Food Web Research Articles

The impact of structured higher-order interactions on ecological network stability

The impact of higher-order interactions, those involving more than two species, is increasingly appreciated as having the potential to strongly influence the dynamics of complex ecological systems. However, although the critical importance of the structure of pairwise interaction networks is well established, studies of higher-order interactions still largely assume random structures. Here, we demonstrate the strong impact of structured higher-order interactions on simulated ecological communities. We focus on effects caused by interaction modifications within food webs, where a consumer resource interaction is modified by a third species, and for which plausible structures can be hypothesised. We show how interaction modifications introduced under a range of non-random distributions may impact the overall network structure. Local stability and the size of the feasibility domain are critically dependent on the inter-relationship between trophic and non-trophic effects. Where interaction modifications are structured into mutual interference motifs (associated with consumers switching between resources) synergistic signs and topological effects have particularly consequential impacts. Furthermore, we show that previous results of the impact of higher-order interactions on diversity-stability relationships can be reversed when higher-order interactions are structured, not random. Empirical data on interaction modifications will be a key part of improving understanding the dynamics of communities, particularly the distribution of interaction modification signs across networks.

Habitat engineering by an apex predator generates spatial trophic dynamics across a temporal environmental stress gradient.

Ecosystem engineering is a facilitative interaction that generates bottom-up extrinsic variability that may increase species coexistence, particularly along a stress/disturbance gradient. American alligators (Alligator mississippiensis) create and maintain 'alligator ponds' that serve as dry-season refuges for other animals. During seasonal water recession, these ponds present an opportunity to examine predictions of the stress-gradient (SGH) and intermediate disturbance hypotheses (IDH). To test the assumption that engineering would facilitate species coexistence in ponds along a stress gradient (seasonal drying), we modelled fish catch-per-unit-effort (CPUE) in ponds and marshes using a long-term dataset (1997-2022). Stomach contents (n = 1677 from 46 species) and stable isotopes of carbon and nitrogen (n = 3978 representing 91 taxa) from 2018 to 2019 were used to evaluate effects of engineering on trophic dynamics. We quantified diets, trophic niche areas, trophic positions and basal-resource use among habitats and between seasons. As environmental stress increases, we used seasonal changes in trophic niche areas as a proxy for competition to examine SGH and IDH. Across long-term data, fish CPUE increased by a factor of 12 in alligator ponds as the marsh dried. This validates the assumption that ponds are an important dry-season refuge. We found that 73% of diet shifts occurred during the dry season but that diets differed among habitats in only 11% of comparisons. From wet season to dry season, both stomach contents and stable isotopes revealed changes in niche areas. Direction of change depended on trophic guild but was opposite between stable-isotope and stomach-content niches, except for detritivores. Stomach-content niches generally increased suggesting decreased competition in the dry season consistent with existing theory, but stable-isotope niches yielded the opposite. This may result from a temporal mismatch with stomach contents reflecting diets over hours, while stable isotopes integrate diet over weeks. Consumptive effects may have a stronger effect than competition on niche areas over longer time intervals. Overall, our results demonstrated that alligators ameliorated dry-season stress by engineering deep-water habitats and altering food-web dynamics. We propose that ecosystem engineers facilitate coexistence at intermediate values of stress/disturbance consistent with predictions of both the SGH and IDH.

Shared community history strengthens plant diversity effects on below-ground multitrophic functioning.

The relationship of plant diversity and several ecosystem functions strengthens over time. This suggests that the restructuring of biotic interactions in the process of a community's assembly and the associated changes in function differ between species-rich and species-poor communities. An important component of these changes is the feedback between plant and soil community history. In this study, we examined the interactive effects of plant richness and community history on the trophic functions of the soil fauna community. We hypothesized that experimental removal of either soil or plant community history would diminish the positive effects of plant richness on the multitrophic functions of the soil food web, compared to mature communities. We tested this hypothesis in a long-term grassland biodiversity experiment by comparing plots across three treatments (without plant history, without plant and soil history, controls with ~20 years of plot-specific community history). We found that the relationship between plant richness and below-ground multitrophic functionality is indeed stronger in communities with shared plant and soil community history. Our findings indicate that anthropogenic disturbance can impact the functioning of the soil community through the loss of plant species but also by preventing feedbacks that develop in the process of community assembly.

Ценотичні зв’язки в межах гетеротрофних консорцій на прикладі деяких ключових видів тварин

The role of animal key species in forest, wetland and fresh-water ecosystems as the concentrators of species diversity of the individuals of different taxa (consorts) is described in the article from the heterotrophic determinated paradigm point of view. The analysis of consortive relations was based on the research of key species’ representatives trophics mainly, less attention was paid to other relation types (topic, fabric and foric). Mammals, birds, amphibians, insects, mollusks and the representatives of zooplankton were the study objects of our key species research. In particular, our attention was paid to Asplanchna trophic relations, which largely determine the trophic dynamics of the investigated hydroecosystems, as well as topic relations of the littoral key zooplankton taxa with plants were in our research focus. All the types of consortive relations in various species’ habitats were analyzed on the example of Lymnaea stagnalis. It was determined that over 30 species of oligolectic bees are connected with over 14 feeding plant taxa by trophic relations. Feeding of two the most numerous Amphibia species in the forest habitats of the research territory (Bufo bufo and Rana temporaria) witness the relations with at least 13 taxa of Invertebrates, moreover their trophic preferences are largely species-specific. The pellet analyses of Asio otus and Athene noctua show the victim identity to 19 and 28 Vertebrate taxa with the dominance of Muridae and Arvicolidae, respectively. Our research describes the tight trophic relations of 10 Carnivora species (Mustelidae and Canidae) with 65 plant and animal species. Besides, the analysis of brown bear trophics shows its seasonal character and euryphagy, with much higher part of plant components in the diet contra animal ones along the year. Thus, the obtained data show that the key species are connected with dozens of other heterotrophic and autotrophic species by consortive, first of all trophic, relations. The disappearance of key species can lead to the significant changes in the ecosystem structure. There is drawn a conclusion that the consortive approach to the key species research gives us an opportunity to dive deeply into the problem of ecosystem components functioning and their changes in uncertain environmental conditions.

Mercury patterns in lakes within a natural hotspot in the Southern Volcanic Zone of the Andes (Nahuel Huapi National Park, Patagonia, South America)

Environmental context The pristine oligotrophic lakes of Andean Patagonia are influenced by volcanic eruptions and atmospheric deposition. This study focuses on mercury (Hg) dynamics in two connected lakes in a natural Hg hotspot of the southern Andes. The lake waters have low dissolved organic carbon and moderate to high Hg concentrations, resulting in high Hg availability. These promote Hg binding to natural particulates, thereby favouring its incorporation into food webs. Rationale Mercury hotspots have been identified in pristine volcanic areas of the northern Patagonian Andes (South America). In this study, we investigated spatial and seasonal patterns of total mercury (THg) in two oligotrophic lakes in Nahuel Huapi National Park (Argentina), adjacent to the Puyehue Cordón Caulle volcanic complex (Chile). We hypothesise that THg levels in the lakes are linked to seasonal terrestrial inputs and that in-lake processes influence its distribution and availability. Methodology Water samples were collected seasonally in the connected lakes Pire (shallow) and Brazo Rincón branch of L. Nahuel Huapi (BR, deep). The concentration of THg was studied together with physicochemical variables, including the concentration and quality of dissolved organic matter (DOM). THg was measured by cold vapour atomic fluorescence spectrometry (CVAF) and DOM was characterised through absorbtion and fluorescence spectroscopy. Results Lakes showed moderate to high THg concentrations and remarkable Hg availability. THg increased downwards in the landscape and was associated with DOM terrestrial prints, indicating its co-transport from the catchment during high connectivity periods (from winter to early summer). In summer, THg levels were associated with higher mineralisation (higher dissolved inorganic carbon, DIC) and diffusion from sediments, especially in the shallow lake. THg availability and distribution were related to the quality of the DOM pool and the total suspended solids (TSS) year round. The high biotic contribution to TSS (higher chlorophyll-a:TSS) in BR indicated Hg binding to phytoplankton and incorporation into lake food webs. Discussion Pristine oligotrophic lakes influenced by natural Hg sources have a high potential for Hg accumulation in food webs because their typically high Hg and low DOC concentrations result in high Hg availability, promoting Hg binding to abiotic and biotic particles.

The protist community of the oligotrophic waters of the Gulf of Mexico is distinctly shaped by depth-specific physicochemical conditions during the warm season.

Marine protists are key components of biogeochemical cycles and microbial food webs, which respond quickly to environmental factors. In the Gulf of Mexico (GoM), the Loop Current intensifies in summer and supplies the gulf with warm and oligotrophic waters. However, the cyclonic eddies within the GoM create favorable conditions for biological productivity by bringing nutrient-rich water to the subsurface layer. In this study, we investigated the response of the protist community to the regional physicochemical conditions, its spatial and temporal variability, the influence of mesoscale structures, and its ecological roles in the mixed layer (ML) and deep chlorophyll maximum (DCM). This is the first study to conduct a V9-18S rRNA gene survey for this community in the Mexican Exclusive Economic Zone of the GoM. The regional distribution, temporal changes, and mesoscale structures significantly affected the structure of the protist community in the ML. In contrast, only mesoscale structures significantly affected the protist community in the DCM. Different protist assemblages were also present between the ML and DCM, with Alveolata representing ∼60% of the community in both layers, followed by Haptophytes and Marine Stramenopiles in the ML; Pelagophytes and Radiolarians were the more prevalent taxa in the DCM. Finally, co-occurrence analyses revealed that competition, parasitism, and predation were the potential interactions shaping these communities at both depths.

Variation in weed seed DNA detectability among arable carabids with different trophic specialization

While most ground beetles (Coleoptera: Carabidae) include seeds in their diet, preferences for seed feeding vary among carabid species and range from facultative diet supplementation to obligate seed feeding. DNA-based diet analyses have been used to study their regulatory effect on soil seedbanks. It is unknown whether specialized granivores digest seed species they are adapted to (‘essential seeds’) faster, and whether this affects food web construction based on molecular data. We hypothesized that specialized granivores digest their essential seed faster than other seeds, and at faster rates than generalist granivores or carnivores. Further, we assumed that generalist granivores digest different seeds equally fast, while carnivorous carabids digest seeds slower than granivores. In feeding experiments, three carabid species—Amara similata (specialized granivore), Harpalus affinis (generalist granivore), and Poecilus cupreus (generalist carnivore)—were fed either a broadly accepted seed or the specialist's essential seed. Gut content samples were collected 0, 6, 12, 24, 48, and 72 h after feeding and screened with plant-primers to trace seed DNA. Time until 50% detection probability in the specialists was shorter for its essential than the broadly accepted seed and shorter than in the generalist granivore, which digested both seed species equally fast. The carnivore was reluctant to feed on the seed species offered, and detection probabilities did not significantly decrease with digestion time. Our findings suggest that the strength of specialized granivores’ feeding interactions and their role in weed seed regulation might be underestimated when assessed with DNA-based diet analysis, due to their more efficient seed digestion.

Trophic ecology of squids in the Benguela Upwelling System elucidated by combining stomach content, stable isotope and fatty acid analyses

Squids occur worldwide in marine ecosystems and play a major role in pelagic food webs by connecting lower and higher trophic levels. Their high feeding intensities and pronounced diel vertical migrations make squids important components of nutrient cycles in marine ecosystems. This study assessed the trophic position and nutritional ecology of a squid species assemblage in the Benguela Upwelling System (BUS) by combining stomach content, stable isotope and fatty acid trophic marker analyses. Samples were collected in the northern (nBUS) and southern (sBUS) BUS in austral spring 2021. A total of 20 squid species from eleven families were identified. Stomach content analyses showed that squid species preyed on a variety of organisms ranging from crustaceans to lanternfishes (Myctophidae) and flying squids (Ommastrephidae). Stable isotope analyses revealed significant differences in δ15N values of small squids (dorsal mantle length < 10 cm) between the two subsystems, but none in those of large squids (dorsal mantle length > 10 cm). Trophic levels ranged from 2.2 to 5.0. Isotopic niche width was widest in the families Ommastrephidae and Cranchiidae. Principal component analyses of fatty acid compositions displayed distinct clusters separating squid families and different prey taxa. This study shows that nBUS and sBUS squids exploit a large variety of pelagic prey organisms and that trophic differences are primarily dependent on squid species and size. The results emphasize the squids’ importance as interlinking element in pelagic food webs and their key function in energy transfer between epi- and mesopelagic layers.

Paralytic Shellfish Toxin Concentrations Measured in Alaskan Arctic Clams Using ELISA and HPLC Methods

Clams are efficient vectors of potent algal neurotoxins, a suite of saxitoxin (STX) congeners collectively called paralytic shellfish toxins (PSTs), to higher trophic levels. The Alaskan Arctic is a region facing an expanding threat from PSTs due to ocean warming, yet little is known about PSTs in clams from this region. Quantifying total toxicity in bivalves requires analytical techniques, such as high-performance liquid chromatography (HPLC). Enzyme-linked immunosorbent assays (ELISAs) are an efficient but only semi-quantitative method for measuring clam toxicity. PSTs (STX eq.) were measured in split clam samples (n = 16) from the Alaskan Arctic using ELISA and HPLC methods to develop a preliminary linear model for conservatively estimating total toxicity in clams from ELISA toxin values (R2adj = 0.95, p &lt; 0.001). Profiles of PST congeners and total toxicity using HPLC were also assessed in additional clams (n = 36 additional, n = 52 total). Clams contained mostly potent PST congeners, and over half of the clams had PST concentrations above the seafood regulatory limit. These data will help assess the exposure risks of PSTs in Arctic marine food webs, as harmful algal bloom activity is predicted to increase as the Arctic continues to warm.

Spatiotemporal Patterns of Chlorophyll-a Concentration in a Hypersaline Lake Using High Temporal Resolution Remotely Sensed Imagery

The Great Salt Lake (GSL) is the largest saline lake in the Western Hemisphere. It supports billion-dollar industries and recreational activities, and is a vital stopping point for migratory birds. However, little is known about the spatiotemporal variation of phytoplankton biomass in the lake that supports these resources. Spectral reflectance provided by three remote sensing products was compared relative to their relationship with field measurements of chlorophyll a (Chl a). The MODIS product MCD43A4 with a 500 m spatial resolution provided the best overall ability to map the daily distribution of Chl a. The imagery indicated significant spatial variation in Chl a, with low concentrations in littoral areas and high concentrations in a nutrient-rich plume coming out of polluted embayment. Seasonal differences in Chl a showed higher concentrations in winter but lower in summer due to heavy brine shrimp (Artemia franciscana) grazing pressure. Twenty years of imagery revealed a 68% increase in Chl a, coinciding with a period of declining lake levels and increasing local human populations, with potentially major implications for the food web and biogeochemical cycling dynamics in the lake. The MCD43A4 daily cloud-free images produced by 16-day temporal composites of MODIS imagery provide a cost-effective and temporally dense means to monitor phytoplankton in the southern (47% surface area) portion of the GSL, but its remaining bays could not be effectively monitored due to shallow depths, and/or plankton with different pigments given extreme hypersaline conditions.

Modeling the advective supply of Calanus finmarchicus to Stellwagen Bank as an indicator of sand lance foraging habitat, and the climate vulnerability of a National Marine Sanctuary

The northern sand lance (Ammodytes dubius), a key species in the food web supporting the Stellwagen Bank National Marine Sanctuary (SBNMS), feeds primarily on the lipid-rich copepod Calanus finmarchicus. Climate change poses a significant threat to this dynamic, as C. finmarchicus populations are at the southern edge of their subarctic distribution and are vulnerable to warming waters and changing oceanographic conditions. Declines in the advective supply of C. finmarchicus to Stellwagen Bank could adversely affect sand lance populations and, consequently, the ecological and economic resources that depend on them. To quantify the connectivity between SBNMS and potential sources of C. finmarchicus, we used the Finite-Volume Community Ocean Model (FVCOM) coupled with Lagrangian particle tracking over the years 1978 to 2016. Numerical experiments revealed that Stellwagen Bank is highly connected to upstream areas in the Maine Coastal Current (MCC), where existing time series monitoring stations observe C. finmarchicus populations. The connectivity exhibited strong seasonal patterns, with peak connectivity occurring during spring and early summer, aligning with the sand lance feeding period on C. finmarchicus. We found significant interannual variability, influenced by changes in the strength of the MCC and circulation patterns in the western Gulf of Maine. Years with stronger MCC flow showed higher connectivity and a greater potential supply of C. finmarchicus particles to Stellwagen Bank. Conversely, periods of reduced flow corresponded with decreased connectivity, potentially limiting the availability of C. finmarchicus to sand lance populations. Meanwhile, observations from drifters and buoys since 2001 have documented decreases in MCC current speed which has been linked to a climate driven strengthening of southwesterly winds. These findings underscore the importance of pelagic habitat connectivity in assessing the climate vulnerability of marine protected areas (MPAs) like SBNMS. Furthermore, monitoring C. finmarchicus populations at upstream time series stations can provide information on downstream foraging habitat in MPAs, and potentially in other vulnerable areas of ecological and socioeconomic interest. By incorporating these indicators of connectivity and upstream C. finmarchicus population abundance into decision support tools, Sanctuary managers and stakeholders can make informed decisions to mitigate potential climate impacts.

Cyclical, multi-trophic-level responses to a volatile, introduced forage fish: Learning from four decades of food web observation to inform management

Abstract Species introductions can have significant effects on recipient ecosystems. Anticipating potential ecosystem change in response to introduced species based on historical information can help managers prepare for future conditions. Rainbow Smelt Osmerus mordax have been introduced widely to improve sport fish growth. As intended, Walleye Sander vitreus growth in Horsetooth Reservoir, Colorado increased after Rainbow Smelt introduction, but poor Walleye recruitment occurred as well. Additionally, opossum shrimp Mysis diluviana became absent from both predator diets and intermittent surveys, the dominant Daphnia species in Horsetooth Reservoir shifted and Daphnia densities declined significantly. These patterns were repeated during two different time periods of increased Rainbow Smelt abundance, suggesting that Rainbow Smelt have a strong influence on multiple components of the ecosystem. The repetition of responses to Rainbow Smelt offered the opportunity to evaluate indicators to anticipate potential ecosystem regime shifts that restructure predator–prey dynamics across trophic levels. Three predictors (i.e., high estimated Rainbow Smelt abundance, high catch rates of large Walleye, and low Daphnia densities) were associated with poor Walleye recruitment. Simple indicators like these could inform timely management decisions to take advantage of the benefits Rainbow Smelt offer, while lessening their undesirable effects. For example, management decisions could be made, such as preparing for Walleye egg collections, rearing and stocking of Walleye, increasing availability or quality of Walleye spawning habitat, allowing more protective or liberalized adult Walleye harvest to promote natural recruitment, and limiting Rainbow Smelt access to their spawning habitat.

Phytoplankton-environment dynamics in a tropical estuary of the northeastern Arabian Sea: a Generalized Additive Model (GAM) approach.

Phytoplankton are diverse photosynthetic organisms in estuarine ecosystems and sensitive indicators of environmental changes. This study employed Generalized Additive Model (GAM) to explore the impact of environmental variables on the abundance of six dominant phytoplankton species in the tropical Karanja estuary, India. Data were collected from five sampling stations between January 2022 and March 2023. The GAM model explained ≥ 55% of the variability in species distribution, predicting that the Karanja estuary provides a suitable habitat for these phytoplankton. Spatiotemporal predictions revealed higher abundances of Asterionellopsis glacialis, Coscinodiscus sp., Pseudo-nitzschia pungens, Skeletonema costatum and Thalassionema frauenfeldii during post-monsoon and lower in pre-monsoon. Conversely, Odontella sinensis thrived during pre-monsoon. Optimal growth conditions included a water temperature range of 24-32°C for O. sinensis, P. pungens and S. costatum, while chlorophyll-b concentrations between 1 and 20mg/m3 favored A. glacialis, O. sinensis, P. pungens, S. costatum and T. frauenfeldii. P. pungens, S. costatum and T. frauenfeldii exhibited broad salinity tolerance ranging from 10-40‰. Additionally, Coscinodiscus sp., P. pungens and T. frauenfeldii were found in environments with nitrate content of 0.1-1mg/L, while O. sinensis preferred silicate levels of 1-10mg/L. Notably, these species serve as indicators of eutrophication, providing insights into ecosystem health. This study represents the first application of GAM for exploring phytoplankton-environment interactions in India, offering critical data for water quality management, pollution control and food web preservation. Policymakers can use these findings to develop evidence-based regulations that support proactive coastal management, enhance estuarine resilience to climate stressors and ensure sustainable resource conservation.

Diatom responses to rapid light and temperature fluctuations: adaptive strategies and natural variability

Diatoms are crucial in global primary productivity and carbon sequestration, contributing significantly to marine food webs and biogeochemical cycles. With the projected increase in sea surface temperatures, climate change poses significant threats to these essential organisms. This study investigates the photobiological responses of nine diatom species to rapid changes in light and temperature, aiming to understand their adaptability and resilience to climate-induced environmental fluctuations. Using a high-throughput phenoplate assay, we evaluated the maximum quantum yield of photosystem 2 (Fv/Fm), non-photochemical quenching (NPQ) and additional photosynthetic parameters under varying temperature conditions. Our results revealed significant variability in the photophysiological responses among the species, with temperature emerging as a dominant abiotic factor relative to light, accounting for 13.2%–37.5% of the measured variability. Measurements of effect size of temperature and light on Fv/Fm showed that there is additional significant innate variability in the samples when a homogeneous culture is fractioned in 384 subpopulations. Furthermore, hierarchical clustering analysis of the effect size of temperature, light and innate variability on all measured photosynthetic parameters identified two distinct diatom groups. One group exhibited strong interaction between light intensity and temperature, suggesting active synergetic mechanisms to cope with fluctuating environments, while the other showed potential limitations in this regard. These findings highlight diatoms’ diverse strategies to optimize photosynthesis and manage light and thermal stress, providing insights into their potential responses to future climate scenarios. Furthermore, we demonstrate that using the method presented in this work we can functionally cluster different diatom species.

Soil fauna trophic multifunctionality mediates the release of elements from decomposing typhoon‐generated leaf litter

Abstract Tropical cyclones (i.e. hurricanes, typhoons) cause large pulse fluxes of leaves that have not undergone senescence (i.e. green litter) to forest soils, with consequences for biogeochemical cycling. Energy and mineral nutrient concentrations of green litter are higher than the naturally senesced litter, likely affecting rates of decomposition and nutrient release, as well as the structure and composition of detrital food webs, but these effects have not been well quantified. During the typhoon ‘Hagubit’, we collected green and senesced litter from three common urban greening species, and then conducted a 316‐day field experiment to evaluate substrate quality affected the trophic multifunctionality of soil faunal communities and ultimately elemental release from the decomposing litter. Nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca) and magnesium (Mg) were released at significantly higher rates from green litter than senesced litter. Aluminium (Al), manganese (Mn) and iron (Fe) displayed a net accumulation during litter decomposition, and the immobilization of these elements was significantly higher in green than senesced litter. Litter substrate chemistry directly affected the release rates of elements, but its influence was stronger in decomposing senesced litter compared to green litter. Detritivores dominated green and senesced litter faunal communities relative to predators, omnivores and herbivores, and these distinct fauna functional groups showed significantly positive correlation during decomposition, but soil fauna trophic multifunctionality was significantly higher in green litter and stimulated the release of elements. These findings suggest that typhoons dramatically alter the dynamics of nutrient release during litter decomposition, and the influences are mediated in part by its substrate quality and changes in soil fauna trophic multifunctionality, which has significant implications for the magnitude and timing of soil nutrient availability after typhoon disturbances. Read the free Plain Language Summary for this article on the Journal blog.

Prokaryotic and eukaryotic periphyton responses to warming, nutrient enrichment and small omnivorous fish: a shallow lake mesocosms experiment.

Global change stressors, including climate warming, eutrophication, and small-sized omnivorous fish, may exert interactive effects on the food webs and functioning of shallow lakes. Periphyton plays a central role in the primary production and nutrient cycling of shallow lakes but constitutes a complex community composed of eukaryotes and prokaryotes that may exhibit different responses to multiple environmental stressors with implications for the projections of the effects of global change on shallow lakes. We analyzed the effects of warming, nutrient enrichment, small omnivorous fish and their interactions on eukaryotic and prokaryotic periphyton structures in shallow lake mesocosms. We performed 16S and 18S rRNA high-throughput sequencing to elucidate the effect of the abovementioned stressors. We found that warming promoted periphytic alpha diversity and network complexity, with multi-tolerant genera becoming dominating (e.g. Spirosomaceae and Azospirillaceae). Contrastingly, nutrient enrichment led to reduced prokaryotic diversity and network complexity and stability, with weak disruption of the eukaryotic structure. Small omnivorous fish were major drivers of changes eukaryotic periphyton, facilitating diversity and network complexity, and increasing prokaryotic and eukaryotic biomarker diversity. Omnivorous fish reduced the grazing pressure on periphyton mainly through selective grazing on zooplankton, contributing to periphytic structural stability and functional diversity, especially the proliferation of prokaryotic biomarkers. Nutrient enrichment counteracted the positive effects of warming on periphyton, while concerted action with omnivorous fish led to high TN and TP concentrations and accelerated the negative development of periphytic alpha diversity and network structure. The co-occurrence of the three environmental pressures ultimately resulted in a disruption of periphytic biodiversity and community structure and weakened connectivity with the environment. Our study provided new insights into the understanding of the response of prokaryotic and eukaryotic community structure and ecological functions of freshwater periphyton to global environmental change.

Development, optimization and validation of a highly sensitive and selective method for the determination of PFAS in animal-based food.

Perfluorocarboxylic acids and perfluorosulfonic acids accumulate in food webs, thus posing a serious threat to food safety. The European Food Safety Authority (EFSA) derived a tolerable weekly intake (TWI) of 4.4ng/kg body weight for the sum of the four so-called EFSA-PFAS in 2020. More sensitive analytical methods are urgently needed, not only to monitor maximum levels, but also for future toxicological assessments of these substances. Therefore, in the present study a dual SPE approach for the purification of the extracts was chosen to attain high and valid sensitivity for the matrices egg, liver, milk and dairy products using liquid chromatography coupled with tandem mass spectrometry. This method achieved limits of quantification of 2.60 (PFOS) - 6.80ng/kg (PFHxS) for egg, 9.80 (PFOS) - 46.0ng/kg (PFHxS) for liver and 0.165 (PFNA) - 0.455ng/kg (PFOS) for milk for the 4 EFSA-PFAS. Summed medians for the 4 EFSA-PFAS of 396ng/kg in bovine liver and 54.0ng/kg in pork liver, as well as 8.46ng/kg in cheese and 4.57ng/kg in milk were detected. The results were subjected to correlation analysis. Statistically significant strong correlations were identified between bovine and porcine liver for PFNA, PFDA, PFUnDA and PFOS. To summarize the PFAS content and the PFAS spectrum detected depend on the animal species examined. Furthermore, an estimation of the exhaustion of the TWI for children, women and men was conducted. In our model, a TWI exhaustion of more than 27.0% (children) was calculated for liver, milk and cheese.

Proliferative and viability effects of two cyanophages on freshwater bloom-forming species Microcystis aeruginosa and Raphidiopsis raciborskii vary between strains

Viruses that infect cyanobacteria are an integral part of aquatic food webs, influencing nutrient cycling and ecosystem health. However, the significance of virus host range, replication efficiency, and host compatibility on cyanobacterial dynamics, growth, and toxicity remains poorly understood. In this study, we examined the effects of cyanophage additions on the dynamics and activity of optimal, sub-optimal, and non-permissive cyanobacterial hosts in cultures of Microcystis aeruginosa and Raphidiopsis raciborskii. Our findings reveal that cross-infectivity can substantially reduce the proliferative success of the cyanophage under conditions of high-density of sub-optimal hosts which suggests phage dispersal limitation as a result of shared infections, in turn impairing their top-down control over the host community. Furthermore, we found that cyanophage addition triggers host strain-specific responses in photosynthetic performance, population size and toxin production, even among non-permissive hosts. These non-lytic effects suggest indirect impacts on co-existing cyanobacteria, increasing the overall complexity and variance in many ecologically relevant cyanobacterial traits. The high variability in responses observed with a limited subset of cyanophage-cyanobacteria combinations not only highlights the intricate role of viral infections in microbial ecosystems but also underscores the significant challenges in predicting the composition, toxicity, and dynamics of cyanobacterial blooms.

Pollen Resource Repartition Between Managed Honey Bees (Apis mellifera L. 1758) and Unmanaged Bees in Three Italian National Parks

Despite its global importance for the maintenance of healthy ecosystems and its contribution in providing economic benefits to human society, the clade Anthophila is in severe decline worldwide. In this context, counteracting the decline in Apoidea is of fundamental importance. Honey bee density and beekeeping are believed to negatively impact wild bee populations, mostly through competition for food sources. In this study, interspecific trophic competition was investigated using the still seldom exploited approach of a palynological analysis combined with a metabarcoding analysis of the pollen gathered by both managed honey bees and wild bees in three Italian national parks. The entire trophic network was identified as highly specialized (H2′ = 0.933). The results obtained suggest that, overall, wild bee species are sustained by different pollen sources than honey bees. This low sharing of resources could be due to the natural trend occurring in natural populations, where species tend to minimize the competitive overlap through niche differentiation or niche complementarity as a result of coevolution. National parks play a fundamental role in animal and plant species protection and conservation. Therefore, plans should focus on evaluating honey bee densities in the interests of achieving less intensive, more traditional, and sustainable beekeeping, as well as habitat restoration, to promote the survival and reproduction of wild bee populations.

The effect of water motion and elevated carbon on two green algae Ulva intestinalis and Cladophora glomerata DIC acquisition and DOC release in the brackish Baltic Sea

ABSTRACT Macrophytes play a key role in coastal environments, acting to transform inorganic carbon into biologically available organic matter. This process supports the marine food web at large, however, the dynamics behind macrophyte carbon acquisition are not fully understood with factors influencing their ability to utilize different carbon forms (HCO3 − and/or CO2) and subsequent release mechanics of this carbon remaining rather poorly understood. This study aims to investigate the physiological responses of two important Baltic Sea macrophytes, Ulva intestinalis and Cladophora glomerata. By examining the effects of pH drift inhibitors, coupled with carbon-concentrating mechanisms (CCMs) and dissolved organic carbon (DOC) dynamics, we provide insights into the complex adaptations of these macroalgae to changing environmental conditions. The results demonstrate that both species exhibit distinct capabilities to adapt their carbon concentration mechanisms (CCMs) but suggest that C. glomerata may potentially gain a photosynthetic advantage in future high CO2. The observed differences between pH and water motion highlight species-specific nuances in the regulation of dissolved organic carbon (DOC) release, aligning with current theories on DOC dynamics. This research underscores the importance of understanding macroalgal adaptation and fitness in both present and future coastal ecosystems, particularly as environmental changes continue to evolve. By examining these factors, the study contributes valuable insights into how macroalgae may respond to future climate shifts.