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• shifts in abiotic parameters can affect the structure and function of ecosystems. • Ecological network analysis lacks the ability to resolve these dynamic shifts. • new method "Flipbook-ENA" allows an approximation of corresponding system responses. • it provides a quantitative assessment basis for socio-balanced ecosystem management. Changes in abiotic parameters can affect ecosystem structure and function. Network models with subsequent Ecological Network Analysis (ENA) are often used for the quantification of ecosystem-wide properties with descriptive system indices. However, dynamic abiotic alterations of an ecosystem cannot be resolved with the "state of the art" ENA as the methodology of analyses is static in both space and time. In this study, we present a new, almost dynamic ENA "Flipbook-ENA" which allows for the trend analysis of system indices over a defined range of abiotic factors. Flipbook-ENA enables an approximation of the dynamic system response by discretizing the continuous influence of abiotic factors and by calculating the corresponding changes in the model for each discretization step. ENA indices are therefore obtained as a discrete function of the abiotic conditions. We applied this new concept to two aquatic food web models as case studies, using temperature as the influencing abiotic factor. Flipbook-ENA can be considered an enhancement of ENA flexibility, also facilitating the provision of a quantitative assessment basis for socially, economically and ecologically-balanced management of ecosystems in unstable environmental conditions under the pressure of climate change. [ABSTRACT FROM AUTHOR]

• Allometric trophic network model built for boreal Lake Oulujärvi. • No clear trophic cascades from pikeperch to phytoplankton. • Fishing and pikeperch had both direct and indirect effects in the food web. • Fishing and pikeperch together had synergistic negative effects on vendace and smelt. • Fishing and pikeperch together reduced whitefish, but less than expected. Fish communities face changes in environmental conditions and fishing that affects the abundances and structures of the populations. Before 1960s there were abundant stocks of both pikeperch (Stizostedion lucioperca) and whitefish (Coregonus lavaretus) in Lake Oulujärvi, but in 1960s–1970s the stock of pikeperch declined to very low levels while whitefish stock remained abundant. Due to massive re-introductions, pikeperch recovered since 1999 and is again common while whitefish stock has declined. To understand the ecosystem-level changes observed along the recovery of the pikeperch stock, we constructed a food web model capturing the two most recent states of pikeperch abundance in Lake Oulujärvi. We used Allometric Trophic Network (ATN) model to simulate the pelagic food web in the presence and absence of pikeperch and in the presence and absence of fishing. To parametrize ATN model based on body masses and food web interactions, we used data collections of fish cohort analyses, fish individuals, fish stomach contents, zooplankton, and phytoplankton in Lake Oulujärvi. Pikeperch decreased the biomasses of its planktivorous prey. Fishing truncated the age distribution of planktivorous fish. Pikeperch and fishing had synergistic negative effects on vendace (Coregonus albula) and smelt (Osmerus eperlanus) percentages of fish biomass, and antagonistic negative effect on whitefish and brown trout (Salmo trutta) percentages of fish biomass. Mysis relicta, Chaoborus flavicans, Leptodora and other predatory zooplankton, and Cyclopoida zooplankton guilds increased with fishing and pikeperch. Fishing, and pikeperch in the presence of fishing, increased biomass of Crustacean zooplankton guild. There were marked differences between the ATN model simulations and empirically observed time series of fish stock abundances suggesting that the observed changes are partially caused by environmental or fishing-related factors that were not included in the model. [ABSTRACT FROM AUTHOR]

• Endangered fish populations may experience stressors mediated via the food web. • A hybrid model for Topeka shiner (Notropis topeka) populations was developed. • Comparison between stand-alone food-web model (CASM) and hybrid model was conducted. • Impacts of hypothetical changes in food availability on populations were assessed. • Hybrid model provides assessment tool for direct and food-web mediated impacts. The Topeka shiner, a small cyprinid fish, is a seminal example of an endangered aquatic species in the Midwestern USA. Populations and their associated critical habitats may experience potential direct and/or indirect effects from anthropogenic activity. However, potential impacts on fish populations from alterations in the food web are difficult to predict because they are based on complex dynamics of food web interactions. In order to simulate Topeka shiner population dynamics under different food-web scenarios, a hybrid modeling approach was developed by linking an aquatic food web model (comprehensive aquatic systems model, CASM TS) with a species-specific, individual-based population model (TS-IBM). The CASM TS was parameterized and calibrated to represent the waterbody conditions and aquatic species community in a small headwater pool in Iowa, representative of key habitat for the Topeka shiner within its geographical range. In the TS-IBM, life history, growth, and diet are represented and based on data available from the literature for the Topeka shiner and/or surrogate species. The two models are linked by the transfer of daily biomasses of Topeka shiner diet items. We simulated the effects of alterations of the food web on the Topeka shiner populations by systematically reducing the available prey base biomass. Reductions in different food groups had varying impacts on the simulated Topeka shiner populations and were dependent on the species' preference for detritus consumption. Simulations also included predation and identified predator densities to which Topeka shiner populations were vulnerable. The hybrid model provides a platform for the assessment of potential direct and food-web mediated indirect effects of stressors for the purposes of risk assessment, habitat management, and species recovery plans. [ABSTRACT FROM AUTHOR]

Highlights • Spatialized dynamic model linking the coupled model Eco3M-S/SYMPHONIE to OSMOSE. • The model was calibrated and evaluated with satellite, biomass, landings, and trophic data. • Outputs of the end-to-end OSMOSE-GoL model are similar to field and literature data. Abstract An end-to-end model named OSMOSE-GoL has been built for the Gulf of Lions, the main French Mediterranean fishing area. This spatialized dynamic model links the coupled hydrodynamic and biogeochemical model Eco3M-S/SYMPHONIE (LTL – low trophic level model) to OSMOSE (HTL – high trophic level model). It includes 15 compartments of living organisms, five from the LTL model (i.e. nanophytoplankton, microphytoplankton, nanozooplankton, microzooplankton and mesozooplankton) and ten from the HTL model (northern krill, southern shortfin squid, European pilchard, European anchovy, European sprat, Atlantic horse mackerel, Atlantic mackerel, blue whiting, European hake and Atlantic bluefin tuna). With the exception of northern krill and European sprat, all HTL species are commercially exploited and undergo fisheries mortality pressure. The modeled species represent more than 70% of annual catches in this area. This paper presents the parameterization, calibration and evaluation of this model with satellite data for phytoplankton and with biomass, landings, diet and trophic level data for HTL groups. For most species, the diets in output of OSMOSE-GoL are similar to field and literature data in terms of dominant prey groups and species. However, some differences were observed. Various reasons may explain the mismatch between the modeled diet and field data. Benthic prey sometimes observed in the stomach content of the HTL predators were not modeled in OSMOSE-GoL. Field studies were carried out at specific periods and locations, while our data concern the period 2001–2004 and the entire modeled domain. Inter- and intra-annual variations in spatial distribution and density of prey may also explain these differences. The model estimates trophic level values similar to those cited in the literature for all the HTL compartments. These values are also close to the trophic levels estimated by a previous Ecopath model for the same area and period. Even though some improvements are still possible, this model may already be of use to explore fishery or Marine Protected Areas scenarios for socio-ecosystem management issues. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Upstream insects, midstream molluscs, and downstream zooplankton determined basic flows. • Keystone groups shifted from odonates to piscivores and to plankton along the river. • Lack of carnivores and low predation on molluscs/plankton limited transfer efficiency. • As prey in short supply, insects, epiphytes, and hydrophytes restrained mass balance. • Downstream urban systems were immature due to excessive phytoplankton production. Abstract To understand the longitudinal variation in the structure and functioning of large river ecosystems, six Ecopath models were constructed to exhibit the energy flows of aquatic food webs along the subtropical East River in China. Input parameters were primarily obtained from field data collected in 2012–2016; model outputs were estimated by network analysis. Longitudinally, ecosystem characteristics of the East River had high spatial heterogeneity. The biomass, production, and consumption, of which >75.8% of each was distributed at trophic level (TL) II, were determined by aquatic insects upstream, molluscs midstream, and zooplankton downstream. Carnivorous fish occupied the maximal TL of 2.95–3.50. Due to the different trophic interactions of regional food webs, the keystone groups shifted from odonate larvae in headwaters to piscivorous fish upstream/midstream, to zooplankton downstream, and to phytoplankton near the estuary. Aquatic insects, insectivorous fish, epiphytes, and hydrophytes, all of which had ecotrophic efficiencies >0.99, were critical groups that influenced mass balance through short prey supply. The mean transfer efficiencies (TEs) through TLs II IV had the lowest values of 1.8–4.1% upstream and increased to the highest levels of 8.0–8.4% midstream before they decreased to 6.4–7.0% downstream. The low TEs along the river were limited mainly by the lack of carnivorous fish upstream and the low predation on mollus and plankton midstream/downstream. A series of theory and information indices showed that the pristine upstream system was mature but underdeveloped in organisation; in contrast, the downstream systems in the urban and industrial reaches were immature and stressed in terms of excessive phytoplankton production and short cycling. [ABSTRACT FROM AUTHOR]

An ecosystem model called the “EMAGIN-B.C. ver 1.0 (Ecosystem Model for Aquatic Geologic Integrated Network for Blue Carbon)”, describing the Carbon-Nitrogen-Phosphorus-Oxygen-Calcium cycle was developed to estimate/predict carbon capture and storage in estuaries. EMAGIN-B.C. analyzes (1) carbon burial, wherein carbon is captured biologically in the pelagic and benthic ecosystems and stored in deeper sediments, (2) CO 2 uptake at the ocean surface while considering the carbonate chemistry with total alkalinity and Dissolved Inorganic Carbon (DIC) production/consumption due to biochemical processes, (3) DIC capture associated with grazing at the trophic level among phytoplankton, zooplankton, and benthic fauna, (4) the effects of hypoxia on benthic fauna and bacteria by precise modeling of the biochemical oxygen production/consumption and the resultant hypoxia, and (5) the carbon transport by integration with the hydrodynamic model. EMAGIN-B.C. was applied to Tokyo Bay, a eutrophic, shallow coastal area, and reproduced the observations well. From the model outputs, it can be observed that Tokyo Bay shows functions of climate change mitigation. In the one-year carbon budget, Tokyo Bay captured 16.6% of the DIC from the atmosphere and river as organic matter by biological processes, and 3.9% of the total carbon flowing from the atmosphere and river was stored in the deeper sediment layer. [ABSTRACT FROM AUTHOR]

Ecological Network Analysis (ENA) combines modeling and analysis used to investigate the structure, function, and evolution of ecosystems and other complex systems. ENA is applied to network models that trace the movement of thermodynamically conserved energy or matter through the system. Investigators use ENA to answer a range of questions such as the following. What is the impact of fishing on the marine food web? Which species control the flux of nitrogen in an estuary? What is the ecological relationship among species in the food web when direct and indirect influences are considered? Would a proposed regulation make a city more sustainable? The field has grown since its inception in the 1970s, but it has rarely been systematically reviewed. This absence of reviews likely hinders the development of the field as a whole, obscures the diversity of its applications, and makes it difficult for new investigators to learn, develop, and apply the techniques. The objective of the work presented in this paper was to systematically review ENA research published in 2010 through 2016 to (1) identify the topic diversity, (2) expose methodological development, (3) highlight applications, and (4) assess collaboration among ENA scholars. To accomplish this, we used a combination of bibliometric, network (e.g., social network), and feature analyses. Our search identified 186 records. A topic network built from the bibliographic records revealed eight major topic clusters. The largest groups centered on food webs, urban metabolism, and ecosystem theory. Co-author analysis identified 387 authors in a collaboration network with eight larger components. The largest component contained 56% of the authors. This review shows ENA to be a topically diverse and collaborative science domain, and suggests opportunities to further develop ENA to better address issues in theoretical ecology and for environmental impact assessment and management. [ABSTRACT FROM AUTHOR]

The study aims to describe the energy flow and trophic structure, to assess the ecological stage of maturity, the ecosystem impact of the introduced exotic carp species and the current fishery on the Lake Koka ecosystem using a mass-balance trophic model. The Ecopath approach and software were used to represent the lake ecosystem, and input parameters were obtained from in-situ surveys and from published lake specific sources. The model was balanced as per the recommended ecological and thermodynamic constraints. The low ecotrophic efficiency found for adult catfish, primary producers and detritus suggest that these resources are not fully utilized, while other groups have moderate to high values. The annual fishery catch represents only about one sixth of the total fish biomass, and the exploitation rates of target species are well below 0.5 suggesting under-exploitation. The dietary intake of fish-eating birds is 5.8 t km –2  year –1 almost twice the catch, showing the lake’s important role for sustaining the bird populations and hence, caution needs to be taken before implementing any further fisheries development intervention. The mean trophic level of the catch (2.55) is intermediate when compared to other tropical lake systems and reflects the mixed fishery of the lake. Mixed Trophic Impact and Niche Overlap analysis reveals that, contrary to what may be expected, the impact of the introduced exotic carp species on the lake system is less significant than that of the native species. Besides its socio-economic significance, the detritivorous carp seems to fill an unutilized niche and helps the system in recycling organic matter. The P/R value (3.2) and other system maturity indices indicate that Lake Koka is as yet an immature, developing system. The model can be used as a reference for exploring ecosystem-based fisheries management scenarios aimed at sustaining fish stocks, ecosystem services as well as ecological integrity. [ABSTRACT FROM AUTHOR]

Using network analysis for making predictions about food web dynamics is one of the major challenges in systems ecology. Since there are several notoriously difficult methodological problems with food webs, only a comparative perspective can help. We study a standard database for trophic flow networks and analyse the correlation between structure and dynamics in strictly hierarchical food webs (directed acyclic graphs, DAGs). To characterize the structural information about trophic nodes in food webs (their positional importance), we use 8 topological indices that had been developed for quantifying DAGs (3 indices related to status, s , and 5 indices related to the keystone index, K ). For dynamics, we use the KS (keystoneness) index that quantifies the importance of trophic nodes in the food web, considering also carbon flows and biomass. We statistically compare the structural and dynamical importance of each network node and find that the K indices are much better predictors of KS than the s indices. Based on these results, we suggest that functional studies have to consider both bottom-up and top-down effects as well as indirect effects that are dampening with distance. We suggest that this kind of study can be helpful to better understand the relevance and applicability of network analysis, an otherwise popular research methodology with continuously increasing predictive power. [ABSTRACT FROM AUTHOR]

When attempting to model an ecosystem, compromises must be made to retain the essence of the system and its functioning. Here, we explore the implications of these aggregations on a modelled ecosystem by using Ecopath to model the plankton food web in the Strait of Georgia (SoG), a temperate coastal system on the west coast of Canada, in three seasons. The food web is defined by fifteen functional groups representing autotrophic phytoplankton, the microbial loop, and mesozooplankton in three seasons, differentiated by node biomass, productivity, and diet. Variations in the community composition lead to shifts in trophic behaviour and food-web structure seasonally. In spring, autotrophic phytoplankton (i.e. diatoms) are the main source of carbon for the system. In summer and winter, the microbial loop becomes more important due to limited primary production. These structural changes within the plankton food web throughout a year have implications for higher trophic levels, including the seasonal availability and quality of food for planktivorous fish. Finally, we compared this detailed seasonal approach to plankton modelling with a more common simplified approach and examined its impacts on the entire ecosystem. The microbial loop is often excluded from coastal ecosystem models but is an important component, influencing trophic positions and transfer efficiencies. However, aggregating plankton groups appears to be an adequate approach to plankton modelling in the SoG, but modelling decisions should be driven by the research question. • Ecosystem models often highly simplify plankton at the base of the food web. • Plankton community and interactions vary seasonally in the Strait of Georgia. • Food web models representing seasonal trophic structure with plankton are built. • Models provide insights into ecosystem functioning and food availability for fish. • Simplistic models may be appropriate in some cases. [ABSTRACT FROM AUTHOR]

Anthropogenic intervention along with natural variability can both influence and compromise continued ecosystem functioning. Ecological network analysis (ENA) was used to explore ecosystem functioning following disturbances to food web networks of a South African estuary, Mdloti, under different seasons. Keystone species, in particular, play an important structural role in spite of having low levels of presence in terms of biomass. From networks of carbon exchanges, the keystone species are identified which include high trophic level carnivorous fish species like Argyrosomus japonicus, Caranx sexfasciatus and Monodactylus falciformis. It is observed that keystone species differed between seasons, according to changing conditions of the estuary. The positive and negative direct and indirect effects that the keystone species have on the different components of the system are evaluated by a Mixed Trophic Impacts (MTI) analysis and results of the direct-indirect impacts analysis are not consistent across seasons.Results reinforce the fact that the keystone species are context dependent as they show variation over the different networks following species composition change following alteration of the estuaries physical status and season. To simulate disturbance, the keystone species biomass in the initial five networks was changed by 10% in stepwise intervals up to ± 99% and it was observed that the system is somewhat resistant to the perturbation effects of the keystone species. [ABSTRACT FROM AUTHOR]

Two mass-balanced network models of Hooghly Matla estuarine system, from two different time periods (less exploited phase → 1985–1990 and highly exploited phase → 1998–2003) have been constructed for quantitative comparison. The models are used to estimate the important biological interactions and relationships among different ecologically important groups. 20 functional groups based on species of different habitats from coastal areas in this ecosystem have been identified, including shrimps, squids, crabs, mackerel, small pelagics, demersal fishes, benthic feeders, predator fishes and trash fish. The biomass values for these components are estimated from catch production and bottom trawling surveys. The values of Ecotrophic Efficiency in the models are high (>0.5) for most groups of higher trophic levels. Interactions among different components are clearly understood from the outputs of models with a focus on energy flow. Most fish population are observed to approach high degree of exploitation with change in the overall trophic structure mainly due to top down effects. Several system statistics and network flow indices from the model outputs indicate that this estuary is facing degradation and stress resulting in some degrees of instability. [ABSTRACT FROM AUTHOR]

The mechanisms for maintenance of food web structure and function in the face of frequent disturbance has been a question in ecology for many years. Local point-wise stability of theoretical food webs or robustness assessment of empirical binary food webs are the two principal techniques that have been used to address this question. However, many theoretical webs are often small, constructed randomly or from theoretical algorithms (such as Cascade or Niche models), and assume Lotka-Volterra dynamics. Whilst the binary webs used also assume all interactions are equal and that webs are donor controlled. Recent dynamic stability analysis of empirical quantitative webs has sought to improve this assessment. Here we investigate how aquatic food web structure and the direction of trophic cascades interact to affect the robustness of total carbon flow between species after a disturbance. The robustness of the 18 food webs is higher if predator control dominates. Webs with predator control were however stabilised by weak indirect interactions and short food chains. [ABSTRACT FROM AUTHOR]

Aggregation of data and incomplete sampling are two notoriuos problems of food web research. We suggest to look at them in parallel since their effects are interdependent. Different aggregation methods are not equally sensitive to missing data and they lead to different biases in describing food web structure. In this paper, we construct a low-quality food web of Lake Balaton (based only on high-quality literature), aggregate it in several ways, compare the different versions of the food web by network analysis and discuss how the results can help future sampling, field work and data management. We identify groups where resolution or aggregation should be increased. [ABSTRACT FROM AUTHOR]

Given the ecological importance and high socio-economic value of the fishery of the Gulf of Gabes, an end-to-end model was applied to its continental shelf ecosystem to characterize the structure of the food web in the 2000s. This approach consisted in forcing a high trophic level model (OSMOSE) with an existing biogeochemical model (Eco3M-MED) representing the seasonal dynamics of the low trophic levels. The two models were linked through trophic interactions to represent the ecosystem dynamics from primary producers to top predators. In this study, we developed the multispecies, individual-based model OSMOSE in the Gulf of Gabes (OSMOSE-GoG). This model aims to capture the main processes that influence species life cycle and simulate the functioning of the ecosystem according to opportunistic predation process based on size selection and spatio-temporal co-occurrence between a predator and its prey. The spatial distribution of the eleven modelled species was derived from a Multi-Scale Species Distribution Modelling approach. We calibrated OSMOSE-GoG model with available data of biomass and fishing yield, using an optimization method based on evolutionary algorithms which is suitable for complex and stochastic models. Finally, OSMOSE-GoG was validated against independent data sets at different hierarchical levels: the individual (diet composition), population (mean size of commercial catch) and community levels (mean trophic level) following the Pattern-Oriented Modelling approach. The model outputs were overall consistent with the diet compositions and mean trophic levels derived from the ECOPATH model of the Gulf of Gabes (ECOPATH-GoG) and the observations of mean size of catches. The OSMOSE-GoG can be considered as a baseline model to investigate ecosystem responses to environmental changes and fishing management measures in the Gulf of Gabes. [ABSTRACT FROM AUTHOR]

As species biology and ecology is profoundly influenced by climate, any climatic alteration may have severe consequences on marine pelagic ecosystems and their food webs. It remains challenging to estimate the influence of climate on both structural and functional properties of food webs. In this study, we proposed an innovative approach to assess the propagating effects of climate change on ecosystem food web. The approach is based on a sensitivity analysis of a food-web model, a linear inverse model using a Monte Carlo method coupled with a Markov Chain , in which changes in the values of parameters are driven by external Ecological Niche Model outputs. Our sensitivity analysis was restricted to parameters regarding a keystone functional group in marine ecosystems, i.e. small pelagic fish. At the ecosystem level, the consequences were evaluated using both structural and functional ecological network indices. The approach is innovative as it is the first time that these three methods were combined to assess ecological network indices sensitivity to future climatic pressure. This coupling method was applied on the French continental shelf of the Bay of Biscay for which a food-web model already exists and where future changes in the distribution of small pelagic fish have already been examined through model building and projections. In response to the sensitivity analysis corresponding to an increase in small pelagics production only, our results suggested a more active system with an intense plankton-small pelagics-seabirds chain and an efficient recycling to maximize detritus use in the system in relation with detritus export. All results combined together seemed to be in favor of a system adapting to sustain the tested increase in production of small pelagic planktivores. Finally, regarding the innovative combination of numerical tools presented, even if further investigations are still necessary to get a more realistic view of cumulative effects resulting from one given pressure (or more) on a food web (e.g. altering different biological compartments at the same time), the Ecological Network Analysis indices values showed a higher variability under the scenarios of change. Our study thus pointed out a promising methodology to assess propagating changes in structural and functional ecosystem properties. [ABSTRACT FROM AUTHOR]

The San Matías Gulf (SMG) is a semi-enclosed ecosystem where the Argentine hake Merluccius hubbsi (AH) has been the main fishery resource since 1971. During the 20th century the South American sea lion Otaria flavescens (SASL) population was severely reduced in this ecosystem due an intense hunting, but in the 1970's conservation was promoted and hunting was banned. As a consequence SASL have been slowly recovering, until the 1990's when rapidly rebuilt their populations. Recent studies indicate that they feed mostly over commercially profitable medium-sized AH. Also, medium-sized and large hake are well-known cannibals that feed heavily over smaller AH. Fishing trawlers affect juvenile and medium-sized AH and artisanal long-liners capture exclusively large AH. The objective of this study was to evaluate the effect of a growing SASL population over the AH in the SMG, considering the changes in the fishing activity as well as the size-structured cannibalism within the AH population. The evaluations were based on time series of hake and SASL biomass using the “Ecopath with Ecosim” dynamic modelling approach. The analyses show that over 4 decades the increase in Sea Lions biomass has not generated a significant increase in the predation mortality over AH. On the other hand, an increase and subsequent variations in the fishing mortality seems to be related with long-term variations in large AH abundance, and a decrease in medium-sized AH abundance, constraining the cannibalism mortality. This led to a positive effect over juvenile AH abundance due to a released cannibalism pressure, even considering that the less abundant larger AH are also the main spawners of the population. In this scenario, where it seems that trawlers and long-liners have replaced several predators over the SMG food web, SLAS population is still growing but they may not reach the pristine abundance levels of the time before hunting. [ABSTRACT FROM AUTHOR]

Tonle Sap Great Lake (TSL) is the largest freshwater lake ecosystem in Southeast Asia and receptacle of impressive biodiversity. However, there is surprisingly little knowledge of its ecosystem structure and functioning. The main objective of the current work was to quantify the food web structure and assess the ecosystem health status of the TSL system by constructing the first holistic food web model using Ecopath with Ecosim (EwE). The results indicate that the ecotrophic efficiency (EE) values were very high for most of functional groups (EE > 0.5) except molluscs (0.146) and macrophytes (0.102). The high EE values together with the MTI (Mixed Trophic Impact) analysis indicated the overexploitation and degradation of fishery resources in the TSL system. The discrete trophic levels varied from 1 (phytoplankton, macrophytes and detritus) to 3.17 (snakehead). The energy transfer in the TSL food web was based mostly on the detrital food chain (77.9%) rather than the grazing food chain (22.1%), with an average transfer efficiency of 8.27%. The ratios of total primary production to respiration (TPP/TR) and to biomass (TPP/TB) were 1.23 and 2.04, respectively, while the Ascendency and Finn cycling index (FCI) of the system were estimated at 27.4% and 23.62%. Nevertheless, the connectance index (CI: 0.253) and system omnivory index (SOI: 0.075) were in-between compared to other lake ecosystems, which indicated that the food web structure was characterized by linear, rather than web-like features. Systematic analysis and indicators suggested that the ecosystem was a relatively healthy ecosystem achieving a certain stage of maturity, albeit with a vulnerable food web structure. Accordingly, some ecosystem-based strategies are presented for the improvement of fishery management and ecosystem conservation in TSL. [ABSTRACT FROM AUTHOR]

Ecosystem management requires a large base of knowledge regarding the main factors of the components in the system, the relationship between them and their relationships with the external forces that affect ecosystem behavior. In many cases, this knowledge is not always available. Therefore, analyzing previous events and determining the effects they had on the ecosystem can provide insights regarding the factors that caused the changes and their continuing effect on the ecosystem. This task is not simple, due to a large variability of factors in the ecosystem and the difficulty in identifying them. Based on the Ecopath approach, we developed a means for analyzing the Lake Kinneret ecosystem by comparing two mass balance models representing two very different periods. The first model is based on the period of 1990–1993, prior to a regime shift that occurred in the ecosystem and the second model is based on 2006–2010, a period characterized by unstable behavior in the ecosystem. Examining the differences between the two models allowed us to map changes in the ecosystem and to identify the changes and the ecosystem components affected by the regime shift. Using the results we demonstrate the potential of providing management recommendations regarding Lake Kinneret's ecosystem and fishery. [ABSTRACT FROM AUTHOR]

• Free and open-source software for ecological network analysis and visualisation. • Tool implemented in Python and adapted to ecologists' needs. • Enables study of topology and dynamics of ecological networks. • Data preprocessing, interactive visualisation, network analysis, machine learning. • Demonstration of components and functionalities by detrital soil food web analysis. BEFANA is a free and open-source software tool for ecological network analysis and visualisation. It is adapted to ecologists' needs and allows them to study the topology and dynamics of ecological networks as well as to apply selected machine learning algorithms. BEFANA is implemented in Python, and structured as an ordered collection of interactive computational notebooks. It relies on widely used open-source libraries, and aims to achieve simplicity, interactivity, and extensibility. BEFANA provides methods and implementations for data loading and pre-processing, network analysis and interactive visualisation, modelling with experimental data, and predictive modelling with machine learning. We showcase BEFANA through a concrete example of a detrital soil food web of one agricultural grassland, and demonstrate all of its main components and functionalities. [ABSTRACT FROM AUTHOR]

The trophic structure of a subtropical bay in Taiwan Strait was analyzed by using two methods: mass balance modeling (Ecopath) and stable isotopic analysis (SIA). Trophic levels (TLs) of main functional groups estimated from the two methods were compared. The Ecopath model was built based on the fishery resource survey in Xiamen Bay in 2009. Specifically, data on species composition, biomass, mortality rates, diet composition and fisheries catches were obtained from the survey in and around the bay. The model consisted of 26 functional groups, including plankton, benthos, fish, cephalopods, shrimps, crabs and marine mammals. TLs of the main functional groups were estimated to be between 2.89 (cephalopods) and 3.94 (congers), with an average of 3.11. Trophic transfer efficiencies from levels II to V were 12.8%, 19.2%, 19.7% and 12.1%, respectively. Catfish ( Tachysurus sinensis and Netuma thalassina ) and the fisheries have major trophic impacts on most functional groups in the Xiamen Bay ecosystem. Total system throughput was estimated to be 411 t km −2 year −1 . TLs derived from isotopic analysis were highly correlated with those estimated from Ecopath (Linear regression: R 2 = 0.696, n = 23, p < 0.001). On an average, Ecopath underestimated TLs of the functional groups by about 12.2% compared to those estimated from SIA, with TLs from Ecopath being slightly higher at low TLs and lower at high TLs. This studies support value of using both stable isotopes and Ecopath methods to analyze this food web. [ABSTRACT FROM AUTHOR]

Ecological network analysis was applied in the Seine estuary ecosystem, northern France, integrating ecological data from the years 1996 to 2002. The Ecopath with Ecosim (EwE) approach was used to model the trophic flows in 6 spatial compartments leading to 6 distinct EwE models: the navigation channel and the two channel flanks in the estuary proper, and 3 marine habitats in the eastern Seine Bay. Each model included 12 consumer groups, 2 primary producers, and one detritus group. Ecological network analysis was performed, including a set of indices, keystoneness, and trophic spectrum analysis to describe the contribution of the 6 habitats to the Seine estuary ecosystem functioning. Results showed that the two habitats with a functioning most related to a stressed state were the northern and central navigation channels, where building works and constant maritime traffic are considered major anthropogenic stressors. The strong top-down control highlighted in the other 4 habitats was not present in the central channel, showing instead (i) a change in keystone roles in the ecosystem towards sediment-based, lower trophic levels, and (ii) a higher system omnivory. The southern channel evidenced the highest system activity (total system throughput), the higher trophic specialisation (low system omnivory), and the lowest indication of stress (low cycling and relative redundancy). Marine habitats showed higher fish biomass proportions and higher transfer efficiencies per trophic levels than the estuarine habitats, with a transition area between the two that presented intermediate ecosystem structure. The modelling of separate habitats permitted disclosing each one's response to the different pressures, based on their a priori knowledge. Network indices, although non-monotonously, responded to these differences and seem a promising operational tool to define the ecological status of transitional water ecosystems. [ABSTRACT FROM AUTHOR]

The ‘Ecopath’, later expanded to ‘Ecopath with Ecosim’ (‘EwE’), modeling approach has been applied to hundreds of ecosystems around the world, since its first implementation in 1984. The ‘EcoBase’ model repository was developed to gather EwE models published worldwide. For the 433 unique models documented in EcoBase, we compiled, standardized, and analyzed all available metadata describing critical aspects of the models. We proposed a general description of the EwE applications and we analyzed their evolution over the last 30 years, based on the year of publication of the models. Then, we performed a correspondence analysis on the metadata to identify the main types of EwE models. Overall, most models were built to analyze ecosystem functioning and fisheries, principally in the Northern and Central Atlantic Ocean. During the first decade (1984–1993), most EwE applications were Ecopath models representing tropical marine systems and using simple food web representations to analyze trophic functioning only. Over the last two decades (1994–2014), EwE models were applied to study a wider variety of ecosystems, including polar regions and terrestrial systems, and a wider range of research topics , including pollution, aquaculture and Marine Protected Areas. The modeling practices also evolved toward Ecopath (but also Ecosim and Ecospace) models with larger spatial scales, shorter temporal scales, and more complex representations of the food web. In parallel, the numbers of both publications and modelers have steadily increased, while the proportion of journal articles presenting EwE-based studies has been growing. The correspondence analysis confirmed these trends and discriminated three types of models: the basic Ecopath models developed during the first decade, the average models developed over the last two decades using Ecopath and Ecosim routines and an intermediate number of groups, and the most elaborated models including Ecospace simulations and a high number of groups with multi-stanza. We concluded by discussing the challenges and potentials of the compilation and meta-analysis of EwE models, notably by using the EcoBase repository. This global overview showed that the usage of and interest for the EwE modeling approach in the scientific community had evolved and expended over the last three decades to support ecosystem-based fishery management. [ABSTRACT FROM AUTHOR]

Species importance is often defined by how central the role a species plays in a food web. Here we argue that species importance should also incorporate the concept of uniqueness of its network position. By developing a previous methodology, we propose a new approach for species uniqueness. Our methodology quantifies the interaction structure of species, separates strong and weak interactors in a threshold-dependent way and measures the similarity of strong interactors’ identity for pairs of species. By exploring various threshold values systematically, the profile of a species’ trophic overlap can be constructed. Summing up the extent of trophic overlap across the whole profile for a species, we then obtain a new measure for species uniqueness. A unique species should overlap less with other species and therefore has a low value for this new measure. We demonstrate our methodology by using the food web representation of Prince Williams Sound ecosystem. Drastic differences between our new result and that derived from the previous approach are found. We further compare the result with other network indices and found that the information generated from our new approach differs from the majority others. This in turn implies our approach offer an alternative view on species importance that may complement the existing methodologies in the literature. [ABSTRACT FROM AUTHOR]

Lake Dianchi is the largest shallow lake in Yunnan-Guizhou plateau and the sixth largest one in China. The lake has been experiencing cyanobacterial blooms in the last two decades. Although a few studies have investigated the tempo-spatial dynamics of cyanobacterial blooms and their underlying mechanisms, knowledge regarding the food web structure and trophic interactions in bloom-dominated ecosystems is scarce. In the present study, an Ecopath model was developed to assess the entire lake ecosystem on the basis of historical and survey data obtained between 2009 and 2010 at Lake Dianchi. The results showed that the aggregation of flows sensu Lindeman refers to six trophic levels (TLs), and most biomasses and trophic flows were primarily concentrated at the first three levels. About 77.5% of the trophic flows from TLI to TLII originated from detritus, whereas high proportions of under-utilised zooplankton biomass returned to the detritus because of low transfer efficiencies (2.9%) in TLII. The microbial loop was considered to be involved in linking the transfer between detritus and TLII. In addition, low values of connectance index and average mutual information implied that the food web tended to be lost in information diversity and had a less complicated structure. High cycling flows concentrated in the microbial loop reflected that the ecosystem enhanced recycling to forms positive feedback by which ecosystem locked the nutrients and promoted the inflation of biomass in plankton communities. Thus, Dianchi Lake was clearly thought to be a bottom-up control ecosystem. These characteristics of the food web partly explained why cyanobacterial blooms were exceptionally heavy and durable in this lake. Finally, the implications of artificially stocking filter-feeding fish (bighead and silver fish) and exotic zooplantivorous icefish on the ecosystem structure and function are discussed herein. [ABSTRACT FROM AUTHOR]

Highlights: [•] Supply–demand balance of energy of food webs is sensitive to biomass of species. [•] Changes in autotrophic biomass increase the oversupply of resources. [•] Changes in heterotrophic biomass decrease the oversupply of resources. [•] Oversupply increases are related to a flow control bottom-up. [•] Oversupply decreases are related to a flow control top-down. [Copyright &y& Elsevier]

Highlights: [•] We have developed a present day ecosystem model for the Taputeranga MR. [•] We have historically reconstructed the ecosystem state prior to commercial fishing. [•] We have run future simulations to predict ecosystem response to marine protection. [•] The keystone role of lobster has changed since historical times due to fishing. [•] The Taputeranga MR is predicted to return the ecosystem to a more historical state. [Copyright &y& Elsevier]

Highlights: [•] We modeled an intertidal seagrass food web of France using linear inverse analysis. [•] Bayesian isotope mixing model output was coupled with the food web model. [•] δ 13C and δ 15N isotope data significantly constrained the food web model. [•] Coupling isotope mixing models with ecosystem models reduces model uncertainty. [Copyright &y& Elsevier]

Highlights: [•] The first food web model (Ecopath) for a typical macrophytic lake in Yangtze River basin was constructed. [•] We found the macrophytic lake ecosystem was a mature system but with simple and vulnerable foodweb structure. [•] The results indicated an urgent need for fishery resources management to shift from traditional population-based to ecosystem-based models in these lakes. [•] Based on the modeling, available measures have been presented to the conservation and utilization of these kinds of freshwater ecosystems. [Copyright &y& Elsevier]

Highlights: [•] We model stochastic ecological networks with multiple interaction types. [•] We vary the color and degree of interspecific synchrony of noise. [•] We measure ecosystem variability under different noise conditions. [•] Colored and synchronized noise increase ecosystem variability. [Copyright &y& Elsevier]

The N:P stoichiometry of a water body is one of the most commonly used indicators of its nutrient status and algal growth. However, in a dynamic aquatic ecosystem the N:P stoichiometry of phytoplankton is highly variable and depends on environmental conditions and key microbial interactions that influence their growth, such as grazing pressures and the microbial loop. Here we determine the influence of the nutrient-dependent microbial interactions between zooplankton, phytoplankton and bacteria on the ecological stoichiometry at different trophic levels and how they relate to water column properties. A 1D hydrodynamic–ecological model (DYRESM–CAEDYM) was applied to Lake Kinneret (Israel) for examining how the internal nutrient ratios of several phytoplankton functional groups correlate with nutrient ratios within the water column, and further explore how the microbial loop shapes the patterns of stoichiometry within the food web by testing two microbial loop configurations. The results showed that the average internal N:P ratios of the phytoplankton community followed their total carbon biomass patterns, and that seasonal patterns of simulated dissolved inorganic N to total P (DIN:TP) ratios in the water column were a useful indicator for reflecting the bulk phytoplankton N:P stoichiometry as compared with total N to total P (TN:TP) ratios and dissolved inorganic N to dissolved inorganic P (DIN:DIP) ratios. However, the internal N:P ratio patterns of individual phytoplankton groups did not necessarily correlate with DIN:TP ratio patterns in the water column. This was because different microbial processes regulate nutrient flows to individual phytoplankton groups. Our simulations with the microbial loop highlight the ability of bacteria to regulate phytoplankton stoichiometry. These results provide an improved mechanistic understanding of the food web in aquatic ecosystems. [Copyright &y& Elsevier]

Abstract: In the past two decades, several models for food webs have been proposed. Those models provide possible explanations on how the food webs we observe today arrive at their respective network structure. Those well established models almost all rely on two common parameters, the numbers of species and trophic links, as well as assuming that species are ranked in some hierarchical order or ecological dimensions. Under those model assumptions species are then allowed to interact with each other depending on their relative positions in relevant ecological dimensions, resulting in simulated food webs that can capture the characteristics of their real-life counterparts. In this paper, we propose a simple model for food webs following biological intuitions. Our model differs from others in that we do not have the prior assumption of species being ordered in any ecological dimensions, and we do not assume a particular number of trophic links. Our model here takes two basic parameters, the number of species and the number of resources, and allows the random encounter between species and resources, and as a result forming trophic interactions. One critical assumption in this model is that after a species obtains resources, it will then become new resources for other species to utilise. In essence, the model here constructs food webs by passing resources among different species. Our model predicts the maximum number of trophic links of a food web when given the number of species, and shows that connectance is a non-linear decreasing function of species number. Furthermore, this simple model also demonstrates that the number of trophic levels tends to decrease when resource number is larger, echoing empirical studies from the literature. We further modified our simple model to fit a particular food web data and suggest the possible mechanism underlying the growth of the empirical food web. Lastly, we assessed the performance of our model by fitting it to a wide range of real food webs and compared the result with those derived from other models. [Copyright &y& Elsevier]

Abstract: Nearly a century ago A.J. Lotka provided fundamental formulations for population modeling; less appreciated are his explorations of the underlying material (elemental) basis of life and its implications for ecology and evolution. This paper describes recent developments in ecological and biological stoichiometry that unify these aspects of Lotka''s work. Stoichiometrically explicit versions of the Lotka–Volterra equations capture key missing aspects of food web interactions, such as the effects of food quality and nutrient recycling feedbacks, and encompass a richer, and potentially more realistic, set of dynamics than non-stoichiometric models. These stoichiometric models are now being further extended to include the recently discovered effects of excess dietary nutrient content on consumer performance. The multi-dimensional capacity of stoichiometric models is likely to be of particular value given the pressing need to anticipate the ecological effects of globally dynamic perturbations of multiple chemical elements (e.g. C, N, and P) due to human actions. [Copyright &y& Elsevier]

Abstract: We provide a modeling framework that fully couples a one-dimensional physical mixed layer model, a biogeochemical model, and an upper trophic level fisheries model. For validation purposes, the model has been parameterized for the pelagic Eastern Pacific Subarctic Gyre ecosystem. This paper presents a thorough description of the model itself, as well as an ensemble-based parameterization process that allows the model to incorporate the high level of uncertainty associated with many upper trophic level predator-prey processes. Through a series of model architecture experiments, we demonstrate that the use of a consistent functional response for all predator-prey interactions, as well as the use of density-dependent mortality rates for planktonic functional groups, are important factors in reproducing annual and seasonal observations. We present the results of a 50-year climatological simulation, which demonstrates that under contemporary physical forcing, the model is capable of reproducing long-term seasonal dynamics in primary production and biogeochemical cycling, while maintaining steady-state coexistence of upper trophic level functional groups at levels consistent with observations. [Copyright &y& Elsevier]

Parasites with complex life cycles frequently increase their transmission to definitive hosts (where reproduction occurs) by increasing the susceptibility of intermediate hosts to predation by definitive hosts. While recent evidence finds that anthropogenic driven habitat alterations can alter host–parasite relationships, whether such alterations interact with intermediate host manipulation to influence infection prevalence and food web structure remains unknown. We develop a nutrient-limited food web model to investigate how manipulation of intermediate host susceptibility, nutrient supply, and predator diversity determine parasite abundance and infection prevalence in intermediate and definitive hosts. We show that the effects of intermediate host manipulation on parasite abundance and infection prevalence depend on nutrient supply while the coexistence of competing definitive hosts and “dead-ends” (where parasites cannot reproduce) depends primarily on intermediate host susceptibility to predation. Our results suggest that anthropogenic changes in nutrient supply will interact with host–parasite relationships to determine parasite abundance, infection prevalence, and food web structure. [Copyright &y& Elsevier]

A steady-state model of the Venice lagoon food web was constructed, based on a comprehensive set of data, which were collected in the years 2001–2005. Energy flows were estimated by means of an inverse methodology of constrained optimization based on the Minimum Norm criterion, i.e. on the minimization of both the sum of squares of the residuals and of the sum of squares of energy flows. The solution was constrained by a set inequalities, which were derived from general eco-physiological knowledge and site specific data on energy flows. The trophic network was represented by thirty-two nodes, including single-species compartments for the species of high economical or ecological relevance. Mass balance equations were weighted, in order to obtain meaningful results in presence of large differences, up to 5 orders of magnitude, among biomasses. A perturbation technique was applied, with the purpose of reducing the risk of finding solutions heavily affected by the set of constraints and of obtaining a more robust representation of the energy flows. The main patterns of energy flow are consistent with those obtained in previous attempts at modelling the Venice lagoon food web. Micro- and macro-phytobenthos account for the largest fraction of the primary production. Energy is then transferred towards higher trophic levels by means of two main pathways: the recycling of dead biomass through the detritus compartment and the direct consumption by grazers. The first pathway is the most important and accounts for approximately two/thirds of the energy transferred to the second trophic level. [Copyright &y& Elsevier]

The development of approaches to estimate the vulnerability of biological communities and ecosystems to extirpations and reductions of species is a central challenge of conservation biology. One key aim of this challenge is to develop quantitative approaches to estimate and rank interaction strengths and keystoneness of species and functional groups, i.e. to quantify the relative importance of species. Network analysis can be a powerful tool for this because certain structural aspects of ecological networks are good indicators of the mechanisms that maintain co-evolved, biotic interactions. A static view of ecological networks would lead us to focus research on highly-central species in food webs (topological key players in ecosystems). There are a variety of centrality indices, developed for several types of ecological networks (e.g. for weighted and un-weighted webs). However, truly understanding extinction and its community-wide effects requires the use of dynamic models. Deterministic dynamic models are feasible when population sizes are sufficiently large to minimize noise in the overall system. In models with small population sizes, stochasticity can be modelled explicitly. We present a stochastic simulation-based ecosystem model for identification of “dynamic key species” in situations where stochastic models are appropriate. To demonstrate this approach, we simulated ecosystem dynamics and performed sensitivity analysis using data from the Prince William Sound, Alaska ecosystem model. We then compare these results to those of purely topological analyses and deterministic dynamic (Ecosim) studies. We present the relationships between various topological and dynamic indices and discuss their biological relevance. The trophic group with the largest effect on others is nearshore demersals, the species mostly sensitive to others is halibut, and the group of both considerable effect on and sensitivity to others is juvenile herring. The most important trophic groups in our dynamical simulations appear to have intermediate trophic levels. [Copyright &y& Elsevier]

Environment is an ecologically important but often ill-defined concept. Environs are an operationalization of environments that let us study their organization and activity. Specifically, environs are the directed (input and output), within-system environments of species (or more generally holons) in ecosystems. Scientists primarily study environs through Network Environ Analysis (NEA). Quantifying general environ properties was an important step in the development of NEA. However, some of the standard NEA whole-system indicator calculations contain a hidden assumption that every system component has a unit input (output). While this can facilitate within system analysis, the even distribution assumption of inputs or outputs is unlikely to be true in many systems. Importantly, it also decouples the environ properties from the influence of the external system environment. We contend that for many applications we should use the observed or realized inputs (outputs) in the NEA calculations rather than the unit vector. We illustrate the effect of the alternative formulations for the ratio of indirect-to-direct flows, network homogenization, and network aggradation in 50 trophically based ecosystem models. Our results reveal that while the unit and realized indicators tend to be well correlated, the qualitative interpretations can be affected. We generalize these specific results by analytically investigating the sensitivity of the ratio of indirect to direct flows (I/D) to variation in the input distribution. We provide sufficient conditions on the direct flow intensity matrix G for which the computed value of I/D is less than unity for arbitrary input, as well as sufficient conditions on G for which the computed value I/D is larger than unity for arbitrary input. These results suggest that different formulations for the environ properties can alter the qualitative assessment of the ecosystem organization. We conclude that the realized formulation reconnects the environ properties to the system environment, producing a more internally consistent and applicable theory of environment. [Copyright &y& Elsevier]

A new understanding of the consequences of how ecosystem elements are interconnected is emerging from the development and application of Ecological Network Analysis. The relative importance of indirect effects is central to this understanding, and the ratio of indirect flow to direct flow (I/D) is one indicator of their importance. Two methods have been proposed for calculating this indicator. The unit approach shows what would happen if each system member had a unit input or output, while the realized technique determines the ratio using the observed system inputs or outputs. When using the unit method, the input oriented and output oriented ratios can be different, potentially leading to conflicting results. However, we show that the input and output oriented I/D ratios are identical using the realized method when the system is at steady state. This work is a step in the maturation of Ecological Network Analysis that will let it be more readily testable empirically and ultimately more useful for environmental assessment and management. [Copyright &y& Elsevier]

Human-mediated and natural disturbances such as nutrient enrichment, habitat modification, and flood events often result in significant shifts in species composition and abundance that translate into changes in the food web structure. Six mass-balanced models were developed using the “Ecopath with Ecosim” software package to assess changes in benthic food web properties in the Mondego estuarine ecosystem (Portugal). Field, laboratory and literature information were used to construct the models. The main study objective was to assess at 2 sites (a Zostera meadow and a bare sediment area) the effects of: (1) a period of anthropogenic enrichment, which led to excessive production of organic matter in the form of algal blooms (1993/1994); (2) the implementation of mitigation measures, following a long period of eutrophication (1999/2000); and (3) a centenary flood (winter 2000/2001). Different numbers of compartments were identified at each site and in each time period. In general, the Zostera site, due to its complex community, showed a higher number of compartments and a higher level of system activity (i.e. sum of consumptions, respiration, flow to detritus, production, total system throughput, net primary production and system omnivory index). The differences at the two sites in the three time periods in the breakdown of throughput were mainly due to differences in the biomass of the primary producers (higher primary production at the Zostera site). Consumption, respiration and flow to detritus were dominated by the grazers Hydrobia ulvae and Scrobicularia plana at the Zostera and bare sediment sites respectively. At both sites, after recovery measures were implemented there was an increase in S. plana and Hediste diversicolor biomass, consumption, respiration and flows to detritus, and a decrease in H. ulvae biomass and associated flows, which increased again after the flood event. The mass-balanced models showed that the trophic structure of the benthic communities in Mondego estuary was affected differently by each disturbance event. Interestingly, in our study a high system throughput seems to be associated with higher stress levels, which contradicts the idea that higher system activity is always a sign of healthier conditions. [Copyright &y& Elsevier]

Replicate mass-balanced solutions to Ecopath models describing carbon-based trophic structures and flows were developed for the Lake Ontario offshore food web before and after invasion-induced disruption. The food webs link two pathways of energy and matter flow: the grazing chain (phytoplankton–zooplankton-fish) and the microbial loop (bacteria–protozoans) and include 19 species-groups and three detrital groups. Mass-balance was achieved by using constrained optimization techniques to randomly vary initial estimates of biomass and diet composition. After the invasion, production declined for all trophic levels and species-groups except Chinook salmon. The trophic level (TL) increased for smelt, adult sculpin, adult alewife and Chinook salmon. Changes to ecotrophic efficiencies indicate a reduction in phytoplankton grazing, increased predation pressure on Mysis, adult smelt and alewife and decreased predation pressure on protozoans. Specific resource to consumer TTE changed; increasing for protozoans (8.0–11.5%), Mysis (0.6–1.0%), and Chinook salmon (1.0–2.3%) and other salmonines (0.4–0.5%) and decreasing for zooplankton (20.2–15.1%), prey-fish (9.7–8.8%), and benthos (1.7–0.6%). Direct trophic influences of recent invasive species were low. The synchrony of the decline in PP and species-group production indicates strong bottom-up influence. Mass balance required an increase of two to threefold in lower trophic level biomass and production, confirming a previously observed paradoxical deficit in lower trophic level production. Analysis of food web changes suggest hypotheses that may apply to other similar large pelagic systems including, (1) as pelagic primary productivity declines, overgrazing of zooplankton results in an increase in protozoan production and a loss of trophic transfer efficiency, (2) habitat and food web changes increased Mysis predation on Diporeia and contributed to their recent decline, and (3) production of Chinook salmon, the primary piscivore, was uncoupled from pelagic production processes. This study demonstrates the value of food web models to better understand the impact of invasive species and to develop novel hypotheses concerning trophic influences. [Copyright &y& Elsevier]

We generated a mass-balance model to figure out the food web structure and trophic interactions of the major functional groups of the Ethiopian highland Lake Hayq. Moreover, the study lay down a baseline data for future ecosystem-based investigations and management activities. Extensive data collection has been taken place between October 2007 and May 2009. Ecotrophic efficiency (EE) of several functional groups including phytoplankton (0.8) and detritus (0.85) was high indicating the utilization of the groups within the system. However, the EE of Mesocyclops (0.03) and Thermocyclops (0.30) was very low implying these resources were rather a ‘sink’ in the trophic hierarchy. Flows based on aggregated trophic level sensu Lindeman revealed the importance of both phytoplankton and detritus to higher trophic levels. The computed average transfer efficiency of 11.5% for the first four trophic levels was within the range for highly efficient African lakes. The primary production to respiration (P/R) ratio (1.05) of Lake Hayq indicates the maturity of the ecosystem. We also modeled the food-web by excluding Tilapia and reduced phytoplankton biomass to get insight into the mass balance before Tilapia was introduced. The analysis resulted in a lower system omnivory index (SOI=0.016) and a reduced P/R ratio (0.13) that described the lake as immature ecosystem, suggesting the introduction of Tilapia might have contributed to the maturity of the lake. Tilapia in Lake Hayq filled an ecological empty niche of pelagic planktivores, and contributed for the better transfer efficiency observed from primary production to fish yield. [Copyright &y& Elsevier]