Potential impact of the main benthic amphipods on the eastern Weddell Sea shelf ecosystem (Antarctica)

As they represent one of the most diversified taxonomic groups on Antarctic bottoms, amphipods are likely to play a complex role in biogeochemical fluxes that occur within benthic ecosystems. The aim of this paper is to present, using both digestive tract analyses and relative species abundance data, the impact of amphipod feeding on different potential preys of the Weddell Sea. The study is based on data obtained for 29 representative amphipod species collected at 130 stations distributed along the eastern shelf of the Weddell Sea (depth range: 60-2,000 m) during three summer cruises, from 1989 to 1998. Sedimenting plankton particles (10-27%), crustaceans (22-32%) and fish carrion (5-18%) are the main food resources. Other abundant potential preys, such as molluscs or tunicates, do not seem to be consumed. Variations in the proportions of the different preyed food items are observed, mainly related to differences in relative amphipod species composition in samples. Presented results will help in refining ecological models of the prospected area, but also underline the need for accurate and reliable measurements of the feeding rates of Antarctic benthic organisms.     

A study on octopodids from the eastern Weddell Sea, Antarctica

A comprehensive study of octopodids in the Weddell Sea was conducted during cruise ANT XIII/3 of RV "Polarstern". The study yielded eight species of incirrate octopodids, three of which were undescribed. There appeared to be no differences in octopodid species assemblage in the two sampling areas (Kapp Norvegia and south of Drescher Inlet), supporting the theory that there is a single macrobenthic assemblage on the eastern shelf of the Weddell Sea. Six of the octopodid species belonged to the genus Pareledone, illustrating the extensive radiation of this endemic genus within the Southern Ocean. The fragmented nature of suitable habitats and disturbance caused by glaciation cycles are proposed as mechanisms for this radiation. Comparative data illustrate that both the number of octopodid species present and their abundance are greater at higher latitudes than close to the Antarctic Polar Frontal Zone.     

Determining trophic niche width: an experimental test of the stable isotope approach

Determining the trophic niche width of an animal population and the relative degree to which a generalist population consists of dietary specialists are long‐standing problems of ecology. It has been proposed that the variance of stable isotope values in consumer tissues could be used to quantify trophic niche width of consumer populations. However, this promising idea has not yet been rigorously tested. By conducting controlled laboratory experiments using model consumer populations (Daphnia sp., Crustacea) with controlled diets, we investigated the effect of individual‐ and population‐level specialisation and generalism on consumer δ¹³C mean and variance values. While our experimental data follow general expectations, we extend current qualitative models to quantitative predictions of the dependence of isotopic variance on dietary correlation time, a measure for the typical time over which a consumer changes its diet. This quantitative approach allows us to pinpoint possible procedural pitfalls and critical sources of measurement uncertainty. Our results show that the stable isotope approach represents a powerful method for estimating trophic niche widths, especially when taking the quantitative concept of dietary correlation time into account.     

Response of Antarctic benthic communities to disturbance: first results from the artificial Benthic Disturbance Experiment on the eastern Weddell Sea Shelf, Antarctica

The long-term benthic disturbance experiment (BENDEX) was started on the eastern Weddell Sea shelf off Austasen (Antarctica) during ‘Polarstern’ cruise ANT XXI/2 in December 2003 to simulate the impact of grounding icebergs on the seabed and follow the steps and timescales of recovery of disturbed benthos and demersal fish communities. Here, we report the basic approach and first results for this experimental field study. By means of 11 densely-placed hauls with a modified bottom trawl, a seabed area of approximately 100 × 1000 m was artificially scoured to inflict a similar damage to the benthic habitats as a grounding iceberg. Before the disturbance event and 11 days after it, the seafloor communities were sampled (invertebrate assemblages by multibox corers, the fish fauna by trawl hauls) and comparatively analyzed. Sediment texture and chemistry was not significantly altered by the heavy disturbance inflicted by repeated trawling, whereas the fauna was negatively affected. Invertebrate benthic biomass was drastically reduced by a factor of 10, while mean abundances were only slightly reduced. Demersal fish biomass and abundance were slightly but not significantly smaller after the disturbance. Effects of disturbance became more evident in the composition of the fish fauna, with Trematomus pennelli and T. hansoni being dominant at disturbed sites, whereas Chionodraco myersi was the dominant species in trawl catches from undisturbed stations.     

Revolution in food web analysis and trophic ecology: diet analysis by DNA and stable isotope analysis

Characterization of energy flow in ecosystems is one of the primary goals of ecology, and the analysis of trophic interactions and food web dynamics is key to quantifying energy flow. Predator‐prey interactions define the majority of trophic interactions and food web dynamics, and visual analysis of stomach, gut or fecal content composition is the technique traditionally used to quantify predator‐prey interactions. Unfortunately such techniques may be biased and inaccurate due to variation in digestion rates ( Sheppard & Hardwood 2005 ); however, those limitations can be largely overcome with new technology. In the last 20 years, the use of molecular genetic techniques in ecology has exploded ( King et al. 2008 ). The growing availability of molecular genetic methods and data has fostered the use of PCR‐based techniques to accurately distinguish and identify prey items in stomach, gut and fecal samples. In this month’s issue of Molecular Ecology Resources, Corse et al. (2010) describe and apply a new approach to quantifying predator‐prey relationships using an ecosystem‐level genetic characterization of available and consumed prey in European freshwater habitats ( Fig. 1a ). In this issue of Molecular Ecology, Hardy et al. (2010) marry the molecular genetic analysis of prey with a stable isotope (SI) analysis of trophic interactions in an Australian reservoir community ( Fig. 1b ). Both papers demonstrate novel and innovative approaches to an old problem – how do we effectively explore food webs and energy movement in ecosystems?

Figure 1 Open in figure viewer PowerPoint The aquatic habitats used for two studies of diet and trophic interactions that employed molecular genetic and stable isotope analyses. Panel a: Example of Rhone basin habitat (France) where fish diet was determined using PCR to classify prey to a series of ecological clades (photo by Emmanuel Corse). Panel b: A weir pool on the lower Murray River (Australia) where food web and prey use was evaluated using a combination of advanced molecular genetic and stable isotope analyses (photo credit: CSIRO).     

Trophic diversity within the eastern Weddell Sea amphipod community

Amphipod crustaceans form one of the most diversified animal groups within the Antarctic macrozoobenthos, both from the taxonomic point of view (more than 800 species have been recorded in the Southern Ocean) as by niche occupation and at the community level. Thus, amphipods are likely to play an important role in the organic matter fluxes that occur on the Antarctic sea floor. The dietary behaviour of these peracarids is still poorly known, and only few species have been analysed. This paper describes the trophic preferences of some dominant amphipod species of the Eastern Weddell Sea benthos, deduced from stomach content analyses and behavioural observations in aquaria. More than 1000 specimens, belonging to 40 species (representing 27 genera and 15 families) were dissected; and several thousands of individuals were kept in aquaria for 6–9 weeks and presented with various potential foods. These two approaches revealed at least eight different feeding types: suspension-feeding, deposit-feeding, deposit-feeding coupled with predation, opportunistic predation, micropredatory browsing, macropredation coupled with scavenging, opportunistic necrophagy and true necrophagy. These different behaviours cover almost all the possible feeding types with the exception of macroherbivorous browsing. Among the eight described feeding types, no particular one is dominant. In the same way, types involving microphagy and macrophagy are equally represented. Predatory types (opportunistic or exclusive) account for 64% of the species analysed, while scavenging types (facultative or obligate) account for 60%. The overlap suggests that many amphipod species have a wide dietary spectrum and are able to take advantage of different food resources.     

应用稳定同位素技术构建胶州湾食物网的连续营养谱

根据2011年春季和秋季在胶州湾进行的渔业资源综合调查,应用稳定同位素示踪技术,分析了胶州湾主要渔业生物的碳、氮稳定同位素比值(δ13C,δ15N),并计算其营养级,进而构建胶州湾食物网的连续营养谱。分析的生物种类包括浮游植物、浮游动物、大型无脊椎动物和鱼类,其生物量之和占总渔获量的95%。结果表明,胶州湾食物网的δ13C值范围是-25.63‰—-17.16‰,跨度为8.47‰,平均值为(-19.42±1.80)‰;δ15N值范围是4.15‰—14.11‰,跨度为9.96‰,平均值为(11.98±1.77)‰。胶州湾食物网中的主要生物种类可以划分为4个营养组群,即初级生产者、初级消费者、次级消费者以及顶级捕食者。δ15N值分析显示,胶州湾主要生物种类的营养级范围是1.10—4.03。与文献中基于胃含物分析计算的营养级相比较,37个种类中有29种的营养级分析结果基本一致(在0.5个营养级的误差范围之内)。因此,氮稳定同位素法是一种研究水生生态系统食物网营养位置的有效方法。其中,有8种鱼类的营养级与历史文献相比有所下降,分析方法的不同可能是原因之一,此外,这些鱼种摄食饵料生物营养级的下降也是导致其营养级降低的另一个主要原因。根据营养级计算的结果,构建了胶州湾食物网的连续营养谱,胶州湾食物网中,绝大多数生物种类都属于初级和中级肉食性种类。     

TDFCAM: A method for estimating stable isotope trophic discrimination in wild populations

1. Stable isotope mixing models (SIMMs) are widely used for characterizing wild animal diets. Such models rely upon using accurate trophic discrimination factors (TDFs) to account for the digestion, incorporation, and assimilation of food. Existing methods to calculate TDFs rely on controlled feeding trials that are time-consuming, often impractical for the study taxon, and may not reflect natural variability of TDFs present in wild populations.
2. We present TDF_CAM as an alternative approach to estimating TDFs in wild populations, by using high-precision diet estimates from a secondary methodological source—in this case nest cameras—in lieu of controlled feeding trials, and provide a framework for how and when it should be applied.
3. In this study, we evaluate the TDF_CAM approach in three datasets gathered on wild raptor nestlings (gyrfalcons Falco rusticolus; peregrine falcons Falco perigrinus; common buzzards Buteo buteo) comprising contemporaneous δ¹³C & δ¹⁵N stable isotope data and high-quality nest camera dietary data. We formulate Bayesian SIMMs (BSIMMs) incorporating TDFs from TDF_CAM and analyze their agreement with nest camera data, comparing model performance with those based on other relevant TDFs. Additionally, we perform sensitivity analyses to characterize TDF_CAM variability, and identify ecological and physiological factors contributing to that variability in wild populations.
4. Across species and tissue types, BSIMMs incorporating a TDF_CAM outperformed any other TDF tested, producing reliable population-level estimates of diet composition. We demonstrate that applying this approach even with a relatively low sample size (n < 10 individuals) produced more accurate estimates of trophic discrimination than a controlled feeding study conducted on the same species. Between-individual variability in TDF_CAM estimates for ∆¹³C & ∆¹⁵ N increased with analytical imprecision in the source dietary data (nest cameras) but was also explained by natural variables in the study population (e.g., nestling nutritional/growth status and dietary composition).
5. TDF_CAM is an effective method of estimating trophic discrimination in wild animal populations. Here, we use nest cameras as source dietary data, but this approach is applicable to any high-accuracy method of measuring diet, so long as diet can be monitored over an interval contemporaneous with a tissue's isotopic turnover rate.

     

Using stable isotope data to advance marine food web modelling

Reviews in Fish Biology and Fisheries - Marine ecosystem models that incorporate fisheries and climate change are essential for forecasting and guiding sustainable ecosystem management decisions. A...     

稳定同位素分析在鸟类食性及营养级结构中的应用

稳定同位素分析(stable isotope analysis,SIA)自20世纪70年代末引入鸟类生态学领域以来,在研究鸟类食性和营养级结构方面展现了强大的发展潜力和广泛的应用前景。总结了该技术在鸟类食源组成和营养级结构方面研究的前期准备、实验流程、数据分析和研究进展等,重点阐述了其在鸟类保护与管理方面的应用。鉴于稳定同位素在生物体内存在分馏现象,从鸟类不同组织和部位对营养级富集因子、转化周期、同位素印记的差异,提出了完善该方法的建议和应用前景。     

Establishment of trophic continuum in the food web of the Yellow Sea and East China Sea ecosystem: Insight from carbon and nitrogen stable isotopes

The determination of trophic level for the biology in a marine ecosystem is very important as alteration of its structure and function may be reflected in the tro-phic level of component species. A change in trophic level indicates variation in an organism’s feeding bi-ology or in the pathway of energy flow from primary producers to the consumer. The gut content analysis is a traditional method for studying trophodynamics of food web in marine ecosystems. Species composition and amounts in al…     

Establishment of trophic continuum in the food web of the Yellow Sea and East China Sea ecosystem: Insight from carbon and nitrogen stable isotopes

Stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) are used to study the trophic structure of food web in the Yellow Sea and East China Sea ecosystem. The trophic continuum of pelagic food web from phytoplankton to top preyer was elementarily established, and a trophic structure diagram in the Yellow Sea and East China Sea was outlined in combination with carbon isotopic data of benthic organisms, which is basically consistent with and makes some improvements on the simplified Yellow Sea food web and the trophic structure diagram drawn based on the biomass of main resource population during 1985–1986. This result indicates that the stable isotope method is a potential useful means for further studying the complete marine food web trophic continuum from viruses to top predators and food web stability.     

Food and feeding ecology of emperor penguins in the eastern Weddell Sea

Summary The diet of the emperor penguin Aptenodytes forsteri in the eastern Weddell Sea, Antarctica was studied during October and November 1986 by stomach content analysis. Emperor penguins fed mainly on Antarctic krill Euphausia superba, Antarctic silverfish Pleuragramma antarcticum and squid Psychroteuthis glacialis. Benthic prey was not found. The prey composition suggests two different feeding strategies, shallow dives exploring the rugged underside of sea ice where krill is taken, and deep dives when mesopelagic fish and squid are consumed. Chicks were fed on average every 1.44 days.     

Copepods in summer platelet ice in the eastern Weddell Sea,Antarctica

Copepods in platelet-ice layers underlying fast ice and in the water column below were studied at Drescher Inlet, eastern Weddell Sea in February 1998. Three copepod species were found: Drescheriella glacialis and Paralabidocera antarctica occurred in platelet-ice layers, while Stephos longipes was only present in the water column. The distribution of all species varied considerably between station and depth. D. glacialis dominated the platelet-ice community and occurred at all five platelet-ice sampling sites, except one, with numbers of up to 26 ind. l^–1. In contrast, P. antarctica was only found in low numbers (up to 2 ind. l^–1) at one site. The total copepod abundance in the platelet ice was not associated with algal biomass, although it was strongly correlated with high ammonium concentrations (up to 9 M) in the interstitial water between the platelets. This is the first indirect evidence to support the hypothesis that zooplankton excretion can partly account for the high ammonium values often found in platelet-ice layers.     

Application of CO2 carbon stable isotope analysis to ant trophic ecology

Stable isotope analysis of animal tissues is commonly used to infer diet and trophic position. However, it requires destructive sampling. The analysis of carbon isotopes from exhaled CO₂ is non-invasive and can provide useful ecological information because isotopic CO₂ signatures can reflect the diet and metabolism of an animal. However, this methodology has rarely been used on invertebrates and never on social insects. Here, we first tested whether this method reflects differences in δ¹³C-CO₂ between workers of the Mediterranean ant Crematogaster scutellaris (Olivier) (Hymenoptera: Formicidae, Crematogastrini) fed with sugar from beet (C3; Beta vulgaris L., Amaranthaceae) or cane (C4; Saccharum officinarum L., Poaceae). We found that a significant difference can be obtained after 24 h. Consequently, we used this technique on wild co-occurring ant species with different feeding preferences to assess their reliance on C3 or C4 sources. For this purpose, we sampled workers of C. scutellaris, the invasive garden ant Lasius neglectus (van Loon et al.) (Lasiini), and the harvester ant Messor capitatus (Latreille) (Stenammini). No significant differences in their carbon isotopic signatures were recorded, suggesting that in our study site no niche partitioning occurs based on the carbon pathway, with all species sharing similar resources. However, further analysis revealed that M. capitatus, a seed-eating ant, can be regarded as a C3 specialist, whereas L. neglectus and C. scutellaris are generalists that rely on both C3 and C4 pathways, though with a preference for the former. Our results show that this methodology can be applied even to small animals such as ants and can provide useful information on the diets of generalist omnivores.     

Summer diet of Weddell Seals (Leptonychotes weddelli) in the eastern and southern Weddell Sea,Antarctica

Summary Stomach and intestine samples from 21 adult Weddell seals were used to study the diet of these seals from the eastern and southern Weddell Sea coast from January to February 1983 and 1985. Fish occurred in all seals, squid in five, octopods in three and Euphausia crystallorophias in one seal. Pleuragramma antarcticum was the predominant fish in the diet, constituting 61.1% of otoliths in 1983 samples and 93.8% in 1985. Aethotaxis mitopteryx, Dissostichus mawsoni, unidentified Trematomus spp. and channichthyids were also recorded. Size and wet weight of P. antarcticum were calculated from uneroded otoliths, found in 6 seal stomachs with liquid food pulp, collected during early morning hours in 1985. Size distribution of P. antarcticum from individual seals was reasonably constant, ranging between 5.0 and 22.0 cm SL; adult fish from about 14.0 to 19.0 cm SL predominated. P. antarcticum in seals from the southern area had a larger median size (16.5 cm SL), than those from further east (15.5 cm SL). Calculated wet weights of all P. antarcticum from individual seal stomachs ranged between 4.7 and 16.9 kg the mean was 12.8 kg. Comparisons with net-hauls from the southern Gould Bay suggest that Weddell seals feed mainly in deeper water layers (>400 m) where adult P. antarcticum occur at higher densities.     

A trophic mass balance model of the eastern Chukchi Sea with comparisons to other high-latitude systems

The Chukchi Sea is a seasonally ice-covered, marginal Arctic-shelf sea that possesses both large petroleum reserves and abundant biological communities, including migratory mammals and seabirds. We developed a mass balance food web model for the eastern Chukchi Sea to evaluate the trophic structure of this ecosystem and to compare food web properties of the Chukchi Sea to those of other high-latitude marine ecosystems. We compiled data on biomass levels, diet composition, demographic rates (production, consumption), and fishery removals, and used these data to construct an Ecopath trophic mass balance model. The majority of biomass was concentrated in benthic invertebrates and most of the mass flow above trophic level 2.0 was through these groups. We found that density estimates of most fish groups derived from trawl survey data using area-swept methods were insufficient to match the consumptive demands of predators, and that densities needed to be several-fold greater to meet modeled demand. We also used a set of system metrics derived from a common modeling framework to highlight differences in ecosystem structure between the eastern Chukchi Sea and other high-latitude systems. The extent of benthic dominance observed in the eastern Chukchi Sea was unique among the systems examined, both in terms of food web structure and associated mass flows between benthic and pelagic components. In relation to total biomass density, the eastern Chukchi Sea had low production when compared with the other systems, and this lower turnover rate suggests that recovery from disturbance might be slow.     

Food sources and trophic structure of fishes and benthic macroinvertebrates in a tropical seagrass meadow revealed by stable isotope analysis

Stable carbon and nitrogen isotope analysis was used to examine the food sources and trophic structure of 17 fish species and six groups of benthic macroinvertebrates in a seagrass meadow in North Sulawesi, Indonesia. The seagrass, their associated epiphytes, sediment organic matter (SOM) and particulate organic matter (POM) were identified to be the food sources, with δ¹³C values ranging from ?19.49 (POM) to ?9.66‰ (seagrass). The δ¹³C of the 23 fauna taxa were between ?18.57 (Arothron manilensis) and ?11.62‰ (Protoreaster sp.). For five of the six groups of benthic macroinvertebrates, seagrass and their epiphytes contributed more than 69.4%. For 14 of the 17 fish species, seagrass and their epiphytes are the main contributors. For 15 of the 17 fishes, the trophic levels inferred from SIA are lower than those from the previously reported diet composition analysis. These findings show that seagrass and their epiphytes are consumed by most of the fish and benthic macroinvertebrates, and are important for a large portion of the food web in seagrass meadows in the Coral Triangle area.