Search

Polychaetes are typically found in marine environments with limited species adapting to semi-terrestrial habitats. The genus Stygocapitella comprises interstitial polychaetes dwelling in sandy beach areas around or above the high-water line. Based on molecular data, previous studies suggested the presence of multiple cryptic species in some different localities in the world lumped together as Stygocapitella subterranea . In Japan, reports on Stygocapitella were scarce, with only one species having been documented 40 years ago at Ishikari Beach in Hokkaido by the name of S. subterranea . We revisited these earlier findings and uncovered the presence of two distinct species in Stygocapitella . One of these species is herein named Stygocapitella itoi sp. nov., while the other corresponds to S. budaevae , originally described from the Russian Far East. Stygocapitella itoi sp. nov. possesses a chaetal pattern similar to that of S. australis , S. furcata and S. pacifica but can be distinguished from the congeners by two characters: a slightly forked pygidium and forked chaetae consisting of two teeth and two outer prongs. Our multi-locus phylogenetic analysis showed close relationships across the Pacific Ocean in two separated lineages in the genus, suggesting ancient dispersal or allopatric speciation after vicariance events., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)

Meiofauna (invertebrates that pass through a 1‐mm mesh sieve, but are retained on a 40‐µm mesh) represent the most abundant and diverse animal group on Earth, but empirical evidence of their role in benthic respiration, production and carbon cycling across ecosystems is not well documented. Moreover, how meiofauna respond to changing oxygen conditions is poorly understood.We further developed an incubation system, in which oxygen and temperature conditions are easily controlled and single meiofaunal nematode respiration is resolved in glass capillary tubes, using Clark‐type oxygen microsensor. We performed the respiration measurements after exposing nematodes to different ambient oxygen concentrations, which resulted in 3–60 µM O2 during hypoxic and 80–210 µM O2 during oxic incubations in close proximity to the respective nematodes.Individual nematode respiration rates ranged from 0.02 to 1.30 nmol O2 ind.−1 day−1 and were 27% lower during hypoxic than oxic incubations. Rates derived from established allometric relations were on average fourfold higher than our direct measurements.The presented method is suitable for single nematode respiration measurements and can be adapted to a wide range of experimental conditions. Therefore, it can be used to assess meiofauna contribution to ecosystem processes and investigate species‐specific responses to changing environmental conditions, for example, oxygen stress, increasing water temperature. [ABSTRACT FROM AUTHOR]

The shallow water benthic foraminiferal and ostracod assemblages of the Gulf of Pozzuoli, located in the central Tyrrhenian Sea, were studied to investigate the relationship between calcareous meiofaunas and contaminant concentrations in bottom sediments exposed to prolonged industrial pollution. Both benthic foraminifers and ostracods displayed high-diversity and low-dominance, unusual features in highly contaminated environments. High-diversity values were possibly linked to the oligotrophic, well-oxygenated, and CaCO3-supersaturated coastal Mediterranean waters. The comparison with historical data suggested that assemblage composition changed in the last decades, with an increase in the relative abundance of benthic foraminiferal (Quinqueloculina seminulum, Bulimina elongata) and ostracod (Xestoleberis, Loxoconcha, Semicytherura rarecostata) taxa. They probably represent organisms tolerant to the environmental variations in the last decades. The relationships between granulometry and diversity indices, high correlation values between Quinqueloculina lata and heavy metal pollution, and the preference of the ostracod genera Urocythereis and Paracytheridea for very shallow marine waters were highlighted. [ABSTRACT FROM AUTHOR]

Meiofaunal animals, roughly between 0.045 and 1 mm in size, are ubiquitous and ecologically important inhabitants of benthic marine ecosystems. Their high species richness and rapid response to environmental change make them promising targets for ecological and biomonitoring studies. However, diversity patterns of benthic marine meiofauna remain poorly known due to challenges in species identification using classical morphological methods. DNA metabarcoding is a powerful tool to overcome this limitation. Here, we review DNA metabarcoding approaches used in studies on marine meiobenthos with the aim of facilitating researchers to make informed decisions for the implementation of DNA metabarcoding in meiofaunal biodiversity monitoring. We found that the applied methods vary greatly between researchers and studies, and concluded that further explicit comparisons of protocols are needed to apply DNA metabarcoding as a standard tool for assessing benthic meiofaunal community composition. Key aspects that require additional consideration include: (1) comparability of sample pre-treatment methods; (2) integration of different primers and molecular markers for both the mitochondrial cytochrome c oxidase subunit I (COI) and the nuclear 18S rRNA genes to maximize taxon recovery; (3) precise and standardized description of sampling methods to allow for comparison and replication; and (4) evaluation and testing of bioinformatic pipelines to enhance comparability between studies. By enhancing comparability between the various approaches currently used for the different aspects of the analyses, DNA metabarcoding will improve the long-term integrative potential for surveying and biomonitoring marine benthic meiofauna.

In estuarine sediment, meiobenthos serve as an excellent candidate to perform a range of ecosystem services. However, even though the taxonomic sufficiency of meiobenthos in detecting spatiotemporal gradients is well recognized, very little is known about their functional attributes in response to environmental descriptors. To bridge this knowledge gap, the taxonomic structure and trait-based functional diversity patterns of meiobenthic assemblage, focusing on nematode species composition, were assessed for the first time from the unexplored central sector of Sundarbans Estuarine System (SES). Sediment samples were collected seasonally (monsoon, winter, spring, and summer) selecting a total of eight stations across River Matla (the widest and longest river of SES). Distinct seasonal successional patterns had been observed in meiobenthic abundance modulated by seasonal alteration in the sedimentary environment (PERMANOVA, p < 0.05). Our study revealed a strong preponderance of meiobenthic density in spring (2978 ± 689.98 ind. 10 cm–2) and lowest during monsoon (405 ± 51.22 ind. 10 cm–2). A total of 11 meiobenthic taxa were identified with the dominance of nematodes. Altogether, 79 species of nematode belonging to 22 families had been identified across the entire study area and nematode assemblage was dominated by Sabatieria praedatrix, Sphaerolaimus balticus, Desmodora communis, Dorylaimopsis punctata, and Daptonema hirsutum. Principal component analysis depicted a distinct separation of seasons with reference to environmental variables. Distance-based redundancy analysis delineated that meiobenthic communities were mainly structured by organic matter, salinity, and dissolved oxygen concentration. Biological trait analyses of nematode assemblages were applied to gather the ecological information based on morphological and ecological characteristics. The most common morphotypes were slender body shape, clavate tail shape, striated cuticle pattern, and non-selective deposit feeders with colonizing abilities of 2–3 (c–p score in a scale from 1 to 5). Results from BIO-ENV showed that sediment organic matter and dissolved oxygen played overriding roles in shaping the functional compositions of nematodes. Thus, the characterization of meiobenthos and nematode assemblages in the context of taxonomic as well as functional attributes represents a first step toward building of baseline data which could help to evaluate the ecological status of SES and direct future research priorities concurrently.

Copyright of Review of Hydrobiology is the property of NK Yayincilik Egitim Hizmetleri and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As established by numerous research the community of bottom meiofauna (meiobenthos) plays an important role in the diversity, quantitative characteristics and trophic relationships of the hydrofauna, as well as in the general flow of matter and energy of both marine and freshwater ecosystems. At the same time, to date it remains poorly studied in many types of water bodies, for example, in highly mineralised rivers. In 2009–2017 a study of meiobenthos was conducted for the first time in the saline tributaries of the hypergalin Lake Elton, located in the protected area of the Eltonsky Nature Park (Volgograd Region, Russia). This current paper provides information on the overall taxonomic composition of the community in rivers, as well as an annotated checklist of identified species. The data on the structure and abundance of the species populations, their occurrence, ecology, global and local distribution are given in the checklist along with taxonomic and other comments. In total 73 taxa of 12 systematic groups of hydrobionts have been recorded. There are 38 representatives identified to species level. Among them, there are three species (nematodes Diplolaimelloides delyi, Ethmolaimus multipapillatus, and Monhystrella parvella) that had not been recorded previously from Russia and five species (nematodes Allodiplogaster media, Calodorylaimus salinus, Daptonema salinae, Mesodorylaimus rivalis, and Oncholaimus rivalis) which have been collected here for the first time and described as new to science. The presence of rare and new species shows a certain uniqueness of the ecosystems of the tributaries of Lake Elton and indicates the need for their further study and conservation.

We present the compilation of published and unpublished records of continental copepods of Colombia, as well as personal observations by the authors, yielding an additional list of 52 species and subspecies (7 calanoids, 20 cyclopoids, 25 harpacticoids). In addition to our former inventory (2007) of 69 species, the total number now reaches 121 taxa, increasing by 75 % the known number of continental copepods. Freshwater taxa increased in 15 species and subspecies. The number of brackish species (and marine species collected in brackish environments), recorded from coastal lagoons and temporal offshore ponds reached 39 species and subspecies. Thirteen taxa with locus typicus in Colombia have been described since 2007. Between 2007 and 2018, thirty-nine departmental records were made, and 43 new habitat records were reported (not including the species recorded as new for the country). Parasitic copepods of fish reached six species. However, the number of species is expected to increase with the survey of poorly studied regions like the Amazon and the Eastern Plains, and habitats like groundwater, benthos of lakes and ponds, semiterrestrial environments and additional coastal lagoons.

The Putorana Plateau (Krasnoyarsk Territory, Russia) is one of the largest mountainous regions of subarctic Eurasia. Studies of aquatic ecosystems of this are far from complete. In particular, microcrustaceans (Cladocera и Copepoda) of the Putorana Plateau are poorly investigated, although they are one of the main components of meiobenthic and zooplanktonic communities and a target for monitoring of the anthropogenic influence and climate change. An open question is a biogeographical status of the crustacean fauna of the plateau. Additionally, it is unknown which environmental factors significantly affect benthic and planktonic crustacean assemblages? Based on the samples collected in tundra and forest tundra ponds in the western and central parts of the plateau, analysis of the composition of crustacean fauna and factors regulating the assemblage structure was performed. In total, 36 Cladocera and 24 Copepoda species were found. Of these, 23 taxa are new for the region, and four are new to science. Species richness of Copepoda is higher in the central part and on the western slopes of the plateau than in foothills, while number of the Cladocera species in contrast decreases in mountainous areas. Variations in meiobenthic assemblages are due to the research area, type of water supply and less affected by altitude above sea level. For planktonic assemblages the size of the water body and, to a lesser degree, by macrophytes species composition was significant. Almost 12.8% of microcrustacean species of the Putorana Plateau can be attributed to glacial relics. Crustacean fauna of the Putorana Plateau has a high species richness and distinguishes significantly from the fauna of both western and eastern regions of the Arctic. The specifics of faunal composition of the region are connected to the climatic features of Middle Siberia and the retaining of the Pleistocene fauna in some glacial refugia.

Meiobenthos has been considered as an excellent tool for biomonitoring assessment. Elevated temperature and oil pollution are considered as the most pervasive aspects of global environmental changes and matter of concern for contemporary society. Presently, very limited information is available about the synergistic effect of these stressors on meiobenthic community structure and tolerance potential from tropical intertidal environment. Here, we assessed their impacts on meiobenthic community by conducting a 60 days long benthocosm experiment selecting three sets of temperature (25°, 30° and 35 °C) and two sets of diesel oil (low and high) combinations. Gradual changes in their community composition were revealed discernibly with exposures to both the disturbances after 30 and 60 days of experimental period. Diversity profiles for the nematodes were less affected, but copepods showed a graded response of decreasing density with increasing dose of both the stressors. Other meiobenthic taxa such as halacarid mite, turbellaria and polycheate juveniles were adversely affected and eliminated from the treatments, howbeit abundance of ostracods, foraminiferans and bivalve settlers varied significantly. A 3-factor PERMANOVA indicated a significant effect of temperature, diesel, between their interaction and interaction among stressors and time on meiofaunal abundances. In case of free-living nematodes, temperature rise and diesel contamination synchronously led to an elimination of k-selected species like Halalaimus gracilis, H. longicaudatus, Oxystomina aesetosa and Pomponema sp. with a significant decrease in abundance of H. capitulatus and Oncholaimus sp. The r-selected species Daptonema invagiferoum, Sabatieria praedatrix, Theristus acer, Monhystera sp. and Thalassomonhystera sp. had endured even at high doses of diesel treatment in three different temperatures set up. The effects were evident in term of changes in life strategies with an increment of opportunistic species and increased trophic diversity of deposit feeders in treated sediments. Overall, elevated temperature together with diesel oil contamination were found to alter species dynamics within shallow intertidal meiobenthic communities, which might have significant Armageddon on benthic ecosystem functioning.

Meiofauna includes an astonishing diversity of organisms, whose census is far from being complete. Most classic ecological studies have focused on hard-bodied Ecdysozoan taxa (notably Copepoda and Nematoda), whose cuticle allows determination at species-level after fixation, rather than soft-bodied, Spiralian taxa, which most often lose any diagnostic feature in fixed samples. Yet, metabarcoding studies have recently revealed a species-richness of soft-bodied taxa comparable, and in cases superior, to that of Copepoda and Nematoda together. However, given objective difficulties inherent to their study, which necessarily has to be performed on living individuals, and their limited utilisation for ecological and applicative research, taxonomic expertise on soft-bodied organisms has declined over the years, and diversity of these phyla in most areas of the world is presently completely unknown. Here we present an expert-based survey of current knowledge on the composition and distribution of soft-bodied meiofaunal taxa in Italy, with special references to the predominantly or exclusively meiobenthic phyla Gastrotricha, Gnathostomulida, Platyhelminthes, Rotifera, Xenacoelomorpha, and macrofaunal taxa with conspicuous meiofaunal representatives (Annelida, Mollusca and Nemertea). A total of 638 described species have been reported from Italian coasts; furthermore, the existence of a large number of undescribed species is mentioned. Knowledge of Annelida, Gastrotricha, and Rotifera appears particularly detailed, placing Italy among the best-known country worldwide. In contrast, knowledge of Platyhelminthes and Xenacoelomorpha appears patchy, and limited to few areas. Sampling effort has been uneven, with most species recorded from the Tyrrhenian Sea, while large sections of the Adriatic and Ionian seas have been poorly explored. Results highlight the role that Marine Biological Stations, notably the Zoological Station "Anton Dohrn" in Naples, have had in promoting the study of soft-bodied taxa in Italy. [ABSTRACT FROM AUTHOR]

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 order 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 and 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 contaminants. 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 Paraplectana 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 contaminants 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.

Gaoping Submarine Canyon (GPSC) off southwestern Taiwan is a high energy canyon connected to a small mountain river with extremely high sediment load (∼10 kt km–2 y–1). Due to heavy seasonal precipitation (>3,000 mm y–1) and high tectonic activity in the region, the GPSC is known for active sediment transport processes and associated submarine geohazards (e.g., submarine cable breaks). More importantly, strong internal tides have been recorded in the GPSC to drive head-ward, bottom-intensified currents, which result in sediment erosion and resuspension in response to the tidal cycles. To understand the effects of extreme physical conditions on marine nematodes, we sampled the surface sediments along the thalweg of upper GPSC and adjacent slope (200–1,100 m) using a multicorer in the summer and fall of 2015. We found that the nematode species, functional, trophic diversity and maturity dropped significantly in the GPSC as compared with slope communities, but the nematode abundances were not affected by the adverse conditions in the canyon. The non-selective deposit-feeding, fast colonizing nematodes (e.g., Sabatieria, Daptonema, Axonolaimus, and Metadesmolaimus) dominated the canyon seafloor. In contrast, other species of non-selective deposit feeders (Setosabatieria and Elzalia), epigrowth feeders (Craspodema), omnivores/predators (Paramesacanthion), and other species constituted the diverse nematode assemblages on the slope. We found that the strong bottom currents in the GPSC may depress the local nematode diversity by removing the organic-rich, fine-grained sediments; therefore, only the resilient or fast recovering nematode species could survive and prevail. The high species turnover with depth and between the canyon and slope habitats demonstrates that strong environmental filtering processes were the primary mechanism shaping the nematode community assembly off SW Taiwan. Between the canyon and slope, a considerable contribution of nestedness pattern also indicates some degree of local extinction and dispersal limitation in the dynamic GPSC.

The risk assessment of seafloor massive sulfide (SMS) mining on meiobenthic organisms, specifically on soft-sediment meiofauna, is impeded by a lack of knowledge on the biology and ecology of these communities. In this study, we investigated sediment samples taken in proximity of active vents at Trans-Atlantic Geotraverse (TAG) and Snake Pit, two hydrothermal vent fields of the Mid-Atlantic Ridge, in order to explore metazoan meiofauna, particularly nematode community, and its relation to organic carbon, total nitrogen, total sulfur, and dissolved oxygen. Organic carbon and nitrogen contents were low at both sites. High concentrations of total sulfur and low oxygen penetration were found at Snake Pit compared to TAG. Snake Pit showed approximately four times higher meiofauna and nematode density compared to TAG, as well as a dissimilar nematode community composition. We hypothesize that high sulfur concentrations at Snake Pit may support high microbial growth, which represents one of the main food source for nematodes. Moreover, TAG nematode community mostly consisted of persisters (K-strategists), whereas Snake Pit one was composed by both persisters (Desmoscolecidae family) and colonizers (r-strategists Metalinhomoeus and Halomonhystera), whose presence can be facilitated by the bioturbation effect of polychaetes observed on the sediment surface. Therefore, food availability, geochemical settings, and biotic interactions seem to drive the local meiofauna and nematode community. Our study also draws attention to the opportunity of including meiofauna and specifically nematodes in impact studies conducted in this area in order to assess and monitor the impact of SMS mining.

A new species of Sarsamphiascus Huys, 2009 was collected from sandy sediments of Hawaii at 12 –18 m depth. While the new species, Sarsamphiascus hawaiiensis sp. nov., is morphologically most closely related to S. kawamurai (Ueda & Nagai, 2005), the two species can be distinguished by the combination of the following morphological characteristics: elongated segments of the antennule in the new species, type of outer setae of the P5 exopod (bare in S. kawamurai), position of the inner seta of the P5 exopod in both sexes (more proximal in S. kawamurai), length and type of the setae of female P6 (shorter and bare in S. kawamurai). This is the first species of Sarsamphiascus from Hawaii to be discovered. Molecular analyses of mitochondrial cytochrome c oxidase subunit I (mtCOI) and nuclear 18S ribosomal RNA (18S rRNA) genes confirmed that S. hawaiiensis and S. kawamurai are distinct species.

During several sampling campaigns in the regions of Galicia and Andalusia in Spain and the Algarve region in Portugal, specimens of twelve species of schizorhynch rhabdocoels were collected. Four of these are new to science: three species of Proschizorhynchus (P. algarvensis sp. nov., P. arnautsae sp. nov. and P. troglodytus sp. nov.) and one species of Schizochilus (S. coninxae sp. nov.). The new species of Proschizorhynchus can be distinguished from their congeners by the curvature and length of their stylet, as well as the cirrus sheath and the organisation of the genital system. Schizochilus coninxae sp. nov. has a distinct two-part stylet that is unique within the genus. In addition to these new species, new data are reported for the diascorhynchid Diascorhynchus caligatus and the schizorhynchids Carcharodorhynchus multidentatus, C. tenuis, C. flavidus, Proschizorhynchus pectinatus and P. reniformis. Finally, new records for C. flavidus from the Hawaiian archipelago are presented.

This paper presents results of comprehensive studies of saline rivers in the arid Elton Lake region based on hydrobiological surveys of planktonic and bottom communities. Two tables representing the species structure of communities and produced on the basis of survey data collected on 13 river sites in 2013 and 2018, including data on the abundance of hydrobionts belonging to 94 different taxonomic groups of macrozoobenthos, meiobenthos, and zooplankton, have been compared. The co-inertia analysis has identified a high statistical consistency of the data matrices determined by objective spatial distribution patterns of aquatic organisms. A randomization test was applied to the Procrustean correlation coefficient, and it showed that the conjugacy of the two species structures in the space of latent variables is statistically significant (p = 0.00026). Concurrently, a change trend was noted for the taxonomic composition of some surveyed communities affected by dynamic abiotic factors. The relationship between the taxonomic structure of hydrobionts and the combination of 30 abiotic environmental factors measured in the course of the hydrobiological and hydrochemical monitoring of the studied river sites was analyzed. Using canonical correlation analysis and the technique of projection to latent structures, a complex of ordination diagrams has been produced permitting the identification of specific "environmental niches" for each species group, including certain sets of biotope characteristics. A significant mutual correlation between the planktonic and bottom communities has been established. This correlation indicates close interrelations between these communities determined both by biotic interactions and by mutually consistent reactions to changes in aquatic environmental factors. [ABSTRACT FROM AUTHOR]

Intermittent streams (IS) comprise a large proportion of the drainage network in many parts of the world. The non‐flow period of IS are known to impact stream biota because aquatic habitats dry out. However, less well understood are the relative effects of the temporal component of these drying events including their duration and frequency.Here, we characterised effects of temporal component of drying events on abundant and species‐rich meiofauna. The effects were assessed in 22 streams in the north‐eastern Iberian Peninsula. The duration and frequency of non‐flow events was characterized over a period of 250 days prior to sampling the sediment‐dwelling meiofauna in riffle zones that completely dried out.Overall, meiofauna abundances were amongst the highest ever reported for streambeds. Most meiofaunal taxa correlated positively with the frequency of drying events and correlated positively with the length of dry periods recorded shortly before sampling, suggesting that the community was able to recover quickly. Tardigrades were the only group to correlate positively with the longest dry periods, suggesting that they had the best resilience capabilities in streams that had experienced the longest droughts.On average, nematodes made up half of the meiofauna. We identified a total of 113 different nematode species. The nematode community was more taxonomically diverse in IS, with a smaller proportion of bacterivores and a higher proportion of fungivore species such as Filenchus vulgaris. Thereby resembling the trophic structure commonly observed in soil ecosystems.Our results show that most meiofauna were positively influenced by drying disturbance, that is being able to quickly recover after them. This suggests outstanding resilience capabilities, and points out meiofaunal organisms as key players for kick‐starting stream food webs and functions once flow returns. [ABSTRACT FROM AUTHOR]

A statistical analysis was performed on hydrochemical and hydrobiological data obtained from samples of macrozoobenthos, meiobenthos, and zooplankton in 2013 and 2018 from different biotopes of the five highly mineralized rivers of the basin of the hyperhaline Lake Elton. The general trends in the formation of the species structure of the metacommunity of aquatic organisms are considered based on the Lybold-Mikkelson concepts. Randomized null models are used to test hypotheses on the consistent occurrence of species (coherence), the formation of compact species associations (boundary clumping), and the regular change in the species composition along environmental gradients (turnover). The nature of changes in biotic diversity were determined to be nonstationary and intermittent, and the taxonomic structure was highly mosaic, which is characteristic of stochastic-type ecosystems. A close correlation was established within individual mixed associations of benthic and planktonic species due to biotic interactions and the coordinated response of organisms to environmental factors. Statistical models Random Forest and subsequent multivariate analysis were used to identify groups of species by the degree of tolerance to external abiotic influences, and the sets of factors having a significant impact were established. [ABSTRACT FROM AUTHOR]

The metacommunity concept incorporates spatial dynamics into community ecology, shedding light on how local and regional processes interact in structuring ecological communities, and to which measure they are deterministic or stochastic. We reviewed metacommunity studies on freshwater meiobenthos published since 2004, when the main principles of metacommunity theory were conceptualized. The studies (together 19) were observational, focused mainly on ostracods, and rarely on rotifers and nematodes. In accordance with general expectations, the prevalent structuring force was species sorting. Ostracods showed more dispersal limitations than nematodes and rotifers, and there was very little support for dispersal surplus. We discussed the role of body size, dispersal mode, and attachment to sediment for the meiofauna dispersal. Effects of metacommunity context (habitat connectivity, spatial extent, and environmental heterogeneity), study design (e.g., sample size), and statistical approach could not be sufficiently disentangled due to the low number of studies. Local stochasticity, consistent with neutral theory and patch dynamics, was indicated for taxa with weak specialization and metacommunities in small habitats. Our understanding of meiofaunal metacommunities is only fragmentary and it would highly benefit from direct comparisons of taxa with different species traits and between different spatial scales, and studies incorporating temporal dynamics and hypothesis-driven experiments. [ABSTRACT FROM AUTHOR]

Never heard of harpacticoids, ostracods, gastrotrichs or microturbellarians? This is no surprise, they are so tiny! Yet these taxa and many others more famous (nematodes, rotifers, or tardigrades) show complex behaviours and extraordinary physiologies that allow them to colonize inland waters worldwide. This exuberant fauna is better known as the meiofauna (or meiobenthos). Meiofaunal organisms have been fascinating study objects for zoologists since the seventeenth century and recent research has demonstrated their intermediate role in benthic food webs. This special issue highlights how meiofauna can help freshwater ecologists to describe and predict species distribution patterns, to assess production of biomass and trait functions relationships, as well as to examine the trophic links between microscopic and macroscopic worlds and to better understand species' resilience to environmental extremes. Overall, meiofaunal organisms are bridging scales, and as such they deserve better integration to develop more comprehensive concepts and theories in ecology. [ABSTRACT FROM AUTHOR]

Meiofaunal organisms are diverse, and so is their diet comprising bacteria, fungi, micro-algae, flagellates, ciliates, and other meiofauna. Studies have inferred diet from correlative evidences, observations of feeding or gut contents. Incubation experiments have also helped to link meiofauna's role to microbially mediated ecosystem processes, reporting in most cases beneficial effects on microbial activity. Nevertheless, our knowledge of meiofauna's trophic ecology still lags far behind that of other aquatic fauna (i.e. zooplankton, macroinvertebrates, vertebrates), probably because the small-size and the cryptic nature of the meiofauna becomes an issue when it comes to detect their isotopic or lipid composition. Here, we provide a critical review of diverse methodologies used while examining meiofaunal diets. Observation of feeding, incubation experiments, gut content analyses, calorimetry, stable isotopic and fatty acid analyses are very helpful and some modifications of standard materials and methods can help reduce the time-consuming sorting of individuals. Other analytic tools used by microbial ecologists like compound-specific stable isotopic analysis, DNA-stable isotopic probing, confocal laser scanning microscopy, coherent anti-stokes Raman spectrometry and nanoscale secondary ion mass spectrometry have the potential to unravel hidden trophic channels between meiofauna and microbes. [ABSTRACT FROM AUTHOR]

Understanding the drivers of species distribution is an important topic in conservation biology and ecology, pertaining to species traits like dispersal strategies and species–environment interactions. Here we examined the drivers of benthic species distribution at 20 sections of a second-order stream network. Environmental and spatial factors and the dispersal modes of the organisms were considered. We expected that species with aerial dispersal capabilities like insects would be less restrained by distance between sites and thus mostly affected by environmental factors. In contrast, we hypothesized that completely benthic species would mainly be affected by spatial factors due to limited dispersal. However, microscopic species like nematodes characterized by a high passive dispersal potential may be less limited by spatial factors. When using redundancy analyses and subsequent variance partitioning, the included variables explained 24% (insects), 24% (non-flying macrobenthos), and 32% (nematodes) of the variance in the respective community composition. Spatial factors mainly explained the species composition of all tested groups. In contrast with other larger species, nematodes were characterized by fine-scale patterns that might have been induced by random processes (e.g., random distribution and priority effects). Our study showed that dispersal processes are crucial in shaping benthic communities along streams albeit the relatively small sampling area (max. distance between sampling sites: 2 km). The demonstration of spatial factors as important drivers of the species distribution of passively dispersing benthic organismal groups highlights the role played by connectivity in determining species distribution patterns in river systems. [ABSTRACT FROM AUTHOR]

Ecological quality (EcoQ) status of the Southwest and West coasts of South Korea was evaluated within the "National Investigation of Marine Ecosystems in Korea" in the 2015. In particular, the study dealt to assess the ecological quality of the sediments using free-living nematode communities. A total of 149 species were found in the study area, and Daptonema, Sabatieria, Parodontophora, Sphaerolaimus, and Viscosia were found as dominant genera. Statistical analysis of both environmental and faunal parameters showed an increasing human pressure from Western to Southern coasts. The community structure changed with the environmental features of the study area and allowed the detection of a suite of possible nematode indicators that might be used in monitoring studies. In particular, Dorylaimopsis spp. appeared heavy metal and organic matter resistant taxa, Sabatieria an eutrophication resistant genus, while Paracanthonchus and Neotonchus as heavy metal and organic matter sensitive genera. The principal component analysis (PCA) results showed a clear negative correlation between maturity index and both heavy metal and organic matter increasing, while diversity indices did not appear to be significantly influenced by them. Appling the thresholds of the synthetic nematode indices, the EcoQ of the study area was assessed as poor to moderate. [ABSTRACT FROM AUTHOR]

We present the results of a comprehensive study of five saline rivers in the arid region of Lake Elton, including hydrobiological surveys of plankton and benthic communities. The DIABLO method was used for a statistical analysis of the associative links between the species structures of the macrozoobenthos, meiobenthos, and zooplankton communities. This method combines multidimensional ordinations based on n blocks of observations and uses special algorithms of canonical correlation. It is shown that a significant portion of the cumulative variation in the data can be explained by a consensus configuration based on information common for all the three groups of observations. The diagrams, constructed and analyzed with the use of the cluster and Generalized Procrustes analysis, enable us to isolate stable associations of taxa typical for particular biotopes with homogeneous environmental conditions. We have constructed graphs of correlation pleiades and calculated indicator significance for particular species of macrozoobenthos, meiobenthos, and zooplankton. It is shown that highly mineralized systems of arid regions are not always characterized by a pronounced specification of life forms of plankton and benthic communities. The interpenetration between benthic and plankton animals results in a high portion of mixed ecological groups. Plankton and benthic communities correlate well enough with each other, which testifies to a close relationship between them due to both biotic interactions and a mutually agreed response to changes in aquatic environment factors. These data enable us to consider the plankton and benthic communities of highly mineralized rivers a nonequilibrium dynamically changing consortia of species. [ABSTRACT FROM AUTHOR]

In various biotopic groups of invertebrates of small rivers, the species richness and nematode abundance vary. Periphyton is poorer than meiobenthos. Along with common species, a number of worms are found only in biofouling or only in meiobenthos. A significant increase in species richness, diversity of ecological groups, and abundance of worms in meiobenthos and periphyton of small rivers is observed in zones contaminated with organic substances of anthropogenic and zoogenic origin. The biocenotic and functional role of nematodes in these groups depends to a higher extent on the level of food availability than on a number of other environmental factors that limit their development. [ABSTRACT FROM AUTHOR]

The Antarctic region is usually considered a pristine area. Nevertheless, regional warming effects and increasing human activities, including the presence of several research stations, are inducing considerable environmental changes that may affect the ecosystem’s functions. Therefore, during the XXXIII Antarctic expedition, we carried out an investigation in Terra Nova bay (Ross Sea), close to the Antarctic Specially Protected Area (ASPA) n.161. In particular, we compared the effects of two different types of impacts on the meiobenthic assemblages: anthropogenic impact (AI), associated with the activity of Mario Zucchelli Research Station (MZS), and natural impact (NI) attributable to a large colony of Adélie penguins (Pygoscelis adeliae) in Adelie Cove. For each impacted site, a respective control site and two sampling depths (20 and 50 m) were selected. Several environmental variables (pH, dissolved oxygen, major and minor ions, heavy metals, organic load, and sediment grain size) were measured and analysed, to allow a comprehensive characterization of the sampling areas. According to the criteria defined by Unites States Environmental Protection Agency (US EPA 2009), heavy metal concentrations did not reveal critical conditions. However, both the MZS (AI20) and penguin colony (NI20) sites showed higher heavy metal concentrations, the former due to human activities related to the Italian research station, with the latter caused by the penguins excrements. Meiobenthic richness and abundance values suggested that the worst ecological condition was consistently related to the Adélie penguins colony. Furthermore, the higher contribution of r-strategists corroborates the hypothesis that the chronic impact of the penguin colonies may have stronger effects on the meiobenthos than the human activities at the MZS. Food is not limited in shallow Antarctic bottoms, and microscale differences in primary and secondary production processes can likely explain the greater spatial heterogeneity, highlighted both by the univariate and multivariate attributes of meiobenthic assemblage (i.e., richness, diversity, abundance, whole structure assemblage, and rare taxa) at the deeper stations. As reported in other geographical regions, the assemblage structure of rare meiobenthic taxa is confirmed to be more susceptible to environmental variations, rather than the whole assemblage structure.

Information about invertebrates in the low-flow water bodies of northeastern Siberia is far from complete. In particular, little is known about crustaceans—one of the main components of meiobenthic and zooplanktonic communities. An open question is which environmental factors significantly affect the crustaceans in different taxonomic and ecological groups? Based on the data collected on the zooplankton and meiobenthos in the tundra ponds in the southern part of the Lena River Delta, analysis of the crustacean taxocene structure was performed. In total, 59 crustacean species and taxa were found. Five of these are new for the region. The species richness was higher in the large thermokarst lakes than in the small water bodies, and the abundance was higher in small polygonal ponds than in the other water bodies. Variations in the Cladocera assemblages were mainly affected by the annual differences in the water temperature; non-harpacticoid copepods were generally determined by hydrochemical factors; and for Harpacticoida, the macrophyte composition was significant. Three types of the crustacean assemblages characteristic of different stages of tundra lake development were distinguished. The hypothesis that the formation of crustacean taxocenes in the Lena River Delta is mainly determined by two types of ecological filters, temperature and local features of the water body, was confirmed.

We re-examined the type material of five of the seven described species of the marine tardigrade genus Angursa Pollock, 1979, namely, A. abyssalis Renaud-Mornant, 1981, A. bicuspis Pollock, 1979 (type species), A. capsula Bussau, 1992, A. lanceolata Renaud-Mornant, 1981, and A. lingua Bussau, 1992. In addition, we describe A. seisuimaruae sp. nov. from the Sea of Kumano, Japan. Based on new data obtained, we amend the diagnosis of this genus, provide a taxonomic key to species, and discuss their geographical distributions.

A new species belonging to the genus Haloschizopera Lang, 1944 (Copepoda, Harpacticoida, Miraciidae, Diosaccinae) was identified based on the samples collected from the East China Sea, near the offshore of Zhejiang Province, East China. The new species is closely related to H. pygmaea Norman & Sccot T., 1905 and shares a combination of the following features: A1 eight-segmented; A2 exp-2 with one distal seta, exp-3 with three setae; P1 endopodal segments subequal, enp-1 not exceeding exp-2; exp-3 of P3 with one inner seta, of P4 with two inner setae. The new species is characterized by the presence of one inner seta on P2 exp-3 of both sexes. It can also be distinguished from its congeners by the characters of female: P5 exopod subcircular, endopodal lobe extending beyond half-length of exopod; genital double-somite ornamented with three dorsolateral rows of spinules on anterior part. [ABSTRACT FROM AUTHOR]

Havana bay is one of the most polluted semi-enclosed basins in the world due to deleterious influence of urban and industrial effluents originated from Havana city. The sustained impact of contamination for decades have practically defaunated the benthic system affecting the monitoring of the environmental quality. In this study, we compared the free-living nematode assemblages between 2006 and 2016 to assess the changes in the sediment and estimate if the environmental quality has improved in 10 years. Nematodes were collected from four sites in the bay in 2006 and 2016 and identified to species level using the same methodology. Havana bay has improved some environmental variables in 2016 compared with 2006. However, still exist synergistic deleterious effects on the nematofauna of stressors such as hypoxia and toxicity by heavy metals and petroleum hydrocarbons. Nematodes showed extremely impoverished assemblages dominated by two cosmopolitan, detritivores and tolerant species: Terschellingia longicaudata and Sabatieria pulchra. The synthesis of our results indicates that environmental quality of Havana bay remains precarious and there is a necessity to reformulate the program of mitigation because the reduction of pollution has not significantly improved the benthic communities. [ABSTRACT FROM AUTHOR]

Metacommunity theory is a conceptual framework addressing the interdependence of local interactions and regional processes, especially when it is difficult to relate community structure and the environment at different spatial scales. To test the applicability of this theory to meiobenthos, 27 deep-sea sediment samples from the Gulf of Mexico were analyzed for meiobenthic and nematode community distribution and structure along with a set of environmental variables. Spatial and temporal heterogeneity in environmental conditions were found among sampling stations, and some variables, such as depth, inorganic carbon, carbon/nitrogen ratio, bottom-water oxygen, and percentage of sand, proved influential on total community abundance. Nematodes were the dominant meiofaunal group and its abundance highly variable among sites and sampling periods. Nematofauna was dominated by bacterivores, which also possessed the highest maturity index. Environmental characteristics showed a significant relation with community structure, not so the dispersal of nematode genera. In light of our findings, we posit that the deep-sea meiobenthos of the Gulf of Mexico may represent a metacommunity following the "species-sorting model." This inference is based on the different taxonomic structures among sampling stations correlating with environmental differences, in the presence of local niche diversification and limited dispersal. [ABSTRACT FROM AUTHOR]

The kinorhynch fauna from Svalbard and the Arctic Ocean north of Svalbard was explored, and a total of nine species of Echinoderes was identified. Two species were new to science, and one, Echinoderes balerioni sp. nov., is described. Echinoderes balerioni sp. nov. is characterized by the presence of short middorsal spines on segments 4, 6, and 8, and in lateroventral positions on segments 6 to 9. Tubes are present in laterodorsal, sublateral, and ventrolateral positions on segment 2, lateroventral positions on segment 5, and lateral accessory positions on segment 8, and tergal extensions conspicuously long and spiniform. The collected material also offered the first chance to examine specimens of Echinoderes arlis with scanning electron microscopy, which prompted a redescription of the species. The recorded species are compared with all other known records of Echinoderes in the Arctic region, and the summarized data suggests that at least some species show a circumpolar distribution. [ABSTRACT FROM AUTHOR]

Summary: Sivash Bay is the largest hypersaline lagoon in the world. In 1963-1975 the North Crimean Canal was constructed, with water from the River Dnieper and discharge of drainage water collected from agricultural lands into Sivash Bay. Salinity in Sivash Bay began to drop, resulting in a new brackish water ecosystem. The political decision to stop supplying water from the River Dnieper to the Canal was made in 2014, and the discharge of fresh water into the lagoon ended, resulting in an increase in salinity up to 60-75 g l−1. This study showed that the abundance of meiobenthos increased, with Nematoda dominating. The composition of nematode species in the lagoon has not previously been studied. Using samples from 1979, 2013 and 2015, 50 nematode species and forms were identified in 1979, 32 in 2013 and 21 in 2015. The species composition of nematodes at different periods was significantly different. The average abundance of nematodes was 134 198 ind. m−2 in 2013 and 606 660 ind. m−2 in 2015. [ABSTRACT FROM AUTHOR]

Abstract Understanding community assembly and processes driving diversity in deep-sea environments is a major challenge in marine ecosystems. In this paper, we investigated the importance of environmental gradients at different spatial scales in structuring deep-sea canyon and continental slope meiobenthic nematode communities in the NW Mediterranean Sea. Three scales were investigated 1) Ecosystem: Blanes Canyon vs. adjacent open slope; 2) Water-depth within each ecosystem: 1500, 1750 and 2000 m; and 3) Vertical profile (three layers within the first 5 cm of sediment). Nematode communities were analysed in terms of density, biomass, diversity and community structure. Grain size, Chl a , Chl a : phaeopigments, CPE, organic carbon and total nitrogen were measured to assess the relationships with nematode assemblages. Blanes Canyon harbours more abundant and diverse assemblages than the slope, particularly at 1750 m and 2000 m depth respectively. The higher canyon values may be related to the higher food availability there, which can be a consequence of the so-called "canyon effect". Slope assemblages were overall more uniform than those in the canyon, where there were greater bathymetrical differences in community structure. Densities in the canyon peaked at 1750 m depth, which did not correspond with the bathymetric gradient in food availability. The deepest canyon station was the most similar to the slope stations in terms of both environmental conditions and nematode communities, suggesting it lie outside the canyon influence. The higher habitat heterogeneity of the canyon (indicated by its greater vertical sediment and water depth differences) played a key role in structuring nematode spatial distribution. Independently of the ecosystem, however, the vertical sediment profile was the most determinative factor for density, community structure, and diversity. Highlights • Nematode community (standing stocks, diversity and community structure) differed between canyon and slope. • Blanes Canyon harbours more spatially heterogeneous and diverse nematode communities than its adjacent open slope. • Vertical sediment profile was significantly affecting the community structure and diversity, both in canyon and slope. [ABSTRACT FROM AUTHOR]

An assessment of the current ecological state of Sivash Bay (southern part of the Eastern Sivash) under the conditions of changes in its water regime is given in this study. Judging from the concentrations of the main pollutant classes, the prevailing type of anthropogenic impact on the ecosystem state of the studied area is the reduction of freshwater runoff, which caused the growth of salinity. Quantitative indicators of the microbial community of the bay bottom sediments characterize their pollution with organic substances. The increase in salinity of the reservoir caused a restructuring of the main components of the bottom community, such as meio and macrozoobenthos, expressed in a lowering of the biodiversity indicators and a change in the biocenosis taxonomic structure. [ABSTRACT FROM AUTHOR]

A new species of free-living marine nematode (Chromadorida: Chromadoridae), Graphonema antarcticum sp. nov., is described. The nematode was found in the shallow water of Kita-no-ura, off Syowa Station in Lützow-Holm Bay, Antarctica. Graphonema antarcticum sp. nov. is similar to G. metuliferum Kito, 1981 in the ratios of the spicules length to the body diameter at the cloaca, the well-developed gubernaculum with L-shaped lateral pieces bending at an obtuse angle and equipped with minute denticles at the distal end, and the tail length in both sexes. However, G. antarcticum sp. nov. differs from the latter in having a larger body size and presence of the lateral differentiation. The new diagnosis of the genus and the key to the species are provided. Graphonema achaeta Platonova, 1971 was transferred to Endeolophos due to the absence of the lateral pieces of gubernaculum that are present in the genus Graphonema. [ABSTRACT FROM AUTHOR]

We present the compilation of published and unpublished records of continental copepods of Colombia, as well as personal observations by the authors, yielding an additional list of 52 species and subspecies (7 calanoids, 20 cyclopoids, 25 harpacticoids). In addition to our former inventory (2007) of 69 species, the total number now reaches 121 taxa, increasing by 75% the known number of continental copepods. Freshwater taxa increased in 15 species and subspecies. The number of brackish species (and marine species collected in brackish environments), recorded from coastal lagoons and temporal offshore ponds reached 39 species and subspecies. Thirteen taxa with locus typicus in Colombia have been described since 2007. Between 2007 and 2018, thirty-nine departmental records were made, and 43 new habitat records were reported (not including the species recorded as new for the country). Parasitic copepods of fish reached six species. However, the number of species is expected to increase with the survey of poorly studied regions like the Amazon and the Eastern Plains, and habitats like groundwater, benthos of lakes and ponds, semiterrestrial environments and additional coastal lagoons. [ABSTRACT FROM AUTHOR]

Spatial distribution patterns (both horizontal and vertical) of meiofauna, with special focus on nematodes, on a tropical macrotidal beach across different climatic periods were analyzed in this study. Samplings were carried out at five stations in the intertidal zone in June (rainy season) and December (dry season), 2011. At each station, three samples were taken using a corer with 3cm diameter, which was thrust 10cm into the substrate and stratified in 0-2, 2-5, and 5-10cm. Meiofauna was comprised of 16 groups and Nematoda was the dominant. Meiofauna density during rainy season was higher at the central intertidal station and during dry season it was lower near the high tide mark, followed by an increasing trend towards the low tide mark. Meiofauna was more concentrated in the upper sediment layer during rainy season. However, during dry season, the highest density occurred in the lower sediment layer at both stations near the high tide mark. Nematoda association was comprised of 72 genera, with Daptonema and Theristus (both from the family Xyalidae) as the dominant ones in most stations and strata. The genera richness and diversity increased towards the low tide mark, with lower richness in the upper stratum at most stations. Non-selective deposit-feeders predominated during rainy season, while at dry season there was an alternation of dominance between non-selective deposit-feeders and epistrate feeders. Significant differences were found in the meiofauna community, as well as in the Nematoda association in regard to the months, stations, and sediment layers. The distribution patterns of interstitial organisms found in this study, in part, follow what is already known for microtidal beaches but other differential aspects were observed even if compared to environments of macrotidal beaches in temperate regions. [ABSTRACT FROM AUTHOR]

Copyright of Knowledge & Management of Aquatic Ecosystems is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study presents patterns of spatial and temporal variation in the meiofaunal community and nematode associations on the volcanic sandy beaches of Trindade Island, a remote oceanic island in the South-east Atlantic Ocean. Samples were collected in August (rainy season) and December 2014 (dry season) on four beaches (Tartarugas, Parcel, Cabritos and Portugueses) at three zones of the intertidal (high, mid and low). A total of 10 meiofaunal groups were found. Copepods (31%) and nematodes (27%) dominated the meiofauna in all beaches and zones, regardless of the season. Nematodes were comprised mainly of non-selective deposit feeders, with a total of 27 genera from 12 families, with Cyatholaimidae, Xyalidae and Oncholaimidae as the most diverse and abundant. Significant differences were found in the meiofaunal community, as well as in nematode associations, among seasons and intertidal zones but not among beaches. The sediment characteristics were the main drivers regulating the structure of meiobenthic fauna in Trindade Island. Our findings are also compared to other studies focusing on the meiofauna and nematodes of oceanic islands with carbonate and volcanic sediments; the major patterns are herein presented. [ABSTRACT FROM AUTHOR]