Free-living Nematode Assemblages Research Articles

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.

Free-living nematode assemblages along a water-depth gradient in the Perdido belt, northwestern Gulf of Mexico

This study investigated nematode assemblages in the Perdido belt, northwestern Gulf of Mexico (GoM) in terms of species composition, distribution, density, and diversity. We examined 27 sediment samples collected at depths of 44-3466 m. The nematodes were identified at the lowest level possible and classified into four trophic groups based on their buccal cavity. Additionally, their sex and stage of life were determined. The sediment composition was determined, as well as the percentage of organic carbon (OC). The density per site fluctuated between 0.02 and 13.30 ind/10 cm2. A total of 1768 nematodes were identified, belonging to 9 orders, 35 families, 96 genera, and 153 species, of which 9 genera and 15 species are new records for the GoM. The families Xyalidae and Comesomatidae were the most diverse genera (9 and 8, respectively). Sabatieria sp. 1 was the most abundant and widely distributed species. The number of species varied at different depths (range 1-60 species) and Pielou evenness (0.7-1). Most of the organisms collected were adult females. The non-selective deposit feeders were the most abundant (49%), followed by epigrowth feeders (20%). Most of the sites consisted of sand (range 10.1-70.2%). The percentage of OC varied at different depths (0.1-1.4%). No significant correlation was found between species richness and depth. The species composition changes with depth, density and most of the trophic groups tend to decrease with increasing depth. The dominant species are more related to the percentage of sands and silts than to clays and OC.

Assessment of Benthic Free-Living Nematode Assemblages Diversity in Kune – Vain Wetland (Adriatic Coast, Albania)

This work presents preliminary data on benthic free-living nematode assemblages from Kune-Vain Wetland Complex, situated in the northern part of the Adriatic coast in Albania. The study was carried out during a joint ecological approach, to collect chemical-physical and biological data of the wetland and evaluate the hydrological intervention in improving the environmental situation and increase resilience to climate change. The sampling was conducted bimonthly from July 2018 – July 2019, in three main water body component of Kune-Vain wetland, Ceka, Zaje and Merxhani. Nematode assemblages were analyzed in term of composition and structure, determining taxonomic composition up to genus level and biological traits. Nematodes were the dominant component of meiobenthos in all three water bodies, comprising 98-100%. Their taxonomic composition reflected the chemical features of transitional habitat dominated by brackish genera. Genera composition revealed different diversity patterns among water bodies. The most dominant genera were Sabatieria and Terschellingia, both deposit feeders and characteristic of bad ecological quality status.

Free-living nematode assemblages associated with maize residues and their ecological significance.

Return of plant residues to the soil is a sustainable way of enhancing plant growth, health, and levels of soil quality. In Kenya, maize plant residues are the most commonly returned plant material in many agro-ecosystems. For any plant material to release nutrients into the soil, it must undergo a decomposition process that is usually affected by various organisms, especially nematodes. Despite their great contribution to the breakdown of plant organic matter, there is a dearth of information on the interaction between maize residues and free-living nematodes (FLN) in Kenya. In this respect, this study aimed to assess the influence of decomposing maize residues on FLN dynamics and the soil food web in Mwea, Kenya. The experimental plots were set up in a randomized complete block design, comprising of decomposition plots (incorporated with maize residue to a depth of 30 cm at a rate of 5 tons/hectare), while the plots unincorporated with maize residues were used as the control. Each treatment consisted of four replicates. In all, 30 FLN genera were recovered from the field trials, whereby Acrobeles was significantly abundant in decomposition plots in both seasons. We subsequently found that maize residues reduced the abundance of enrichment opportunist bacterivores (cp-1) relative to general opportunist (cp-2) bacterivores and fungivores. Notably, the results of the channel index showed that the decomposition of maize residues was dominated by fungal energy channels throughout the study in the two seasons. These results suggest that maize residues need to be coupled with a suitable labile organic matter. This would lead to sustainable, active, and reliable turn-over of maize residues into the soil food web ecosystems. The application of labile materials can also help to improve the population of enrichment bacterivores that are essential in the decomposition process. This study shows that the decomposition of maize residues influenced FLN composition, mainly the enrichment opportunist bacterivores whose abundance was lower.

Diversity patterns of free-living nematode assemblages in seagrass beds from the Cuban archipelago (Caribbean Sea).

Diversity patterns of free-living marine nematodes in tropical seagrass beds are understudied. Here, we describe the species richness and assemblage composition of nematodes in 13 seagrass sites covering the whole Cuban archipelago. Nematodes were collected from Thalassia testudinum seagrass beds and identified to species level. We provide a checklist of nematode species from seagrass beds. The species richness of nematode assemblages is high, with 215 species, 138 genus, 35 families, seven orders and two classes. That γ-diversity is higher than other studies and points to seagrass beds as diversity hotspots of free-living marine nematodes. Local species richness in seagrass bed sites is about 57 ± 17 species and broadly similar across the sites, despite the environmental heterogeneity. The geographical distance plays a weak, but significant, role on the decay of similarity likely affected by limited dispersal of nematodes. The pairwise similarity values, related to poor-coloniser nematodes, were twice more affected by the distance than those related to good-colonisers, possibly due to differential success of transport and settlement.

Soil nematodes in the rhizosphere of a metal accumulating plant in a pollution gradient from a non-ferrous metal factory in Bulgaria

Nematodes were studied at sites with low, medium and high level of soil metal contamination in the area of a non-ferrous metal plant. Soil total metal concentrations ranged from values below their maximum permissible concentrations (MPC) in soil to 48, 44, 16 and 4 times higher than the MPC for Cd, Pb, Zn and Cu, respectively. Nematodes were isolated from uncultivated, monoculture stands of the metal accumulating mustard weed (Lepidium draba L., Brassicaceae) in April, May and June 2015. Overall, 55 nematode genera were identified during the investigation: 50 genera at low, 39 at medium, 37 at high levels of soil metal pollution. Several nematode diversity measures and the specific responses of some nematode genera differentiated the three investigated sites. Both nematode richness (S) and diversity (H') of genera correlated negatively with the soil metal concentrations in the following order: Cd>Pb>Zn>Cu. Several genera (Alaimus, Cylindrolaimus, Paramphidelus, Scutylenchus, Steinernema) were common at the least contaminated site and were either rare or not found at the rest of the sites. Some genera (Clarkus, Filenchus) were most abundant at the medium level of contamination. The abundance of eleven genera correlated negatively with the metal concentrations in the samples. Most of the negative correlations (Acrobeles, Coslenchus, Geomonhystera, Plectus) were in the following order: Cd>Zn>Pb>Cu. The abundance of nine genera correlated positively with the metal concentrations and most of their correlations were in the order: Cu>Pb>Zn>Cd. Faunal profile analyses of the free living nematode assemblages revealed higher values of Structure index (SI) at low (75–91%) and medium (77–87%) levels of contamination in comparison with the most polluted site (35–46%). Nematode structure metabolic footprints (SFP) at low and medium levels of contamination were much higher than at the high pollution level. Both SI and SFP at the medium level of metal contamination indicated low bioavailability and low toxicity of Pb (1290 mg kg-1soil), Cd (34 mg kg-1soil), Zn (1779 mg kg-1soil) and Cu (190 mg kg-1soil) for the free-living nematodes, isolated from the rhizosphere of the mustard weed at this site. The rhizosphere of the metal accumulating plant might be protective for these nematodes, providing conditions of reduced bioavailable metals in contaminated soil during the vegetation period of the plants.

Spatial scale influences diversity patterns of free-living nematode assemblages in coral degradation zones from the Caribbean Sea

Diversity of marine nematodes in coral degradation zones (CDZs) has been poorly studied despite of its contribution to global coral reef diversity; additionally, effects of spatial scales on nematode assemblages are also largely unknown. To fill this gap, we studied the marine nematode assemblages in CDZs from two coral reefs in the Caribbean Sea to describe the diversity, test the effects of spatial scales, and explore if there were adaptive biological trait combinations. We sampled 2 reefs (Ballenatos and Punta Frances), 6 sites, and 20 dead coral piles in a fully nested design identifying the nematodes to species level. CDZs harbored a diverse nematode assemblage of 112 species with large spatial turnover. Differences between reefs in abundance and species density were probably related to differential energy availability, with Punta Frances receiving larger input of material and energy from land. The spatial scale had a significant effect on the species richness, whereas differences in species composition were mainly driven by the scale at which ecological drivers operated (10−1 m for interstitial heterogeneity vs. 105 m for dispersal). Geographical distances in the order of 180 km likely constituted barriers to nematode dispersal and as such promoted assemblage dissimilarity. Our evidence indicated that a particular set of biological traits favored the adaptation of nematodes to CDZs, namely a distinctive combination of armed stoma, ornamented cuticle, and conical tail.

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

Response of estuarine free-living nematode assemblages to organic enrichment: an experimental approach

Response of estuarine free-living nematode assemblages to organic enrichment: an experimental approach

Interannual patterns of the large free-living nematode assemblages in the Mexican Exclusive Economic Zone, NW Gulf of Mexico after the Deepwater Horizon oil spill

The presence and abundance of particular nematode genera in marine sediments are bioindicators of environmental disturbance. They can even reveal the existence of specific toxicants, such as trace-metals and hydrocarbons derived from fossil fuels. We studied this important infaunal component during a three-year monitoring program in Mexico’s Exclusive Economic Zone (EEZ) in the aftermath of a major oil spill in the northern Gulf of Mexico caused by the sinking of the Deepwater Horizon platform (DWH) in April of 2010. A closer look at the nematode composition and density values throughout and after the DWH oil spill revealed considerable changes. Continental shelf and upper slope sediments sampled in the summer of 2010 included 48 genera and a density of 44.45 ind/10cm−2. Eight months later in the winter of 2011, there was a critical decrement in genera number (23) and density (25.22 ind/10cm−2). However, in 2012, the nematode community showed signs of recovery: genus diversity was 58 with a density of 91.45 ind/10cm−2. Significant differences were recorded between the first and the last sampling periods, driven by a remarkable turn-over in genera composition, and by an increase in density of the genera Sabatieria, Dorylaimopsis, and Cheironchus. Similarly, significant spatial differences between the nematofauna of the inner-middle shelf and the deepest zone (>2000m) were detected. Correlation analyses confirmed the tolerant behavior of the above genera to Ni and Co, and their proliferation when hydrocarbon compounds presumably derived from the DWH oil spill increased throughout the study. The Maturity Index (MI) estimated for each survey ranged from 2.35 to 2.6. Environmental Quality Status conditions in the summer of 2010 were good while in the winter of 2011 were poor, and moderate towards the winter of 2012. Index of Trophic Diversity (ITD) values for each survey were high: 0.70, 0.68, and 0.74, respectively. A high predominance of feeding guilds 1B and 2B was recorded throughout the study.The estimated Index of Trophic Diversity (ITD) values resulted high (Table 5). These values apparently indicated that the four feeding types were proportionally distributed in the nematode assemblage. This fact was better reflected during the winter of 2012. Nonetheless, these results are not congruent with the high predominance of feeding guilds 1B and 2B observed throughout the study.

Evaluating environmental drivers of spatial variability in free-living nematode assemblages along the Portuguese margin

Abstract. Understanding processes responsible for shaping biodiversity patterns on continental margins is an important requirement for comprehending anthropogenic impacts in these environments and further management of biodiversity. Continental margins perform crucial functions linked to key ecological processes which are mainly structured by surface primary productivity and particulate organic matter flux to the seafloor, but also by heterogeneity in seafloor characteristics. However, to what extent these processes control local and regional biodiversity remains unclear. In this study, two isobathic parallel transects located at the shelf break (300–400 m) and upper slope (1000 m) of the western Iberian margin were used to test how food input and sediment heterogeneity affect nematode diversity independently from the spatial factors geographical distance and water depth. We also examined the potential role of connectedness between both depth transects through molecular phylogenetic analyses. Regional generic diversity and turnover were investigated at three levels: within a station, between stations from the same depth transect, and between transects. High variability in food availability and high sediment heterogeneity at the shelf-break transect were directly linked to high diversity within stations and higher variation in community structure across stations compared to the upper slope transect. Contrastingly, environmental factors (food availability and sediment) did not vary significantly between stations located at the upper slope, and this lack of differences were also reflected in a low community turnover between these deeper stations. Finally, differences in nematode communities between both transects were more pronounced than differences within each of the isobathic transects, but these changes were paralleled by the previously mentioned environmental changes. These results suggest that changes in community structure are mainly dictated by environmental factors rather than spatial differences at the western Iberian margin. Furthermore, phylogenetic relationships revealed no evidence for depth-endemic lineages, indicating regular species interchanges across different depths.

Effect of heavy metals on soil nematode communities in the vicinity of a metallurgical plant in North Slovakia

Abstract The effect of industrial pollution from chromium ferroalloys production on soil free-living nematode assemblages, c-p groups and generic composition was investigated along 7-km transect. From trace elements (Cr, Cu, Ni and Pb), only chromium exceeded the thresholds for uncontaminated soils (10 mg.kg-1) near the pollution source. In contrast mobilizable fraction of Cr has increased with the distance from the pollution source and was found to be positively correlated with Cox, soil pH, and moisture. Generic richness (nematode diversity) was also higher at remote sites. The low contamination has no significant impact on the nematode communities as illustrated by the c-p groups composition and balanced community structure. Widely applied ecological indices SI and EI also proved maturing ecosystem without any significant stress responses

Spatial and seasonal variations of subtidal free-living nematode assemblages in the northern Beibu Gulf, South China Sea

This study determined the spatial and seasonal density, number of genera, genera composition, maturity index and trophic structure of free-living nematode assemblages in the subtidal waters of the northern Beibu Gulf, South China Sea, and explored whether these five biotic characteristics were related to various environmental variables. Based on the data derived from samples collected seasonally at nine stations, the mean densities of nematodes decreased from alongshore to offshore station in the northern Beibu Gulf. However, the number of nematode genera increased from alongshore to offshore station. Non-parametric multidimensional scaling analysis showed no clear seasonal changes for nematode assemblages in most sampling stations. Higher densities of the generaElzaliaandTricomawere found in offshore sampling stations, and a higher density of the genusCheironchuswas found in alongshore sampling stations. The mean percentage of each feeding type compared to the total numbers was highest in epigrowth feeders (2A), second highest in non-selective deposit feeders (1B), third highest in predators (2B), and lowest in selective deposit feeders (1A). There were significant negative correlations between nematode density and water depth and temperature; significant positive correlations between the number of nematode genera and water depth and salinity; and significant negative correlation between the maturity index of the nematode assemblage and organic matter. BIOENV analysis indicated that water depth, salinity, pH, median sediment particle size and organic matter were the most correlated combination of environmental variables affecting the nematode assemblages.

Effect of disturbances on trophic groups in soil nematode assemblages

AbstractFree-living nematodes in soil ecosystems are vital in the decomposition of organic matter and recycling of nutrients. The effects of various types of disturbances on nematode assemblages were examined in several experiments on a single soil: a short-term detrimental disturbance from solarisation, a short-term beneficial disturbance from amendment addition, and a long-term detrimental disturbance from bare ground without plant cover. Comparison of solarised and non-solarised field plots revealed lower numbers of fungivores in solarised plots. As a result, indices involving ratios of fungivores to bacterivores and fungivores to total free-living nematodes were decreased as well. Addition of an amendment increased numbers of bacterivores. This change was also reflected in calculated indices that expressed trophic groups as percentages of the total free-living nematodes. A severely disturbed site with bare ground that was without plant cover for more than 5 years was compared with an adjacent site maintained in grass. No plant-parasitic nematodes were recovered from the bare ground site, which contained lower numbers of nematodes in all trophic groups than the grass site. However, the structure of the free-living nematode assemblages in both sites was similar, as indicated by the proportions of various trophic groups and by ratios of fungivores and bacterivores. The free-living nematode assemblage in a site with a perceived severe long-term disturbance maintained a trophic structure similar to a site with perennial plant cover.

The response of nematode assemblages to intensive mussel farming in coastal sediments (Southern Brazil)

The impact of mussel farms on the benthic environment was investigated using free-living nematode assemblages as indicators of environmental condition of the Enseada do Brito, a shallow embayment in South Brazil. The studied area is located at the State of Santa Catarina, responsible for 90% of the production of mussel farmed in the country. Samplings were carried out quarterly, from July 2004 to May 2005, below mussel ropes and at control sites located 300 m apart from the longlines. The results suggested that the mussel culture changed ecological functioning of the benthic environment at studied coastal embayment. The intense organic loads due to the biodeposition of the mussel farms, which had been in production for more than 10 years, have turned fine and well-sorted sand bottoms into a muddy deposit with significantly higher total organic content than the control. The number of nematode genera, diversity, dominance and trophic diversity were significantly lower under the mussel farms than at the control sites. The mussel farms biodeposition had also affected the temporal variability of nematode assemblages, which was detected only for samples at the control sites. The low depth and environmental energy, together with the age of the farms, were probably responsible for the observed changes in the nematode assemblages.

Spatial and seasonal variations in the ecological characteristics of the free-living nematode assemblages in a large microtidal estuary

This study has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large southern hemisphere microtidal estuary change spatially and seasonally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at this time and thus when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material (%POM) in the sediment. Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum.

Meiofauna as descriptor of tourism-induced changes at sandy beaches

Tourism has long been considered as a 'clean industry' with almost no negative effects on the environment. This study demonstrated, in two different coastal systems (Mediterranean and Baltic), that tourism related activities are particularly affecting the sandy beach meio- and nematofauna in the upper beach zone, the specific ecotone in which many meiofauna species from both the marine and the terrestrial environment congregate. Tourist upper beaches are characterized by a lower % total organic matter (%TOM), lower densities, lower diversities (absence of Insecta, Harpacticoida, Oligochaeta, terrestrial nematodes and marine Ironidae nematodes) and higher community stress compared to nearby non-tourist locations. The %TOM was found to be the single most important factor for the observed differences in meiofauna assemblage structure at tourist versus non-tourist beaches in both the Mediterranean and the Baltic region. The free-living nematode assemblages from tourist upper zones depart significantly from expectations based on random selections from the regional nematode species pool. Furthermore upper zone assemblages are characterised by a low species diversity consisting of taxonomically closely related nematode species with r-strategist features. Generally, faunal differences between tourist and non-tourist beaches are decreasing towards the lower beach zones.

Nematode communities under stress: the long-term effects of heavy metals in soil treated with sewage sludge

The long-term effects of Ni, Zn+Ni, Cu, Zn+Cu and Zn on the nematode communities in soil treated with sewage sludge were studied in an agroecosystem. The soil was a sandy loam with 9% clay, 1.6–4.0% organic matter (OM) and pH 5.8–7.2. Sewage sludge, artificially enriched with four concentrations of each heavy metal or combinations was applied in 1982 and again in 1986 to some of the plots. Ni and Zn+Ni treatments did not have significant effects on the soil nematode assemblages. Some of the Cu, Zn+Cu and Zn treatments had adverse effects, which correlated with the following changes in their structure, decrease in genus/family richness, decrease in maturity indices (MI and MI 2–5) of the free-living nematode assemblages, reduction or elimination of the persisters ( K-strategists) in favor of colonizers ( r-strategists), decrease or elimination of omnivorous nematodes (Order Dorylaimida, Suborder Dorylaimina) and predatory nematodes (Order Dorylaimida, Suborder Mononchina). The increase in plant-feeding nematodes in the Zn treated plots may be due to the negative effects of the heavy metals on some of their antagonists (e.g., mycorrhizal fungi, root-nodule bacteria from Rhizobium spp .) and the elimination of predacious nematodes in these treatments. Some bacterial-feeding nematodes were found to increase, which was related to the indirect long-term effects of the heavy metals (e.g., lower competition and reduced predation pressure). The most common responses of the nematode communities to soil heavy metal pollution were found to be in agreement with the trends expected in stressed ecosystems and communities, predicted by the hypothesis that stress forces ecosystems into an early stage of development.