Stable Isotope Ratios Research Articles

Effect of starvation on physiological and survival traits of Mimachlamys varia (Linneaus, 1758)

In order to better understand Mimachlamys varia (Linneaus, 1758) response to nutritional stress, a controlled-condition experiment was conducted. Two scallop batches (i.e. juveniles and adults) were completely food-deprived for 3 months. Changes in mass and energy content of tissues (adductor muscle, digestive gland, rest of the soft tissues), as well as stable carbon and nitrogen isotope ratios of the adductor muscle were monitored weekly. Both batches exhibited a 3-phase response to starvation. For adults, phase 1, was characterized by a fast loss in mass, an δ15N-enrichment, a stable calorific power, and a low mortality, corresponding to a transitional stage associated with protein-storage consumption. Phase 2 (day 28–42) exhibited a stabilization of mass and δ15N values, coinciding with a digestive gland calorific power drop and an acceleration in mortality. This corresponds to a “protein sparing” stage where highly energetic fuel such as lipids, which are stored especially in the digestive gland in pectinids, are consumed in priority. Juveniles exhibited a distinct response characterized by a significant mass loss and an increase in calorific power during the first phase (day 0–28). This body weight decrease may involve the remobilization of low-caloric biochemical compounds (e.g. proteins) using the structure as internal fuel, thus limiting somatic maintenance costs. During the second month, body mass and calorific power stabilized, indicating a “protein sparing” stage. In a third phase for both age classes, mass decreased again together with a sharp increase in mortality: essential structure was ultimately remobilized. The survival rate of juveniles was higher than that of adults during the first two months of the experiment (97% and 64%, respectively). Although the time required for starvation to deplete of half the cohort is higher for juveniles than for mature individuals, increase in mortality rate after reaching the “Point of No Return”, (e.g. the beginning of the last phase) was higher in juveniles than in adults. These results highlight the potential impacts of starvation at the population level, beyond the direct impact on individual survival. For instance, individuals may not effectively contribute to reproduction during the spawning period if exposed to a prolonged winter starvation episode. In particular, since highly energetic compounds stored in the digestive gland are often used as fuel to initiate gametogenesis in pectinids. Similarly, decrease in somatic weight in juveniles may delay their sexual maturity and hence their ability to contribute to population reproductive potential.

Trophic history of Hawaiian green turtles as revealed by stable isotope ratios (δ13C, δ15N and δ34S) in the bones of museum specimens

Abstract Understanding consumer trophic status and long‐term dietary changes can yield information about impacts of altered habitats on their ecology. In Hawai'i, coastal ecosystems have been significantly modified by the introduction of invasive seaweeds and mangroves, high nutrient load and overfishing, but so far, much is still to be understood about how these changes have affected the green turtle (Chelonia mydas). This study analyzed stable carbon, nitrogen, and sulfur isotope ratios in the bone tissue of modern and museum specimens of green turtles collected from 1901 to 2020 in Oahu and the North‐western Hawaiian Islands to understand how their isotopic niche has changed through time, a crucial step towards restoring the ecological role of a formerly decimated species. The standard ellipse size and the total area of the convex hull of the isotopic niche of green turtles in three periods (1901–1951, 1992–2008, and 2018–2020) were calculated. The stable isotope values of ancient green turtles (1901–1951) suggest that they relied heavily on macroalgae even before the introduction of exotic species and eutrophication promoted the development of algal pastures. However, a few ancient green turtles relied heavily on seagrasses, and others complemented their macroalgae‐based diets with significant amounts of animal matter. Such diet specialists were missing from the sample of current green sea turtles, suggesting that these foraging strategies are less common or perhaps even absent in the current population. The results suggest that green turtles have converged on the use of the most abundant resource, red macroalgae, likely because of the homogenization and simplification of coastal habitats and food webs due to anthropogenic influences. Restoring the population size of herbivorous fishes and a more diverse ecosystem structure may be necessary to recover the array of trophic strategies formerly present in the Hawaiian green turtle population.

In situ precise determination of stable Mo isotope ratios in molybdenite by femtosecond LA-MC-ICP-MS

We developed a new method for in situ measurement of Mo stable isotope ratios using femtosecond laser ablation coupled with MC-ICP-MS. Additionally, experiments were conducted on nine natural molybdenite samples from different ore deposits in China.

Multi‐Proxy Evidence for Atlantic Meridional Overturning Circulation (AMOC) Weakening During Deglaciations of the Past 150,000 Years

AbstractDespite decades of research, the cause of deglaciations is not fully understood, leaving a critical gap in our understanding of Earth's climate system. During the most recent deglaciation (Termination I (T I)), abrupt declines in the stable carbon isotope ratio (δ13C) of benthic foraminifera occurred throughout the mid‐depth (1,500–2,500 m) Atlantic. The spatial pattern in δ13C anomalies was likely due to Atlantic Meridional Overturning Circulation (AMOC) weakening and the accumulation of respired carbon, which also yields negative excursions in carbonate ion concentration (). To investigate whether a similar pattern occurred during prior deglaciations, we developed δ13C and records from 1,800 and 2,300 m water depth in the Southwest Atlantic spanning the last 150 ka. The new records reveal negative δ13C and anomalies during Termination II (TII) and the smaller deglaciations of Marine Isotope Stages (MIS) 4/3, 5b/a, and 5d/c, suggesting AMOC weakening is a common feature of deglaciation. The anomalies are more pronounced in the shallower core following MIS 2, 4, and 6 and in the deeper core following MIS 5b and 5d. The depth‐dependent pattern is most likely due to shoaling of Northern Source Water during glacial maxima and deepening during interglacial intervals. Comparison of records from TI and TII suggests similar levels of carbon accumulation in the mid‐depth Atlantic. The Brazil Margin δ13C and results indicate the AMOC plays a key role in the series of events causing deglaciation, regardless of differences in orbital configuration, ice volume, and mean global temperature.

Growth and carbon turnover of Piaractus mesopotamicus Holmberg, 1887 (Osteicthyes: Characidae): contribution of extruded feed and natural food.

Piaractus mesopotamicus, is a fish usually farmed in semi-intensive systems with access to natural food and supplementary feed. This study evaluates effects of feed allowance on the productive performance, carbon turnover and proportions of nutrient (carbon) contribution of feed and natural food for the growth of pacu. Juvenile fish were stocked in fiberglass tanks and fed to 100, 75, 50, 25, 0% apparent satiety (ApS), with a practical, extruded (C4 photosynthetic pathway) feed in a randomized design trial (n=3); plankton production for simulated semi-intensive farming system condition was induced by chemical fertilization. A control treatment was set up in tanks devoid of natural food. Data on muscle stable carbon isotope ratios were used to study carbon turnover using a relative growth-based model. Low variation of the δ13C impaired fitting a turnover model curve for the 0 and 25 % ApS treatments. Fish of the 100% and 75% ApS treatments reached circa 95% and 82.85% of the carbon turnover, respectively. Extruded feed was the main nutrient source for the growth of pacu in the semi-intensive, simulated farming condition. The current study contributes to the knowledge of the relationship between feeding rates and carbon turnover rates in the pacu muscle.

Dissolved nitrogen uptake versus nitrogen fixation: Mode of nitrogen acquisition affects stable isotope signatures of a diazotrophic cyanobacterium and its grazer.

Field studies suggest that changes in the stable isotope ratios of phytoplankton communities can be used to track changes in the utilization of different nitrogen sources, i.e., to detect shifts from dissolved inorganic nitrogen (DIN) uptake to atmospheric nitrogen (N2) fixation by diazotrophic cyanobacteria as an indication of nitrogen limitation. We explored changes in the stable isotope signature of the diazotrophic cyanobacterium Trichormus variabilis in response to increasing nitrate (NO3-) concentrations (0 to 170 mg L-1) under controlled laboratory conditions. In addition, we explored the influence of nitrogen utilization at the primary producer level on trophic fractionation by studying potential changes in isotope ratios in the freshwater model Daphnia magna feeding on the differently grown cyanobacteria. We show that δ 15N values of the cyanobacterium increase asymptotically with DIN availability, from -0.7 ‰ in the absence of DIN (suggesting N2 fixation) to 2.9 ‰ at the highest DIN concentration (exclusive DIN uptake). In contrast, δ 13C values of the cyanobacterium did not show a clear relationship with DIN availability. The stable isotope ratios of the consumer reflected those of the differently grown cyanobacteria but also revealed significant trophic fractionation in response to nitrogen utilization at the primary producer level. Nitrogen isotope turnover rates of Daphnia were highest in the absence of DIN as a consequence of N2 fixation and resulting depletion in 15N at the primary producer level. Our results highlight the potential of stable isotopes to assess nitrogen limitation and to explore diazotrophy in aquatic food webs.

Human diet of premodern mainland Japan: a meta-analysis of carbon and nitrogen stable isotope ratios

Human diet of premodern mainland Japan: a meta-analysis of carbon and nitrogen stable isotope ratios

Integrated approach for the isotope trophic position of black-tailed gull (Larus crassirostris) eggs over a decade: Combining stable isotopes of amino acids and fatty acids composition

Recently, compound-specific isotope analysis (CSIA) using the amino acid nitrogen stable isotope ratio (δ15NAAs) has been widely used for accurate estimation of trophic position (TP). In addition, a quantitative fatty acid signature analysis (QFASA) offers insights into diet sources. In this study, we used these techniques to estimate the TP for seabirds that rely on diverse food sources across multiple ecosystems. This allows for the proper combination of factors used in TP calculation which are different for each ecosystem. The approach involved the application of a multi-mixing trophic discrimination factor (TDF) and mixing β which is a Δδ15N between trophic and source amino acid of primary producer. Since the black-tailed gulls (BTGs) are income-breeding seabirds, which rely on energy sources obtained around their breeding sites, they and their eggs could be useful bioindicators for environmental monitoring. However, the ecological properties of BTGs such as habitats, diets, and TP are not well known due to their large migration range for wintering or breeding and their feeding habits on both aquatic and terrestrial prey. In this study, the eggs were used for estimating TP and for predicting TP of mother birds to overcome difficulties such as capturing birds and collecting non-invasive tissue samples. Eggs, sampled over a decade from three Korean islands, showed spatial differences in diet origin. Considering both the food chain and physiology of BTG, the TP of eggs was estimated to be 3.3–4.0. Notably, the TP was significantly higher at site H (3.8 ± 0.1) than at site B (3.5 ± 0.2), which indicated a higher contribution of marine diet as confirmed by QFASA. Using a reproductive shift of δ15NAAs, the TP of the mother birds was predicted to be 3.6–4.3, positioning them as the top predator in the food web. The advanced integration of multiple approaches provides valuable insights into bird ecology.

Effects of sampling time and location on the geographical origin traceability of protected geographical indication (PGI) Hongyuan yak milk: Based on stable isotope ratios

Hongyuan yak milk is a protected geographical indication (PGI) product of rich nutritional value, which is popular among consumers. Stable isotope ratio analysis (SIRA) is an effective way to protect the authenticity of the geographical origin of PGI products, and it is crucial to study the factors affecting stable isotopes. Firstly, we proved that the SIRA could be used to identify the geographical origin of Hongyuan yak milk, and that the identification accuracy in combination with δ13C and δ18O was 100 %. Secondly, we analyzed the effect of sampling selection on the stable isotopes of Hongyuan yak milk in practical applications, which showed that sampling time influenced the δ13C, δ2H, and δ18O, while the sampling locations did not. There were interactions between the effect of sampling time and location on δ2H and δ18O. These results provide a reliable method for identifying PGI products and also provide new guidance on sampling models.

Biology of kawakawa Euthynnus affinis in the East China Sea: Growth, reproduction, and stable isotope ratios

This study elucidated the age–growth relationship, maturation body size, and stable isotope ratios of kawakawa Euthynnus affinis in the East China Sea. A total of 396 individuals were collected, of which 266 were captured off the west coast of Kyushu and 130 around Okinawa. Ages were determined from otolith analysis, and the estimated von Bertalanffy growth functions were FLt = 1007{1 – exp[–0.107(t + 3.835)]} near Kyushu and FLt = 640{1 – exp[–0.381(t + 1.111)]} around Okinawa, where FLt is fork length (mm) at age t for ages 0.25 to 5. The estimated fork lengths of the fish near Kyushu were larger than those around Okinawa. The smallest fork length of a fish in the spawning stages was about 440 mm. Mature females and males were observed from May to October near Kyushu and from March to July around Okinawa. Females in the spawning stages were observed from July to September near Kyushu and from April to June around Okinawa. The δ15N of fish captured near Kyushu (12.39‰ ± 0.55‰, mean ± standard deviation) was higher than that of those captured around Okinawa (9.94‰ ± 1.39‰). This suggests that the kawakawa caught in each area occupy distinct habitats, although some mixing of individuals between the two habitats might occur.

Preservation of bone organic fraction is not predictive of the preservation of bone inorganic fraction when assessing stable isotope analysis sample quality control measures

Stable isotope analysis of carbon (C), nitrogen (N), hydrogen (H), and oxygen (O) of archaeological bone has become an increasingly common research method for interpreting human behavior in the past. However, diagenesis of skeletal material can invalidate stable isotope ratios, thereby compromising interpretations. We examine patterns of bone diagenesis using infrared spectroscopy of bone bioapatite samples in relation to indicators of organic preservation quality indicators. We assess crystallinity, an indicator of bioapatite preservation, using the infrared splitting factor (IR-SF) and carbonate content (carbonate to phosphate ratio, C/P) calculated from infrared spectra. We then test the assumption that if the organic fraction of bone is preserved, the mineral fraction will also be unaffected by postmortem chemical alteration. We analyzed 454 bone bioapatite and extracted bone organic sample pairs from modern, historic, and prehistoric humans. Consistent with previous studies, we observed a strong, statistically significant negative linear relationship between IR-SF and C/P (r = −0.855, p < 0.001). Modern bone bioapatite samples unaltered by diagenesis have low IR-SF and high C/P values. There was no significant association between the collagen yield or atomic C:N ratio and IR-SF or C/P values. The range of variation in IR-SF and C/P values for samples with organic yields between 0 and >20 percent spanned the range of modern bone bioapatite unaltered by diagenesis as well as bone bioapatite significantly affected by diagenesis. The lack of predictive patterning between bone inorganic and organic diagenesis suggests that the depositional context and site formation history play critical and independent roles in the organic and mineral fraction of bone. Thus, the preservation of the organic fraction of bone is not predictive of the preservation of the inorganic fraction (e.g., bioapatite).

Iron, Nickel, Copper, Zinc, and their stable isotopes along a salinity gradient in the Pearl River Estuary, southeastern China

Although the crucial role that dissolved trace metals (dTMs) play in both carbon cycling and climate have been revealed over the past three decades, much about the oceanic budgets of dTMs remains unknown. Rivers are one of the most important dTM sources to the ocean, and estuaries are a key interface between land and ocean. However, our understanding of how dTMs behave as they pass through the estuarine transition is limited, leading to uncertainties in estimating fluvial metal fluxes to the ocean and balancing oceanic dTM budgets. Alongside concentrations, metal stable isotopes offer an additional dimension to constrain estuarine processes, but data on metal isotopes in estuaries are scarce. Here we present dTM concentrations and their stable isotope ratios along a full salinity gradient in the Pearl River Estuary (PRE), southeastern China. Concentration data show a large apparent loss of dFe (86%) during estuarine mixing, moderate losses of dNi (13%) and dZn (36%), and nearly conservative behavior for dCu. However, examination of metal isotope data (δ56Fe, δ60Ni, δ65Cu, and δ66Zn) reveals more complex biogeochemistry, requiring either a two-stage scenario or a three-endmember mixing process. The two-stage process involves fractionation of dTM isotopes at low salinities, likely driven by particle adsorption and colloidal flocculation, followed by conservative mixing between intermediate-salinity estuarine waters and South China Sea waters. Alternatively, the three-endmember mixing process includes influences from riverine, oceanic endmembers, and external sources such as benthic flux and industrial activities, shaping dTM isotope distributions. Specifically, capturing δ56Fe fully proves challenging, yet it appears strongly influenced by inputs of benthic Fe within the PRE, characterized by dFe > 13 nmol kg−1 and δ56Fe < −0.80‰. δ60Ni and δ66Zn can be described by either two-stage or there-endmember mixing processes. In the former, the Rayleigh fractionation with αd-p of 1.00004 for δ60Ni and 1.0001 for δ66Zn, or the steady state fractionation with αd-p of 1.00005 for δ60Ni and 1.0002 for δ66Zn, could be derived to explain their patterns at low salinity, likely driven by colloidal flocculation. Additionally, a third source with dNi > 33 nmol kg−1 and δ60Ni > +1.26‰ and a third source with dZn > 13 nmol kg−1 and δ66Zn > +0.96‰, both influenced by human activities, could also shape the δ60Ni and δ66Zn patterns in the PRE, respectively. The description of δ65Cu is best achieved by a three-endmember mixing process, with the external source having dCu > 20 nmol kg−1 andδ65Cu < +1.3‰, indicative of processes like organic matter remineralization or discharge from wastewater treatment plant. Our study highlights the need for more extensive and detailed studies on estuarine settings to elucidate their potentially crucial role in global dTMs budgets.

Geographical verification of Pleuropterus multiflorus thunb. by functional compounds, stable isotope ratios, and multielement combined with machine learning methods

The dry roots of Pleuropterus multiflorus Thunb. (PM) have been traditionally utilized as functional foods and medicines China and various Asian countries. They are extensively cultivated in multiple provinces in China, with variations in prices and qualities. This study aims to investigate the regional characteristics of PM by 4 stable isotope ratios, 40 multielement and 16 functional compounds contents, using a total of 357 samples from 8 different geographical origins. Machine learning methods were developed to authenticating the geographical origins of PM, yielding the accuracy range from 94.44 % to 100 % in the test set. Notably, the protected designation of origin, Deqing PM, exhibited a high accuracy of 100 % in most models, A total of 30 significant prediction variables, encompassing 16 functional compounds, δ2H, 12 rare earth elements, and Cu, were identified. Additionally, the study identified altitude, high temperature, and dry or moisture index as the primary influenced environmental factors.

Detection of dilution due to turbulent mixing vs. precipitation scavenging effects on biomass burning aerosol concentrations using stable water isotope ratios during ORACLES

Abstract. The interaction between biomass burning aerosols and clouds remains challenging to accurately determine, in part because of difficulties using direct observations to account for influences on aerosol concentrations from precipitation scavenging and dilution due to air mass mixing and separating those signals from source contributions. The prevalence of mixing versus precipitation processes in air laden with biomass burning aerosol (BBA) in the southeast Atlantic lower free troposphere (FT) and marine boundary layer (MBL) is assessed during three observation periods (September 2016, August 2017, and October 2018) during the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) campaign. Significant sources of BBAs over the African continent combined with regional circulation patterns result in BBA-laden air flowing from the continent over the southeast Atlantic in the lower FT, then subsiding onto the semi-permanent stratocumulus cloud deck, and entraining into the MBL. This study is broken into two parts, first analyzing hydrologic histories of the BBA air in the lower FT and then carrying out a similar assessment in the underlying MBL. Both analyses leverage joint measurements of water concentration and its heavy isotope ratio, interpreted in the previously established (q, δD) phase space framework. For the lower-FT analysis, in situ observations (water concentration, water isotope ratios) in the lower FT are combined with satellite and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), global reanalysis data into simple analytical models to constrain hydrologic histories. We find that even simple models are capable of detecting and constraining the primary processes at play, e.g., distinguishing air masses that experienced moist convection and precipitation (likely over the continent) from those that underwent dry convection and turbulent mixing. Regression of the aircraft data onto a simple model of convective detrainment is used to develop a metric of total precipitation for the in situ measurements and then compared to an aerosol metric of black carbon scavenging also derived from the in situ measurements (the ratio of black carbon to carbon monoxide, BC/CO). There is a strong correlation between the two, suggesting black carbon scavenging has been detected and partially quantified, if only in a relative manner. In comparison, weak correlation is found between BC/CO and the total water concentration itself. The above method is expanded to test for entrainment and precipitation influences on BBA concentrations in the MBL. This is more difficult than the FT analysis since signals are subtle and limited by imperfect knowledge of the water and isotope ratios of the entrained air mass at cloud top. For some of the MBLs observed during 2016 and 2018, lower cloud condensation nuclei (CCN) concentrations occur in the sub-cloud layer coincident with isotopic evidence of precipitation, indicating aerosol scavenging, but more complex models are needed to produce definitive conclusions. For the 2017 observation period, with the highest sub-cloud CCN concentrations, there is no connection between precipitation signals and CCN concentrations, likely indicating the importance of different geographic sampling and air mass history in that year. Nonetheless, these findings along with the FT analysis suggest that utilizing isotope ratio signals may be an aid in addressing cloud–aerosol challenges. Especially for the FT case, these findings support the pursuit of more complex models combined with targeted in situ data to constrain BC scavenging coefficients in a manner which can guide model parameterizations, leading to improvements in the accuracy of simulated BC concentrations and lifetimes in climate models.

Early Neolithic pastoral land use at Alsónyék-Bátaszék, Hungary (Starčevo culture): New insights from stable isotope ratios

The earliest introduction of livestock (cattle, goats, sheep, pigs) into the Carpathian Basin was an important step towards farming expansion into continental Europe. This spread beyond the environments of the southern Balkans was accompanied by a reduction in the spectrum of cultivated crops, changes in the relative representation of different domestic animals, and, most likely, adaptations of husbandry practices. How the earliest farmers in the Carpathian Basin kept their domestic stock is still understudied. We explored early animal management and land use strategies at the Starčevo settlement at Alsónyék-Bátaszék, Hungary (Early Neolithic, ca. 5800–5600 cal BC). Settled at the intersection of wide alluvial plains, waterlogged meadows and marshes to the east, and forested hills to the west, early farmers at Alsónyék had a wide variety of options for nourishing their livestock. We performed stable isotope ratio analysis of bone collagen (n = 99; δ13C, δ15N) and tooth enamel (nteeth = 28, sequentially sampled for δ13C and δ18O) from wild and domestic animals to locate them in the landscape and investigate herding practices on a seasonal scale. The bone collagen isotope ratios mostly indicate feeding in open environments. However, results from the sequential analysis of cattle and sheep enamel suggest diverse dietary strategies for winters, including consumption of forest resources, consumption of summer hay and grazing in an open environment. Most pigs appear to have had herbivorous diets, but several individuals likely supplemented their diet with animal protein. Stable isotope ratio results from the Lengyel phase at Alsónyék (ca. 4800–4300 cal BC) suggest more access to animal protein for pigs, and feeding in more open areas by wild boar, red deer and cattle compared to the Starčevo phase. This study’s results demonstrate considerable variability in early animal husbandry practices at Alsónyék.

An Assessment of Mangrove Ecosystem Condition by Foliar Stable Nitrogen Isotope Ratio Index in Okinawa, Japan

Despite providing valuable ecosystem services, mangroves are endangered under the recent global natural as well as anthropogenic changes. Conservation of mangroves is now one of the pillars of Sustainable Development Goals (SDG) 2030. An assessment of mangrove is essential before initializing any conservation strategy. This paper aimed to assess the ecosystem conditions of mangroves and the relative changes in ecosystem conditions from the natural background under different scales of anthropogenic interruption in Okinawa Prefecture, Japan. To assess mangrove’s ecosystem condition, foliar stable nitrogen isotope ratio (δ15N) of mangroves is used as ecosystem monitoring indicator. Whereas, a difference index (DI) of mangrove foliar δ15N is established to compare the relative deviation in ecosystem conditions of anthropogenically impacted mangroves from reference mangroves. Results showed that the mean foliar δ15N values of Bruguiera gymnorrhiza, Kandelia obovata, and Rhizophora stylosa on Okinawa Island (Is.) are 5.12 ± 2.32‰, 7.54 ± 2.85‰ and 7.09 ± 3.29‰, respectively, on Iriomote Is., 1.83 ± 1.93‰, 2.01 ± 0.31‰ and 1.04 ± 2.38‰, respectively, and on Ishigaki Is., foliar δ15N values of Bruguiera gymnorrhiza and Rhizophora stylosa are 5.23 ± 3.33‰ and 6.00 ± 3.63‰, respectively. A range of negative to positive values from -0.54 to 3.66 of DI indicates different level of changes in ecosystem conditions of the mangroves compared to the reference sites, which is set at zero. A significant negative correlation between DI values and the forest area ratio of the watersheds has been observed. It indicates that the forest cover is the driver of maintaining pristine condition of an ecosystem. Findings of the study recommended that Todoroki and Manko mangrove watersheds in Okinawa, Japan should be taken into consideration for necessary conservation on priority basis.

Relationship between stable cesium concentration and body size of Japanese flounder Paralichthys olivaceus and the effect of a size-dependent shift in diet.

To understand the relationship between the radioactive cesium (Cs) concentration in muscle of Japanese flounder Paralichthys olivaceus and the species' biological characteristics (size, sex, and age) under conditions of ecological equilibrium (i.e., distributed among ecosystem components over sufficient time, and with nearly constant ratios of Cs concentration in organisms to the concentration in water) as existed before the accident at the Fukushima Dai-ichi Nuclear Power Station (FDNPS), Japan, in 2011, we examined stable Cs, as it is thought to exist in equilibrium in the environment and behave similarly to radioactive Cs in aquatic animals. The concentration of stable Cs in 241 P. olivaceus (range 216-782 mm total length [TL]) collected in Sendai Bay, approximately 90 km north of the FDNPS, in June-July 2015 was expressed as an exponential function with size as an independent variable; the results show the concentration of stable Cs doubled with an increase in TL of 442 mm. Next, to evaluate the cause of the size-dependent change in stable Cs concentration, we examined 909 individuals (200-770 mm TL) collected in September 2013-July 2015 to determine their feeding habit based on size. Analysis of the frequency of occurrence of prey organisms in stomach contents showed that sand lance Ammodytes japonicus (55-180 mm standard length [SL]) was the most consistently consumed across size classes. Analysis on a wet-mass basis showed that A. japonicus and anchovy Engraulis japonicus (65-130 mm SL) were the main food of P. olivaceus sized 200-599 mm TL, whereas chub mackerel Scomber japonicus (120-230 mm SL) and two species of flatfishes (180-205 mm SL) were abundant in the diet of P. olivaceus sized ≥600 mm TL. All these prey items were presumed to have similar concentrations of stable Cs. Based on the above, the effect of diet on the relationship between stable Cs in muscle and fish size was considered negligible. That the diet of P. olivaceus largely did not change with size was also confirmed by C and N stable isotope ratios in P. olivaceus and their prey species. Therefore, the Cs-size relationship is probably determined by changes in the balance between the rate of Cs intake from food and seawater and the excretion rate during growth, both of which change as functions of body mass. Values of stable Cs concentrations among environmental components and animals appear to be a valid indicator for understanding the radioactive Cs distribution in the marine environment and aquatic animals under the equilibrium state, as existed before the 2011 nuclear accident.

Changes in the Baltic Sea coastal food web: A case study on the invasion of Round goby Neogobius melanostomus (Pallas, 1814)

We used dynamic food web modeling to assess the trophic effects of the increased abundance of the invasive Round goby Neogobius melanostomus (Pallas, 1814) on network flows and trophic levels in the open coastal zone of the south-eastern Baltic Sea. Available data on biomass and diet changes were incorporated in the Ecopath with Ecosim model, which estimated non-available data. Flow changes were related to Round goby predation on Blue mussels Mytilus edulis (Linnaeus, 1758), as well as to its contribution to the diet of piscivorous groups. The model presented changes in Long-tailed duck Clangula hyemalis (Linnaeus, 1758) biomass and consumption and an increase in its trophic level. However, the results showed no changes in the trophic level of other compartments nor average path length, the trophic level of fishery catch or the average trophic level of the community. This demonstrates the network's ability to maintain flows within given input and retain stability under conditions of changes induced by an invasive species. In regards to validating the model results in the representation of the study, trophic levels estimated by the dynamic model strongly correlated to ones calculated from stable nitrogen isotope (δ15N) ratios of consumers.

Large shift in the upper water column characteristics of the west-central Bay of Bengal during the last glacial-interglacial transition

The upper water column structure in the Bay of Bengal is strongly influenced by the monsoon and associated processes. However, the records of variation in water column stratification during different monsoon phases, are scarce from this region. Here, we have reconstructed the variation in monsoon induced upwelling, mixed layer and thermocline during the last glacial-interglacial transition, by using the relative abundance of mixed layer and thermocline dwelling planktic foraminifera, relative abundance of Globigerina bulloides and the stable oxygen isotopic ratio (δ18O) of surface dwelling Globigerinoides ruber. We report a weaker upwelling during the last glacial interval and late Greenlandian-Northgrippian Age, and strong upwelling during the deglaciation and Meghalayan Age. The intense upwelling shoaled the thermocline during the early glacial interval, last glacial maximum, late deglaciation and the Meghalayan Age. The mixed layer depth increased during the early deglaciation and Late Greenlandian-Northgrippian due to the reduced upwelling and stronger winter monsoon. The shift in the position of the core site with respect to the low salinity coastal currents, due to the rising sea level, also influenced the upper water column structure in the west-central Bay of Bengal. Therefore, the reorganization of the upper water column structure in the west-central Bay of Bengal, on the glacial-interglacial time scale, was mainly influenced by a combination of the upwelling, fresh water influx, sea level and winter monsoon.

Early Byzantine fish consumption and trade revealed by archaeoichthyology and isotopic analysis at Sagalassos, Turkey

We document the dietary and economic role of fish at Sagalassos, a town in ancient Pisidia (southwest Turkey) for the Early Byzantine period (c. 550 – 700 CE) through a detailed analysis of animal bones and stable isotopes. The role of fish in the diet is quantified, for the first time, based on large samples of sieved remains retrieved during the excavation of a number of spaces in an urban residence. The table and kitchen refuse from the mansion shows that fish was a regular part of the diet. However, past isotopic work focused on human individuals excavated in the city’s necropolises, slightly postdating the faunal remains examined, did not reflect this consumption of aquatic food. The studied assemblage comprises at least 12 different fish taxa, including five marine species, a Nilotic fish and six Anatolian freshwater species. Since the origin of the freshwater fishes could not be unambiguously determined by zoogeography alone, we analyzed carbon, nitrogen and sulphur stable isotope ratios in archaeological fish bones from Sagalassos as well as in bones of modern fish collected at different sites in Turkey. We show that most freshwater fish, i.e., all cyprinid species, came from Lake Eğirdir. No evidence was found for fish from the local Aksu River basin. The exact origin of pike, which account for 3% of all freshwater fish, could not be directly determined due to a shortage of modern comparative data. Using the data obtained on the provenance of the fish, the ancient trade routes possibly used in the Early Byzantine period are reconstructed using a combination of archaeological, numismatic and historical data on past commercial relations.