Macroinvertebrate Predators Research Articles

Stream Algal Biomass Associations with Environmental Variables in a Temperate Rainforest

Benthic algae and autotrophic seston are important bases of stream food webs, and several different environmental factors may influence their biomass. We explored how benthic algae and autotrophic seston biomass (using chlorophyll-a as a proxy for algal biomass) were associated with stream temperature, channel width, canopy cover, stream cardinal orientation, benthic macroinvertebrate functional feeding group abundance, salmonid biomass, and water velocity in 16 small, fish-bearing streams in the temperate rainforest of the Olympic Peninsula in Washington State, USA, in the summer of 2020. We performed a mixed-effects regression analysis of extracted chlorophyll-a (chl-a) and then used model averaging to determine significant (α = 0.05) algal–environmental associations for benthic algae and autotrophic seston separately. We found that benthic algae chl-a concentration increased significantly with stream temperature (p = 0.0085) and decreased significantly with water velocity (p = 0.0053). For autotrophic seston, we found that chl-a concentration increased significantly with benthic macroinvertebrate predator abundance (p = 0.0007) and stream temperature (p = 0.0160). This study underscores the need to consider a broad range of environmental variables when making research and management decisions concerning stream ecology.

The impacts of non-native watercress in Oklahoma spring ecosystems

Watercress (Nasturtium officinale) has spread widely from Europe and commonly occurs in Oklahoma (USA) springs. Watercress is usually an emergent plant and affects water flow patterns and may provide habitat for biota. Although watercress is not considered an invasive species, its impacts in springs have not been reported. With a goal to describe possible impacts of watercress in springs, 14 karst-associated springs (12 with watercress) were surveyed for sediment characteristics, macroinvertebrates, and diatoms in July 2021. The effects of watercress were evident. Sediment particle size was unaffected by the presence of watercress but sediment organic matter was higher under watercress beds than outside of beds. Although there was no difference in total benthic macroinvertebrate density or richness, higher organic matter was associated with slightly higher abundances of detritivorous and predatory macroinvertebrates (SIMPER). Submerged portions of watercress had significantly much lower diatom density than other spring substrates, with diatom composition similar to other plants but different from that of rocks. Self-shading or possible allelopathy may cause the low diatom density. The significantly lower macroinvertebrate density within watercress mats relative to that of other plants may result from a reduced food source because the plant’s low diatom density. Only predatory damselflies were more common in watercress than in other plants, which had more abundant grazers. Although watercress can increase heterogeneity in sediments and is sometimes valued as an edible plant, watercress supports low algal and macroinvertebrate densities, such that extensive growth of watercress can have an overall negative impact on spring ecosystems.

Enhanced diversity of aquatic macroinvertebrate predators and biological pest control but reduced crop establishment in organic rice farming

Organic farming has been adopted as the main alternative to reduce the environmental impact of intensive agriculture by banning the use of synthetic inputs and bolstering key ecological functions such as biological pest control. Yet the potential cascading effects of farming management on the communities of natural enemies, the provisioning of pest control, and the ultimate impact on crop performance remain poorly explored. This is especially true for semi-aquatic crops such as rice (Oryza sativa, L) that largely depend on aquatic macroinvertebrate predators for biological pest control. Here we performed two consecutive landscape-scale field experiments by combining monthly surveys of macroinvertebrate aquatic predators with both pest predation and seed rice germination trials to assess differences between conventional and organic rice farming in all the above-mentioned issues. Specifically, we selected 6 organic and 6 conventionally managed rice paddies and evaluated differences in i) the diversity of aquatic macroinvertebrate predators (taxa richness and evenness), ii) the infestation level of a seed pest (chironomids larvae), iii) the efficiency of biological pest control provisioning and iv) the impact on germination of rice seeds. Communities of macroinvertebrate aquatic predators were more diverse (taxa richness) and abundant in organic than in conventional fields, yet community evenness was higher in conventionally-managed fields. Accordingly, we found that macroinvertebrate-mediated pest control was markedly more efficient in organic farms during the establishment crop stage. Pest infestation, however, remained also higher in organic farming, most likely because biological pest control in organic fields is not able to outcompete chemical control provided in conventional fields. Finally, the increased infestation level observed in organic fields ultimately resulted in reduced germination rates of rice seeds, thus limiting crop performance. Our results highlight the potential positive effects of pesticide banning in organic rice farming on aquatic macroinvertebrate communities and the consequently improvement of biological pest control provisioning. Yet conditions enhancing biodiversity may also favor pest infestation and ultimately increase crop damage. Management recommendations should therefore account for potential services and disservices associated to organic farming in order to avoid negative yield outcomes for rice farmers.

Top-Down Effect of Arthropod Predator Chinese Mitten Crab on Freshwater Nutrient Cycling.

Aquatic litter decomposition is highly dependent on contributions and interactions at different trophic levels. The invasion of alien aquatic organisms like the channeled apple snail (Pomacea canaliculata) might lead to changes in the decomposition process through new species interactions in the invaded wetland. However, it is not clear how aquatic macroinvertebrate predators like the Chinese mitten crab (Eriocheir sinensis) will affect the nutrient cycle in freshwater ecosystems in the face of new benthic invasion. We used the litter bag method to explore the top-down effect of crabs on the freshwater nutrient cycle with the help of soil zymography (a technology previously used in terrestrial ecosystems). The results showed significant feeding effects of crabs and snails on lotus leaf litter and cotton strips. Crabs significantly inhibited the intake of lotus litter and cotton strips and the ability to transform the environment of snails by predation. Crabs promoted the decomposition of various litter substrates by affecting the microbial community structure in the sediment. These results suggest that arthropod predators increase the complexity of detrital food webs through direct and indirect interactions, and consequently have an important impact on the material cycle and stability of freshwater ecosystems. This top-down effect makes macrobenthos play a key role in the biological control and engineering construction of freshwater ecosystems.

Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa

Our knowledge of the ecology of non-marine Ostracoda inhabiting endorheic wetlands (pans) of the semi-arid regions of South Africa is very scarce. The present study investigates the distribution of ostracod species in grass, open, and salt pans in the central part of the North West province and tests ostracod response to abiotic and biotic predictor variables operating at a local scale. Distance-based linear models revealed three variables (pan type, water electrical conductivity and abundance of macroinvertebrate predators, and collector-gatherers) that best explained variation in the ostracod dataset. Ostracod assemblages from the three studied pan types differed by the dominance structure rather than by the species composition. Salt pans with high conductivity and high ratio of predaceous macroinvertebrates were dominated by Heterocypris giesbrechti, with accessory presence of Plesiocypridopsis newtoni. In open pans with low conductivities and the lowest ratio of predators (but highest ratio of collector-gatherers) Potamocypris mastigophora was typically a dominant species, while in grass pans, all the three mentioned species had similar relative abundances. Although our findings lend provisional support to some models of ostracod assemblage diversity across different pan types, more studies replicating endorheic depression wetlands in other regions are required before generalizations can be made.

Rotenone Has Little Effect on Water Quality, Phytoplankton, Zooplankton, or Macroinvertebrates in Aquaculture Nursery Ponds

AbstractRotenone application has been reported to cause significant declines in zooplankton populations, with cladocerans and copepods being the most susceptible and possibly taking months to recover. Because copepods and cladocerans are preferred by fry of catfish Ictalurus spp., rotenone application could have significant effects on nursery pond production. Effects of rotenone on zooplankton and time required for recovery has not been studied in eutrophic aquaculture ponds typically drained and refilled yearly. We quantified rotenone application effects to either mostly drained ponds or full ponds (0.04 ha) in northwestern Mississippi on water quality, phytoplankton, zooplankton, and aquatic macroinvertebrates during May (23°C) and June (30°C) when most catfish fry ponds are stocked. For study 1, nine ponds were drained to about 15 cm of water. Six ponds were treated with 4 μL/L rotenone; three treated ponds were then treated with 4 mg/L potassium permanganate (KMnO4). The three additional ponds were drained but untreated. All ponds were then filled and fertilized with urea. In study 2, six full ponds were treated with 4 μL/L rotenone. Three of those ponds were then treated the next day with 4 mg/L KMnO4. An additional three ponds were left as untreated controls. Applying rotenone to the experimental ponds with 15 cm or less of water (study 1) had no effect on water quality, phytoplankton, or zooplankton. Neutralization with KMnO4 did not affect any measured variables. Desirable zooplankton numbers for catfish culture reached 100 organisms/L 11–14 d after treatment. In study 2, when a whole pond was treated with rotenone, desirable zooplankton numbers reached 100 organisms/L 7 d after treatment if neutralized with KMnO4 and about 11 d after treatment without neutralization. Rotenone treatment did not reduce predatory macroinvertebrate risk, and this should be addressed using additional management strategies.

Asynchronous recovery of predators and prey conditions resilience to drought in a neotropical ecosystem

The predicted increase in the intensity and frequency of drought events associated with global climate change will impose severe hydrological stress to freshwater ecosystems, potentially altering their structure and function. Unlike freshwater communities’ direct response to drought, their post-drought recovery capacities remain understudied despite being an essential component driving ecosystem resilience. Here we used tank bromeliad as model ecosystem to emulate droughts of different duration and then assess the recovery capacities of ecosystem structure and function. We followed macroinvertebrate predator and prey biomass to characterize the recovery dynamics of trophic structure (i.e. predator–prey biomass ratio) during the post-drought rewetting phase. We showed that drought significantly affects the trophic structure of macroinvertebrates by reducing the predator–prey biomass ratio. The asynchronous recovery of predator and prey biomass appeared as a critical driver of the post-drought recovery trajectory of trophic structure. Litter decomposition rate, which is an essential ecosystem function, remained stable after drought events, indicating the presence of compensatory effects between detritivores biomass and detritivores feeding activity. We conclude that, in a context of global change, the asynchrony in post-drought recovery of different trophic levels may impact the overall drought resilience of small freshwater ecosystems in a more complex way than expected.

Stable carbon and nitrogen isotopes explain methylmercury concentrations in stream food webs of Lake George, New York (USA).

Mercury has been studied extensively in lakes due to health risks associated with the consumption of contaminated fish, while stream ecosystems have received less attention. To better understand mercury bioavailability in the lower food web of streams, we collected macroinvertebrates (predators and detritivore) along with autochthonous (epilithic algae) and allochthonous (leaf litter) basal resources in eight streams entering Lake George. Samples were analyzed for methylmercury (MeHg), total mercury, and carbon and nitrogen isotopes (δ13C & δ15N) to determine how mercury concentrations in basal resources, biomagnification rates, and environmental factors (watershed characteristics and water chemistry) effected MeHg concentrations in predatory macroinvertebrates. While biomagnification rates, calculated as trophic magnification slope, explained between 68% and 98% of MeHg variability within a stream food web, the range was small (0.310-0.387) resulting in the biotic components following a consistent pattern of increasing MeHg among streams. The stream order was negatively related to basin slope for all biotic components and explained 70% of MeHg variability in predatory macroinvertebrates. Methylmercury concentrations were significantly and negatively related to δ13C in predators, epilithic algae, and leaf litter. We believe the biofilms on leaf litter utilized bacterial-respired carbon dioxide decreasing δ13C (<-28‰) and increasing MeHg while epilithic algal δ13C increased due to enhanced primary production resulting in biodilution of MeHg. Methylmercury in basal resources responded to δ13C similarly but through different processes. Our findings show shallow slopes elevate MeHg in basal resources and explain most of the predator MeHg variation among streams with little influence of biomagnification rates.

Habitat preference of blackflies in Omo Gibe river basin (southwest Ethiopia): Implications for onchocerciasis elimination and control.

Ecological control of blackflies (Simulium damnosum) can be an alternative or additional tool to enhance onchocerciasis elimination efforts. However, limited research is conducted on the ecology of blackflies in Ethiopia. In this study, we determined the habitat preference of blackfly larvae and their relationship with aquatic macroinvertebrate predators in the Omo Gibe river basin of southwest Ethiopia. Environmental and biological data were collected from 150 sampling sites during both dry and wet seasons in 2019. Generalized Linear Models (GLMs) were used to identify factors affecting the occurrence and abundance of S. damnosum larvae. Canonical Correspondence Analysis (CCA) was used to investigate the relationship between environmental and biological variables and the abundance of S. damnosum larvae. The findings of this study indicated the abundance of S. damnosum larvae increased with increasing turbidity, alkalinity and altitude, but decreased with increasing concentrations of five-day Biological Oxygen Demand (BOD5), orthophosphate and magnesium ion. Both the presence and abundance of S. damnosum larvae decreased with the increasing abundance of stonefly larvae (Perlidae). Simulium damnosum larvae were found less likely in the presence of mayfly larvae (Baetidae) and were less abundant where Chironomidae are abundant. In conclusion, the findings of this study showed that the habitat preference of S. damnosum larvae is determined by environmental factors and that the presence and abundance of the larvae are affected by macroinvertebrate predators. It is essential to establish buffer zones as a part of watershed management to retain pollutants and prevent them from entering directly into water courses to improve water quality and the assemblages of macroinvertebrate predators and enhance biocontrol of blackflies.

Does the size structure of the littoral community reflect water level fluctuations in shallow waterbodies?

The littoral zone of shallow water bodies (SWB) is highly susceptible to water level fluctuations (WLF) caused by ongoing climate-related hydrologic regime changes. The present study assessed the macrozoobenthos structure in the littoral of three temperate SWB after pronounced WLF and accompanying reduction of macrophyte coverage caused by excessive precipitation. The three SWB differed in environmental conditions – S1 (transparent lake covered with submerged macrophytes dominated by Ceratophyllum demersum); S2 (turbid lake without macrophyte coverage) represented the two interconnected backwater basins of the Sutla River watershed; and SK (Škrčev kut oxbow; highly turbid lake sparsely covered by floating-leaved Nuphar lutea) located in the Krapina River watershed (Croatia). With the aim to disentangle the littoral food web structure, and interactions among environmental conditions as well as structural and functional traits of the littoral community within the three SWB, the macrozoobenthos functional traits, trophic guilds and body size were correlated with the littoral environmental conditions, and with the traits of the potential macrozoobenthos prey (zooplankton) and predators (fish). Our results suggest that the littoral macrozoobenthos assemblage responded to the water level increase mainly by the decline of macroinvertebrate diversity and abundance. Due to loss of habitat heterogeneity, in general, larger-sized macroinvertebrates dominated the littoral zone of turbid SWB, particularly with high WLF, while smaller-sized detritivores and grazers prevailed in the littoral zone of the transparent SWB covered by submerged macrophytes. The correlations between different macrozoobenthos, zooplankton and fish size classes indicated that the larger-sized predatory macroinvertebrates prey on smaller-sized zooplankters and avoid predation of mid-sized fish. On the other hand, the abundance of smaller-sized macroinvertebrate detritivores and grazers, which were significantly correlated with concentrations of suspended detritus and algae, prevailed in the SWB covered by submerged macrophytes. Within the macrophyte-covered littoral habitats, macroinvertebrates coexisted with small-sized fish and zooplankters as well as with large-sized pelagic zooplankters, likely seeking shelter from fish. We assume that the increased abundance of larger-sized specimens affected macroinvertebrates and fish within the littoral community upon water level increase. Such a pattern could be recognized as an indicative trait in the evaluation of ecosystem functioning. Furthermore, we conclude that the structural and functional traits of the SWBs’ littoral communities could help us predict the ecological consequences of the climate-induced WLF.

Drainage increases species richness and density of soil macro-invertebrates in the Zoige peatland of eastern Tibetan Plateau

Soil macro-invertebrates play an important role in the decomposition process of soil organic matter. As the world’s largest alpine peatland, the Zoige peatland on the eastern Tibetan Plateau is experiencing the decline in water table level primarily because of historic drainage. However, little is known about the responses of soil macro-invertebrate communities to water table decline. To address this issue, we established a field drainage experimental platform in 2013, which consists of low (50 cm deep drainage ditch) and intermediate (20 cm deep drainage ditch) water table level treatments, and the ambient (no drainage ditch) plots. In July (warm season) and November (cold season) of 2019, we examined the species composition, richness, densities and the vertical distribution of soil macro-invertebrates. Results showed that the species composition differed significantly among treatments. Species richness and densities of overall and different trophic groups (i.e., detritivores, herbivores and predators) of soil macro-invertebrates were significantly higher in the drained treatments compared to the ambient plots. Moreover, soil macro-invertebrates moved down to deeper soil layers in the low water table treatments compared to the ambient plots. In addition, sampling season (warm vs. cold) did not affect the responses of soil macro-invertebrates to water table decline. These results indicate that soil macro-invertebrate community is sensitive to water table decline in the Zoige peatland. Given the recognized importance of soil fauna to ecosystem functioning, more attention should be paid to the conservation of peatlands.

Cambrian comb jellies from Utah illuminate the early evolution of nervous and sensory systems in ctenophores

SummaryCtenophores are a group of predatory macroinvertebrates whose controversial phylogenetic position has prompted several competing hypotheses regarding the evolution of animal organ systems. Although ctenophores date back at least to the Cambrian, they have a poor fossil record due to their gelatinous bodies. Here, we describe two ctenophore species from the Cambrian of Utah, which illuminate the early evolution of nervous and sensory features in the phylum. Thalassostaphylos elegans has 16 comb rows, an oral skirt, and an apical organ with polar fields. Ctenorhabdotus campanelliformis has 24 comb rows, an oral skirt, an apical organ enclosed by a capsule and neurological tissues preserved as carbonaceous films. These are concentrated around the apical organ and ciliated furrows, which connect to a circumoral nerve ring via longitudinal axons. C. campanelliformis deviates from the neuroanatomy of living ctenophores and demonstrates a substantial complexity in the nervous system of Cambrian ctenophores.

A likely association of damselflies with the habitat heterogeneity provided by the freshwater swamp lily, Ottelia ovalifolia, in Eyre Peninsula granite rock-holes, with a review of potential threats to this ephemeral habitat

ABSTRACT The granite rock-holes (sometimes called gnammas) across northern Eyre Peninsula (EP), South Australia, are a unique but poorly studied ephemeral freshwater habitat containing a complex invertebrate community. Macroinvertebrate predator occurrence is often sporadic, both spatially and temporally. We aimed to determine if environmental conditions might predict predator occurrence in EP rock-holes. A total of 14 rock-holes were sampled across five granite outcrops along the Eyre Highway. Extensive dip-net sampling was undertaken and nymphs of three damselfly species were recorded from the rock-holes: Austrolestes annulosus (Lestidae), Ischnura aurora, and Xanthagrion erythroneurum (both Coenagrionidae), all in a single rock-hole at Pildappa Rock. This sole rock-hole contained a prominent floating-leaved, rooted aquatic macrophyte: the swamp lily, Ottelia ovalifolia (Hydrocharitaceae), which forms a complex, three-dimensional vegetative structure. Damselflies were hypothesised to be associated with the presence of O. ovalifolia, possibly as a result of the plant providing both suitable oviposition sites for the adults and habitat for nymphs throughout the water column, opportunities not afforded by the aquatic vegetation present in shallow rock-holes. Our findings contribute to the limited ecological information regarding EP rock-holes. We also briefly review potential threats to these ecosystems, an understanding of which will be critical to their management and conservation.

Mesocosm Experiments to Quantify Predation of Mosquito Larvae by Aquatic Predators to Determine Potential of Ecological Control of Malaria Vectors in Ethiopia.

Malaria parasites are transmitted to humans by infectious female Anopheles mosquitoes. Chemical-insecticide-based mosquito control has been successful in reducing the burden of malaria. However, the emergence of insecticide resistance in malaria vectors and concerns about the effect of the chemicals on the environment, human health, and non-target organisms present a need for new or alternative vector control intervention tools. Biocontrol methods using aquatic invertebrate predators have emerged as a potential alternative and additional tool to control mosquito populations. Ecological control specifically makes use of species insights for improving the physical habitat conditions of competitors and predators of vectors. A first step towards this is to gain knowledge on the predation potential of several typically present macroinvertebrates. Hence, this study aimed at (1) examining the influence of the predation of hemipterans on the number of emerging adult mosquitoes and (2) detecting Anopheles mosquito DNA in the gut of those predators. The prey and predators were collected from a range of water bodies located in the Gilgel Gibe watershed, southwest Ethiopia. A semi-field study was carried out using mesocosms which were constructed using plastic containers mimicking the natural aquatic habitat of immature Anopheles mosquitoes. Adult mosquitoes that emerged from the mesocosms were collected using a mechanical aspirator. At the end of the experiment, predators were withdrawn from the mesocosms and identified to genus level. Polymerase Chain Reaction (PCR) was employed to identify sibling species of Anopheles gambiae s.l. and to detect Anopheles mosquito DNA in the gut of the predators. Data were analysed using R software. Giant water bugs (belostomatids) were the most aggressive predators of Anopheles larvae, followed by backswimmers (notonectids) and water boatmen (corixids). All female Anopheles gambiae s.l. emerged from the mesocosms were identified as Anopheles arabiensis. Anopheles arabiensis DNA was detected in the gut content of hemipteran specimens analysed from the three families. The number of the adult mosquitoes emerging from the mesocosms was affected by the presence of predators. The findings of this study provide evidence of the potential use of aquatic macroinvertebrate predators as biocontrol agents against immature Anopheles mosquitoes and their potential to be considered as a component of integrated vector management for insecticide resistance and the combined restoration of aquatic ecosystems via smart ecological engineering.

Greening of the boreal peatland food web: Periphyton supports secondary production in northern peatlands

AbstractCharacterizing spatial and temporal variability of food web dynamics is necessary to predict how wetter and more nutrient‐rich conditions expected with climate change will influence the fate of organic matter within northern peatlands. The goals of this study were to (1) document spatial and temporal variability in the contribution of periphyton to peatland food webs using isotope analysis (13C and 15N), and (2) quantify the influence of increased nutrient availability on primary and secondary production across a gradient of rich, moderate, and poor fen peatlands common to the northern boreal biome. We established replicate m2 plots within each fen located in interior Alaska to quantify periphyton (algae and bacteria) and macroinvertebrate biomass with and without nutrient addition throughout a growing season (May–August). Stable isotope analysis showed that periphyton contributed = 65% of organic matter to the food web over time and across fens compared to = 7% from plants or detritus. The transfer of basal resources was reflected in an increase in herbivore biomass as algal biomass increased over time in all fens, followed by an increase in predatory macroinvertebrates during the latter part of the growing season. Furthermore, all measures of periphyton and macroinvertebrate biomass were enhanced by nutrient addition. These data provide insight into patterns of natural variation within the aquatic food web of boreal peatlands and show that basal resources within this ecosystem, which are generally considered to be “detritus‐based,” are actually driven by periphyton with minimal input from plant detrital pathways.

Omnivore density affects community structure through multiple trophic cascades.

Omnivores can dampen trophic cascades by feeding at multiple trophic levels, yet few studies have evaluated how intraspecific variation of omnivores influences community structure. The speckled dace (Rhinichthys osculus) is a common and omnivorous minnow that consumes algae and invertebrates. We studied effects of size and size structure on top-down control by dace and how effects scaled with density. Dace were manipulated in a mesocosm experiment and changes in invertebrate and algal communities and ecosystem function were monitored. Omnivores affected experimental communities via two distinct trophic pathways (benthic and pelagic). In the benthic pathway, dace reduced macroinvertebrate biomass, thereby causing density-mediated indirect effects that led to increased benthic algal biomass. Dace also reduced pelagic predatory macroinvertebrate biomass (hemipterans), thereby increasing the abundance of emerging insects. The effect of dace and hemipterans on emerging insects was mediated by a non-linear response to dace with peak emergence at intermediate dace density. In contrast with recent studies, omnivore size and size structure had no clear effect, indicating that small and large dace in our experiment shared similar functional roles. Our results support that the degree to which omnivores dampen trophic cascades depends on their relative effect on multiple trophic levels, such that the more omnivorous a predator is, the more likely cascades will be dampened. Availability of abundant macroinvertebrates, and the absence of top predators, may have shifted dace diets from primary to secondary consumption, strengthening density-dependent trophic cascades. Both omnivore density and dietary shifts are important factors influencing omnivore-mediated communities.

The importance of aquatic plants in maintaining zooplankton diversity and abundance: An experimental approach

The influence of different species and ecological forms of higher aquatic plants on the abundance, biomass and species diversity of zooplankton was investigated in experimental ecosystems (microcosms). It was shown that in the absence of fish and macroinvertebrate predators, the abundance and diversity of zooplankton in the plants beds increased. Not only phytophilous, littoral, and small planktonic crustaceans, but also some large obligate planktonic crustaceans, reached a high abundance among the plants. Plants belonging to different ecological groups stimulated an increase in the abundance of different groups of zooplankton. In the beds of submerged plants, the number of Cladocera increased to a greater extent than Copepoda or Rotifera. The abundance of Copepoda, both Cyclopoida and Calanoida, grew in the beds of helophytes. The relative number of predators in the community increased among the plants. The species structure and quantitative parameters of zooplankton had their own characteristics in monospecies and mixed phytocenoses of the same plant species. The index of species diversity of zooplankton acquired the highest values in the mixed phytocenosis. Higher aquatic plants increase spatial heterogeneity, which stimulates the development of facultative planktonic and benthic species. The formation of phytogenic detritus and the lifetime release of organic substances by plants into the water causes the development of bacteria and protozoa, which expands the quality and size range of food organisms for zooplankton. Therefore, zooplankton becomes more diverse in terms of the set of trophic groups.

Predation and competition induce variable organ size trade‐offs in larval anurans

AbstractInducible defenses allow organisms that live in variable environments to invest energy into defense when necessary. These responses are common in aquatic organisms and are particularly notable in larval anurans, which tend to develop deeper tails under sit‐and‐wait macroinvertebrate predation threat. Although trade‐offs between defense and growth have been well‐studied, trade‐offs with internal organ sizes have rarely been considered. The purpose of our study was to investigate the effects of predation and competition on trade‐offs associated with total length (body + tail), tail size and internal organ size (gut, pancreas, liver and fat body) in two larval anurans, red‐eyed treefrogs (Agalychnis callidryas) and gray treefrogs (Hyla versicolor). In two separate experiments, we reared larvae in outdoor mesocosms with and without competition in the presence and absence of a caged predator. We subsampled larvae from each mesocosm and measured tail and internal organ sizes. Both competition and predation exerted strong effects on total length and morphology, although each experiment produced unique results. Competition increased gut size in both species, supporting a previously reported trade‐off between gut and tail size. Competition also reduced total length in both experiments: Gray treefrogs balanced total length with lipid deposition, and red‐eyed treefrogs favored total length at the expense of lipid reserves. Predation threat elicited an increase in tail depth but a reduction in tail muscle size in gray treefrogs, which may have allowed larvae to maintain pancreas size and total length. Conversely, red‐eyed treefrogs developed larger tails with more muscle area, allocating resources in a way that sacrificed both liver and pancreas size, as well as total length. Although the specific tail response was different, both species prioritized larger guts over tail modifications when faced with both competition and predation, as large gut sizes were maintained in competitive environments even when predators were present.

Cross-ecosystem impacts of non-native ungulates on wetland communities

Herbivory by non-native species can create strong direct and indirect effects on plant and arthropods communities that can potentially cross ecosystem boundaries. Yet, the cross-ecosystems impacts of non-native species are poorly understood. We took advantage of ongoing invasions by non-native ungulates in Patagonia, Argentina, to examine their cross-ecosystem impacts on water parameters, littoral vegetation and aquatic macroinvertebrate assemblages in wetlands. We found a gradient of invasion by non-native ungulates from intact (non-invaded) to highly invaded wetlands. These highly invaded wetlands had ~ 24% less vegetation cover, which was 72% shorter in height than vegetation in intact wetlands. As a result, the abundance of predatory macroinvertebrates such as Odonata (dragonflies) was reduced by ~ 90%; while Diptera were ~ 170% more abundant, and Oligochaeta were recorded mostly at invaded sites. In contrast, we did not find evidence that non-native ungulates altered water parameters. Understanding the indirect consequences of invasive non-native species is crucial for quantifying the real impacts of global change. Our results show strong cross-ecosystem impacts of non-native ungulates on macroinvertebrate wetland communities, highlighting the importance of indirect interactions beyond ecosystem boundaries.

Aquatic macrophytes and macroinvertebrate predators affect densities of snail hosts and local production of schistosome cercariae that cause human schistosomiasis.

BackgroundSchistosomiasis is responsible for the second highest burden of disease among neglected tropical diseases globally, with over 90 percent of cases occurring in African regions where drugs to treat the disease are only sporadically available. Additionally, human re-infection after treatment can be a problem where there are high numbers of infected snails in the environment. Recent experiments indicate that aquatic factors, including plants, nutrients, or predators, can influence snail abundance and parasite production within infected snails, both components of human risk. This study investigated how snail host abundance and release of cercariae (the free swimming stage infective to humans) varies at water access sites in an endemic region in Senegal, a setting where human schistosomiasis prevalence is among the highest globally.Methods/Principal findingsWe collected snail intermediate hosts at 15 random points stratified by three habitat types at 36 water access sites, and counted cercarial production by each snail after transfer to the laboratory on the same day. We found that aquatic vegetation was positively associated with per-capita cercarial release by snails, probably because macrophytes harbor periphyton resources that snails feed upon, and well-fed snails tend to produce more parasites. In contrast, the abundance of aquatic macroinvertebrate snail predators was negatively associated with per-capita cercarial release by snails, probably because of several potential sublethal effects on snails or snail infection, despite a positive association between snail predators and total snail numbers at a site, possibly due to shared habitat usage or prey tracking by the predators. Thus, complex bottom-up and top-down ecological effects in this region plausibly influence the snail shedding rate and thus, total local density of schistosome cercariae.Conclusions/SignificanceOur study suggests that aquatic macrophytes and snail predators can influence per-capita cercarial production and total abundance of snails. Thus, snail control efforts might benefit by targeting specific snail habitats where parasite production is greatest. In conclusion, a better understanding of top-down and bottom-up ecological factors that regulate densities of cercarial release by snails, rather than solely snail densities or snail infection prevalence, might facilitate improved schistosomiasis control.