Chironomid Larvae Research Articles

Influence of habitat complexity on the prey mortality in IGP system involving insect predators (Heteroptera) and prey (Diptera): Implications in biological control.

Intraguild predation (IGP) is common in the freshwater insect communities, involving a top predator, intraguild prey (IG prey) and a shared prey. Influence of the habitat complexity on the prey-predator interactions is well established through several studies. In the present instance, the IGP involving the heteropteran predators and the dipteran prey were assessed in the background of the habitat complexity. The three predators Diplonychus rusticus, Ranatra filiformis, and Laccotrephes griseus, one intraguild prey Anisops bouvieri and two dipteran prey Culex quinquefasciatus and Chironomus sp. were used in different relative density against the complex habitat conditions to deduce the impact on the mortality on the prey. In comparison to the open conditions, the presence of the macrophytes and pebbles reduced the mortality of the shared prey under intraguild system as well as single predator system. The mortality of the shared prey was however dependent on the density of the predator and prey. Considering the shared prey mortality, predation on mosquito larvae was always higher in single predator system than chironomid larvae irrespective of identity and density of predators. However, for both the shared prey, complexity of habitat reduced the prey vulnerability in comparison to the simple habitat condition. Higher observed prey consumption depicts the higher risk to predation of shared prey, though the values varied with habitat conditions. Mortality of IG prey (A. bouvieri) in IGP system followed the opposite trend of the shared prey. The lower mortality in simple habitat and higher mortality in complex habitat conditions was observed for the IG prey, irrespective of shared prey and predator density. In IGP system, the shared prey mortality was influenced by the habitat conditions, with more complex habitat reducing the vulnerability of the shared prey and increased mortality of the IG prey. This implies that the regulation of the mosquitoes, in the IGP system will be impeded by the habitat conditions, with the heteropteran predators as the top predator.

Meat storage under acoustic freezing conditions and assessment of its biotoxicity (part 1)

The necessity of developing new technologies for refrigerated storage, providing improved quality and safety of meat products, is shown. A critical analysis of cold storage methods has been carried out and the choice of the acoustic freezing method has been substantiated. As a result of the joint work of the students of school No. 2083, “Acoustic Freezing” company and the Institute of Biotechnology and Fisheries, Moscow State University of Technology and Management named after K.G. Razumovsky, studies were carried out to establish the degree of toxicity of pork subjected to refrigeration storage under conditions of shock and acoustic freezing. Histological studies of fresh meat and meat after acoustic and shock freezing have shown that shock freezing leads to a violation of the structure of striated muscles due to the formation of large ice crystals during freezing. The method of fractal analysis of proteins in fresh meat and meat after acoustic freezing showed that the ice crystallization in muscle tissue leads to the formation of different types of fractals. Fractal analysis can be used to select physical factors when improving the technology of acoustic freezing. Toxicological studies were carried out on juvenile clawed frogs Xenopus laevis fed with chironomid larvae, California worms Eisenia fetida (control), fresh meat and meat after acoustic freezing. Studies have shown that there are no significant deviations in the cytological parameters of red blood in frogs eating natural food (worms) and meat after acoustic freezing. Meat after shock freezing is eaten poorly by frogs, which indicates a significant loss of its quality compared to fresh meat. Comparative studies on the effects of feeding fresh meat and meat after acoustic freezing, carried out on the blood of laboratory fish Danio rerio, demonstrated that fresh meat and meat after acoustic freezing do not cause harmful effects on the red blood of fish. The work was carried out within the framework of the program for the introduction of project methods of school education in the secondary school of the Moscow State Budgetary Educational Institution “School No. 2083”.

Effects of chronic exposure to microcystin-LR on life-history traits, intestinal microbiota and transcriptomic responses in Chironomus pallidivittatus

Microcystins (MCs) are the most widely distributed cyanobacterial toxins that can exert adverse effects on aquatic organisms, but aside from the study of the harmful effect of cyanobacterial blooms, little is known about the effect of released MCs on the growth and development of chironomid larvae. To assess the harmful effect and the toxic mechanism of MCs on midges, the life-history traits, intestinal microbiota, and transcriptome of Chironomus pallidivittatus were analyzed after chronic exposure to 30 μg/L of MC-LR. Exposure inhibited larvae body length by 35.61% and wet weight by 21.92%, increased emergence time of midges, damaged mitochondria in the intestine, promoted oxidative stress, dysregulated lipid metabolism of chironomid larvae, and increased detoxification enzymes glutathione S-transferase (GST) and superoxide dismutase (SOD) by 32.44% and 17.41%, respectively. Exposure also altered the diversity and abundance of the intestinal microbiota, favoring pathogenic and MC degradation bacteria. RNA sequencing identified 261 differentially expressed genes under MC-LR stress, suggesting that impairment of the peroxisome proliferator-activated receptor signaling pathway upregulated fatty acid biosynthesis and elongation to promote lipid accumulation. In addition, exposure-induced detoxification and antioxidant responses, indicating that the chironomid larvae had the potential ability to resist MC-LR. To our knowledge, this is the first time that lipid accumulation, oxidative stress, and detoxification have been studied in this organism at the environmentally relevant concentration of MC-LR; the information may assist in ecological risk assessment of cyanobacterial toxins and their effects on benthic organisms.

Response of stream ecosystem structure to heavy metal pollution: context-dependency of top-down control by fish

The stress-gradient hypothesis predicts that biotic interactions within food webs are context dependent, since environmental stressors can attenuate consumer–prey interactions. Yet, how heavy metal pollution influences the impacts of predatory fish on ecosystem structure is unknown. This study was conducted in the Osor stream (Spain), which features a metal (mainly Zn) pollution gradient. We aimed to determine how the responses of benthic communities to the presence and absence of predatory fish interact with environmental stress and to test whether the top-down control of top predators is context dependent. To address these questions, periphyton biomass and macroinvertebrate densities were determined throughout an exclosure/enclosure mesocosm experiment using the Mediterranean barbel (Barbus meridionalis) as a top predator. The monitoring study showed that metal accumulation in periphyton and macroinvertebrates reflected patterns observed in water. The mesocosm study showed that fish predation effects on larval chironomids were not context-dependent and that periphyton biomass was markedly lower in the presence of fish regardless of metal pollution levels. This strong top-down control on periphytic algae was attributed to the foraging behaviour of fish causing bioturbation. In contrast, the top predator removal revealed grazer-periphyton interactions, which were mediated by heavy metal pollution. That is, periphyton benefitted from a lower grazing pressure in the metal-polluted sites. Together, our results suggest that the top–down control by fishes depends more on functional traits (e.g. feeding behaviour) than on feeding guild, and demonstrate the capacity of top predators to modify anthropogenic stressor effects on stream food-web structure.

Improved Chironomid Barcode Database Enhances Identification of Water Mite Dietary Content

Chironomids are one of the most biodiverse and abundant members of freshwater ecosystems. They are a food source for many organisms, including fish and water mites. The accurate identification of chironomids is essential for many applications in ecological research, including determining which chironomid species are present in the diets of diverse predators. Larval and adult chironomids from diverse habitats, including lakes, rivers, inland gardens, coastal vegetation, and nearshore habitats of the Great Lakes, were collected from 2012 to 2019. After morphological identification of chironomids, DNA was extracted and cytochrome oxidase I (COI) barcodes were PCR amplified and sequenced. Here we describe an analysis of biodiverse adult and larval chironomids in the Great Lakes region of North America based on new collections to improve chironomid identification by curating a chironomid DNA barcode database, thereby expanding the diversity and taxonomic specificity of DNA reference libraries for the Chironomidae family. In addition to reporting many novel chironomid DNA barcodes, we demonstrate here the use of this chironomid COI barcode database to improve the identification of DNA barcodes of prey in the liquefied diets of water mites. The species identifications of the COI barcodes of chironomids ingested by Lebertia davidcooki and L. quinquemaculosa are more diverse for L. davidcooki and include Parachironomus abortivus, Cryptochironomus ponderosus. Parachironomus tenuicaudatus, Glyptotendipes senilis, Dicrotendipes modestus, Chironomus riparius, Chironomus entis/plumosus, Chironomus maturus, Chironomus crassicaudatus, Endochironomus subtendens, Cricotopus sylvestris, Cricotopus festivellus, Orthocladius obumbratus, Tanypus punctipennis, Rheotanytarsus exiguus gr., and Paratanytarsus nr. bituberculatus.

Passability of Chironomid Larvae in Granular Activated Carbon.

We conducted an experiment to confirm the passability of chironomid larvae (Glyptotendipes tokunagai) in granular activated carbon (GAC) used in water treatment plants. After injecting larvae at different growth stages (first through fourth instars) into circular columns filled with GAC, the number of individuals and their locations within the GAC columns were recorded after 168 h. We found that more than 80% of the injected larvae in the first instar and 3.3% in the second instar passed, whereas none from the third and fourth instars had passed through the column. The second instar larvae were evenly distributed within the column, whereas the third and fourth instar larvae were mostly distributed within 10 cm of the upper layer of the GAC. Our results demonstrate the passability of chironomid larvae in GAC and can be used as basic information for water quality management in water treatment plants.

Структура макрозообентоса водотоков в бассейне Верхней Лены. Сообщение 1. Структура макрозообентоса основного русла р. Лены (на участке Жигалово – Усть-Кут)

Lena River is one of the largest watercourses in Siberia. It is 4,400 km long with a catchment area of 2,490,000 km2. The upper section of the river begins from its source to the Vitim River mouth (1,690 km long). Studies of the current state of the macrozoobenthos of the main riverbed of Upper Lena were conducted in the section from Zhigalovo settl. to Ust-Kut sity in summer 2017, 2018 and 2021. In the studied river section was found to contain more than 24 groups of benthic invertebrates of different taxonomic ranks: Hydrozoa (hydras), Planaria (planaria), Oligochaeta (earthworms), Hirudinea (leeches), Nematoda (roundworms), Gastropoda (gastropods), Bivalvia (bivalves), Ostracoda (seed shrimps), Amphipoda (freshwater shrimps), Ephemeroptera (mayflies), Plecoptera (stoneflies), Odonata (dragonflies), Megaloptera (alderflies), Trichoptera (caddisflies), Acariformes (water mites), Corixidae and other Heteroptera (true bugs), Dytiscidae (diving beetles), Chironomidae (chironomids), Ceratopogonidae (biting midges), Dolichopodidae (longlegged flies), Psychodidae (drain flies), Tipulidae (crane flies), Limoniidae (limoniid crane flies), Stratiomyidae (soldier flies) and other dipterans. The highest number of taxonomic groups of benthic animals is found on coarse gravel substrates with moss, chara or eleocharis (23 groups). The lowest diversity was found on clean gravels (9 groups). For the main riverbed of Upper Lena there is considerable heterogeneity in the distribution of both the main zoobenthos taxonomic groups and quantitative indicators (abundance and biomass). Mean values of zoobenthos number and biomass varied within a wide range: on gravel substrates from 784 to 17.296 individuals/m–2 in abundance and from 1.104 to 24.416 g/m–2 in biomass, on silty substrates from 3.650 to 74.783 individuals/m-2 and from 2.48 to 107.07 g/m–2, respectively. The larvae of chironomids, mayflies and oligochaetes are the main component of the macrozoobenthos structure of the Upper Lena, with the larvae of stoneflies and caddisflies playing a secondary role. On gravel substrates the structure-forming element in terms of numbers and biomass is the larvae of chironomids and mayflies, and much less frequently bivalves. In silty substrates the larvae of chironomids, oligochaetes and leeches are most important, in some areas the larvae of mayflies Ephemera orientalis or Gammarus lacustris are of primary importance.

Functional responses of an invasive mud crab across a salinity gradient

Environmental gradients may alter the ecological impacts of invasive alien species. In marine systems such as the Baltic Sea, current salinity is variable and seawater freshening is projected in future, potentially facilitating novel keystone predators. Here, we examine the influence of salinity variation in the western Baltic Sea (i.e. ambient 10, then 7 and 4 ppt) on the functional response (FR) of the Harris mud crab Rhithropanopeus harrisii towards benthic macroinvertebrate prey at different densities. Rhithropanopeus harrisii displayed a Type II FR across salinities towards larval chironomids, due to a consistently high resource consumption rate at low prey densities. Feeding rates were significantly reduced at 4 ppt (mean 6 chironomid prey killed day−1) compared to 10 ppt and 7 ppt (9 killed day−1). Search efficiencies tended to be greatest at 10 ppt, whereas handling times were shortest — and maximum feeding rate highest — at the intermediate 7 ppt. These results suggest a slight reduction in predatory impact by R. harrisii at lower salinities. Nevertheless, across most prey densities, FRs were not significantly different, indicating sustained interaction strength across a range of salinity regimes.

Food sources of common carp in a Hani Terrace integrated rice-fish system (Yunnan Province, China)

Integrated rice-carp farming is commonly employed on Hani terraces in China. However, the altitude within a Hani terrace can vary greatly, and thus the solutions for such a farming approach must vary with altitude. Research on common carp food sources in an integrated rice-carp farm at different altitudes helps to understand the food requirements of carp across periods and provides guidance for production. In this study, the composition of eukaryotic food sources of common carp (Cyprinus carpio) growing on Hani rice terraces at low and high altitudes (570 m and 1840 m) from May to August 2019 was surveyed by high-throughput DNA sequencing. The 18 s v4 gene sequences were amplified to provide 2243,095 valid reads and 2485 operational taxonomic units. In addition, the relative abundance of the gut contents of each food source varied by month and altitude. Chlorella, Necator, Oedogonium, Oryza and Scenedesmus were the dominant C. carpio food sources at the high altitude, while Chironomus, Gieysztoria, Scenedesmus, Oryza, and Lemna were the dominant species at the low altitude. The Lemna biomass identified in the C. carpio gut contents in the low altitude terrace decreased from 39.75% in June to 0.05% in August, while the Oryza biomass increased with time. The Oryza biomass observed in the gut contents of C. carpio growing in high and low altitude terraced fields increased with time. Rice pests, including the rice gall midge, rice bugs, nematodes, and chironomid larvae were found in the stomachs of C. carpio in the high and low altitude terraced fields. The maximum proportion of chironomid larvae in the gut contents of C. carpio in the low altitude terraces reached 39.29%, while the maximum proportion of nematodes was 5.38%. However, only chironomid larvae and nematodes were found in the gut contents of C. carpio growing in the high altitude terrace, reaching maximum proportions of 0.17% and 3.63%, respectively. Furthermore, a variety of rice pests were detected in the gut contents of C. carpio, indicating that C. carpio effectively preyed on rice pests and reduced rice diseased in the integrated rice-carp farming terraces.

FRESHWATER INVERTEBRATES OF LAKE ZAISAN

In this article, freshwater invertebrates are studied. Lake Zaisan is considered as an object. The article updates the list of invertebrate fauna of Lake Zaisan, which is currently relevant. The article presents steps for collecting invertebrates and determining their species composition. According to the results of the study, the species composition of thirty-nine invertebrates was determined. The author notes that the species composition of invertebrates is higher on the coast than in the lake environment, that is, the number of planktonic invertebrates is higher than that of benthos invertebrates. The author notes that the Reed thickets and kelp areas along the Lake Shore are a favorable environment for the growth of benthos organisms, that is, the predominance of benthos invertebrates, and on the sandy shores of the lake there are no invertebrates. In the course of the study, it was found that the lake is dominated by OAR-footed Scorpions, oligochetes, chironomid larvae, ashamurt Scorpions, slug worms. High-altitude Scorpions, leeches, leeches, and water mites are rare. The article considers the problem of reducing the water level of Lake Zaisan from one hundred to five hundred meters over the past year. It is worth noting that the number of benthos organisms has also decreased, as the areas of coastal reeds and algae have dried up. In addition, it is concluded that the ichthyofauna of the lake has also decreased. The result of this research work can be applied to the standard curriculum of the discipline zoology. The information contained in the article can be used by students studying at biological faculties of higher educational institutions, biology teachers in secondary schools. It will be interesting for secondary schools near Lake zaisan to use the identified invertebrates and their photos as a local component.

What is the spatial-temporal behavior of a low, medium and high adsorptive compound in two contrasting natural sediments in OECD 218/219 test systems?

Artificial sediment used in studies according to OECD 218/219 (Sediment Water Chironomid Toxicity Test Using Spiked Sediment/Water) does not necessarily mirror the characteristics of natural sediments. To investigate the influence of sediment characteristics on the spatial-temporal behaviors of bixafen (KfOM = 2244 mL/g), fluopyram (KfOM = 162 mL/g) and N,N-dimethylsulfamide (KfOM ≈ 0 mL/g), experiments according to OECD 218/219 with two contrasting natural sediments were conducted. The silt loam sediment provided a high content of organic matter (OM) (13.1%), while the OM (0.45%) of the sandy sediment was low. Diffusion into (OECD 219) or out (OECD 218) of the sediment was dependent on the extent of adsorption, which is linked to the model compounds ́ adsorption affinities and the sediments ́ OM. Consequently, N,N-dimethylsulfamide showed unhindered mobility in each experimental set up, while the high adsorption affinities of fluopyram and bixafen limited the diffusion in the respective sediments. Therefore, in experiments with the silt loam sediment, both compounds revealed a limited mobility and either accumulated in the top 5 mm of the sediment (OECD 219) or remained homogenously distributed over the sediment depth (OECD 218). A greater mobility was observed within the sandy sediment.The influence of OM as found in a study using artificial sediment could be confirmed. Moreover, the applicability of a TOXSWA model was reassured to predict the measured concentrations at different sediment depths. TOXSWA is used in the regulatory exposure assessment to simulate the behavior of pesticides in surface waters. Calibration of three driving input parameters by inverse modelling (diffusion-, adsorption coefficient and OM) revealed no potential for improvement. The core sampling technique used and the model may contribute to a more realistic determination of concentration to which the Chironomid larvae are exposed to. This applies to water sediment test systems where the test organisms do not evenly inhabit the sediment.

The Level of Ecological and Hydrobiological Indicators in the Cheboksary Reservoir

The paper assesses the ecological state of the Cheboksary reservoir based on the criteria of the total abundance, biomass, and species diversity of phytoplankton, zooplankton, and benthos. During the study period, no significant changes in the indicators of the development of algocenoses, their distribution over the water area of the reservoir were noted. The average phytoplankton biomass for the reservoir turned out to be in the dynamic norm, the trophic status was assessed as eutrophic; The revealed ratios of the leading systematic groups of planktonic algae and the composition of cenosis-forming species had also been in the previous years of the study. According to the level of the saprobity index, all sampling stations belong to class III (moderately polluted waters). The benthos of the reservoir was also characterized by sufficient diversity with the dominance of mollusks and chironomid larvae in the taxonomic composition. Thus, despite the presence of a certain anthropogenic impact on the water area of the Cheboksary reservoir, its hydrobiological state remains satisfactory, which is determined by a wide buffer limit to the level of pollution of the water body.

New technique of sample preparation of Quaternary lake sediments for palynological and chironomid (Insecta: Diptera) analyses

Almost six-years’ experience of my work on isolation and study of macrofossils of chironomid larvae showed that the conventional technique of lake sediment sampling has significant drawbacks. This paper describes the author’s method of sample preparation of lake sediments to isolate and determine macrofossils of Chironomidae larvae for paleoclimatic reconstruction. The advantage of the proposed technique is better washing of sediment samples, which facilitates a more complete sampling of the macrofossils, as well as its applicability for palynological analysis.

Вирощування цьоголіток коропа із застосуванням суспензії хлорели (Chlorella (Beijerinck,1890))

Purpose. Investigate ecological conditions and determine fish productivity of ponds when growing young-of-the-year carp using a suspension of chlorella. Methodology. During the study, we used methods generally accepted in hydrochemistry, hydrobiology and fish farming. Findings. The article presents the results of the study on the use of chlorella suspension in the cultivation of carp. It was found that the use of chlorella suspension created favorable hydrochemical conditions resulting in intensive development of zooplankton, which had a positive effect on the growth of young-of-the-year carp and fish productivity of the pond. The development of the natural food supply was sufficient to meet the nutritional needs of juvenile carp. The average seasonal biomass of zooplankton in the experimental pond was 28.68 g/m3 that was 1.5 times higher than in the control. The share of cladocerans in the total biomass of zooplankton in the experimental pond was 76.6%, versus 36.8% in the control. The average biomass of zoobenthos for the growing season in the experimental was 1.3 times higher than in the control, and was formed by chironomid larvae, which are valuable in the food chain. Originality. The study investigated ecological conditions and fish productivity of growing ponds under conditions of the application of cattle manure and suspension of chlorella when growing carp in monoculture. Practical value. It was found that the use of chlorella suspension promotes the intensification of the development of zooplankton organisms in ponds. The obtained data can be used to develop practical recommendations for optimizing the conditions for growing carp seeds and increasing the biological productivity of ponds. Key words: nursery ponds, natural food supply, phytoplankton, zooplankton, zoobenthos, young-of-the-year carp, chlorella suspension, fish productivity.

Warming Decreases Bioconversion of Polyunsaturated Fatty Acids in Chironomid Larvae Maintained on Cyanobacterium Microcystis.

Cyanobacteria dominance and warming have been suggested to decrease the production of polyunsaturated fatty acids (PUFA) in freshwater ecosystems. Physiological adaptations of poikilothermic animals to higher temperatures may further decrease PUFA levels in aquatic food webs. We conducted diet manipulation experiments to investigate the combined effects of dietary PUFA and warming on the proportions of eicosapentaenoic acid (EPA) and arachidonic acid (ARA) in Chironomus riparius. The experimental diet consisted of a nontoxic cyanobacterium Microcystis, which contained C20 PUFA: 20:3n-3, 20:4n-3, and 20:3n-6, but no EPA or ARA. Additionally, we used TetraMin® fish flakes as a control treatment. A temperature increase from 20 °C to 25 °C decreased the proportion of n-3 C20 PUFA and the n-3/n-6 ratio in Microcystis. Diet manipulation experiments indicated that Chironomus desaturated dietary C20 precursors to EPA and ARA, but warming decreased this bioconversion and resulted in lower levels of EPA and ARA in Chironomus. Warming did not alter the proportions of EPA and ARA in Chironomus larvae if these PUFA were readily available in the diet (TetraMin® control treatment). In conclusion, warming and cyanobacteria dominance may decrease the production and trophic transfer of physiologically important PUFA in freshwaters by (1) decreasing the n-3/n-6 ratio and the abundance of n-3 C20 precursors in Microcystis, and (2) decreasing the bioconversion of n-3 and n-6 C20 precursors to EPA and ARA in chironomids. These changes may have cascading effects throughout the food web and decrease the content of EPA in fish, potentially affecting its availability to humans.

Growth and diet of inanga (Galaxias maculatus) within a small New Zealand coastal pond system

ABSTRACT Inanga (Galaxias maculatus) are found in a range of freshwater habitats around much of the Southern Hemisphere. Although they are reasonably well studied within New Zealand, little is known about the populations found in coastal pond systems. This study focussed on inanga diet and population dynamics within a shallow pond complex in coastal Southland, investigating age, growth, distribution, and diet of juvenile inanga over a spring to autumn period. Otolith analysis indicated a three-month period (September to November) during which fish are hatching, with fish that hatched earlier growing more slowly than later fish. Inanga were found in only one location within the pond complex – a site featuring low water nutrient levels and less access by trout. Diet analysis showed high selectivity for chydorids and chironomid larvae, indicating a mixture of both benthic and pelagic foraging. Overall, this study has provided insight into inanga population dynamics in ponds, which have not previously been observed.

A preliminary investigation of umbellate inflorescences in Vallisneria americana populations of Central Florida

Vallisneria americana typically produces solitary pistillate inflorescences; however, unusual umbellate flowers have been observed in sub-tropical populations and are reported as rare. There are multiple hypotheses regarding the origin or cause of umbellate inflorescences—they may be relics of ancestral stocks surviving through asexual reproduction, heritable traits worthy of taxonomic recognition, or teratological specimens resulting from injury during flower formation. Through surveys of Vallisneria populations in four lakes in Central Florida, USA, we show these umbellate flowers are broadly distributed and we document their physical and reproductive traits, contrasted with solitary capsules (capsule number, capsule length and width, seed number, germination). Umbellate inflorescences were found frequently across space and time—capsules were found in three of four lakes, 40–80 % of the times flowering was observed. Umbellate inflorescences produced fewer seeds than solitary capsules, despite having 2–33 capsules per inflorescence. Seeds from umbellate capsules were viable, but germination occurred more slowly and at a lower percentage than seeds from solitary capsules. Nematodes were not detected within sampled inflorescences. Chironomid larvae were detected at a high rate (75–80 %) in umbellate capsules from two of three lakes but were not found on solitary capsules, suggesting they may be a possible cause for teratological growth. We conclude umbellate inflorescences are broadly distributed in Central Florida lakes and, while not sterile, they may have reproductive costs. Further study is needed to fully evaluate the cause of umbellate formation, population-level effects, and their range within Vallisneria americana.

Accumulation of polychlorinated biphenyls (PCB) associated with bottom sediments in larvae of Chironomus riparius Meigen

Patterns of bioaccumulation of polychlorinated biphenyls (PCBs) by chironomid larvae (Chironomus riparius Meigen) were studied under laboratory conditions. Larvae were maintained for 20 days, separately in two batches of natural bottom sediments sampled from Rybinsk Reservoir (Russia), each differing in PCB content (425.6 μg / kg or 24.8 μg / kg dry weight, respectively). The study revealed that chironomid larvae accumulated PCBs at levels comparable to the PCB content measured in sediments from each exposure. The bioaccumulation coefficient (1.11 and 1.59, respectively, as per dry weight for compared sediment batches) depended directly on the sum PCB content in sediments. At high sediment PCB content, the ratios of homologous groups of PCBs in larvae and sediment were identical and corresponded to the Aroclor 1254 congeners profile; at lower PCB content, pronounced differences were revealed. In larvae, the ratios of 3, 4, 5, and 6CB homologues were evenly distributed at levels of 20–34 %, while the 4CB homologues prevailed (47 %) in sediments. The content of the latter compounds in larvae was lower than in sediments, and higher for the other homologous groups. The study indicates selective bioaccumulation of various homologous groups of PCBs under conditions of low sediment PCB content.

Carbon sources of benthic fauna in temperate lakes across multiple trophic states

Abstract. Previous studies have shown that microbially produced methane can be a dominant carbon source of lacustrine sedimentary macrofauna in eutrophic lakes, most likely through grazing on methane-oxidizing bacteria. Here we investigate the contributions of different carbon sources to macrofaunal biomass across five lakes in central Switzerland that range from oligotrophic to highly eutrophic. Macrofaunal communities change with trophic state, with chironomid larvae dominating oligotrophic and tubificid oligochaetes dominating eutrophic lake sediments. The 13C-isotopic data suggest that the average contribution of methane-derived carbon to the biomass of both macrofaunal groups is similar but consistently remains minor, ranging from only ∼1 % in the oligotrophic lake to at most 12 % in the eutrophic lakes. The remaining biomass can be explained by the assimilation of detritus-derived organic carbon. Low abundances of methane-cycling microorganisms in macrofaunal specimens, burrows, and surrounding sediment based on 16S ribosomal RNA (rRNA) gene sequences and copy numbers of genes involved in anaerobic and aerobic methane cycling (mcrA, pmoA) support the interpretation of isotopic data. Notably, 16S rRNA gene sequences of macrofauna, including macrofaunal guts, are highly divergent from those in tubes or sediments. Many macrofaunal specimens are dominated by a single 16S rRNA phylotype of Fusobacteria, α-, β-, γ-, or ε-Proteobacteria, Bacteroidetes, or Parcubacteria. This raises the question of whether dominant lake macrofauna live in so far uncharacterized relationships with detrital organic-matter-degrading bacterial endosymbionts.

Single and combined effects of microplastics, pyrethroid and food resources on the life-history traits and microbiome of Chironomus riparius

There is growing evidence of widespread contamination of freshwater ecosystems with microplastics. However, the effects of chronic microplastic ingestion and its interaction with other pollutants and stress factors on the life-history traits and the host-microbiome of aquatic invertebrates are not well understood. This study investigates the effects of exposure to sediment spiked with 1 μm polystyrene-based latex microplastic spheres, an environmentally realistic concentration of a pyrethroid pesticide (esfenvalerate), and a combination of both treatments on the life-history traits of the benthic-dwelling invertebrate, Chironomus riparius and its microbial community. The chironomid larvae were also exposed to two food conditions: abundant or limited food in the sediment, monitored for 28 and 34 days respectively. The microplastics and esfenvalerate had negative effects on adult emergence and survival, and these effects differed between the food level treatments. The microbiome diversity was negatively affected by the exposure to microplastics, while the relative abundances of the four top phyla were significantly affected only in the high food level treatment. Although the combined exposure to microplastics and esfenvalerate showed some negative effects on survival and emergence, there was little evidence for synergistic effects when compared to the single exposure. The food level affected all life-history traits and the microbiota, and lower food levels intensified the negative effects of the exposure to microplastics, esfenvalerate and their combination. We argue that these pollutants can affect crucial life-history traits such as successful metamorphosis and the host-microbiome. Therefore, it should be taken into consideration for toxicological assessment of pollutant acceptability. Our study highlights the importance of investigating possible additive and synergic activities between stressors to understand the effects of pollutants in the life story traits and host-microbiome.