Article

Trophic network and food web characteristics in a small tropical monsoonal estuary: A comparison with other estuarine systems

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Abstract

A mass-balance trophic model for a monsoon-influenced tropical estuary, Zuari along the central west coast of India, has been constructed to understand the trophic flows, to measure the ecosystem indices and flow characteristics, and to understand the stage of the ecosystem development, maturity, and stability. Twenty-two functional groups were identified in the ecosystem model starting from primary producers (trophic level=1) to top predators (trophic level=4.7). The ecosystem structure indicated that the estuarine food web is a bottom-up control trophic organization based on primary producers and detritus. Phytoplankton, zooplankton, clupeids & anchovies and heterotrophic benthos were the keystone groups in the estuarine food web. The trophic network has high total system throughput (23333.9 t km-2 year-1), and lower dimensions for recycling capacity (Finn’s cycling index: 2.78%), system omnivory index (0.25), and relative ascendency (39.9%). These results suggest that the estuary is an immature, and developing ecosystem. Based on the ecosystem indices, Zuari estuary is relatively small, well-mixed, highly productive and diverse ecosystem, which is resilient to the external disturbances on the system. This trophic model is the first Ecopath model for tropical monsoonal estuaries and fourth model for the estuaries along the Indian coast. The Zuari estuary model showed resemblance to the sub-tropical and tropical estuarine Ecopath models and differed from estuaries of India and temperate estuaries. This Ecopath model would be also useful for simulating the variations in trophic flows and biomass for functional groups under the impacts of fishing and anthropogenic activities on the ecosystem

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... Moreover, tropical estuarine ecosystems are under stress from both natural and anthropogenic stressors (Looi et al. 2013;Sivadas et al. 2016;Sreekanth et al. 2019). Yet, despite the presence of estuarine ecosystems across the globe, studies on their structure and trophic functioning have not attracted the attention they deserve (Patricio et al. 2004;Scharler and Baird 2005;Lobry et al. 2008;Lira et al. 2018;Mukherjee et al. 2019;Sreekanth et al. 2020a;Lal et al. 2021). ...
... However, studies on the holistic status of ecosystem structure are rare. The fisheries of these estuaries are over-exploited, as evident in the declining catches and the volume of a catch per unit effort (Ansari et al. 2003;Sreekanth et al. 2020aSreekanth et al. , 2021a. In the estuaries along India's west coast, fisheries have been directly affected by tourism and indirectly as a result of pollution (from mining, other industries, tourism, and agricultural run-off), destruction of mangrove habitats, and overfishing-activities that have degraded water quality and disturbed the ecological functioning of these ecosystems (Shetye 2011;Banerjee et al. 2012;Deshkar et al. 2012;Gaonkar et al. 2013;Sruthy and Ramaswamy 2017). ...
... In the following sections, the properties of the ME ecosystem are discussed and compared with the values of other global and Indian estuaries (Supplementary material 3). The highest trophic level groups in the ME were dolphins (4.51) and birds (4.46), a pattern similar to that of the model for the Zuari (Sreekanth et al. 2020a). The Ecopath models for other Indian estuaries and coastal ecosystems showed that the highest values of TL were lower than the corresponding values in the ME (Fig. 3). ...
Article
Estuaries provide life support to aquatic biota and livelihood support to fishermen and local inhabitants. However, the ecosystem function of estuaries is impaired due to anthropogenic stressors and hence, the assessment of ecosystem health using ecological indicators will deliver the status of stability, maturity, and integrity of an estuary. In this paper, we compiled comprehensive ecological data into an Ecopath model from 2018 to 2019 for a tropical Indian estuary, Mandovi (ME) located along the western coast of India. The functional groups (22) identified in the food web ranged from primary producers (trophic level (TL) = 1) to dolphins (TL 4.4). The indices; biomass/total system throughput (0.01), primary production/respiration (11.04), and primary production/ biomass (35.7) showed that the estuary is a developing ecosystem far from maturity. The ME food web is an immature, complex and organized trophic network with a medium rate of recycling (Finn's Cycling Index= 9.75%), high total system throughput (17132.33 tonnes km-2 year-1), low ascendency (19610 tonnes km-2 year-1), high relative ascendency (47.8%), moderate connectance (0.36), and omnivory indices (0.26). The health indices: eco-exergy index (21471.33 gm detritus equivalent m-2) and system robustness (0.153) showed that the ecosystem is immature but resilient to unexpected perturbations in the ecosystem. The ecological indicators were compared with other global estuaries, and the environmental indices were developed for the ME. Based on the ecological indices, the estuarine system is immature, moderately developed, and not well organized in terms of its ecological components. The study also indicates that an ecological approach would be more appropriate and essential in analyzing tropical transitional waters' health and sustainability.
... Estuaries function as nursery habitats, migration channels, and reproduction sites for fish and other aquatic organisms Nicolas et al., 2010). They also provide foraging habitats for aquatic species at all levels of the trophic hierarchy and offer fisheries resources to traditional fisherfolk living on the banks of these ecosystems (Beck et al., 2001;Cabral et al., 2007;Sreekanth et al., 2020a). However, these ecosystems are under stress all over the world because of various anthropogenic pressures such as overfishing, pollution, and habitat destruction (Coates et al., 2007;Diaz and Rosenberg, 2008;Lal et al., 2021). ...
... The ecological functioning of an estuary is supported by diverse functional groups and their complex trophic interactions with each other, which ultimately reflects the ecosystem integrity (Lal et al., 2021;Lobry et al., 2008;Mukherjee et al., 2019). Assessing the food web, energy flows, and other features of the ecosystem network would help in characterizing the ecological structure and health status of estuaries (Lal et al., 2021;Manju Lekshmi et al., 2020;Mukherjee et al., 2019;Rakshit et al., 2017;Selleslagh et al., 2012;Sreekanth et al., 2020a;Vassallo et al., 2006). ...
... Ecosystem network analysis (ENA) and food-web-based studies are becoming increasingly important in delineating ecosystem structure of estuaries (Lal et al., 2021;Lira et al., 2018;Mukherjee et al., 2019;Sreekanth et al., 2020a). Such analysis using the Ecopath modelling tool takes a holistic approach and identifies patterns in ecosystem structure, energy fluxes, key indices, and the network of flows between ecological compartments (Christensen et al., 2005). ...
Article
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 (12043.6 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 gm 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.
... Traditional gillnet fishery (70 vessels) in the estuary provides employment to about 500 traditional fishermen (Sreekanth et al., 2020). However, the indiscriminate operation of trawlers and mini-purse seiners creates overexploitation of fisheries resources. ...
... The time dynamic simulation was performed based on the Ecopath model developed in the year 2016 for Zuari estuary using EwE version 6.4 in previous studies (Fig. 3, Sreekanth et al., 2020), in which the fishing fleet were divided into three types (trawl, purse seine and gillnet) for simulations. The trophic network flow diagram of Zuari estuary food web is presented in Fig. 3. ...
... The variations were evident in the shrimp biomass when the fishing regulations were implemented. The former group was the main target species for the gillnet fishery and also served as the major prey resource for top predators (Sreekanth et al., 2020). Therefore, the fishing regulations influenced the groups in two ways: (1) increase in capture by gillnet fleet, (2) increase in predation by the predator groups. ...
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In this study, we measured the impacts of an effective fishing regulation on the sustainability of fisheries in Zuari estuary, a tropical estuary situated along western coast of India through an Ecosim approach. Ecosystem indicators for 2016 and 2031 (for each Ecosim scenario) were measured to compare and contrast the decadal changes in the status of the ecosystem between these two periods. Four different hypothetical fishing patterns were simulated to explore the best suited management scenario. The ecosystem indices of 2031 ecosystem were compared with that obtained for 2016 to evaluatethe possible effects of fishing regulations. The functional groups showed a decline in their biomass when no fishing regulations are implemented (S1). The direct fishing effort reductions of all the fleets (S4) and ban/reduction of indiscriminate fishing fleets (S2-immediate ban and S3-gradual reduction) showed a more or less similar trend for recovery of fish stocks through diverse fisheries policies. A complete ban of indiscriminate fishing seems to slightly more advantageous than the direct reductions in the fishing effort for all the fleets in terms of stock recovery (130%), Q statistic (1.15), Shannon diversity (1.43), mean trophic level of ecosystem (2.98), mean trophic level of the catch (2.91) and fish catch in the gillnet fleet (200%). The simulations have also suggested that a complete control for mechanized fishing fleets will be the best possible management strategy for the recovery of fish stocks in the ecosystem.
... Studies have also documented that the recycling and ascendancy are the relevant indicators of anthropogenic impacts on ecosystem functioning (Patrıcio et al. 2004;Christian et al. 2005;Selleslagh et al. 2009). In the past two decades, several successful attempts have been made to depict the ecosystem structure through Ecopath model from Indian's western and eastern coasts (Vivekanandan et al. 2003;Mohamed et al. 2008;Dutta et al. 2017;Das et al. 2018;Mukherjee et al. 2019;Sreekanth et al. 2020). ...
... A few functional groups were retained as individual species compartments (BD and AC) due to their disproportionately higher abundance in the samples. The functional grouping is mainly based on diet composition, size, common predators, ecological niche, and commercial landing patterns (Vivekanandan et al. 2003;Mohamed et al. 2008;Sreekanth et al. 2020). ...
... For birds, each input parameter values were collected and modified from similar and adjacent ecosystems (Mohamed et al. 2008;Sreekanth et al. 2020). ...
Article
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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.
... For zooplankton and phytoplankton, the count for different groups obtained during the standard sampling procedure were converted into g m -2 to estimate the biomass. P/B values for zooplankton were calculated from the empirical formula given by Banse and Mosher (1980): Q/B values were collected and modified from other published sources (Shetye et al., 2007;Selleslagh et al., 2012;Sreekanth et al., 2020). P/B value of phytoplankton was collected and modified from already published sources (Pitcher et al., 2002;Mohamed et al., 2008;Sreekanth et al., 2020). ...
... P/B values for zooplankton were calculated from the empirical formula given by Banse and Mosher (1980): Q/B values were collected and modified from other published sources (Shetye et al., 2007;Selleslagh et al., 2012;Sreekanth et al., 2020). P/B value of phytoplankton was collected and modified from already published sources (Pitcher et al., 2002;Mohamed et al., 2008;Sreekanth et al., 2020). For benthic groups, the total weight of sample was measured and expressed in t km -2 . ...
... For benthic groups, the total weight of sample was measured and expressed in t km -2 . The P/B values for benthic groups were also calculated as per Banse and Mosher (1980 (Pitcher et al., 2002;Mohamed et al., 2008;Sreekanth et al., 2020). ...
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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 organised 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. The study provided useful insights and methodology towards assessing aquaculture in coastal ecosystems in terms of ecosystem structure and function.
... Tropical estuaries have a huge diversity of fish species; however, the studies pertaining the Indian coast are limited (Ansari et al. 1995;Sreekanth et al. 2017;Roshith et al. 2013). In Indian monsoonal estuaries, the variations in the amount of freshwater discharge to the estuary determine the stability and assimilative capacity of the ecosystem (Sreekanth et al. 2018). These estuaries receive approximately 9 km 3 of annual freshwater runoff at an average rate of 145.4 m 3 /s from the upper reaches (Shetye et al. 2007). ...
... These estuaries receive approximately 9 km 3 of annual freshwater runoff at an average rate of 145.4 m 3 /s from the upper reaches (Shetye et al. 2007). This discharge rate in a small tropical monsoonal estuaries would be the highest compared to all the other tropical, sub-tropical, and temperate estuaries (Sreekanth et al. 2018). The greater runoff to the estuary is the end result of heavy precipitation (3000 mm) through the monsoon phenomenon. ...
... There are high nutrient, biomass, and energy inputs into Zuari estuary in terms of freshwater effluents, marine influx, and immigration of juveniles and sub-adults of aquatic species as well as export from the system in terms of outflow as emigrating subadult and adult populations (Ansari et al. 1995;Sreekanth et al. 2017). These input and output flows are essential to maintain the complex food web and this trophic organization is one of the important criteria that an ecosystem should satisfy to function as a nursery ground (Beck et al. 2001;Sreekanth et al. 2018). ...
Article
This study analyses the trophic structure of fish assemblages in a well-mixed tropical estuary, Zuari located in southwest coast of India. A total of 224 fish species were collected between September 2013 and August 2016 from 324 sampling events from 9 sampling stations using surface and bottom set gillnets. The sampling events were designed to cover three major seasons such as the pre-monsoon, monsoon and postmonsoon. For each sampling event, abiotic variables such as temperature, salinity, dissolved oxygen and transparency of the water were recorded. The data obtained for abundance of fish species was subjected to cluster analysis and non-metric multidimensional scaling. The results defined six spatio-temporally varying groups (clusters) within Zuari estuary. Canonical correspondence analysis demonstrated that temperature, salinity, dissolved oxygen and transparency were important in determining the fish assemblages in Zuari. The estuarine resident species were abundant in the inner zone (riverine side) of the estuary, where the salinity and temperature recorded lower dimensions compared to middle and outer zones (marine side). However, the inner shallow zone of the estuary was not a preferred habitat for the migrating marine species. Majority of the fish species preferred middle and outer zones and post-monsoon and pre-monsoon seasons for inhabiting the estuary. The present study furnishes a reference data for the spatio-temporal dynamics of fish assemblages in tropical monsoonal estuaries.
... The higher the value is, the higher the proportion of recycling energy flow is, indicating a higher maturity of the ecosystem (Christensen et al., 2008). Generally, the FCI of the estuarine ecosystem ranged from 0.19% to 24.8% (Sreekanth et al., 2020). In the Minjiang Estuary, FCI in 2016 was 0.92%, significantly lower than the Pearl River Estuary (Wang et al., 2015), the Yangtze Estuary (Han et al., 2016), and the Hooghly-Matla Estuary in India (Mukherjee et al., 2019), suggesting that the Minjiang Estuary ecosystem was in a low cycle and an immature state. ...
Article
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China’s marine fisheries have made a huge contribution to the world’s food supply at the expense of wild resources collapse by overfishing. Accordingly, the government has introduced a series of measures represented by seasonal fishing moratorium to achieve sustainable fisheries. To evaluate the impact of the seasonal fishing moratorium on the ecosystem of the Minjiang Estuary in southeastern China, three ecosystem models, one in 2006, one in 2016 after 10 years seasonal fishing moratorium, and one in 2016 simulated under the scenario without a fishing moratorium, were constructed by Ecopath with Ecosim. Based on the 2016 model, the status of the Minjiang Estuary ecosystem after 50 years was simulated under four scenarios of different combinations of fishing pressure and durations of the fishing moratorium. The results showed that in the 2016 model, parameters as total ecosystem flow, mean fishing trophic level, and Finn’s index were 9,235.407 t km−2 year−1, 2.94, and 0.920, respectively, all significantly higher than those extracted from the 2016 simulated model, suggesting the effectiveness of the seasonal fishing moratorium. Under scenario analysis, extending the fishing moratorium by 3 months and reducing fishing pressure by 50% showed synergistic effects to achieve a better result than the current fishing moratorium strategy.
... It would be worth noting that the IFLH showed a low value of FCI compared to other ecosystems (Fig. 8). The index generally ranges from 0.2 to 25 in estuaries and coastal ecosystems (Mohamed et al., 2008;Lira et al., 2018;Mukherjee et al., 2019;Sreekanth et al., 2020;Lal et al., 2021). The high values of FCI will be observed in ecosystems subjected to stressors and low stability (Odum, 1969). ...
Article
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 (22417.9 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.
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Aim: The assessment of tropical coastal ecosystems involving small scale fisheries is a pre-requisite for fisheries management. With a total area of 39.9 km² Zuari estuary in Goa is one of the major estuaries located along the southwest coast of India and it holds a small scale fishery for the tribal fishermen residing along the coastal stretch of the estuary. The main objective of the study wasto analyse seasonal patterns in fish species composition, catch rates and catch value inthe small scale fishery of Zuari Methodology: Insitu fishing operations were carried out on monthly basis in Zuari estuary from September, 2013 to August, 2015 and fish and shellfish fauna collected during the study were identified to the family, genus and species levels. The data collected on the species assemblages were used to study the seasonal patterns in fish assemblages, catch rates (CPUE) and catch value (VPUE) in Zuari estuary. Results: Atotal of 68, 715 organisms weighing 13980.4 kg were caught in 288 fishing operations from 2013 to 2015 in Zuari estuary. Two hundred and thirteen species from 74 families were identified and 30 species contributed about 60-70% of the catch. Escualosa thoracata, Sardinella longiceps, Mugil cephalus, Tenualosa toli, Fenneropenaues indicus, Portunus pelagicus, Thryssa malabarica, Rastrelligerkanagurta, Nematalosa nasus and Metapenaeus dobsonii were the dominant species on the basis of relative importance index (RH). There were significant seasonal variations in abundance, species composition, catch rate (CPUE) and catch value (VPUE). There was seasonality in fish species composition and maximum species diversity was observed during pre-monsoon season. The ecologically vulnerable aquatic species contributed 20-25% of the total catch and it is inferred that the estuary has a greater role in protecting these species. Interpretation: Small scale gillnet fishery of the estuary is analysed and documented in this study. The seasonal patterns in fish species composition catch rate and catch value are essential requirements for designing fisheries management. The present study gives insights formulate fisheries management actions to monitor and protect the fisheries resources of the estuary to ensure sustainable fisheries.
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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.
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The composition of fish communities in tropical coastal ecosystems is regulated by seasonal patterns in the oceanographic environment. In the present study, the authors have studied the temporal variation of fish assemblages and environmental variables in a tropical coastal ecosystem, Zuari estuary in Goa located along the west coast of India. The species abundance and environmental data were subjected to multivariate analysis (canonical correspondence analysis and non-metric multidimensional scaling) and showed seasonal differences in fish communities. The second canonical axis was loaded with salinity, temperature, dissolved oxygen, transparency and depth separating the seasons into discrete groupings. The authors also found that the species diversity is significantly less during the monsoon season in comparison to pre- and post-monsoon seasons. Moreover, season-specific diagnostic species were identified using SIMPER analysis. The seasonal migration of species mediated by environmental factors seems to be an important element which determines the temporal pattern in fish communities. The results of the study have implications on fish diversity, conservation and coastal fisheries management.
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Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight') single channel; net sand transport is headward in these areas. -from Authors
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The linear equations that describe trophic fluxes in mass-balance, equilibrium assessments of ecosystems (such as in the ECOPATH approach) can be re-expressed as differential equations defining trophic interactions as dynamic relationships varying with biomasses and harvest regimes. Time patterns of biomass predicted by these differential equations, and equilibrium system responses under different exploitation regimes, are found by setting the differential equations equal to zero and solving for biomasses at different levels of fishing mortality. Incorporation of our approach as the ECOSIM routine into the well-documented ECOPATH software will enable a wide range of potential users to conduct fisheries policy analyses that explicitly account for ecosystem trophic interactions, without requiring the users to engage in complex modelling or information gathering much beyond that required for ECOPATH. While the ECOSIM predictions can be expected to fail under fishing regimes very different from those leading to the ECOPATH input data, ECOSIM will at least indicate likely directions of biomass change in various trophic groups under incremental experimental policies aimed at improving overall ecosystem management. That is, ECOSIM can be a valuable tool for design of ecosystem-scale adaptive management experiments
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The degree of relationship between trawl catch and environmental variables was assessed in a bay-estuarine system of Goa, west coast of India using multivariate techniques. The demersal fish assemblage was dominated by the families, Leiognathidae, Sciaenidae, Clupeidae, Cynoglossidae and Stromateidae and were considered to be typical for the Indo-Pacific. Patterns in community-structure were analyzed by principal component analysis (PCA) which identified five major species-groups that explained 66% of the variation in absolute fish biomass. PCA was also performed using 13 environmental variables to reduce data set variability to four components which accounted for 75% of environmental variation. The model that best explained variation in absolute biomass based on maximum R2 (adjusted) and minimum Mallows' Cp statistic was 71% and included six variables such as dissolved oxygen, macrobenthic density, sediment pH, photosynthetic pigment (Chl a), particulate organic carbon (POC) and seston. The regression coefficients were significant (P<0.05) and small values of Cp indicated the preciseness of the developed model. Path analysis was used to construct a hypothetical causal path diagram to depict the interaction between fish biomass and environmental variables. The study demonstrated the most important variables with regard to environmental–biotic interactions, although the measured variables did not account for all the variation in trawl catches. Further studies elucidating ecologically meaningful relationships should be helpful in bay-estuarine fisheries management.
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Two rivers, the Mandovi and the Zuari, with their interconnecting canal, form an estuarine system in Goa on the west coast of India. Physical, chemical and biological features of this estuary are adapted to a seasonal rhythm induced by the annual cycle of the monsoon. Heavy precipitation and land runoff from June to September bring about large changes in temperature, salinity, flow pattern, dissolved oxygen and nutrients when the estuary becomes freshwater dominated. The monsoon season (July–September) is followed by a recovery period during the post-monsoon season (October–January) and thereafter a stable period of the pre-monsoon season (February–May) when the estuary becomes marine dominated. During the pre-monsoon (dry) season, the water in the estuarine system remains well mixed and the intrusion of salt water is felt as far as 65 km upstream in both the rivers; but during the monsoon season the rivers become stratified and a salt wedge is formed in each river which extends up to about 10 km upstream in the Mandovi and 12 km in the Zuari. The flow of the estuarine system is regulated by the entry of seawater with the incoming tide through Zuari which reaches Mandovi through the canal. The flow is reversed during the outgoing tide when the estuarine system is flushed. Dilution factors in both the estuaries are similar and vary from 1·2 to 8; highest values occur during the pre-monsoon season. Two shoals/sand bars occur permanently in Mandovi (Aguada Bay) close to a ramp-like inlet to the sea. This inlet poses no navigational problems for about 9 months during the dry season; but for a 3-month period during the monsoon, the waterway becomes hazardous and is closed to boat traffic. Heavy swell and intense wave activity lead to the transfer of sediments into the navigational inlet and the calm season brings the materials back to their original position with practically no overall change in the bathymetry of the bay.The oxygen cycle in the estuarine system is closely related to seasonal changes in temperature and bears an inverse relationship with salinity. In both the estuaries, the sulphate/chlorinity relationship remains uniform and similar to that of the sea except during the monsoon months when the relationship gets disturbed. Changes in phosphorus, nitrogen and silicon are largely regulated by rainfall and land runoff. There is no significant difference in the phytoplankton counts between Mandovi and Zuari which follow a rhythm similar to that of nitrate. Zooplankton biomass is higher in Zuari because of its greater marine influence. No seasonal variation was observed in the density of microflora in the two rivers. Bacterial counts were higher in the lower reaches of the estuarine system and decreased upstream.From its environmental features, the estuarine system can be classified as a tide-dominated coastal plain estuary.
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A 26-compartment steady-state trophic model (1997–1999) was constructed using the Ecopath with Ecosim software to study the general status and development trends of the Pearl River Delta coastal ecosystem. The results show that the values of effective trophic level ranged from 1.00 to 4.21. It was found that a high trophic niche overlap existed in the typical estuarine ecosystem. Mixed trophic impacts show that detritus and the groups at the low trophic levels had positive influences on most groups. The ecosystem was found to be in an immature state during 1997–1999 based on the system statistics.
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Structure and seasonal variation of an inshore demersal fish assemblage have been described from 52 trawl samples collected between November 1988–November 1989 from Aguada and Marmugao Bays at Goa (west coast of India). A total of 12 519 individuals belonging to 59 species were collected. There was a clear seasonal fluctuation in relative abundance, biomass, species occurrence and species dominance. Families such as Sciaenidae, Leiognathidae, Cynoglossidae, Clupeidae and Ariidae dominated the demersal fish community, both in abundance and in biomass over the two areas. About 50% of the recorded species regularly occurred in the two areas. Density and biomass were high during post- and pre-monsoon seasons and low during the monsoon seasons. The species assemblages at the two sites were similar and showed much overlap of dominant species. Resident and quasi-resident species were dominant throughout the year and the overall population consisted mainly of marine coastal species. Cluster analysis showed species segregation into seasonal groups and intense association among different species groups. There was seasonal fluctuation in diversity indices and a marginal increase in species richness in Aguada bay was noticed. The dominance of juveniles in the catches indicate that the two areas serve as nursery grounds for the juveniles of several commercially important marine teleosts.
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The Caeté Estuary lies within the world's second largest mangrove region, 200 km south-east of the Amazon delta. It has an extension of about 220 km2and is subjected to a considerable human impact through intensive harvest of mangrove crabs (Ucides cordatus) and logging of mangroves. In order to integrate available information on biomass, catches, food spectrum and dynamics of the main species populations of the system, a trophic steady state model of 19 compartments was constructed using the ECOPATH II software (Christensen & Pauly, 1992). Ninety-nine percent of total system biomass is made up by mangroves (Rhizophora mangle, Avicennia germinans andLaguncularia racemosa ), which are assumed to cover about 45% of the total area and contribute about 60% to the system's primary production. The remaining biomass (132 g m−2) is distributed between the pelagic and benthic domains in proportions of 10% and 90% respectively. Through litter fall, mangroves inject the main primary food source into the system, which is either consumed directly by herbivores (principally land crabs, Ucides cordatus) or, when already metabolized by bacteria, by detritivors (principally fiddler crabs, Uca spp.). These two groups are prominent in terms of biomass (80 g and 14·5 g m−2), and food intake (1120 g m−2 yr−1and 1378 g m−2 yr−1respectively). According to the model estimates, energy flow through the fish and shrimp compartments is of relatively low importance for the energy cycling within the system, a finding which is contrary to the situation in other mangrove estuaries reported in the literature. The dominance of mangrove epibenthos is attributed to the fact that a large part of the system's production remains within the mangrove forest as material export to the estuary is restricted to spring tides, when the forest is completely indundated. This is also the reason for the low abundance of suspension feeders, which are restricted to a small belt along the Caeté River and the small creeks which are watered daily. Phytoplankton, temporarily refloating benthic diatoms, neritic zooplankton and small pelagic fish dominate the (low) pelagic biomass. Total system throughput (10 559 g m−2 yr−1) and mean transfer efficiency between trophic levels (9·8%) calculated by the model fit well into the range reported for other tropical coastal ecosystems. The very high gross efficiency of the fishery (catch/net primary production) of 8·6% and its low trophic level (2·1) is explained by a high harvesting rate of mangroves and the fact that the main animal resource in the system are the mangrove crabs (Ucides cordatus), which feed at the first trophic level. The model was balanced asuming a turnover rate for the land crabs of P/B=0·25 (P/B: production per unit of biomass) which is possibly too high. If this value was replaced by a (possibly more realistic) lower value, the model would not balance, suggesting a situation in which more biomass is being harvested than produced, which hints to an overexploitation of this resource A ranking of the various system components in terms of their contribution to the system function (ascendency sensu Ulanowicz, 1997) revealed that detritus and associated bacteria contribute 34%, mangroves 19%, fiddler crabs 13%, phytoplankton and microphytobenthos 10%, mangrove crabs 10%, and the remaining 14 groups 14% to the total ascendency. Summary statistics of the model are given and compared with those of other coastal ecosystems.
Article
Measurement on primary production, phytoplankton biomass, POC and PON were made for a period of ten months at a coastal station and for fourteen months at two estuarine stations in Goa (west coast of India). Irrespective of surface and bottom, chlorophyll a ranged from 0.07- 2.68 mg/m³ at the coastal station at off Cabo (Stn 1); 0.01-4.33 mg/m³ at Mandovi (Stn 2) and 0.16 to 3.95 mg/m³ at Zuari (Stn 3). PP varied from 0.5 - 54.69 mgC/m³/hr at Stn 1, 0.19-67.69 mgC/m³/hr at Stn 2 and 0.17-63.24 mgC/m³/hr at Stn 3. Column productivity ranged from 18.98 to 795.52 mgC/m²/hr (av: 206.21 mgC/m² /hr ) at Stn 1, 1.46 to l45.98 mgC/m²/hr (52.78) at Stn 2 and 6.71 to l35.34 mgC/m²/hr (av: 69.98) at Stn. 3.Column chlorophyll ranged from 4.35 to 36.23 mg/m² (av: 6.19 mg/m²) at Stn 3. Phytoplankton biomass in terms of cell density was high in surface waters at Stn 1 and in bottom waters at Stn 2 and 3. Seasonwise surface PP was high during premonsoon at Stn 2 (av: 50.61 mgC/m³/hr) and at Stn 3 (av: 46.72 mgC/m³/ hr) and post monsoon at Stn 1 (av: 18.68 mgC/m³/hr). Estimated division rate of phytoplankton ranged from 0.12 to 10 (av: 1.8), 0.11 to 5.9 (av:0.9) and 0.15 to 0.63 (av:0.32) per day respectively for Stn 1, 2 and 3. Spatial and temporal difference in surface Chl a and PP between the three stations was found to be significant (P-0.01).
Article
The main goal of the EU Water Framework Directive (WFD) is to achieve good ecological status across European surface waters by 2015 and as such, it offers the opportunity and thus the challenge to improve the protection of our coastal systems. It is the main example for Europe's increasing desire to conserve aquatic ecosystems. Ironically, since c. 1975 the increasing adoption of EU directives has been accompanied by a decreasing interest of, for example, the Dutch government to assess the quality of its coastal and marine ecosystems. The surveillance and monitoring started in NL in 1971 has declined since the 1980s resulting in a 35% reduction of sampling stations. Given this and interruptions the remaining data series is considered to be insufficient for purposes other than trend analysis and compliance. The Dutch marine managers have apparently chosen a minimal (cost-effective) approach despite the WFD implicitly requiring the incorporation of the system's 'ecological complexity' in indices used to evaluate the ecological status of highly variable systems such as transitional and coastal waters. These indices should include both the community structure and system functioning and to make this really cost-effective a new monitoring strategy is required with a tailor-made programme. Since the adoption of the WFD in 2000 and the launching of the European Marine Strategy in 2002 (and the recently proposed Marine Framework Directive) we suggest reviewing national monitoring programmes in order to integrate water quality monitoring and biological monitoring and change from 'station oriented monitoring' to 'basin or system oriented monitoring' in combination with specific 'cause-effect' studies for highly dynamic coastal systems. Progress will be made if the collected information is integrated and aggregated in valuable tools such as structure- and functioning-oriented computer simulation models and Decision Support Systems. The development of ecological indices integrating community structure and system functioning, such as in Ecological Network Analysis, are proposed to meet a cost-effective approach at the national level and full assessment of the ecosystem status at the EU level. The WFD offers the opportunity to re-consider and re-invest in environmental research and monitoring. Using examples from the Netherlands and, to a lesser extent, the United Kingdom, the present paper therefore reviews marine monitoring and marine environmental research in combination and in the light of such major policy initiatives such as the WFD.
Article
The estuary of the Danshuei River, a hypoxic subtropical estuary, receives a high rate of untreated sewage effluent. The Ecopath with Ecosim software system was used to construct a mass-balanced trophic model for the estuary, and network analysis was used to characterize the structure and matter flow in the food web. The estuary model was comprised of 16 compartments, and the trophic levels varied from 1.0 for primary producers and detritus to 3.0 for carnivorous and piscivorous fishes. The large organic nutrient loading from the upper reaches has resulted in detritivory being more important than herbivory in the food web. The food-chain length of the estuary was relatively short when compared with other tropical/subtropical coastal systems. The shortness of food-chain length in the estuary could be attributed to the low biomass of the top predators. Consequently, the trophic efficiencies declined sharply for higher trophic levels due to low fractions of flows to the top predators and then high fractions to detritus. The low biomass of the top predators in the estuary was likely subject to over-exploitation and/or hypoxic water. Summation of individual rate measurements for primary production and respiration yielded an estimate of -1791 g WW m(-2) year(-1), or -95 g C m(-2) year(-1), suggesting a heterotrophic ecosystem, which implies that more organic matter was consumed than was produced in the estuary.
Fisheries of Hooghly-Matlah estuarine system: further appraisal 1994-95 to
  • P M Mitra
  • H C Karmakar
  • A K Ghosh
Mitra, P.M., Karmakar, H.C. & Ghosh, A.K., Fisheries of Hooghly-Matlah estuarine system: further appraisal 1994-95 to 1999-2000, Central Inland Capture Fisheries Research Institute, Kolkata, Bulletin no. 109, 2001.
Mandovi and Zuari estuaries
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  • M Kumar
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Shetye, S.R., Dileep Kumar, M. & Shankar, D., Mandovi and Zuari estuaries. Goa, India, CSIR-National Institute of Oceanography, Goa, India, 2007.
Improved construction, parameterization and interpretation of steady state ecosystem models
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  • M L Soriano
  • M L Palomares
Pauly, D., Soriano, M.L. & Palomares, M.L., Improved construction, parameterization and interpretation of steady state ecosystem models, in: Trophic models of Aquatic Ecosystems, edited by V. Christensen & D. Pauly, (ICLARM Conference Proceedings, Manila, Philippines), 1993, pp. 1-13.
Studying single species dynamics in a tropical multispecies context, in: Theory and Management of Tropical Fisheries
  • D Pauly
Pauly, D., Studying single species dynamics in a tropical multispecies context, in: Theory and Management of Tropical Fisheries, edited by D. Pauly & G.J. Murphy, (ICLARM Conference Proceedings, Manila, Philippines and CSIRO, Cronulla, Australia), 1982, pp. 33-70.
Fishbase World Wide Web electronic publication
  • R Froese
  • D Pauly
Froese, R. & Pauly, D., Fishbase World Wide Web electronic publication. http://www.fishbase.org, 2016.
Trophic model of the coastal fisheries ecosystem of the southwest coast of India, in: Assessment, Management and Future Directions for Coastal Fisheries in Asian Countries
  • E Vivekanandan
  • M Srinath
  • V N Pillai
  • S Immanuel
  • K N Kurup
Vivekanandan, E., Srinath, M., Pillai, V.N., Immanuel, S. and Kurup, K.N., Trophic model of the coastal fisheries ecosystem of the southwest coast of India, in: Assessment, Management and Future Directions for Coastal Fisheries in Asian Countries, edited by G. Silvestre et al, (World Fish Centre Conference Proceedings, Manila, Philippines), 2003, pp. 281-298.