Structure Of Aquatic Food Webs Research Articles

Pollen as food: effects of consumption on tadpole growth, development, and mobility

The structure of many aquatic food webs is influenced by tadpole survivorship and duration of seasonal occupancy, which depend on tadpole diet. Pollen has been occasionally reported to occur in tadpole diets, and the available studies show that tadpoles have a strong preference for this supposedly nutritive resource. Thus, we aimed to test whether a diet composed of pollen from varied plant species would boost tadpole growth, development, and agility/mobility, compared to a regular artificial balanced and nutritive diet. Tadpoles in initial developmental stages 25 and 30 grew more when fed with pollen, compared to artificial food and a mixture of both diets. Those initially in stage 30 advanced more developmental stages during one month when fed exclusively with pollen. Tadpoles fed with pollen moved longer distances in response to an aversive stimulus simulating a predatory attack than tadpoles fed with artificial food or a mixed diet. Our results corroborate the hypotheses of pollen being a very important food source to aquatic consumers such as tadpoles, being likely to influence the structure of aquatic food webs through tadpole nutrition and modulation of growth/development speed, as well as tadpole ability to escape predators.

What constrains food webs? A maximum entropy framework for predicting their structure with minimal biases.

Food webs are complex ecological networks whose structure is both ecologically and statistically constrained, with many network properties being correlated with each other. Despite the recognition of these invariable relationships in food webs, the use of the principle of maximum entropy (MaxEnt) in network ecology is still rare. This is surprising considering that MaxEnt is a statistical tool precisely designed for understanding and predicting many types of constrained systems. This principle asserts that the least-biased probability distribution of a system's property, constrained by prior knowledge about that system, is the one with maximum information entropy. MaxEnt has been proven useful in many ecological modeling problems, but its application in food webs and other ecological networks is limited. Here we show how MaxEnt can be used to derive many food-web properties both analytically and heuristically. First, we show how the joint degree distribution (the joint probability distribution of the numbers of prey and predators for each species in the network) can be derived analytically using the number of species and the number of interactions in food webs. Second, we present a heuristic and flexible approach of finding a network's adjacency matrix (the network's representation in matrix format) based on simulated annealing and SVD entropy. We built two heuristic models using the connectance and the joint degree sequence as statistical constraints, respectively. We compared both models' predictions against corresponding null and neutral models commonly used in network ecology using open access data of terrestrial and aquatic food webs sampled globally (N = 257). We found that the heuristic model constrained by the joint degree sequence was a good predictor of many measures of food-web structure, especially the nestedness and motifs distribution. Specifically, our results suggest that the structure of terrestrial and aquatic food webs is mainly driven by their joint degree distribution.

Influence of hydroperiod on aquatic food-web structure and energy production in a floodplain wetland: implications for environmental flow management

Context Environmental water is often used to manage floodplain wetlands that support many taxa, both terrestrial and aquatic. It is important to optimise the managed hydroperiod to maximise the provision of aquatically derived resources from wetlands. Aims To test the hypothesis that increasing hydroperiod affects food-web structure and energy production in floodplain wetlands. Methods Fatty acids and stable isotopes of δ13C and δ15N were used to define food-web structure, and estimate total energy production throughout a managed inundation event in a wetland in the northern Murray–Darling Basin. Key results Food-web complexity increased with an increasing hydroperiod in line with predictable patterns of community assemblage development, before reducing sharply immediately prior to drying. Energy availability increased with an increasing hydroperiod and there was a strong correlation (ρ = 0.669, P = 0.0001) between energy availability and fatty acid concentration, which was in turn related to patterns of taxon occurrence. Conclusions and implications Hydroperiod exerts a strong influence on aquatic invertebrate community trophic dynamics and energy provision. Planned flows should support maturation and stabilisation of the invertebrate community to optimise energy provision to consumers.

Invasive alien aquatic plant species management drives aquatic ecosystem community recovery: An exploration using stable isotope analysis

The socio-economic and ecological impacts of invasive alien aquatic plant (IAAP) species have been well studied globally. However less is known about ecosystem recovery following the management of IAAP species. This study employed a before-after study design to investigate ecological recovery following the management of Salvinia molesta D.S. Mitchell, at four field sites in South Africa. We hypothesized that the presence of S. molesta would have a negative impact on the ecosystem food web structure, and that following S. molesta control, the systems would show positive ecosystem recovery. Aquatic macroinvertebrate and macrophyte samples collected before and after mechanical or biological control of S. molesta, were analysed for δ13C and δ15N stable isotopes. Salvinia molesta infestations negatively impacted the food web structure, indicated by reduced food chain length, trophic diversity and basal resources. This represented an altered aquatic food web structure, that in some cases, led to the collapse of the aquatic community. In contrast, after either mechanical or biological control, there were increases in food chain length, trophic diversity and abundance of energy resources accessed by consumers, indicating improved food web structure. Although the study showed positive ecosystem recovery following control, we noted that each control method followed a different recovery trajectory. We conclude that S. molesta invasions reduce aquatic biodiversity and alter ecosystem trophic dynamics and related ecosystem processes, necessitating control.

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.

Impact of heavy metal exposure on biological control of a deadly amphibian pathogen by zooplankton

Despite devastating effects on global biodiversity, efficient mitigation strategies against amphibian chytridiomycosis are lacking. Since the free-living pathogenic zoospores of Batrachochytrium dendrobatidis (Bd), the infective stage of this disease, can serve as a nutritious food source for components of zooplankton communities, these groups may act as biological control agents by eliminating zoospores from the aquatic environment. Such pathogen-predator interaction is, however, embedded in the aquatic food web structure and is therefore affected by abiotic factors interfering with these networks. Heavy metals, released from both natural and anthropogenic sources, are widespread contaminants of aquatic ecosystems and may interfere with planktonic communities and thus pathogen elimination rates. We investigated the interaction between zooplankton communities and chytridiomycosis infections in a Flemish agricultural region. Moreover, we also investigated the impact of heavy metal contamination, that was previously investigated in the region and presented in recent work, on zooplankton assemblages and chytridiomycosis infections. Finally, we tested the effect of sublethal concentrations of copper and zinc on Bd removal rates by Daphnia magna in a laboratory assay. Although zinc, copper, nickel and chromium were widely abundant pollutants, heavy metals were no driving force for zooplankton assemblages at our study locations. Moreover, our field survey did not reveal indirect effects of zooplankton assemblages on chytridiomycosis infections. However, sampling occasions testing negative for Bd showed a higher degree of copper contamination compared to positive sampling occasions, indicating a potential inhibitory effect of copper on Bd prevalence. Finally, whereas D. magna significantly reduced zoospore densities in its environment, sublethal concentrations of copper and zinc showed no interference with pathogen removal in the laboratory assay. Our results provide perspectives for further research on such a biological control strategy against chytridiomycosis by optimizing environmental conditions for pathogen predation.

The impacts of climate change on plankton as live food: A review

Climate change is expected to warm up the ocean surface where majority of life inhabits. Ocean warming influences vertical mixing and stratification patterns, which alter nutrient cycle, plankton production, and aquatic food web. Plankton serves as the first food source for all larval organisms and the base of aquatic ecosystem. Zooplankton community is a crucial component of the aquatic food web. They are critical components in an ecosystem of aquatic and worldwide biogeochemical cycles. Zooplankton contributes as food source to economically valuable fishes, primary-production grazers, and carbon and nutrient cycle drivers. Climate change contributes to dire consequences by altering the baseline of aquatic food web structure. However, the ocean biota itself can influence climate change, and the implications of this are evident from the increase and decrease of wild fisheries production. This review highlights the effect of climate change on phytoplankton and zooplankton production.

Microbial river-to-sea continuum: gradients in benthic and planktonic diversity, osmoregulation and nutrient cycling

BackgroundCoastal aquatic ecosystems include chemically distinct, but highly interconnected environments. Across a freshwater-to-marine transect, aquatic communities are exposed to large variations in salinity and nutrient availability as tidal cycles create periodic fluctuations in local conditions. These factors are predicted to strongly influence the resident microbial community structure and functioning, and alter the structure of aquatic food webs and biogeochemical cycles. Nevertheless, little is known about the spatial distribution of metabolic properties across salinity gradients, and no study has simultaneously surveyed the sediment and water environments. Here, we determined patterns and drivers of benthic and planktonic prokaryotic and microeukaryotic community assembly across a river and tidal lagoon system by collecting sediments and planktonic biomass at nine shallow subtidal sites in the summer. Genomic and transcriptomic analyses, alongside a suite of complementary geochemical data, were used to determine patterns in the distribution of taxa, mechanisms of salt tolerance, and nutrient cycling.ResultsTaxonomic and metabolic profiles related to salt tolerance and nutrient cycling of the aquatic microbiome were found to decrease in similarity with increasing salinity, and distinct trends in diversity were observed between the water column and sediment. Non-saline and saline communities adopted divergent strategies for osmoregulation, with an increase in osmoregulation-related transcript expression as salinity increased in the water column due to lineage-specific adaptations to salt tolerance. Results indicated a transition from phosphate limitation in freshwater habitats to nutrient-rich conditions in the brackish zone, where distinct carbon, nitrogen and sulfur cycling processes dominated. Phosphorus acquisition-related activity was highest in the freshwater zone, along with dissimilatory nitrate reduction to ammonium in freshwater sediment. Activity associated with denitrification, sulfur metabolism and photosynthesis were instead highest in the brackish zone, where photosynthesis was dominated by distinct microeukaryotes in water (Cryptophyta) and sediment (diatoms). Despite microeukaryotes and archaea being rare relative to bacteria, results indicate that they contributed more to photosynthesis and ammonia oxidation, respectively.ConclusionsOur study demonstrates clear freshwater–saline and sediment–water ecosystem boundaries in an interconnected coastal aquatic system and provides a framework for understanding the relative importance of salinity, planktonic-versus-benthic habitats and nutrient availability in shaping aquatic microbial metabolic processes, particularly in tidal lagoon systems.72ugw57JLuZNUPngo1htqPVideo abstract

Isotopic composition of aquatic and semiaquatic plants from the Mexican Caribbean: A baseline for regional ecological studies

Primary producers in the aquatic community structure are fundamental elements because they are the first link in the trophic network as occur in most ecosystems. They produce oxygen and biomass, act as a shelter for several species, and provide food for a wide variety of megaherbivore species like manatees and sea turtles. Physicochemical processes taken place in primary producers can be determined through stable isotope analysis (SIA) as natural tracers from elements like carbon and nitrogen, applied in ecological, and physiological studies. In the Mexican Caribbean ecosystems, SIA has been little applied in aquatic plants, where Thalassia testudinum is the main seagrass species studied. Here, we present the isotopic composition (δ13C and δ15N) from 95 aquatic and semiaquatic plant species of four vegetation types, from three different environments, hydroclimatic seasons, and geographical zones in the Mexican Caribbean. Main statistical differences in δ13C and δ15N were found according to vegetation type and environment. Besides, for δ13C were also found statistical differences among seasons, while for δ15N differences were found among zones (H-Test, p < 0.05). This study provides an isotopic baseline for further ecological studies in the region. This information can contribute to understanding the structure of aquatic food webs and infer the diet and feedings habits of aquatic species, as well as to detect possible changes related to anthropogenic activities that can affect the survival of these plant species, and the fauna depending on them.

Chemical and morphological defenses of Pseudo-nitzschia multiseries in response to zooplankton grazing

Pseudo-nitzschia species frequently blooms in coastal waters, and some species are able to produce the toxin domoic acid (DA), hereby causing harm to the marine ecosystem and humans. Laboratory studies were conducted to investigate the influence of different levels of grazing pressure on the morphological and chemical response (in terms of cellular DA production) of Pseudo-nitzschia. Subsequently, zooplankton grazer responses to these defenses were examined. The cellular DA content of P. multiseries ranged from 0.11-0.27 pg cell−1 without grazers, and increased up to 44% with the presence of grazers (Artemia nauplii) and with grazer concentration. Grazing also affected the density of P. multiseries chains and average chain length which became ~25% higher and ~8% longer, respectively, than without grazers. These effects could either be caused by size-dependent grazing or by grazer-cue-induced effects on chain formation. A negative correlation between cellular DA content in P. multiseries and clearance and/or ingestion rates of Artemia nauplii indicate that DA might have a negative effect on the grazing of Artemia nauplii. Such interaction might result in a decrease in grazing pressure on toxic blooming species, like P. multiseries, and hence potentially a prolonged bloom. This indicates that the interaction between toxic diatoms and grazers may have implications on aquatic food web structure and the progression of Pseudo-nitzschia blooms.

Geophysical templates modulate the structure of stream food webs dominated by omnivory

AbstractFood webs show the architecture of trophic relationships, revealing the biodiversity and species interactions in an ecosystem. Understanding which factors modulate the structure of food webs offers us the ability to predict how they will change when influential factors are altered. To date, most of the research about food webs has focused on species interactions whereas the influences of surrounding environments have been overlooked. Here, using network analysis, we identified how the structure of aquatic food webs varied across a range of geophysical conditions within a whole stream system. Within a headwater basin in the Cascade Mountain Range, Oregon, USA, macroinvertebrate and vertebrate composition was investigated at 18 sites. Predator–prey interactions were compiled based on existing literature and dietary analysis. Several structural network metrics were calculated for each food web. We show that the structure of food webs was predictable based on geophysical features at both local (i.e., slope) and broader (i.e., basin size) spatial extents. Increased omnivory, greater connectance, shorter path lengths, and ultimately greater complexity and resilience existed downstream compared to upstream in the stream network. Surprisingly, the variation in food web structure was not associated with geographic proximity. Structural metric values and abundance of omnivory suggest high levels of stability for these food webs. There is a predictable variation in the structure of food webs across the network that is influenced by both longitudinal position within streams and patchy discontinuities in habitat. Hence, findings illustrate that the slightly differing perspectives from the River Continuum Concept, Discontinuity Patch Dynamics, and Process Domains can be integrated and unified using food web networks. Our analyses extend ecologists’ understanding of the stability of food webs and are a vital step toward predicting how webs and communities may respond to both natural disturbances and current global environmental change.

Changing Water Levels in Lake Superior, MI (USA) Impact Periphytic Diatom Assemblages in the Keweenaw Peninsula

Predicted climate-induced changes in the Great Lakes include increased variability in water levels, which may shift periphyton habitat. Our goal was to determine the impacts of water level changes in Lake Superior on the periphyton community assemblages in the Keweenaw Peninsula with different surface geology. At three sites, we identified periphyton assemblages as a function of depth, determined surface area of periphyton habitat using high resolution bathymetry, and estimated the impact of water level changes in Lake Superior on periphyton habitat. Our results suggest that substrate geology influences periphyton community assemblages in the Keweenaw Peninsula. Using predicted changes in water levels, we found that a decrease in levels of 0.63 m resulted in a loss of available surface area for periphyton habitat by 600 to 3000 m2 per 100 m of shoreline with slopes ranging 2 to 9°. If water levels rise, the surface area of substrate will increase by 150 to 370 m2 per 100 m of shoreline, as the slopes above the lake levels are steeper (8–20°). Since periphyton communities vary per site, changes in the surface area of the substrate will likely result in a shift in species composition, which could alter the structure of aquatic food webs and ecological processes.

Effects and prediction of nonpoint source pollution on the structure of aquatic food webs

AbstractNonpoint source pollution entering rivers will pollute water quality, degrading the health of aquatic ecosystems. However, owing to the lack of quantitative research on the effects of nonpoint source pollution on the structure of aquatic food webs, there is a lack of quantitative basis for river management. Nonpoint source pollution is not only difficult to control effectively, but also the success rate of water ecological restoration projects is low. With the increasing proportion of nonpoint source pollution in water environmental problems, it is urgent to quantitatively assess and predict the impact of nonpoint source pollution on the structure of food webs. Therefore, this thesis presents a method for quantitatively assessing and predicting the impact of nonpoint source pollution on the structure of food webs through using fuzzy clustering to screen the typical points of the impact of nonpoint source pollution, then using canonical correspondence analysis (CCA) and partial least squares regression analysis to comprehensively filtrate the driving factors affect food web that results in nonpoint source pollution, and then determining the impact of each driving factor on the structure of food webs. Finally, the change trend of food web structure is predicted. The results show that (1) the driving factors that the nonpoint source pollution that affects the food web structure is NH3‐N and chemical oxygen demand (COD). The increase in NH3‐N and COD promotes the growth of phytoplankton, causing the change of the primary productivity of the ecosystem, and ultimately changes the entire food web structure; (2) NH3‐N and COD affect the stability, maturity, connectivity and complexity of the aquatic food web structure. The increase of NH3‐N increases the connectivity and maturity of the food web structure but reduces complexity and stability; the increase of COD increases the connection of the food web structure, while reducing the other three indicators; (3) in some areas with good water quality, aquatic species diversity is high, the relationship of interspecies dietary is complex, food web structure level index is high and the structure of food web is stable. The food web structure in the rainy season will be better than that in the dry season. In some areas with severe water pollution and poor food web structure, the ability of the food web to resist external interference is weak. The food web structure in the rainy season will be worse than that in the dry season owing to rainfall into the river. The methods and conclusions in this treatise can provide a reliable and quantitative scientific basis for river ecosystem management and ecosystem restoration and can improve the success rate of ecological restoration projects.

Riparian condition influences spider community structure and the contribution of aquatic carbon subsidies to terrestrial habitats

Degradation of riparian zones can alter aquatic and terrestrial communities of flora and fauna and disrupt their role in assimilating and mobilising carbon between the two ecosystems. Riparian spiders that predate on emergent aquatic invertebrates can contribute to carbon flux and the structure of aquatic and riparian food webs. The impact of riparian degradation on spiders in temperate rivers of Australia and their role in this broader ecosystem function is poorly understood. We surveyed the riparian zone of four rivers of south-western Australia in areas of natural intact vegetation and degraded agricultural land to explore whether riparian spider abundance, and diversity may be affected by changes to riparian condition. We also assessed the impact of the riparian condition on carbon fluxes between aquatic and terrestrial environments, using stable isotope analysis. We found overall abundance of riparian spiders was higher in degraded agricultural sites compared to natural intact sites and the structure of spider assemblages was different. Orb-weaver spiders (Araneidae and Tetragnathidae) were found to be more abundant in agricultural areas where canopy cover and understory are sparse as a result of livestock grazing and trampling. The contribution of carbon from aquatic invertebrates in a natural intact site was 48.5% for Orb-weavers and 41.6% for Cursorial Hunter spiders but reduced to 19.6% and 39.9% respectively in a degraded agricultural site. These results suggest that the position of spiders in riparian food webs and the amount of aquatic subsidy may change according to the condition and complexity of the riparian zone.

Physiological and morphological responses of green microalgae Chlorella vulgaris to silver nanoparticles

The toxic effects of silver nanoparticles (AgNPs) on the physiology and morphology of the green microalga Chlorella vulgaris were studied. AgNPs were characterized by particle size distribution, ζ potential measurement, and atomic force microscopy (AFM). Chlorella vulgaris was exposed to 90–1440 μg/L of AgNPs range in Bold's Basal Medium for 96 h. The inhibition of algae growth rate and changes in the concentrations of chlorophyll-a, chlorophyll-b, pheophytin, and carotenoids was determined at the beginning and end of the trial. Cell diameter and volume, carbohydrate, total lipids, and protein content were also determined. Our data strongly suggest that the toxic effects of the AgNPs resulted in concentration and time-dependent. AgNPs altered C. vulgaris growth kinetics and cell metabolism expressed in photosynthetic pigments and biochemical composition. Our study confirmed the cytotoxicity of AgNPs through the algal growth inhibition with an EC50 value of 110 μg/L. Also, changes of chlorophyll-a, chlorophyll-b, pheophytin, and carotenoids concentrations were observed associated with a color shift from green to pale brown of algae cultures exposed to AgNPs for 96 h. Furthermore, algae cell concentration, diameter, and volume, plus total lipid, protein, and carbohydrates contents in the presence of AgNPs, were significantly altered compared to untreated cells. In synthesis, this study highlighted AgNPs toxic effects on morphological and physiological traits of C. vulgaris and warns about possible impacts on energy flow and aquatic food web structure, and on the transfer efficiency of energy to higher trophic levels.

Palynomorphs in surface sediments of the North-Western Black Sea as indicators of environmental conditions

Most previous Black Sea palynology studies have used pollen-spore assemblages as proxies for climate and landscape changes, and dinocyst assemblages as proxies for surface water salinity. However, there are few data on within-region variations in these assemblages using large sets of surface samples and a full suite of palynomorphs, including terrigenous pollen + spores, freshwater algal spores, and organic remains of marine microplankton, micro- and meiobenthos. Here we fill this knowledge gap, using results from a palynological study of 43 surface samples from water depths of 71–905 mbsl on the Ukrainian Shelf and adjoining continental slope, NW Black Sea. The palynology samples were collected in conjunction with water and sediment chemistry data, grain-size, micropaleontological and meiobenthos data from the EU-FP6 project HERMES “Hotspot Ecosystems Research on the Margins of European Seas”. This dataset uniquely covers shelf and upper slope areas east and west of the Odessa-Sinop Fault Zone (OSFZ) that delimits areas of lower and higher hydrocarbon gas contents, respectively.The new data show that on the wide shelf with a shallow (ca. 80 m) oxycline, pollen assemblages differ from classical models for marine pollen transport. On the Ukrainian Shelf, pollen concentrations are extraordinarily high far offshore and the grains are often pyrite-infilled. These features apparently reflect high pollen preservation potential in low oxygen sediments, probably enhanced by cross-shelf transport of land-derived particulate organic matter. The new data have important consequences for accurate modelling of carbon burial and storage in epicontinental seas, and they provide a baseline for evaluating marine pollen concentrations expected to reflect the early Neolithic farming on the Ukrainian shelf. Furthermore, although large concentrations of dinocysts comprise more than half of the total Non-Pollen Palynomorphs (NPP), the high pollen concentrations skew the P:D index (pollen:dinocyst ratio) commonly used to evaluate changes in paleo-shoreline (proxy sea-level) positions. Despite the discharge of several large rivers to the Ukrainian Shelf, there are negligible traces of freshwater algae in the HERMES samples except at Sta. 15 where Pediastrum is abundant. Overall, palynomorphs of terrestrial origin make up about half (52%) of the acid-resistant organic-walled particles on the outer NW Black Sea Shelf and adjacent slope.The abundances of the major micro- and meiobenthic palynomorph groups show the same trends east and west of the OSFZ as the micropaleontological data reported for the HERMES samples taken at the same sites. The combined microzooplankton and zoobenthos surface assemblage data provide an important new baseline for evaluating historical and past changes in biodiversity and aquatic foodweb structure in the now polluted NW Black Sea. Comparison can also be made with foodweb reconstructions for Permian black shales.

Cyanobacterial blooms modify food web structure and interactions in western Lake Erie

With anthropogenic eutrophication and climate change causing an increase in cyanobacterial blooms worldwide, the need to understand the consequences of these blooms on aquatic ecosystems is paramount. Key questions remain unanswered with respect to how cyanobacteria blooms affect the structure of aquatic food webs, the foraging abilities of higher consumers, and the potential for cyanotoxins (e.g., microcystins [MCs]) to accumulate in fish. Toward addressing these uncertainties, physicochemical attributes, water (for MCs), phytoplankton, zooplankton, and epipelagic and benthic age-0 fish were sampled at 75 sites (44 sites for fish) of varying cyanobacteria concentration (0.1–44 μg/L) in western Lake Erie during the cyanobacteria bloom season, 2013–2014. Sites with high cyanobacteria biomass were characterized by Microcystis spp. (84–100% of biomass), detectible levels of MCs (maximum = 10.8 μg/L), and low water transparency (minimum = 0.25 m). Counter to expectations, strong positive relationships were found between cyanobacteria concentration and the biomass of several herbivorous zooplankton taxa (e.g., Daphnia, Diaphanosoma spp., Bosmina (formerly Eubosmina) coregoni, and Calanoida spp.). Expectations regarding fish were partly supported (e.g., diet selectivity varied across a cyanobacteria gradient) and partly not (e.g., consumption of zooplankton did not differ between bloom and non-bloom sites). These findings show that cyanobacterial blooms can strongly affect the distribution, composition, and interactions of zooplankton and fish, sometimes in surprising ways, highlighting the need to further explore their impact on aquatic food webs.

Evidence for lasting alterations to aquatic food webs with short-duration reservoir draining

Large dams and their respective reservoirs provide renewable energy and water security, but also can profoundly alter riverine ecosystems. Here, we present evidence of changing aquatic food web structure in the seasons following short-duration, extreme manipulation of water levels in a reservoir (i.e., draining of the reservoir to the original riverbed during fall to assist outmigration of juvenile Chinook Salmon). We find unintended and lagged consequences of transitioning from a lake to a river, even temporarily, that resulted in trophic shifts away from piscivory and towards feeding at lower trophic levels for two common piscivorous fishes in reservoirs. Using natural abundances of nitrogen stable isotopes, we observed lower trophic level of feeding for invasive Largemouth Bass (Micropterus salmoides) and native Rainbow Trout (Oncorhynchus mykiss) during the summers following reservoir refilling than in nearby reference reservoirs that were not temporarily drained during fall. Declines in trophic levels of aquatic top predators have been rarely documented outside of controlled laboratory conditions. While useful for assisting outmigration of juvenile salmonids, the temporary draining of a reservoir to riverbed can also result in novel shifts in foodweb dynamics including reduced piscivory. As large dams continue to be operated and constructed worldwide, increased understanding of the community and ecosystem-level effects of reservoir management will be critical to evaluating trade-offs between human water needs, conservation of high value species, and ecosystem services impacted by river fragmentation.

Impact of spatial variations in water quality and hydrological factors on the food-web structure in urban aquatic environments

Global aquatic ecosystems are essential to human existence and have deteriorated seriously in recent years. Understanding the influence mechanism of habitat variation on the structure of the food-web allows the effective recovery of the health of degraded ecosystems. Whereas most previous studies focused on the selection of driving habitat factors, the impact of habitat variation on the food-web structure was rarely studied, resulting in the low success rate of ecosystem restoration projects globally. This paper presents a framework for exploring the effects of spatial variations in water quality and hydrological habitat factors on the food-web structure in city waters. Indices for the evaluation of the food-web structure are first determined by integrating model-parameter extraction via literature refinement. The key water quality and hydrological factors are then determined by coupling canonical correspondence analysis with partial least squares regression. Their spatial variation is investigated using spatial autocorrelation. Finally, fuzzy clustering is applied to analyze the influence of the spatial variations in water quality and hydrological factors on the food-web structure. The results obtained in Ji'nan, the pilot city of water ecological civilization in China, show that the Shannon diversity index, connectance index, omnivory index, and the ratio of total primary production to the total respiration are important indicators of food-web structural change. They show that the driving factors affecting the aquatic food-web structure in Ji'nan are hydrological factors (e.g., river width, water depth, and stream flow), physical aspects of water quality (e.g., air temperature, water temperature, electrical conductivity, and transparency), and chemical aspects (e.g., potassium, dissolved oxygen, calcium, and total hardness). They also show that the stability of the food-web is more prone to spatial variations in water quality than in hydrological factors. Higher electrical conductivity, potassium, total hardness, and air temperature lead to deteriorated food-web structures, whereas better transparency improves structure and stability. We found that water and air temperature are the most important factors in the spatial variation of the food-web structure in the study area, followed by total hardness. Transparency is the least important factor. Large disparities and varied spatial distributions exist in the driving effects of water quality and hydrological factors across regions attributable to differences in geographical environments, water salinity (fresh vs. sea water), and environmental factors (e.g., water pollution). The above methods and results serve as a theoretical and scientific basis for a high success rate of aquatic ecosystem restoration projects in the study area and other cities worldwide.

CLIMATE CHANGE EFFECTS ON AQUATIC ECOSYSTEM: STRUCTURE AND DISEASE

Climate change is projected to cause significant alterations to aquatic biogeochemical processes, (including carbon dynamics), aquatic food web structure, dynamics and biodiversity, primary and secondary production; and, affect the range, distribution and habitat quality/quantity of aquatic. Nutrient and carbon enrichment will enhance nutrient cycling and productivity, and alter the generation and consumption of carbon-based trace gases. Consequently, the status of aquatic ecosystems as carbon sinks or sources is very likely to change. The magnitude, extent, and duration of the impacts and responses will be system and location-dependent