Meiofaunal Communities Research Articles

Effects of Recreational Boating on Microbial and Meiofauna Diversity in Coastal Shallow Ecosystems of the Baltic Sea

ABSTRACTRecreational boating can impact benthic ecosystems in coastal waters. Reduced height and cover of aquatic vegetation in shallow Baltic Sea inlets with high boat traffic have raised concerns about cascading effects on benthic communities in these ecosystems. Here, we characterized the diversity and composition of sediment-associated microbial and meiofaunal communities across five bays subjected to low and high degrees of boating activity and examined the community-environment relationships and association with bay morphometry. We found that recreational boating activity altered meiofauna alpha diversity and the composition of both micro- and meiobenthic communities, and there were strong correlations between community structure and morphometric variables like topographic openness, wave exposure, water surface area, and total phosphorous concentrations. Inlets with high boat traffic showed an increase of bacterial taxa like Hydrogenophilaceae and Burkholderiaceae. Several meiofauna taxa previously reported to respond positively to high levels of suspended organic matter were found in higher relative abundances in the bays with high boat traffic. Overall, our results show that morphometric characteristics of inlets are the strongest drivers of benthic diversity in shallow coastal environments. However, while the effects were small, we found significant effects of recreational boating on benthic community structure that should be considered when evaluating the new mooring projects.IMPORTANCE With the increase of recreational boating activity and development of boating infrastructure in shallow, wave-protected areas, there is growing concern for their impact on coastal ecosystems. In order to properly assess the effects and consider the potential for recovery, it is important to investigate microbial and meiofaunal communities that underpin the functioning of these ecosystems. Here, we present the first study that uses DNA metabarcoding to assess how benthic biodiversity in shallow coastal areas is impacted by recreational boating. Our study shows a relatively small, but significant, effect of recreational boating both on meiofauna alpha diversity and meiofauna and bacterial community composition. However, both meiofauna and bacterial community composition in shallow benthic habitats is mediated to a higher degree by abiotic variables, such as topographic openness, area or size of the inlets, and wave exposure. Despite the fact that the effects were small, such impacts on benthic biodiversity should be considered in the management of coastal shallow habitats.

Distribution Pattern of the Benthic Meiofaunal Community Along the Depth Gradient of the Western Indian Continental Margin, Including the OMZ and Abyssal Plain

The continental margin harbors a variety of habitats that support incredible biodiversity and the function of their oceans' ecosystems. The meiofauna is considered a significant component of the benthic faunal community from the polar to the tropical regions. The meiofaunal community in the deep Indian Ocean, especially along the depth gradient, is poorly investigated. The present study aims to explore the benthic meiofaunal community structure along the depth gradients and its associated environment in the western Indian continental margin (WICM) and abyssal plain in the eastern Arabian Sea. Sediment samples were collected from seven different depths (111–3,918 m) along the WICM including the oxygen minimum zone (OMZ) and abyssal plain. A total of 22 taxa (groups) were encountered along the WICM. The nematodes (85%) were the most dominant taxa in all the depths, followed by copepods (11%), nauplii (5%), and polychaetes (1.36%). Our results suggest that (a) the organic matter has accumulated in OMZ sites; (b) a high amount of total organic carbon did not influence the meiofaunal density or biomass; (c) oxygen and depth gradients were significant drivers of the meiofaunal community, low levels of oxygen contributed to lower taxa diversity and density at 485 and 724 m depths; (d) a significant relationship of meiofaunal density and biomass with chloroplastic pigment equivalent (CPE) values indicates pelagic-benthic coupling. Copepods, nauplii, tanaidaceans, isopods, kinorhynchs, and cumaceans were affected by the low-oxygen conditions at the OMZ sites. Enhanced meiofaunal diversity, density, and biomass at deeper sites (non-OMZ-D) was attributed to increased abundance of copepods, nauplii, tanaidaceans, isopods, kinorhynchs, and cumaceans and were mostly concentrated on the surface sediment (0–4 cm) triggered by enhanced bottom-water oxygen and freshness of available food outside the OMZ except 3,918 m. Therefore, the present study showed the meiofaunal community pattern with respect to depth gradients and their related environmental changes, including the OMZ along the WICM and abyssal plain in the Arabian Sea. Based on this study, the future extent of these underestimated marine ecosystems must be considered a priority to understand its functional consequences.

Analysis of similarities (ANOSIM) for 2‐way layouts using a generalised ANOSIM statistic, with comparative notes on Permutational Multivariate Analysis of Variance (PERMANOVA)

AbstractANOSIM (Analysis of Similarities) is a robust non‐parametric hypothesis testing framework for differences in resemblances among groups of samples. The generalised ANOSIM statistic RO is defined as the slope of the linear regression of ranked resemblances from observations against ranked distances in a model describing the unordered or ordered distances among samples under an alternative to the null hypothesis. In the absence of ordering, this becomes the standard ANOSIM R statistic. The construction of 2‐way tests using the generalised statistic in various nested and crossed designs, with and without ordered factors, and with or without replication, is described. Examples are given of 2‐way tests with ordered factors in marine ecological studies: 1. phytal meiofaunal communities in species of macroalgae with increasing physical complexity, among islands in the Isles of Scilly; 2. coral community composition across intertidal flats in Thailand, sampled in different years; 3. macrofauna inhabiting kelp holdfasts from different places in response to an oil spill; 4. experimental effects of salinity stress and food restriction on nematode communities. ANOSIM is fully non‐parametric and thus cannot, for two‐way crossed designs, decompose factors into (metric‐based) main effects and interactions; this requires at least semi‐parametric modelling, such as provided by PERMANOVA. The two approaches therefore test very different hypotheses: ANOSIM gives a robust, comparable and globally interpretable measure of magnitude of overall community change associated with each factor, having excised any possible effect from the factor(s) it is crossed with, irrespective of whether the factors interact or not. PERMANOVA cannot do this because the presence of interactions will compromise (sometimes totally) any overall measures of the main effects of each factor. Conversely, PERMANOVA can test for interactions involving directional (but non‐magnitudinal) community change, which are entirely invisible to ANOSIM. The two methods are therefore seen as complementary, rather than as alternatives.

Meiofauna and nematode community composition in a hydrothermal vent and deep-sea sediments in the Central Indian Ridge

The hydrothermal ecosystem is very unusual, yet little research has so far been conducted on meiofauna in hydrothermal zones. To identify the communities of both meiofauna and nematodes around the Onnuri Vent Field (OVF), we collected sediment from a hydrothermal zone in the OVF and deep-sea (DS) sediments (non-vent) outside the OVF. Sampling was conducted at seven stations using multiple corers on the Research Vessel ISABU in June 2018 and June–July 2019. The average densities of meiofauna ± standard deviation ranged from 21.7 ± 5.2 to 122.3 ± 45.0 individuals/10 cm2. The structure of the meiofaunal community differed between the OVF and DS. The two most dominant groups of meiofauna in both environments were nematodes and harpacticoids. Statistical analyses showed significant differences in the structure of the nematode community between OVF and DS. We also found that the richness, evenness, and diversity of nematodes in the OVF were lower than those in the DS.

A generalised analysis of similarities (ANOSIM) statistic for designs with ordered factors

AbstractIn the study of multivariate data, for example of change in ecological communities, ANOSIM is a robust non‐parametric hypothesis‐testing framework for differences in resemblances among groups of samples. RELATE is a non‐parametric Mantel test of the hypothesis of no relationship between two resemblance matrices. Details are given of the explicit link between the RELATE statistic, a Spearman rank correlation (ρ) between corresponding elements in the two resemblance matrices, and the ANOSIM statistic R, a scaled contrast between the among‐ and within‐group ranks. It is seen that R can equivalently be defined as the slope of the linear regression of ranked resemblances from observations against ranked distances among samples, the latter from a simple model matrix assigning the values 1 and 0 to between‐ and within‐group distances, respectively. Re‐defining this model matrix to represent ordered distances among groups leads naturally to a generalised ANOSIM statistic, RO, suitable for testing, for example, ordered factor levels in space or time, or an environmental or pollution gradient. Two variants of the generalised ANOSIM statistic are described, namely ROc where there are replicates within groups, and ROs where there are only single samples (no replicates) within groups, for which an ANOSIM test was not previously available. Three marine ecological examples using ANOSIM to analyse an ordered factor in one‐way designs are provided. These are: (1) changes in macrofaunal composition with increasing distance from an oil rig; (2) differences in phytal meiofaunal community composition with increasing macroalgal complexity; and (3) changes in average community composition of free‐living nematodes along a long‐term heavy metal gradient. Incorporating knowledge of an ordering structure is seen to provide more focussed, and thus stronger, ANOSIM tests, but inevitably risks losing power if that prior knowledge is incorrect or inappropriate.

Rotifers stimulate the specific uptake rate in lotic phototrophic biofilms

Abstract Stream biofilms can improve water quality (e.g. excessive nitrogen loads) because their microorganisms such as microphytobenthos and bacteria, are involved in self‐depuration processes in the biofilm. In marine sediments, meiofauna can influence primary productivity of phototrophic biofilms, stimulate bacterial growth, and exert a significant role on nitrogen cycling. We hypothesised that in rivers biofilms, increased meiofauna abundance in combination with nutrient enrichment can lead to improve biofilm nutrient uptake ability. River biofilms (from the Garonne River, France) were incubated in flumes supplied with natural river water. The uptake rates of the biofilms as well as the response of microorganisms were studied under different conditions of meiofaunal density and concentration over a 10‐day experiment. Rotifers dominated the meiofauna community in all biofilms. Under high nitrate conditions, the biofilm uptake rate was significantly higher in meiofauna‐enriched than non‐enriched biofilms over the first 2 days. This suggests that under high nitrate concentration conditions, high densities of rotifers enhanced the nitrogen uptake capacity of phototrophic biofilm despite a lower biomass. Densities of rotifers and bacteria in biofilms were positively correlated under enriched conditions suggesting that these two communities interacted over the experimental period. Signature pigment concentrations show that, under low concentrations of , biomasses of diatoms and green microalgae were higher in meiofaunal‐enriched than non‐enriched biofilms, indicating that rotifer activity favoured biomass accumulation of these algae. This study demonstrates that meiofauna inhabiting biofilms may contribute to the limitation of nitrogen loads in stream water and supports the thesis that the potential interactions between faunal groups and microbial communities of biofilms merits further investigation to improve our understanding of processes which regulate interactions between biofilms and the overlying water in rivers.

The Three Domains of Life Within the Discharge Area of a Shallow Subterranean Estuary at a High Energy Beach

Subterranean estuaries (STEs) play an important role in linking nutrient cycling between marine and terrestrial systems. As being the primary drivers of nutrient cycling, the composition of microbial communities and their adaptation toward both, terrestrial and marine conditions are of special interest. While bacterial communities of STEs have received increasing scientific attention, archaeal and meiofaunal diversity was mostly neglected. Previous studies at the investigated sampling site, the STE of a mesotidal beach at the German North Sea island of Spiekeroog, focused on spatial and seasonal patterns of geochemical and bacterial diversity. By additionally investigating the archaeal and meiofaunal diversity and distribution, we now aimed to fill this gap of knowledge to understand the microbial response to submarine groundwater discharge (SGD). The topography of Spiekeroog beach and associated geochemical gradients in porewater displayed a distinct cross-shore zonation, with seawater infiltration on the upper beach at the high water line (HWL), and saline and brackish porewater exfiltration (SGD) at the ridge-runnel structure and the low water line (LWL) on the lower beach. This led to a higher evenness of prokaryotic communities in lower beach areas impacted by SGD compared to unimpacted areas. Archaea contributed 1–4% to the 16S rRNA gene sequence dataset. Those were dominated by Nitrosopumilaceae, corresponding well to higher concentrations of NH4+ in the discharge area of the STE. The unimpacted sites had elevated abundances of Wosearchaeia, which were also detected previously in impacted areas of an STE at Mobile Bay (Gulf of Mexico). While a large proportion of prokaryotes were present in the entire intertidal area, meiofaunal community compositions were site specific and dominated by nematodes. Nematode communities of the high-water line differed distinctively from the other sites. Overall, our data indicates that the three domains of life display distinctly different adaptations when facing the same conditions within the STE. Therefore, distribution patterns of any domain can only be understood if all of them, together with basic environmental information are investigated in an integrated context.

Organic biomarkers and Meiofauna diversity reflect distinct carbon sources to sediments transecting the Mackenzie continental shelf

During the Arctic spring freshet, the Mackenzie River delivers large amounts of dissolved and particulate terrestrial organic carbon to the Canadian Beaufort Sea shelf. This pulse of material and nutrients fuels phytoplankton blooms in late spring and summer and together with under ice primary production contributes to the organic carbon reservoir of the coastal shelf sediments. As a component of the Marine Arctic Ecosystem Study (MARES), samples transecting the Canadian Mackenzie Trough were collected in fall before ice cover to examine the balance of marine and terrestrial carbon in sediments and its relationship with sediment meiobenthic diversity and abundance. Organic biomarker analysis of lipid proxies together with total hydrolyzable amino acids (THAA) defined organic matter sources and potential lability. Across the shelf transect, consistent values observed in sedimentary total organic carbon (1.09%–1.62%) belied a shift in the balance of terrestrial and marine carbon sources. Predominately terrestrial inputs at the shallow site near the delta outflow appeared to constrain meiofaunal populations while the deepest location off shelf reflected lower labile marine organic carbon reaching the sediments that limited benthic production. Surface sediments at the mid-shelf, however, showed a near 3-fold increase (to 1.16 mg C OC-1) in contributions by diatoms and dinoflagellates markers plus a peak in total amino acids (9.53 mg g OC-1) which corresponded with higher meiofauna abundance. The combination of detailed organic analysis together with meiofaunal community measures suggest that mid-shelf sediments receive higher contributions of labile marine carbon which drive increased meiofauna diversity and abundance despite the large background of terrestrial organic material exiting the Mackenzie River outflow.

Meiofaunal Community Spatial Distribution and Diversity as Indicators of Ecological Quality in the Bohai Sea, China

The Bohai Sea is a semi-enclosed marginal sea in the North West Pacific. Meiofauna samples were collected from 22 stations in the Bohai Sea to document the spatial distribution, structure, and diversity of the meiofaunal community and investigate the major factors influencing the community features. A total of 20 higher taxa of meiofauna were identified. The dominant group was Nematoda, accounting for 90.8% of the total meiofaunal abundance on average, followed by Copepoda, Bivalvia, Polychaeta, Kinorhyncha, and Ostracoda. Meiofaunal abundance ranged from 121 ± 89 ind (10 cm2)−1 to 3042 ± 1054 ind (10 cm2)−1. Diversity indices also varied among different stations, with a Margalef’s richness index (d) of 1.1–3.1, Shannon-Wiener diversity index (H′) of 0.7–1.8, and Pielou’s evenness index (J′) of 0.4–0.8. Meiofaunal abundance and diversity indices were significantly lower in the areas of Bohai Bay and adjacent to Laizhou Bay. The correlation analysis showed that meiofaunal abundance and diversity indices are closely linked to variations in sediment silt-clay content, medium grain size (MDΦ), and chlorophyll-a concentrations. The ecological quality status of most stations can be ranked from poor to moderate based on meiofaunal richness. According to the value of nematode to copepod ratio (Ne:Co ratio), most stations are uncontaminated, except seven stations are slightly or moderately contaminated. Both meiofaunal richness and Ne:Co ratio indicate the poor ecological quality of three stations adjacent to Laizhou Bay. The efficiency of the meiofauna communities as environmental indicators will be tested in a greater area in the future studies.

Recreational activities trigger changes in meiofauna and free-living nematodes on Amazonian macrotidal sandy beaches

Sandy beaches are key economic assets worldwide, however, recreational activities are an important source of disturbance in these ecosystems. Intensive human use of beaches has a negative effect on benthic communities as it alters species abundance, diversity, and/or distribution. Here, we report the impacts of recreational activities (trampling and vehicles) on meiobenthic communities and nematode assemblages on Amazonian sandy beaches for the first time. For this purpose, samples were carried out in four consecutive months encompassing a period of high visitation peak (one month Before Vacation, During Vacation, and two months After Vacation) on three contrasting beaches regarding disturbances (Urban: Atalaia; Intermediary: Farol-Velho; and Protected: Corvinas) at seven equidistant sampling stations (50 m apart) from the high tide water mark to the swash zone. At each sampling station, three biological samples and sediments samples were collected haphazardly. Also, in each station, the sediment compaction was determined using a manual penetrometer. Overall, physical sediment variables (grain size, sorting) were constant over time in all beaches, whereas differences in intensity of recreational activities and sediment compaction were found between beaches and months. Sediment compaction was considered the most important factor for the differences observed in meiofauna community structure in the study areas, and it was related to intensity of recreational activities. Variations in density and changes in richness between periods were observed in Atalaia and Farol-Velho beaches. On the other hand, Corvinas beach remained the same throughout the study. In the first month after vacation, density and richness were similar to those in the period before vacation, thus indicating that the beaches had recovered in one month. Furthermore, vulnerabilities of Tardigrada and Copepoda, as well as of the Nematoda genera Daptonema, and Chromadorita, indicate that they might be potential indicators of recreational activities.

Dynamic of organic matter and meiofaunal community on a river-dominated shelf (Rhône prodelta, NW Mediterranean Sea): Responses to river regime

In the oligotrophic context of the Mediterranean Sea, riverine inputs of particulate organic matter represent an important source of food for benthic communities. However, since most of these inputs are delivered during short, but intense flood events, communities living in the vicinity of river mouths are also exposed to strong and frequent physical disturbances. A very tight and complex relationship links river dynamic and macrofaunal communities in Mediterranean deltas, but less is known on the response of meiobenthic communities to river regime. In 2010, sediments cores were collected in the Rhône River prodelta in winter and spring before the flooding of the Rhône River tributaries in June, and then twice in the early and late summer. The hypothesis was that increased runoff and export of terrigenous material would induce major changes in the sediment biochemistry, which would in turn trigger modifications in abundances and vertical distribution of the meiofauna. The origin and quality (lability, degradation state) of the different pools of organic matter preserved in these recent sediments were determined using bulk geochemical and molecular analyses (fatty acids, amino acids). Vertical profiles of descriptors for organic matter origin and quality revealed major changes in the nature of the inputs occurring at monthly time scales. Inputs of plant detritus from autumnal and winter flood events were still visible in the cores collected in February and April. A few days after the June 2010 high-discharge event, a newly deposit (~7 cm) containing soil organic matter has recovered the prodeltaic sediments and the resident meiofaunal community, but at the end of August only 2 cm of this deposit remained. Multivariate analyses furthermore highlighted that the meiofaunal community was driven by both the trophic conditions and the deposition of a new sediment layer driven by the hydrological regime of the Rhône River. In April, increased abundances of meiofauna were observed in response to the sedimentation of labile organic matter after the spring bloom. The June high-discharge event affected the meiofauna with a reduction of its abundance and the burial of the resident meiobenthic community. However, the meiofauna recovered in less than two months after this disturbance, showing the strong resilience of this component of the benthic ecosystem in this high energy environment.

Seasonality of pluviosity and saline intrusion drive meiofauna and nematodes on an Amazon freshwater-oligohaline beach

Salinity in estuarine environments is one of the most important influencing factors for meiofauna. The effects of seasonal variation in rainfall and saline intrusion on meiofauna/nematodes diversity and abundance on a mesotidal beach located in the mixing zone of an Amazon estuary were analyzed. Samplings occurred bimonthly over one year at four stations in the intertidal zone. Density variation in meiofauna community had a direct relationship with increased rainfall and decreased salinity. Oligochaeta had the highest density during the months with the highest rainfall and lowest salinity. The highest total Nematoda richness value, as well as richness of brackish water genera value, was registered in September and gradually decreased until March, a month with the highest rainfall. Enoplolaimus, a typical predator, had the highest densities in the months with the highest rainfall, probably due to the food availability (Oligochaeta). The highest Nematoda density at the station closest to the high-tide mark occurred due to detritus accumulation. On the other hand, the lower densities at the middle stations are due to the higher desiccation that occurs in these regions compared to the station closer to the low-tide mark. Meiofauna was strongly affected by seasonal changes in rain and salinity, both at the level of large groups and at the level of Nematoda genera. In addition, seasonal changes in salinity clearly affected organisms indirectly through their prey-predator interactions.

Influence of habitat on meiofaunal abundance and distribution in a New Zealand temperate estuary

ABSTRACT Meiofaunal assemblages are often overlooked, yet they are important ecological components of estuarine ecosystems. To evaluate variations in meiofaunal communities in estuarine habitats, we conducted a comprehensive analysis of meiofaunal density, distribution and relationships with environmental parameters in a mangrove-dominated ecosystem at Mangawhai, Northern New Zealand, in summer (March) and winter (October), 2013. Five habitat types were studied including mangrove stands, pneumatophore zones, sandflats, mudflats and saltmarshes. In addition, data were recorded for sediment grain size, organic content, and primary benthic productivity (chlorophyll a). Twelve major taxa were identified, with meiofaunal densities ranging between 269 and 8090 ind. 10 cm−2. Highest abundances were found in fine-grained organic-rich sediments compared to coarse-grained organically poor sediments; the former were generally associated with mangroves stands and pneumatophore zones. Nematodes dominated all observed habitats. Foraminifera ranked second in fine-grained organically rich sediments, whereas copepods ranked second in coarser-grained sediments. Results suggest that meiofaunal taxonomic abundance and distribution are highly sensitive to local physical and biological parameters (e.g. sediment grain size, organic content, benthic primary productivity). The findings revealed that environmental characteristics have an important influence within this temperate estuary.

From biggest to smallest mud dragons: size-latitude trends in a group of meiobenthic animals worldwide

Size-latitude trends in the meiobenthic phylum Kinorhyncha, commonly known as mud dragons, have been explored in oceans worldwide. Generalized least squares regression was used to assess relationships between size and latitude, as well as between size, latitude, and two selected environmental variables that exhibit latitudinal gradation: the sea surface temperature and the net primary productivity. Different structures of spatial autocorrelation and potential confounding factors, such as the species richness and the number of kinorhynch records that could affect latitudinal gradients, were also addressed. In addition, generalized mixed models were used to determine the influence of the phylogeny on body size. Size-latitude relationships of Kinorhyncha were commonly found globally, as well as for particular geographic regions (hemispheres and/or coastlines), with important differences between taxonomic groups. These size-latitude trends were heterogeneous and implied the influence of the latitude itself, environmental variables, and phylogeny. These facts indicate that a single underlying process is not likely to explain the observed relationships but a complex interaction of several macroecological patterns both present and past. Perhaps, the inclusion of future new reports, conducted in undersampled areas, may shed some light on the matter and reveal more generalized size-latitude patterns. Nevertheless, it is also likely that broadly generalizable size-latitude relationships may not exist in meiofaunal communities.

Impact of mechanical Arenicola dredging on the benthic fauna communities: assessed by a morphological and molecular approach

LugwormArenicolaspp. dredging affects the intertidal benthic community in the Dutch Wadden Sea. Previous studies have found contradicting results regarding the recovery rates of targeted and non-targeted macrozoobenthic species, and meiobenthic communities have been neglected in these studies. The current study explores the short-term effects of dredging on both the macrofaunal and the meiofaunal communities using both a morphological and molecular approach. Benthic samples were collected right before and regularly after dredging for up to 1.5 yr at both control and fished transects. Significant differences between the control and fished transects were found by morphological and molecular approaches. Ordination analysis suggests distinct community compositions between control and fished transects in the first months after dredging. Opportunistic species with short life cycles, typically more than 1 generation yr-1, thrived more in the fished transects during the spring/summer season compared to these species in the control transects in the same season, whereas recovery for long-lived species was slow. Both approaches showed similar results; however, compared to the morphological approach, the molecular approach was more sensitive to the effects due to a larger set of benthic taxa.

Meiofauna in a Potential Deep-Sea Mining Area—Influence of Temporal and Spatial Variability on Small-Scale Abundance Models

In large areas of the Clarion Clipperton Fracture Zone (northeast Pacific), exploration of deep-sea polymetallic nodules as a potential source of high-technology metals is ongoing. Deep-sea mining may have a severe impact on the benthic communities. Here, we investigated meiofauna communities in the abyss at the scale of a prospective mining operation area. Random forest regressions were computed to spatially predict continuous layers of environmental variables as well as the distribution of meiofauna abundance across the area. Significant models could be computed for 26 sediment and polymetallic nodule parameters. Meiofauna abundance, taxon richness and diversity were also modelled, as well as abundance of the taxon Nematoda. Spatial correlation is high if the predictions of meiofauna are either based on bathymetry and backscatter or include sediment and nodule variables; Pearson’s correlation coefficient varies between 0.42 and 0.91. Comparison of differences in meiofauna abundance between different years shows that spatial patterns do change, with an elevated abundance of meiofauna in the eastern part of the study area in 2013. On the spatial scale of a potential mining operation, distribution models prove to be a useful tool to gain insight into both temporal variability and the influence of potential environmental drivers on meiofauna distribution.

Seawater Acidification Affects Beta-Diversity of Benthic Communities at a Shallow Hydrothermal Vent in a Mediterranean Marine Protected Area (Underwater Archaeological Park of Baia, Naples, Italy)

One of the most important pieces of climate change evidence is ocean acidification. Acidification effects on marine organisms are widely studied, while very little is known regarding its effects on assemblages’ β-diversity. In this framework, shallow hydrothermal vents within a Marine Protected Area (MPA) represent natural ecosystems acting as laboratory set-ups where the continuous carbon dioxide emissions affect assemblages with consequences that can be reasonably comparable to the effects of global water acidification. The aim of the present study is to test the impact of seawater acidification on the β-diversity of soft-bottom assemblages in a shallow vent field located in the Underwater Archeological Park of Baia MPA (Gulf of Naples, Mediterranean Sea). We investigated macro- and meiofauna communities of the ‘Secca delle fumose’ vent system in sites characterized by sulfurous (G) and carbon dioxide emissions (H) that are compared with control/inactive sites (CN and CS). Statistical analyses were performed on the most represented macrobenthic (Mollusca, Polychaeta, and Crustacea), and meiobenthic (Nematoda) taxa. Results show that the lowest synecological values are detected at H and, to a lesser extent, at G. Multivariate analyses show significant differences between hydrothermal vents (G, H) and control/inactive sites; the highest small-scale heterogeneities (measure of β-diversity) are detected at sites H and G and are mainly affected by pH, TOC (Total Organic Carbon), and cations concentrations. Such findings are probably related to acidification effects, since MPA excludes anthropic impacts. In particular, acidification markedly affects β-diversity and an increase in heterogeneity among sample replicates coupled to a decrease in number of taxa is an indicator of redundancy loss and, thus, of resilience capacity. The survival is assured to either tolerant species or those opportunistic taxa that can find good environmental conditions among gravels of sand.

Evaluation of freshwater benthic communities: a case study in an urban

The environmental damage suffered by urban water bodies and the need for public water supply result in a greater interest in techniques that enable water treatment in an efficient and ecological way, such as River Bank Filtration (RBF). This technique uses the soil as a filtering medium, as well as the biological activities of organisms that dwell in the Hyporheic Zone (HZ), the zone of interaction between the surface water body and its underlying aquifer. Knowledge of sediments and hyporheic organisms is indispensable to study RBF. The present paper aimed to characterize the HZ of the middle section of Beberibe river (Pernambuco State, Brazil) in its sedimentological and biological aspects, with sampling druing the rainy and dry seasons, in two distinct sampling sites, one in a conserved area and the other in a highly urbanized area. Biological characterization was performed at the level of large taxonomic groups of meiofauna, accounting for 982 individuals, with the three most abundant taxa being Nematoda, Annelida, and Rotifera. Permutational Analysis of Variance (PERMANOVA) statistical tests were performed, showing significant differences for the season and point factors (p < 0.05) in relation to abundance. The highest concentration of individuals and total organic matter were seen in the rainy season, especially at the point located in the urbanized area. With sedimentological characterization by grain size tests of the hyporheic sediments, the predominance of silt was observed during the rainy season, and sandy during the dry season. It was concluded that the main factor that influenced the structure of the meiofauna community was the release of domestic effluents. The information obtained by the present work helps to understand some features of the HZ, which is essential for RBF or other techniques that use the interstitial matrix.

Organic Contaminant Mixture Significantly Changes Microbenthic Community Structure and Increases the Expression of PAH Degradation Genes

Studying the effects of chemical contaminants on the structure and function of microbial and meiofauna communities have traditionally focused on specific effects of single contaminants on single species. This has left the complex interactions between mixtures of contaminants and its non-specific toxicity effects on the functions and structure of sediment microbial communities mostly overlooked. In an effort to improve our insights on such questions, we performed an experiment where Baltic Sea sediments were spiked with an ecologically relevant mixture of seven organic contaminants below specific toxicity levels. We then used 16S and 18S rRNA metabarcoding from RNA extracts to monitor changes in active microbial and meiofauna diversity and community structure in the spiked treatment compared to controls. In addition, we investigated the effects of exposure to this contaminant mixture on potential nitrification rates and on the expression of key-genes in the microbial nitrification and PAH degradation pathways with qPCR. There were significant differences in both eukaryotic and microbial community structures in sediments spiked with a mixture of organic pollutants. Nematoda showed a significant increase in overall relative abundance to the added contaminants (5.5±.1.1% higher in spiked), particularly taxa of the genus Leptolaimus (increased from 10.2±.5.4% in the controls to 32.5±.10.2% in the spiked treatment). Conversely, a significant decrease in relative abundance from 18.2±.5.6% in control to 7±.3.4% in of the genus Paraplectonemus was also detected. Additionally, while the abundance of active PAH degraders was significantly higher in spiked sediments than in the controls, no significant effect of our organic mixture was found on nitrification rates or the expression of AmoA (bacterial ammonia oxidizer gene). Our data indicate that mixtures of organic pollutants can have significant effects on microbenthic community structure even when its individual components are present at concentrations below its specific toxicity. In addition, we suggest that eRNA-based metabarcoding can offer important insights in microbenthic community structure and activities and further empathizes the potential of meiofauna as bio-indicators of chemical contamination in benthic ecosystems.

Benthic meiofauna with emphasis on nematode assemblage response to environmental variation in the intertidal zone of the Danshuei River estuary, northwest Taiwan

AbstractThis study aims to determine whether the benthic meiofaunal assemblages on the intertidal zone of Danshuei River estuary (DRE) in Taiwan vary from the estuary to the upper stream, and in response to different habitats. A total of six major taxa (Nematoda, Copepoda, Ostracoda, Polychaeta, Oligochaeta and Gastrotricha) of meiofauna and 44 nematode genera were recorded at 12 sampling stations in DRE in October, 2013. Meiofauna densities ranged between 4.67 ± 2.08 and 294.00 ± 180.40 ind./10 cm2, the average was 162.31 ± 84.36 ind./10 cm2. Nematodes were the dominant group (relative abundance, RA: 89.27%) in the meiofaunal community at all stations, with its assemblage in DRE dominated by nonselective deposit feeders (55.14%). There were striking differences in nematode assemblages between mangroves and mangroves with reed habitats. Pearson's correlation analysis showed that the dominances of the genera Anoplostoma, Metacylicolaimus and Deontostoma were significantly negative while Terschellingia correlated positively with salinity. These genera showed either decreasing or increasing trends at stations from the estuary to the upper stream. The dominances of the genera Megadesmolaimus and Theristus were significantly positively correlated with the proportion of sand and negatively correlated with the proportion of silt and clay. Our results indicate that salinity and sediment type influenced nematode assemblages in the DRE.