Web Structure Research Articles

Diet-habitat ecology of invasive tilapia and native fish in a tropical river catchment following a tilapia invasion

Many species of tilapia (a collection of fish species from the cichlidae family) have biological traits that make them successful invaders. Widespread herbivory has been observed across tilapia species, however knowledge on habitat preferences and tilapia interactions with native fish food webs is limited. This study was conducted three years after spotted (Pelmatolapia mariae) and Mozambique (Oreochromis mossambicus) tilapia were detected in the Mitchell River catchment, northern Australia. Tilapia diet and habitat preferences and their trophic position in native fish food webs was determined using a combination of stomach content, stable isotope, and habitat assessment analyses. Plant material was the most abundant item in tilapia stomachs, and some stomachs also contained other items in small quantities, such as fish eggs, small shrimp, and bivalves. Some niche overlap occurred between P. mariae and native omnivore or herbivore fish species. Macrohabitat type (in-channel (no tilapia), floodplain (no tilapia), weir (tilapia present)) was related to native fish food web structure, with weir food webs showing similarities to floodplain food webs. Floodplain habitats including creeks and wetlands were also most similar to weir habitats and may therefore be most at risk of colonization as tilapia spread throughout the catchment. This study clearly demonstrated that the successful rapid invasion of these two tilapia species is linked to suitable habitat with abundant food that fuels growth and reproduction. These findings increase understanding of diet related habitat use during new tilapia invasions and trophic interactions with native species.

Biological invasions alter the structure of a tropical freshwater food web.

Biological invasions are expected to alter food web structure, but there are limited empirical data directly comparing invaded versus uninvaded food webs, particularly in species-rich, tropical systems. We characterize for the first time the food web of Lake Gatun-a diverse and highly invaded tropical freshwater lake within the Panama Canal. We used stable isotope analysis to reconstruct the trophic structure of the fish community of Lake Gatun and to compare it to that of a minimally invaded reference lake, Lake Bayano. We found significant differences between the trophic structures of these two Neotropical lakes, notably that Lake Gatun's fish community was characterized by a longer food chain, greater isotopic diversity, a broader range of trophic positions and body sizes, and shifts in the isotopic positions of several native taxa relative to Lake Bayano. The degree of isotopic overlap between native and non-native trophic guilds in Lake Gatun was variable, with herbivores exhibiting the lowest (20%-29%) overlap and carnivores the greatest (81%-100%). Overall, our results provide some of the first empirical evidence for the ways in which multiple introduced and native species may partition isotopic space in a species-rich tropical freshwater food web.

Water-Level Fluctuation Control of the Trophic Structure of a Yangtze River Oxbow.

Seasonal water-level fluctuations can profoundly impact nutrient dynamics in aquatic ecosystems, influencing trophic structures and overall ecosystem functions. The Tian-e-Zhou Oxbow of the Yangtze River is China's first ex situ reserve and the world's first successful case of ex situ conservation for cetaceans. In order to better protect the Yangtze finless porpoise, the effects of water-level fluctuations on the trophic structure in this oxbow cannot be ignored. Therefore, we employed stable isotope analysis to investigate the changes in the trophic position, trophic niche, and contribution of basal food sources to fish during the wet and dry seasons of 2021-2022. The research results indicate that based on stable isotope analysis of the trophic levels of different dietary fish species, fish trophic levels during the wet season were generally higher than those during the dry season, but the difference was not significant (p > 0.05). Fish communities in the Tian-e-Zhou Oxbow exhibited broader trophic niche space and lower trophic redundancy during the wet season (p < 0.05), indicating a more complex and stable food web structure. In both the wet and dry seasons, fish in the oxbow primarily relied on endogenous carbon sources, but there were significant differences in the way they were utilized between the two seasons (p < 0.05). In light of the changes in the trophic structure of the fish during the wet and dry seasons, and to ensure the stable development of the Yangtze finless porpoise population, we recommend strengthening the connectivity between the Tian-e-Zhou Oxbow and the Yangtze River.

Seasonal upwelling influence on trophic indices of mesozooplankton in a coastal food web estimated from δ15N in amino acids

Mesozooplankton communities in upwelling ecosystems are known to be influenced by seasonal upwelling enhancing primary productivity. However, the extent to which changes in trophic dynamics of mesozooplankton are driven by variations in the baseline of nitrogen or in the trophic position (TP) is poorly understood. We used nitrogen stable isotopes (δ15N) in bulk and in specific amino acids (CSIA-AA), as well as the taxonomic composition of mesozooplankton samples collected monthly during two full years, to investigate whether the upwelling intensity affects the isotopic N baseline and other trophic indices at the community level in the coastal system off NW Iberian Peninsula. We hypothesized that enhanced phytoplankton productivity during upwelling events would lead to a shorter and more efficient food web. Upwelling induced mesozooplankton herbivory (by increasing the abundance and biomass of omnivorous-herbivorous copepods and other taxa), resulting in a linear decrease of TPGlx (estimated using Glx = glutamic acid + glutamine, which mainly involves metazoan links) from downwelling to upwelling situations. In contrast, TPAla (estimated using alanine, which also reflects microbial trophic pathways) was highest in low-moderate upwelling and decreased with upwelling strength. Thus, an optimal coupling between metazoan and microbial food webs was reached at low-moderate upwelling intensities when the microbial contribution was ca. 25 %, while this contribution decreased (<15 %) either during downwelling or during strong upwelling. However, the significance of differences in mean values of TP and zooplankton composition was small due to the rapid succession of upwelling and downwelling events. Our results illustrate how a combination of CSIA-AA and community data can provide valuable information on rapid changes in mesozooplankton food web structure in highly dynamic upwelling systems.

Examining the Shift in the Decomposition Channel Structure of the Soil Decomposer Food Web: A Methods Comparison.

Selecting the appropriate indicators and measuring time point numbers is important for accurately examining the shift in soil gross decomposition channel structure. Through a selected case study on a natural forest vs. rainfed arable system over a two-month-long experiment, the utility of three commonly employed indicators (fungi to bacteria ratio (F:B), fungivore to bacterivore ratio (FF:BF), and glucosamine to muramic acid ratio (GlcN:MurN)) were compared to reflect the shift in soil gross decomposition channel structure. The requirement of measuring the time point numbers for the three indicators was also assessed, and we suggest a potential methodology. Our results revealed that the GlcN:MurN ratio was more reliable for assessing the shifts in gross decomposition channel structure for long-term land use changes, while it was less sensitive to short-term drought compared with the other two indicators. The F:B ratio was more applicable than the FF:BF ratio for reflecting both long- and short-term changes. Furthermore, the reliability of the GlcN:MurN ratio was the least dependent on measuring time point numbers. We suggest the use of multiple indicators and the adoption of multiple measuring time points for the overall methodology.

Effects on the food-web structure and bioaccumulation patterns of organic contaminants in a climate-altered Bothnian Sea mesocosms

Climate change is expected to alter global temperature and precipitation patterns resulting in complex environmental impacts. The proposed higher precipitation in northern Scandinavia would increase runoff from land, hence increase the inflow of terrestrial dissolved organic matter (tDOM) in coastal regions. This could promote heterotrophic bacterial production and shift the food web structure, by favoring the microbial food web. The altered climate is also expected to affect transport and availability of organic micropollutants (MPs), with downstream effects on exposure and accumulation in biota. This study aimed to assess climate-induced changes in a Bothnian Sea food web structure as well as bioaccumulation patterns of MPs. We performed a mesocosms-study, focusing on aquatic food webs with fish as top predator. Alongside increased temperature, mesocosm treatments included tDOM and MP addition. The tDOM addition affected nutrient availability and boosted both phytoplankton and heterotrophic bacteria in our fairly shallow mesocosms. The increased tDOM further benefitted flagellates, ciliates and mesozooplankton, while the temperature increase and MP addition had minor effect on those organism groups. Temperature, on the other hand, had a negative impact on fish growth and survival, whereas tDOM and MP addition only had minor impact on fish. Moreover, there were indications that bioaccumulation of MPs in fish either increased with tDOM addition or decreased at higher temperatures. If there was an impact on bioaccumulation, moderately lipophilic MPs (log Kow 3.6 – 4.6) were generally affected by tDOM addition and more lipophilic MPs (log Kow 3.8 to 6.4) were generally affected by increased temperature. This study suggest that both increased temperatures and addition of tDOM likely will affect bioaccumulation patterns of MPs in shallow coastal regions, albeit with counteracting effects.

Trophic Transfer of Halogenated Organic Pollutants in a Wetland Food Web: Insights from Compound-Specific Nitrogen Isotope of Amino Acids and Food Source Analysis.

A trophic position (TP) model (TPmix model) that simultaneously considered trophic discrimination factor and βGlu/Phe variations was developed in this study and was first applied to investigate the trophic transfer of halogenated organic pollutants (HOPs) in wetland food webs. The TPmix model characterized the structure of the wetland food web more accurately and significantly improved the reliability of TMF compared to the TPbulk, TPAAs, and TPsimmr models, which were calculated based on the methods of stable nitrogen isotope analysis of bulk, traditional AAs-N-CSIA, and weighted βGlu/Phe, respectively. Food source analysis revealed three interlocking food webs (kingfisher, crab, and frogs) in this wetland. The highest HOP biomagnification capacities (TMFmix) were found in the kingfisher food web (0.24-82.0), followed by the frog (0.08-34.0) and crab (0.56-11.7) food webs. The parabolic trends of TMFmix across combinations of log KOW in the frog food web were distinct from those of aquatic food webs (kingfisher and crab), which may be related to differences in food web composition and HOP bioaccumulation behaviors between aquatic and terrestrial organisms. This study provides a new tool to accurately study the trophic transfer of contaminants in wetlands and terrestrial food webs with diverse species and complex feeding relationships.

Habitat complexity drives food web structure along a dynamic mangrove coast

Structurally complex habitats, such as mangrove forests, allow for rich assemblages of species that benefit from the provided space, volume and substrate. Changes in habitat complexity can affect species abundance, diversity and resilience. In this study, we explored the effects of habitat complexity on food web networks in four developmental stages of mangrove forests with differing structural complexities: climax > degrading > colonizing > bare, by analyzing food web structure, stable isotopes and habitat complexity. We found that food webs became gradually more biodiverse (species richness: +119 %), complex (link density: +39 %), and robust (connectance: −35 %) in climax versus bare stages with increasing complexity of the mangrove forest (i.e., number of trees, leaf cover, and pneumatophore densities). This study shows that habitat complexity drives food web network structure in dynamic mangrove forests. We recommend restoration practitioners to use this food web network approach to quantify habitat restoration successes complementary to traditional biodiversity metrics.

Long-term changes as oil palm plantation age simplify the structure of host-parasitoid food webs.

Understanding host-parasitoid food webs, as well as the factors affecting species interactions, is important for developing pest management strategies in an agroecosystem. This research aimed to study how the long-term change in oil palm plantations, specifically the tree age, affect the structure of host-parasitoid food webs. The field research was conducted on an oil palm plantation located in Central Kalimantan and Jambi Province, Indonesia. In Central Kalimantan, we conducted observations of lepidopteran larvae and parasitoid wasps at different tree ages, ranging from 3 to 18 years old. For tree ages from 3 to 10 years, observations of host-parasitoid food webs were conducted by collecting the lepidopteran larvae using a hand-collection method in each oil palm tree within a hundred trees and they were later reared in the laboratory for observing the emerging parasitoids. The fogging method was applied for trees aged 12 to 18 years because the tree height was too high, and hand-collection was difficult to perform. To compare host-parasitoid food webs between different regions, we also conducted a hand-collection method in Jambi, but only for trees aged 3 years old. The food-web structure that was analyzed included the species number of lepidopteran larvae and parasitoid wasps, linkage density, and interaction diversity. We found 32 species of lepidopteran pests and 16 species of associated parasitoids in Central Kalimantan and 12 species of lepidopteran pests, and 11 species of parasitoids in Jambi. Based on the GLM analysis, tree age had a negative relationship with the species number of lepidopteran larvae and parasitoids as well as linkage density and interaction diversity. Different geographical regions showed different host-parasitoid food web structures, especially the species number of lepidopteran larvae and interaction diversity, which were higher in Central Kalimantan than in Jambi. However, some parasitoids can be found across different tree ages. For example, Fornicia sp (Hymenoptera: Braconidae) was recorded in all ages of oil palm sampled. Results of the GLM analysis showed that the abundance of Fornicia sp and its host (lepidopteran larvae abundance) were not affected by the tree age of the oil palm. In conclusion, the long-term change in oil palm plantations simplifies the structure of host-parasitoid food webs. This highlights the importance of long-term studies across geographical regions for a better understanding of the consequences that wide monoculture oil palm plantations have on biological control services.

Functional ecological metrics of good ecological quality – Needs of managers and data from pristine lakes

Anthropogenic eutrophication and overfishing of top predators have put our lakes in danger, and coping mechanisms like The European Water Framework Directive have been put in place to mitigatetheireffects. However, the discussion on the means we employ to monitor lake ecosystems and establish their ecological status is ongoing. Importantly, it has been suggested that universal, functional indicators of healthy reference ecosystems could be identified, measured and used for comparison purposes across ecological types of lakes. An equally important issue is to develop such metrics that can be employed by lake managers, who are the end users of the scientific data when planning everyday management practices. We employed bioenergetic food web approach with Ecological Network Analysis to assess organic matter fluxes and food web structure in 13 lakes in Latvia – including 3 pristine bog lakes - and combined the acquired functional descriptors with simple and well-known ecological descriptors. We conclude that information on the functioning of pristine lakes provides a potentially valuable tool for setting functional reference conditions for lake management. We also found that the ecological parameters - the percentage of piscivorous fish and the abundance of cyanobacteria - correlate well with the functional food web descriptors. Thus, they could be valuable tools to both managers and scientists when evaluating lake ecological status across the boundaries of ecological types.

Warming indirectly simplifies food webs through effects on apex predators

Warming alters ecosystems through direct physiological effects on organisms and indirect effects via biotic interactions, but their relative impacts in the wild are unknown due to the difficulty in warming natural environments. Here we bridge this gap by embedding manipulative field experiments within a natural stream temperature gradient to test whether warming and apex fish predators have interactive effects on freshwater ecosystems. Fish exerted cascading effects on algal production and microbial decomposition via both green and brown pathways in the food web, but only under warming. Neither temperature nor the presence of fish altered food web structure alone, but connectance and mean trophic level declined as consumer species were lost when both drivers acted together. A mechanistic model indicates that this temperature-induced trophic cascade is determined primarily by altered interactions, which cautions against extrapolating the impacts of warming from reductionist approaches that do not consider the wider food web.

Predation has a significant impact on the complexity and stability of microbial food webs in subalpine lakes.

As an important part of microbial food webs, protists transfer organic carbon and nutrients to higher trophic levels in aquatic ecosystems. Protist predation often influences the abundance and composition of bacterial communities. However, we still do not understand whether and how predation affects the complexity and stability of microbial food webs. This study assessed the seasonal dynamic characteristics and driving factors of microbial food webs in terms of complexity and stability. Our findings have implications for future surveys to reveal the effects of climate and environmental changes.

Biochar improves soil quality prior to prairie restoration

Intensive agriculture has led to widespread losses of native grasslands. Restoration projects are trying to reestablish native communities. However, the poor quality and altered food webs of former agricultural soils act as barriers to establishing diverse plant communities. Soil amendments such as biochar have been used to improve soil quality and increase crop yield, but little research has been on biochar in restoration settings. Eastern Washington University is attempting to restore a former wheat field to native Palouse prairie vegetation. In this study, we compared (1) soil abiotic properties and food webs between Palouse prairie remnants and Eastern Washington University's (EWU) restoration site and (2) tested whether biochar can move soil conditions at EWU's restoration site closer to those of remnant sites. We compared soils from three Palouse prairie remnants and EWU's restoration site, and compared soils at the restoration site that were treated with different levels of biochar. Soil nematodes were extracted and sorted to functional groups as an assay of the structure and functional diversity of the soil food web. The soil at EWU's restoration site had significantly lower nematode abundance, pH, and organic matter compared to prairie remnants. In addition, nematode abundance and pH increased significantly at the EWU site with the addition of biochar, both increasing to conditions similar to what is found at the prairie remnant sites. These results suggest biochar can improve some soil conditions in former agricultural lands even prior to native plant restoration.

Energy flow across soil food webs of different ecosystems: Food webs with complex structures support higher energy flux

Energy flux in food webs is a fundamental feature of ecosystems and an important link between biodiversity and ecosystem function. Studies of energy flow through the soil nematode food web have emerged in recent year; however, it is not clear whether and how the nematode food web structure affects the energy flow. In this study, the structures and carbon flux of soil nematode food webs in four different ecosystems, namely, forageland, cropland, secondary forest, and grass-shrubland, were assessed. The food web structure was represented by nematode community indices such as maturity index, structure index, genus and trophic group diversity, and slope of size spectra. The results showed that carbon flux through the nematode food webs was the highest and lowest in the secondary forest and forageland, respectively. The total carbon flux of nematode food web was higher in the cropland than that in the grass-shrubland. The magnitudes of bacterial and fungal energy channels were basicallyequal in the forageland and secondary forest. The energy flow through the bacterial channel was greater than that through the fungal channel in the grass-shrubland, whereas the pattern was reversed in the cropland. The total carbon flux through the nematode food web, the carbon fluxes through the bacterial or fungal channel, and the energy flow uniformity were positively correlated with the nematode structure index, maturity index, and genus diversity index. The trophic group diversity and size spectra slope of nematode communities were not significantly correlated with the carbon flux. The results indicate that mature and complex soil communities support high energy flux across soil food webs.

Direct and indirect relationships of climate and land use change with food webs in lakes and streams

AbstractAimClimate and land use change can independently affect food web structure. However, their direct and indirect relationships with food webs are not well‐understood. This is particularly relevant for freshwater ecosystems, which are strongly affected by global threats and differ substantially in attributes and functioning. Here, we investigated direct and indirect relationships between climate and land use changes and freshwater food web structure, while considering the differences between lakes and streams.LocationMulticontinental.Time periodCurrent.Major taxa studiedFreshwater taxa.MethodsWe compiled 51 food webs, spanning 12 countries and six continents to investigate the direct and indirect relationships between land use intensity, changes in air temperature and precipitation and food web structure, using structural equation modelling (SEM). We further tested how lake and stream food webs differ in their responses to environmental change by applying a multigroup analysis to our SEM.ResultsWe found that connectance was positively related to both land use intensity and increases in air temperature and precipitation in stream food webs, whereas in lakes, it was only related to temperature. These findings suggest a dominance of generalists where conversion to agriculture and urbanization has been intensified, and temperature has increased. Food web vertical structure was negatively related to land use and increases in air temperature and precipitation, but climatic predictors were only linked to network structure through a negative relationship with the fraction of top consumers.Main conclusionsWhile land use intensity was directly related to food web structure, complex relationships between changes in climate and network topology were mediated by the fraction of top consumers. Also, as food webs in lakes and streams responded differently to land use and climate change, we suggest that their intrinsic characteristics must be explicitly considered to fully understand the effects of global changes on freshwater biodiversity.

Trophic functioning of a small, anthropogenically disturbed, tropical estuary

A trophic model was constructed for the Poonthura Estuary, a small, anthropogenically impacted estuary along the south-western coast of India. An Ecopath with Ecosim based trophic modelling approach, based on observations made between 2016 and 2020, revealed that the Poonthura Estuary had a low total system throughput (3044.2 t km-2 year-1), low ascendancy (15%), high Finn’s cycling index (17.9%), low primary production/total biomass (5.2 t km-2 year-1), high mean transfer efficiency (12.4%), and low eco-exergy (14,455.46 gm detritus equivalent m-2). These values indicated that the estuary is an immature, less organized, and unhealthy system. The evaluation of Ecological Network Analysis, and ecosystem health indices revealed that the ecological structure and functioning of the estuary are impaired to a large extent from multiple anthropogenic stressors. The Poonthura Estuary trophic model revealed the total primary production/respiration value as 0.46, indicative of the massive pollution that the system is subjected to, particularly from organic sources. Small benthic carnivores were the most important keystone groups recorded from the Poonthura Estuary, despite their low biomass. The comparison of ecological indices of Poonthura Estuary, with those recorded for other small estuaries from various geographical locations, suggested dissimilar trophic functioning and food web structures from estuaries with similar physical features. Our study is a pioneering step to reveal the ecosystem status and functioning of small, anthropogenically disturbed estuaries, besides offering theoretical and scientific basis for the management, supervision and restoration of the Poonthura Estuary as well as other small estuaries, around the world.

A study of the feeding characteristics of a small and medium-sized copepod species (Sinocalanus tenellus) using genetic analysis techniques: seasonal comparison of potential/eaten food sources focused on phytoplankton

In aquatic ecosystem, the food web structure based on composition and abundance of prey species influences the feeding characteristics of predators, resulting in changes to the structure and function of the entire food web. Zooplankton mainly feed on phytoplankton, but the method of analyzing the feed source through visual and microscopic identification of gut contents has limitations in applicable species and the low resolution of the analysis results. In this study, potential vs. eaten food sources of Sinocalanus tenellus, a small and medium-sized copepod species dominant in brackish waters, were analyzed based on phytoplankton operational taxonomic units detected from the habitat’s raw water and treated whole bodies of S. tenellus. The alpha diversity and dominant/subdominant species of each potential and eaten food source were identified, and they were compared across seasons. At the same time, the feeding selectivity index (Ei) was calculated by identifying overlapping species in the potential vs. eaten food source pool. As a result, it was confirmed that not all surrounding potential food sources are fed on by S. tenellus, and that its diet can vary depending on the presence/absence of preferred prey. Metabarcoding techniques is considered to be an effective way to identify fluctuations in major food sources of zooplankton at the genus or species level. If uncertainties such as incomplete species identification as identified from the results of this study are improved through improving of analysis methods such as application of species-specific primers in the future, it will be useful for securing information on the feeding characteristics of small to medium-sized zooplankton.

Statistics of tidal and deformation eigenvalue fields in the primordial Gaussian matter distribution: the two-dimensional case

ABSTRACT We study the statistical properties of the eigenvalues of the primordial tidal and deformation tensor for two-dimensional random Gaussian cosmic density fields. With the tidal and deformation tensors, Hessians of the gravitational and velocity potential, being Gaussian, the eigenvalue fields are distinctly non-Gaussian. We extend the Doroshkevich formula for the joined distribution of eigenvalues to two-dimensional fields and evaluate the two- and three-point correlation functions. In addition, we assess the number densities of singular points of the eigenvalue fields and find their corresponding two- and three-point correlation functions. The incentive for the present study is based on our interest in developing a fully analytical theory for the structure and dynamics of the cosmic web. The tidal forces and the resulting mass element deformation shape the prominent anisotropic wall-like and filamentary components of the cosmic web. Less well-known is that the web-like spatial pattern is already recognizable in the primordial tidal and deformation eigenvalue field. Against the full phase-space assessment of structure formation in the Universe, the caustic skeleton theory entails an analytical framework for the non-linear evolution of the cosmic web. It accomplishes this by describing the folding of the dark matter sheet and quantifying the emerging caustic singularities, which are fully specified by the spatial properties of the deformation eigenvalues and eigenvectors. Finally, the eigenvalues of the primordial tidal tensor are crucial in the generation of the angular momentum of galaxies. Understanding their spatial distribution is a critical element in predicting the resulting rotation amplitude and orientation.

Seasonal variation in the use of food resources by sperm whales in a submarine canyon

Understanding the food and habitat requirements of apex predators relies on characterising the food web structure and carbon sources that support them. We examined the food web of sperm whales (parāoa, Physeter macrocephalus) foraging in the submarine canyon of Kaikōura (Aotearoa New Zealand) by measuring bulk stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in sperm whale skin, potential prey and two candidate primary producers. To determine the underlying drivers of variability in bulk ratios, we measured δ13C and δ15N from individual amino acids (AAs) in a subset of whale samples. Mixing models and food web δ13C:δ15N correlations strongly suggest a food web sustained mostly by pelagic production, with a marginal contribution from coastal macroalgae. In contrast to the cephalopod-based diet recorded in most populations, the sperm whales' diet at Kaikōura appeared to be a mixture of squid and demersal fish, which may be related to the extremely high benthic productivity of the canyon. Combined with evidence from studies of habitat use, differences in the whales’ stable isotope values between summer and winter suggested seasonal variability in targeted prey, and ultimately different utilisation of organic carbon sources at the base of the food web. In summer, sperm whales appear to depend mostly on mesopelagic squid, with an increased contribution from demersal fish in winter, consistent with patterns in diving behaviour and spatial distribution. This seasonal shift in food resources suggests that submarine canyons offer a temporally dynamic range of foraging opportunities for this apex predator. Our results provide new insights into the structure of food webs supporting sperm whales, and advance our understanding of the seasonal dynamics in the use of food resources by apex predators in submarine canyons.

New insight into biomagnification factor of mercury based on food web structure using stable isotopes of amino acids

Although many attempts have been carried out to elaborate trophic magnification factor (TMF) and biomagnification factor (BMF), such as normalizing the concentration of pollutants and averaging diet sources, the uncertainty of the indexes still need to be improved to assess the bioaccumulation of pollutants. This study first suggests an improved BMF (i.e., BMF′) applied to mercury bioaccumulation in freshwater fish from four sites before and after rainfall. The diet source and TP of each fish were identified using nitrogen stable isotope of amino acids (δ15NAAs) combined with bulk carbon stable isotope (δ13C). The BMF′ was calculated normalizing with TP and diet contributions derived from MixSIAR. The BMF′ values (1.3–27.2 and 1.2–27.8), which are representative of the entire food web, were generally higher than TMF (1.5–13.9 and 1.5–14.5) for both total mercury and methyl mercury, respectively. The BMF′ implying actual mercury transfer pathway is more reliable index than relatively underestimated TMF for risk assessment. The ecological approach for BMF calculations provides novel insight into the behavior and trophic transfer of pollutants like mercury.