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This study presents a comprehensive assessment of persistent organic pollutants (POPs) in the blubber of a stranded blue whale found on the coast of Taiwan. The analysis included polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), Hexachlorobenzene (HCB), and polybrominated diphenyl ethers (PBDEs). The whale exhibited evident signs of emaciation, including low body weight, reduced blubber fat content, and thin blubber thickness. The dominant fatty acid type detected in the blubber was short-chain monounsaturated fatty acids (SC-MUFA), known to aid in thermoregulation. Stable isotope ratios indicated that the blue whale occupied a lower trophic position compared to a fin whale, suggesting its proximity to krill habitats in the Southern Ocean for feeding. The average concentrations of DDTs (1089.2 ± 4.7 ng/g lw; ΣDDT) and PCBs (1057.1 ± 49.8 ng/g lw) in the blubber were almost one order of magnitude higher than PAHs (41.7 ± 10.0 ng/g lw), HCB (70.6 ± 2. ng/g lw), and PBDEs (7.2 ± 1.2 ng/g lw). Pollutant concentrations in this individual blue whale were comparable to levels found in Norway, higher than those found in Chile, and notably lower than those found in Canada and Mexico. Calculating the biomagnification factor (BMF) for the POPs from krill (Euphausia superba) to the blue whale revealed significant bioaccumulation of pollutants in this particular whale. Additional research is imperative to achieve a thorough comprehension of bioaccumulation of POPs and their potential toxicological impacts on whale health. [ABSTRACT FROM AUTHOR]

The results of analysis on the feeding patterns and assessment of the trophic levels and niches in two Zoarcidae species Bothrocara brunneum and B. zestum from the deep-water areas in the Sea of Okhotsk and the Pacific Ocean off the Lesser Kuril Ridge have been reported. Both species feed on various benthic and mesobenthic forage organisms including crustaceans, mesopelagic fishes, cephalopods, bivalved mollusks, polychaetes, and echinoderms. Despite the dominant food component variability across different water areas, crustaceans represent the major food group. In addition, both fish species have similar food sources and, therefore, trophic niches. It is proven by estimation with the standard ellipse area method via the Bayesian probability, showing rather similar widths of trophic niches: 17.7 for B. zestum and 16.6 for B. brunneum. The actual values for stable nitrogen isotope ratios (δ15N) in food components indicate a wide range of trophic levels in the analyzed species: from 2.08 to 4.36 in B. zestum and from 1.97 to 4.42 in B. brunneum, which can prove their plasticity in selecting the food items. The ranges of values for the stable carbon isotope ratios (δ13C) in food components indicating the basal food sources reached 15.04 to 23.43‰ for B. zestum and 15.07 to 23.43‰ for B. brunneum. The survey-based new information on two species feeding was obtained to determine their roles in the trophic structures of ecosystems in the studied water areas. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the trophic structure and carbon sources supporting fish assemblages of five low-productivity rivers with different dimensions. Using carbon (δ13C) and nitrogen (δ15N) isotope ratios, we identified the major carbon sources to fish species and estimated fish trophic positions in each river. We observed a similar trophic structure in almost all low-productivity rivers. Detritus (allochthonous resources derived from riparian zone—CPOM and processed organic matter from upstream sources—FPOM) were important to sustain the fish assemblages, especially in smaller rivers. We also observed a growing consumption of autochthonous primary producers, algae and periphyton, with the increase in river dimensions and especially for primary consumers. Fishes from the smallest river occupied lower mean trophic positions; however, the assemblage exhibited wider food-chain length than those from larger rivers. Our results indicate an important role of autochthonous primary producers even in rivers with low nutrient concentrations. These results are important to increase the knowledge about medium-size oligotrophic rivers, especially because tropical rivers can support highly diverse fish assemblages and productive fisheries even exhibiting low in situ primary productivity. [ABSTRACT FROM AUTHOR]

Stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N) in soft tissues of 41 abundant macrobenthic species from the continental slope of the Sea of Okhotsk were determined. The δ15N and δ13С values of invertebrate species and groups studied were highly variable, reflecting the diversity of their ratio compositions. The range of δ 15N values (from 6.8 to 18.3‰) corresponded to four trophic levels: from second (for detritivorous bivalve molluscs) to fifth (for some species of carnivorous gastropods and starfish). [ABSTRACT FROM AUTHOR]

The order of magnitude of biomass and production at various trophic levels in the epipelagic community has been calculated, and the main pathways for the transformation of matter and energy in the Bering Sea have been identified. For each group of aquatic organisms, the average indicators of biomass, production, and grazing (feeding) consumption were estimated. According to long-term average data (1986–2020), 1054.7 million tons C/year of organic matter was produced in epipelagic zone of the Bering Sea at the 1st trophic level, 120.4 million tons C/year, at the 2nd trophic level, 20.7 million tons C/year, at the 3rd trophic level, 0.93 million tons C/year, at the 4th one, 0.015 million tons C/year, at the 5th level. The annual production of aquatic organisms in the epipelagic zone of the Bering Sea is exceeds 1 billion tons C/year (1196.8 million tons C/year) or 21.4 billion tons of wet weight. Excluding primary production, which is 72.6% of gross production in carbon equivalent, microheterotrophs (15.5%) and dominant zooplankton groups (copepods—7.3%, euphausiids—1.9%, chaetognaths—1.1%, and hyperiids—0.5%) contribute most significantly to annual production. The contribution of the functional groups of the nekton (pollock Gadus chalcogrammus, squid, salmon, and mesopelagic fish) is approximately 1–2 orders of magnitude lower. Altogether, the share of the heterotrophic part of the biocenosis in the epipelagic zone of the Bering Sea accounts for about 27% of production. The powerful development of representatives of the 2nd trophic level (mainly copepods and, to a lesser extent, euphausiids) suggests that the level of grazing pressure from planktonic and nektonic predators may be higher. The forage base of the Bering Sea is capable of providing food for nekton stock exceeding the current level. This conclusion is important from the standpoint of the development of grazing aquaculture of valuable pelagic fish, including salmon. [ABSTRACT FROM AUTHOR]

Archaeofaunal remains from the central Georgia Bight (USA) are used in a case study for assessing coastal fisheries between 2760 BCE and 1500 CE, particularly from the perspective of sustainability. The longevity of this fishery is evaluated in terms of taxonomic attributions, richness, ubiquity, diversity, and mean trophic level (TL) of fish individuals (MNI) in assemblages from 22 coastal archaeological sites. The average pre-1500 TL (TL = 3.1) is below that of fish populations in a mid-twentieth-century ecological study (TL = 3.3). Although broad features of the regional fishery were sustained for millennia, practices at specific locations were influenced by environmental and cultural phenomena. [ABSTRACT FROM AUTHOR]

Aims: Root lesion nematodes (RLN) have negative impacts on legume-grass systems. These impacts might be moderated by bacterial feeding nematodes (BFN) presence. It remains unknown how these trophic groups of nematodes interactively impact plant productivity and dynamics of carbon (C) and nitrogen (N) in grass-legume mixtures. We addressed this research gap using inter-kingdom interactions in a model system. Methods: Chickpea and oat were grown in mono- and mixed cultures, and RLN and BFN were applied alone and in combination. Plant biomass, shoot C and N content and isotopic composition, and mineral N in soil were measured. Results: RLN presence reduced root biomass across treatments. This reduction was stronger in the grass than the legume and was not modified by BFN. Nematodes increased plant shoot N concentrations. RLN and BFN had interactive effects on shoot nutrient concentration resulting in reduced shoot C concentration when both trophic groups were combined. Shoot δ15N data revealed transfer of symbiotically fixed N from chickpea to oat in the presence of RLN. However, this N transfer did not result in improved oat growth. Conclusions: Interactive effects of soil organisms can cascade aboveground, influencing C and N dynamics and ecosystem productivity. [ABSTRACT FROM AUTHOR]

Most research reports changes in biological communities and environmental stability by using community estimators (e.g. species richness and relative abundance) and food-web metrics (e.g. connectance and vulnerability), yet only a few studies have examined how both community and food-web estimators temporally change in tropical terrestrial environments. Here, we sampled 1399 fruits and 12,647 seeds from the climbing shrub Senegalia tenuifolia (Fabaceae: Mimosoideae) across eight fragments in three areas of Brazilian savannah sampled annually during 4 years to assess the temporal variation within community and food-web metrics commonly used in the tropical research. While resource availability and the abundance of insects from the second and third trophic levels changed with time, species richness from all trophic levels and food-web metrics remained temporally stable. We found that α-diversity was the most important diversity-component influencing the herbivore communities when partitioning the diversity using raw species richness and the Shannon entropy, while for parasitoids the contributions of α and ß varied. These findings provide insights into the temporal variation of terrestrial food webs, while highlighting the need for further research considering both community metrics and food-web estimators to better understand the stability of tropical environments. We bring empirical evidence that communities within plant–herbivore–parasitoid networks may be dynamic, but food-web metrics are likely to remain temporally stable within undisturbed environments. [ABSTRACT FROM AUTHOR]

To trace predator‒prey interactions in the marine environment, fatty acids (FAs) were widely applied as qualitative markers. Recently, two tetracosapolyenoic acids (TPA), which are specific markers of soft corals, have been found in the nudibranch mollusk Tritonia tetraquetra collected in the deep waters of the Sea of Okhotsk. This mollusk does not synthesize TPA but preys mostly on the soft coral Gersemia fruticosa. Both invertebrates are common species in Arctic and boreal regions and may be a simple model for the investigation of FA marker transfer from one trophic level to another. A lipidomic approach was applied to study the transfer of the FA markers in this predator-prey system. The structure and content of the molecular species of polar lipids (polar lipidome) of both animal species were analyzed by high-performance liquid chromatography with high-resolution tandem mass spectrometry. The distribution of several principal FA markers in lipid molecular species was determined. C20 monoenoic FAs of the coral were not integrated in the most of nudibranch lipids. Arachidonic and eicosapentaenoic acids mainly esterified ethanolamine and choline glycerophospholipids (PE and PC) in both invertebrates. In the coral polar lipidome, TPA concentrated in serine glycerophospholipids (PS). The nudibranch decomposed coral lipids and reallocated TPA to PS, PE, and PC. We suppose that this reallocation is responsible for the accumulation of TPA in the nudibranch. The nudibranch differed from the coral in biosynthetic relationships of phospholipid classes. The lipidomic approach explains the rearrangement of dietary FAs in the predator lipids. This rearrangement can be important for the trophic uptake and transfer of lipids in polar marine ecosystems. [ABSTRACT FROM AUTHOR]

Decomposition processes are a major source of energy in lagoon ecosystems, but compared to primary production, little quantitative information is available on their relative importance for energy pathways within lagoon food webs. Here, the ability of cross-community scaling relationships (CCSRs) to describe energy pathways in macroinvertebrate guilds from size-specific density estimates was tested in order to determine whether CCSRs distinguish between i. predators and prey guilds in energetic terms, ii. suspension and deposit feeders in terms of their energy sources, iii. deposit feeder sub-guilds (i.e. scrapers/shredders and gathering collectors), and iv. phyto-benthic habitats in terms of their influence on energy pathways. CCSRs differentiated predator from prey guilds, with the size-specific density of prey being one order of magnitude higher than that of predators, and deposit from suspension feeder guilds, to a similar degree. CCSRs differentiated vegetated from non-vegetated benthic habitats, with higher size-specific density in the former than in the latter, while they did not differentiate large- from small-particle feeders. Based on simple data collection and widely available data on 15 Mediterranean and Black Sea lagoons, CCSRs seem to be able to quantitatively describe energy pathways in benthic macroinvertebrate communities, expanding our knowledge of biodiversity drivers in lagoon ecosystems. [ABSTRACT FROM AUTHOR]

Zooplankton plays an important role in aquatic food webs by fluxing of energy from primary producer to subsequent trophic levels in the food chain. The annual pattern of zooplankton communities and potential environmental drivers were studied in the Kohelia channel, Bangladesh from summer 2014 to spring 2015. Samples were collected using net at a depth of 1 m. A total of 32 species belonged to 18 orders, 27 families and 15 taxonomic groups were identified. Of these species, 22 distributed in all four seasons of which 8 were dominant and highly contributing to the total communities. Species number peaked in summer next to winter and fall in spring while maximum abundance was in summer and minimum in spring. Multivariate analyses showed that there was a clear annual pattern in the zooplankton communities. Species diversity and evenness peaked in spring but fall in autumn while the high value of species richness was found in winter. Biological-environmental best matching (BIO-ENV) analyses conformed that community pattern of zooplankton was mainly driven by transparency salinity, and temperature individually or combined with water nutrients. These results demonstrate that annual pattern of the zooplankton community shaped by channel environmental factors in subtropical channel ecosystems, thus might be used for community-based subtropical coastal water bioassessment. [ABSTRACT FROM AUTHOR]

Background and aims: Irrigation-maintained artificial oases (AO) in arid regions of northwestern China provide vital human settlement sites. Recent human population increases has caused rapid AO expansion, mainly through transforming natural grassland to arable and afforested land. Here, we assessed how soil biodiversity is affected by various AO expansion strategies, each representing historical land-use regimes.Methods: We sampled six dominant functional groups of soil biota, covering multiple trophic levels: macrofauna consumers (predators and insect herbivores), mesofauna decomposers (Oribatida and Collembola), and microbial decomposers (bacteria and fungi). Sampling was carried out in three AO sites of northwestern China, each containing distinct land uses: natural grasslands (NG; non-irrigated), shrub (Haloxylon ammodendron) plantations (SP; non-irrigated), tree (Populus gansuensis) plantations (TP; irrigated), and arable lands (AL; irrigated).Results: The conversion of NG to SP, TP, and AL eliminated or reduced the abundance of some NG-adapted taxa. Their replacements were exotic species better suited for anthropogenic habitats. As a result, community composition shifted in all six functional groups, with greater differences between NG and TP and AL than between NG and SP. Based on taxonomic gains and losses within each group, we determined that NG to SP conversion positively affected diversity among predators, Collembola, and fungi, but negatively affected diversity of insect herbivores and Oribatida. Bacterial diversity remained unaffected. However, converting NG to TP and AL significantly promoted diversity in all six functional groups, although effect sizes differed.Conclusions: Our results suggest that different AO expansion strategies differentially affected the diversity and structure of belowground communities, which in turn, cascaded down to ecosystem functioning differently. These findings not only contribute to a better understanding of how the diversity and community composition within soil food-webs respond to land-use change but also provide key insights into the development of management strategies for AO ecosystems in drylands to mitigate the negative impact of land-use change on soil biodiversity and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Data on the biochemical composition and caloric content of common species of the zoobenthos of the western Kamchatka shelf were estimated for the entire body of an organism together with the integument and separately for muscle tissue. Estimates of the gross biomass of zoobenthos at different trophic levels calculated from bottom trawl and dredge sampling data, taking the isotope composition of benthic invertebrates into account, showed that the proportion of zoobenthos at the second trophic level was approximately 87%, while at the subsequent trophic levels it only slightly exceeded 13%. More than 70% of the energy was concentrated in valuable forage species. The total amount of energy at the second trophic level was 77.8%, while at the third and fourth levels it was 22.2%. [ABSTRACT FROM AUTHOR]

Soil food webs of the McMurdo Dry Valleys, Antarctica are simple. These include primary trophic levels of mosses, algae, cyanobacteria, bacteria, archaea, and fungi, and their protozoan and metazoan consumers (including relatively few species of nematodes, tardigrades, rotifers, and microarthropods). These biota are patchily distributed across the landscape, with greatest faunal biodiversity associated with wet soil. Understanding trophic structure is critical to studies of biotic interactions and distribution; yet, McMurdo Dry Valley soil food web structure has been inferred from limited laboratory culturing and microscopic observations. To address this, we measured stable isotope natural abundance ratios of C (13C/12C) and N (15N/14N) for different metazoan taxa (using whole body biomass) to determine soil food web structure in Taylor Valley, Antarctica. Nitrogen isotopes were most useful in differentiating trophic levels because they fractionated predictably at higher trophic levels. Using 15N/14N, we found that three trophic levels were present in wet soil habitats. While cyanobacterial mats were the primary trophic level, the nematode Plectus murrayi, tardigrade Acutuncus antarcticus, and rotifers composed a secondary trophic level of grazers. Eudorylaimus antarcticus had a 15N/14N ratio that was 2-4‰ higher than that of grazers, indicating that this species is the sole member of a tertiary trophic level. Understanding the trophic positions of soil fauna is critical to predictions of current and future species interactions and their distributions for the McMurdo Dry Valleys, Antarctica. [ABSTRACT FROM AUTHOR]

Recent influxes of warm Atlantic water into the fjords of west Spitsbergen have led to concomitant influx of more temperate and boreal fish species. The changes in the water masses within the fjords naturally affect all trophic levels of the sympagic, benthic, and pelagic food chains in the area. The most abundant marine mammal species in the fjords of west Spitsbergen is the ringed seal ( Pusa hispida), which feeds, breeds, and moults in this area. In this study, we used isotopic data from whiskers of two cohorts of adult ringed seals (sampled in 1990 and 2013) to determine whether signals of ecosystem changes were detectable in this top marine predator. Acknowledging the limitations to our understanding of whisker growth in phocid seals, we interpreted the isotopic data from whiskers under two alternate hypotheses of whisker replacement dynamics and the dietary periods that might be represented. Even under the most conservative hypothesis, it is clear from our data that changes in the marine food web of the west Spitsbergen coast have occurred over the last 20 years, and that these are detectable in the isotopes incorporated into higher trophic predators. Concluding which aspect of the food web has been modified is complicated by a lack of recent ringed seal dietary studies, a knowledge gap that should be prioritised as the climate continues to change. [ABSTRACT FROM AUTHOR]

Interaction webs, or networks, define how the members of two or more trophic levels interact. However, the traits that mediate network structure have not been widely investigated. Generally, the mechanism that determines plant-pollinator partnerships is thought to involve the matching of a suite of species traits (such as abundance, phenology, morphology) between trophic levels. These traits are often unknown or hard to measure, but may reflect phylogenetic history. We asked whether morphological traits or phylogenetic history were more important in mediating network structure in mutualistic plant-pollinator interaction networks from Western Canada. At the plant species level, sexual system, growth form, and flower symmetry were the most important traits. For example species with radially symmetrical flowers had more connections within their modules (a subset of species that interact more among one another than outside of the module) than species with bilaterally symmetrical flowers. At the pollinator species level, social species had more connections within and among modules. In addition, larger pollinators tended to be more specialized. As traits mediate interactions and have a phylogenetic signal, we found that phylogenetically close species tend to interact with a similar set of species. At the network level, patterns were weak, but we found increasing functional trait and phylogenetic diversity of plants associated with increased weighted nestedness. These results provide evidence that both specific traits and phylogenetic history can contribute to the nature of mutualistic interactions within networks, but they explain less variation between networks. [ABSTRACT FROM AUTHOR]

In this study, concentration of mercury was determined in the trophic levels of benthic, benthopelagic, pelagic fish species, and river birds from Arvand River, located in the Khuzestan province in the lowlands of southwestern Iran at the head of the Persian Gulf. The order of mercury concentrations in tissues of the fish species was as follows: liver>gill>muscle and in tissues of the kingfisher species was as follows: feather>liver>kidney>muscle. Therefore, liver in fish and feather in kingfisher exhibited higher mercury concentration than the other tissues. There was a positive correlation between mercury concentrations in fish and kingfisher species with size of its food items. We expected to see higher mercury levels in tissues of female species because they are larger and can eat larger food items. The results of this study show that the highest mean mercury level were found in the kingfisher ( Anas crecca), followed by benthic ( Epinephelus diacanthus), benthopelagic ( Chanos chanos), and pelagic fish ( Strongylura strongylura). Mean value of mercury in fish species, S. strongylura were (0.61 μg g −1 dry weight), C. chanos (0.45 μg g −1 dry weight), E. diacanthus (0.87 μg g −1 dry weight), and in kingfisher species A. crecca was (2.64 μg g −1 dry weight). Significant correlation between mercury concentration in fish and kingfisher may be related to high variability of mercury in the fish. [ABSTRACT FROM AUTHOR]

While numerous studies have examined the effects of increased primary production on higher trophic levels, most studies have focused primarily on the grazing food web and have not considered the importance of alternate prey channels. This has happened despite the fact that fertilization not only increases grazing herbivore abundance, but other types of consumers such as detritivores that serve as alternate prey for generalist predators. Alternate prey channels can sustain generalist predators at times when prey abundance in the grazing food web is low, thus increasing predator densities and the potential for trophic cascades. Using arthropod data from a fertilization experiment, we constructed a hierarchical Bayesian model to examine the direct and indirect effects of plant production and alternate prey channels on predators in a salt marsh. We found that increased plant production positively affected the density of top predators via effects on lower trophic level herbivores and mesopredators. Additionally, while the abundance of algivores and detritivores positively affected mesopredators and top predators, respectively, the effects of alternate prey were relatively weak. Because previous studies in the same system have found that mesopredators and top predators rely on alternate prey such as algivores and detritivores, future studies should examine whether fertilization shifts patterns of prey use by predators from alternate channels to the grazing channel. Finally, the hierarchical Bayesian model used in this study provided a useful method for exploring trophic relationships in the salt marsh food web, especially where causal relationships among trophic groups were unknown. [ABSTRACT FROM AUTHOR]

Purpose: In order to assess possible adverse effects originating from pulp deposits in a Swiss lake, a sediment quality triad approach was applied with chemical, ecotoxicological and ecological assessment methods. Materials and methods: To obtain an integrative picture of the potential ecotoxicological effects on organisms of different trophic levels, four test procedures were applied. The acute effects of pulp deposit pore water on a decomposer, the amphipod Gammarus fossarum, were monitored. Chronic toxicity of the pore water was evaluated on primary producers via a growth inhibition test with unicellular green algae ( Pseudokirchneriella subcapitata) and on secondary consumers in a reproduction test with the water flea Ceriodaphnia dubia. To evaluate the effects of the pulp deposit on sediment inhabitants, a whole-life-cycle test with the non-biting midge Chironomus riparius was undertaken. Chemical assessment included dissolved organic carbon, extractable organic halogenic compounds, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and heavy metals. The composition of the macrozoobenthos community was analysed in order to assess the ecological effects. Results and discussion: G. fossarum displayed increased locomotor activity at 12.5% but not at 25% sample concentration during a short-time exposure of 20 h. Chronic effects compromised the reproduction and growth of C. dubia (lowest observed effect concentration, 12.5% sample concentration) with zero population growth in 100% pulp deposit pore water. In 100% pulp deposit, C. riparius exhibited increased mortality at 10 and 17 days after oviposition. Pulp deposits of 50% and 100% concentration caused a significantly lower emergence compared with the reference treatments (lake sediment and quartz sand). Additionally, the locomotor activity of chironomids decreased significantly in 25-100% pulp deposit. No chronic effects of pulp deposit pore water on algae photosynthesis and growth could be detected. The bioassay results were in accordance with an elevated content of PAHs, PCBs and metals in the pulp deposit. Significantly more organisms known to be tolerant to organic pollution were present within the macrozoobenthos community. Conclusions: In general, for sediment inhabitants such as chironomids, the pulp deposit has to be classified toxic. In the present test setup, the toxicity of the pulp deposit was reflected better by the chronic test systems applied than by the acute ones. The applied testing framework could be a suitable tool to assess the risk of contaminated sites, and this information will help decide whether risk mitigation measures should be taken. In addition, with a similar approach, the success of any mitigation measures taken can be assessed. [ABSTRACT FROM AUTHOR]

Lake Taihu is a large, shallow, and eutrophic lake in China. It has provided local communities with valuable fisheries for centuries, but little is known of the trophodynamics, or of its faunal communities. Carbon and nitrogen isotopic composition was used to assess its trophic pathways and the food web structure [food sources and trophic levels (TL)]. Basal food sources were distinguishable based on their δC values, ranging from −27.2 to −15.2‰. Consumers were also well separated in δC (−26.9 to −17.9‰ for invertebrates and −25.7 to −18.1‰ for fishes), which allowed for an effective discrimination of carbon sources between these fauna. An average trophic enrichment factor of 3.4‰ was used to calculate the TLs based on δN of zooplankton, with results indicating a food web having four TLs. Although δN values overlap and cover a large range within trophic compartments, the isotopic signatures of the species assessed revealed a general trend of N enrichment with increasing TL. Stable isotope signatures were also used to establish a general food web scheme in which five main trophic pathways were analyzed. [ABSTRACT FROM AUTHOR]

Organism growth and reproduction are often limited by nutrient availability in freshwater ecosystems where, in some cases, food webs are primarily supported by allochthonous organic matter. Therefore, we hypothesized that the composition of riparian vegetation would influence the variability of N, P, and fatty acid content of in-stream consumers. Specifically, we predicted that organisms living in alder streams would have higher levels of N, P, and polyunsaturated fatty acids than organisms in coniferous streams. To determine this, we sampled fresh and aged leaf litter, periphyton, invertebrates, and cutthroat trout ( Oncorhynchus clarki) from 6 streams in western Washington state: 3 streams had high densities of nitrogen-fixing red alder ( Alnus rubra) in the riparian zone, whereas 3 had high densities of conifers. We found fresh alder litter had twice the total polyunsaturated fatty acid concentrations of hemlock vegetation while there were few statistical differences among aged alder and aged hemlock vegetation. Multidimensional plots showed fatty acid profiles were unique to vegetation and fish while periphyton and invertebrates shared the same multidimensional space. We used a mixed model to determine the relative importance of vegetation type (fixed factor: conifer or alder), trophic levels (fixed factor: periphyton, primary consumer, or fish), and streams (random factor) on individual fatty acid concentrations. Total polyunsaturated fatty acids, 16:0, 20:1, 20:3n6 and total n3 were the only fatty acids influenced by stream vegetation (vegetation + stream model or full model). 67% of the fatty acids were best supported by the trophic + stream model. Nitrogen, P, Ca, Fe, C:N, N:P, and C:N:P were all best supported by the trophic level + stream model, and Zn was the only nutrient supported best by the full model. Correlations of n3 and n6 fatty acid concentrations between periphyton and primary consumers, and primary consumers with trout indicated several fatty acid metrics, such as n3:n6, showed food resources may affect relative fatty acid abundances of consumers. Although vegetation type did not influence relative fatty acids of stream organisms, the importance of trophic level likely indicates organisms have different physical requirements for fatty acids. The significance of a random factor, 'stream,' suggests that the relative abundances of fatty acids in periphyton, invertebrates, and trout are stream-specific and are responding to local environmental or communal variables. [ABSTRACT FROM AUTHOR]

In marine food web studies, stable isotopes of nitrogen (δN) and carbon (δC) are widely used to estimate organisms' trophic levels (TL) and carbon sources, respectively. For smaller organisms, whole specimens are commonly analyzed. However, this 'bulk method' involves several pitfalls since different tissues may fractionate stable isotopes differently. We compared the δN and δC values of exoskeleton versus soft tissue, in relation to whole specimens, of three common Arctic amphipods in Svalbard waters: the benthic Anonyx nugax, the sympagic (ice-associated) Gammarus wilkitzkii and the pelagic Themisto libellula. The δN values of the exoskeletons were significantly lower than those of the soft tissues for A. nugax (10.5 ± 0.7‰ vs. 15.7 ± 0.7‰), G. wilkitzkii (3.3 ± 0.3‰ vs. 8.3 ± 0.4‰) and T. libellula (8.6 ± 0.3‰ vs.10.8 ± 0.3‰). The differences in δC values between exoskeletons and soft tissues were insignificant, except for A. nugax (−21.2 ± 0.2‰ vs. −20.3 ± 0.2‰, respectively). The δN values of whole organisms were between those of the exoskeletons and the soft tissues, being similarly enriched in N as the exoskeletons (except G. wilkitzkii) and depleted in N by 1.2-3.7‰ compared to the soft tissues. The δN-derived TLs of the soft tissues agreed best with the known feeding preferences of the three amphipods, which suggest a potential underestimation of 0.5-1.0 TL when stable isotope analyses are performed on whole crustaceans with thick exoskeletons. The insignificant or small differences in δC values among exoskeletons, soft tissues and whole specimens, however, suggest low probability for misinterpretations of crustaceans' primary carbon source in marine ecosystems with distinctly different δC-carbon sources. [ABSTRACT FROM AUTHOR]

The Ponto-Caspian round goby ( Neogobius melanostomus, Pallas 1814) most probably was established in the Gulf of Gdańsk, Baltic Sea, in the late 1980’s and has since become one of the dominant species in the region. In this study we assess the role of round gobies as prey for two important fish species in the Gulf of Gdańsk, cod ( Gadus morhua) and perch ( Perca fluviatilis). We compared their present diet with stomach analyses from the area prior the round goby establishment, as well as with diet analysis from Baltic regions where round gobies are absent. There were large differences in the diet between cods from the Gulf of Gdańsk 2003–2006 compared to cods in earlier studies (1977–1981) from the Southern Baltic Sea. There were also large differences in cod and perch diets from areas with and without round goby. Presently, round goby constitutes the most important prey for medium sized cods in Gulf of Gdańsk, and perch from the same area almost exclusively feed on gobiids. Stomach analysis, trophic level estimates, and stable isotope analyses all indicated that cod and perch in Gulf of Gdańsk after the round goby establishment belonged to a similar trophic level. Beside round goby, no mussel feeding fish contributed much to the diet of cod or at all to the diet of perch. Thus, it is likely that round gobies constitute a new energetic pathway from mussels to top predators. However, due to the short time elapsed after round goby establishment, we can only speculate on the species future impacts on Baltic food webs. [ABSTRACT FROM AUTHOR]

Brassica crops are grown worldwide for oil, food and feed purposes, and constitute a significant economic value due to their nutritional, medicinal, bioindustrial, biocontrol and crop rotation properties. Insect pests cause enormous yield and economic losses in Brassica crop production every year, and are a threat to global agriculture. In order to overcome these insect pests, Brassica species themselves use multiple defence mechanisms, which can be constitutive, inducible, induced, direct or indirect depending upon the insect or the degree of insect attack. Firstly, we give an overview of different Brassica species with the main focus on cultivated brassicas. Secondly, we describe insect pests that attack brassicas. Thirdly, we address multiple defence mechanisms, with the main focus on phytoalexins, sulphur, glucosinolates, the glucosinolate-myrosinase system and their breakdown products. In order to develop pest control strategies, it is important to study the chemical ecology, and insect behaviour. We review studies on oviposition regulation, multitrophic interactions involving feeding and host selection behaviour of parasitoids and predators of herbivores on brassicas. Regarding oviposition and trophic interactions, we outline insect oviposition behaviour, the importance of chemical stimulation, oviposition-deterring pheromones, glucosinolates, isothiocyanates, nitriles, and phytoalexins and their importance towards pest management. Finally, we review brassicas as cover and trap crops, and as biocontrol, biofumigant and biocidal agents against insects and pathogens. Again, we emphasise glucosinolates, their breakdown products, and plant volatile compounds as key components in these processes, which have been considered beneficial in the past and hold great prospects for the future with respect to an integrated pest management. [ABSTRACT FROM AUTHOR]

Background, Aim and Scope. The toxicity of contaminated sediments should be evaluated considering the direct exposure of laboratory organisms to whole sediments and the indirect exposure to elutriates or extracts (Tay et al. 1992, Byrne and Halloran 1999, Nendza 2002). The alga Dunaliella tertiolecta is indicated for the use in toxicity bioassays because it is highly sensitive to several xenobiotics. Harpacticoid copepods have been already used for toxicity testing and Tigriopus fulvus is a promising Mediterranean target-species in ecotoxicology (Todaro et al. 2001, Faraponova et al. 2003, Pane et al. 2005a). In this study, the toxicity of sediments collected in harbour sites of the Northeastern Adriatic Sea was evaluated by growth inhibition test with free living and alginate-immobilized Dunaliella tertiolecta and acute toxicity test with nauplii and adult Tigriopus fulvus with the aim of pointing out the importance to utilize model organisms from different trophic levels in sediment ecotoxicology. Methodology. Elutriates and whole sediments were tested on free living and immobilized (Pane et al. 1998) algal cells, and on laboratory reared copepods. Free-living D. tertiolecta were ex- posed to diluted elutriates in a static, multi-well plate system. Na-alginate immobilized D. tertiolecta were placed in polystyrene inserts fitted with polyester mesh bottoms and exposed to a thin layer (2 mm) of whole sediments in multi-well plates (EPS 1992, Pane and Bertino 1999). Toxicity tests with copepods were carried out on Tigriopus fulvus nauplii (elutriates) and adults (whole sediments and elutriates). Same-aged nauplii useful for toxicity tests were obtained by egg sac detaching and consequent hatching stimulation (Pane et al. 2006). Newborn nauplii (I-II stage) were exposed to elutriates in multi-well plates provided with polystyrene inserts. Adult T. fulvus maintained in polystyrene inserts fitted with polyester mesh bottoms were placed in con- tact with a thin layer (2 mm) of whole sediment placed on multi- well plate bottoms. All end-points were evaluated after 96 h. Results. In general, the effects increased with the increasing of elutriate concentration up to 50%; the stimulation or inhibition of algal growth was statistically significant in comparison to the control. The inhibiting elutriates induced EC50 variations of algal growth ranging from 66.9% to 74.3%. The mortality of T. fulvus nauplii was always < 25% after treatment with 100% elutriates and < 10% after treatment with 50% dilution; no effect was shown up with 25% dilution; therefore LC50 was not calculable. The effect of elutriates was negligible on adult copepods and LC50 values were never calculable; percent mortality always resulted in < 10% after treatment with whole sediments. Discussion. Both experimental systems gave substantially similar results after exposition to whole sediments and elutriates. During the experiment with algal cells, the immobilization in Na-alginate and the employment of inserts which allowed the contact of organisms with sediments and their easy counting were particularly useful. Likewise, the employment of inserts of adequate mesh size in the tests with copepods allowed the con- tact of organisms with the sediment and made organism handling and counting easy, as well as the evaluation of mortality. The methodology here described and the utilization of the proposed test-species could have an importance also considering that the current trend in ecotoxicological research is towards finding the most appropriate organism for specific areas of concern by using indigenous species (Mariani et al. 2006) and towards the major significance of chronic and reproductive end-points. Conclusions.… [ABSTRACT FROM AUTHOR]

Phosphorus (P) to chlorophyll ratios and zooplankton–phytoplankton (Z:P) biomass ratios were assessed in 400 temperate lakes over a gradient of phosphorus (P) and with different fish communities. Most of the lakes in this survey were oligotrophic, with a median total P of 7.3 μg P L−1. Thus, the survey provided information on food web effects during the early phase of eutrophication. There was no tendency toward a reduced yield of autotrophs per unit of P over the gradient covered in this survey. The zooplankton yield per unit of P or chlorophyll a decreased slightly with increased nutrient concentrations, and Z:P biomass ratios decreased with fish community classes, reflecting increased fish predation pressure. However, the variability in biomass ratios within a given range of P and fish class was some 100 times higher than the difference over the gradients. This finding suggests that lake-specific properties, community composition, and food quality are by far the most important determinants of biomass ratios and probably also trophic efficiency in lakes; it further suggests that these factors are superimposed on the general effect of eutrophication, at least up to 30 μg P L−1. [ABSTRACT FROM AUTHOR]

For diverse communities of omnivorous insects such as ants, the extent of direct consumption of plant-derived resources vs. predation is largely unknown. However, determination of the extent of "herbivory" among ants may be crucial to understand the hyper-dominance of ants in tropical tree crowns, where prey organisms tend to occur scarcely and unpredictably. We therefore examined N and C stable isotope ratios (δ15N and δ13C) in 50 ant species and associated insects and plants from a tropical rainforest in North Queensland, Australia. Variation between ant species was pronounced (range of species means: 7.1‰ in δ15N and 6.8‰ in δ13C). Isotope signatures of the entire ant community overlapped with those of several herbivorous as well as predacious arthropods. Variability in δ15N between ants was not correlated with plant δ15N from which they were collected. Ant species spread out in a continuum between largely herbivorous and purely predacious taxa, with a high degree of omnivory. Ant species' δ15N were consistent with the trophic level predicted by natural feeding observations, but not their δ13C. Low δ15N levels were recorded for ant species that commonly forage for nectar on understorey or canopy plants, intermediate levels for species with large colonies that were highly abundant on nectar and honeydew sources and were predacious, and the highest levels for predominantly predatory ground-foraging species. Colonies of the dominant weaver-ants ( Oecophylla smaragdina) had significantly lower δ15N in mature forests (where preferred honeydew and nectar sources are abundant) than in open secondary vegetation. N concentration of ant dry mass showed only very limited variability across species and no correlation with trophic levels. This study demonstrates that stable isotopes provide a powerful tool for quantitative analyses of trophic niche partitioning and plasticity in complex and diverse tropical omnivore communities. [ABSTRACT FROM AUTHOR]

Effects of habitat fragmentation on species diversity and herbivore-parasitoid interactions were analyzed using the insect community of seed feeders and their parasitoids in the pods of the bush vetch (Vicia sepium L.). Field studies were carried out on 18 old meadows differing in area and isolation. The area of these meadows was found to be the major determinant of species diversity and population abundance of endophagous insects. Effects of isolation were further analyzed experimentally using 16 small plots with potted vetch plants isolated by 100–500 m from vetch populations on large old meadows. The results showed that colonization success greatly decreased with increasing isolation. In both cases, insect species were not equally affected. Parasitoids suffered more from habitat loss and isolation than their phytophagous hosts. Minimum area requirements, calculated from logistic regressions, were higher for parasitoids than for herbivores. In addition, percent parasitism of the herbivores significantly decreased with area loss and increasing isolation of Vicia sepium plots, supporting the trophic-level hypothesis of island biogeography. Species with high rates of absence on meadows and isolated plant plots were not only characterized by their high trophic level, but also by low abundance and high spatial population variability. Thus conservation of large and less isolated habitat remnants enhances species diversity and parasitism of potential pest insects, i.e., the stability of ecosystem functions. [ABSTRACT FROM AUTHOR]

The effects of an insect herbivore-resistant soybean genotype on relationships between four levels of a trophic system were examined in the laboratory using both greenhouse and field-grown plants. Pre-imaginal development of the predatory pentatomid, Podisus maculiventris (Say), was affected by soybean antibiosis in a manner similar to that of its lepidopteran prey, Pseudoplusia includens (Walker). Pre-imaginal development time was increased, and cumulative weight gain tended to be reduced on both greenhouse and field-grown resistant foliage; although mortality was increased on greenhouse-grown resistant foliage, it appeared unchanged on field-grown foliage. Reproductive capacity of P. maculiventris reared on P. includens larvae that were fed resistant soybean generally was unaffected, although peak progeny production was delayed and extended slightly. Pre-imaginal development and adult emergence of the egg parasitoid Telenomus podisi Ashmead from eggs of P. maculiventris reared on P. includens larvae that were fed resistant soybean were unaffected. However, the overall reproductive capabilities of this parasitoid were reduced. Our results demonstrate that plant antibiosis can influence the biology of organisms over four trophic levels, thus documenting a relationship heretofore undescribed. Determination of the final outcome of the interaction between plant resistance and biological control is difficult. The four trophic level model reported in this study further illustrates the complexity which hinhers a general understanding of these interactions. [ABSTRACT FROM AUTHOR]

Since the presentation of the Leopold Report (Leopold et al. 1963) to the United States Secretary of the Interior, recommendations in the document for managing natural park resources on the ecosystem level have been included in the management policies of the National Park Service. In many instances, however, management programs have continued to focus on individual resource problems, without apparent concern for the ecological consequences on ecosystems. Without knowledge of the interrelationships of ecosystem components, solving one problem may result in other resource problems. Graphic approaches are presented as potential tools to view these complex interrelationships relative to the needs of the resource manager. Interpreting the dynamics of aquatic systems is emphasized. [ABSTRACT FROM AUTHOR]

Nematodes have four juvenile stages and there is significant growth during development. The stages may differ in their respiratory and metabolic rates, and one stage may have significantly greater resistance to environmental stress. The mode of life of successive stages may vary from migratory to sessile. In both the Diplogasterida and Mononchida initial stages may be bacterial-feeding and later stages predatory on protozoa or nematodes. If the role of nematode species in promoting mineralization of nutrients is to be fully understood it is necessary to determine the trophic and metabolic characters of each stage under field conditions. [ABSTRACT FROM AUTHOR]