Trophic Links Research Articles

Impact Assessment of the Amur Sleeper Perccottus glenii Dybowski, 1877 on Amphibians in Samara Oblast

The author found that in the study area, an invasive alien species of fish, the Amur sleeper Perccottus glenii, lives in 35 amphibian habitats. Of these, 14 are large water bodies, coastal areas and bays of watercourses, 21 are small water bodies. Larval development is completed by 8 species of tailless amphibians when they have the same habitats with the Amur sleeper. In 4 out of 17 examined populations of the European fire-bellied toad Bombina bombina, the cessation of larval development is noted in syntopic habitats with the Amur sleeper. The author assumes that the distribution of this invasive species is one of the factors in the disappearance of the common newt Lissotriton vulgaris and the European fire-bellied toad Bombina bombina populations in the reservoirs of Samara and Samarskaya Luka National Park. In the natural biotopes the distribution of the Amur sleeper is slower due to the presence of predators-fish and fish-eating reptiles. The marsh frog and the pool frog co-exist with the Amur sleeper; the green toad successfully spawns and undergoes larval development. The absence of common species of helminths confirms the absence of trophic links between the populations of the Amur sleeper and Amphibians in natural habitats of the study area

Do predatory adult odonates estimate their adult prey odonates’ body size and dispersal ability to proceed with a successful attack?

Predator-prey encounters are one of the most challenging behaviors that animals engage in and play a key role in structuring trophic linkages within food webs. Empirical studies suggest that predators (except pathogens, parasites, and parasitoids) tend to be larger in body size and have better dispersal ability than their prey items; however, when predators prey upon members of the same taxonomic group, it is unclear whether such relationships exist between predators and their prey items since both groups may have similar body sizes and dispersal abilities. Adult odonates can be used to test this as they prey upon other odonates within the same suborder, family, genus or species, although such records are uncommon. Using a dataset collected from Sri Lanka and India from 2012 to 2020, this study identified three types of predation behaviors between two suborders of Odonata, i.e., (i) Anisoptera (dragonflies) prey upon Anisoptera, (ii) Anisoptera prey upon Zygoptera (damselflies), and (iii) Zygoptera prey upon Zygoptera. There was no evidence of Anisoptera predation by Zygoptera. Study results showed strong evidence that there is a significant difference in body size (i.e., body length) and dispersal ability (i.e., hind-wing length) between adult predatory odonates and adult prey odonates for all three types of predations. This may indicate that predatory odonates estimate other odonate prey precisely to proceed with a successful attack.

Trophic ecology of a tropical scyphozoan community in coastal waters: Insights from stomach content and stable isotope analyses

Despite the growing concern of scyphozoan jellyfish blooms and their associated threats, there is an acute lack of baseline knowledge regarding the trophic ecology of scyphozoans in tropical waters where blooms of several species sometimes occur at once or successively. Therefore, this study was conducted from June 2010 to December 2011 in the Klang Strait (Malaysia) to elucidate the trophic ecology of eight sympatric species of scyphozoan that occurred in a conjoint mangrove-mudflat habitat. The species diet, trophic position and the relative contribution of primary producers to their nutrition were determined by integrating stomach content examination with stable isotope analysis. Scyphozoans in the Klang Strait are principally carnivores and can be grouped into three major trophic guilds: specialized copepod feeder, copepod and macrozooplankton feeder, and mixed plankton feeder. Bayesian mixing model of δ13C isotope values indicates that the scyphozoans mainly derived their basal carbon source from microphytobenthos and phytoplankton. Analysis of δ15N isotope values reveals that all species are positioned at the third trophic level after mixed zooplankton groups (second) and primary producers (first) in the food web. Scyphozoans thus represent an important trophic link coupling benthic and pelagic primary production to higher-level predators and humans, and are important carbon exporters from nearshore to neritic and offshore waters.

High biomass and productivity of epifaunal invertebrates living amongst dead coral

Climate change is transforming coral reef structures, with important yet largely unknown consequences for reef food webs. Crustaceans, molluscs, polychaetes, and other small motile invertebrates living as epifauna on coral habitats represent an essential trophic link between primary producers and a diverse and abundant invertivorous fish fauna. Here, we investigate variation in assemblages of motile epifaunal invertebrates on live coral and dead coral heavily overgrown by turf algae. Sampling was conducted 2–3 years following mass bleaching within the study region at four locations broadly spanning the distribution of corals on the eastern seaboard of Australia—along the northern and central Great Barrier Reef, and, adjacent to the central east coast, the Solitary Islands and offshore Elizabeth and Middleton Reefs (> 2000 km total distance). Epifaunal assemblages differed significantly between live and dead ‘turf-covered’ coral habitats, with overall density, biomass, and productivity of epifauna more than an order of magnitude greater on dead than on live coral. The size structure and composition of assemblages also differed: turf-covered dead coral supported greater abundances of small animals than live coral, notably harpacticoid copepods, while live coral assemblages had proportionally greater abundances of larger decapods. A ten-fold increase in secondary productivity of motile invertebrates is predicted as live corals are replaced by turf-covered dead coral, however, this productivity will predominantly be available as small harpacticoid copepod prey (size range: 0.125–0.25 mm). Associated flow-on effects through reef food webs are likely, as changes to epifauna will directly affect invertivore communities, which in turn potentially influence larger carnivores and other functional groups.

Structure of canopy and ground-dwelling arthropod communities in olive orchards is determined by the type of soil cover

The intensification of agriculture in olive groves, especially the modification or elimination of spontaneous vegetation, alters the relationships in arthropod communities and reduces their interactions and ecosystem services. This study was carried out in nine olive groves in which there was either a planted cover crop, spontaneous cover crop or bare ground. The interactions of ground-dwelling, canopy and flying arthropods in trophic webs were calculated for each olive grove soil management regime at the family level taking into consideration their different functional traits: feeding guilds, specific agricultural traits and trophic level. Olive groves with spontaneous cover had trophic webs with a higher number of plausible links between arthropod families and a more balanced distribution of specimens among trophic levels compared to those with planted cover and bare ground. There was a similar number of arthropod families consisting of both pests and their natural enemies in the planted cover regime, while olive groves with bare ground had simpler trophic webs. The complexity of plausible trophic links was greater in olive groves with spontaneous plant cover despite the similar values for family richness in the three-olive grove soil management regimes. Qualitative values (such as functional traits) were more diverse in agroecosystems with spontaneous plant cover in which there were more sources of food.

Long-Term Trends in the Occurrence of Disseminated Neoplasia in a Population of Mya arenaria (Softshell Clam) from a New Hampshire Estuary

Mya arenaria (Softshell Clam) is an important recreational and commercial bivalve in coastal New England, the mid-Atlantic, and elsewhere. The Softshell Clam is a filter feeder that provides a trophic link between planktonic food items and benthic predators. We quantified annual trends of disseminated neoplasia in Softshell Clams in the Hampton–Seabrook estuary in New Hampshire using logistic regression from 3975 individuals collected from 2002 to 2018. There was a negative trend in the incidence of Softshell Clams with non-detectable amounts of neoplastic cells, there was no significant trend in the incidence of stage 1 neoplasia (1–25% neoplastic cells), positive trends in the incidences of stages 2 and 3 (26–50% and 51–75% neoplastic cells), and no significant trends in incidence of stage 4 (76–100% neoplastic cells). The significant changes in neoplasia development suggest that the incidence of the disease is increasing. The lack of a significant trend in the terminal stage 4 neoplasia may be due to the short duration of this stage prior to death. Probabilities of acquiring stages 2 and 3 neoplasia in 2018 were 0.19 and 0.12, respectively. The mean length of Softshell Clams with stage 4 neoplasia was 66.7 mm (min–max = 53.2–78.1 mm), which indicates that terminal neoplasia occurs primarily in reproductive adults. The presence of advanced stages of the disease in sexually mature individuals can reduce the reproductive potential of that population.

Measuring Alloxanthin as a Proxy Approach in a Study of Trophic Relationships between Zooplankton and Cryptophyte Algae in Lake Shira

Cryptophyte algae are an important trophic link in many aquatic ecosystems, but they remain insufficiently studied in terms of trophic interactions with other components of ecosystems. They are better quality food than most other algae and, therefore, can be subject to selective grazing by zooplankton; thus, direct measurements of the dynamics of their concentration in lakes may give very low productivity indicators. One way to assess the consumption of cryptophyte algae by zooplankton is to determine the content of alloxanthin, a carotenoid specific for cryptophyte algae, in zooplankton. The present study investigated the alloxanthin content of sedimentary silts, sedimentation traps, and zooplankton of Lake Shira using high performance liquid chromatography. A significant correlation was found between the abundance of some zooplankton species capable of consuming cryptophyte algae and the flux of precipitated alloxanthin recorded in sedimentation traps. Analysis of zooplankton samples (the largest contribution to the biomass of which was made by the copepod Arctodiaptomus salinus (Daday, 1885)) for the content of carotenoids during the spring-summer season showed the presence of alloxanthin amounts reaching 80 μg/g, which decreased by the end of the season, and that correlated with the biomass of cryptophyte algae in the lake. Carotenoids associated with other groups of algae were observed in considerably smaller amounts. Thus, the copepod A. salinus exhibits high selective consumption of cryptophyte algae, which may serve as a confirmation of a close trophic relationship between them

Reconciling Behavioural, Bioenergetic, and Oceanographic Views of Bowhead Whale Predation on Overwintering Copepods at an Arctic Hotspot (Disko Bay, Greenland)

Bowhead whales (Balaena mysticetus) visit Disko Bay, West Greenland in winter and early spring to feed onCalanusspp., at a time of year when the copepods are still mostly in diapause and concentrated in near-bottom patches. Combining past observations of copepod abundance and distribution with detailed observations of bowhead whale foraging behaviour from telemetry suggests that if the whales target the highest-density patches, they likely consume 26–75% of theCalanusstanding stock annually. A parallel bioenergetic calculation further suggests that the whales' patch selection must be close to optimally efficient at finding hotspots of high density copepods near the sea floor in order for foraging in Disko Bay to be a net energetic gain. AnnualCalanusconsumption by bowhead whales is similar to median estimates of consumption by each of three zooplankton taxa (jellies, chaetognaths, and predatory copepods), and much greater than the median estimate of consumption by fish larvae, as derived from seasonal abundance and specific ingestion rates from the literature. The copepods' self-concentration during diapause, far from providing a refuge from predation, is the behaviour that makes this strong trophic link possible. Because the grazing impact of the whales comes 6–10 months later than the annual peak in primary production, and because Disko Bay sits at the end of rapid advective pathways (here delineated by a simple numerical particle-tracking experiment), it is likely that theseCalanuspopulations act in part as a long-distance energetic bridge between the whales and primary production hundreds or thousands of km away.

Role of food web interactions in promoting resilience to nutrient enrichment in a brackish water eelgrass (Zostera marina) ecosystem

AbstractUnderstanding the ecological interactions that enhance the resilience of threatened ecosystems is essential in assuring their conservation and restoration. Top‐down trophic interactions can increase resilience to bottom‐up nutrient enrichment, however, as many seagrass ecosystems are threatened by both eutrophication and trophic modifications, understanding how these processes interact is important. Using a combination of approaches, we explored how bottom‐up and top‐down processes, acting individually or in conjunction, can affect eelgrass meadows and associated communities in the northern Baltic Sea. Field surveys along with fish diet and stable isotope analyses revealed that the eelgrass trophic network included two main top predatory fish species, each of which feeds on a separate group of invertebrate mesograzers (crustaceans or gastropods). Mesograzer abundance in the study area was high, and capable of mitigating the effects of increased algal biomass that resulted from experimental nutrient enrichment in the field. When crustacean mesograzers were experimentally excluded, gastropod mesograzers were able to compensate and limit the effects of nutrient enrichment on eelgrass biomass and growth. Our results suggest that top‐down processes (i.e., suppression of algae by different mesograzer groups) may ensure eelgrass resilience to nutrient enrichment in the northern Baltic Sea, and the existence of multiple trophic pathways can provide additional resilience in the face of trophic modifications. However, the future resilience of these meadows is likely threatened by additional local stressors and global environmental change. Understanding the trophic links and interactions that ensure resilience is essential for managing and conserving these important ecosystems and the services they provide.

Food Web Trophic Structure at Marine Ranch Sites off the East Coast of Korea

Understanding the trophic ecology of the giant Pacific octopus Enteroctopus dofleini is challenging in developing marine ranches and in reestablishing its regional stocks against the severe stress of fishing. We adopted carbon and nitrogen stable isotope techniques (termed δ13C and δ15N, respectively) to identify the trophic niche (i.e., pathways and positions) of this species systematically in the entire food webs of two marine ranches off the east coast of the Korean peninsula. While a slight spatial shift in the isotopic nestedness of faunal communities was observed, the δ13C and δ15N values of consumers were distinct and separate among functional groups at both ranches. The consumer δ13C values spanned a broad range between pelagic and benthic sources of organic matter, and their δ15N values recorded a stepwise trophic-level enrichment, indicating that suspension feeders and herbivore-deposit feeders served as baselines of pelagic- and benthic-based trophic pathways, respectively. The δ13C values of predators, including E. dofleini, were arrayed between the two primary consumer groups. Neither δ13C nor δ15N values showed any remarkable variations with increasing octopus weight. Dietary mixing-model calculations indicated that E. dofleini is a generalist predator relying on both benthic- and pelagic-affinity prey, similar to some teleost species that consume a diverse spectrum of prey. In contrast, other teleost groups showed prevalent trophic links with either pelagic- or benthic-based pathways. The trophic-level estimations revealed that E. dofleini occupies an intermediate position slightly below the teleosts. A lack of discrete trophic positions between E. dofleini and teleosts seemed to be indicative of the released teleost predation but instead reflects the imposed food competition. Overall, the results demonstrated that despite compositional changes in the taxa constituting individual trophic groups, E. dofleini occupied a very similar trophic niche in both ranching systems. Finally, as extracted from information based on octopus marine ranches launched on natural rocky bottoms, our isotopic evidence provides a greater understanding of the trophic ecology of this octopus species in nearshore natural habitats along the southwestern margin of its distribution range.

Bat responses to changes in forest composition and prey abundance depend on landscape matrix and stand structure

Despite the key importance of the landscape matrix for bats, we still not fully understand how the effect of forest composition interacts at combined stand and landscape scales to shape bat communities. In addition, we lack detailed knowledge on the effects of local habitat structure on bat-prey relationships in forested landscapes. We tested the assumptions that (i) forest composition has interacting effects on bats between stand and landscape scales; and (ii) stand structure mediates prey abundance effects on bat activity. Our results indicated that in conifer-dominated landscapes (> 80% of coniferous forests) bat activity was higher in stands with a higher proportion of deciduous trees while bats were less active in stands with a higher proportion of deciduous trees in mixed forest landscapes (~ 50% of deciduous forests). Moth abundance was selected in the best models for six among nine bat species. The positive effect of moth abundance on Barbastella barbastellus was mediated by vegetation clutter, with dense understory cover likely reducing prey accessibility. Altogether, our findings deepen our understanding of the ecological processes affecting bats in forest landscapes and strengthen the need to consider both landscape context and trophic linkage when assessing the effects of stand-scale compositional and structural attributes on bats.

Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analyses

The deployment of artificial reefs (ARs) has become a popular technique for creating new hard-bottom habitats, and for enhancing biodiversity and resource abundance for fisheries. We compared colonizing faunal assemblages and reef-associated food-web structures between ARs and nearby natural reefs (NRs) off the Korean coast using stable isotope techniques. Reef communities showed high compositional disparities in colonizing assemblages. Distinct δ13C and δ15N ranges of functional groups could be used to distinguish pelagic from benthic trophic pathways in the reef food web. The isotopic niches of entire faunal assemblages, as well as individual functional groups, overlapped between NRs and ARs, resulting in equivalency for the isotopic functional indices. Mixing model estimates for carnivorous invertebrates and fish suggested strong trophic links to reef-associated faunal prey at both reef types. Finally, these results highlight a convergence in trophic structure between ARs and NRs in accordance with functional diversity in the colonized faunal assemblages.

Arctic lagoon and nearshore food webs: Relative contributions of terrestrial organic matter, phytoplankton, and phytobenthos vary with consumer foraging dynamics

Characterizing energy flow and trophic linkages is fundamental to understanding the functioning and resilience of Arctic ecosystems under increasing pressure from climate change and anthropogenic exploitation. We used carbon and nitrogen stable isotopes to examine trophic dynamics and the relative contribution of terrestrial organic matter, water column phytoplankton, and phytobenthos (benthic micro- and macro-autotrophs as well as sea ice algae) to the food webs supporting 45 macroconsumers in three Arctic coastal lagoon ecosystems (Krusenstern, Sisualik, Akulaaq) and the adjacent Kotzebue Sound with varying degrees of connectivity in Cape Krusenstern National Monument, Alaska. A two-source (water column particulate organic matter and benthic sediment organic matter), two-isotope trophic dynamics model informed by a Bayesian isotope mixing model revealed that the Lagoon-Kotzebue Sound coastal ecosystem supported consumers along a trophic position continuum from primary consumers, including amphipods, copepods, and clams to trophic level five predators, such as seastars, piscivorous fishes, seals, and seabirds. The relative contribution of the three primary producer end members, terrestrial organic matter (41 ± 21%), phytoplankton (25 ± 21%), and phytobenthos (34 ± 23%) varied as a function of: 1) consumer foraging ecology and 2) consumer location. Suspension feeders received most of their carbon from food webs based on phytoplankton (49 ± 11%) and terrestrial organic matter (23 ± 5%), whereas herbivores and detritivores received the majority of their carbon from phytobenthos-based food webs, 58 ± 10% and 60 ± 8%, respectively. Omnivores and predators showed more even distributions of resource reliance and greater overall variance among species. Within the invertebrates, the importance of terrestrial organic matter decreased and phytobenthos increased with increasing trophic position. The importance of terrestrial organic matter contribution increased with lagoon proximity to major rivers inputs and isolation from Kotzebue Sound. Several taxa with cultural and subsistence food importance to local communities showed significant reliance (30–90% of baseline carbon) on food chains linked to fresh terrestrial organic matter. Our study indicates that terrestrial-marine linkages are important to the function of Arctic coastal lagoon ecosystems and artisanal fisheries. These linkages are likely to strengthen in the future with regional changes in erosion and runoff associated with climate change and anthropogenic disturbance.

Sifting environmental DNA metabarcoding data sets for rapid reconstruction of marine food webs

AbstractMarine ecosystems are changing rapidly due to ocean warming, overfishing and a raft of other anthropogenic impacts. Such changes are expected to disrupt productivity dynamics and alter marine food webs, with likely negative consequences for ecosystem services. It is, therefore, essential to devise and implement methods that can rapidly and inexpensively monitor changes in the marine food web structure. Unfortunately, conventional methods for surveying marine food webs are typically laborious, expensive and often destructive, resulting in only a small fraction of marine ecosystems being well studied, and an even smaller subset of them being studied through time. Here, we pilot a low‐cost approach to reconstructing trophic networks of marine tropical, temperate and polar regions, using taxonomical inventories arising from published environmental DNA (eDNA) metabarcoding studies, and building trophic links based on primary literature information. Although the trophic webs obtained are a simplified approximation of those constructed with traditional methods, they generate realistic networks that fit with expectations, and allow ecological inference over time scales and costs that are orders of magnitude smaller than that traditionally achieved. We show the potential of a new application of environmental DNA analysis that promises to offer a rapid and scalable approach to gather vital information on ecosystem structure, hence boosting marine monitoring at a time of increasingly rapid environmental changes.

Zooplankton and profundal macroinvertebrate responses to hypolimnetic oxygenation in North Twin Lake, Washington

Cross BK, Taylor TN, Moore BC, Lanouette BP. 2021. Zooplankton and profundal macroinvertebrate responses to hypolimnetic oxygenation in North Twin Lake, Washington. Lake Reserv Manage. 37:275–288. Hypolimnetic oxygenation (HO) has been used to address lake eutrophication and fish habitat limitations, but details on zooplankton and profundal macroinvertebrate community responses are required to fully understand the trophic linkages and impacts. Compared to adjacent South Twin Lake (an unoxygenated reference), zooplankton and profundal macroinvertebrate densities and distributions were altered by HO in North Twin Lake. Overall, temporal trends in zooplankton density were similar between lakes despite oxygenation, suggesting annual and seasonal influences remained a primary factor affecting their density trends. During the day, Chaoborus density was significantly greater in the water column of unoxygenated South Twin Lake compared to oxygenated North Twin Lake (P < 0.0001) as the oxygenated hypolimnion no longer provided refuge from fish predation. Daphnia and copepod densities were greater in North Twin Lake during oxygenation compared to South Twin Lake (P = 0.0011 and P = 0.0005), which may reflect increases in zooplankton habitat availability and reduced predation from Chaoborus in response to HO. With higher levels of dissolved oxygen near the sediment–water interface in North Twin Lake, larval Chaoborus and chironomid densities in the benthic sediments were significantly higher compared to South Twin Lake (P < 0.0001 in both cases). Vertical distribution of zooplankton likely reflected some balance between habitat availability, energetic costs, and predation risk. Lakes with different fish species assemblages may not respond similarly, so managers should reflect on lake similarities between North Twin Lake and systems they manage to understand potential effects of HO and how those effects align with management objectives.

Limnoecosystems of the Kurgan region with domination in the zooplankton of the species group Daphnia (Daphnia)

The paper presents data on the state of populations of species of the genus Daphnia in the ecosystems of small lakes in the forest-steppe zone of the south-west of Western Siberia, in which they are the highest trophic link. The research was conducted in 2017 on the territory of the Kurgan region. In total, 5 lakes (Lysanovo, Dolgoe, Golovka, Second Mogilnoye, Krutoyar) located between 66°30’ and 67°00 ‘ were studied.d. and 55°00’ and 55°30 ‘ s. The studied lakes are typical for the forest-steppe zone of Western Siberia. According to the chemical composition, the lake waters of the studied limnoecosystems can be attributed to the bicarbonate and chloride classes, the sodium group. 5 species of the genus Daphnia were found in the reservoirs: Daphnia (Daphnia) - D.(D.) pulex, D.(D.) obtusa, D.(D.) longispina, D.(D.) galeata, and Daphnia (Ctenodaphnia)- D. (C.) magna. Populations of D. (D.) pulex are found in all the studied reservoirs. The maximum density and biomass of crustaceans of this species is noted in Lake Mogilnoye of 51 thousand individuals/m² and 3.62 g/m², respectively. The minimum, in the lake Dolgoe – 3.8 thousand individuals/m² and 0.019 g/m². Of the other species, D. (C.) magna is most common-in three reservoirs. At the same time, there is a significant variability in the population density from 0.478 thousand. individuals/m² (Lake Krutoyar) up to 9,864 thousand. individuals/ m² (lake Dolgoe). D. (D.) longispina is found in two lakes – the Golovka (25,230 thousand. individuals/m²) and Krutoyar (6,428 thous. individuals/m²). The lowest occurrence is typical for D. (D.) obtusa (Lake Golovka) and D. (D.) galeata (Lake Lysanovo). The greatest species diversity of the genus Daphnia was observed in Lake Golovka (3 species) and Krutoyar (3 species). It is concluded that the studied limnoecosystems are characteristic daphnia reservoirs with the dominance of one or two species from the genus Daphnia.

Disentangling the nonlinear effects of habitat complexity on functional responses.

Structural complexity of habitats modifies trophic interactions by providing refuges and altering predator and prey behaviour. Nonlinear effects on trophic interaction strengths driven by these mechanisms may alter food web dynamics and community structure in response to habitat modifications. However, changes in functional response, the relationship between prey density and feeding rate, along habitat complexity (HC) gradients are little understood. We quantified functional responses along a HC gradient from an entirely unstructured to highly structured habitat in a freshwater system, using dragonfly larvae (Aeshna cyanea) preying on Chaoborus obscuripes larvae. To disentangle mechanisms by which changes in HC affect functional responses, we used two different approaches-a population-level and a behavioural experiment-applied an information theoretic approach to identify plausible links between HC and functional response parameters, and compared our results to previous studies. Functional response shape did not change, but we found strong evidence for nonlinear dependence of attack rate and handling time on HC in our study. Combined results from both experiments imply that attack rate increased stepwise between the unstructured and structured habitats in line with the threshold hypothesis, because the predators gained better access to the prey. Handling time was lowest at an intermediate HC level in the population-level experiment while the direct estimate of handling time did not vary with HC in the behavioural experiment. These differences point towards HC-driven changes in foraging activity and other predator and prey behaviour. Most previous studies reported stepwise decrease in attack rate in line with the threshold hypothesis or no change with increasing HC. Moreover, changes in the handling time parameter with HC appear to be relatively common but not conforming to the threshold hypothesis. Overall, increased HC appears to, respectively, weaken and strengthen trophic links in 2D and 3D predator-prey interactions. We conclude that detailed understanding of HC effects on food webs requires complementary experimental approaches across HC gradients that consider predator foraging strategies and predator and prey behaviour. Such studies can also help guide conservation efforts as addition of structural elements is frequently used for restoration of degraded aquatic habitats.

Winter Carnivory and Diapause Counteract the Reliance on Ice Algae by Barents Sea Zooplankton

The Barents Sea is a hotspot for environmental change due to its rapid warming, and information on dietary preferences of zooplankton is crucial to better understand the impacts of these changes on food-web dynamics. We combined lipid-based trophic marker approaches, namely analysis of fatty acids (FAs), highly branched isoprenoids (HBIs) and sterols, to compare late summer (August) and early winter (November/December) feeding of key Barents Sea zooplankters; the copepods Calanus glacialis, C. hyperboreus and C. finmarchicus and the amphipods Themisto libellula and T. abyssorum. Based on FAs, copepods showed a stronger reliance on a diatom-based diet. Phytosterols, produced mainly by diatoms, declined from summer to winter in C. glacialis and C. hyperboreus, indicating the strong direct linkage of their feeding to primary production. By contrast, C. finmarchicus showed evidence of year-round feeding, indicated by the higher winter carnivory FA ratios of 18:1(n-9)/18:1(n-7) than its larger congeners. This, plus differences in seasonal lipid dynamics, suggests varied overwintering strategies among the copepods; namely diapause in C. glacialis and C. hyperboreus and continued feeding activity in C. finmarchicus. Based on the absence of sea ice algae-associated HBIs (IP25 and IPSO25) in the three copepod species during both seasons, their carbon sources were likely primarily of pelagic origin. In both amphipods, increased FA carnivory ratios during winter indicated that they relied strongly on heterotrophic prey during the polar night. Both amphipod species contained sea ice algae-derived HBIs, present in broadly similar concentrations between species and seasons. Our results indicate that sea ice-derived carbon forms a supplementary food rather than a crucial dietary component for these two amphipod species in summer and winter, with carnivory potentially providing them with a degree of resilience to the rapid decline in Barents Sea (winter) sea-ice extent and thickness. The weak trophic link of both zooplankton taxa to sea ice-derived carbon in our study likely reflects the low abundance and quality of ice-associated carbon during late summer and the inaccessibility of algae trapped inside the ice during winter.

Land-use change erodes trophic redundancy in tropical forest streams: Evidence from amino acid stable isotope analysis.

Studies have shown that food chain length is governed by interactions between species richness, ecosystem size and resource availability. While redundant trophic links may buffer impacts of species loss on food chain length, higher extinction risks associated with predators may result in bottom-heavy food webs with shorter food chains. The lack of consensus in earlier empirical studies relating species richness and food chain length reflects the need to account robustly for the factors described above. In response to this, we conducted an empirical study to elucidate impacts of land-use change on food chain length in tropical forest streams of Southeast Asia. Despite species losses associated with forest loss at our study areas, results from amino acid isotope analyses showed that food chain length was not linked to land use, ecosystem size or resource availability. Correspondingly, species losses did not have a significant effect on occurrence likelihoods of all trophic guilds except herbivores. Impacts of species losses were likely buffered by initial high levels of trophic redundancy, which declined with canopy cover. Declines in trophic redundancy were most drastic amongst invertivorous fishes. Declines in redundancy across trophic guilds were also more pronounced in wider and more resource-rich streams. While our study found limited evidence for immediate land-use impacts on stream food chains, the potential loss of trophic redundancy in the longer term implies increasing vulnerability of streams to future perturbations, as long as land conversion continues unabated.

BIOLOGICAL AND ECOLOGICAL PECULIARITIES OF AQUATIC SEMIOPTERA (HETEROPTERA) OF THE SHARYN SNNP

As a result of a study on the territory of the Sharyn SNNP in 2018-2019. 72 species of 13 families of aquatic hemiptera insects were identified. Among them, a large number of species stand out. Corixidae (27 species, 40%), Saldidae (10 species, 25%), Gerridae (9 species, 13%), in the remaining 8 families only 1-3 species are known. Salda sahlbergi Reuter from the Saldidae family, 1870, was first recorded in Kazakhstan. By trophic links, zoophages predominate - 40 species, 60%; zoophytophages - 27 species, 40%. According to their association with habitats, aquatic hemiptera are subdivided into several groups: periphyton, nekton, pleiston, and supralittoral. Depending on the number of offspring per year, aquatic hemiptera of the Charyn State National Research and Production Enterprise is divided into three groups, which means that the number of species that reproduce several times a year is 13 (19%), twice a year - 8 species (12%), one once a year - 46 species (69%). Stages of wintering of aquatic hemiptera: adults - 59 species (88%), larvae - 3 species (5%), eggs - 5 species (7%). Key words: aquatic hemiptera, Charyn State National Natural Park, South-East Kazakhstan.