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Meiobenthic samples collected on the Côn Đảo archipelago (Vietnam) from two biotopes, in mangroves and on the adjacent reef flat areas, are analyzed. Quantitative characteristics of the dominant groups of meiobenthos are presented, and taxonomic composition of dominant taxa, nematodes, and harpacticoid copepods, are analyzed. It is shown that analysis of species composition is uninformative for a high species richness and a large number of unique species in each sample. It is more informative to use the generalized characteristics of communities, such as spectra of families and ecological and morphological groups of species. At the level of families and subfamilies, there are well-defined differences in the population of the sandy bottom and mangroves. The proportion of life forms in the different biotypes is informative for harpacticoid copepods. Big differences in the taxonomic composition of the studied bays are shown, interbiotopic differences make a smaller contribution to the overall diversity; i.e., each bay has its own set of species, which forms the population of each biotope. Nematodes and harpacticoids are distributed in space independently of each other. [ABSTRACT FROM AUTHOR]

The article describes the results of studies of two main components of meiobenthos—nematodes and harpacticoid copepods—conducted in Blagopoluchiya Bay (Novaya Zemlya, Kara Sea) in 2013 and 2020. The mosaic distribution of these two taxonomic groups was due to high species diversity and low occurrence of most species. Nevertheless, the authors identified patterns in the changes in the species structure of both groups related to the effect of two main environmental gradients (a spatial gradient related to the distance from the bay mouth to the sea and a depth-related gradient), as well as to the patchiness of sediment distribution. In 7 years between the two surveys in Blagopoluchiya Bay the abundance of nematodes increased tenfold, the copepod abundance also increased, but to a much lesser extent. Taxonomic changes in these two groups were observed at both species and family levels, with no differences in the taxa functional structure. The observed changes can be related to changes in abiotic factors and to general changes in the trophic system of the bay due to the establishment of the snow crab Chionoecetes opilio. [ABSTRACT FROM AUTHOR]

Background: Due to the copious disposal of plastics, marine ecosystems receive a large part of this waste. Microplastics (MPs) are solid particles smaller than 5 millimeters in size. Among the plastic polymers, polystyrene (PS) is one of the most commonly used and discarded. Due to its density being greater than that of water, it accumulates in marine sediments, potentially affecting benthic communities. This study investigated the ingestion of MP and their effect on the meiofauna community of a sandy beach. Meiofauna are an important trophic link between the basal and higher trophic levels of sedimentary food webs and may therefore be substantially involved in trophic transfer of MP and their associated compounds. Methods: We incubated microcosms without addition of MP (controls) and treatments contaminated with PS MP (1-µm) in marine sediments at three nominal concentrations (103, 105, 107particles/mL), for nine days, and sampled for meiofauna with collections every three days. At each sampling time, meiofauna were collected, quantified and identified to higher-taxon level, and ingestion of MP was quantified under an epifluorescence microscope. Results: Except for Tardigrada, all meiofauna taxa (Nematoda, turbellarians, Copepoda, Nauplii, Acari and Gastrotricha) ingested MP. Absorption was strongly dose dependent, being highest at 107 particles/mL, very low at 105 particles/mL and non-demonstrable at 103 particles/mL. Nematodes accumulated MP mainly in the intestine; MP abundance in the intestine increased with increasing incubation time. The total meiofauna density and species richness were significantly lower at the lowest MP concentration, while at the highest concentration these parameters were very similar to the control. In contrast, Shannon-Wiener diversity and evenness were greater in treatments with low MP concentration. However, these results should be interpreted with caution because of the low meiofauna abundances at the lower two MP concentrations. Conclusion: At the highest MP concentration, abundance, taxonomic diversity and community structure of a beach meiofauna community were not significantly affected, suggesting that MP effects on meiofauna are at most subtle. However, lower MP concentrations did cause substantial declines in abundance and diversity, in line with previous studies at the population and community level. While we can only speculate on the underlying mechanism(s) of this counterintuitive response, results suggest that further research is needed to better understand MP effects on marine benthic communities. [ABSTRACT FROM AUTHOR]

Characterizations of meiofauna, as well as of Nematoda assemblages, are rare in oceanic islands due to logistical difficulties and, until now, no study on the vertical distribution of this fauna has been conducted in these environments. Therefore, this study shows vertical distribution patterns in the meiofauna community and Nematoda assemblage on two beaches with different sediment characteristic (volcanic and carbonate) of Trindade Island, a remote oceanic island in the Atlantic Ocean. Samples were collected in December 2014 at Príncipe and Portugueses beaches in three intertidal zones (high, mid-, and low) at two sedimentary column depths (0–10 and 10–20 cm). Overall, meiofauna was comprised of seven major groups, with Oligochaeta (57%) and Nematoda (12%) as the most abundant. Higher density and richness of meiofauna and Nematoda assemblage were found at Portugueses beach with the carbonate sediment. Nematoda assemblage was mainly comprised of non-selective deposit-feeders, with a total of 27 genera and 12 families; Cyatholaimidae and Xyalidae were the most abundant and had the highest diversity. Composition and density of meiofauna and Nematoda assemblage showed similar vertical distribution where the surface layer (0–10 cm) presented lower densities. Sediment characteristics (grain size, sorting, and composition) were primarily responsible for the regulation of the structure and distribution of meiofauna and Nematoda assemblage in Trindade Island beaches. [ABSTRACT FROM AUTHOR]

ABSTRACT This study characterized the hyporheic zone of a stretch of the Ipojuca River through analysis of the sediments and meiofauna of this environment. Samples were collected at two points (Point 1: 8°17'28.2” S; 35°59'38.6” W and Point 2: 8°17'48.1” S; 35°56'12.2” W) and in three periods: summer (November/2018), transition period (March/2018), and winter (June/2018). The most representative material was classified as silt, varying between coarse, medium, and fine. 678 meiofauna individuals were counted, distributed in four more representative taxa, Rotifera (41%), Nematoda (40%), Annelida (11%), and Copepoda (5%). The PERMANOVA analysis indicated significant differences for the period (p = 0.0009) and space (p = 0.0261) factors. There was no significant relationship between the meiofauna community structure and hyporheic environment variables. The observed differences may be linked to water quality, which also varied between the points and periods studied.

Abstract Aim The Brazilian tropical semiarid is a biome with small freshwater ecosystems, often intermittent, acting as a mosaic in constant transformation between dry and rainy seasons. Meiobenthic communities play crucial roles in these environments, and understanding their colonization and succession processes is essential to comprehend how these organisms’ structure in a defaunated habitat. In addition to the traditional taxonomic approach, functional traits provide valuable insights into the dynamics of these processes. In this study, we tested the following hypotheses: i) although meiofauna consists of microscopic organisms with limited active dispersion, they quickly colonize new substrates, increasing in abundance, richness, and diversity; ii) functional traits of freshwater Nematoda are a good tool for view an early succession on hard artificial substrate in a lentic reservoir. Methods We placed 27 ceramic plates in a reservoir in the Brazilian semiarid and randomly sampled three replicates each week over nine weeks. Weekly differences in community abundance, richness, and diversity were tested with one-way ANOVA and pairwise PERMANOVA. Results Nematoda predominated in the first week, with Rotifera taking over from the second week of the experiment. No differences were observed in the Nematode taxonomic structure over the weeks. There was an increase in the functional complexity of the Nematoda community over time, as indicated by the maturity index and trophic structure. Colonizers/persistents emerged quickly in the first week. Deposit feeders dominated, but an increase in trophic diversity was observed with the growing presence of chewers over the weeks. Conclusions This study highlights that the functional traits of Nematoda represent a robust tool for assessing ecological succession in freshwater lentic environments in the tropical semiarid.

The current state of aquatic ecosystems was assessed for lakes in two river–lake systems: Święta Struga (Święte and Ocypelek) and Kałębnica (Czarne Południowe and Kałębie). Trophic states were determined using the Vollenweider, Nürnberg, and Carlson methods. Additionally, shoreline changes were analyzed for all lakes concerning their natural character, and physicochemical parameters were utilized as auxiliary elements in the assessment of the ecological state following the guidelines of Directive 2000/60/EC. Supplementary to these methods, the ecological evaluation of the littoral zone utilized meiobenthic organism grouping as an indicator. The results indicate significant differences among the studied reservoirs. Lake Święte is a reservoir bordering mesotrophy and eutrophy, with the ecological state of the littoral zone showing ongoing trophic development. Lake Ocypelek exemplifies a eutrophic reservoir undergoing progressive degradation. The lakes in the Kałębnica system also exhibit advanced trophic conditions, with Lake Kałębie being a eutrophic reservoir. Its shoreline has been significantly altered due to the development of the direct catchment area. In contrast, Lake Czarne Południowe serves as an example of a mesotrophic reservoir, with a substantially changed shoreline. Considering physicochemical elements and chlorophyll a concentration, the water quality for all examined lakes was found to be below the good category. The diagnosis of the condition of lake aquatic ecosystems requires an individualized approach to each of them. Therefore, employing various methods for their assessment, encompassing physico-chemical, biological, and morphological parameters, provides the opportunity to initiate potential remedial actions that will effectively contribute to their improvement. Conducting low-cost research involving a multidisciplinary approach to diagnose the state of aquatic ecosystems is becoming a crucial element in lake monitoring.

We present here a first comprehensive database on the diversity of proseriate flatworms (Platyhelminthes: Rhabditophora: Proseriata) on Western Mediterranean microtidal, wave dominated beaches. We sampled 116 stations in two years, through Spain (22 beaches, including Balearic Islands), France (25 beaches, including Corsica), Italy (63 beaches, including Sardinia, Sicily, and Lampedusa), and Tunisia (6 beaches). In each beach, we sampled at three depths, corresponding to the swash, shoal, and subtidal zones. For each sample, we obtained environmental data. The research yielded a total of 152 species, of which 93 were new to science. For each of the species found, we coded and described 16 functional traits. We discuss the functional meaning of the selected traits, as well as on diversity patterns and emerging biogeographic signals across the investigated regions. We particularly focused on the most widespread and dominant species in our dataset, concentrating on their putative adaptations to high energy environments; as well as the high number (58) of the species only found once. Finally, we discussed the coverage of our sampling by estimating the diversity at each investigated region and comparing it to the actual diversity. All information provided is available through the Global Biodiversity Information Facility (GBIF) and the Open Science Framework (OSF) following the Darwin Core Standard.

The current state of aquatic ecosystems was assessed for lakes in two river–lake systems: Święta Struga (Święte and Ocypelek) and Kałębnica (Czarne Południowe and Kałębie). Trophic states were determined using the Vollenweider, Nürnberg, and Carlson methods. Additionally, shoreline changes were analyzed for all lakes concerning their natural character, and physicochemical parameters were utilized as auxiliary elements in the assessment of the ecological state following the guidelines of Directive 2000/60/EC. Supplementary to these methods, the ecological evaluation of the littoral zone utilized meiobenthic organism grouping as an indicator. The results indicate significant differences among the studied reservoirs. Lake Święte is a reservoir bordering mesotrophy and eutrophy, with the ecological state of the littoral zone showing ongoing trophic development. Lake Ocypelek exemplifies a eutrophic reservoir undergoing progressive degradation. The lakes in the Kałębnica system also exhibit advanced trophic conditions, with Lake Kałębie being a eutrophic reservoir. Its shoreline has been significantly altered due to the development of the direct catchment area. In contrast, Lake Czarne Południowe serves as an example of a mesotrophic reservoir, with a substantially changed shoreline. Considering physicochemical elements and chlorophyll a concentration, the water quality for all examined lakes was found to be below the good category. The diagnosis of the condition of lake aquatic ecosystems requires an individualized approach to each of them. Therefore, employing various methods for their assessment, encompassing physico-chemical, biological, and morphological parameters, provides the opportunity to initiate potential remedial actions that will effectively contribute to their improvement. Conducting low-cost research involving a multidisciplinary approach to diagnose the state of aquatic ecosystems is becoming a crucial element in lake monitoring. [ABSTRACT FROM AUTHOR]

Background Due to the copious disposal of plastics, marine ecosystems receive a large part of this waste. Microplastics (MPs) are solid particles smaller than 5 millimeters in size. Among the plastic polymers, polystyrene (PS) is one of the most commonly used and discarded. Due to its density being greater than that of water, it accumulates in marine sediments, potentially affecting benthic communities. This study investigated the ingestion of MP and their effect on the meiofauna community of a sandy beach. Meiofauna are an important trophic link between the basal and higher trophic levels of sedimentary food webs and may therefore be substantially involved in trophic transfer of MP and their associated compounds. Methods We incubated microcosms without addition of MP (controls) and treatments contaminated with PS MP (1-µm) in marine sediments at three nominal concentrations (103, 105, 107particles/mL), for nine days, and sampled for meiofauna with collections every three days. At each sampling time, meiofauna were collected, quantified and identified to higher-taxon level, and ingestion of MP was quantified under an epifluorescence microscope. Results Except for Tardigrada, all meiofauna taxa (Nematoda, turbellarians, Copepoda, Nauplii, Acari and Gastrotricha) ingested MP. Absorption was strongly dose dependent, being highest at 107 particles/mL, very low at 105 particles/mL and non-demonstrable at 103 particles/mL. Nematodes accumulated MP mainly in the intestine; MP abundance in the intestine increased with increasing incubation time. The total meiofauna density and species richness were significantly lower at the lowest MP concentration, while at the highest concentration these parameters were very similar to the control. In contrast, Shannon-Wiener diversity and evenness were greater in treatments with low MP concentration. However, these results should be interpreted with caution because of the low meiofauna abundances at the lower two MP concentrations. Conclusion At the highest MP concentration, abundance, taxonomic diversity and community structure of a beach meiofauna community were not significantly affected, suggesting that MP effects on meiofauna are at most subtle. However, lower MP concentrations did cause substantial declines in abundance and diversity, in line with previous studies at the population and community level. While we can only speculate on the underlying mechanism(s) of this counterintuitive response, results suggest that further research is needed to better understand MP effects on marine benthic communities.

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.

The study of benthic meiofauna has been undertaken in Latin America since the beginning of the 20th century, recently gaining attention due to its recognized role on the ecological functioning of meiofauna assemblages. Bibliometric data provide information regarding research results, explain the degree to which a subject has advanced, and identify its major strengths and weaknesses. In Latin American countries, this type of review is scarce for meiofauna communities. This study analyzes knowledge of marine meiofauna by focusing on the documents Latin American authors published from 1990 to 2021. Documents from three bibliographic databases were analyzed to obtain the most relevant bibliometric indicators. Moreover, the interrelationships between authors, countries, and concepts were analyzed using science mapping techniques. Latin American research on marine meiofauna has increased since the 1990s, producing a total of 399 documents over three decades by almost 1,000 authors. Brazil produced the majority of these documents (predominantly published by Brazilian authors and institutions). The number of documents by country was associated with five development indicators. Their main sources and keywords indicate that ecology, oceanography, and biogeography were the main addressed topics, especially on deep marine environments. Most productive authors were clustered into main research groups with varying degrees of links. We conclude that research efforts on marine meiofauna are gaining importance despite the small number of documents by a relatively low number of research groups. We found a high centralization of documents by countries and a relation with four indicators, such as country size and research spending. Greater regional collaboration could further expand the knowledge of marine meiofauna in Latin America. [ABSTRACT FROM AUTHOR]

The term “meiobenthos” refers to a diverse community of organisms inhabiting the interstitial spaces between sand grains retained on sieve sizes ranging between 38 to 500 μm. This study investigates the diversity and density of meiobenthic communities across five locations along the Chennai coast. We examined the dominant meiobenthic groups, with nematodes exhibiting high dominance at Napier station (288.6 ± 91.07 ind.10cm²) and harpacticoids dominating at Marina station (449.88 ± 264.3 ind.10cm²). To establish the relationship between meiobenthic organisms and environmental parameters, we analyzed seven physicochemical factors throughout the study period. The results indicate a negative correlation between ammonia, nitrate, and phosphate levels in the water and a few meiobenthic groups, notably harpacticoids and ostracods. However, no significant relationship was observed between physicochemical parameters and dominant groups of this study, such as nematodes and polychaetes. These findings highlight substantial fluctuations in the diversity and density of meiobenthos and physicochemical parameters throughout the study period, emphasizing the dynamic nature of these coastal ecosystems. Moreover, the results of this study contribute to our understanding of meiobenthic dynamics and their interactions with the environment. [ABSTRACT FROM AUTHOR]

The present study is the first structured attempt to analyze the species composition and distribution of freshwater invertebrates in the lakes, streams, and rivers of the Shantar Islands and to compare the diversity of the hydrobiont fauna of the archipelago and the continental part of Khabarovsk Krai on the basis of the original and literature data. The research revealed 57 zooplanktonic, 47 meiobenthic, and 142 macrobenthic taxa in the waters of the island and the adjacent continental areas. Different patterns of variability in the species richness, abundance, and the community structure are observed for different groups of hydrobionts along the salinity gradient in the unique, brackish Lake Bolshoe. Zooplankton show no directional variability, reaching a maximum in a frontal zone where riverine and brackish water mix. Meiobenthos show the highest diversity in the most saline zone of the lake, where marine species are abundant. The characteristics of the macrozoobenthos gradually increase with the salinity of the lake, with a dramatic change in the dominance structure at the critical salinity threshold, where amphibiotic insects, dominant in the desalinated water zone, are replaced by amphipods. Latitudinal variability in species richness and biogeographic structure of the fauna are closely related for different groups of freshwater invertebrates. A smooth decline in species richness from southern to northern areas was observed when comparing the faunas of the Shantar water bodies with those located to the south. This trend is shown for amphibiotic insects and microcrustaceans and is most pronounced for mollusks. The fauna of the Shantar Islands is predominantly represented by species with a wide Palaearctic, Holarctic, and cosmopolitan range, with a small proportion of species restricted to the Arctic zone of Eurasia or specific to Eastern Siberia and the Far East. Only three brackish water species have a Beringian type of distribution. The assemblage structures of the zooplankton and meiobenthos communities of continental coastal and island lakes do not greatly differ. On the contrary, brackish communities are clearly distinct from the others. The taxonomic composition of macroinvertebrates differed significantly between the islands and the mainland. [ABSTRACT FROM AUTHOR]

The taxonomic and quantitative composition of the meiobenthos, with an emphasis on foraminifera and gromiids were studied on the coast of Primorsky krai, northwestern part of the Sea of Japan, at water depths of 0.3–86.0 m. The Protozoa were evaluated for the first time in this region as a component of the meiobenthic communities. The protozoa are represented by four morpho-ecological groups: Ciliophora (free-moving and epibionts), both hard-shelled and soft-walled Foraminifera, and Cercozoa (class Gromiidea). The total abundance of the meiobenthos varied from 32 500 to 2 107 500 ind./m2. The presence of Protozoa was extremely variable. They were completely absent (station 62) and reached a maximum 155 000 ind./m2 (station 42). Among the protozoans, soft-walled foraminifers (SWF) and gromiids (GR) dominated. GRs accounted for up to 51–85% of the abundance of the total protozoa at some stations in Peter the Great Bay. At other stations, SWFs prevailed and reached 93–100% of the total protozoa. The most numerous hard-shelled foraminifers (HSF) and ciliates (CL) were obtained in the Vladimir Bay and at individual stations off the eastern coast of Primorsky krai. Brief descriptions with illustrations are given for 45 representatives of the SWF belonging to the families Allogromiidae and Saccamminidae, of which 22 of them are identified to the species or genus level, and 23 morphotypes are identified to the family level. The gromiid fauna is represented by six morphotypes. [ABSTRACT FROM AUTHOR]

This study provided a preliminary comparative analysis of meiobenthic assemblages in different habitats of the Snake Island Marine Protected Area (MPA). Meiobenthos was studied in three habitats: Exposed Black Sea upper infralittoral rock with Corallinales turf (MB142), Mytilid dominated exposed Black Sea upper infralittoral rock with foliose algae (no Fucales) (MB143) and Black Sea infralittoral sand and muddy sand without macroalgae (MB542). A total of 10 higher meiobenthos taxa were recorded in the different habitats: 5 permanent groups (Platyhelminthes, Nematoda, Harpacticoida (Copepoda), Ostracoda, Halacaridae) and 5 temporary groups (Oligochaeta, Polychaeta, Bivalvia, Gastropoda, Cyrripedia). The preliminary study of meiobenthos in the habitats of the Snake Island MPA showed that habitat MB143 was more favourable for meiobenthos, with the highest mean density and biomass (190 655 ± 23 004 ind.-m-2 and 3170.90 ± 412.15 mg-m-2, respectively). The comparative nMDS and cluster analyses based on the density of meiobenthos taxa in the Snake Island MPA showed that the meiofauna of both MB142 and MB143 differed significantly from the MB542 habitat, with Bivalvia and Ostracoda making the largest percentage contribution to these differences. The meiobenthos assemblages in the different habitats of the Snake Island MPA were similar to the other regions of the Black Sea with some unique features (e. g. relatively lower total meiobenthos density, high percentage of ostracodes on the algal substrate, etc.). Further studies on the characteristics of meiobenthos taxa assemblages in other Black Sea MPAs could lead to the estimation of meiobenthos assemblage patterns and their possible use in biomonitoring. [ABSTRACT FROM AUTHOR]

Salt marshes are regarded as among the most productive coastal ecosystems, important “blue carbon” sinks and a support for benthic communities with large abundances, whose structure may be strongly influenced by salt marsh vegetation. During the last few decades, Spartina alterniflora has been colonizing bare mudflats in the Bahía Blanca estuary, and a large increase in the area covered by salt marshes has been reported. This colonization can strongly influence the structure of benthic fauna and its role in the carbon cycle. The hypothesis of this study was that the community structure and the organic carbon contained in the meio- and macrobenthos change between tidal flats and salt marshes recently colonized by S. alterniflora. Response variables studied to compare the tidal flat and salt marsh were density, biomass and production to biomass (P/B) ratio of macro- and meiobenthos. Density and biomass of Gastropoda and P/B ratio of Nematoda were higher on the salt marsh than on the tidal flat. By contrast, density and biomass of Polychaeta were higher on the tidal flat. These results suggest that the expansion of S. alterniflora marshes on tidal flats produces changes in the structure of the macro- and meiobenthos community (taxonomic composition and biomass) that have an influence on carbon cycling.

Aim: The interplay between distribution ranges, species traits and sampling and taxonomic biases remains elusive amongst microscopic animals. This ignorance obscures our understanding of the diversity patterns of a major component of biodiversity. Here, we used marine Halacaridae to explore whether differences between marine provinces can explain their distribution patterns or if differential sampling efforts across regions prevent any macroecological inference. Furthermore, we test if certain functional traits influence their distribution patterns. Location: Europe. Results: Whereas geographical variables provided a better explanation for differences in species composition, sampling effort and distance from marine biological stations accounted for the majority of differences in European Halacaridae richness. Species occurring in more habitats showed broader geographical ranges and accumulated more records. Species traits like generalism affected the distribution of halacarid species. Main Conclusions: We propose that the sampling effort of halacarid mites in Europe might be explained by two different cognitive biases: the convenience of selecting certain sampling localities compared to others and the tendency of zoologists to scrutinise habitats where their target organisms are more common. [ABSTRACT FROM AUTHOR]

Despite long-term research on marine litter there is still insufficient knowledge about benthic organisms associated with these substrates, especially experimental studies and methodology of sampling for complex biofouling assemblages. To predict the fate of plastic in the marine environment it is necessary to know how long the macrolitter can stay in different sea matrices and what are the steps of colonisation by marine organisms. The experiments were carried out during various seasons in situ in the north-western Black Sea coastal area. Three new types of the experimental constructions intended for different durations of exposure (1–10 months) were designed. This article is the first to present the methodology and the results of complex experiments investigating marine fouling (from microalgae to meio- and macrofauna) on plastic surfaces. Overall, 28 genera of microalgae, 13 major groups of meiobenthos and 36 species of macrofauna were found on plastic during the experiments. The microalgae fouling was mainly formed by representatives of genus Cocconeis. The species composition of microalgae was common for the research area. The average density and biomass of meiobenthos were the greatest on I construction type after 8 months of exposure. In the total macrozoobenthos biomass and density of Bivalvia and Crustacea dominated, respectively. The obtained results on the interaction between fouling organisms and plastic materials in the marine environment form an important contribution to the understanding of the "good ecological status" of the sea. Additional studies based on the tested methodology could be used as a component of ecological monitoring during development and implementation of the approaches of the Marine Strategy (descriptor 10).

Meiofauna (body size within 30–1000 µm) are the community of microscopic invertebrates that live at the bottom of marine and freshwater ecosystems and play a key role in the food webs of these environments. Several studies have addressed the adverse effects of anthropic stressors on meiofauna; however, data on the presence and impact of plastic debris in wild meiofaunal organisms are scant. Since the amount of microplastic waste in sediments may surge rapidly, ascertaining the ingestion of these xenobiotics by the abundant micrometazoan community is necessary to understand their potential accumulation in aquatic food webs and their hazard to the health of the ecosystem. The absence of documentation in this regard may be due to the difficulty in detecting the small size of the plastic fragments meiofauna may potentially ingest. To overcome this difficulty, we developed an integrated approach based on different microscopic/spectroscopic techniques suitable for detecting plastic particles of sizes down to 200 nm. [ABSTRACT FROM AUTHOR]

This study provided a preliminary comparative analysis of meiobenthic assemblages in different habitats of the Snake Island Marine Protected Area (MPA). Meiobenthos was studied in three habitats: Exposed Black Sea upper infralittoral rock with Corallinales turf (MB142), Mytilid dominated exposed Black Sea upper infralittoral rock with foliose algae (no Fucales) (MB143) and Black Sea infralittoral sand and muddy sand without macroalgae (MB542). A total of 10 higher meiobenthos taxa were recorded in the different habitats: 5 permanent groups (Platyhelminthes, Nematoda, Harpacticoida (Copepoda), Ostracoda, Halacaridae) and 5 temporary groups (Oligochaeta, Polychaeta, Bivalvia, Gastropoda, Cyrripedia). The preliminary study of meiobenthos in the habitats of the Snake Island MPA showed that habitat MB143 was more favourable for meiobenthos, with the highest mean density and biomass (190655 ± 23004 ind.-m-2 and 3170.90 ± 412.15 mg-m-2, respectively). The comparative nMDS and cluster analyses based on the density of meiobenthos taxa in the Snake Island MPA showed that the meiofauna of both MB142 and MB143 differed significantly from the MB542 habitat, with Bivalvia and Ostracoda making the largest percentage contribution to these differences. The meiobenthos assemblages in the different habitats of the Snake Island MPA were similar to the other regions of the Black Sea with some unique features (e.g. relatively lower total meiobenthos density, high percentage of ostracodes on the algal substrate, etc.). Further studies on the characteristics of meiobenthos taxa assemblages in other Black Sea MPAs could lead to the estimation of meiobenthos assemblage patterns and their possible use in biomonitoring.

The present study is the first structured attempt to analyze the species composition and distribution of freshwater invertebrates in the lakes, streams, and rivers of the Shantar Islands and to compare the diversity of the hydrobiont fauna of the archipelago and the continental part of Khabarovsk Krai on the basis of the original and literature data. The research revealed 57 zooplanktonic, 47 meiobenthic, and 142 macrobenthic taxa in the waters of the island and the adjacent continental areas. Different patterns of variability in the species richness, abundance, and the community structure are observed for different groups of hydrobionts along the salinity gradient in the unique, brackish Lake Bolshoe. Zooplankton show no directional variability, reaching a maximum in a frontal zone where riverine and brackish water mix. Meiobenthos show the highest diversity in the most saline zone of the lake, where marine species are abundant. The characteristics of the macrozoobenthos gradually increase with the salinity of the lake, with a dramatic change in the dominance structure at the critical salinity threshold, where amphibiotic insects, dominant in the desalinated water zone, are replaced by amphipods. Latitudinal variability in species richness and biogeographic structure of the fauna are closely related for different groups of freshwater invertebrates. A smooth decline in species richness from southern to northern areas was observed when comparing the faunas of the Shantar water bodies with those located to the south. This trend is shown for amphibiotic insects and microcrustaceans and is most pronounced for mollusks. The fauna of the Shantar Islands is predominantly represented by species with a wide Palaearctic, Holarctic, and cosmopolitan range, with a small proportion of species restricted to the Arctic zone of Eurasia or specific to Eastern Siberia and the Far East. Only three brackish water species have a Beringian type of distribution. The assemblage structures of the zooplankton and meiobenthos communities of continental coastal and island lakes do not greatly differ. On the contrary, brackish communities are clearly distinct from the others. The taxonomic composition of macroinvertebrates differed significantly between the islands and the mainland.

IntroductionBody size regulates all biological processes, including growth, reproduction, metabolism, trophic interactions, etc., and is the master trait across organisms, populations, and communities. Despite a rich literature on the impacts of human and natural disturbances on body size, a clear knowledge gap is the effect of the submarine canyons on the benthic size structures in the deep sea, hindering our understanding of the ecological processes of these dominant ecosystems on the continental margin.MethodsTherefore, we conducted repeated sediment sampling to compare meiofauna and macrofauna biomass body-size spectrum, growth, metabolism, and size composition from a high-energy submarine canyon, Gaoping Submarine Canyon (GPSC), and the adjacent continental slope off SW Taiwan. The GPSC is a dynamic ecosystem connected to a high sediment-yield small mountain river subjected to strong internal-tide energy, swift bottom currents, frequent mass wasting events, and high terrestrial sediment inputs.ResultsWe found that the meiofauna and macrofauna were characterized by relatively larger individuals dominating on the slope to smaller ones dominating in the canyon. As a result, the community biomass, secondary production, and respiration were depressed with distinctive biomass-size composition in the canyon compared to the non-canyon slope. The environmental factors related to internal tide disturbance (i.e., bottom current velocity, duration of sediment erosion, or low light transmission) substantially influence the body size composition of the canyon benthos, while food supplies (i.e., TOC and C/N ratio) and sediment characters (i.e., grain size and porosity) correlated closely with the slope communities.DiscussionWe concluded that the disturbed condition in the GPSC may have wiped out or depressed the local benthic assemblages, and only the smaller, more resilient species could persist. Our results also highlight that the alterations of the canyon benthic community could be a reference to deep-sea ecosystems under anthropogenic disturbances or global climate change.

Over the past 70 years, numerous authors studied the platyhelminth fauna near the island of Sylt in the eastern North Sea, each with a specific focus on varying aspects of ecology, morphology or systematics, and most of them dealing with a single habitat type. These data are combined with new data to get a comprehensive view of species richness, the distribution of individual species across tidal levels and sediment types and the resulting communities. So far, 398 platyhelminth species have been recorded around Sylt island, plus a still growing number of unidentified or undescribed species, in particular from subtidal waters. The distribution over habitat types (as defined by sediment types and tidal level) is described for the known species. Neighbouring habitat types overlap in species composition, and faunal composition changes continuously over environmental gradients. The number of species recorded per habitat type mirrors the sampling intensity and varied between some 20 species in poorly studied habitats and 150 in the well-studied intertidal sand flats. Corrected for variations in sampling intensity, platyhelminth species richness showed no significant differences between sediment types and only moderate variation over tidal levels. On a larger spatial scale, three faunal assemblages can be differentiated: the supratidal harbours brackish-water species (mesohaline in the upper and polyhaline in the lower supratidal), the intertidal polyhaline-marine species with a wide tolerance of variations in physical factors and the subtidal marine (± stenohaline) species. With respect to sediment type, mud and sand dwellers are well separated in the supra- and subtidal belt but less in the intertidal. Provided these rules are general, I conclude platyhelminth species richness in a given section of coastline mainly depends on the ranges of environmental factors covered. Nineteen new species encountered during this study are described. [ABSTRACT FROM AUTHOR]

This study aims model the distribution of meiofauna indicators in relation to environmental variables from the Santos Basin continental margin, SE Brazil, using machine learning techniques, to provide baseline information and foster future monitoring programs. A total of 100 sampling stations were distributed in eight transects and 11 isobaths (25 to 2,400 m) perpendicular to the coast. In each station, three replicates were sampled for meiofauna and 38 environmental parameters. A total of 28 meiofauna taxa were found, with a mean richness varying from 3 to 15 taxa per station. Meiofauna mean density varied between 55 and 2,001 ind. 10 cm-2. Density of meiofauna and its most frequent taxa (Nematoda, Copepoda, Kinorhyncha, and Polychaeta), and taxa richness were used as descriptors for the models. Meiofauna and nematode density showed the highest training and testing accuracies, with R2 values above 0.74. Based on the distribution of meiofauna descriptors and their responses to environmental conditions, we suggest a mosaic of six benthic zones. The La Plata Plume zone and the Cabo Frio Upwelling zone are two of the most diverse and productive zones in the continental shelf, wich are separated by the less productive Central Continental Shelf zone. A fourth zone, with very low meiofauna densities, corresponds to the carbonated sediments of the shelf-break. The Upper and Mid-Slope is a narrow zone along the entire basin, with intermediate densities and small amounts of high-quality organic carbon. The largest, impoverished zone, the Lower Slope and Plateau comprises the deepest areas and the São Paulo Plateau. The study showed that, although some zones can be recognized by most meiofauna descriptors, others are better characterized by specific ones, implying that meiofauna indicators should be monitored concomitantly. We recommend the optimization of sampling design based on our model to reduce costs and increase our understanding of the system. [ABSTRACT FROM AUTHOR]

During the research cruise MSM 14/1 of RV M.S. MERIAN to the eastern Mediterranean Eratosthenes Seamount in 2009/2010, samples were taken with a multiple corer to get first insights into the composition, abundance, and diversity of the meiofauna. Along two transects, a north–south and a west–east ones, 14 sites were sampled on the seamount. Additionally, a distant deep-sea site provided meiobenthic material for comparison with that of the seamount. Altogether, 15 meiobenthic major taxa were found. Nematoda and Copepoda Harpacticoida strongly dominated all sites, followed by Annelida and Tardigrada at most sites. Although direct comparison pointed towards a northern seamount community, this could not be confirmed by a detailed community analysis regarding taxa composition, abundance expressed by density (ind./10 cm2), and taxa diversity. It revealed neither a homogeneous seamount community nor any faunistic relation with bathymetric or geographic gradients, with exception of the taxa diversity that apparently followed a latitudinal gradient. Generally, Eratosthenes Seamount presents a quite heterogeneous meiobenthic assemblage that may be linked to small-scale biotic and abiotic variables. Moreover, also the distant reference site did not differ significantly from the seamount sites. A brief comparison with other Atlantic and Mediterranean seamounts and islands indicates that Eratosthenes Seamount is not characterized by an impoverished meiobenthic fauna. [ABSTRACT FROM AUTHOR]

The Antarctic Ocean hosts several species adapted to polar environments. However, the Antarctic marine environment is rapidly changing. We studied the meiofauna and nematode communities in Maxwell Bay, King George Island, Antarctica. The meiofaunal densities ranged from 174.3 ± 6.2 to 377.9 ± 7.0 individuals/10 cm2. The nematodes and harpacticoids accounted for 89.7% of the total meiofaunal density. A total of 1448 nematode individuals across 34 genera were recorded. The dominant nematode genus was Molgolaimus. This study offers guidance for future studies on polar benthic organisms and a reference to evaluate anthropogenic effects on polar ecosystems. [ABSTRACT FROM AUTHOR]

The southwest coast of India is densely populated and experiences a wide range of natural and anthropogenic pressures. The diversity of macro and meiobenthos was documented in order to assess the ecosystem health of an anthropogenically impacted coastal ecosystem for the first time along the southwest coast of Tamil Nadu. Offshore sediment and water samples (n = 63) were collected from 14 sampling stations using the grid sampling method. Water and sediment samples were analysed for environmental variables such as pH, temperature, electrical conductivity (EC), total dissolved solids (TDS), salinity, sulphate, dissolved oxygen (DO), carbohydrate (CHO), protein, lipid, labile organic matter (LOM), total organic carbon (Corg), total organic matter (TOM) and sediment texture. Benthic macro and meiobenthos were isolated and identified using standard identification keys. A total of 5 phyla of macrobenthos with 29 species and 5 phyla of meiobenthos with 60 species were identified in the study area. Relative abundance analysis showed that the largest numbers of species belonged to Polychaeta for macrobenthos and foraminifera for meiobenthos. Redundancy analysis indicated that sediment carbohydrate content was the highest determining factor for explaining variation in the diversity of benthos. AMBI & M−AMBI results revealed that among the 14 stations, 2 were categorized as “poor” and 9 as “bad”. Multiple anthropogenic activities in the coastal environment leading to increased organic matter input have resulted in a decline in the ecosystem health of this region, which warrants site-specific management to control organic pollution.

Summary: A new species of free-living marine nematode, Deontostoma quadridentatum sp. nov., is described from a deep-sea sediment sample collected off the South Orkney Islands, the Southern Ocean, during a cruise (KH-19-6-Leg 4) conducted on the R/V Hakuho-Maru. Deontostoma quadridentatum sp. nov. differs from its congeners by the possession of: i) a cephalic capsule with a smooth posterior edge and without intralobar lacunae; ii) interlobar fenestrae with two posterior incisions; iii) four odontia on each mandible; iv) three onchia; v) spicules with velum and lateral process; vi) gubernacula with a hollow triangular crus, vii) one ventromedian supplement; viii) two precloacal subventral rows consisting of 8-10 setae and 12-20 papillae; and ix) by the lack of ocelli. Partial 18S rRNA and cytochrome c oxidase subunit I gene sequences were determined for D. quadridentatum sp. nov., and the diagnosis of Deontostoma and the dichotomous keys to the subfamilies of Leptosomatidae, genera of Deontostomatinae, and species of Deontostoma were revised. Two known species, Triceratonema montredonense comb. nov. and Triceratonema papillosum comb. nov., were transferred from Deontostoma. Our molecular phylogenetic analysis did not clarify the position of Deontostoma quadridentatum sp. nov., but we placed this species into Deontostoma based on morphological observations. We also tried to find a relationship between distribution and morphological characteristic because it seems that there are two phylogenetic lineages that exist in Deontostoma based on the distribution of all species. However, no such relationships could be found from our literature survey. [ABSTRACT FROM AUTHOR]

Abstract 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.

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. [ABSTRACT FROM AUTHOR]

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

Meiofauna (body size within 30–1000 µm) are the community of microscopic invertebrates that live at the bottom of marine and freshwater ecosystems and play a key role in the food webs of these environments. Several studies have addressed the adverse effects of anthropic stressors on meiofauna; however, data on the presence and impact of plastic debris in wild meiofaunal organisms are scant. Since the amount of microplastic waste in sediments may surge rapidly, ascertaining the ingestion of these xenobiotics by the abundant micrometazoan community is necessary to understand their potential accumulation in aquatic food webs and their hazard to the health of the ecosystem. The absence of documentation in this regard may be due to the difficulty in detecting the small size of the plastic fragments meiofauna may potentially ingest. To overcome this difficulty, we developed an integrated approach based on different microscopic/spectroscopic techniques suitable for detecting plastic particles of sizes down to 200 nm.

Data about meiobenthic ostracodes species on the different substrates of Zmiiniy Island nearshore water area are presented. The density and biomass means of the ostracodes were higher on the algal substrates (on Laurencia paniculata made up 41931 ± 12689 ind.·m-2 and 400.56 ± 125.65 mg·m-2 respectively). In the current study for the first time 13 ostracodes species were found, most of which are common in all types of substrate. The dominant species were Loxoconcha pontica Klie, 1937, Paradoxostoma intermedium Müller, 1894, Xestoleberis cornelii Caraion, 1963 and Xestoleberis decipiens (Müller, 1894). All of them are common species in the north-western Black Sea. Non-metric multidimensional scaling (nMDS) analysis of ostracodes species abundance shown that the samples of sandy-shells bottom differed significantly from algal and mussel substrates. According to the cluster analysis sand-shells bottom samples on almost 80 % differed from hard substrates. [ABSTRACT FROM AUTHOR]

Macro- and meiobenthos of the Blagopoluchiya Bay (Novaya Zemlya, Kara Sea) have undergone significant changes in their quantitative distribution from 2013 to 2020. During this period, meiobenthos abundance has increased greatly, whereas macrobenthos abundance has decreased. Mean meiobenthos density has tripled (from 702 to 2293 ind./10 cm2), while mean macrobenthos density decreased by more than a half (from 1530 to 645 ind./m2). The observed growth of meiobenthos density was mainly due to an increase in the abundance of free-living nematodes. We suggest that the invasion of snow crab Chionoecetes opilio is one of the most important drivers of changes in benthos distribution. Following the crab invasion, there was a reduction of macrobenthic density and biomass and a compensatory increase in those in meiobenthos in the Blagopoluchiya Bay. [ABSTRACT FROM AUTHOR]

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

Data about meiobenthic ostracodes species on the different substrates of Zmiiniy Island nearshore water area are presented. The density and biomass means of the ostracodes were higher on the algal substrates (on Laurencia paniculata made up 41931 ± 12689 ind.·m-2 and 400.56 ± 125.65 mg·m-2 respectively). In the current study for the first time 13 ostracodes species were found, most of which are common in all types of substrate. The dominant species were Loxoconcha pontica Klie, 1937, Paradoxostoma intermedium Müller, 1894, Xestoleberis cornelii Caraion, 1963 and Xestoleberis decipiens (Müller, 1894). All of them are common species in the north-western Black Sea. Non-metric multidimensional scaling (nMDS) analysis of ostracodes species abundance shown that the samples of sandy-shells bottom differed significantly from algal and mussel substrates. According to the cluster analysis sand-shells bottom samples on almost 80 % differed from hard substrates.

Maerl beds, particularly those of Brittany, are important, structurally complex biogenic coastal habitats that form a unique ecosystem with high benthic biodiversity. Although they are relatively well studied throughout Europe, several faunal groups of maerl beds, such as those belonging to the meiofauna, have received little attention. We investigated the meiofaunal abundance, distribution and community structure, with a focus on nematode biomass and diversity, in a maerl area in the Bay of Brest, Brittany, compared with that on a sandy beach (Anse de Dinan, Brittany). Meiofauna was five times more abundant on the maerl bed than on the sandy beach, and 1.5 times more diversified (12 vs. 8 taxa, respectively). Nematode diversity was more than three times higher on the maerl bed than on the sandy beach and showed a distinctive nematode community that was absent from the sandy beach. Maerl beds create more heterogeneous microhabitats and promote a higher diversification of meiofauna and nematode communities than sandy beaches.

The suitability of using meiobenthic communities and especially the nematodes-based indices to assess the ecological quality of the Ukrainian Danube delta coastal area was tested in one control and two sites impacted by dredging/dumping activities. The study is based on the results of benthic surveys carried out in November 2015 and August 2018 and 2020 in the area of the "Danube-Black Sea" navigable canal. The values of the taxonomic richness of the meiobenthos varied from 6 taxa in the dredging sites to 9 taxa at background stations. According to the species richness, the ecological quality in the dredging area fell into the Poor class (EQS), while the background and dumping areas into the Moderate class. TThe Shannon index (H') of the nematodes in the dredging sites varied from 0 to 1.8. Low values of these indices indicate Bad ecological status in the dredging sites and Poor in the rest. There was a high percentage of c-p2 (r-strategists) in all sites. Average values of the maturity index (MI) varied from 1.5 ± 0.2 in the dredging sites to 2.3 ± 0.1 at dumping and 2.6 ± 0.1 at background stations. The Maturity Index also indicates that the dredging site is in Bad condition, the dumping one is in Poor and the background stations are in Moderate. Non-selective deposit feeders (1B) dominated at most stations. According to the values of the trophic diversity index (ITD), the study area can be classified as Poor. For the study sites, species that can be considered potential biological indicators are evinced. [ABSTRACT FROM AUTHOR]

Distinctive studies were conducted for the identification of meiobenthos and zooplankton at Farasan Islands and Jizan sandy shores. The present work compares the meiobenthos and zooplankton communities at Alhsas sandy shore at Farasan Islands and As-Suways sandy shore at Jizan. Population density, species richness and Shannon-Weiner diversity index were determined for meiobenthos and zooplankton inhabiting both the studied sites. Water criteria; surface water temperature, pH and conductivity were determined for each investigated site. Eleven zooplankton species were defined at Alhsas sandy shore Farasan, nine species were identified at the littoral zone at As-Suways sandy shore, Jizan. Ten meiobenthos species were defined at Alhsas site, Farasan. Only eight meiobenthos species were defined at the intertidal zone of As-Suways site, Jizan. The results were discussed to highlight the effect of water criteria on the spatial distribution of zooplankton and meiobenthos at the investigated sites. [ABSTRACT FROM AUTHOR]

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.

The aim of the work was to describe the variability of a group of meiobenthos inhabiting a tidal flat in Nottinghambukta which is influenced by the diverse conditions of a seasonal as well as multi-annual cyclicity. Samples were collected in five series, i.e. during the Arctic spring (2001), summer (2000 and 2001) and autumn (2001). The material for qualitative analysis was collected from sites with different hydrological characteristics. The following major meiobenthic taxa were found: Metazoa, i.e. Nematoda and Crustacea (Ostracoda and Copepoda-Harpacticoida), and Foraminifera. Unstable conditions in the bay result in a seasonal variability in the species composition as well as an uneven colonisation of the Nottinghambukta area by meiobenthos. The lowest taxonomic diversity occurs in summer, but it increases in autumn when the land runoff ceases. Based on the conducted analysis, it can be concluded that the inflow of seawater in autumn brings on the occurrence of new taxa, which probably inhabit the bay temporarily until the summer season during which the highly variable conditions cause a change in the species composition. For the series of samples collected in July 2000 and 2001, the species composition for Harpacticoida was determined. The taxonomic diversity of the harpacticoid assemblage inhabiting the bay was observed in the two subsequent years. Moreover, during the study duration a considerable decrease was observed in the abundance of Ostracoda in Nottinghambukta.

Mangroves develop under environmental conditions and anthropogenic pressures whose impact on benthic meiofauna remains poorly understood. It is unclear how meiofauna communities are structured according to local sedimentary conditions. This study was designed to characterize the community structure of meiofauna and nematodes (dominant taxa) and the associated environmental forcings in intertidal mangrove sediments from Mayotte (Indo-West-Pacific), Martinique and Guadeloupe (Caribbean). Sediment cores were sampled at the end of the dry season at low tide on adult mangrove stands with similar immersion time. In each sediment layer, we analyzed redox potential, pH, porewater salinity, grain size, organic matter, metals, organic contaminants, prokaryotes and meiofauna. Our results show that sediments far from cities and agricultural fields trapped site-specific contaminants due to local water transport processes. Some metals, PAHs or pesticides exceeded toxicity thresholds in most of the studied stations, thus being harmful to benthic fauna. The sedimentary environment acts as a filter selecting specific meiofauna communities at station scale only in the Caribbean. In Mayotte, horizontal homogeneity contrasts with vertical heterogeneity of the sedimentary environment and the meiofauna. Nematode genera showed particular distribution patterns horizontally and vertically, suggesting the presence of sediment patches suitable for a restricted pool of genera on each island. Results in the Caribbean are consistent with nested diversity patterns due to environmental filtering. Conversely, horizontal homogeneity at Mayotte would reflect greater dispersal between stations or more spatially homogeneous anthropogenic pressures. The nematode genera present at depth may not be the most specialized, but the most versatile, capable of thriving in different conditions. Terschellingia and Daptonema showed contrasted responses to environmental forcing, likely due to their versatility, while Desmodora showed uniform responses between study areas, except when toxicity thresholds were exceeded. Our results emphasize that a given genus of nematode may respond differently to sedimentary conditions depending on sites., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)