Food Web Ecosystem Research Articles

Mercury biomagnification in benthic, pelagic, and benthopelagic food webs in an Arctic marine ecosystem

Mercury (Hg) is a ubiquitous toxic metal that biomagnifies in food webs, and can reach high concentrations in top predators. Evaluating Hg biomagnification in Arctic marine food webs is critical for understanding Hg dynamics and estimating exposure to understudied fish and wildlife consumed by humans. The majority of studies conducted on Hg biomagnification in the Arctic have focused on pelagic food webs. Benthic and benthopelagic food webs in Arctic marine ecosystems also support many species of subsistence and commercial importance, and data are lacking for these systems. In this study, we investigated food web structure and Hg biomagnification for the benthic, pelagic, and benthopelagic marine food webs of inner Frobisher Bay in Nunavut. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N), as well as total (THg) and methyl (MeHg) mercury concentrations were measured in fish, invertebrates, and zooplankton. Biomagnification in each food web was quantified with Trophic Magnification Slopes (TMS) and Trophic Magnification Factors (TMF). The highest TMS and TMF values were exhibited by the benthopelagic food web (TMS = 0.201; TMF = 1.59), followed by the pelagic food web (TMS = 0.183; TMF = 1.52), and lastly the benthic food web (TMS = 0.079; TMF = 1.20), with δ15N explaining 88%, 79%, and 9% of variation in Hg concentrations, respectively. TMS and TMF values were generally low compared to other Arctic marine food webs. Results from food web structure analyses indicated that the benthic food web had the greatest trophic diversity, trophic redundancy, and largest isotopic niche area of all food webs studied. Greater food web complexity may thus result in reduced MeHg biomagnification, but further study is required. Acquiring Hg and food web structure data is critical for predicting the effects of climate-induced environmental change on Hg dynamics, especially in the context of Arctic marine ecosystems.

Applications of Mercury Stable Isotopes in Environmental Forensics

Mercury is a globally distributed toxic trace metal, which can travel long distances in the atmosphere and bioaccumulate to elevated levels in ecosystem food webs. Since 2013, various parts of the mercury life cycle, including the production, use, emissions, releases, as well as the environmental and ecosystem fate, have been governed via the global treaty on mercury, the Minamata Convention of Mercury. The convention also calls attention to the application of mercury stable isotopes for distinguishing between various mercury sources in environmental media and for identifying sources, which require targeted risk management. Here, we introduce ways in which mercury stable isotopes can be applied in the field of environmental forensics to identify sources responsible for local contamination and global cycling that require international governance. This review is divided into: 1) the general overview on the mercury speciation and cycling, 2) the nomenclature of mercury stable isotope systems, and 3) the introduction of case studies that have successfully utilized mercury isotopes to interpret legacy and recent mercury sources in atmospheric and freshwater environments. We conclude the review by making specific recommendations as to how mercury stable isotopes can be better utilized in the field of local and global environmental forensics. These recommendations include the development of comprehensive anthropogenic mercury source inventories and isotopic-based evidence on the transboundary transport of mercury.

Spatiotemporal carbon, nitrogen and phosphorus stoichiometry in planktonic food web in a northern coastal area

The concentrations of ambient nutrients and dissolved organic carbon (DOC) in northern coastal ecosystems often show large variations, due to the spatiotemporal differences in terrestial inputs. How these variations affect the stoichiometry of coastal planktonic organisms is, however, poorly known. Here we assessed the spatiotemporal variability of C, nitrogen (N), and phosphorous (P) concentrations of the seawater on the elemental stoichiometry of seston and dominant mesozooplankton taxa in a coastal area of the northern Baltic Sea. The freshwater inflow peaked in spring following the snowmelt and brought a significant amount of DOC, but not N and P to the coastal system. DOC was the main environmental descriptor for seston C:N stoichiometry. The C:N ratio of seston from 0.7 to 50 μm and mesozooplankton followed the temporal pattern of water C:N ratio, while the temporal trend of bacteria C:N showed an opposite pattern. Our results also indicated that the C:N ratio of seawater controlled both seston and mesozooplankton C:N ratios. Our findings imply that inflows of terrestrial DOC alter the stoichiometry and reduce the nutritional quality of planktonic food webs in northern coastal ecosystems.

Integrated model for food-energy-water (FEW) nexus to study global sustainability: The main generalized global sustainability model (GGSM).

Over the years, several global models have been proposed to forecast global sustainability, provide a framework for sustainable policy-making, or to study sustainability across the FEW nexus. An integrated model is presented here with components like food-web ecosystem dynamics, microeconomics components, including energy producers and industries, and various socio-techno-economic policy dimensions. The model consists of 15 compartments representing a simplified ecological food-web set in a macroeconomic framework along with a rudimentary legal system. The food-web is modeled by Lotka-Volterra type expressions, whereas the economy is represented by a price-setting model wherein firms and human households attempt to maximize their economic well-being. The model development is done using global-scale data for stocks and flows of food, energy, and water, which were used to parameterize this model. Appropriate proportions for some of the ecological compartments like herbivores and carnivores are used to model those compartments. The modeling of the human compartment was carried out using historical data for the global mortality rate. Historical data were used to parameterize the model. Data for key variables like the human population, GDP growth, greenhouse gases like CO2 and NOX emissions were used to validate the model. The model was then used to make long-term forecasts and to study global sustainability over an extended time. The purpose of this study was to create a global model which can provide techno-socio-economic policy solutions for global sustainability. Further, scenario analysis was conducted for cases where the human population or human consumption increases rapidly to observe the impact on the sustainability of the planet over the next century. The results indicated that the planet can support increased population if the per capita consumption levels do not rise. However, increased consumption resulted in exhaustion of natural resources and increased the CO2 emissions by a multiple of 100.

Large herbivorous wildlife and livestock differentially influence the relative importance of different sources of energy for riverine food webs

In many regions of the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences for terrestrial-aquatic ecosystem connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of energy supplying aquatic food webs along rivers: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. In Afromontane-savanna landscapes, the shifting numbers of large mammalian wildlife present a physical continuum whose ecological implications for rivers is not clearly understood. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the fractional contribution of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial organic matter and nutrients mediated by large mammalian herbivores (LMH), both wildlife and livestock, in its middle and lower reaches. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns in the fractional contribution of allochthonous organic matter from C3 and C4 plants (woody vegetation and grasses, respectively) and autochthonous energy from periphyton for macroinvertebrates at various sites of the Mara River and its tributaries. Potential energy sources and invertebrates were sampled at 80 sites spanning stream orders 1 to 7, various catchment land uses (forest, agriculture and grasslands) and different loading rates of organic matter and nutrients by LMH (livestock and wildlife, i.e., hippopotamus). The fractional contribution of different sources of energy for macroinvertebrates along the river did not follow predictions of the RCC and RPM. First, the fractional contribution of C3 and C4 carbon was not related to river order or location along the fluvial continuum but to the loading of organic matter (dung) by both wildlife and livestock. Notably, C4 carbon was important for macroinvertebrates even in large river sections inhabited by hippos. Second, even in small 1st -3rd order forested streams, periphyton was a major source of energy for macroinvertebrates, and this was fostered by livestock inputs fuelling aquatic primary production throughout the river network. Importantly, our results show that replacing wildlife (hippos) with livestock shifts river systems towards greater reliance on autochthonous sources of energy through an algae-grazer pathway as opposed to reliance on allochthonous inputs of C4 carbon through a detrital pathway.

Extinction transition of hantavirus-infected rodents in a hostile environment.

The spatial critical shelter sizes above which populations would survive are investigated for the infection of hantavirus among rodent populations surrounded by a deadly environment. We show that the critical shelter sizes for the infected population and the susceptible population are different due to symmetry breaking in the reproduction and the transmission processes. Therefore, there exists a shelter size gap within which the infected population becomes extinct while only the susceptible population survives. With the field data reported in the literature, we estimate that, if one confines the rodent population within a stripe region surrounded by a deadly environment with the shorter dimension between 335.5±27.2m and 547.9±78.3m, the infected population would become extinct. In addition, we introduce two factors that influence the movement of rodents, namely, the spatial asymmetry of the landscape and the sociality of rodents, to study their effects on the shelter size gap. The effects on the critical size due to environmental bias are twofold: it enhances the overall competition among rodents which increases the critical size, but on the other hand it promotes the spread of the hantavirus which reduces the critical size for the infected population. On the contrary, the sociality of rodents gives rise to a more localized population profile which promotes the spread of the hantavirus and reduces the shelter size gap. The results shed light on a possible strategy of eliminating hantavirus while preserving the integrity of food webs in ecosystems.

Historical trophic ecology of some divergent shark and skate species in the Dutch coastal North Sea zone

Over the last century the fish community of the Dutch coastal North Sea zone has lost most its shark and skate species. Whether their disappearance has changed the trophic structure of these shallow waters has not been properly investigated. In this study historical dietary data of sharks and skates, being in the past (near)-residents, juvenile marine migrants and marine seasonal visitors of the Dutch coastal North Sea zone were analyzed for the period 1946–1954. Near-resident and juvenile marine migrant species were demersal while all marine seasonal visitors species were pelagic. Based on stomach content composition, the trophic position of four of the various shark and skate species could be reconstructed. The (near)-resident species, the lesser spotted dogfish, the marine juvenile migrant, the starry smooth hound, and the benthopelagic marine seasonal visitor, the thornback ray, had a benthic/demersal diet (polychaetes, molluscs and crustaceans), while the pelagic marine seasonal visitor, the tope shark, fed dominantly on cephalopods and fishes. Diet overlap occurred for fish (tope shark and lesser spotted dogfish), for hermit crabs (lesser spotted dogfish and starry smooth hound) and for shrimps (thornback ray and starry smooth hound). Trophic position ranged from 3.2 for thornback ray preying exclusively on crustaceans to 4.6 for the tope shark consuming higher trophic prey (crustaceans and fish). The analysis indicates that most of the shark and skate species were generalist predators. The calculated trophic positions of shark and skate species indicate that those species were not necessarily at the top of the marine ecosystem food web, but they might have been the top predators of their particular ecological assemblage.

Community Profile and Drivers of Predatory Myxobacteria under Different Compost Manures.

Myxobacteria are unique predatory microorganisms with a distinctive social lifestyle. These taxa play key roles in the microbial food webs in different ecosystems and regulate the community structures of soil microbial communities. Compared with conditions under conventional management, myxobacteria abundance increases in the organic soil, which could be related to the presence of abundant myxobacteria in the applied compost manure during organic conditions. In the present study,16S rRNA genes sequencing technology was used to investigate the community profile and drivers of predatory myxobacteria in four common compost manures. According to the results, there was a significant difference in predatory myxobacteria community structure among different compost manure treatments (p < 0.05). The alpha-diversity indices of myxobacteria community under swine manure compost were the lowest (Observed OTU richness = 13.25, Chao1 = 14.83, Shannon = 0.61), and those under wormcast were the highest (Observed OTU richness = 30.25, Chao1 = 31.65, Shannon = 2.62). Bacterial community diversity and Mg2+ and Ca2+ concentrations were the major factors influencing the myxobacteria community under different compost manure treatments. In addition, organic carbon, pH, and total nitrogen influenced the community profile of myxobacteria in compost manure. The interaction between myxobacteria and specific bacterial taxa (Micrococcales) in compost manure may explain the influence of bacteria on myxobacteria community structure. Further investigations on the in-situ community profile of predatory myxobacteria and the key microorganism influencing their community would advance our understanding of the community profile and functions of predatory microorganisms in the microbial world.

Intra-Body Variations of Stable Isotope Ratios (δ13C, δ15N) and Influence of Storage Methods in Aquatic and Post-Aquatic Stages of the Common Toad, Bufo bufo

Isotopic signatures of carbon and nitrogen are widely used for analysis of the structure of food webs in aquatic ecosystems. The study of animals raises a number of methodological questions, including choice of representative tissues and organs for sampling as well as storage of the studied organisms. Furthermore, the impacts of preservation methods can be tissue-specific, age-specific, and even taxon-specific; thus, studies of these impacts on particular taxa are necessary. We focused on the C and N isotope composition of the common toad (Bufo bufo), one of the most widespread European anuran amphibians. We hypothesized that its different tissues and organs may vary in isotopic composition, and ethanol and freezing may have different effects on isotopic values. Our results showed that both “tissue” and “storage method” factors significantly affected the δ13C values of tadpoles and postmetamorphic juveniles, whereas only the “tissue” factor had a significant effect on the δ15N values. The two stages, tadpoles and postmetamorphs, should be analyzed separately despite the brief postmetamorphic period of the juveniles. The skin, legs, muscles, and tail in tadpoles and legs, muscles and heart in juveniles can be used for δ13C and δ15N analysis regardless of the method of storage. The results will serve for the optimization of future study designs in isotopic ecology.

Phytoplankton communities in temporary ponds under different climate scenarios

Temporary water bodies, especially vernal pools, are the most sensitive aquatic environments to climate change yet the least studied. Their functioning largely depends on their phytoplankton community structure. This study aimed to determine how temperature and photoperiod length (by simulating inundation in different parts of the year under five climate scenarios) affect the succession and structure of phytoplankton communities soon after inundation. Photoperiod was the most important factor affecting phytoplankton species richness, total abundance and the abundance of taxonomic groups in the course of succession. A long photoperiod (16 h) and a moderate temperature (16 °C) in vernal pool microcosms (late spring inundation after a warm snowless winter) were the most favourable conditions for phytoplankton growth (especially for the main taxonomic groups: chlorophytes and cryptophytes) and species richness. With short photoperiods (inundation in winter) and low temperatures, the communities transformed towards diatoms, euglenoids and cyanobacteria. In line with our predictions, a high temperature (25 °C) favoured a decline in phytoplankton species diversity. Our study shows that climate change will result in seasonal shifts in species abundance or even in their disappearance and, finally, in potential strong changes in the biodiversity and food webs of aquatic ecosystems in the future.

Potential analysis of Asian toad (Duttaphrynus melanostictus) as a controller of harmful insects and their substitutions in elementary school science lessons

The house toad (Duttaphrynus melanostictus) is a highly adaptable amphibian species, and is commonly found in urban areas. On Lombok Island, this species has the highest abundance in non-forest habitat types. In their habit, amphibians function as predators of various types of insects and various types of invertebrates. There are several research reports on prey items from Duttaphrynus melanostictus, but information regarding its role as control of harmful insects is still limited, especially on the island of Lombok. On the other hand, science learning aims to introduce the surrounding environment to students. Therefore, integrating the roles of species commonly found in these settlements is a necessity. The purpose of this study was to analyze the potential of Duttaphrynus melanostictus as a pest control insect, and its urgency in science learning, especially in elementary schools. The study was conducted using gastric surgery analysis method. The frog's stomach was taken continuously until the data was saturated, i.e. the data obtained were the same as the previous surgeries. The results showed that Duttaphrynus melanostictus preyed on 14 types of insects. There are 12 species (85.71%) of which are harmful insects. If classified, 9 species (75%) are insect pests, and 3 species (25%) are disease vectors. Information on the role of this species can be substituted for science lessons in elementary school. The appropriate topics are (1) the importance of balancing and preserving natural resources in the environment, and (2) the relationship between ecosystem components and food webs in the surrounding environment.

Elevated temperature and browning increase dietary methylmercury, but decrease essential fatty acids at the base of lake food webs

Climate change scenarios predict increases in temperature and organic matter supply from land to water, which affect trophic transfer of nutrients and contaminants in aquatic food webs. How essential nutrients, such as polyunsaturated fatty acids (PUFA), and potentially toxic contaminants, such as methylmercury (MeHg), at the base of aquatic food webs will be affected under climate change scenarios, remains unclear. The objective of this outdoor mesocosm study was to examine how increased water temperature and terrestrially-derived dissolved organic matter supply (tDOM; i.e., lake browning), and the interaction of both, will influence MeHg and PUFA in organisms at the base of food webs (i.e. seston; the most edible plankton size for zooplankton) in subalpine lake ecosystems. The interaction of higher temperature and tDOM increased the burden of MeHg in seston (< 40 μm) and larger sized plankton (microplankton; 40–200 μm), while the MeHg content per unit biomass remained stable. However, PUFA decreased in seston, but increased in microplankton, consisting mainly of filamentous algae, which are less readily bioavailable to zooplankton. We revealed elevated dietary exposure to MeHg, yet decreased supply of dietary PUFA to aquatic consumers with increasing temperature and tDOM supply. This experimental study provides evidence that the overall food quality at the base of aquatic food webs deteriorates during ongoing climate change scenarios by increasing the supply of toxic MeHg and lowering the dietary access to essential nutrients of consumers at higher trophic levels.

Three dimensions of biodiversity: New perspectives and methods

Although the knowledge and understanding of biodiversity is rapidly increasing, very little of the total biodiversity is currently considered in applied conservation actions. In this sense, it is crucial to integrate independent fields of biodiversity models and perspectives with conservation issues, in particular, the views that address the links between biodiversity, ecosystem services and human well-being, species interaction, and focal charismatic species. This study overcomes the lack of framework necessary for this integration, and proposes three perspectives and approaches to assess biodiversity. The first perspective is biodiversity potential. It considers the correlation between renewable resources in local ecosystems and biodiversity potential, in terms of the possibility of maintaining a high degree of biodiversity. The energy cost is evaluated using both static and dynamic methods, based on the measure of the emergy of local renewable resources and of the total emergy throughput needed by components in ecosystem food webs, respectively, also highlighting the link between biodiversity and ecosystem services, species interactions via energy transfer respectively. The second perspective considers the contribution of biodiversity to human well-being, such as domestication. In this approach, we assess the contribution of biodiversity to humans by calculating the emergy of non-renewable resources required to domesticate animals or plants into agricultural products. The third perspective highlights the significance of local focal charismatic species to global biodiversity conservation. Taking rare species as an example, the emergy required to maintain rare species per unit area is used as a quantitative indicator of the role of local rare species in maintaining global biodiversity. By measuring biodiversity from these three perspectives (potential, contribution and significance) simultaneously, biodiversity conservation strategies are addressed for different regions. Taking China as a case study, it shows that the provinces featuring high potential, low contribution and low significance can moderately increase biodiversity development. The provinces with high significance to global biodiversity should strengthen conservation to halt biodiversity loss. The areas exhibiting overexploitation of biodiversity should in turn restrict biodiversity exploitation. The general approaches proposed in this study could be applied to different cases, situations and species, promoting the integration to biodiversity conservation actions at different scales.

The effect of habitat restoration on macroinvertebrate communities in Shaoxi rivers, China.

In recent decades, the biodiversity of freshwater environments has decreased sharply due to anthropogenic disturbances that damaged ecosystem structures and functions. Habitat restoration has emerged as an important method to mitigate the degradation of river ecosystems. Although in many cases a post-project monitoring has been promoted to access the restoration progress, it is still unclear how aquatic community changes following river habitat restoration in China. Macroinvertebrate communities intermediately positioned within ecosystem food webs play a key role in ecosystem processes within river ecosystem, driving energy flow and nutrient cycling. Here, benthic macroinvertebrates are used as bio-indicators to assess the ecosystem health of degraded urban rivers, restored urban rivers, and undisturbed rivers. This study aims to determine (i) how habitat restoration influences macroinvertebrates diversity and how this compared to degraded and reference conditions; (ii) how did macroinvertebrate community compositions differ in restored, degraded, and reference sites; and (iii) the environmental factors shaping macroinvertebrate communities. Habitat restoration significantly increased the diversity and richness of macroinvertebrate community and intolerant species and shifted the community composition towards reference status. Habitat characteristics and water chemistry, including substrate diversity, water velocity, and both nutrients (TN) and organic pollutants (TOC), appeared to shape the turnover of these communities. Habitat characteristics contributed to most of the variation of the entire macroinvertebrate community. Our research indicates that habitat restoration is an efficient approach to restore the aquatic community and hence improve river ecosystem health for freshwater conservation and sustainable management in Zhejiang province. This study strengthens our understanding of the changes of macroinvertebrate community after habitat restoration and important controlling variables that attribute to these changes, which provides an important guidance for future freshwater management.

Diet composition of Korean water deer (Hydropotes inermis argyropus) from the Han River Estuary Wetland in Korea using fecal DNA

Abstract To investigate the foraging preferences of the Korean water deer (Hydropotes inermis argyropus) from the Janghang wetlands located in Han River estuary in South Korea, we elucidated their diet compositions using DNA extracted from their fecal samples. Samples were collected from the Janghang wetlands from June 2013 to January 2015. For dietary analysis, we amplified the internal transcribed spacer 2 (ITS2) and the large subunit of ribulose-1,5-bisphosphate carboxylase (rbcL) regions, followed by cloning and sequencing. We were able to detect 20 families and 35 genera of plants from 77 fecal samples, showing that water deer in the Janghang wetlands mainly preferred Salicaceae (27.5%), Fabaceae (17.5%), and Poaceae (14.2%). In winter, the relative frequency of woody plant detection (81.3%) was much higher than that in other seasons. Our results suggest that Korean water deer in Janghang wetlands browse or graze depending on the locally-available plants species in their habitat as intermediate feeders. Non-invasive approaches using fecal samples could be applied to study food webs of various species and ecosystems for conservation and management of wildlife.

Dynamics of Free-Living and Attached Bacterial Assemblages in Skeletonema sp. Diatom Cultures at Elevated Temperatures

In the context of global warming, changes in phytoplankton-associated bacterial communities have the potential to change biogeochemical cycling and food webs in marine ecosystems. Skeletonema is a cosmopolitan diatom genus in coastal waters worldwide. Here, we grew a Skeletonema strain with its native bacterial assemblage at different temperatures and examined cell concentrations of Skeletonema sp. and free-living bacteria, dissolved organic carbon (DOC) concentrations of cultures, and the community structure of both free-living and attached bacteria at different culture stages. The results showed that elevated temperature increased the specific growth rates of both Skeletonema and free-living bacteria. Different growth stages had a more pronounced effect on community structure compared with temperatures and different physical states of bacteria. The effects of temperature on the structure of the free-living bacterial community were more pronounced compared with diatom-attached bacteria. Carbon metabolism genes and those for some specific amino acid pathways were found to be positively correlated with elevated temperature, which may have profound implications on the oceanic carbon cycle and the marine microbial loop. Network analysis revealed evidence of enhanced cooperation with an increase in positive interactions among different bacteria at elevated temperature. This may help the whole community to overcome the stress of elevated temperature. We speculate that different bacterial species may build more integrated networks with a modified functional profile of the whole community to cope with elevated temperature. This study contributes to an improved understanding of the response of diatom-associated bacterial communities to elevated temperature.

Disturbance by invasive pathogenic fungus alters arthropod predator-prey food-webs in ash plantations.

According to the disturbance-succession theory, natural disturbances support biodiversity and are expected to increase the complexity of food-webs in forest ecosystems by opening canopies and creating a heterogeneous environment. However, a limited number of studies have investigated the impact of disturbance by invasive pathogenic species and succession on arthropod predator-prey food-webs in forest ecosystems. Hymenoscyphus fraxineus is a pathogenic fungus of ash trees that is invasive in Europe and causes massive dieback, mainly of the common ash Fraxinus excelsior across its native range. Here we investigated how this pathogenic fungus affects food-webs of web-building spiders and their prey in understorey vegetation of ash plantations. In 23 young and middle-aged ash plantations that were distributed along a gradient of infestation by H. fraxineus (29%-86% infestation), we measured the vegetation structure (canopy openness, shrub coverage, herb/grass coverage), the trait composition of local spider communities (web type, body size), the prey availability and the prey intercepted by spider webs. We then evaluated the multivariate prey composition (prey type, body size) and network properties. Hymenoscyphus fraxineus opened the ash tree canopy, which resulted in denser shrub coverage. The dense shrub vegetation changed the composition of web types in local spider communities and increasing fungus infestation resulted in reduced mean body size of spiders. Infestation by H. fraxineus reduced the availability of predaceous Coleoptera and increased the availability of herbivorous Coleoptera as potential prey. The mean body size of captured prey and the per capita capture rates of most prey groups decreased with increasing fungus infestation. Hymenoscyphus fraxineus infestation indirectly reduced the complexity in bipartite networks and the trophic functional complementarity in local web-building spider communities. The plantation age affected the vegetation structure but did not affect the studied food-webs. Forest disturbance by the invasive pathogen affected four trophic levels (plant-herbivore-coleopteran intermediate predator-top predator web-building spiders) and, contrary to the disturbance-succession theory, disturbance by the fungus simplified the web-building spider-prey food-webs. The results support the view that H. fraxineus represents a threat to the biodiversity and ecosystem functioning in the simplified ecosystems of ash plantations.

Food Web Responses to a Cyanobacterial Bloom in a Freshwater Eutrophic Lake

The microbial food web is an important part in aquatic ecosystem, but studies on the microbial food web in freshwater ecosystem, especially in freshwater eutrophic lakes, still need further investigation. In the present study, using eutrophic Lake Nanhu as model, the community changes of phytoplankton, zooplankton, and bacteria between the bloom and non-bloom period were analyzed, and microzooplankton grazing experiments were also conducted to measure the grazing pressure and selectivity of microzooplankton on phytoplankton community. Phytoplankton community in Lake Nanhu was mainly dominated by Cyanophyta (49.44%), especially Anabaena circinalis and Microcystis flos-aquae, during bloom period. Rotifers were the main components of zooplankton in Lake Nanhu (44.15%), Brachionus calyciflorus and Moina macrocopa were the most dominant zooplankton in the non-bloom and bloom period, respectively. Bacteroidetes showed significantly higher mean proportion in bloom period than that in non-bloom period (p &lt; 0.001). The growth rates of phytoplankton ranged from −1.00 d−1 to 1.29 d−1, while grazing rates of microzooplankton ranged from −1.15 d−1 to 1.05 d−1. Results indicated that microzooplankton could respond quickly to the increase of phytoplankton during bloom period. Meanwhile, microzooplankton showed grazing preference on Cyanophyta and Cryptophyta during bloom period and non-bloom period, respectively. The microzooplankton grazing selectivity during bloom period might depend on phytoplankton community composition.

Isotopic niche plasticity in a marine top predator as indicator of a large marine ecosystem food web status

As marine ecosystems are harvested or modified by anthropogenic or natural factors, there is an increasing demand for indicators of trophic web health or status. The Magellanic Penguin (Spheniscus magellanicus) is a widely distributed species that forages in the Patagonian Shelf. During breeding, this species is a central-place forager that feeds mainly on schooling fish, with Argentine anchovy (Engraulis anchoita) being the dominant prey in the north and Fuegian sprat (Sprattus fuegensis) in the south of the Argentine Patagonian distribution (40–55°S). Like most forage fish, both prey species display large natural interannual recruitment fluctuations. We used stable isotope analysis of adult Magellanic penguin blood obtained at twelve colonies along its Patagonian latitudinal range to assess changes in isotopic niche and in trophic level as a response to interannual changes in abundance and spatial segregation of forage fish size classes, respectively. Magellanic penguins showed large isotopic niche fluctuations among breeding seasons, explained by the contribution of forage fish in their diet. Furthermore, the size of the isotopic niche negatively correlated with forage fish biomass estimated from acoustic surveys and with their contribution in penguin diet. We defined an isotopic niche size threshold that indicates low abundance of forage fish in nearby feeding grounds. In addition, the trophic level of Magellanic penguins increased with latitude, which corresponds to the size-distribution of both main forage fish species, showing that penguins from different colonies target different size classes of their main prey. We present here a simple and easy to implement indicator to monitor the status of the base of the food web in one of the most productive marine areas in the world, which constitutes the feeding ground of a diverse group of high trophic level predators and sustains large-scale fisheries.

Review: DNA metabarcoding approach for fisheries management

Increased publications on meta-barcoding promote interests in studies associated with fisheries biodiversity, diet, and biomonitoring. These studies primarily concentrated on an ecosystem that has implications for fisheries management with complex interpretation. Various theories have arisen to describe the interactions among aquatic species and eventually contribute to the roles they play in ecology. Identifying organisms is also a prerequisite for answering questions in the field of ecology, which shows that reliable and accurate knowledge is important and desirable. Therefore, as a modern molecular technique, metabarcoding provides a realistic approach that lets ecologists analyze organisms in complex environmental samples and rapidly solve the problem associated with the food web in the coral reef ecosystem. This research explores the use of metabarcoding in fisheries management research and highlights the drawback and value of the future process.