Omnivory Index Research Articles

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.

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.

Ecosystem Characteristics and Trophic Model of the Artificial Reef Ecosystem in the Sea of Oman, Sultanate of Oman

This study aimed to understand the structure and function of the artificial reef ecosystem of the Sea of Oman and its stability and maturity. For this study, the trophic model of the Sea of Oman’s artificial reef ecosystem was described using the Ecopath with Ecosim (EwE) ecosystem modeling software (Version 6.6.7). The essential characteristics of the aquatic system were identified using a total of 38 fish species/functional groups, spread across an area of 140 km2 of artificial reef farm. The mean trophic level of the artificial reef ecosystem of the Sea of Oman was 3.039. Sharks were the keystone species of the studied ecosystem. Heniochus acuminatus and Chaetodon gardneri were the species with the highest niche overlap, whereas Acanthurus sohal and other crustaceans, and Terapon puta and Saurida undosquamis were the species with the lowest niche overlap. It was found that the ratio of total primary production to total respiration of the ecosystem studied was more than one, indicating that the system produces more energy than it uses to respire, and the ecosystem of the Sea of Oman can be regarded as a developing system because of its low degree of stability and maturity. The omnivory index was 0.260, the connectance index was 0.159, the total biomass to total throughput ratio was 0.006, Finn’s cycling index was 5.41, the total primary production to total biomass ratio was 64.895, and the total primary production to total respiration ratio was 4.424. The results indicate that the artificial reef ecosystem in the Sea of Oman can be categorized as immature (in the early developmental stage). Further study is needed to improve the input data and track ecosystem health, as well as exploring other management strategies. Based on the outcomes of the study, it is suggested that environmental management of the reef ecosystem, along with the fish catch data, should be taken into consideration for future research.

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.

Trophic structure using ecological relationships between five dominant commercial fish in Kolahi to Dargahan

AbstractThe purpose of this study was to determine the effects of frequent species population fluctuations and the impact of different rates of exploitation on other ecological links in the food web. The mass‐balanced Ecopath model represents the trophic interactions among the 31 defined functional groups in the Kolahi to Dargahan area, with five main species, including Trichiurus lepturus, Saurida tumbil, Nemipterus japonicus, Sillago sihama, and Cynoglossus arel (from April 2018 to April 2019). To investigate the effects of fishing and environmental disturbances, the Ecopath modeling approach combines software for analyzing ecosystem trophic‐level balances with population dynamic models. In the past 5 years, Hormozgan province has caught more than 45% of the benthic fish caught off the northern coasts of the Persian Gulf. From Kolahi to Dargahan, one of the most important fishing grounds in this province's southeast is located. Food web models are used to represent a marine system's current state, assess stock levels, and predict change over time. Over a year, the first five dominant fish in the study area, S. tumbil, S. sihama, C. arel, N. japonicus, and T. lepturus, were biometrically measured, and their population dynamics parameters as well as feeding ecology indices were analyzed. According to the trophic‐level index results, the five most common species studied in this study belonged to the third (N. Japonicas, S. sihama, and C. arel) and fourth (T. lepturus, and S. tumbil) trophic levels. The key species with the greatest impact on other groups of studied species were identified as S. tumbil and T. lepturus, respectively. The estimated ecosystem indicators were the system operational power (75846.797), the primary production/respiration ratio (0.034), the connectance index (0.159), and the system omnivory index (0.253). A pedigree index (PI) of 0.38 was estimated for the present model. Overexploitation of T. lepturus could disrupt the aquatic food web and adversely affect the long‐term sustainable use of aquatic resources, according to data. As a result, ecosystem‐based fisheries management should be implemented to find a more appropriate solution to sustainable exploitation in the studied habitat, an important fishing area in the Persian Gulf's north.

Analysis of the Ecosystem Characteristics and Ecological Carrying Capacity of the Main Commercial Fish in the Artificial Reef Ecosystem in Laizhou Bay Using the Ecopath Model

In this study, we constructed an Ecopath model of the artificial reef ecosystem in Laizhou Bay, with special emphasis on the stock enhancement opportunities. Laizhou Bay is the largest semi-enclosed bay in the Bohai Sea, China, where multiple factors, especially overfishing, have led to the decline of many commercial marine fish stocks. Artificial oyster reefs were developed in 2011 in this region, providing shelter, feeding, and breeding sites for marine organisms. Additionally, stock enhancement by release can be used to replenish fishery species resources. Ad hoc stock enhancement, however, can fail to bring economic benefits and may impact ecosystem stability. Therefore, we estimated the ecological carrying capacity of the three main economic fish species in Laizhou Bay, including black rockfish (Sebastes schlegelii), fat greening (Hexagrammos otakii), and Chinese seabass (Lateolabrax maculatus) before release to ensure the sustainable use of fishery resources. The Ecopath model in Laizhou Bay was divided into 17 functional groups based on commercial relevance, dietary similarity, and habitat needs of the species present in the area. The ecological parameters, such as the ratio of total primary productivity to total respiration (1.205), connectance index (0.207), and system omnivory index (0.090) indicated that the artificial reef ecosystem in Laizhou Bay has a relatively simple food web structure. The ecological carrying capacities of S. schlegelii, H. otakii, and L. maculatus were assessed at 0.4676 t/km2, 0.5472 t/km2, and 0.3275 t/km2, respectively. This study provides a reference for the formulation of fishery strategies to maintain ecosystem stability and biodiversity and to maximize fishery returns and sustainability in Laizhou Bay.

Using Ecopath Models to Explore Differences in Ecosystem Characteristics Between an Artificial Reef and a Nearby Natural Reef on the Coast of the North Yellow Sea, China

The comparison of trophic structure and energy flow between natural and artificial reefs is imperative to evaluate whether these man-made structures work similarly to comparable natural reefs. Here, to characterize the potential difference in functioning between two types of reef ecosystems, two trophic models (Ecopath) at an artificial reef and an adjacent natural reef on the coast of the north Yellow Sea, China, were established. Both Ecopath models were divided into 18 functional groups from primary producers (algae and phytoplankton) and detritus to predatory species (e.g., Sebastes schlegelii). Model outputs showed that the ecosystem scale was smaller in the artificial reef (total system throughput (TPP) = 6,455.47 t·km−2·year−1) relative to its natural counterpart (TPP = 9,490.48 t·km−2·year−1). At both reef types, a large proportion of energy occurred at trophic levels I and II, and most of the primary production was utilized through a detritus pathway. This result implies a bottom-up energy flow control for both cases. However, two types of reef systems were behaving in a reasonable manner, as mean transfer efficiencies were similar to the Lindeman efficiency (10%). The ecosystem maturity of the artificial reef is not comparable to that of the natural reef for its inferior value of total primary production/total respiration (TPP/TR). Moreover, both the connectance index (CI) and system omnivory index (SOI) were slightly higher at the artificial reef relative to the natural reef as well as other coastal systems with parallel latitudes, suggesting that the current artificial system has formed complicated interspecies relations and high-level stability. This work updates our knowledge about the functioning evolvement of established artificial reefs and provides a baseline for the efficient management of coastal zones and further investigations.

Comparison of Marine Ecosystems of Haizhou Bay and Lvsi Fishing Ground in China Based on the Ecopath Model

Recently, under the impacts of environmental shifts and human activities, marine ecosystem conservation and recovery have become increasingly important for the management and sustainable development of fishery resources. We construct two Ecopath models to describe and compare the similarities and differences in the structure and function of the ecosystems in Haizhou Bay (HZB) for 2020–2021 and Lvsi Fishing Ground (LSFG) for 2018–2019 in this study. Our results highlight the similarities of the two ecosystems in which plankton (e.g., zooplankton and phytoplankton) are important functional groups with bottom-up effect control and congers control the top-down effect. The differences between the two ecosystems indicate that the HZB ecosystem is relatively mature due to higher Finn’s cycling index (FCI), Finn’s mean path length (FMPL), Connectance Index (CI), System Omnivory Index (SOI), and Ascendency/capacity (A/C). However the food web structure in the LSFG is more diverse and stable with higher Overhead/capacity (O/C) and Overhead/capacity (H). The differences are possibly due to the low trophic level (TL) species composition in the two ecosystems. Therefore, we suggest that stock enhancement and release methods should be deployed to release high TL species into designated water areas to increase food web complexity and ecosystem maturity in HZB and LSFG. This study will help inform ecosystem and fishery regulations in different ways and facilitate discussion towards the establishment of strategic conservation planning and adaptive management.

Energy transfer and trophic organization in an Integrated Fish-Livestock-Horticulture System (IFLH) from Bicholim (Goa), the western coast of India

An integrated farming system (IFS) is a farming approach that helps to conserve agrobiodiversity, provides food security, enhances ecosystem services, maintains environmental quality, and also achieves sustainability. In this study, we analyzed the energy transfer and trophic organization in an IFS comprising of fish (seabass, catfish, tilapia), livestock (piggery and poultry), and horticulture components situated in Goa, western coast of India. The ‘IFS’ is designated as ‘Integrated Fish Livestock Horticulture system (IFLH)’. An Ecopath model was constructed for the IFLH to delineate the trophic organization and generate ecological indicators on energy transfer, resource use and recycling, ecosystem maturity and stability. In the IFLH model, thirteen ecological groups were defined ranging from trophic level 1.00 (detritus and benthic nitrogen fixers (BNF)) to 4.00 (catfish), seabass (0.99) and piggery (0.98) demonstrated the highest ecotrophic efficiencies and the lowest value was recorded for detritus (0.20). The energy transfer from detritus (90%) was much higher than the transfer from primary producers (10%). The transfer efficiency at the second trophic level was as high as 0.6 for the IFLH. The fish and livestock components (tilapia-31%, weedfish-21%, piggery-20%, and seabass-8%) showed the highest consumption rates in the IFLH. A high total system throughput (22,417.9 kg N ha−1 year−1) and gross efficiency (0.34) for the IFLH indicated greater levels of ecosystem activity and growth rate at low maintenance energy costs. The system yielded moderate values for Finn's cycling index (8.51), system omnivory index (0.32), and connectance index (0.18). Thus, these ecological indices showed that the IFLH system is moderately mature, stable, and resilient. The ecological indices; ascendency (44%), system overhead (56%), mean path length (3.4) and Finn's cycling index suggested that the ecosystem is comparatively stable, developing, resource-efficient, and sustainable system based on the ecosystem properties. The eco-exergy index (4434.25 g detritus equivalent m−2), specific eco-exergy (55.86), and robustness index (0.13) also classified the IFLH as moderately mature, relatively stable, and reasonably organized. To date, this model serves as the first IFLH model from India's western coast and would supplement the evaluation of other IFS using the modeling approach. However, the ecosystem indices also indicated further scope for improvement in the IFLH system to improve energy utilization, resource recycling and stability.

Ecosystem structure and function of Sanmen Bay based on Ecopath model.

Ecosystem structure determines material circulation, energy flow, and system function. Based on field investigation data in the Sanmen Bay, East China Sea from 2017 to 2018, ecological channel model was constructed by Ecopath, describing energy flow routes and functional characteristics of the Sanmen Bay ecosystem. Results showed that grazing food chain was the main energy circulation channel, and the trophic level of each functional group ranged from 1 to 3.80. Energy flow of the system was mainly concentrated in the first five levels, with an average energy conversion efficiency of 13.0%. Energy conversion efficiency was 12.8% and 14.5% from primary producers and debris, respectively. Connectance index (CI) and system omnivory index (SOI) were 0.40 and 0.24 respectively. Finn's cycling index (FIC) was 0.40, and Finn's mean path length (MPL) was 2.06. The ratio of total primary productivity to total respiration was 13.59. In conclusion, Sanmen Bay ecosystem was immature in material circulation and energy flow. This work is helpful to understand the structural and functional traits of coastal ecosystems in China.

Analysis of Energy Flow in the Sea Area of Zhongjieshan Islands and Assessment of Ecological Capacity of Sepiella Maindroni Based on Ecopath Model

Sepiella maindroni was once one of the four traditional marine products in our country. In order to evaluate the ecological capacity of Sepiella maindroni in the sea area of Zhongjieshan Islands, this study used Ecopath with Ecosim 6.5 (EwE) software to construct an Ecopath model composed of 17 functional groups in the sea area of Zhongjieshan Islands. The nutrient structure and energy flow characteristics of the sea area of Zhongjieshan Islands are analyzed from the ecosystem level, and the reasonable ecological capacity of the sea area of Zhongjieshan Islands is estimated by the model.The results show that the trophic level of each functional group in the marine ecosystem of the Zhongjieshan Islands is between 1-4.648, total primary production/total respiration is 4.539, the system Connectance Index is 0.478, the System Omnivory Index is 0.389, The trophic level of Sepiella maindroni is 3.562, and the Ecotrophic Efficiency is 0.306, indicating that the Ecotrophic Efficiency of each trophic level in the system is low and the energy is not fully utilized. There is still room for breeding and exile for the Sepiella maindroni. The model estimates that the ecological capacity of Sepiella maindroni is about 2t·km2.

Ecosystem modelling to understand the trophic dynamics and ecosystem health of a small tropical Indian estuary

Estuaries provide enumerable ecosystem services to mankind in terms of provisional, regulating, supporting, recreational and information services. However, the persistent human-environment interactions for these services altered the ecological integrity of estuaries. Although the small estuaries receive little attraction in scientific studies due to their low surface area and regional importance, these ecosystems are more vulnerable to anthropogenic pressures and require urgent attention from the scientific fraternity. The Terekhol Estuary (TRE) is a small tropical estuary situated along Goa, west coast of India, gaining recognition in recent years due to the pollution risk from tourism activities. Moreover, the estuary also behaves as an extension of the marine realm during the dry season. The food web structure and network flow indices of the TRE was assessed to reveal its present ecological status. The Ecopath modelling approach was employed to delineate the ecosystem structure and trophic functioning of the estuary distributed in 22 ecological compartments from 2018 to 2019. The trophic level of the food web ranged from detritus (TL-1) to sharks (TL- 4.53). The ecosystem structure demonstrated a grazing chain (herbivory) based organization over the detritus-based pathway. The proportion of exports to the total flows was 35% for the TRE. The model has a high total system throughput (12,043.6 t km−2 year−1), low system omnivory index (0.17) and connectance index (0.21), and a moderate relative ascendency (45.1%). Finn's cycling index (2.17%) indicated very low recycling in the system. All these indicators along with the eco-exergy index (8567.22 g detritus equivalent m−2), specific eco-exergy (38.25) and robustness index (0.11) classified the estuary as be immature, less stable and less organized and is in the initial stages of its development. The ecological indicators analyzed here point towards a medium to a high level of impact in the TRE due to anthropogenic activities. We also highlight the management measures to be implemented in order to restore the ecological quality of the TRE.

Evaluation of the trophic structure and energy flow of a rice-crayfish integrated farming ecosystem based on the Ecopath model

Rice field integrated farming combining aquaculture and rice cultivation effectively stabilizes food security and maintains sustainable agricultural development. To analyze the trophic structure and energy flow of rice field integrated farming ecosystem, the food web model of a rice-crayfish ecosystem was developed based on the Ecopath model approach. The functional group with the highest ecotrophic efficiency (EE) value was crayfish Procambarus clarkii (0.97), and those with the lowest EE values were chironomid larvae and benthic bacteria (0.02) in the rice-crayfish systems. The effective trophic level of P. clarkii was 2.20 with consumer consumption share of 19%. The transfer efficiency of trophic level II was 3.90% in the rice-crayfish system. The total system throughput was 19,262 g/m2/90 days, showing very high scale and activity. The rice-crayfish ecosystem showed high value of Finn's cycling index (0.266), and low value of connectance index (0.252) and system omnivory index (0.053). Therefore, the food web model structures of the rice-crayfish integrated farming ecosystem in this study was unstable, simple, and linear. The carrying capacity of P. clarkii was 138.85 g/m2. Ecosystem properties such as scale, energy consumption, and stability indicated that this farming model has room for improvement, and rice-crayfish integrated farming should be further optimized to improve energy utilization, stability, and comprehensive benefits based on the different ecosystem properties.

Ecosystem health status and trophic modeling of an anthropogenically impacted small tropical estuary along India's west coast.

The tropical estuaries are characterized with high biological production and also impacted by anthropogenic activities. Describing these estuaries in terms of ecological data and trophic dynamics to reveal the ecological impacts is gaining attention recently. In this study, the ecological structure is analyzed for a heavily impacted small macrotidal tropical estuary, Ulhas river estuary (URE), situated near Mumbai megacity in the western coast of India, to delineate the impact of anthropogenic stressors on the ecosystem functioning. The URE is being exploited for sand and fisheries resources, and also faces risks from anthropogenic activities. The ecological data of URE were compiled for 2017-18 together with the most relevant literature estimates to construct an ecosystem model. A trophic organization in 20 functional groups was identified for URE using Ecopath modeling approach. The functional groups identified in the food web ranged from detritus and primary producers (trophic level (TL) = 1) to large pelagics (TL = 4.14). Detritivory: herbivory ratio (1.35) indicated that the detritus chain is dominant over the primary producer's chain. The total system throughput (TST) was estimated as 16 736.2 t km-2year-1. The indices such as net system production (NSP = 1 398.781 t km-2 year-1), total primary production/total biomass (TPP/TB = 25.17), biomass/total system throughput (TB/TST = 0.01), recycling index (Finn's Cycling Index = 13.94%), system omnivory index (0.3), relative ascendency (25.6%), and system overhead (74.4%) classified URE as an immature system. The eco-exergy index (30748.54 gm detritus equivalent m-2) showed that the ecosystem is a moderately stable and relatively less organized network. The estuarine fish community index (EFCI) yielded a value of 38 indicating the poor health status of the fish community in URE. The study delivers a comprehensive understanding of the ecosystem setting in URE and characterizes the prevailing condition. The ecological indicators analyzed here point towards a medium to a high level of impact in URE due to anthropogenic activities.

Evaluating the macroscopic system properties of kelp species planted on two artificial reefs: Implications for the restoration of perturbed subtidal areas

Macroscopic ecosystem properties based on an Ascendency theoretical framework were assessed for mass-balance trophic models representing ecological systems constructed by the kelp species Macrocystis pyrifera planted on artificial reefs installed on subtidal barren rocky and sandy bottoms (Antofagasta Peninsula, Chile). Information on biomass, production, diet and consumption was needed. The magnitudes of relative Ascendency, relative Overhead and Redundancy values indicated that kelp planted on artificial reefs allocated on soft bottoms would be more highly developed and less resistant to perturbations than ecological systems on artificial reefs disposed on barren and natural systems inhabiting soft bottoms and kelp habitats. The relative Ascendency corresponding to each component of the ecological systems constructed on artificial reefs on both habitats was represented principally by detritus (~37%), M. pyrifera (between 22 and 26%) and phytoplankton (between 10 and 13%). The compartments of Rhodophyta, Chlorophyta Mesophyllum sp. and the sea star Heliaster helianthus accounted for the system complexity in terms of flow, exhibiting the lowest Average Mutual Information. The Finn cycling index – considered as a ecosystem maturity index – showed contradictory outcomes compared to Ascendency. However, the values of System omnivory index and Average path length quantified for the ecological systems constructed on both artificial reefs showed similar network topologies compared to natural kelp beds. Based on our findings, artificial reefs seeded with M. pyrifera could be used to restore perturbed local marine benthic ecological systems along the Chilean coast. Likewise, this work shows that the trajectory of local ecological systems can be modified, enhancing their global-system health.

Estimated flows and biomass in a no-take coral reef from the eastern tropical Pacific through network analysis

In the southern Gulf of California, the Cabo Pulmo reef has been the focus of many studies because it is the northern-most coral reef in the eastern Pacific. It is a paragon of a well-managed marine protected area. Under the assumption that fishing mortality is negligible, we want to identify and quantify major energy flows in an ecosystem without human intervention and describe the ecosystem resources and their interactions among species, to provide a tool for ecosystem-based management. We built a trophodynamic model using Ecopath to perform network analysis. Based on fieldwork (October 2017 – May 2018) and literature review, we identified 57 functional groups comprising 51 consumers (including 15 top predators), five primary producers plus detritus, and cluster analysis of trait profiles. The connectance index (0.17) and the system omnivory index (0.22) are low, suggesting that consumers feed on a few discrete trophic levels. Biomass of primary producers (grazing food chain; 186.8 t km−2) provides 9,813 t km−2 y−1, whereas flow from detritus supply 344.9 t km−2 y−1. The transfer efficiency decreases as flows go up the food web, from 12% at TL II to 4% at TL X, and throughput cycled (including detritus) = 118.7 t km−2 y−1. In comparison with other coral reefs, we found that Cabo Pulmo complies with the attributes to resist disturbances, with an estimated total system throughput = 95,789 t km−2 y−1, a net system production = 38,535 t km−2 y−1, a large mean path length = 12.11, ascendency = 123,662 (52%) flowbits and overhead = 116,164 (48%) flowbits. The high quality of the ecosystem services provided by Cabo Pulmo and the scenic beauty appeals to developers. Although the system is resilient, unregulated human activities may impact the reef condition and decrease the residents' quality of life and that of all the people who make a living from the low impact activities currently in effect. The trophic web model presented here may help to improve the response capacity of the coalition of residents, authorities, diving companies, and NGO's to preserve the reef and be a key element to conserve the system by contributing to its best management.

Research Article: Trophic dynamics analysis and ecosystem structure for some fish species of northern Oman Sea

In the present study, a trophic structure model for some fish species of the northern Oman Sea is developed through using mass balance modeling software, Ecopath with Ecosim (EwE). In this model, we simulated 16 functional groups spread across an area of 3998.20 km2 from 2017 to 2018. Mean trophic level in the area of the present study was 3.49. Values calculated for system omnivory and connectance indices were 0.42 and 0.44, respectively. However, the values of ecotrophic efficiency in the model were high (>0.5) for most consumers of high trophic levels except for sharks and rays because of their high fishing mortality. Accordingly, mixed trophic impact showed that phytoplankton and detritus positively impacted almost all ecological groups. Also bentho-pelagics, the medium demersals, benthos, and crustaceans had a very negative impact on themselves due to cannibalism. Furthermore, the highest realized trophic level was 4.34 for sharks. The maximum omnivory index is calculated as 0.99 for medium demersals for feeding on a wide variety of preys. Also, the average catch per net primary production, i.e., the gross efficiency of the system was around 0.000198 (lower than the global average) indicating that the fishery is harvesting fishes high in the food chain. The primary production/respiration (PP/R) ratio is found to be 3.57 and the values of ascendancy (45.40%) and overhead (54.60%) showed stability of the ecosystem. Thus northern Oman Sea can be classified as an immature ecosystem (in the developmental stage), although it has some kind of system maturity. Accordingly, the food web of northern Oman Sea is consisted mostly of detritivorous, planktivorous, and carnivorous fish species. Besides, Ecopath with Ecosim (EwE) software can be an excellent option to examine interactions among ecological groups, and the impact of fishing in northern Oman Sea which is unquestionably helpful to develop concrete management strategies. The proper ecosystem-based fisheries management practice can improve the efficiency of this overexploited ecosystem.

Ecopath modelling approach for the impact assessment of a small-scale coastal aquaculture system in Goa, India

In this study, the ecological impacts of introduction of cage aquaculture employing small cages integrating shellfish and finfish in coastal water bodies of Goa, situated in the west coast of India were analysed using Ecopath with Ecosim model. A multispecies cage aquaculture system incorporating Lutjanus argentimaculatus, Etroplus suratensis and Perna viridis was established in an estuarine ecosystem. The Ecopath model identified 12 functional groups starting from detritus (trophic level=1) to large benthic carnivores (trophic level=3.72). The ecosystem statistics such as total system throughput (8672 g m-2 year-1), gross efficiency (0.001), primary production/respiration (1.4), net system production (1028.2 g m-2 year-1) and system omnivory index (0.26) indicated that the ecosystem was highly productive and in a developing stage. With a medium rate of recycling (Finn’s Cycling Index=11.7%), high system throughput, high system overhead (79%) and moderate omnivory index (0.26), the food web was found to be immature having an organized trophic network with high production. Simulations of the various expanding scenarios for the cage culture within the ecosystem were explored using Ecosim. A scenario in which two cages each for pearlspot and red snapper and 20 mussel ropes was identified as a sustainable solution without sacrificing the threshold biomass for the functional groups of fish species [WU1] . The study provided useful insights and methodology towards assessing aquaculture in coastal ecosystems in terms of ecosystem structure and function.

Temporal changes in food web structure in semiarid waterholes

ABSTRACT High seasonality of semiarid aquatic ecosystems may be due to large-amplitude water level fluctuations. The resulting habitat changes impact aquatic communities and food web structures as a result of species replacement or loss. To study the impact of water level fluctuations on planktonic food web structure, we compared food web descriptors in contrasting seasons. We examined the planktonic food webs associated with semiarid natural and artificial waterholes sampled in Hwange National Pak, Zimbabwe, during the hot dry (HDS), wet (WS), and cold dry seasons (CDS). Natural waterholes are filled by rainwater, while underground water is pumped into artificial waterholes to provide drinking water to wildlife during the dry season. We computed the descriptors of 66 food webs. WS food webs tended to be more complex than those of HDS and CDS; the percentage of basal species was lower, whereas the food web connectance, percentage of intermediate species, omnivory index, mean trophic level, and maximum trophic height of species were higher. Pumping water to maintain pans in the dry season had no effect on food web properties. The drying up of waterholes in semiarid environments simplifies planktonic food webs. The dominance of small rotifers may explain the observed low omnivory index and food web connectance in HDS compared to those observed in other studies.

Trophic fingerprinting of Chilika, a Ramsar site and the largest lagoon of Asia using Ecopath

The constructed mass balanced Ecopath model illustrates the trophic interactions among 22 defined functional groups of Chilika lagoon ecosystem. The estimated trophic levels (TL) in this model are in the range of 1.0 to 3.416. Elopiformes were found as the top predator with a TL value of 3.416 followed by Belonids (3.411). Zooplankton was found as the most utilized group expressing the highest ecotrophic efficiency of 0.944. Network analysis of the model indicates a mean transfer efficiencies of 8.233% from primary producers and 6.198% from detritus. The ecosystem indices: total primary production/total respiration (7.803), Finn’s cycle index (1.662), mean path length (2.185), connectance index (0.460), system omnivory index (0.237), ascendancy (47.38) and overhead (52.62) were estimated by the model. The estimated pedigree index (PI) of 0.5 for the present model indicates the ecopath model of the lagoon is a robust model. The indices indicate that the Chilika lagoon ecosystem is on its developing stage and possessing a stable ecosystem with a moderate resilience capacity to overcome the perturbations.