Ecopath Model Research Articles

Assessment of Ecosystem Characteristics and Fishery Carbon Sink Potential of Qianxiahu Reservoir Based on Trophic Level and Carbon Content Methods

Optimizing biological carbon sequestration has become a primary strategy in global low-carbon-emission initiatives. Freshwater fisheries in reservoirs play an important role in aquatic biological carbon sequestration. However, a standard method for evaluating the carbon sink capacity of inland fisheries has not been developed. Therefore, this study aimed to assess and compare the carbon sequestration potential of the Qianxiahu Reservoir’s fisheries using the trophic level and mass-balance methodologies. The Ecopath model was employed to determine the trophic levels of aquatic organisms within the Qianxiahu Reservoir ecosystem, with input parameters sourced from in situ surveys and the literature on reservoirs. The model includes 21 functional groups, with trophic levels ranging from 1.000 to 3.281. The key species identified are silver carp, bighead carp, and crucian carp. The indices of Finn’s cycling index (FCI), connectivity index (CI), system omnivory index (SOI), and total primary production/total respiration (TPP/TR) for the Qianxiahu Reservoir are 11.35, 0.27, 0.196, and 1.540, respectively. These values indicate a high degree of material recycling and complex interconnections among functional groups. The fishery carbon sink potential of the Qianxiahu Reservoir, calculated using the trophic level and carbon content methods, yielded values of 261.8362 tons/km2 and 66.6818 tons/km2, respectively. The trophic level method showed a notable increase of 195,1544 tons/km2 compared to the carbon content method, underscoring significant differences in results between the two methods. The study concludes with recommendations for research on methods to assess the carbon sink capacity of freshwater fisheries, aiming to establish a scientific framework for this evaluation.

Study on the structure and energy flow of the salt marsh wetland ecosystem in Liaohe Estuary based on the Ecopath model

Salt marshes are one of the three blue carbon ecosystems recognized by the Intergovernmental Panel on Climate Change (IPCC). However, coastal salt marshes in China are facing the risk of degradation. To reveal the status of the salt marsh wetland ecosystem in Liaohe Estuary, an Ecopath model composed of 14 functional groups was constructed based on the 2019 ecological survey data. A comprehensive analysis of the system’s food web structure, energy flow processes, and overall ecosystem characteristics was conducted. The results show that the energy flow in the Liaohe Estuary salt marsh wetland ecosystem is mainly distributed in three integrated trophic levels. The utilization rates of trophic levels II and III are low, easily causing blockages in the lower trophic levels of the ecosystem’s energy flow. The total system throughput of the Liaohe Estuary salt marsh wetland ecosystem is 49,099.039 t·km²·a−1;. The system connectivity index and the system omnivory index are 0.207 and 0.109, respectively. Compared with other wetland systems, the ecosystem has a larger scale, but the overall ecosystem characteristic index reveals lower stability and complexity of the Liaohe Estuary salt marsh wetland system.

Bonifacio strait natural reserve (BSNR): Investigating ecosystem functioning through comparative modelling of marine protected areas

The Bonifacio Straits Natural Reserve (BSNR) is a Mediterranean Marine Protected Area (MPA) located in Corsica, characterized by rocky coasts, steep bathymetry, and regulated exploitation of marine resources. In this study, we updated the BSNR Ecopath model from 2010, providing a re-evaluation of the MPA's impact 13 years after the reserve's establishment and incorporating improved catch estimates, particularly for recreational fisheries. The model encompassed four primary producer groups, fourteen invertebrate groups, two Chondrichthyes groups, sixteen teleost groups, one seabird group, and one cetacean group. The BSNR model depicted a Mediterranean ecosystem where piscivorous fishes and cephalopods link primary producers to top predators (Tursiops truncatus, Dentex dentex and Epinephelus marginatus), emphasizing complex trophic relationships. Although the ecosystem faced moderate fishing pressure, the model revealed uneven pressure among groups, with rays, for example, being particularly vulnerable to fishing nets. Additionally, a mixed trophic impact analysis revealed an absence of competition among fishing fleets for resources, suggesting that, overall, recreational and artisanal fisheries do not impact each other. By comparing MPA models across the Mediterranean Sea, our research suggests that MPA establishment might enhance the overall biomass of ecosystems within their boundaries. This abundance can spill over into adjacent areas, thereby increasing biomass and diversity in those regions. In more exploited MPAs, higher values for the Finn cycling index and the consumption to total system throughput ratio indicated that fishing activities increased pressure on prey resources by diminishing the system's energy, pushing the ecosystem to optimize recycling.

Impacts of regime shift on the fishery ecosystem in the coastal area of Kyoto prefecture, Sea of Japan, assessed using the Ecopath model

Impacts of regime shift on the fishery ecosystem in the coastal area of Kyoto prefecture, Sea of Japan, assessed using the Ecopath model

Modeling food web and fisheries dynamics in Lake Baringo, Kenya

AbstractLakes are important in supporting ecosystem services and livelihoods. However, their food webs and ecological functioning are continuously threatened by anthropogenic influences. Food web models have been widely used in studying trophodynamics, fisheries impacts, and ecological functioning of temperate lakes, but less often in Afrotropical lake systems. We used Ecopath mass‐balanced trophic models annually in 1999, 2010, and 2020 to assess trends in ecosystem function, and the impact of fisheries on the Lake Baringo Ecosystem, a shallow freshwater lake in Kenya. Pre‐balance (PREBAL) and Pedigree analyses supplemented Ecopath models. Model input data were from field sampling, published and gray literature. Food web trophic models indicated a bottom‐up grazer and detrital food chains in all 3 years. Odum's ecosystem development indicators (total productivity to total biomass and total respiration ratios; TPP/TB and TPP/TR) showed that the lake was in a low to intermediate developmental stage, with room for bio‐manipulation, and a highly reduced mean transfer efficiency (TE) (6.4%–0.49%) indicated low trophic transfer of internal production. System omnivory (SOI) and connectance (CI) indices that varied among years indicated temporal variation in food web complexity. Indices of system resilience (overhead and ascendency) indicated an increasing potential for the lake to recover from perturbations. The mean trophic level of the catch (MTLc) increased from 1999 to 2010 and decreased in 2020, by fishing down the food chain as fishing pressure increased. Oreochromis niloticus, an endemic cichlid, was the keystone species (KSi >0) controlling community structure, while the lungfish Protopterus aethiopicus, the top predator in the lake, was not a keystone species (KSi <0). We recommend an integrated approach to lake management that incorporates watershed regulations, regulates fishing effort on the keystone species (O. niloticus), and monitors water quality for sustainable management of the Lake Baringo ecosystem.

Ecosystem-level response to complex disturbances of an interconnected river–lake system based on Ecopath model over the last 30 years

Ecosystem-level response to complex disturbances of an interconnected river–lake system based on Ecopath model over the last 30 years

Ecosystem structure and function of the North Water Polynya

The North Water Polynya is one of the most productive Arctic regions on Earth, sustaining the world's northernmost Inuit communities for millennia. The polynya is a large and persistent region of open water surrounded by sea ice and exhibits high primary productivity, is a biodiversity hotspot, and is a key habitat and migration corridor for Arctic species. Many aspects of the ecosystem structure and the role of resident species in the North Water Polynya remain uncertain. To shed light on these, we developed the first representation of the North Water Polynya food web using the Ecopath modelling framework. Modelled trophic flows indicated that pelagic and benthic communities were primarily connected by Age 1+ Arctic cod ( Boreogadus saida), walrus ( Odobenus rosmarus), and ringed seal ( Pusa hispida). Large copepods, Age 1+ Arctic cod, and bivalves were key prey species. Overall productivity in the North Water Polynya was higher compared to Western Baffin Bay and Western Greenland, corroborating expectations of relatively high productivity within the polynya. This model provides a baseline description of the North Water Polynya ecosystem structure and function prior to future climate-driven food web changes and the emergence of large-scale commercial fisheries.

Lake food web structure in Teici Nature reserve, Latvia: fish presence shapes functioning of pristine bog lake food webs

AbstractStudies on the effects of fish presence on lake ecosystems are widespread but only a few have been conducted in pristine aquatic environments. We employed Ecopath model for assessing food web structure in two fish-inhabited and one fishless lake in a pristine bog area. We hypothesized that: (a) fish absence will raise trophic positions of macroinvertebrate predators; (b) fish predation will lead to higher overall predation rates on zooplankton; (c) fish predation on large bodied zooplankton will result in top-down cascading effect, increasing phytoplankton biomasses. We found that fish have direct and indirect effects on zoobenthic communities. Chironomid biomass was greater and predatory macroinvertebrate groups had a higher trophic level in the fishless lake than in fish-inhabited lakes. Consumption rates of the benthic consumer fraction were greater than that of the planktonic fraction in the fishless lake; the opposite was found in the two lakes with fish. No effects of fish presence on zooplankton were found and we explain this partly by the low water transparency masking the impact of fish. Terrestrial insects constituted a crucial part of adult fish diet and we conclude that terrestrial secondary production contributes to the trophic support of fish communities in pristine bog lakes.

Evaluating the Effects and Mechanisms of the Eco–Substrate in Aquaculture Environment Restoration from an Ecosystem Perspective via the Ecopath Model

Aquaculture supplies high-quality and healthy proteins. With the increasing human demand for aquaculture production, intensive pond aquaculture developed rapidly and results in environmental deterioration. To solve this problem, the eco-substrate (ES), which is the biofilm carrier, has been utilized in aquaculture ponds. Studying the ecological mechanisms of ES from the perspective of the ecosystem may be conducive to the sustainable development of aquaculture. In this study, it was evaluated how ES makes a difference to the trophic structure, energy flow, and system characteristics of two different aquaculture pond ecosystems via the ecopath model. Three aquaculture ponds with ES were designed as the treatment ecosystem and three aquaculture ponds without ES were designed as the control ecosystem. There were 13 and 14 functional groups in the control and treatment ecosystems, respectively. The results showed that (1) the macrozooplankton and microzooplankton showed strong effects on the ecosystem in the keystoneness index; (2) energy transfer pathways in the treatment system with ES increased by 26.23% compared to the control system; (3) the ES improved the utilization rate of detritus, which was 14.91% higher than that of the control ecosystem; (4) the material and energy flow index and network information characteristics demonstrated the ES enhanced the complexity and stability of the treatment system. To improve the energy utilization efficiency, filter feeders can be introduced to ES ponds. Overall, the ES can alter the trophic structure, improve the energy utilization efficiency, and enhance the stability and maturity of aquaculture ecosystems, representing a sustainable practice. Considering the total area of aquaculture ponds on the earth reaching more than 5 million hectares, the application prospect of ES is broad.

Enhancing Fishery Management in Tanghe Reservoir, China: Insights from Food Web Structure and Ecosystem Analysis

Situated within China’s Liaoning Province, Tanghe Reservoir stands as an exemplar in the realm of reservoirs dedicated to eco-friendly fisheries development. Regrettably, frequent incidents compromising water quality and substantial reductions in reservoir fishery profits have plagued the area due to the absence of effective stocking theory guidance. However, the internal ecosystem drivers responsible for these outcomes have remained elusive. This study, leveraging an Ecopath model, delves into an exploration of the food web structure and ecosystem characteristics inherent to Tanghe Reservoir. The findings gleaned from this research demonstrate that the Tanghe Reservoir ecosystem boasts a considerable capacity for material cycling, yet it has not reached full maturity. A multitude of fish species, zoobenthos, and even zooplankton entities exhibit eco-trophic efficiencies exceeding 0.9, indicative of their rampant overexploitation. Notably, the primary cultured species, Aristichthys nobilis and Hypophthalmichthys molitrix, command significant biomass levels but register lower nutritional conversion efficiencies, signifying their overstocked status. Drawing from the tenets of maximum sustainable yield (MSY) theory, we advocate for a heightened emphasis on the harvest of Aristichthys nobilis and Hypophthalmichthys molitrix.

Unveiling the wasp-waist structure of the Falkland shelf ecosystem: the role of Doryteuthis gahi as a keystone species and its trophic influences

Abstract The Falkland Shelf is a highly productive ecosystem in the Southwest Atlantic Ocean. It is characterized by upwelling oceanographic dynamics and displays a wasp-waist structure, with few intermediate trophic-level species and many top predators that migrate on the shelf for feeding. One of these resident intermediate trophic-level species, the Patagonian longfin-squid Doryteuthis gahi, is abundant and plays an important role in the ecosystem. We used two methods to estimate the trophic structure of the Falkland Shelf food web, focusing on the trophic niche of D. gahi and its impacts on other species and functional groups to highlight the importance of D. gahi in the ecosystem. First, stable isotope measurements served to calculate trophic levels based on an established nitrogen baseline. Second, an Ecopath model was built to corroborate trophic levels derived from stable isotopes and inform about trophic interactions of D. gahi with other functional groups. The results of both methods placed D. gahi in the centre of the ecosystem with a trophic level of ~ 3. The Ecopath model predicted high impacts and therefore a high keystoneness for both seasonal cohorts of D. gahi. Our results show that the Falkland Shelf is not only controlled by species feeding at the top and the bottom of the trophic chain. The importance of species feeding at the third trophic level (e.g. D. gahi and Patagonotothen ramsayi) and observed architecture of energy flows confirm the ecosystem's wasp-waist structure with middle-out control mechanisms at play.

Effects of jellyfish and black seabream releasing on marine ecosystems: A mass balance approach for the coastal area of southern Zhejiang, China

This study evaluated the potential effect of stock enhancement on a coastal ecosystem. Based on data collected from the 2020 bottom trawl survey and literature information, an Ecopath model was constructed containing 19 functional groups representing the coastal area of southern Zhejiang, China. Jellyfish (Rhopilema esculenta) and black seabream Acanthopagrus schlegelii were selected as target-enhancing species based on their extensive juvenile release records. The maximum carrying capacity of these two species was estimated by static Ecopath and the potential ecological effects of enhancement activity for these two species were evaluated by the Ecosim routine. The trophic level (TL) of the functional groups in the coastal area of southern Zhejiang ecosystem ranged from 1 (primary producers) to 4.56 (sharks). The mean transfer efficiency of the coastal area ecosystem of southern Zhejiang was 8.71%, in which the relatively low transfer efficiency from TL2 to 3 was considered the main bottleneck that limited the biomass of higher TL species in this ecosystem. System characteristics indicated that the coastal area ecosystem of southern Zhejiang was vulnerable to disturbances and had low recovery ability. Enhancement simulation results indicated that the enhancement of jellyfish and black seabream had a partial impact on the functional groups of the ecosystem. Both jellyfish and black seabream enhancements adversely affected most groups of fish, cephalopods, and crabs, while jellyfish release stimulated the biomass of crabs. Ultimately, the present study indicates that the enhancement of black seabream decreased the total fish biomass via complex trophic interactions in the food web. Additionally, this study shows that recapture rates might not be sufficient to evaluate the net effect of stock enhancement, and therefore highlight the importance of ecosystem-based assessments for stock enhancement.

Influence of fishery management on trophic interactions and biomass fluxes in Lake Taihu based on a trophic mass-balance model exercise on a long-term data series

With increasing anthropogenic activities, freshwater ecosystems around the world are becoming increasingly affected by various pressures, including eutrophication, overfishing, and irrational stocking, which may have a negative impact on the food web structure. Despite the extensive research and proposed management measures for eutrophic lakes, there are only few analysis on long-term monitoring data regarding fishery resources. Additionally, there is a lack of evaluation and prediction of the effectiveness of current fish management policies. To remedy this, we analyzed long-term monitoring data from Lake Taihu, China, a severely eutrophicated lake with a skewed fish size structure exhibiting dominance of small individuals. We first constructed 14 Ecopath models to investigate how trophic interactions and biomass fluxes changed from 2007 to 2020. Subsequently, the Ecosim model was used to predict how the biomass of fish and the ecosystem network respond to the initiated 10-years fishing ban. Our results demonstrate long-term changes in fish biomass and ecosystem stability. The analyses revealed that 1) the biomass development in different feeding types of fish is controlled by human activities (mainly catches and stocking) and trophic interactions and 2) the rate of decline in ecosystem network stability slows down during the fishing ban. The primary focus of this study was to fill the gap in long-term serial studies of fish monitoring data and ecosystem stability in the lake and, for the first time, to predict the outcome of the fishing ban from an ecosystem perspective using the Ecosim model. Overall, our results emphasize the importance of rational stocking and fishing policies and provide a better understanding of the changes in the ecological dynamics in Lake Taihu of relevance for the management and restoration of the lake.

Long-term response of trophic structure and function to dam removal in a subtropical mountain stream

Although dam removal has been considered a viable strategy to mitigate habitat fragmentation within a stream, long-term ecosystem effects after dam removal have rarely been discussed. In an effort to enhance the resilience of the critically endangered Formosan salmon (Oncorhynchus masou formosanus) in response to climate change, a 15-m-high check dam in a subtropical high-mountain stream was half-removed. The aim of this study was to analyze the long-term response of trophic structure and function to dam removal by constructing Ecopath models upstream and downstream of the removed dam at different times. Field surveys for model parameters were conducted for a complete seasonal cycle 1 year before dam removal, 1 and 2 years (short-term) after dam removal and 7 and 8 years (long-term) after dam removal. Both upstream and downstream systems moved toward maturity after dam removal. In the short term after dam removal, more energy can be transferred further up in the food webs. The vitality and diversity of both systems also increased. In the long term after dam removal, although the transfer efficiencies of both systems generally showed a decreasing pattern, the resilience increased. Compared to the upstream system, the effects of dam removal on the downstream system were more evident. In the downstream system, dam removal enhanced the vitality of the Formosan salmon and thus the top-down control. The dominance of detritivory flow in the food web also shifted toward the dominance of herbivory flow. Consequently, the downstream system reached more maturity, and the food web was more closely linked. The ecosystem attributes of the upstream and downstream systems converged, suggesting that the decoupling between upstream and downstream systems resulting from damming disappeared 8 years after dam removal.

An Ecopath perspective on the maximum sustainable yield of a macrophyte infested wetland in Eastern India

Wetlands are recognized as one of the most productive aquatic ecosystems. This high productivity supports its enormous biodiversity, aiding a scope for the small scale fisheries within it. Basically, these wetlands act as platforms for culture-based fisheries (CBF) i.e practice of stocking fish seeds and harvesting the grow out fishes at later. Often in tropical wetlands, the high nutrient load and high temperature enable the luxurious growth of macrophytes. Moreover, this macrophyte infestation is considered as a bottleneck for wetland managers. Facing a similar situation our studied Beledanga wetland is a macrophyte-infested wetland and the invasive Eichhornia crassipes is the most dominant macrophyte species. Owing to the macrophyte problem, Grass carp have been stocked in it as a biocontrol agent, as grass carp is a known biocontrol agent for the macrophyte infestation situation and simultaneously it will raise the fish production. To ensure maximum sustainable production from the wetland by harnessing with the available resources, it is necessary to acquire knowledge about the system’s ecological status and its ecological networks. Thus, the Ecopath based mass-balanced model is one of the best suitable tools to know about the ecological organization of this Beledanga wetland. Considering the available data (observational and literature data), this study has constructed a mass-balanced Ecopath model with 14 functional groups including all fish groups, birds, plankton, benthos and detritus. It has been found that the zooplankton and benthos are the most utilized group and the birds are the keystone group in this wetland system. This wetland possesses a lower transfer efficiency as well as a low Finn’s cycling index (0.224%). The system is found as an immature system with moderate ascendancy and system reserve (overhead). Moreover, concerning the ecologically sustainable production from this wetland more virtual mass-balanced models were developed (i) to evaluate the optimum grass carp stocking to manage the macrophyte population and (ii) to assess the impact of the Eichhornia on the system functioning. The results show that the system can harbour 1.5 times more grass carp biomass than the present without hampering sustainability. Concerning the impact of Eichhornia, it has been noticed that this macrophyte affects the maturity and transfer process of the system. Moreover, its huge biomass only accumulates more detritus in the ecosystem.

ELASTICITY ANALYSIS OF THE GRAZING AND DETRITAL PATHWAYS IN A SHALLOW PHILIPPINE SEAGRASS MEADOW

Ecotrophic efficiency (EE) is an estimate of the proportion of production that is utilized by the next trophic level through direct predation or fishing or exported out of the ecosystem. In seagrass systems, analysis of EE provides crucial information on how biomass, when used or lost in biological functioning, affects the higher trophic levels via death or grazing relative to the energy lost via decomposition (i.e., Flow to the detritus, FTD) and exports to another ecosystem (i.e., Sum of all exports, SAE). In this study, projections on the effect of change in the EE of functional groups in seagrass systems due to the alteration of biomass were established heuristically using Elasticity Analysis. Using a previously constructed Ecopath model for a shallow Philippine seagrass meadow, the simulations of altering the biomass of seagrasses and their grazers were done to determine the change in EE, FTD, and SAE, thereby generating information on the dynamics of the grazing and detrital pathways in the seagrass ecosystem. Results showed the effects of biomass increase and decrease of grazers (herbivorous gastropods, Tripneustes gratilla, and polychaetes). If the grazers’ biomass increases, their EE tends to decrease, and biomass accumulation tends to increase. This implies that a fraction of their production used in the system is reduced even if their predators' density and feeding rate are still constant. In addition, the EE of seagrasses tends to increase, leading to a decrease in biomass accumulation at the primary producers’ trophic level. Lastly, the EE of detritus decreased because the FTD and SAE of its major contributors (the seagrasses) had also decreased. The findings contribute to the ongoing analysis of the role of herbivores versus detritivores in the energetics of seagrass habitats.

A food-web model as a tool for the ecosystem-level management of bivalves in an Atlantic coastal lagoon

The Ria de Aveiro is an important coastal lagoon for wildlife in Portugal, where the production of bivalves reaches approximately 2700 tons annually. However, the illegal overfishing of bivalves is frequent in this lagoon, which causes critical changes in the ecosystem. In this study, using a developed food-web model (Ecopath model), the ecological carrying capacity (ECC) and maximum sustained yield (MSY) of the Manila clam, Ruditapes philippinarum were estimated, and the effects of further increases in clam biomass on other species were investigated. The results showed that 1) the current biomass and legal catch of R. philippinarum do not yet exceed the ECC (172.40 tons km−2) or the MSY (86.20 tons km−2 year−1) in Ria de Aveiro; 2) the harvested Manila clams of the MSY represent removing from the ecosystem ∼ 581 tons carbon (C) and ∼83 tons nitrogen (N) annually, with substantial ecological and economic implications; and 3) a further increase in the biomass levels of this species may cause the ecotrophic efficiency of other groups to become unrealistic, potentially leading to decreases in ecosystem transfer efficiency, biodiversity and health. The results here are expected to guide the sustainable development and management of bivalve aquaculture in Ria de Aveiro and the protection of the local environment.

Impacts of regime shift on the fishery ecosystem in the coastal area of Kyoto prefecture, Sea of Japan, assessed using the Ecopath model

The present study assessed the impact of regime shifts on the ecosystems that support fisheries in the coastal area of Kyoto Prefecture, the Sea of Japan. Ecopath models were constructed during cold (1985) and warm (2013) regime periods, when the fishery structures were different. Both models evaluated by pre-balance diagnostics were reliably constructed. Multiple ecosystem indicator values were compared between the two periods to assess changes in the ecosystem structure and the impact of fisheries on the ecosystem. The major change in catches in the coastal area of Kyoto Prefecture between 1985 and 2013 was that the Japanese sardine drastically declined and Spanish mackerel increased. The primary production requirements of fisheries (%PPR) were higher in 1985, reflecting the greater impact of sardine. The mean trophic level of catch and system omnivory index suggested that stability of trophic network increased after the sharp decline in sardine biomass. The %PPR, the loss of secondary production due to fisheries exploitation and probability analysis of fishery sustainability suggested that the fishery structure in 2013, which was dominated by set nets, contributed to a more sustainable fishery than the structure in 1985, when fishery was dominated by purse seines and set nets.

Energy flow analysis of grass carp pond system based on Ecopath model

Grass carp (Ctenopharyngodon idellus) is the most productive freshwater fish in China, but its traditional aquaculture model still has problems, such as poor water quality and frequent diseases. We have taken monoculture and 80:20 polyculture grass carp ponds as the research object and used EwE software to build the Ecopath model of two ponds. We analyzed and compared the characteristics of ecological structure and energy flow in two ponds. The result showed the highest effective trophic level in the polyculture pond that was higher than that in the monoculture pond, and fish in polyculture had higher EE values which showed the production of fish in polyculture contributed more to the energy conversion efficiency of the ecosystem. Flows into detritus were the largest component of TST both in the two ponds, which accounted for 49.34% and 50.37%. And the average transfer efficiency in monoculture was 13.07%, while that in polyculture was 15.6%. The ascendency/total development capacity (A/TDC) and overhead/total development capacity (O/TDC) were 0.35 and 0.65 both in the two ponds, respectively, which indicated that both systems had a strong anti-perturbation ability, but the stability could be improved. Finn’s cycling index (FCI) in polyculture was higher and showed that the polyculture pond was more mature and stable. Unused energy of functional groups will flow to detritus, and that in the monoculture pond was higher, the energy of C. idellus that flowed to detritus in monoculture was 48.17% higher than that in polyculture; unused energy of bacteria and phytoplankton were also high. The result showed that polyculture could improve energy utilization, increase transfer efficiency, and raise the stability of the ecosystem. Grass carp ponds still need to be improved in the aspects of mixed species and energy consumption. It is necessary to improve the ecological and economic benefits of grass carp ponds by optimizing the aquaculture structure and adjusting the aquaculture proportion.

Ecotrophic perspective in fisheries management: a review of Ecopath with Ecosim models in European marine ecosystems

The aim of this work is to present the food web models developed using the Ecopath with Ecosim (EwE) software tool to describe structure and functioning of various European marine ecosystems (eastern, central and western Mediterranean Sea; Black Sea; Bay of Biscay, Celtic Sea and Iberian coast; Baltic Sea; North Sea; English Channel, Irish Sea and west Scottish Sea; and Norwegian and Barents Seas). A total of 195 Ecopath models based on 168 scientific publications, which report original, updated and modified versions, were reviewed. Seventy models included Ecosim temporal simulations while 28 implemented Ecospace spatiotemporal dynamics. Most of the models and publications referred to the western Mediterranean Sea followed by the English Channel, Irish Sea and west Scottish Sea sub-regions. In the Mediterranean Sea, the western region had the largest number of models and publications, followed by the central and eastern regions; similar trends were observed in previous literature reviews. Most models addressed ecosystem functioning and fisheries-related hypotheses while several investigated the impact of climate change, the presence of alien species, aquaculture, chemical pollution, infrastructure, and energy production. Model complexity (i.e., number of functional groups) increased over time. Main forcing factors considered to run spatial and temporal simulations were trophic interactions, fishery, and primary production. Average scores of ecosystem indicators derived from the Ecopath summary statistics were compared. Uncertainty was also investigated based on the use of the Ecosampler plug-in and the Monte Carlo routine; only one third of the reviewed publications incorporated uncertainty analysis. Only a limited number of the models included the use of the ECOIND plug-in which provides the user with quantitative output of ecological indicators. We assert that the EwE modelling approach is a successful tool which provides a quantitative framework to analyse the structure and dynamics of ecosystems, and to evaluate the potential impacts of different management scenarios.