Spatial distribution of subtidal Nematoda communities along the salinity gradient in southern European estuaries

Nematode community structures in the presence of wastewater treatment plant discharge

Wastewater treatment plants (WWTPs) represent major point sources of pollution in coastal systems, affecting benthic ecosystems. In the present study, we assessed the potential role that WWTPs have in shaping nematode communities and established baseline knowledge of free-living nematode community structures in St. Andrew Bay, Florida. Sediment samples were collected from four sites representing areas of WWTP outflow and areas with no apparent outflow, during the winter and summer. Nematode communities across sites were significantly different, and the differences were strongly associated with the distance to the nearest WWTP. While the communities were not different along transects at each site, nor across seasons, community dissimilarity across sites was high, implying strong contrasts throughout the bay system. Dominance of tolerant, opportunistic genera and Ecological Quality Status assessments suggest that the system is stressed by organic enrichment, possibly linked to the WWTPs. Our results suggest that knowledge on the life-history of dominant genera is imperative to assess the ecological quality of a benthic system, in addition to taxonomic and functional metrics. Considering the value of marine nematodes as bioindicators, more work should be done to monitor temporal variability in nematode communities in this system as future infrastructure changes alter its dynamics.

Transition of an estuarine benthic meiofauna assemblage 1.7 and 2.8 years after a mining disaster

Background

Estuaries are transitional coastal ecosystems that are threatened by multiple sources of human pollution. In 2015, mining tailings from an upstream dam failure caused massive metal contamination that impacted benthic assemblages on the Brazilian Rio Doce estuary.

Methods

In this study, we investigate and compare meiofaunal assemblages with eDNA metabarcoding 1.7 years (2017) and 2.8 years (2018) after the initial contamination by mine tailings in order to evaluate the continued impact of sediment mine tailing contaminants on the structure of benthic assemblages after the disaster.

Results

The community was dominated by Arthropoda and Nematoda 1.7 yr after the impacts (42 and 29% of meiofaunal sequence reads, respectively) but after 2.8 years Arthropoda (64.8% of meiofaunal sequence reads) and Rotifera (11.8%) were the most common taxa. This continued impact on meiofaunal assemblage revealed a lower phylogenetic diversity (7.8-fold) in 2018, despite overall decrease in metal concentration (Al, Ba, Cr, As, Fe, Zn, Mn, Pb, Cd, Co) in sediments. Our data suggests that differences in benthic assemblages and loss of diversity may be influenced by contaminants in sediments of this estuary, and indicate that broad eDNA assessments are greatly useful to understand the full range of biodiversity changes in dynamic estuarine ecosystems.

Impact of a dam construction on the intertidal environment and free-living nematodes in the Ba Lai, Mekong Estuaries, Vietnam

The impact of high siltation and accumulation of organic and waste material in the intertidal of the dammed Ba Lai River in Vietnam as part of the Mekong estuarine system was investigated by means of marine free-living nematodes. Nutrients content (nitrate, ammonium, total phosphorus, total nitrogen), total suspended solids, total organic carbon, coliform, bacteria E. coli, pH, dissolved oxygen, total dissolved solids, methane and hydrogen sulfide concentration, and the nematode communities were characterized in sediment at selected stations along the river above and below the dam. Our results found elevated methane concentrations at the upstream side of the dam while hydrogen sulfide concentrations found to be highest in the downstream side of the dam. Furthermore, methane and hydrogen sulfide concentrations were correlated to nematode community characteristics such as trophic composition densities and genera composition. There was a clear difference between the communities above and below the dam. The discontinuous nematode community distribution indicated that the Ba Lai River is impacted by dam construction. Potentially the high deposition and eutrophication could turn the area into a methane-rich area related to predicted impact on nematodes.

Influence of salinity on the meiofaunal distribution in a hypersaline lake along the southeast coast of India

The present study highlights that seasonal salinity variability plays a significant role in meiobenthic distribution with special reference to nematode assemblages. Sediment and water samples were collected from Pulicat Lake, a hypersaline lake along the southeast coast of India during two seasons (Southwest Monsoon (SWM) and Northeast Monsoon (NEM)). Based on the salinity distribution, the lake is categorized into four regions, viz., southern inlet, central region, middle inlet, and northern inlet. Meiobenthic abundance was higher during SWM (226-12,206 Ind/10 cm²) than in NEM (640-10,424 Ind/10 cm²). The meiofaunal abundance was high in the central region during both the seasons, followed by the southern, northern, and middle inlet. The nematode was the dominant meiobenthic group, followed by copepod, polychaete, and foraminifera. Due to high organic matter, the central region was dominated by deposit feeding nematode species like Halalaimus longicaudatus and Terschellingia longicaudata. The southern and northern regions were dominated by free-living nematodes Rhabditis olitoria, Mesorhabditis capitata, Mononochus bastian, Paramononchus sp., Piranchulus sp., and Diploscapter cylindricus. Oncholaimus sp., a hypersaline indicator species, was reported from the middle inlet location. Statistical analysis suggests salinity as a critical parameter for the distribution and diversity of nematodes.

Environmental drivers of meiofaunal natural variability, Egypt, Southeastern Mediterranean

Sandy beaches are challenging ecosystems, in which biota experience extreme physical conditions. We sampled meiofauna in conjunction with environmental factors that are well-known to affect faunal associations to describe the ecological state of sandy beaches that experience natural and human-made disturbances. We applied a random stratified sampling design with monthly collections (1800 cores) at three beaches on the Alexandria, Egypt, coast during two sampling periods over 1 year from November to April and May to September. We used multivariate analyses to compare beaches for water quality, particle size, and meiofaunal assemblages. The environmental analysis explained 60% of the total variation of physical factors among beaches and grouped beaches that moderately sorted fine-grained sand and high water salinity vs. the beach with well-sorted, coarse-grain, and low salinity. Meiofaunal analyses revealed unexpected results. The abundance and temporal variation were low, and the explained proportion of natural variation by the putative environmental factors was small. The natural variation was an indicator of long-term beach ruin and oligotrophic conditions. Our results suggest that a large fraction of natural variation in beach meiofauna is stochastic or that other, non-measured, the natural forces (e.g., storm events) or human-made forces (e.g., tourism activities) are essential contributors to variation. Our best models indicate that meiofauna is more resilient to natural disturbances than to human-made stressors, and the higher the beach exposure to the synergetic effects of natural forces and anthropogenic stressors, the lower the ecological state is.

The Effect of a Dam Construction on Subtidal Nematode Communities in the Ba Lai Estuary, Vietnam

Nematode communities and relevant environmental variables were investigated to assess how the presence of a dam affects the Ba Lai estuary benthic ecosystem, in comparison to the adjacent dam-free estuary Ham Luong. Both estuaries are part of the Mekong delta system in Vietnam. This study has shown that the dam’s construction had an effect on the biochemical components of the Ba Lai estuary, as observed by the local increase in total suspended solids and heavy metal concentrations (Hg and Pb) and by a significant oxygen depletion compared to the natural river of Ham Luong. The nematode communities were also different between the two estuaries in terms of density, genus richness, Shannon–Wiener diversity, and dominant genera. The Ba Lai estuary exhibited lower nematode densities but a higher diversity, while the genus composition only slightly differed between estuaries. The results indicate that the present nematode communities may be well adapted to the natural organic load, to the heavy metal accumulation and to the oxygen stress in both estuaries, but the dam presence may potentially continue to drive the Ba Lai’s ecosystem to its tipping point.

Ecostructuring of marine nematode communities by submarine groundwater discharge

Inputs of submarine groundwater discharge (SGD) to the coastal ocean may alter local and regional-scale biology. Here, we report on nematode assemblages along the north shore of Long Island, NY. We test if nematode communities differed between sites impacted by mixed fresh-saline SGD and where SGD is exclusively saline. Diversity of nematodes was low at sites impacted by fresh SGD and communities were dominated by a few opportunistic genera. Moreover, a set of typical freshwater nematode genera restricted to impacted sites was observed. Their presence in the marine coastal zone is exceptional and underlines the structuring role that fresh SGD plays in the local ecosystem. Saline SGD structured nematode assemblages differently compared to sites impacted by fresh SGD. The number of nematode genera was markedly higher at saline SGD sites, with a different community structure. This study highlights the importance to which inputs of fresh SGD may have on local ecosystem diversity in marine coastal environments.

Intertidal nematode communities in the Mekong estuaries of Vietnam and their potential for biomonitoring

Nematode communities in eight Mekong estuaries were investigated during the dry season. The aim of the study was to identify the structure and the diversity of the communities in relation to the main environmental characteristics. In each estuary, three to four intertidal sampling stations were identified at regular distances from the mouth to up to 45 km land inward. The nematode communities showed a strong correlation with sediment composition and to a lesser degree with chlorophyll a concentrations. Multivariate analysis resulted in the identification of four types of communities. We identified two types of Desmodora communities in the sandy mouth stations and two types of Parodontophora communities in the silty sand stations. One of the silt associated communities showed a preference for higher chlorophyll a concentrations, resulting in higher densities and higher diversity, mainly of monhysterid species. Because of the strong association between community structure and sediment composition, nematodes are a meaningful tool for monitoring changes in their environment. In case their community deviates from what is expected based on sediment, it may serve as an early warning for disturbance.

Irrigating poplar energy crops with landfill leachate negatively affects soil micro- and meso-fauna

Increased municipal solid waste generated worldwide combined with substantial demand for renewable energy has prompted testing and deployment of woody feedstock production systems that reuse and recycle wastewaters as irrigation and fertilization. Populus selections are ideal for such systems given their fast growth, extensive root systems, and high water usage rates. Maintaining ecological sustainability (i.e., the capacity for an ecosystem to maintain its function and retain its biodiversity over time) during tree establishment and development is an important component of plantation success, especially for belowground faunal populations. To determine the impact of solid waste leachate on soil micro- and meso-fauna, we compared soilfrom eight different Populus clones receiving municipal solid waste landfill leachate irrigation with clones receiving fertilized (N, P K) well water irrigation. Microfauna (i.e., nematodes) communities were more diverse in control soils. Mesofauna (i.e., insects) were associated with all clones; however, they were four times more abundant around trees found within the control plot than those that received leachate treatments. Nematode and insect abundance varied among Populus clones yet insect diversity was greater in the leachate-treated soils. Phytotechnologies must allow for soil faunal sustainability, as upsetting this balance could lead to great reductions in phytotechnology efficacy.

An Ecological Study of Free-living Marine Nematodes in Teluk Awar, Sarawak, Malaysia

The community structure of marine nematode assemblages in the southern-west of Borneo was investigated with special focus on the horizontal distribution from high tide to subtidal area. A transect study had been conducted in Teluk Awar. Nine stations were chosen from the Mean High Water Neap to Mean Low Water Neap level. The physico-chemical characteristic of water and sediments were determined both ex situ. One-way ANOVA showed that the environmental variables among stations were significantly different (except chlorophyll a and total organic matter). Multi-dimensional scaling demonstrated three distinct patterns among the stations while dendrogram showed high dissimilarity percentage in the species distribution among stations. In conclusion, the results showed that environmental variables such as clay, total organic matter and temperature were affecting the nematode distribution pattern in Teluk Awar.