The food web structure and ecosystem properties of a filter-feeding carps dominated deep reservoir ecosystem

Assessing ecosystem health: A preliminary investigation of the gosikhurd dam ecosystem structure and functioning, an appraisal based on ecological modelling, India

This study aims to comprehensively understand the Gosikhurd Dam ecosystem (GDE) ecosystem by employing the Ecopath with Ecosim software (version 6.6.5) to construct a trophic mass balancing model. This model consisted of 16 functional groups of organisms, and their interactions and trophic levels were explored. The study focuses on various performance indicators to assess the ecosystem's maturity and complexity. To achieve these objectives, monthly fish samples were collected from June 2022 to May 2023. Performance indicators such as the connectance index (CI), system omnivory index (SOI), Finn's cycling index (FCI), mean path length (FML), ascendency, overhead, and Shannon diversity index were calculated to assess ecosystem maturity and complexity. The Finn's cycling index (FCI) and the mean path length (FML) were calculated as 1.81 and 2.20, respectively, indicating the ecosystem's responsiveness to environmental changes and overall system health and stability. Ascendency and overhead values were also analysed, with ascendency being relatively higher (41.58%), reflecting a system that utilises less than half of its total capacity. The overhead value (58.42%) indicated that the ecosystem is relatively stable and capable of adapting to external perturbations. Furthermore, the Shannon diversity index was 1.67, illustrating less diversity and validating the ecosystem's immaturity. The study identifies critical species and their roles in shaping the ecosystem dynamics, highlighting the importance of zooplankton, zoobenthos, and tilapia as keystone species. These indices propound that GDE is in its developmental stage and lacks complexity compared to mature ecosystems. The findings provide valuable insights into the current state of the ecosystem and can guide future management and conservation efforts.

Ecological threshold of phosphorus load in Baiyangdian Lake based on a PCLake model and ecological network analysis

Ecological thresholds are a useful indicator for implementing ecological management. Many studies determine the thresholds for nutrient loads in lakes based on the maximum allowable concentration of chlorophyll a (Chla), although this neglects the overall performance of the ecosystem. A PCLake model of Baiyangdian (BYD) Lake in northern China was constructed with six ecological network analysis (ENA) indicators that characterized the ecosystem function, system maturity, and food web structure to quantify the overall status of the BYD ecosystem. To my knowledge, this is the first study on the system level responses of the BYD Lake to phosphorus load interference. Different phosphorus load scenarios were designed to simulate the ecological responses of BYD Lake. The simulated results were employed to calculate the ENA indicators. Ecological thresholds were determined through the driving response relationship between the phosphorus load gradient and the ENA indicators. The results show a non-linear transition response of ENA indicator under phosphorus load gradient. As phosphorus load increases, D/H, SOI, and FCI decreases while A/DC, TPP/TR, and TPP/TB increases. This indicates that the overall structure and function of the ecosystem will deteriorate if phosphorus load increases. The phosphorus load thresholds for the overall performance of BYD Lake were 0.50-1.32 mg m-2 d-1, slightly wider than that of Chla (0.53-1.26 mg m-2 d-1). The model results clearly indicate that there is a time-lag phenomenon at the switch points in the response of ENA indicators compared to that of single functional group. In addition, the A/DC, TPP/TR, SOI, and FCI present more time-lag than that of other ENA indicators. These time-lag effects provide a particular opportunity for biodiversity conservation. Therefore, a possible management strategy is proposed to combine system-level and function group-level thresholds, with the ENA-based threshold as the bottom line and the phytoplankton's threshold as the early-warning indicator. This design is expected to be more precise and efficient, by exploiting the advantages of two thresholds, and may benefit for ecological management practices.

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.

Silver Carp (Hypophthalmichthys molitrix) (Asian Silver Carp) Presence in Danube Delta and Romania-A Review with Data on Natural Reproduction

The Danube River has a large hydrographical basin, being the second largest river in Europe. The main channel flows through seven European countries with many species of fish inhabiting it. In this review we focused on the invasive species silver carp (Hypophthalmichthys molitrix), which plays an important ecological and economic role in its original habitat, but since introduced in Europe’s rivers, the species has posed a serious ecological risk under global warming. In this review paper, we gathered data regarding silver carp, such as when and how it entered the Danube Delta and the water temperature suitable for its growth and reproduction, mainly in the context of global warming, as well as the nature of nutrition and the ecological risk the species poses.

Application of mass-balance modelling to assess the effects of ecological restoration on energy flows in a subtropical reservoir, China

Eutrophication is a leading cause of impairment of lentic water bodies throughout the world. To inhibit algal blooms and remove excess nutrients, a 10,000 m² restoration project consisting of vegetation establishment and fish manipulation was conducted in the eutrophic bay of the Yantian Reservoir, southern China. Three Ecopath models were constructed to assess the recovery effects at an ecosystem level, and time series data were simulated to propose a fishery policy. During the restoration, 1) the redundant primary production flowing back to detritus decreased due to the increased predation of four stocked fish with different feeding habits; 2) the transfer efficiencies (TEs) through trophic levels increased due to the reinforced energy flows along the planktivorous, herbivorous, and molluscivorous food chains; 3) the groups that had the highest keystoneness shifted from carnivorous fish to invertivorous fish and omnivorous shrimp, indicating the shift of mixed trophic impacts from top-down to wasp-waist control; and 4) the changing indices of path length, flow fluxes, matter cycling, and network information showed that the restored system was more mature, developed, and organized than before. To sustain the long-term energy balance and functioning of the ecosystem, the maximum fishing yields (0.37-8.53 g/m²/year) were determined to maintain the relative biomass (close to 1) of stocked fish and wild tilapia by harvesting their annual production.

Wetland ecosystem status and restoration using the Ecopath with Ecosim (EWE) model

With increasing awareness of the importance of wetlands, the number of new or restored wetlands in China is steadily growing; however, not all of them fulfill their expected ecological function. Maintaining wetlands in their optimal state is an urgent problem that requires research into the ecosystem evaluation, regulation, and biomass management of wetlands. The Ecopath with Ecosim (EWE) model, also known as the ecological channel model, is a balance model that can directly construct the ecological system structure and describe its energy flow and mass transfer through the principle of nutrition dynamics. Here, the EWE model is applied to determine the ecosystem status of a newly restored wetland, Zhushanhu wetland, in the Lake Tai buffer zone of Zhushan Bay, and evaluate the current ecological regulations and biomass control measures. Our results provide theoretical and scientific support for the management and maintenance of wetland ecological restorations.

Use of structured expert judgment to forecast invasions by bighead and silver carp in Lake Erie

Identifying which nonindigenous species will become invasive and forecasting the damage they will cause is difficult and presents a significant problem for natural resource management. Often, the data or resources necessary for ecological risk assessment are incomplete or absent, leaving environmental decision makers ill equipped to effectively manage valuable natural resources. Structured expert judgment (SEJ) is a mathematical and performance-based method of eliciting, weighting, and aggregating expert judgments. In contrast to other methods of eliciting and aggregating expert judgments (where, for example, equal weights may be assigned to experts), SEJ weights each expert on the basis of his or her statistical accuracy and informativeness through performance measurement on a set of calibration variables. We used SEJ to forecast impacts of nonindigenous Asian carp (Hypophthalmichthys spp.) in Lake Erie, where it is believed not to be established. Experts quantified Asian carp biomass, production, and consumption and their impact on 4 fish species if Asian carp were to become established. According to experts, in Lake Erie Asian carp have the potential to achieve biomass levels that are similar to the sum of biomasses for several fishes that are harvested commercially or recreationally. However, the impact of Asian carp on the biomass of these fishes was estimated by experts to be small, relative to long term average biomasses, with little uncertainty. Impacts of Asian carp in tributaries and on recreational activities, water quality, or other species were not addressed. SEJ can be used to quantify key uncertainties of invasion biology and also provide a decision-support tool when the necessary information for natural resource management and policy is not available.

Mercury biomagnification in subtropical reservoir fishes of eastern China

Little is known about mercury (Hg) biomagnification in the subtropics, aquatic systems with high species diversity resulting in complex food webs. High atmospheric Hg emissions and ubiquitous reservoir fisheries may lead to elevated Hg bioaccumulation in Chinese freshwater fishes. However, stocking practices using fast-growing species can result in low fish total Hg (THg) concentrations. Here, we describe Hg transfer within the fish food web of a large subtropical reservoir, Qiandao Hu (Xin'anjiang reservoir) situated in eastern China. We measured food web Hg biomagnification and THg concentrations in 33 species of stocked and wild fishes. Mercury concentrations in most fishes were low, though we also found high Hg concentrations in wild top predators. The food web structure, assessed using stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N), demonstrated a high degree of omnivory and a long food chain. THg concentrations were highly correlated with fish δ(15)N values. The regression of log10THg against δ(15)N revealed the overall Hg biomagnification rate was low. This study shows that where long food chains exist in subtropical reservoirs, elevated Hg accumulation in top predators can occur despite a low Hg biomagnification rate.