Caddisfly Larvae Research Articles

Siberian sturgeon Acipenser baerii (Brandt, 1869) (Acipenseridae) of the Yenisei river. Part 1. Herd structure (overview)

Siberian sturgeon is widely distributed in the river basin. Yenisei. Its range, the structure of the herd, including residential and semi-anadromous forms, and the scheme of migrations are described. The concept of population continuums is analyzed. Sturgeon is one of the largest fish on the river. Yenisei, reaches 124 kg of mass. It is shown that over 100 years of research, the linear and weight growth of the Yenisei sturgeon remains at the same level. Late sexual maturation of this species has been recorded: males become sexually mature at the age of 17–19 years, females mature at the age of 20–24 years. The intervals between successive spawnings in females are 5–6 years, males — 3–4. Absolute individual fecundity ranges from 50 to 750 thousand eggs. By the nature of the diet of sturgeon in the basin of the river. The Yenisei is a benthophage that consumes the larvae of chironomids, caddisflies, stoneflies, mayflies, midges, amphipods, and oligochaetes. Age and sex differences in nutrition are not observed. Information about the organization of sturgeon fishing on the river is given. Yenisei since the middle of the 19th century. The main share of the prey of this species fell on the lower reaches of the river; the catch of the spawning part of the population during the spawning migration brought about 10% of the total prey. It is noted that large-scale anthropogenic impacts have significantly changed the habitat of this species. The number and stocks of the Siberian sturgeon in the basin of the river. The Yenisei was noticeably reduced by the beginning of the 21st century.

Preliminary Study of the Relationship Between Caddisfly Larvae and Environmental Variables in Şimşir Stream (Karabük, TURKEY)

Şimşir Stream is located in Yenice Forest, which has been selected as one of the 100 forest hotspots with high biodiversity and needs urgent protection, and the study area includes two protection zones. Determining the current situation in an area that has not yet been exposed to human influence helps to monitor the response of the rivers in cases that may arise later, such as climate change, pollution, land use, and morphological degradation. Trichoptera are one of the most important groups of macroinvertebrates used to assess such disturbances in streams. Trichoptera larvae were collected from 8 stations along the Şimşir Stream during 2019 and 2020 seasonally by kick-sampling. During this investigation, 17 genera belonging to 15 families were identified. Environmental variables were recorded to determine the relationship with larvae. Most of the stations, except the station located on the tributary, showed positive correlations with water velocity, dissolved oxygen, pH, electrical conductivity, and stream width. It was found that the rate of the boulder in the substrate was one of the most important variables affecting the distribution of larvae. The only station that was sampled in the tributary of the stream had different taxa from other stations, and this showed the contribution of the tributary to the fauna.

Caddisfly Larvae are a Driver of Plastic Litter Breakdown and Microplastic Formation in Freshwater Environments.

Plastic litter is now pervasive in the aquatic environment. Several marine and terrestrial organisms can fragment plastic with their feeding appendages, facilitating its breakdown and generating microplastics. However, similar studies with freshwater organisms are extremely limited. We explored the interactions between the caddisfly larvae Agrypnia sp. and polylactic acid (PLA) film. The use of plastic by larvae to build their protective cases was investigated, along with their ability to fragment the plastic film as they do with leaf litter. Caddisfly consistently incorporated PLA into their cases alongside leaf material. They also used their feeding appendages to rapidly fragment PLA-forming hundreds of submillimeter-sized microplastics. Although larvae showed a preference for leaf material when constructing cases, plastic use and fragmentation still occurred when leaf material was replete, indicating that this behavior is likely to occur in natural environments that are polluted with plastics. This is thought to be the first documented evidence of active plastic modification by a freshwater invertebrate and therefore reveals a previously unidentified mechanism of plastic fragmentation and microplastic formation in freshwater. Further work is now needed to determine the extent of this behavior across freshwater taxa and the potential implications for the wider ecosystem. Environ Toxicol Chem 2022;41:3058-3069. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Case design and flow resistance in high-alpine caddisfly larvae (Insecta, Trichoptera)

For evaluating hydraulic stress reduction strategies of caddisfly larvae, our study has three goals. First, creating a database on Reynolds numbers (Re) and drag coefficients valid for Limnephilidae larvae with cylindrical mineral cases. Second, evaluating the effects of submerged weight and biometry in cases with comparable length/width ratios. And third, collecting field data in an alpine environment for gaining insights into the hydraulic niches occupied by thirteen Drusinae species. Biometric data were subsequently combined with published Reynolds numbers and mean flow velocity data measured immediately upstream of Limnephilidae larvae at the moment of dislodgement. This provides drag coefficients for the range of Reynolds numbers obtained in the field. Data reveal that heavy cases strongly benefit from compensating drag by submerged weight, thereby enabling species to utilize high velocity spots, an important benefit for filtering species.

Mild temperatures differentiate while extreme temperatures unify gene expression profiles among populations of Dicosmoecus gilvipes in California.

Accurately predicting the effects of future warming on aquatic ectotherms requires an understanding how thermal history, including average temperature and variation, affects populations of the same species. However, many laboratory studies simplify the thermal environment to focus on specific organismal responses and sacrifice environmental realism. Here, we paired laboratory-based transcriptomic RNA-seq analysis to identify thermally responsive genes with NanoString analysis of a subset of those genes to characterize natural field-based variation in thermal physiology among populations. We tested gene expression responses of three populations of field-acclimatized larval caddisflies (Dicosmoecus gilvipes) from streams in different eco-regions (mountain, valley, and coast) following exposure to current and future summertime temperatures. We hypothesized that distinct thermal histories across eco-regions could differentiate populations at baseline “control” levels of gene expression, as well as gene expression changes in response to daily warming and heat shock. Population-specific patterns of gene expression were apparent under the control and daily warming conditions suggesting that local acclimatization or local adaptation may differentiate populations, while responses to extreme temperatures were similar across populations, indicating that response to thermal stress is canalized. Underlying gene co-expression patterns in the daily warming and heat shock treatments were different, demonstrating the distinct physiological mechanisms involved with thermal acclimatization and response to thermal stress. These results highlight the importance and limitations of studies of the thermal biology of wild-caught organisms in their natural environment, and provide an important resource for researchers of caddisflies and aquatic insects in general.

Vertical reworking of sediment by the cased caddisfly Glossosomatidae (Agapetus fuscipes) increases sand exposure and availability in armoured gravel-bed rivers

Landscapes and ecosystems are the result of two-way interactions between hydro-geomorphic and biological processes. Many animals, particularly those that build structures or transport sediment, are important biogeomorphic agents. Glossosomatidae caddisfly larvae (Insecta, Trichoptera) are globally widespread and abundant inhabitants of gravel-bed rivers. Glossosomatidae build mobile cases from sand that they transport over the river bed. However, there is limited understanding on how Glossosomatidae bioconstructions may influence sand distribution in rivers or how their zoogeomorphic behaviours are influenced by hydraulics or characteristics of the river bed. First, we conducted surveys to quantify the magnitude of sand incorporated into Glossosomatidae (Agapetus fuscipes) cases within a UK river. Second, we studied A. fuscipes movement behaviour and quantified the direction and magnitude of sediment reworking, in a flume, under differing flow velocity and gravel size treatments. We found that 99 % of A. fuscipes larvae transported sediment vertically upwards. This resulted in an average conveyance per larvae of 0.06 g sand upwards by 25 mm (maximum of 50 mm). In gravel beds with a coarse surface layer, this resulted in displacement of sand from sheltered interstices onto the surface of exposed gravel particles. In the flume, this behaviour was maintained even at high flows, sufficient to entrain empty cases from these locations. Whilst the mass of sediment moved by individual larvae is small, dense populations of Glossosomatidae larvae may have important consequences for the vertical distribution of sand in rivers. At our field site, A. fuscipes case density averaged 2192 cases m−2, equivalent to 1.4 t km−1. This finding is important because in gravel-bed rivers frequented by Glossosomatidae larvae, sediment transport is typically limited by the availability of entrainable fine grain sediment at the surface. We discuss the implications of this sediment movement for river bed sedimentary structure, the transport of sand and gravel, and the possible role of Glossosomatidae larvae as ecosystem engineers.

Habitat preferences and trophic interactions of the benthic invertebrate communities inhabiting depositional and erosional banks of a meander from Danube Delta (Romania)

River restoration and biodiversity conservation programs require an in-depth knowledge of the influence that sediment composition and hydraulic stress have on invertebrate fauna composition and spatial distribution, as well as on nutrients cycling and food webs’ structure and functionality. Compared to low-order streams, the traditional focus of river ecology, the knowledge of these ecosystem properties of the meanders developed along large, lowland watercourses, is currently insufficient. The present study assessed the ecological preferences and the trophic interactions of the benthic invertebrate communities inhabiting erosional and depositional banks developed within a meander of the River Danube flowing through its delta (Danube Delta, Romania). The invertebrates from two mesohabitats, the concave (i.e. erosional) and convex (i.e. depositional) banks developed in the apex region of the meander were sampled quantitatively and qualitatively, along with sediment samples for assessing the grain-size characteristics and hydrodynamic parameters (i.e., critical shear stress, the Reynolds number, the critical velocity and Shields parameter). For assessing their mesohabitat preferences, quantitative samples were taken from both banks, whereas for inferring the trophic interactions, stable isotopes of δ15N and δ13C were measured from qualitative samples, comprising both invertebrates and basal resources. The results showed that increased siltation with fine sediments in the depositional bank led to a community dominated by chironomids, oligochaetes and bivalves, whereas the opposite bank comprised crayfish, caddis fly larvae and amphipods with a preference for coarser sediments. The δ13C of most consumers revealed that the dominant forms of carbon entries in the analysed food webs were photosynthetic based, whereas certain snails, chironomids and basal resources from the depositional bank were 13C depleted (δ13C: −35 to −39 ‰). Such low ratios for δ13C (mean < −35 ‰) reflected the potential of carbon entry through the base of depositional food web as a result of methane oxidation at sediment-water interface (i.e. chemosynthesis), induced by the fine sediments deposition that could have favoured the methane production. Grazing methane-oxidising bacteria in the depositional meander bank could have provided the primary consumers with up to 50 % and the omnivores and predatory invertebrates with up to 30 % of their carbon, which could represent an important subsidy from an additional, chemosynthetic source. The impact of a supplementary carbon input was further reflected in increasing depositional food web basal niche diversity, which led to distinct trophic niches and lower interspecific competition of consumers compared to the erosional bank of the meander.

Caddisflies Stenopsyche marmorata (Trichoptera: Hydropsychidae) exploit river mussels as anchors for their nets

In the foothill rivers of the south of Primorsky Krai (Russian Federation), during the abnormally hot summer-autumn season of 2021, the number of net-spinning larvae of the caddisflies Stenopsyche marmorata Navas, 1920 (Stenopsychidae) sharply increased. Here we describe the phenomenon of widespread use by these caddisfly larvae of the shells of live bivalves Middendorffinaia Moskvicheva et Starobogatov, 1973 (Unionidae) to attach their feeding nets. As a result, the immobilized river mussels could not move to the deeper sites for wintering, and in the coming winter season they died due to freezing into ice. The described phenomenon illustrates the indirect negative impact of climate change on vulnerable species of river biota.

Species-specific traits predict whole-assemblage detritus processing by pond invertebrates.

Functional trait diversity determines if ecosystem processes are sensitive to shifts in species abundances or composition. For example, trait variation suggests detritivores process detritus at different rates and make different contributions to whole-assemblage processing, which could be sensitive to compositional shifts. Here, we used a series of microcosm experiments to quantify species-specific coarse and fine particulate organic matter (CPOM and FPOM) processing for ten larval caddisfly species and three non-caddisfly species in high-elevation wetlands. We then compared trait-based models including life history, dietary, and extrinsic traits to determine which traits explained interspecific variation in detritus processing. Finally, we compared processing by mixed caddisfly assemblages in microcosms and natural ponds to additive predictions based on species-specific processing to determine if single-species effects are additive in multi-species assemblages. We found considerable interspecific variation in biomass-specific CPOM (13-fold differences) and FPOM (8-fold differences) processing. Furthermore, on a mass-specific basis, amphipods, chironomids, and caddisflies processed similar amounts of detritus, suggesting non-shredder taxa could process more than previously recognized. Trait models including dietary percent detritus, development rate, body size, and wetland hydroperiod explained 81 and 57% of interspecific variation in CPOM and FPOM processing, respectively. Finally, species-specific additive predictions were strikingly similar to mixed-assemblage processing in microcosms and natural ponds, with the largest difference being a 15% overestimate. Thus, additivity of species-specific processing suggests single-species rates may be useful for understanding functional consequences of shifting assemblages, and a trait-based approach to predicting species-specific processing could support generating additive predictions of whole-assemblage processing.

Seasonal Occurrence of Caddisfly Larval Communities on a Coarse Substrate in the Upper Nan River, Northern Thailand

Abstract Caddisfly larvae are commonly found in the Nan River. Larvae were collected monthly from a cobble habitat for a period of two years to study the influence of seasonal changes on larval communities. A Surber sampler was placed in the cobble habitat in the riffle zone at four study sites along the upper Nan River. Field-collected larvae were identified at the family level in the laboratory. Physicochemical factors were measured in terms of water temperature, pH, turbidity, dissolved oxygen (DO) and biochemical oxygen demand (BOD5), as well as for concentrations of ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N) and orthophosphate (PO43-). Fifteen families of the caddisflies were found. The cool season was associated with the highest degree of density followed by the summer and rainy seasons. Hydropsychidae was the most common caddisfly present throughout the year. Hydroptilidae was common in the summer and cool seasons. Values of water temperature, pH, turbidity, DO, BOD5 and NO3-N among the three seasons were observed to be significantly different. According to the CCA analysis, water temperature, turbidity, BOD5, NO3-N and NH3-N factors had a positive relation to the density of Ecnomidae, Goeridae, Odontoceridae and Polycentropodidae. Remarkably, caddisfies in the families Hydropsychidae, Rhyacophilidae and Stenopsychidae were intolerant to variations in DO and pH values. The results of our study indicate that the physicochemical factors varied in conjunction with the different seasons, while communities and the degree of density of some caddisfly larvae were associated with variations of the physicochemical factors. Keywords: Trichoptera, Cobble, Environmental factors, Season

Intra- and interspecific competition resulting from spatial coexistence among larvae of closely-related caddisflies from the genus Hydropsyche.

Caddisfly larvae commonly inhabit freshwater ecosystems, where they often create multi-species aggregations. However, while several strategies have been developed to avoid or reduce inter- and intraspecific interactions, most species choose the same time to seek a suitable place for pupation, which can increase competition. The current study assesses the competitive interactions among larvae (5th instar) of three co-existing Hydropsyche species, viz. H. contubernalis, H. pellucidula, and H. modesta, analysing their direct one-on-one interaction and various morphological features, such as size, weight, and mandibles. More than half of the interspecific conflicts ended with a draw, and 80% of intraspecific interactions with a decisive outcome. In fights between species, H. pellucidula was the most successful, and H. modesta the weakest. Our results confirm that among the larvae, competitive interactions were usually decided by body size, especially that of the head capsule. Although wider head capsule and higher weight were advantageous for ~60% of winning larvae, there were no distinct winning species. The chewing mouthpart turned out to be supportive in the fight: regardless of the species, longer and wider mandibles were significant for winning specimens, but not the distance between mandibles. Hence, acquiring a suitable place for pupation is determined by the possession of certain features enhancing the fighting potential of individual larvae, which does not exclude any species from the possibility of closing the life cycle. Future studies on interactions among caddisfly larvae could include experience in fights, volitional features and stridulation (not tested).

Radiocesium-bearing microparticles cause a large variation in 137Cs activity concentration in the aquatic insect Stenopsyche marmorata (Tricoptera: Stenopsychidae) in the Ota River, Fukushima, Japan.

After the Tokyo Electric Power Company Fukushima Daiichi Nuclear Power Plant accident in Japan, freshwater ecosystems near the site remained contaminated by radiocesium (RCs). Clarifying RCs concentrations in aquatic insects is crucial because fishes consume these insects that transfer RCs into freshwater ecosystems. As aquatic insects are usually measured for radioactivity in bulk samples of several tens of insects, variation in RCs concentration among individuals is not captured. In this study, we investigated the variability in 137Cs activity concentration in individual aquatic insects in detritivorous caddisfly (Stenopsyche marmorata) and carnivorous dobsonfly (Protohermes grandis) larvae from the Ota River, Fukushima. Caddisfly larvae showed sporadically higher radioactivity in 4 of the 46 caddisfly larvae, whereas no such outliers were observed in 45 dobsonfly larvae. Autoradiography and scanning electron microscopy analyses confirmed that these caddisfly larvae samples contained radiocesium-bearing microparticles (CsMPs), which are insoluble Cs-bearing silicate glass particles. CsMPs were also found in potential food sources of caddisfly larvae, such as periphyton and drifting particulate organic matter, indicating that larvae may ingest CsMPs along with food particles of similar size. Although CsMP distribution and uptake by organisms in freshwater ecosystems is relatively unknown, our study demonstrates that CsMPs can be taken up by aquatic insects.

Ecological aspects of water quality investigation in connection with projects of hydropower plants' construction on the Timpton River, Yakutia, Russia

An intensification of industrial development of the Republic of Sakha (Yakutia) involves the Kankunskaya hydropower plant construction project, implementation of which would have a drastic impact on the ecological state of surface waters within the Timpton River basin. A necessary stage of all pre-construction survey work is the initial environmental state assessment. In this regard, a study of baseline hydrochemical and hydrobiological state of water, including an investigation of phytoperiphyton and benthic fauna, has been carried out. As a result, it has been found a low salinity of waters, a small nutrients' content, and an increased heavy metals' content. It has been discovered 12 new species of algae for the water bodies of Yakutia and 92 new species in the Aldan River basin. The modern composition of the benthic fauna includes 8 taxonomic groups, the dominant position is occupied by the larvae of caddisflies and chironomids. The quantitative parameters of the zoobenthos of the watercourses of the Timpton River are low: during the study period, the biomass varied within 0–0.9 g/m2 at a density of 0–72 ind./m2.

Pharmaceuticals are identified in insects in River Fyris – A study with both tandem quadrupole and quadrupole-time-of-flight mass spectrometry

The internal concentrations of active pharmaceutical compounds in insects/macroinvertebrates in River Fyris, Uppsala, Sweden, have for the first time been investigated. Specimen of backswimmer, caddisfly larva, damselfly larva, mayfly larva and water louse were caught in the river downstream a waste-water treatment plant. After homogenization and extraction, analysis was carried out with Ultra-High Performance Liquid Chromatography – Electrospray – Tandem Mass Spectrometry (UHPLC-ESI-MS/MS) using both a tandem quadrupole (QqQ) and a quadrupole-time-of-flight (qToF) mass spectrometer. A combined qualitative/quantitative screening method for 89 pharmaceutical compounds in the selective reaction monitoring mode was applied to the samples using the QqQ instrument. Thirty-three different drugs were detected and quantified in the macroinvertebrate samples, covering a wide range of pharmacological classes, the most common being antidepressants, psycholeptics and antihistamines. Drug concentrations up to 260 ng/g (for tetracycline) were determined. A subset of thirteen compounds were selected for a complementary qualitative UHPLC-qToF-MS/MS analysis. This way, the confidence in the substance identifications was significantly strengthened by the availability of full scan high-resolution spectra and accurate mass measurements. This is the first study demonstrating the uptake of pharmaceuticals in water-living macroinvertebrates in Sweden. Since these organisms are in the lower part of the food chain, pharmaceuticals might accumulate in predators leading to ecotoxicological effect at higher trophic levels. Macroinvertebrates might be promising indicator organisms for pharmaceutical pollution.

Following the fate of microplastic in four abiotic and biotic matrices along the Ticino River (North Italy)

Microplastics (MPs) are emerging contaminants in freshwater systems that have already attracted much scientific interest, but little attention has been paid to a multi-matrix analysis of MP occurrences along the length of a river. The present research provides the first record of MP contamination of four abiotic and biotic matrices from a river ecosystem simultaneously analysed. MPs were isolated and identified by micro-Fourier Transform Infrared (μ-FTIR) spectroscopy from samples collected along the Ticino River in North Italy during spring 2019. Abiotic samples were surface water (n = 18, 33 MPs m−3) and sediment (n = 18, 11 MPs kg−1), while biological samples consisted of stomach and gut content of fish (n = 18, wels catfish, Silurus glanis, 0.032 MPs g−1) and macroinvertebrates (n = 90, caddisfly larvae, Hydropsychidae, 0.03 MPs mg−1). MPs were found in biota from all stations; 44% of fish and 61% of macroinvertebrate samples contained MPs. The calculated unit-consistent concentration ratios indicate that both S. glanis and Hydropsychidae larvae had a consistent higher amount of MPs than their respective medium (sediment and water), strongly suggesting an efficient uptake pathway into organisms. MP levels in surface water, sediment, fish and macroinvertebrates were not correlated and did not increase with the river's length. From our mass balance calculations, the Ticino River transports a consistent amount of MP (yearly load of 3.40 × 1011 ± 1.1 × 1011 MPs) to the Po River. This MP load was almost half than an estimated MP load from wastewater treatment plants (WWTPs). On that basis and supported by the finding that MP concentration in sediment was mostly opposed to that in surface water but was on average 750-fold higher compared to the water matrix, we surmise that the complex hydrological network of the Ticino River retains a consistent amount of MPs which might build up over time.

Calcium and strontium stable isotopes reveal similar behaviors of essential Ca and nonessential Sr in stream food webs

AbstractRecent studies showed the potential of stable isotopes of the macronutrient calcium (δ44/40Ca) and nonessential strontium (δ88/86Sr) as new trophic level indicators in terrestrial vertebrates and marine teleost fishes. In this study, we tested whether similar Ca and Sr isotopic fractionation trends existed in macroinvertebrate‐dominated stream food webs compared to vertebrates despite their physiological differences. We have determined the δ44/40Ca and δ88/86Sr values as well as the 87Sr/86Sr ratios of stream macroinvertebrates and small gobies and their potential metal sources (stream water, periphyton, and terrestrial plant litter) in upper and lower reaches of two streams in the Lake Biwa catchment, central Japan. The 87Sr/86Sr ratios revealed that stonefly nymphs, crustacea, and gobies mostly relied on aquatic Sr sources. Higher 87Sr/86Sr ratios of some crane fly and caddisfly larvae, mayfly, dobsonfly, and dragonfly nymphs indicated greater terrestrial contributions via plant litter. Positive correlations between the δ44/40Ca and δ88/86Sr values implied that similar Ca and Sr sources existed, and that Ca and Sr stable isotopes underwent similar fractionation trends although Sr was not essential. The δ44/40Ca and partly the δ88/86Sr values were positively correlated with Sr/Ca ratios and negatively with δ15N values indicating trophic effects on Ca and Sr stable isotopes. The enrichment of 44Ca and 88Sr in large filter‐feeding caddisfly larvae was a notable exception from these trophic trends. Our data confirm that the trophic 44Ca and 88Sr depletion observed for marine teleost fishes and terrestrial vertebrates also applied to macroinvertebrate‐dominated stream food webs despite their different physiologies indicating that shared mechanisms of Ca and Sr isotopic fractionation may exist at the cellular or molecular level between these taxa.

The return to land: association between hairworm infection and aquatic insect development.

Host manipulation by parasites can shape host behaviour, community structure, and the flow of energy through food webs. A well-known example of host manipulation comes from hairworms (phylum Nematomorpha), which somehow cause their terrestrial insect definitive hosts to enter water, a phenomenon that has received lots of attention in recent years. However, little focus has been directed towards the interactions between hairworms and their aquatic insect hosts and the return of dormant hairworms from water to land. Here, we ask whether hairworm cyst infections impact, either directly or indirectly, the life history of their aquatic transport hosts. By observing the development of last-instar Olinga jeanae (Trichoptera: Conoesucidae) caddisfly larvae naturally infected with Gordius-type hairworm cysts under controlled conditions, we found that higher numbers of cysts per infected caddisfly correlated with a decrease in time to pupation. These new observations suggest that, apart from the striking host manipulation that brings the parasite from land to water, the presence of dormant hairworms is associated with changes in the development of their aquatic hosts, either through direct or indirect mechanisms, which may accelerate their transition from water to land.

БИОЛОГИЧЕСКАЯ ХАРАКТЕРИСТИКА НЕРЕСТОВОГО СТАДА СТЕРЛЯДИ ACIPENSER RUTHENUS (LINNAEUS, 1758) Р. СЕВЕРНАЯ ДВИНА

According to results of ichthyological monitoring of the sterlet population in the middle part of the Severnaya Dvina river in the spring period 2018–2020 established a greater dependence of the value of catches in stationary traps on the dynamics of the water level in the river, compared with water temperature. On the spawn places located in the middle part of the Severnaya Dvina river in the catches of stationary traps, sterlet dominates both in quantity and in mass. Average catch per unit of fishing effort (CPUE) is more dependent on water level dynamics than on water temperature. Age and length composition of sterlet catches is represented by two-thirds by fish of the younger age classes (3–5+) and small sizes (30–45 cm and 0.2–0.6 kg). The sexual structure of spawning sterlet represented by about 80% of males. The sterlet in the Severnaya Dvina river is currently grow faster than 70 years ago – probably due to an increase in the average water temperature in the river. In pre-spawning and spawning parts of sterlet population proportion of maturing and sexually mature females and males is 90%. The number of past-spawners increases with increasing water temperature. Currently, sterlet grows more slowly than in the 50–60s of the 20th century. Sterlet is intensively fed in the Severnaya Dvina river during the spawning period. In the middle part of the river, the basis of spring nutrition is chironomids and caddis fly larvae. Secondary fed objects are bivalve mollusks and blackfly. Random objects characterizing the nutritional spectrum in the spring include larvae of flies, butterflies, hemipterous and fish eggs. There are no significant differences in fed of sterlet with an increase in its size in the Severnaya Dvina river.

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.

Predators balance consequences of climate-change-induced habitat shifts for range-shifting and resident species.

While many species distributions are shifting poleward or up in elevation in response to a changing climate, others are shifting their habitats along localized gradients in environmental conditions as abiotic conditions become more stressful. Whether species are moving across regional or local environmental gradients in response to climate change, range-shifting species become embedded in established communities of competitors and predators. The consequences of these shifts for both resident and shifting species are often unknown, as it can be difficult to isolate the effects of multiple species interactions. Using a model system of insects in high-elevation ponds in the Rocky Mountains of Colorado, we sought to disentangle the effects of predation and intraguild interactions on the survival and development of a semi-permanent pond resident caddisfly Limnephilus externus and the habitat-shifting caddis Asynarchus nigriculus that is being forced into semi-permanent ponds as temporary ponds dry too quickly to complete development. We conducted a manipulative in-situ pond cage experiment in which L. externus and A. nigriculus caddisfly larvae in single-species treatments and together were exposed to the presence/absence of predatory Dytiscus diving beetle larvae. This approach allowed us to isolate the effects of intraguild interactions and predation on the survival and development of both the resident and habitat-shifting species. We found that intraguild interactions had strong negative effects on the resident and habitat-shifting species. Intraguild interactions reduced the survival of the resident L. externus and increased the variation in survival of the shifting A. nigriculus. However, Dytiscus predators reduced these negative effects, stabilizing the community by increasing L. externus survival and reducing variation in A. nigriculus survival. We also found that intraguild interactions reduced L. externus biomass but resulted in increased A. nigriculus development. A. nigriculus development was also increased by predation. Our results show that strong intraguild interactions between resident and shifting species are likely to have negative consequences for both species. However, the presence of predators reduces these negative consequences of the habitat shift on both the resident and the shifting.