Pharmaceuticals and endocrine disrupting compounds modulate adverse effects of climate change on resource quality in freshwater food webs

Freshwater biodiversity, ecosystem functions and services are changing at an unprecedented rate due to the impacts of vast number of stressors overlapping in time and space. Our study aimed at characterizing individual and combined impacts of pollution with pharmaceuticals (PhACs) and endocrine disrupting compounds (EDCs) and increased water temperature (as a proxy for climate change) on primary producers and first level consumers in freshwaters. We conducted a microcosm experiment with a simplified freshwater food web containing moss (Bryophyta) and shredding caddisfly larvae of Micropterna nycterobia (Trichoptera). The experiment was conducted with four treatments; control (C), increased water temperature + 4 °C (T2), emerging contaminants' mix (EC = 15 PhACs & 5 EDCs), and multiple stressor treatment (MS = EC + T2). Moss exhibited an overall mild response to selected stressors and their combination. Higher water temperature negatively affected development of M. nycterobia through causing earlier emergence of adults and changes in their lipidome profiles. Pollution with PhACs and EDCs had higher impact on metabolism of all life stages of M. nycterobia than warming. Multiple stressor effect was recorded in M. nycterobia adults in metabolic response, lipidome profiles and as a decrease in total lipid content. Sex specific response to stressor effects was observed in adults, with impacts on metabolome generally more pronounced in females, and on lipidome in males. Thus, our study highlights the variability of both single and multiple stressor impacts on different traits, different life stages and sexes of a single insect species. Furthermore, our research suggests that the combined impacts of warming, linked to climate change, and contamination with PhACs and EDCs could have adverse consequences on the population dynamics of aquatic insects. Additionally, these findings point to a potential decrease in the quality of resources available for both aquatic and potentially terrestrial food webs.

Eutrophication and loss of riparian shading influence food quality and trophic relation in stream food webs

Eutrophication induced by excessive inputs of nutrient is one of the main stressors in aquatic ecosystems. Deforestation in riparian zones alter riparian shading, which together with eutrophication is expected to exert a complex control over stream food webs. We manipulated two levels of riparian shading (open canopy vs. shading canopy) and nutrient supply (ambient vs. nutrient addition) in three headwater streams to investigate the individual and combined effects of eutrophication and loss of riparian shading on carbon sources and nutritional quality of biofilms, and the subsequent trophic effects on macroinvertebrate grazers. Nutrient enrichment increased the autochthonous carbon (i.e., algae especially diatoms) indicated by fatty acid (FA) biomarkers within biofilms and grazers. The nutritional quality indicated by eicosapentaenoic acid (EPA) content of biofilms was increased with nutrient enrichment and more so with the combined effect of an increase in riparian shading, consequently leading to an increase in the nutritional quality, density, and biomass of grazers. In particular, the trophic linkages between biofilms and grazers were mainly influenced by EPA concentration in the biofilms, and strengthened with the combined effects of riparian shading and additional nutrients. Our study emphasizes the nutritional significance of EPA for consumers at higher trophic levels and proposes its potential as an indicator for monitoring the health of aquatic ecosystems.

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

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

Cross-Ecosystem Linkages: Transfer of Polyunsaturated Fatty Acids From Streams to Riparian Spiders via Emergent Insects

Polyunsaturated fatty acids (PUFAs) are essential resources unequally distributed throughout landscapes. Certain PUFAs, such as eicosapentaenoic acid (EPA), are common in aquatic but scarce in terrestrial ecosystems. In environments with low PUFA availability, meeting nutritional needs requires either adaptations in metabolism to PUFA-poor resources or selective foraging for PUFA-rich resources. Amphibiotic organisms that emerge from aquatic ecosystems represent important resources that can be exploited by predators in adjacent terrestrial habitats. Here, we traced PUFA transfer from streams to terrestrial ecosystems, considering benthic algae as the initial PUFA source, through emergent aquatic insects to riparian spiders. We combined carbon stable isotope and fatty acid analyses to follow food web linkages across the ecosystem boundary and investigated the influence of spider lifestyle (web building vs. ground dwelling), season, and ecosystem degradation on PUFA relations. Our data revealed that riparian spiders consumed considerable amounts of aquatic-derived resources. EPA represented on average 15 % of the total fatty acids in riparian spiders. Season had a strong influence on spider PUFA profiles, with highest EPA contents in spring. Isotope data revealed that web-building spiders contain more aquatic-derived carbon than ground dwelling spiders in spring, although both spider types had similarly high EPA levels. Comparing a natural with an anthropogenically degraded fluvial system revealed higher stearidonic acid (SDA) contents and Σω3/Σω6 ratios in spiders collected along the more natural river in spring but no difference in spider EPA content between systems. PUFA profiles of riparian spiders where distinct from other terrestrial organism and more closely resembled that of emergent aquatic insects (higher Σω3/Σω6 ratio). We show here that the extent to which riparian spiders draw on aquatic PUFA subsidies can vary seasonally and depends on the spider’s lifestyle, highlighting the complexity of aquatic-terrestrial linkages.

Polyunsaturated fatty acids in fish tissues more closely resemble algal than terrestrial diet sources

The River Continuum Concept implies that consumers in headwater streams have greater dietary access to terrestrial basal resources, but recent studies have highlighted the dietary importance of high-quality algae. Algae provide consumers with physiologically important omega-3 (n-3) polyunsaturated fatty acids (PUFA), particularly eicosapentaenoic acid (EPA). However, terrestrial plants and most benthic stream algae lack the long-chain (LC) n-3 PUFA docosahexaenoic acid (DHA, 22:6n-3), which is essential for neural development in fish and other vertebrates. We sampled subalpine streams to investigate how the PUFA composition of neural (brain and eyes), muscle, and liver tissues of freshwater fish is related to their potential diets (macroinvertebrates, epilithon, fresh and conditioned terrestrial leaves). The PUFA composition of consumers was more similar to epilithon than to terrestrial leaves. Storage lipids of eyes most closely resembled dietary PUFA (aquatic invertebrates and algae). However, DHA and arachidonic acid (ARA, 20:4n-6) were not directly available in the diet but abundant in organs. This implies that algal PUFA were selectively retained or were produced internally via enzymatic PUFA conversion by aquatic consumers. This field study demonstrates the nutritional importance of algal PUFA for neural organs in aquatic consumers of headwater regions.

Diet quality and NSAIDs promote changes in formation of prostaglandins by an aquatic invertebrate

We used the freshwater insect Hydropsyche sp. to investigate the impact of diets lacking arachidonic acid (ARA) and an environmentally relevant mixture of NSAIDs (Ibuprofen, Ketoprofen, Diclofenac and Naproxen at a nominal concentration of all compounds together 16.75 μg L^-1) on their metabolism of ARA and prostaglandins (PGs). The organisms were exposed for 16 days to four different treatments: a reference (FF), a diet lacking ARA (O), to NSAIDs in water (FFN) and to the combination of the two factors (ON). Mortality, biomass and bioconcentration of pharmaceuticals were investigated. The ARA and PGs levels in the organisms were monitored by utilising a targeted metabolomics approach. NSAIDs or dietary constraints did not produce significant differences in biomass or mortality of Hydropsyche sp. among treatments. In organisms exposed to NSAIDs, all pharmaceuticals were detected, except for Ketoprofen. Metabolomic approach determined the presence of PGH₂, PGE₁ and PGD₁. Levels of ARA diminished significantly in those organisms in treatment ON. The levels of PGs responded negatively to the absence of ARA in diet: PGH₂ diminished significantly with respect to the reference in treatment O while PGE₁ diminished significantly in treatment ON. Regarding the effects of NSAIDs on ARA metabolism, our results suggest that it was sensitive to NSAIDs, but effects were weak and did not imply a general decrease in the PGs. We confirmed that ARA was the main substrate for the synthesis of PGs in Hydropsyche sp, their absence or poor levels of ARA in diet, produced changes in the PG levels.

Origin of Carbon and Essential Fatty Acids in Higher Trophic Level Fish in Headwater Stream Food Webs

Dietary carbon sources in headwater stream food webs are divided into allochthonous and autochthonous organic matters. We hypothesized that: 1) the dietary allochthonous contribution for fish in headwater stream food webs positively relate with canopy cover; and 2) essential fatty acids originate from autochthonous organic matter regardless of canopy covers, because essential fatty acids, such as 20:5ω3 and 22:6ω3, are normally absent in allochthonous organic matters. We investigated predatory fish Salvelinus leucomaenis stomach contents in four headwater stream systems, which are located in subarctic region in northern Japan. In addition, stable carbon and nitrogen isotope ratios, fatty acid profile, and stable carbon isotope ratios of essential fatty acids were analyzed. Bulk stable carbon analysis showed the major contribution of autochthonous sources to assimilated carbon in S. leucomaenis. Surface baits in the stomach had intermediate stable carbon isotope ratios between autochthonous and allochthonous organic matter, indicating aquatic carbon was partly assimilated by surface baits. Stable carbon isotope ratios of essential fatty acids showed a positive relationship between autochthonous sources and S. leucomaenis across four study sites. This study demonstrated that the main supplier of dietary carbon and essential fatty acids was autochthonous organic matter even in headwater stream ecosystems under high canopy cover.

Urbanisation alters fatty acids in stream food webs

Fatty acids are essential to macroinvertebrate growth and reproduction and can indicate food web structure and nutritional quality of basal resources. However, broad-scale examinations of how catchment land cover and associated stressors affect the proportions of fatty acids (FAs) in stream food webs are few.Here, we: (1) examine relationships among proportions of FAs among benthic periphyton and macroinvertebrate collector/gatherers, shredders, and predators; and (2) test if relationships between periphytic and macroinvertebrate FAs were altered due to the intensity of urban development in catchments.Proportions of the ≥20-C eicosapentaenoic acid (EPA 20:5ω3), arachidonic acid (ARA 20:4ω6), and docosahexaenoic acid (22:6ω3) indicated collector/gatherers had a diet richer in periphyton than in shredders, which had significantly lower proportions of these FAs. Collector/gatherers were in turn likely to be high-quality sources of ω3 and ≥ 20-C FAs for predators, which also had significantly greater EPA and ARA proportions than those in shredders. Linoleic (18:2ω6) and α-linolenic acid (18:3ω3) comprised the greatest proportions of FAs in shredders, which suggested a diet dominated by leaf litter and associated hyphomycetes.As catchment urbanisation increased, proportions of total ω3 FAs and EPA in periphyton were significantly greater. This pattern also was seen through macroinvertebrate consumers and predators, given that proportions of these FAs in macroinvertebrates also were significantly correlated with factors associated with catchment urbanisation. The significant increase in total ω3 FAs and EPA proportions within shredders indicated that periphyton growth, and their FAs, increased on leaf litter, probably due to greater nutrient concentrations associated with catchment urbanisation. Proportions of total ω6 FAs in biota were not significantly correlated with factors associated with urban development, which could indicate that they were of sufficient abundance for consumers regardless of urban intensity or possible changes in their sources.Our study provides an informative first step that identified notable differences in proportions of FAs among macroinvertebrates in urban streams and an increase in proportions of total ω3 FAs and EPA in periphyton, consumers, and predators as catchment urbanisation increases. Identifying how FA relationships within food webs change in response to catchment alterations and stressors could inform land use and management decisions by linking environmental changes to measures important to ecosystem outcomes.

Feeding strategies for the acquisition of high-quality food sources in stream macroinvertebrates: Collecting, integrating, and mixed feeding

Aquatic macroinvertebrates play an important functional role in energy transfer in food webs, linking basal food sources to upper trophic levels that include fish, birds, and humans. However, the trophic coupling of nutritional quality between macroinvertebrates and their food sources is still poorly understood. We conducted a field study in subalpine streams in Austria to investigate how the nutritional quality (measured by long-chain polyunsaturated fatty acids, LC-PUFAs) in macroinvertebrates changes relative to their basal food sources. Samples of macroinvertebrates, periphyton, and leaves were collected from 17 streams in July and October 2016 and their fatty acid (FA) composition was analyzed. Periphyton FA varied strongly with time and space, and their trophic effect on macroinvertebrate FA differed among functional feeding groups. The match between periphyton FA and macroinvertebrate FA decreased with increasing trophic levels, but LC-PUFA content increased with each trophic step from periphyton to grazers and finally predators. Macroinvertebrates fed selectively on, assimilated, and/or actively controlled their LC-PUFA, especially eicosapentaenoic acid (EPA, 20 : 5ω3) relative to their basal food sources in the face of spatial and temporal changes. Grazer FA profiles reflected periphyton FA with relatively good fidelity, and especially their EPA feeding strategy was primarily linked to periphyton FA variation across seasons. In contrast, shredders appeared to preferentially assimilate more EPA over other FA, which was determined by the availability of high-quality food over seasons. Predators may more actively control their LC-PUFA distribution with respect to different quality foods and showed less fidelity to the basal FA profiles in plants and prey. Overall, grazers and shredders showed relatively good fidelity to food FA profiles and performed as both "collectors" and "integrators" for LC-PUFA requirements across seasons, while predators at higher trophic levels were more "integrators" with added metabolic complexity leading to somewhat more divergent FA profiles. These results are potentially applicable for other aquatic consumers in freshwater and marine ecosystems.

Seasonality of total fatty acid profiles in acid mine drainage impaired streams

Pre-regulation coal mining and subsequent acid mine drainage (AMD) have drastically altered stream quality in the Appalachian region of the USA. Streams impaired by AMD often times demonstrate lowered pH, increases in specific conductance, and increase in dissolved metal concentrations. These changes in the chemical environment are reflected in the biotic community with drastic reductions in diversity and biomass. Recently, there has been an increase in applying traditional measures of food quality to understand how the biofilm community is altered by environmental condition and use for stream quality monitoring. The purpose of this study was two-fold: (1) to use fatty acid profiles to distinguish between biofilm communities in AMD impaired and unimpaired streams and (2) to determine the consistency of biofilm fatty acid profiles throughout the summer sampling period. Impaired streams showed significantly lower pH and increased specific conductance. Biofilm samples from the AMD impaired streams had lower fatty acid content with a decreased proportion of polyunsaturated fatty acids. Fatty acid profiles easily and rapidly separated biofilm communities into their respective categories, either as being impaired by AMD or unimpaired by AMD, using multivariate statistical approaches. Fatty acid profiles were similar within stream type throughout the summer sampling season, and the profiles were correlated to pH and specific conductance. The results of this study suggest that fatty acid profiles can rapidly and accurately categorize the biofilm community responses to environmental impairment.

Cross-ecosystem fluxes: Export of polyunsaturated fatty acids from aquatic to terrestrial ecosystems via emerging insects

Cross-ecosystem fluxes can crucially influence the productivity of adjacent habitats. Emerging aquatic insects represent one important pathway through which freshwater-derived organic matter can enter terrestrial food webs. Aquatic insects may be of superior food quality for terrestrial consumers because they contain high concentrations of essential polyunsaturated fatty acids (PUFA). We quantified the export of PUFA via emerging insects from a midsize, mesotrophic lake. Insects were collected using emergence traps installed above different water depths and subjected to fatty acid analyses. Insect emergence from different depth zones and seasonal mean fatty acid concentrations in different insect groups were used to estimate PUFA fluxes. In total, 80.5mg PUFA m^-2yr^-1 were exported, of which 32.8mgm^-2yr^-1 were eicosapentaenoic acid (EPA), 7.8mgm^-2yr^-1 were arachidonic acid (ARA), and 2.6mgm^-2yr^-1 were docosahexaenoic acid (DHA). While Chironomidae contributed most to insect biomass and total PUFA export, Chaoborus flavicans contributed most to the export of EPA, ARA, and especially DHA. The export of total insect biomass from one square meter declined with depth and the timing at which 50% of total insect biomass emerged was correlated with the water depths over which the traps were installed, suggesting that insect-mediated PUFA fluxes are strongly affected by lake morphometry. Applying a conceptual model developed to assess insect deposition rates on land to our insect-mediated PUFA export data revealed an average total PUFA deposition rate of 150mgm^-2yr^-1 within 100m inland from the shore. We propose that PUFA export can be reliably estimated using taxon-specific information on emergent insect biomass and seasonal mean body PUFA concentrations of adult insects provided here. Our data indicate that insect-mediated PUFA fluxes from lakes are substantial, implying that freshwater-derived PUFA can crucially influence food web processes in adjacent terrestrial habitats.

A comparison of freeze-drying and oven-drying preparation methods for bulk and compound-specific carbon stable isotope analyses: examples using the benthic macroinvertebrates Stenopsyche marmorata and Epeorus latifolium

RATIONALE

Carbon stable isotope analysis of bulk samples and fatty acids is an established method for tracing carbon flow pathways and reconstructing trophic interactions, but there is no consensus on which sample drying method should be used for sample preparation. The aim of this study was to determine if freeze-drying and oven-drying treatments used to prepare samples of the benthic macroinvertebrates Stenopsyche marmorata and Epeorus latifolium for bulk and fatty-acid-specific carbon stable isotope analysis yield different isotopic ratio values.

METHODS

Five individuals each from two species were split in half; one half was freeze-dried and the other half was oven-dried. The samples were ground and the δ(13)C values of the bulk samples and eight fatty acids were measured following combustion using an isotope ratio mass spectrometer coupled to an elemental analyzer or gas chromatography system.

RESULTS

The mean difference in the bulk and fatty acid δ(13)C values between freeze-dried and oven-dried samples was small (≤0.1‰ in both cases), although relatively large variations were observed in individual fatty-acid-specific δ(13)C values (maximum of ≤0.9 ‰). There were no significant differences in either bulk sample or fatty-acid-specific δ(13)C values between freeze-dried or oven-dried samples of the same species.

CONCLUSIONS

Freeze-drying and oven-drying are equally acceptable methods for preparing freshly caught S. marmorata and E. latifolium samples for bulk and fatty-acid-specific carbon stable isotope analyses.

Is the fatty acid composition of freshwater zoobenthic invertebrates controlled by phylogenetic or trophic factors?

We studied the fatty acid (FA) content and composition of ten zoobenthic species of several taxonomic groups from different freshwater bodies. Special attention was paid to essential polyunsaturated fatty acids, eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), and arachidonic acid (ARA, 20:4n-6); and the n-3/n-6 and DHA/ARA ratios, which are important for consumers of higher trophic levels, i.e., fish. The content and ratios of these FA varied significantly in the studied zoobenthic species, consequently, the invertebrates were of different nutritional quality for fish. Eulimnogammarus viridis (Crustacea) and Dendrocoelopsis sp. (Turbellaria) had the highest nutrition value for fish concerning the content of EPA and DHA and n-3/n-6 and DHA/ARA ratios. Using canonical correspondence analysis we compared the FA profiles of species of the studied taxa taking into account their feeding strategies and habitats. We gained evidence that feeding strategy is of importance to determine fatty acid profiles of zoobenthic species. However, the phylogenetic position of the zoobenthic species is also responsible and may result in a similar fatty acid composition even if species or populations inhabit different water bodies or have different feeding strategies.