the tooth enamel of four other individuals documented at Mini-athiliya in order to determine their dietary reliance on forest, grassland, or coastal resources. Together, our results highlight that, rather than a clear distinction between earlier forest adaptations and later coastal specialisation, the Mini-athiliya individuals provide evidence for a plastic spectrum of ecological adaptation. We argue for continued research on how human populations in different parts of the island interacted and adapted to its diverse tropical settings across space and time.

Isotopic Niche and Trophic Position of the Invasive Portunid Portunus segnis Forskål, (1775) in Elounda Bay (Crete Island, Eastern Mediterranean)

There is a growing recognition that an advanced understanding of the trophic characteristics of an invasive consumer can provide important information on its ecological impact. In recent years, the blue swimming crab Portunus segnis, one of the earliest Lessepsian invaders, has considerably expanded its distribution range in the Mediterranean Sea, yet, its trophic habits in invaded areas remain scarcely investigated. In this study, we used carbon and nitrogen stable isotopes analysis (SIA) to determine the trophic position and isotopic niche of the crab compared with other representatives of the flora and fauna occurring in Elounda Bay (Crete). P. segnis showed a trophic position of 3.9, higher than the values determined by SIA or conventional gut content analysis in other areas of the Mediterranean Sea or in the native range. Crab specimens showed a high inter-individual variability in both δ13C and δ15N values; further analysis indicated negligible differences in the isotopic niche of adult males and females. Conversely, δ15N values were significantly related to the size of the specimens, ultimately suggesting an ontogenetic dietary shift. This study represents the first attempt to characterize the trophic habits of the blue swimming crab in the context of an invaded food web and may contribute to the implementation of long-term management strategies of control and mitigation of its ecological impact.

Stable carbon and nitrogen isotope analyses of human and animal skeletal remains unearthed at Zengpiyan and Dayan sites in Guilin

Abstract Stable carbon and nitrogen isotope analyses, together with AMS radiocarbon dating of human and animal bones unearthed from the Zengpiyan and Dayan sites in Guilin of Guangxi suggest a relatively stable environment dominated by C3 plants, which was supplemented by a small amount of C4 plants. Although inhabitants of the two Neolithic sites relied mainly on freshwater resources, they differed significantly in their dietary structure from the Early to Middle phases. The Early Neolithic inhabitants (n=6) consumed similar foods in their diet. By contrast, the Middle Neolithic people (n=11) procured and consumed more terrestrial foods from diverse sources. The transition to a broad dietary spectrum was likely interlinked to the shifts in population structures, environmental adaptation, and foraging ranges.

Using Stable Isotope Analyses to Assess the Trophic Ecology of Scleractinian Corals

Studies on the trophic ecology of scleractinian corals often include stable isotope analyses of tissue and symbiont carbon and nitrogen. These approaches have provided critical insights into the trophic sources and sinks that are essential to understanding larger-scale carbon and nitrogen budgets on coral reefs. While stable isotopes have identified most shallow water (<30 m) corals as mixotrophic, with variable dependencies on autotrophic versus heterotrophic resources, corals in the mesophotic zone (~30–150 m) transition to heterotrophy with increasing depth because of decreased photosynthetic productivity. Recently, these interpretations of the stable isotope data to distinguish between autotrophy and heterotrophy have been criticized because they are confounded by increased nutrients, reverse translocation of photosynthate, and changes in irradiance that do not influence photosynthate translocation. Here we critically examine the studies that support these criticisms and show that they are contextually not relevant to interpreting the transition to heterotrophy in corals from shallow to mesophotic depths. Additionally, new data and a re-analysis of previously published data show that additional information (e.g., skeletal isotopic analysis) improves the interpretation of bulk stable isotope data in determining when a transition from primary dependence on autotrophy to heterotrophy occurs in scleractinian corals.

The Truth of Unusual Deaths under Military Expansion: Evidence from the Stable Isotopes of a Human Skull Ditch in the Capital City of the Early Shang Dynasty.

The site of Zhengzhou Shang City (ca. 1509-1315 cal. BC) was the capital of the early Shang Dynasty in China. Archaeological excavations have unearthed a ditch containing approximately one hundred unusual dead human skulls in the rammed-earth foundations of the palace area. The identity and origin of the skulls have long been disputed. In this work, strontium, carbon and nitrogen stable isotope analyses were carried out on 11 human skulls and 1 tooth from the ditch, as well as on 11 human bones, 11 human teeth from the ordinary tombs and 10 pig teeth from the Zhengzhou Shang City site. We determined that, in Zhengzhou Shang City, the local strontium isotope ratio ranges from 0.711606 to 0.711884, and ordinary inhabitants consumed mainly C4 plants supplemented by C3 plants. Moreover, humans buried in the ditch have 87Sr/86Sr values from 0.711335 to 0.711741 and consumed only C4 plants. Combining the isotopic data with the archaeological and cultural context, it is concluded that the unusual human skulls in the ditch are most likely those of prisoners of war captured by the central forces conquering the Xiaomintun area of Anyang in the early Shang Dynasty. The results provide valuable insight into the history of violence and military warfare in the early Chinese dynasty.

Multiple trophic pathways support fish on floodplains of California's Central Valley.

We used compound-specific isotope analysis of carbon isotopes in amino acids (AAs) to determine the biosynthetic source of AAs in fish from major tributaries to California's Sacramento-San Joaquin river delta (i.e., the Sacramento, Cosumnes and Mokelumne rivers). Using samples collected in winter and spring between 2016 and 2019, we confirmed that algae are a critical component of floodplain food webs in California's Central Valley. Results from bulk stable isotope analysis of carbon and nitrogen in producers and consumers were adequate to characterize a general trophic structure and identify potential upstream and downstream migration into our study site by American shad Alosa sapidissima and rainbow trout Oncorhynchus mykiss, respectively. However, owing to overlap and variability in source isotope compositions, our bulk data were unsuitable for conventional bulk isotope mixing models. Our results from compound-specific carbon isotope analysis of AAs clearly indicate that algae are important sources of organic matter to fish of conservation concern, such as Chinook salmon Oncorhynchus tshawytscha in California's Central Valley. However, algae were not the exclusive source of energy to metazoan food webs. We also revealed that other sources of AAs, such as bacteria, fungi and higher plants, contributed to fish as well. While consistent with the well-supported notion that algae are critical to aquatic food webs, our results highlight the possibility that detrital subsidies might intermittently support metazoan food webs.