Basal Food Resources Research Articles

Increasing water nutrient reduces the availability of high-quality food resources for aquatic consumers and consequently simplifies river food webs

While eutrophication has led to serious habitat degradation and biotic shifts in freshwater ecosystems, most current studies have focused on changes in community assemblages, with few considering the effect of eutrophication on food webs. We conducted a field study in subtropical headwater streams with a gradient of water nutrient levels to examine the effect of increasing water nutrients on food webs by using the long-chain polyunsaturated fatty acid eicosapentaenoic acid (EPA) as a measure of the nutritional quality of food. Basal food resources (macrophytes, submerged leaf litter, and periphyton), and aquatic consumers (macroinvertebrates and fish) were collected, and their fatty acid (FA) profiles were analyzed. Our results showed that periphyton was the dominant source of EPA for macroinvertebrates and fish, and a high-quality resource for consumers. As water nutrient concentrations increased, nutritional quality of periphyton significantly decreased and, in turn, the correlation between FA profiles of periphyton and macroinvertebrates declined. However, periphyton FA profiles did not account for the variability of fish FA, which may be induced by the increasing proportions of omnivorous fish in eutrophic streams that derived EPA from other sources. Further, the reduced periphyton EPA was associated with decreased trophic links and simplified stream food webs. Our study highlights the importance of high-quality food resources for aquatic food webs as water nutrients increased in stream ecosystems and provides a nutritional perspective to understand the mechanisms how eutrophication affects aquatic ecosystems.

Consumer isoscapes reveal heterogeneous food webs in deep-sea submarine canyons and adjacent slopes

The deep sea is the largest biome on earth, but one of the least studied despite its critical role in global carbon cycling and climate buffering. Deep-sea organisms largely rely on particulate organic matter from the surface ocean for energy – these organisms in turn play critical roles in energy transport, transformation, storage, and sequestration of carbon. Within the deep sea, submarine canyons are amongst the most complex and dynamic environments in our oceans, where varied morphology, powerful currents, and variable nutrient conditions influence the distribution of species and transport of organic material throughout the water column and the seafloor. Significant habitat heterogeneity provides ideal substrates for cold-water corals, making submarine canyons of interest to conservation and management. However, how these and other topographic features in the deep ocean influence energy flow and trophic pathways is poorly known. Thus, submarine canyons serve as model systems to track variability in organic material flux and consequential utilization and assimilation by the benthos. In this study, we used an extensive stable isotope dataset to examine food-web structure in Baltimore and Norfolk submarine canyons and compared them to their adjacent slopes located along the U.S. Atlantic margin. Linear models were used to construct geospatially-explicit consumer isoscapes that predicted variation in carbon and nitrogen isotopes across the canyon-slope seascape, providing a predictive map from which to test hypotheses on the distribution and flow of energy resources, relevant to understanding whole community function. Communities were composed of isotopically diverse feeding groups with photosynthetically-derived organic carbon providing the basal food resource. Canyon communities were distinct from the slope, with canyon consumers significantly 13C-depleted, indicating a greater supply and/or utilization of fresh organic matter compared to the slope. Isoscapes for benthic and suspension feeders were distinct, possibly due to the consumption of different quality organic matter sources (fresh = suspension feeders, old = benthic feeders), each with distinct isotope composition. To our knowledge, our modeled isoscapes represent the first spatially extensive isotopic maps of deep-sea consumers, providing insights into regional-scale variation in stable carbon and nitrogen isotopes for different consumer groups. They provide a baseline for tracking climate-change induced fluctuations in the quality and availability of surface primary production and the consequential impact to benthic communities, which play critical roles in carbon cycling in our world’s oceans.

Food‐web energy fluxes, energy transfer efficiency, and diversity respond distinctively to pollution and water diversion in rivers

Abstract Water diversion and pollution are two pervasive stressors for river ecosystems that often co‐occur. The individual effects of both stressors on river communities and energy transfer across the food webs are well described; however, how they interact remains unknown. We hypothesised that low‐to‐moderate nutrient pollution gradient would cause a mild increase in invertebrate driven herbivory and water diversion a strong reduction in detritivory, whereas their joint effect would reduce invertebrate abundance and diversity, as well as total energy fluxes (from basal resources to invertebrates and fish). We also expected a shift in body size spectra slope with increased energy transfer between trophic levels with moderate pollution, but not with water diversion. To test these hypotheses, we selected four rivers across a range of nutrient pollution levels (a proxy of water quality) subject to similar water diversion schemes and compared food webs upstream and downstream of their diversion weirs. Both stressors changed the availability of basal food resources. Nutrient pollution induced changes in the green food web (i.e., biofilm‐based) by enhancing biofilm stocks, whereas water diversion affected the brown food web (i.e., detritus‐based) by decreasing stocks of detritus. The propagation of the effects to higher trophic levels differed with each stressor: pollution increased the homogeneity of community within the reach, whereas water diversion made communities more heterogeneous. Moreover, pollution induced changes within omnivores, increasing herbivory and carnivory, whereas diversion reduced the total energy fluxes through a decrease in detritivory, especially with pollution. Although most of the variables studied seemed to be more sensitive to water diversion, pollution often accentuated the response, being the interaction between both stressors more explanatory than any of the two stressors on its own. The effects of water diversion on diversity and energy flow through food webs are more detrimental to moderately polluted rivers than to systems with high quality water. We show that the use of tools merging knowledge on trophic relationships among species and their metabolic requirements enables disturbances to be detected that would otherwise go unnoticed.

Nonconsumptive effects of black sea bass (Centropristis striata) on a crustacean mesopredator and the indirect effects on bivalve survival

The consumptive and nonconsumptive effects of predators on their prey and the indirect effects of these interactions that cascade through food webs have been studied for over half a century. In the northwest Atlantic, the stock of black sea bass (Centropristis striata) steeply declined during the 1980s. While population crashes of fished bivalve species coincided with those of black sea bass, the role of black sea bass in driving trophic cascades that indirectly influence bivalve survival has largely been overlooked. Over the past decade, black sea bass have not only been recovering in abundance but warming water temperatures have been driving a northward expansion of the extent of their seasonal migration, resulting in a particularly strong relative recovery along the south shore of Long Island, New York. To explore whether black sea bass alter the foraging rates of mud crabs (Dyspanopeus sayi) on a species of bivalve, blue mussels (Mytilus edulis), we manipulated the presence and position of sea bass within an array of mesocosm tanks. We found that the presence of black sea bass reduced the proportion of blue mussels consumed by mud crabs. Black sea bass presence indirectly elevated blue mussel survival by as much as 47.7% by reducing mud crab per capita consumption of blue mussels by 57.9%. However, there were limitations to the nonconsumptive effects of black sea bass that appeared to depend on their proximity to mud crabs. While our results are from an experimental setup with a simplified food chain and are context dependent, they emphasize the importance of studying how nonconsumptive effects of specific marine predators influence trophic cascades from both conceptual and applied coastal resource management standpoints. Our results suggest that the recovery of black sea bass may bode well for the population restoration of several species of bivalves within estuaries throughout their range. Further, our study provides evidence that indicates that the nonconsumptive effects of a recovering marine predator can indirectly elevate the survival of a basal food resource species.

Can you see the algae for the slime? Temporal patterns of biofilm food quality and quantity in lowland rivers

AbstractAnimals must invest some portion of their metabolism to activities related to physiological maintenance and the remainder to processes related to the production of new biomass for growth and reproduction. Animal metabolism is fuelled by food, and the quality and quantity of food, along with the effort invested to obtain it, are fundamental to supporting populations. Biofilms are a primary basal food resource within riverine food webs, and it is thought that their nutritional value for animals decreases with age due to dynamic changes in community composition. We sought to test assumptions of spatiotemporal changes to biofilm nutritional value by assessing variations in biofilm mass and fatty acid composition in three rivers for 73 days. We also used a multi‐prong eDNA approach to characterize changes to biofilm fungal (ITS1–4), bacterial (16S), and algal (23S) community compositions. We anticipated biofilm food value to decrease with biofilm age due to shifts in composition from high‐quality green algae and diatoms to low‐quality cyanobacteria and filamentous algae. Our results partially support this contention; biofilm food value, assessed as a combination of fatty acid mass per unit area (in grams per square meter) and concentration of fatty acids (in milligrams per gram), was dynamic and peaked between 24 and 43 days following submersion. After 43 days, biofilm food value decreased. However, despite significant temporal changes in biofilm community composition and a decrease in overall lipid concentration, the proportions of different fatty acid classes among total lipids did not vary. Instead, the observed increase in the abundance of cyanobacteria and filamentous algae compared with diatoms and green algae, along with higher quantities of lipid‐poor extracellular polymeric substances (EPS), likely contributed to the reduction in overall lipid concentration relative to the biofilm dry mass. Here we present a novel approach to balance consumer energetic costs with food quality within aquatic food webs. Our results have important implications for river management and provide valuable information for the use of environmental water to support lotic ecosystems.

Treated and highly diluted, but wastewater still impacts diversity and energy fluxes of freshwater food webs

Wastewater treatment plants (WWTPs) have greatly improved water quality globally. However, treated effluents still contain a complex cocktail of pollutants whose environmental effects might go unnoticed, masked by additional stressors in the receiving waters or by spatiotemporal variability. We conducted a BACI (Before-After/Control-Impact) ecosystem manipulation experiment, where we diverted part of the effluent of a large tertiary WWTP into a small, unpolluted stream to assess the effects of a well-treated and highly diluted effluent on riverine diversity and food web dynamics. We sampled basal food resources, benthic invertebrates and fish to search for changes on the structure and energy transfer of the food web with the effluent. Although effluent toxicity was low, it reduced diversity, increased primary production and herbivory, and reduced energy fluxes associated to terrestrial inputs. Altogether, the effluent decreased total energy fluxes in stream food webs, showing that treated wastewater can lead to important ecosystem-level changes, affecting the structure and functioning of stream communities even at high dilution rates. The present study shows that current procedures to treat wastewater can still affect freshwater ecosystems and highlights the need for further efforts to treat polluted waters to conserve aquatic food webs.

Autochthonous Versus Allochthonous Resources in a Tropical Rocky Shore Trophic Web Adjacent to a Marine Riparian Area

Marine riparian areas and coastal vegetation are essential and important to the coastal marine ecosystem, although their interactions and functions are still unknown and ignored in marine ecological studies and integrated management planning. In southeastern Brazil, allochthonous resources derived from riparian Atlantic rainforests bordering rocky shores have been observed in abundance together with the shallow subtidal rocky reef benthos. In this study, we used stable isotopes (δ13C and δ15N) to characterize the main components in a benthic trophic web on a shallow tropical rocky shore, to identify the proportional contributions of allochthonous (marine riparian vegetation—MRV) to autochthonous (phytoplankton and algae) inputs and to test which basal food resources contributed most to the marine community on the Atlantic Forest–rocky coast interface. We found eight major food resources and seventeen consumers that we classified into different groups according to their feeding habits and biology. Although the main source of basal resources in the benthic trophic web in the present study remained autochthonous, the allochthonous resources were assimilated by all consumers. MRV is thus an important resource for some primary consumers and it should be included as a potential source of basal resources in marine ecosystems adjacent to marine riparian areas.

Defining upcycled food: The dual role of upcycling in reducing food loss and waste

BackgroundFood loss and waste over-uses natural resources and is responsible for a considerable share of greenhouse gas (GHG) emissions. Moreover, increasing food prices and growing food insecurity internationally make instances of food wastage appear even more irresponsible and showcase the inefficiencies of the current food system. A new concept in the toolbox for fighting food loss and waste is upcycling – value enhancing use of ingredients otherwise wasted – that leads to upcycled food. However, not all products currently called ‘upcycled food’ live up to the resource-saving and value-adding promise entailed in the idea of ‘upcycling’, and products markedly differ in how ‘radical’ the upcycling is from a consumer perspective. Scope and approachTo shed light on this, we introduce a two-folded definition that hinges on current consumer edibility perception and has a view to changing consumer perception; We show that there are two types of upcycled food which each have a distinct role and contribution to preserving natural resources - one is avoiding resources are wasted that have gone into food production, thus constituting upcycled foods through alternative use, the other is diversifying and broadening the food resource base, thus constituting upcycled foods through novel use. We provide examples of these upcycled food types and highlight potential boundaries from a sustainable development goal perspective. Key findings and conclusionsMainstreaming the idea of upcycling in food systems has huge potential for improving circularity in the food system. Untapping this potential needs collaboration across the whole value chain and taking a food system perspective, such as when being well-aware of the boundaries arising from the dynamic nature of the topic and the interdependencies.

Seasonal Variation in Resource Overlap Between Red Swamp Crayfish (Procambarus clarkii) and Native Species in Poyang Lake Wetland, China

Biological invasions are a significant component of current global environmental change that affect biodiversity as well as ecosystem processes and services. The red swamp crayfish (Procambarus clarkii) is one of the most invasive species worldwide, with a documented ability to deplete basal food resources and alter the structure of aquatic food webs. The red swamp crayfish has extensively invaded the Poyang Lake wetland, located in the middle reach of the Yangtze River basin. Here, we use an isotopic mixing model (MixSIAR) with data from stable isotope ratios (δ13C, δ15N) to estimate relative contributions of potential resources to the biomass of red swamp crayfish and ten common native species, and we use hierarchical clustering analysis to assess basal resource breadth and interspecific similarity of invasive and native species. We hypothesized that red swamp crayfish and several native species have similar trophic niches and may compete for basal resources. Results from the mixing model demonstrated seasonal variation in the basal resource of all species, including the red swamp crayfish and native snails, prawns, and fishes. Submerged macrophytes and detritus were estimated to be the most important sources during the rising-water season; during the high-water season, emergent macrophytes and detritus were most important; and during the falling-water season, detritus, POM, and floating macrophytes were most important. Resource overlap was substantial between the invasive crayfish and dominant native species, particularly the freshwater snail (Bellamya aeruginosa), indicating the potential exists for negative impact from competition under conditions of resource limitation.

Isotopic niche overlap between sympatric Australian snubfin and humpback dolphins.

Ecological niche theory predicts the coexistence of closely related species is promoted by resource partitioning in space and time. Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins live in sympatry throughout most of their range in northern Australian waters. We compared stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in their skin to investigate resource partitioning between these ecologically similar species. Skin samples were collected from live Australian snubfin (n = 31) and humpback dolphins (n = 23) along the east coast of Queensland in 2014–2015. Both species had similar δ13C and δ15N values and high (>50%) isotopic niche space overlap, suggesting that they feed at similar trophic levels, have substantial dietary overlap, and rely on similar basal food resources. Despite similarities, snubfin dolphins were more likely to have a larger δ15N value than humpback dolphins, indicating they may forage on a wider diversity of prey. Humpback dolphins were more likely to have a larger δ13C range suggesting they may forage on a wider range of habitats. Overall, results suggest that subtle differences in habitat use and prey selection are likely the principal resource partitioning mechanisms enabling the coexistence of Australian snubfin and humpback dolphins.

Dietary fatty acid profiles shape crayfish biosynthesis and performance: Implications for riverine food webs

Abstract Alteration of riverine flows can modify the structure and function of ecosystems, changing energy pathways and patterns of micronutrient transfer between trophic levels. Fatty acids (FAs) commonly are used to evaluate food quality, since some FAs required for somatic growth and physiological functions in animals must be obtained from their diet. FAs also are used in food‐web studies as biotracers as a consequence of their constrained metabolic biosynthesis by animals. However, their utility may be confounded by selective retention or modification of dietary FAs by consumers. We conducted a 70‐day feeding trial to compare growth and survival of an abundant and widespread mesoconsumer (Cherax destructor, the common yabby or crayfish) fed three contrasting diets: a poor‐quality detritus‐based diet; a high protein invertebrate diet; and a high‐quality commercial aquaculture pellet. Fatty acid profiles were obtained for each dietary treatment and contrasted with crayfish FA profiles at the end of the experiment to examine patterns of FA retention and integration. We also collected wild crayfish from floodplain wetland and river habitats, and obtained FA profiles from their stomach contents and body tissue to compare with experimental crayfish. Experimental crayfish fed high‐quality commercial pellets doubled in mass during the 70‐day assay, invertebrate fed crayfish growth was intermediate, and growth of crayfish fed detritus was negligible. Fatty acid profiles of crayfish fed our three contrasting diets differed significantly at the end of the experiment. Proportions of the polyunsaturated omega‐6 FA linoleic acid (LIN, 18:2ω6) in crayfish followed the same inequality observed in growth and diets: pellets > invertebrates > detritus. Pellet‐fed crayfish preferentially assimilated greater proportions of FAs 20:4ω6 (ARA), 20:5ω3 (EPA) 18:1ω9 (OA) and 16:1ω7 (POA) into their tissue. Fatty acid profiles of floodplain crayfish differed to profiles of riverine crayfish, and floodplain crayfish had higher proportions of essential FAs ARA and LIN in their tissues. Fatty acid biosynthesis by crayfish was best described by a hypothesis of FA allostasis rather than homeostasis; in this, FA profiles of crayfish were shaped by their diet, and selective integration and modification of high‐quality FAs from basal resources rich in these micronutrients led to higher proportions in crayfish tissues. Here we present evidence for the conversion of shorter‐chain essential FAs by freshwater crayfish to compensate for a lack of long‐chain FAs in their diet. We provide a necessary step for improving our understanding of micronutrient dynamics and the transfer of essential molecules between trophic levels in lowland river food webs. Floodplain habitats are known to provide higher‐quality basal food resources for mesoconsumers than riverine habitats, and here we identify one mechanism by which that may be extended to subsequent trophic levels.

Seasonal variations of 137Cs concentration in freshwater charr through uptake and metabolism in 1–2 years after the Fukushima accident

AbstractUnderstanding the factors influencing 137Cs concentrations in freshwater salmonids is crucial for reviving inland fisheries in polluted regions. We studied seasonal variations of 137Cs concentration in charr (Salvelinus leucomaenis) through uptake and metabolism in forested headwaters at Fukushima and Gunma sites. Charr consumed both terrestrial and aquatic animals, and terrestrial prey was predated more in summer at both sites. The 137Cs concentrations in litter, which is a dominant basal food resource of both forest and stream ecosystems, differed between forest and stream due to 137Cs leaching effect on litter submerged in streams. The concentration difference in both litter and prey was greater at Fukushima site than at Gunma site. The estimated prey 137Cs concentration at Fukushima site peaked in summer when terrestrial preys are most available, whereas it remained relatively constant at Gunma site because of the small difference of 137Cs concentrations in between terrestrial and aquatic preys. The specific metabolic rate of charr was commonly changed with stream water temperature, greatest in summer, and lowest in winter at both sites. Because both prey 137Cs concentrations and specific metabolic rates peaked in summer, the combination of uptake and metabolism at Fukushima site largely negated seasonal 137Cs fluctuations in charr, whereas specific metabolic rate fluctuations could be the major determinant of charr 137Cs concentrations at Gunma site. Our results suggested that 137Cs concentrations in prey items, whose seasonality are varied due to initial 137Cs fallout volume, were expected to be an important determinant for 137Cs concentrations in charr.

Nitrogen pollution promotes changes in the niche space of fish communities.

Historically, anthropogenic fixed nitrogen has been purposely increased to benefit food production and global development. One consequence of this increase has been to raise concentrations of nitrogen in aquatic ecosystems. To evaluate whether nitrogen pollution promotes changes in the estimates of niche space of fish communities, we examined 16 sites along a Brazilian river basin highly impacted by anthropogenic activities, especially discharge of domestic and industrial sewage from a region with more than 5 million inhabitants. We analysed the carbon (δ13C) and nitrogen (δ15N) isotope ratios of fish species and both autochthonous (periphyton) and allochthonous (course and fine particulate organic matter) basal food resources. To estimate the magnitude of nitrogen pollution, we measured the nitrate and ammonium concentrations at each site. Sampling was conducted in the dry and wet seasons to evaluate the influence of seasonality. Nitrogen pollution generally increased estimates of niche space, and seasonality influenced only the niche estimates of fish communities from polluted sites. In addition, isotopic analyses of nitrogen polluted sites yielded unrealistic estimates of trophic positioning (detritivores at the top of the food web). We conclude that changes in niche space estimates reflect both alterations in baseline isotopic values and differential trophic behaviour among fishes. Our study suggests that under conditions of high pollution, other factors appear to influence isotopic estimates of niche, such as isotopically distinct sources that have not been sampled, and/or differences in δ15N turnover rates between fish tissue and basal resources, creating isotopic baselines that are challenging to interpret.

Longitudinal variation in the nutritional quality of basal food sources and its effect on invertebrates and fish in subalpine rivers.

There is growing recognition of the importance of food quality over quantity for aquatic consumers. In streams and rivers, most previous studies considered this primarily in terms of the quality of terrestrial leaf litter and importance of microbial conditioning. However, many recent studies suggest that algae are a more nutritional food source for riverine consumers than leaf litter. To date, few studies have quantified longitudinal shifts in the nutritional quality of basal food resources in river ecosystems and how these may affect consumers. We conducted a field investigation in a subalpine river ecosystem in Austria to investigate longitudinal variations in diet quality of basal food sources (submerged leaves and periphyton) and diet source dependence of stream consumers (invertebrate grazers, shredders, filterers and predators, and fish). Fatty acid (FA) profiles of basal food sources and their consumers were measured. Our results indicate systematic differences between the FA profiles of terrestrial leaves and aquatic biota, that is periphyton, invertebrates and fish. Submerged leaves contained very low proportions of long-chain polyunsaturated fatty acids (LC-PUFAs), which were conversely rich in aquatic biota. While the FA composition of submerged leaves remained similar among sites, the LC-PUFAs of periphyton increased longitudinally, which was associated with increasing nutrients from upstream to downstream. Longitudinal variations in periphyton LC-PUFAs were reflected in the LC-PUFAs of invertebrate grazers and shredders, and further tracked by invertebrate predators and fish. However, brown trout Salmo trutta contained a large proportion of docosahexaenoic acid (DHA, 22:6ω3), a LC-PUFA almost entirely missing in basal sources and invertebrates. The fish accumulated eicosapentaenoic acid (EPA, 20:5ω3) from invertebrate prey and may use this FA to synthesize DHA. Our results provide a nutritional perspective for river food web studies, emphasizing the importance of algal resources to consumer somatic growth and the need to account for the longitudinal shifts in the quality of these basal resources.

Contrasting fatty acids with other indicators to assess nutritional status of suspended particulate organic matter in a turbid estuary

Achieving a precise nutritional characterization of suspended particulate organic matter (SPOM) is key for understanding the efficiency of bottom-up trophic fluxes in estuaries. Assessing the nutritional status of SPOM in turbid estuaries is challenging due to the complex mixing and degradation dynamics of the autotrophic, heterotrophic and detrital sources configuring SPOM. Using a recently described index based on fatty acids (FA), SPOM nutritional value was quantitatively characterized in the Guadalquivir River Estuary (GRE). Over a two-year study, this FA-based nutritional index (FANI) discerned changes in the nutritional value of SPOM to a greater extent than other nutritional indices. Spatiotemporal results of FANI in the GRE indicated SPOM nutritional quality was 2.2-fold higher in the 20–35 salinity range respecting to the 0–5 salinity range and that SPOM in summer was 1.5-fold nutritionally richer than in winter. A mixing model using bacterial FA estimated a maximum 40–60% range of variation for a complementary contribution of autotrophs and heterotrophs to microbial biomass and was in agreement with results of carbon-based estimates of phytoplankton and total microbes. In the spatiotemporal scale, and referred to particulate organic carbon (POC), phytoplankton represented from 9.3% (winter) to 31.0% (summer), and from 15.0% in lower salinity (0–20) to 24.5% in higher salinity reaches (20–35). Phytoplankton was positively correlated with SPOM nutritional value. Specific FA markers indicated a low contribution of land plants to POC. The lipid-based approach here described can improve understanding of the nutritional status of basal food resources in turbid estuaries.

Spatial and temporal dynamics of fish assemblages in a desert reservoir over 38 years

Processes associated with reservoir aging threaten the capacity of systems to continue providing productive fisheries, and declining productivity might be exacerbated by decreasing water level associated with climate change and water abstraction. Despite their prevalence in riverscapes, we know little about long-term fish dynamics in reservoirs. Using a 38-year dataset from Lake Powell, USA, we tested for changes in assemblage structure and changes in fish condition for the most abundant species. The assemblage has undergone re-ordering of species relative abundance, but the same core species captured in 1981 were still present in 2018. Five species increased in relative abundance, while two declined, and seven remained unchanged. Walleye Sander vitreus and Smallmouth Bass Micropterus dolomieu were among those increasing over time, while Channel Catfish Ictalurus punctatus and Common Carp Cyprinus carpio declined. We were not able to attribute changes in fish assemblages with a suite of abiotic and biotic variables. Condition was low and declined over time for four of the six species. Although water level declined over time, we did not observe obvious declines in basal food resources. Declining water level has reduced availability of littoral habitat and likely contributed to declines in some species associated with this zone.

Ecological thresholds and regime shifts within hydrologically modified rivers: A 75+ year retrospective analysis

AbstractTheoretical models have spurred empirical testing to understand how anthropogenic disturbances cause sudden shifts between alternative functional states. Most studies are done over short periods of time, making it difficult to determine the occurrence of ecological thresholds or regime shifts. This study used carbon stable isotope ratios (δ13C) from museum specimens of fish, mussels, and snails over a timeline of 75+ years to ascertain if trophic structure of two hydrologically modified rivers changed between premodification and postmodification periods. An alternative state model following Scheffer's shallow lake model was developed. As long‐lived species, mussels and snails are time integrators with long tissue turnover time and serve as a surrogate for the balance of benthic and pelagic basal food resource contributions to fish biomass. Hydrological datasets over the period of record for the Upper Mississippi (UMR) and lower Ohio (LOR) rivers were placed in 5‐year intervals, as were δ13C data for invertivorous and piscivorous fish. The model indicated changes in δ13C of fish relative to changes in mean stage height (UMR) and mean minimum stage height (LOR) over time. Evidence based on the model and empirical data of δ13C‐stage height relationship suggests a regime shift occurred during the postdam period in the LOR. Postdam, fish from the UMR revealed little change in δ13C of invertivores, whereas postdam decreases in variability of δ13C for piscivores shifted from a threshold to an unstable equilibrium. Decreases in hydrological variability led to a loss of resilience, with both rivers becoming metastable due to hydrological modification.

Diet components, dietary habits, resource and its use in the coexisting catfish species

In over last six decades fisheries of the Ganga river System in general and the Ganga R. in particular have witnessed a radical change in dominance from the carp to catfish and now to invasive exotic species. Has this happened due modified river environment (natural flows, pollution) or have the species modified the food-web of the river is an issue that should be addressed in deep earnest intent. Among many facets that need to be answered, we should know the food resources base available in the river environment, preferences of fish species, if it is selective and the extent of overlap among the sympatric and co-existing species. The present investigation precisely examines this for the co-existing catfish species, Rita rita and Bagarius bagarius. R. rita feeds with greater intensity than B. bagarius. In R. rita intensity was high in pre-monsoon (January to May) compared to B. bagarius where intensity was higher in post monsoon (October to December). R. rita showed +ve preference for chironomid-Diptera and variety of Trichoptera among insects.Others include crustaceans and gastropod molluscs. In contrast B. bagarius shows preferences for a consortium of Diptera (Simuliidae), Trichoptera (Glossosomatidae), Ephemeroptera (Heptageniidae), Coleoptera and Odonata among insect food. It has high preference for fish elements. Both species select these items. There is a biologically significant diet overlap but these species avoid competition not only by selecting different items from the common food resource base but also by seasonal variation in feeding intensity. Such studies need to be extended to fish within and among feeding guilds. Keywords Catfish, diet composition, co-existance

RESULTS DESIGNING AND ANALYSIS WHEN INTRODUCING NEW BEVERAGE IDENTIFICATION CRITERIA

Building a digital profile of food product with use of modern mathematical apparatus of basic matrices is a solution to the problem of designing innovative beverage recipes. In this regard, for the effective use of the food resource base, modeling and production of high-quality food products, there is an acute problem of developing a methodology for identifying food products using the full range of the currently available analytical base. The article discusses an algorithm for constructing a flexible experimental design for the new identification criteria development, taking into account the laboratory research peculiarities in the beverage industry. The application of software in experiment designing is considered and a practical example of integrated designing based on the construction of an identification criterion for wine materials is presented.

Impoundment led to spatial trophic segregation of three closely related catfish species in the Three Gorges Reservoir, China

The construction of the Three Gorges Reservoir (TGR), the largest dam in the world, created novel spatial and seasonal fluctuations in food availability along the Yangtze River. We studied changes in diet and niche overlap of three co-occurring catfish species between the upper and lower sections of the TGR and across four hydrological seasons to investigate whether the diets of native catfish species reflect the fluctuations in food availability. Zoobenthos dominated the diets of the three species in the upper section, but shrimp made the bulk of the diet in the lower section. This was the case in every season except during the rising-water season when all three species increased the consumption of allochthonous foods. Diet breadth was significantly broader in the upper section relative to the lower section, and expanded during the rising-water season in the lower section. Niche overlap was significantly lower in the upper section than in the lower section. A non-significant trend of reduced niche overlap during the rising-water season was observed in both sections. Our results suggest that, in less than a decade, dietary plasticity facilitated the adaptation of these species to novel habitats and a shifted food-resource base formed by the impoundment.