基于碳、氮稳定同位素的雅浦海沟底栖生物食物来源和营养级初探

为了分析雅浦海沟中底栖生物群落的食物来源和营养级,本研究分析了雅浦海沟真光层中浮游植物和浮游动物、海底沉积物和巨型底栖生物（海绵、海参、海蛇尾、海星、海葵和钩虾）中的碳、氮稳定同位素组成。研究发现雅浦海沟真光层中的浮游植物和浮游动物δ13C值[（-22.8±0.4）‰和（-21.8±0.8）‰]和δ15N值[（5.4±0.4）‰和（6.8±0.2）‰]与巨型底栖生物的δ13C值（-20.1‰~-16.8‰）和δ15N值（11.9‰~17.9‰）的差异超过了一个营养级,表明作为底栖生物的初始食物来源的浮游植物和浮游动物在向下输送的过程中经历了食物链传递和细菌的降解。巨型底栖生物的δ15N和δ13C值之间无显著的相关性,此外不同物种之间营养级也存在明显差异,表现为海绵的营养级相对较高（3.4~4.7）,海参（3.3~3.6）、海蛇尾（3.4~3.5）和海星（3.2~3.7）的营养级较为接近,钩虾（2.9~3.3）和海葵（3.1）的营养级则相对略低,反映了底栖生物不同物种之间食物来源的多样化。     

Combined stomach content and δ13C/δ15N analyses of oilfish,escolar, snake mackerel and lancetfish in the western North Atlantic

Large, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length‐at‐maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both δ¹³C and δ¹⁵N. Escolar were the most depleted in δ¹³C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in δ¹³C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in δ¹³C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (δ¹⁵N = 10.20), followed by snake mackerel (δ¹⁵N = 9.66), adult oilfish (δ¹⁵N = 9.32), lancetfish (δ¹⁵N = 9.05) and juvenile oilfish (δ¹⁵N = 7.83). A marked change in oilfish δ¹³C and C/N at 30–35 cm fork length coincided with a presumed length‐at‐maturity.     

Food-web structure and trophodynamics of mesopelagic–suprabenthic bathyal macrofauna of the Algerian Basin based on stable isotopes of carbon and nitrogen

The trophodynamics of mesopelagic (macrozooplankton/micronekton) and benthic boundary layer (suprabenthos=hyperbenthos) faunas from the Algerian Basin were characterized on a seasonal scale through stable carbon and nitrogen isotopic analyses of a total of 34 species and two broad taxa (Copepoda and Cumacea). This is the first study simultaneously focused on trophodynamics of deep-sea zooplankton and suprabenthos. Samples were collected southeast of Mallorca (Algerian Basin, Western Mediterranean), on the continental slope close to Cabrera Archipelago, at 650–780 m depths, ca. bi-monthly between August 2003 and June 2004. Mean δ¹³C values of suprabenthos ranged from ?21.1‰ (Munnopsurus atlanticus) to ?16.7‰ (Cyclaspis longicaudata). Values of δ¹⁵N ranged from 2.8‰ (Lepechinella manco) to 9.9‰ (larvae of Gnathia sp.). The stable isotope ratios of suprabenthic fauna displayed a continuum of values, confirming a wide spectrum of feeding guilds (from filter feeders/surface deposit feeders to predators). According to the available information on diets for suprabenthic species, the highest annual mean δ¹⁵N values were found for the hematophagous isopod Gnathia sp. parasite on fish (represented by Praniza larvae) and carnivorous amphipods (e.g. Rhachotropis spp., Nicippe tumida) consuming copepods, and the lowest δ¹⁵N values were found for two cumaceans (Cyclaspis longicaudata and Platysympus typicus) feeding on detritus. Assuming a ¹⁵N-enrichment factor of 2.5‰ and deposit feeders as baseline, we found three trophic levels in suprabenthic food webs. δ¹³C ranges were particularly wide among deposit feeders (ranging from ?21.8% to ?17.3‰) and omnivores (from ?20.5% to ?18.8‰), suggesting exploitation of particulate organic matter (POM) of different characteristics. Our isotopic analyses revealed lower ranges of δ¹³C and δ¹⁵N for macrozooplankton/micronekton, compared with suprabenthos. δ¹³C values of zooplankton taxa ranged from ?21.1‰ (the hyperiid Phrosina semilunata) to ?19.9‰ (the decapod Pasiphaea multidentata), while δ¹⁵N values ranged from 3.9‰ (P. semilunata) to 7.5‰ (P. multidentata). Among zooplankton, more enriched δ¹⁵N values were found among carnivores (e.g. the fish Cyclothone spp. and Pasiphaea multidentata) preying on copepods, hyperiids, euphausiids and small fish. The lowest δ¹⁵N values were found for hyperiids that feed on the mucus nets of salps (e.g. Vibilia armata). After contrasting isotope analysis with dietary data, we conclude there were two trophic levels among zooplankton/micronekton. Strong correlation between the mean annual δ¹⁵N and δ¹³C values was found for zooplankton (R²=0.7), but not for suprabenthos, which suggests a single source of carbon for plankton. We found a general seasonal trend for δ¹³C enrichment from late autumn (November) to late winter–spring (February–April) for both suprabenthos and zooplankton. The δ¹³C enrichment in February–April was correlated in zooplankton with higher surface chlorophyll a concentration 1 month before sampling. As evidenced by δ¹³C–δ¹⁵N correlations, the response of zooplankton to the peak of surface primary production was almost immediate (an increase of δ¹³C–δ¹⁵N correlations in February), and stronger than for suprabenthos. The response among suprabenthos was weak, with slight increase in δ¹³C–δ¹⁵N relationships in April–June.     

广东流沙湾5种贝类的δ~（13）C值和δ~（15）N值研究

广东流沙湾海水养殖业发达,尤其是贝类增养殖已成为当地的支柱产业.但近年来其养殖环境的恶化对贝类产品的安全输出造成了越来越严重的影响,利用稳定同位素技术研究贝类的新陈代谢过程可为贝类增养殖提供较先进的基础数据.本研究选取流沙湾的5种重要养殖贝类,对其肌肉组织、鳃、外套膜和内脏囊分别进行稳定碳、氮同位素测定分析.结果表明,贝类δ13C值的范围是-19.14‰～-15.11‰,δ15N值的范围是6.10‰～10.57‰.从大小、组织、种类三方面比较5种贝类的稳定碳氮同位素比值,可得出如下结论：同种贝类,大小不同,其δ13C、δ15N值大都随壳长、壳重的增大而减小,但翡翠贻贝（Pernaviridis）的δ13C值和墨西哥湾扇贝（Argopecten irradians concentricus）的δ15N值则相反,无论大、小组之间δ13C、δ15N值的变化是增大还是减小,幅度均不超过1.00‰;同种贝类,组织不同,其δ13C、δ15N的最小值均为内脏囊,δ13C的最大值不定,δ15N的最大值也是内脏囊;相同组织,不同贝类,其δ13C、δ15N值的大小排列顺序各不相同,无统一规律,但华贵栉孔扇贝（Chlamys nobilis）的δ13C值均小于墨西哥湾扇贝,而马氏珠母贝（Pinctada martensii）的δ15N值均小于企鹅珍珠贝（Pteria penguin）.由研究数据可推知流沙湾双壳贝类的物质与能量流动途径基本是由内脏囊到外套膜和鳃,最后到肌肉.     

Carbon and nitrogen dynamics of the intertidal seagrass, <Emphasis Type="Italic">Zostera japonica</Emphasis>, on the southern coast of the Korean peninsula

Seagrasses require a large amount of nutrient assimilation to support high levels of production, and thus nutrient limitation for growth often occurs in seagrass habitats. Seagrasses can take up nutrients from both the water column and sediments. However, since seagrasses inhabiting in the intertidal zones are exposed to the air during low tide, the intertidal species may exhibit significantly different carbon (C) and nitrogen (N) dynamics compared to the subtidal species. To examine C and N dynamics of the intertidal seagrass, Zostera japonica, C and N content and stable isotope ratios of above- and below-ground tissues were measured monthly at the three intertidal zones in Koje Bay on the southern coast of Korea. The C and N content and stable isotope (δ¹³C and δ¹⁵N) ratios of seagrass tissues exhibited significant seasonal variations. Both leaf and rhizome C content were not significantly correlated with productivity. Leaf δ¹³C values usually exhibited negative correlations with leaf productivity. These results of tissue C content and δ¹³C values suggest that photosynthesis of Z. japonica in the study site was not limited by inorganic C supply, and sufficient inorganic C was provided from the atmosphere. The tissue N content usually exhibited negative correlations with leaf productivity except at the upper intertidal zone, suggesting that Z. japonica growth was probably limited by N availability during high growing season. In the upper intertidal zone, no correlations between leaf productivity and tissue elemental content and stable isotope ratios were observed due to the severely suppressed growth caused by strong desiccation stress.     

Trophic structure of mesopelagic fishes in the Gulf of Mexico revealed by gut content and stable isotope analyses

Mesopelagic fishes represent an important component of the marine food web due to their global distributions, high abundances and ability to transport organic material throughout a large part of the water column. This study combined stable isotope (SIAs) and gut content analyses (GCAs) to characterize the trophic structure of mesopelagic fishes in the North‐Central Gulf of Mexico. Additionally, this study examined whether mesopelagic fishes utilized chemosynthetic energy from cold seeps. Specimens were collected (9–25 August 2007) over three deep (>1,000 m) cold seeps at discrete depths (surface to 1,503 m) over the diurnal cycle. GCA classified 31 species (five families) of mesopelagic fishes into five feeding guilds: piscivores, large crustacean consumers, copepod consumers, generalists and mixed zooplanktivores. However, these guilds were less clearly defined based on stable isotope mixing model (MixSIAR) results, suggesting diets may be more mixed over longer time periods (weeks–months) and across co‐occurring species. Copepods were likely important for the majority of mesopelagic fishes, consistent with GCA (this study) and previous literature. MixSIAR results also identified non‐crustacean prey items, including salps and pteropods, as potentially important prey items for mesopelagic fishes, including those fishes not analysed in GCA (Sternoptyx spp. and Melamphaidae). Salps and other soft‐bodied species are often missed in GCAs. Mesopelagic fishes had δ¹³C results consistent with particulate organic matter serving as the baseline organic carbon source, fueling up to three trophic levels. Fishes that undergo diel vertical migration were depleted in ¹⁵N relative to weak migrators, consistent with depth‐specific isotope trends in sources and consumers, and assimilation of ¹⁵N‐depleted organic matter in surface waters. Linear correlations between fish size and δ¹⁵N values suggested ontogenetic changes in fish diets for several species. While there was no direct measure of mesopelagic fishes assimilating chemosynthetic material, detection of infrequent consumption of this food resource may be hindered by the assimilation of isotopically enriched photosynthetic organic matter. By utilizing multiple dietary metrics (e.g. GCA, δ¹³C, δ¹⁵N, MixSIAR), this study better defined the trophic structure of mesopelagic fishes and allowed for insights on feeding, ultimately providing useful baseline information from which to track mesopelagic trophodynamics over time and space.     

Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal

We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ¹³C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ¹³C signatures at two sites where ethane δ¹³C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which ¹³C and deuterium were both highly depleted (mean δ¹³C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C₂ δ¹³C–δD classification for hydrate-bound gas in either freshwater or marine environments.     

Variability in the fractionation of stable isotopes during degradation of two intertidal red algae

Macroalgae contribute to intertidal food webs primarily as detritus, with unclear implications for food web studies using stable isotope analysis. We examined differences in the thallus parts of two South African rhodophytes (Gelidium pristoides and Hypnea spicifera) and changes in overall δ¹³C, δ¹⁵N signatures and C:N ratios during degradation in both the field and laboratory. We hypothesized that both degrading macroalgal tissue and macroalgal-derived suspended particulate material (SPM) would show negligible changes in δ¹³C, but enriched δ¹⁵N signatures and lower C:N ratios relative to healthy plants. Only C:N laboratory ratios conformed to predictions, with both species of macroalgae showing decomposition related changes in δ¹³C and significant depletions in δ¹⁵N in both the field and laboratory. In the laboratory, algal tissue and SPM from each species behaved similarly (though some effects were non-significant) but with differing strengths. Gelidium pristoides δ¹³C increased and C:N ratios decreased over time in tissue and SPM; δ¹⁵N became depleted only in SPM. Hypnea spicifera, δ¹³C, δ¹⁵N and C:N ratios all decreased during degradation in both SPM and algae.     

Trophic relationships along a bathymetric gradient at the deep-sea observatory HAUSGARTEN

Deep-seafloor communities, especially those from the ice-covered Arctic, are subject to severe food limitation as the amount of particulate organic matter (POM) from the surface is attenuated with increasing depth. Here, we use naturally occurring stable isotope tracers (δ¹⁵N) to broaden our rudimentary knowledge of food web structure and the response of benthic organisms to decreasing food supplies along the bathymetric transect (～1300–5600 m water depth) of the deep-sea observatory HAUSGARTEN. Encompassing five trophic levels, the HAUSGARTEN food web is among the longest indicating continuous recycling of organic material typical of food-limited deep-sea ecosystems. The δ¹⁵N signatures ranged from 3.0‰ for Foraminifera to 21.4‰ (±0.4) for starfish (Poraniomorpha tumida). The majority of organisms occupied the second and third trophic level. Demersal fish fed at the third trophic level, consistent with results from stomach contents analysis. There were significant differences in the δ¹⁵N signatures of different functional groups with highest δ¹⁵N values in predators/scavengers (13.2±0.2‰) followed by suspension feeders (11.2±0.2‰) and deposit feeders (10.2±0.3‰). Depth (=increasing food limitation) affected functional groups in different ways. While the isotopic signatures of predators/scavengers did not change, those of suspension feeders increased with depth, and the reverse was found for deposit feeders. In contrast to the results of other studies, the δ¹⁵N signatures in POM samples obtained below 800 m did not vary significantly with depth indicating that changes in δ¹⁵N values are unlikely to be responsible for the depth-related δ¹⁵N signature changes observed for benthic consumers. However, the δ¹⁵N signatures of sediments decreased with increasing depth, which also explains the decrease found for deposit feeders. Suspension feeders may rely increasingly on particles trickling down the HAUSGARTEN slope and carrying higher δ¹⁵N signatures than the decreasing POM supplies, which elevates the δ¹⁵N value of their tissues. Our results imply that a depth-stratified approach should be taken to avoid a misinterpretation of data obtained at different depths.     

Effect of body size and body mass on δC and δN in coastal fishes and cephalopods

Carbon and nitrogen isotopes have been widely used in the investigation of trophic relations, energy pathways, trophic levels and migrations, under the assumption that δ¹³C is independent of body size and that variation in δ¹⁵N occurs exclusively due to ontogenetic changes in diet and not body size increase per se. However, several studies have shown that these assumptions are uncertain. Data from food-webs containing an important number of species lack theoretical support on these assumptions because very few species have been tested for δ¹³C and δ¹⁵N variation in captivity. However, if sampling comprises a wide range of body sizes from various species, the variation of δ¹³C and δ¹⁵N with body size can be investigated. While correlation between body size and δ¹³C and δ¹⁵N can be due to ontogenetic diet shifts, stability in such values throughout the size spectrum can be considered an indication that δ¹³C and δ¹⁵N in muscle tissues of such species is independent of body size within that size range, and thus the basic assumptions can be applied in the interpretation of such food webs. The present study investigated the variation in muscle δ¹³C and δ¹⁵N with body size and body mass of coastal fishes and cephalopods. It was concluded that muscle δ¹³C and δ¹⁵N did not vary with body size or mass for all bony fishes with only one exception, the dragonet Callionymus lyra. Muscle δ¹³C and δ¹⁵N also did not vary with body size or mass in cartilaginous fishes and cephalopods, meaning that body size/mass per se have no effect on δ¹³C or δ¹⁵N, for most species analysed and within the size ranges sampled. The assumption that δ¹³C is independent of body size and that variation in δ¹⁵N is not affected by body size increase per se was upheld for most organisms and can be applied to the coastal food web studied taking into account that C. lyra is an exception.     

Sulfur Isotopes in the Upper Part of the Black Sea Anoxic Zone

New data are reported on the sulfur isotope composition and concentration of sulfide and sulfate in the upper part of the Black Sea anoxic zone as a function of the potential water density. The observations were performed at a station with the coordinates 44.489° N and 37.869° E three times a week every two days. A local negative deficiency in sulfate concentration up to 1.7% related to the sulfate reduction processes was recorded. This anomaly in sulfate concentration was short-lived and did not affect the sulfur isotope composition. In the upper part of the anaerobic zone, the δ³⁴S(SO₄) value varied from 21.2 to 21.5‰, which could have occurred from mixing of water masses from the oxic zone (21.1‰) and the Bottom Convective Layer (23.0 ± 0.2‰). The sulfur isotope composition of sulfide ranged from ?40.8% at a depth of 250 m to ?39.4‰ at the upper boundary of the anoxic zone with a H₂S content of only 2.7 μM. Two models (mass balance and fractionation of sulfur isotopes using the Rayleigh equation) are considered to explain the differences in δ³⁴S(H₂S) values observed.     

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δC, δN and δD) as environmental tracers

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ¹³C, δ¹⁵N and δD measurements of a euryhaline fish, the Mediterranean toothcarp (Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern (Sternula albifrons) and Little Egret (Egretta garzetta), was inferred trough a triple-isotope (δ¹³C, δ¹⁵N and δD) Bayesian mixing model. Isotopic trends for fish δ¹⁵N and δD across the salinity gradient followed the equations: δ¹⁵N = e^{(1.1 + 47.68/Salinity)} and δD = −175.74 + Salinity + Salinity²; whereas fish δ¹³C increased as salinity rose (δ¹³C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ¹³C for salinities <60 = −5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.     

Host‐dependent differences in resource use associated with Anilocra spp. parasitism in two coral reef fishes,as revealed by stable carbon and nitrogen isotope analyses

The role of parasites in trophic ecology is poorly understood in marine ecosystems. Stable isotope analyses (SIA) have been widely used in studies of trophic ecology, but have rarely been applied to study the role of parasites. Considering that some parasites are associated with altered host foraging patterns, SIA can help elucidate whether parasitism influences host trophic interactions. French grunt (Haemulon flavolineatum), an abundant Caribbean coral reef fish, contributes greatly to trophic connectivity. They typically depart the reef at dusk, feed overnight in seagrass beds, and return to the reef at dawn. The large parasitic isopod Anilocra haemuli commonly infects French grunt, and infected fish are less likely to complete their diel migration, and are in poorer condition than uninfected conspecifics. Brown chromis (Chromis multilineata) are diurnally feeding planktivores and infection by Anilocra chromis does not influence host condition. To determine if Anilocra infection influences host diet and foraging locality, we conducted stable carbon and nitrogen isotope analyses on scale, muscle, heart and gill tissues of infected and uninfected French grunt and brown chromis. We determined that all French grunt had δ¹³C values representative of seagrass habitats, but infected French grunt were significantly enriched in ¹³C and ¹⁵N compared to uninfected conspecifics. This suggests that compared to uninfected conspecifics, infected French grunt forage in seagrass, but on isotopically enriched prey, and/or are in poorer condition, which can elevate δ¹³C and δ¹⁵N values. For brown chromis, infection did not significantly influence any δ¹³C and δ¹⁵N values; hence they all foraged in the same environment and on similar prey. This is the first study to use SIA to examine differences in resource use by Caribbean coral reef fishes associated with parasitism and to evaluate how closely related parasites might have host‐dependent effects on host trophic ecology.     

Organic carbon stable isotope ratios of continental margin sediments

Stable isotope ratios (δ¹³C) of total organic carbon were measured in surface sediments from the continental margins of the northern and western Gulf of Mexico, the north coast of Alaska and the Niger Delta. Gulf of Mexico outer-shelf isotope ratios were in the same range as has been reported for Atlantic coastal shelf sediments, ?21.5 to ?20‰. Off large rivers including the Mississippi, Niger and Atchafalaya (Louisiana), δ¹³C values increased from terrigenous-influenced (around ?24‰) to typically marine ($\text{～?20‰}$) within a few tens of kilometers from shore. This change was accompanied by a decrease in the amount of woody terrigenous plant remains in the sediment. Alaskan continental margin samples from the cold Beaufort Sea had isotopically more negative carbon (?25.5 to ?22.6‰) than did warmer-water sediments. The data indicate that the bulk of organic carbon in Recent sediments from nearshore to outer continental shelves is marine derived.     

The influence of lipid-extraction on the δ13C of mesopelagic and demersal fish in the South China Sea: modification and application of lipid normalization models

Mesopelagic fish,the most important daily vertically migrating community in the oceans,are characterized by high lipid content which may obscure the interpretation of stable isotopes analysis.Demersal fish,which are important consumers in the food web dominated by mesopelagic fish,also have a high lipid content.Here we collected 127 fish samples from the South China Sea and evaluated the effect of lipid contents on δ¹³C of mesopelagic and demersal fish.In lipid-extracted mesopelagic f...     

Carbon and nitrogen stable isotope analysis of three types of oyster tissue in an impacted estuary

The stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) of the muscle, ctenidia and viscera of the Sydney rock oyster, Saccostrea glomerata, showed the dilution and assimilation of tertiary treated sewage along an estuarine gradient. The enriched ¹⁵N values of oyster ctenidia and viscera from within 50 m of the sewage outfall indicated the use of ¹⁵N-enriched tertiary treated sewage effluent (16 ± 2.3‰) as a nutrient source. The effect of sewage nitrogen on oyster δ¹⁵N was localised, with oysters 5 km upstream and downstream of the outfall not significantly enriched. Viscera δ¹⁵N was most sensitive to sewage nutrients and δ¹³C significantly defined an ocean-to-estuarine gradient. High variance in isotope ratios of viscera compromised its use as an indicator of anthropogenic nutrients, and this also reduced the utility of whole-body stable isotope ratios. Ctenidia was the most useful indicator tissue of sewage discharge at the scale of this study, being consistently and significantly enriched in δ¹⁵N close to the sewage outfall and δ¹³C clearly defined an estuarine gradient with less internal variability than viscera. Muscle δ¹⁵N was least sensitive to sewage effluent and showed the least variability, making it more suited to investigations of anthropogenic nutrient enrichment over larger spatio-temporal scales.     

Nitrogen and carbon isotopic composition of marine and terrestrial organic matter in Arctic Ocean sediments:: implications for nutrient utilization and organic matter composition

Relationships between organic carbon, total nitrogen and organic nitrogen concentrations and variations in δ¹³C_org and δ¹⁵N_org are examined in surface sediments from the eastern central Arctic Ocean and the Yermak Plateau. Removing the organic matter from samples with KOBr/KOH and determining residual as well as total N shows that there is a significant amount of bound inorganic N in the samples, which causes TOC/N_total ratios to be low (4–10 depending on the organic content). TOC/N_org ratios are significantly higher (8–16). This correction of organic TOC/N ratios for the presence of soil-derived bound ammonium is especially important in samples with high illite concentrations, the clay mineral mainly responsible for ammonium adsorption. The isotopic composition of the organic N fraction was estimated by determining the isotopic composition of the total and inorganic nitrogen fractions and assuming mass-balance. A strong correlation between δ¹⁵N_org values of the sediments and the nitrate concentration of surface waters indicates different relative nitrate utilization rates of the phytoplankton in various regions of the Arctic Ocean. On the Yermak Plateau, low δ¹⁵N_org values correspond to high nitrate concentrations, whereas in the central Arctic Ocean high δ¹⁵N_org values are found beneath low nitrate waters. Sediment δ¹³C_org values are close to −23.0‰ in the Yermak Plateau region and approximately −21.4‰ in the central Arctic Ocean. Particulate organic matter collected from meltwater ponds and ice-cores are relatively enriched in ¹³C (δ¹³C_org=−15.3 to −20.6‰) most likely due to low CO₂(aq) concentrations in these environments. A maximum terrestrial contribution of 30% of the organic matter to sediments in the central Arctic Ocean is derived, based on the carbon isotope data and various assumptions about the isotopic composition of the potential endmembers.     

环境饵料丰度的季节变化对筼筜湖3种大型底栖动物食性的影响——来自稳定同位素的证据

测定了不同时期筼筜湖3种大型底栖动物(沙筛贝Mytilopsis sallei、日本大螯蜚Grandidierella japonica和腺带刺沙蚕Neanthes japonica)及其潜在食源的稳定同位素组成(δ13C和δ15 N),研究环境饵料丰度的季节变化对筼筜湖3种大型底栖动物食性的影响。结果显示,筼筜湖悬浮颗粒有机物(Particulate organic matter∶POM)的δ13C和δ15 N存在明显的季节变化。3月,受到输入筼筜湖的西海域海水大量陆源有机碎屑以及湖区周围的生活污水以及餐饮业输入的影响,筼筜湖POM的δ13 C和δ15 N明显贫化;而在9月,POM中δ13 C和δ15 N明显富集的内源性浮游植物的贡献增加。沙筛贝是典型的底栖滤食者,主要以POM为食,但它比POM富集的δ13 C值(3月和9月二者之间的Δδ13 C分别为2.9‰和1.6‰)表明它还摄入其他δ13 C相对富集的食物来源:石莼来源的有机碎屑可能是3月份沙筛贝δ13C富集的原因,而9月份则是由于再悬浮的底栖微藻对沙筛贝食源的贡献引起的。食碎屑的腺带刺沙蚕和日本大螯蜚在3月以石莼及其表面的附生生物为食,而9月份底栖微藻和浮游植物来源的POM是它们食源的主要贡献者。本研究的结果显示,筼筜湖3种大型底栖动物的δ15 N都出现明显的季节变化(Δδ15 N介于2.2‰~4.3‰),这是由于它们食源稳定同位素的季节性波动及其食性的季节变化引起的,而消费者食性的季节性变化则受到不同时期环境食物可利用性的影响。     

南海北部海域沉积物中生物钡、碳氮同位素的组成特征及其与表层水体初级生产之间的关系

通过对采集自南海北部的D06和S0612两个短柱状沉积物样品中的不同赋存形态钡、有机碳和生物硅的含量以及有机质碳氮同位素组成的分析,结果表明沉积物中的钡主要以碎屑钡和自生的生物钡形式存在。沉积物中生物钡的含量在10.3~385.2 μg/g之间,平均值为177.0 μg/g,据此计算的新生产力在12.3~146.7 mg/（d·m2）（以碳计）之间,平均为78.9 mg/（d·m2）;D06站计算的结果和附近站位的实测值相当。沉积物中有机碳的含量在0.64%~1.34%之间,平均值为0.89%,C/N比值为4.96~5.93,平均值为5.54。有机碳的δ13C值在-22.98‰~-20.73‰之间,平均值为-21.46‰,依据端元组份同位素组成计算的陆源有机质比率显示,D06站位的有机质主要来自海洋生物,而S0612站位则受陆源有机质的影响较大。沉积物中有机质的δ15N值在3.96‰~6.29‰之间,平均值为5.26‰,反映的是该海区氮源的同位素组成,而不受硝酸盐利用率的影响。     

Oxygen isotopic distribution along the otolith growth axis by secondary ion mass spectrometry: Applications for studying ontogenetic change in the depth inhabited by deep-sea fishes

This study using tuna otoliths as working standards established a high lateral resolution and precision analysis to measure δ¹⁸O_otolith by secondary ion mass spectrometry. This analytical approach of the ion probe was applied to deep-sea fishes to reconstruct the likely depths inhabited by the fishes at different life history stages based on the measured δ¹⁸O_otolith values as a proxy of water temperature. Dramatic increases up to 5–6‰ in δ¹⁸O_otolith, representing a temperature decrease of approximately 20 °C, were detected in a blind cusk eel (Barathronus maculatus) otolith and in the otoliths of Synaphobranchus kaupii during leptocephalus metamorphosis to glass eel, inferred from the drop of otolith Sr/Ca ratios and increase of otolith growth increment width. δ¹⁸O_otolith profiles clearly divided the fish's life history into a planktonic stage in the mixed layer of the ocean and a benthic stage on the deep-sea ocean bottom. The habitat shift signal was recorded within a 150 µm width of otolith growth zone, which was too narrow to be clearly detected by mechanical drilling and conventional isotopic ratio mass spectrometry. However, variations down to −7‰ were found in δ¹⁸O_otolith profiles as the result of Cs²⁺ beam sputter in the core and larval portions of the otoliths. Carbon mapping by electron probe microanalyzer and staining by toluidine blue suggested abundant proteins existed in the areas with anomaly negative δ¹⁸O_otolith values, which cannot be interpreted as a habitat change but due to the isotopic fractionation by O emission from the proteins. These results implied that careful design and understanding of the chemical composition of the analytical areas or tracks on the heterogeneous otolith was essential for highly accurate and precise analysis.