Nematode Assemblages Research Articles

Do diatom and nematode assemblages reflect the same ecological status in a tropical eutrophic reservoir?

Do diatom and nematode assemblages reflect the same ecological status in a tropical eutrophic reservoir?

Anisakis spp. as indicators of latitudinal movements of short‐finned pilot whales, Globicephala macrorhynchus, in the Northeast Atlantic

AbstractIn the Northeast Atlantic, it is unclear whether short‐finned pilot whales, Globicephala macrorhynchus (SFPWs), are transient or resident above 40°N. We used Anisakis spp. to identify the latitudes recently visited by a SFPW pod stranded in NW Spain (43°N) in 2020. Analysis of cox2 gene in 30 nematodes from 6 SFPWs revealed the presence of A. simplex sensu stricto (s.s.) (93.3%) and A. pegreffii (6.7%). Morphological analysis of 972 nematodes corroborated species molecular identification and relative proportions; in males (n = 66), the estimated proportions of A. simplex s.s. and A. pegreffii were 86.4% and 13.6%, respectively. These percentages resembled those reported in fish/cetaceans above 40°N, and L4 larvae or adults of A. typica (a tropical‐temperate species found in SFPWs up to 38°N–39°N) were not detected. Population structure of A. simplex s.s. + A. pegreffii in SFPWs suggested a continuous recruitment of nematodes starting at least 3 weeks before stranding. We interpret that either the SFPW pod was within the range of the species (perhaps as a recent northern shift) or represented a vagrant group that visited waters off Northwest Spain for a protracted period. Future analysis on nematode assemblages could shed light on movements and climate‐driven shifts in cetacean distribution.

How morphodynamic gradients shape the distribution of meiofauna and nematodes on sandy beaches of the Amazon region?

The present study analyzed how a small-scale morphodynamic gradient, based on the level of exposure to oceanic waves, shapes the spatial distribution patterns of the local meiofauna, with a special focus on the nematodes, of tropical macrotidal beaches on the Amazon coast (northern Brazil). The study focused on three sandy beaches, first compiling their physical characteristics (waves, currents and morphodynamic state), and then sampling biological and sediment samples at five different levels across the intertidal zone. Meiofauna was composed of 11 different groups, but was dominated by Nematoda. The nematode assemblage had a total of 89 genera, of which Daptonema and Theristus (both from family Xyalidae) were the most abundant on all studied beaches, at most intertidal levels. The diversity of nematode genera increased toward the low tide mark, while nematode density peaked in either the upper (on the protected and tide-dominated beaches) or intermediate levels (on the exposed, tide-modified beach). Distinct faunal zonation patterns were identified on the three beaches, which were influenced by their level of exposure to oceanic conditions, their granulometry, and the moisture of the sediment. While the variation in the characteristics of the meiofauna can be attributed to the level of exposure of beaches, horizontal distribution patterns were also closely related to habitat heterogeneity, including morphological features and freshwater inputs.

Diversity of microbial, biocontrol agents and nematode abundance on a susceptible Prunus rootstock under a Meloidogyne root gradient infection.

Root-knot nematodes (RKNs) of the genus Meloidogyne are one of the most damaging genera to cultivated woody plants with a worldwide distribution. The knowledge of the soil and rhizosphere microbiota of almonds infested with Meloidogyne could help to establish new sustainable and efficient management strategies. However, the soil microbiota interaction in deciduous woody plants infected with RKNs is scarcely studied. This research was carried out in six commercial almond groves located in southern Spain and infested with different levels of Meloidogyne spp. within each grove. Several parameters were measured: nematode assemblages, levels and biocontrol agents in Meloidogyne's eggs, levels of specific biocontrol agents in rhizoplane and soil, levels of bacteria and fungi in rhizoplane and soil, fungal and bacterial communities by high-throughput sequencing of internal transcribed spacer (ITS), and 16S rRNA gene in soil and rhizosphere of the susceptible almond hybrid rootstock GF-677 infested with Meloidogyne spp. The studied almond groves showed soil degradation by nematode assemblies and fungi:bacterial ratio. Fungal parasites of Meloidogyne eggs were found in 56.25% of the samples. However, the percentage of parasitized eggs by fungi ranged from 1% to 8%. Three fungal species were isolated from Meloidogyne eggs, specifically Pochonia chlamydosporia, Purpureocillium lilacinum, and Trichoderma asperellum. The diversity and composition of the microbial communities were more affected by the sample type (soil vs rhizosphere) and by the geographical location of the samples than by the Meloidogyne density, which could be explained by the vigorous hybrid rootstock GF-677 and a possible dilution effect. However, the saprotrophic function in the functional guilds of the fungal ASV was increased in the highly infected roots vs the low infected roots. These results indicate that the presence of biocontrol agents in almond fields and the development of new management strategies could increase their populations to control partially RKN infection levels.

Forest floor nematode communities and associated tree canopies: Is there an ecological linkage?

We searched for patterns supporting the hypothesis of compositional and functional linkage between forest floor nematode communities and dominant tree canopies, while controlling for some relevant soil and climate variables. Twenty-one forest sampling sites scattered throughout the South-Eastern Carpathian basin were selected under spruce, beech, and hornbeam-oak canopies. The relative contribution of forest canopy type to nematode assemblage differentiation was estimated through nematode taxonomic composition and feeding guild structure. The forest canopy type had a significant effect on nematode taxon/feeding guild composition and diversity at stand level. Several (diagnostic) nematode taxa and feeding guilds were positively associated with and accurately predicted the forest canopy types considered. Apart from the herbivorous nematodes, all the other trophic guilds were significantly related, in terms of their relative abundance, to the forest canopy type. Both nematode taxonomic and trophic diversity were significantly higher under beech canopy compared with its two counterparts. The highest total nematode beta diversity, either taxonomic or trophic, was attained between hornbeam-oak and spruce canopies. Nematode taxonomic and trophic beta diversity between forest canopy types were largely determined by taxon replacement and respectively, by a nested trophic structure. Overall, four concordant and two discordant patterns were revealed between nematode taxon and feeding guild composition with respect to overlying forest canopy, all underpinning the addressed ecological linkage. The present results bring evidence regarding the important contribution of the forest canopy, along with climatic variables, in driving the taxonomic and functional composition/diversity of nematode communities from the soil organic horizon.

Re-discovering macerating Posidonia oceanica bottoms: Characterization of meiofaunal community inhabiting a peculiar Mediterranean habitat

The highly efficient carbon storage capacity of beds formed by Posidonia oceanica, an endemic Mediterranean seagrass species, has been widely recognized. Recently, the supra-littoral deposits of leaf litter (i.e., banquettes) have been investigated in terms of their nutrients, biomass and associated community. Nevertheless, an overlooked fraction of the P. oceanica detritus never reaches the shore and sinks far away to deeper seafloor. Additionally, part of the supra-littoral deposit goes back to the sea during winter swells. This deep detrital compartment, mainly composed of sediment mixed with dead leaves and rhizomes coming from P. oceanica beds, has only been described once by Pères in 1953, who focused on the macrofaunal component. Here, we investigated for the first time the meiofaunal community inhabiting sediments characterized by P. oceanica detritus in a deposit located at 65−80 m depth off the Ischia Island (Gulf of Naples, Italy, Tyrrhenian Sea). Our results show that the meiofaunal community appears highly diversified and strongly dominated by nematodes (from 85% to 93%). Differences in meiobenthic assemblage structures were significant only when rare taxa were considered (i.e. taxa found in low abundances and characterized by a sporadic distribution in the study area). The nematode community revealed a very high biodiversity (number of families and genera: 31 and 104, respectively), with a clear prevalence of selective and non-selective deposit feeders that suggest the key role of this habitat in the benthic detrital food web. The richness of meiofauna and the taxonomic and functional diversity of the nematode assemblages account for a “good” to “moderate” ecological quality status. These findings support the high ecological value of the macerating seagrass bottoms, an overlooked component of the blue carbon cycle that deserves to be further investigated.

Diversity of Cryptofaunal Nematode Assemblages along the Jardines de La Reina Coral Reef, Southern Cuba

Cryptofaunal nematodes, those living on the hard substrate of the coral reefs, are largely unknown in terms of diversity and assemblage structure. We described nematode assemblages at seven sites spanning about 200 km along Jardines de La Reina, a well-preserved reef system in the Greater Antilles. We identified about 3000 nematodes, mostly of the families Desmodoridae and Chromadoridae; the most abundant species were Croconema cinctum, Desmodora communis, and Euchromadora vulgaris. The regional richness was moderate with 70 observed species (0.95 confidence interval: 65–75 species) and 75 extrapolated species (0.95 CI: 68–83 species). This richness was lower than in other reef biotopes, maybe reflecting evolutionary constraints due to interactions with stony corals. The local expected richness at 100 individuals was similar among sites, with a median of 26 species (0.95 CI: 20–34 species), and likely caused by diversification rate and evolutionary time acting at the same pace on populations. The taxonomic β-diversity was high and without differences among sites (median: 0.85; 0.95 CI: 0.33–1), probably due to significant substrate heterogeneity at 10-cm scale. The prevalence of replacement over richness difference suggests that local processes (e.g., environmental filtering and competition) contribute more to β-diversity than niche availability, which would be largely similar across the reef terraces. Contrary to our expectations, no gradient of assemblage structure occurred, nor significant effect of benthic cover on nematodes. However, nematode functional structure showed a conservative set of biological traits reflecting adaptations to hydrodynamic regime: armed oral cavity/intermediate colonizing capability/ornamented cuticles/conical tail. Our results provide insights about the taxonomic and functional diversity of nematodes and highlight the vast knowledge gaps about the processes ruling the meiofauna community structure in coral reefs.

Responses of nematodes to oil contamination in a mangrove sediment: A microcosm study

The effects of oil pollution on nematode assemblages were investigated in a mangrove sediment. Microcosms comprised 350 mL plastic jars filled with 250 g sediment. In the oiled treatments (O), 15 mL oil were added to the soil. In the oil and fertiliser treatments (O + F), oil and fertiliser (N: P: K: 3: 2: 5) were added to the soil. After four weeks, nematodes were extracted and identified. The number of nematode taxa was highest in the C (61), intermediate in the O + F (59) and significantly lower in the O (25) treatment. Taxa present in the C but absent in the O treatment were oil-intolerant. Taxa present in the O treatments were oil-tolerant. Five taxa survived oiling probably due to fertiliser amendment. Oiling eliminated oil-intolerant taxa and favoured those that were resistant. In the O+ F treatment, the number and species of nematodes increased significantly.

Investigations on Nematode Community Dynamics on Pepper Monoculture Vegetations in Otuoke, Bayelsa State, Nigeria

Cultivation of Pepper, a vegetable fruit crop of prominence in Otuoke, is often hampered by parasitic nematode infestation. This negatively affects its economic impact on the rural domestic market. Farmers in Otuoke often ascribe reduced yield to inadequate farming strategy, as they are ignorant of nematode dynamics and resulting damages. This study sought to assay soil and roots of pepper plants for the determination of nematode community dynamics with a view of winging-in rural affordable management option for the agronomical parasites. The soil was collected using a hand trowel and roots were gotten using a knife and the extraction of the parasites was achieved by the use of the modified sieve plate method. The actual assemblage of nematodes was 397 from 11 genera, 205 (51.6%) occurred in farm A and 192 (48.4%) were seen in farm B. Dynamics on nematode diversity and occurrence were seen among species between farms. Meloidogyne species (17.9%) display variable populations between Farms A (19.5%) and B (16.1%). Tylenchorhynchus (11.3%) had a higher number in farm A (14.1%) and unlike in farm B (8.3%). However, Gracilachus (3.0%) and Scutellonema (7.3%)) species were reportedly found in Farm A while Tylenchus (6.5%) Hemicyclophora (5.3%) Pratylenchus (10.1%) and Rotylenchus species (10.1%) were peculiar to farm B. The result suggests that extensive fluctuations in nematode assemblage are possible even in fields with similar characteristics. Nematode occurrence on the root tissue of pepper plants in this study implies danger to quality productivity. Therefore, farmers should adopt poultry filters as manure for the cultivation of crops in the area. Farmers should also adopt exposing agricultural land to direct sunshine for a minimum of three weeks after clearing before tillage. The heat will help inhibit nematode profusion and check population abundance in soil for proper cultivation of crops.

Setting an Environmental Baseline for the Deep-Sea Slope Offshore Northwestern Cuba (Southeastern Gulf of Mexico) Using Sediments and Nematode Diversity

Deep-sea offshore northwestern Cuba is the less studied zone of the Gulf of Mexico (GoM). Our study aimed to set an environmental baseline and investigate a potential west-east gradient of sediment properties and nematode diversity along the northwestern Cuba. Sediments were collected by multicorer at nine sites in the insular slope between 974 and 1682 m depth. Sediment texture and composition showed a west-east gradient caused likely by narrowing of shelf width and increasing of downslope transport of terrigenous material. We found clear signatures of heavy metal pollution likely derived from Havana City but also from open-sky mining (Castellanos mining complex) and port dredging operations (Mariel). Nematode assemblages were dominated by the deep-sea genera: Acantholaimus, Metadasynemella, Desmodorella, Cervonema, Daptonema, Halalaimus, and Pselionema. α-diversity was about 20–50 genera and γ-diversity of about 100 genera. The β-diversity was substantial likely because small-scale patchiness of resources and heavy metals stress that increased assemblage variability. Individual weight decreased with depth indicating food-supply limitation in the deep sea; also, heavy metals were negatively correlated with weight suggesting deleterious effects on the growing. Our findings indicate that heavy metal pollution has reached deep-sea sediments and corroborate the long-range effects of anthropogenic activities on deep sea. Taxonomic diversity and biological traits (life strategy and trophic composition) constituted a powerful bioindicator of benthic health and benchmark for future potential disturbances in the region. Northwestern Cuba slope is still an understudied portion of the GoM and more research is needed to fully understand its biodiversity and biogeochemical patterns.

Simple, inexpensive, and rapid approach to detect changes in the structure of soil free-living nematodes.

A general limitation of ecological investigations based on nematodes is related to the difficult and time-consuming taxonomic identification of species. Therefore, nematologists are investing many efforts to develop alternative approaches as proxies applicable in biomonitoring assessment. Recently, an alternative method that combines morpho-functional traits was proposed for detecting assemblage changes of marine nematodes. In view of the promising results, it was tested the same approach to document taxonomic structure changes of soil free-living and plant parasitic nematodes. Specifically, this attempt was carried out using three data sets that include studies from various European regions and different types of ecosystems: forests, grasslands and maize crops. Multivariate statistical analysis revealed that the simple combination of the four traits (i.e., buccal cavity cuticularization occurrence, amphideal fovea size and shape, morphology of the cuticle and pharynx) in a single code number perfectly mirrors the taxonomic structure trends of the nematode assemblage at genus level. Therefore, we predict that similar results can be also obtained by directly encoding nematode specimens with the selected traits and we point to new important advances if this procedure can be coupled with advanced machine learning.

A combined amplicon approach to nematode polyparasitism occurring in captive wild animals in southern China

BackgroundGastrointestinal tract (GIT) nematodes prefer to live in the intestines of wild animals, causing damage and even death, and posing a zoonotic risk. The polyparasitism of GIT nematodes results in the complex dynamics of the nematode communities that occur naturally in wild animals. However, the nematode community in captive wild animals is poorly understood.MethodsWe combined microscopic examination and amplicon sequencing for community diversity.ResultsWe characterized GIT nematode assemblages to one order, one family, four genera, and ten species, in 512 fecal samples of 121 species from captive wild animals in southern China. The positive rate of GIT nematodes was 20.7% (106/512), including 42.3% (11/26) in reptiles, 26.5% (39/147) in herbivores, 25.0% (25/100) in non-human primates, 20.0% (5/25) in omnivores, 12.2% (9/74) in carnivores, and 12.1% (17/140) in avians. The dominant nematodes were Haemonchus contortus in herbivores and Trichuris species in primates. The nematode communities of arboreal primates differed from their terrestrial counterparts, reflecting both host phylogeny and ecological constraints. Soil-transmitted Strongyloides species were widespread throughout the herbivore, primate, avian, and carnivore communities, and tended to infect omnivorous primates and terrestrial herbivores. In addition, new Trichuris and Heterakis species were found in the nematode communities of captive porcupines and peafowls.ConclusionThis study highlights the variation in the composition of the GIT nematode community and strengthens the attention to the harms induced by zoonotic nematodes and co-infective nematodes with low species richness.Graphical

Nematodes as bioindicators of soil health in different land uses in the São Francisco River Valley, Brazil

Summary Brazilian Caatinga is one of the most diverse, seasonally dry, tropical forests of the world and is threatened by strong land use pressure and poor protection. One way of understanding changes in the soil conditions caused by anthropogenic activities is using the nematode assemblages as potential bioindicators. This study analysed changes in nematode communities in three different types of land use (natural forest-CA, natural area with accumulation of salts-SS, and agricultural growing areas, such as cover crops-CC for cattle and fruit trees-IC) in the Caatinga, in the sub-median region of the São Francisco River Valley (SFRV), Pernambuco, northeastern Brazil. We recorded a total of 63 262 nematode individuals, representing 42 genera, belonging to 23 families. Nematode abundance, diversity and maturity indices were highest in the CC and lowest in the SS. Among the nematode trophic groups, bacterivores, omnivores + predators and plant parasites were significantly affected by type of land use. Different soil properties were related to the differences in taxonomic composition among the natural and agricultural areas, accounting for 26.6% of the total variation. In general, our results indicate that soil salinisation and desertification in the natural areas, as well as soils subjected to cover crops and fruit tree production, significantly influenced the composition of nematode communities in the São Francisco River Valley.

Effects of seagrass (Cymodocea nodosa) restoration on nematode biodiversity

Seagrass meadows are hot spots of biodiversity and play a key role in the provisioning of ecosystem goods and services but are often subjected to a regression due to a combination of multiple anthropogenic and climate-induced impacts. The ecological restoration of these habitat-forming species is a priority to reverse biodiversity loss and for the recovery of key ecosystem functions. Here we investigated the effects of seagrass (Cymodocea nodosa) restoration action on benthic biodiversity recovery assessed by a time-series analysis carried out for one year. We used nematode assemblages, the most widespread metazoan on global sediments, as a proxy of benthic biodiversity and compared the species richness, expected species number (ES51) and composition in donor and in restored seagrasses and in the adjacent unvegetated sediments. One year after the intervention, nematode biodiversity in restored seagrasses was more similar to that of the donor site than in unvegetated sediments, suggesting a progressive recovery. Overall, the nematode biodiversity of the restored seagrasses resulted in an intermediate level between unvegetated and pristine seagrass meadows, providing evidence that restoration intervention contributed to biodiversity recovery. Pristine and restored seagrass meadows hosted a high number of exclusive species, which resulted in an increase in the overall biodiversity in the investigated location. Our results indicate that the restoration of seagrass meadows has positive effects on benthic biodiversity and contributes to enhance the local biodiversity.

Impact of metal polluted sewage water on soil nematode assemblages in agricultural settings of Aligarh, India

Impact of metal polluted sewage water on soil nematode assemblages in agricultural settings of Aligarh, India

Emergent properties of free-living nematode assemblages exposed to multiple stresses

Biological communities are currently facing multi-stressor scenarios whose ecological impacts are challenging to estimate. In that respect, considering the complex nature of ecosystems and types and interaction among stressors is mandatory. Microcosm approaches using free-living nematode assemblages can effectively be used to assess complexity since they preserve the interactions inherent to complex systems when testing for multiple stress effects. In this study, we investigated the interaction effects of three stress factors, namely i-metallic mixture of Cu, Pb, Zn, and Hg (control [L0], low, [L1] and high [L2]), ii- CO2-driven acidification (pH 7.6 and 8.0), and iii- temperature rise (26 and 28 °C), on estuarine free-living nematode assemblages. Metal contamination had the greatest influence on free-living nematode assemblages, irrespective of pH and temperature scenarios. Interestingly, whilst the most abundant free-living nematode genera showed significant decreases in their densities when exposed to contamination, other, less abundant, genera were apparently favored and showed significantly higher densities in contaminated treatments. The augmented densities of tolerant genera may be attributed to indirect effects resulting from the impacts of toxicity on other components of the system, indicating the potential for emergent effects in response to stress. Temperature and pH interacted significantly with contamination. Whilst temperature rise had potentialized contamination effects, acidification showed the opposite trend, acting as a buffer to the effects of contamination. Such results show that temperature rise and CO2-driven acidification interact with contamination on coastal waters, highlighting the importance of considering the intricate interplay of these co-occurring stressors when assessing the ecological impacts on coastal ecosystems.

Taxonomic and functional diversity of nematode fauna: two sides of the same coin in the ecological quality assessment of transitional environments

The spatiotemporal variation in taxonomic indices and functional traits of the nematode fauna was investigated along two major environmental (salinity and organic matter enrichment) gradients in the Cabras Lagoon (Sardinia, Italy). We aimed to assess, for the first time in a transitional system of western Mediterranean Sea, how taxonomic and functional components of nematode assemblage respond to such environmental factors. The taxonomic structure was the most sensitive metric to document changes in the nematode assemblage, showing significant differences in relation to all the factors and their interactions. All the taxonomic and functional nematode features, except for the maturity index (MI), proved salinity and organic enrichment to be the primary drivers of nematode distribution. The lack of significant variation in the MI is quite interesting and can be interpreted because of the marked adaptation of nematodes to highly dynamic environmental conditions of brackish and confined habitats. Temperature mainly affected faunal composition, abundance, and diversity, due to its influence on fecundity and biological cycles on almost all species. Integrating the taxonomic and functional components of nematodes as “two-sides of the same coin”, the Shannon diversity index, the percentage of coloniser–persisters and the MI were used together to assess the Ecological Quality Status (EQS) of the study sites, which ranged from poor to bad. Nematodes proved to be good indicators of the environmental variations in the investigated lagoon ecosystem. Importantly, the joint use of taxonomic and functional approaches provided integrative knowledge of nematode response to environmental gradients. We conclude that combining nematode-based taxonomic and functional indicators represent a valuable tool to assess the environmental quality of lagoonal ecosystems and may provide complementary information to macrofauna.

The nematode assemblages of a lake ecosystem (Lake Korugöl Natural Park, Düzce, West Black Sea Cost of Türkiye): ecology and biodiversity patterns with first reports of 10 genera to the Türkiye nematofauna

This research was conducted to reveal the soil nematode fauna of Korugöl, Düzce and to contribute to the nematode diversity of the Western Black Sea Region of Türkiye. Field studies within the scope of the study were implemented in 2021. As a result of the study, 29 families, 45 genera and 46 nematode taxa were identified. 10 nematode taxon, namely Aporcelinus, Baladorylaimus, Dorylaimoides, Euteratocephalus, Labronemella, Laimydorus, Lindseyus, Metateratocephalus, Paractinolaimus and Tripylella are the first report for Türkiye's nematofauna. Classification of nematodes according to their feeding types were: 27.27% bacterivorous nematodes, 2.10% fungivoresnematodes, 1.51% herbivorous nematodes, 16.35% predator nematodes and 52.77% omnivorous nematodes.

Cover crops in pear (Pyrus communis) orchards: effects on soil nematode assemblage

Long-term vegetation cover can affect soil organic carbon content and carbon flow within the soil food web. Nematode trophic structure and soil properties were evaluated in pear rows (intra) maintained without weeds applying herbicide and in the inter-rows (between rows) covered with: Medicago+grasses (MG), fescue or spontaneous vegetation. Soil samples were taken at 0-20 and 20-40 cm depths from 2012 to 2014. Nematode assemblage was different in each inter-row and row, mainly in the topsoil. The inter-rows were reservoirs of omnivores-predators. The MG inter-row promoted the highest accumulation of organic carbon, total N and exchangeable K in the soil. The enrichment index was related to the quantity of dry matter produced by cover crops with the highest index observed in MG. Nematode biomass showed a positive correlation with intra and inter-rows soil organic carbon. Carbon flow through bacterivores prevailed in intra-rows, while bacterivores or herbivores canalized the inter-rows. Highlights: Each cover crop (Medicago+grasses, spontaneous vegetation and fescue) was associated with a different nematode assemblage, mainly in the topsoil. Omnivores-predators were higher in the inter-row than its associated row. Nematode Biomass showed a positive correlation with the content of SOC in the row and in the inter-row. Soil energy channels revealed higher carbon flow within the soil food web under Medicago+grasses and spontaneous vegetation than under fescue.

Distribution patterns of benthic bacteria and nematode communities in estuarine sediments

Benthic organisms are crucial in the regulation of the ecosystem functions. The interactions between benthic nematodes and sediment bacteria across divergent environmental conditions are poorly understood. The main goal of this study was to understand the spatial distribution patterns and diversity of benthic bacterial communities and nematode assemblages of the intertidal sediments in three sampling sites (Navigator, Tróia and Moinho) along Sado Estuary (SW, Portugal). Bacterial communities were described using a 16S metagenomic approach, while nematode assemblages were characterized using morphological identification. Overall, bacterial and nematode communities presented significant diversity between sites (p < 0.05), which is primarily related with the environmental variables (e.g., organic matter and percentage of gravel). The spatial distribution of bacterial communities was in accordance with the ecological conditions of three selected sites at a larger scale than nematode assemblages. Previously described as good ecological indicators, nematode assemblages were separated at sampling site level, suggesting that their response is driven by within site specific factors at a smaller scale. Hence, the present study set a fundamental ground for future research on functional interactions between bacteria and nematodes.