Do the morphological and functional traits of free-living marine nematodes mirror taxonomical diversity?

Are anticoagulant drugs ecotoxic for meiobenthic nematodes from Saudi Arabia? First data on taxon/functional diversity and computational evidences

Community-level effects of anticoagulants have little been studied in the laboratory. In the current study, the different effects of Warfarin and Tinzaparin, individually or in combination, on meiofauna were investigated for the first time using two concentrations (5 and 25 mg·l-1) of Warfarin (W1 and W2) and Tinzaparin (T1 and T2) for 30 days. The results obtained highlighted the highest tolerance of nematodes and amphipods toward the two anticoagulants tested. Moreover, nematode abundance and taxonomic diversity decreased directly after exposure to T2 and T2W1 because of the high mortality of diatom feeders and their replacement by non-selective deposit feeders (case of Tinzaparin) or omnivores-carnivores (case of Warfarin). The relative taxon/functional similarity between controls and mixtures T1W1 and T2W2 recommends that the toxicity of Tinzaparin can be attenuated by Warfarin. Finally, the computational study of Warfarin supports its potential ecotoxicity since it satisfactorily bound and interacted with GLD-3 and SDP macromolecules.

Microbiome predators in changing soils

Microbiome predators shape the soil microbiome and thereby soil functions. However, this knowledge has been obtained from small-scale observations in fundamental rather than applied settings and has focused on a few species under ambient conditions. Therefore, there are several unaddressed questions on soil microbiome predators: (1) What is the role of microbiome predators in soil functioning? (2) How does global change affect microbiome predators and their functions? (3) How can microbiome predators be applied in agriculture? We show that there is sufficient evidence for the vital role of microbiome predators in soils and stress that global changes impact their functions, something that urgently needs to be addressed to better understand soil functioning as a whole. We are convinced that there is a potential for the application of microbiome predators in agricultural settings, as they may help to sustainably increase plant growth. Therefore, we plea for more applied research on microbiome predators.

The multifaceted effects of fluoranthene and polystyrene on the taxonomic composition and associated functional traits of marine meiofauna, by using single and mixture applications

The current experiment measured the multifaceted effects of polystyrene and fluoranthene, acting alone or in a mixture on marine meiofauna, but with a special focus on nematodes' morphological and functional traits. The results showed changes in the abundances for all tested concentrations of both compounds. The nematode communities exposed to the highest concentrations of fluoranthene (30 ng.g-1 Dry Weight (DW)) and polystyrene (100 mg.kg-1 DW) alone or in a mixture, were significantly less diverse compared to control and were associated with significant changes in the percentage of taxonomic composition and feeding-guilds. The most sensitive taxa to fluoranthene comprised epistratum feeders, whereas the nematodes mostly affected by polystyrene were omnivores-carnivores. A new functional tool, the Index of Sensitivity (IOS), proved to be reliable in depicting the changes that occurred in the taxonomic and functional features of the nematofauna.

A functional perspective of nematode assemblages as proxy of quality in tropical estuarine tidal flats

Functional aspects of biological communities influence ecosystem processes and it is urgent to understand how human disturbances affect functional diversity and ecosystem functions and services. Our purpose was to address the use of different functional metrics of nematode assemblages to evaluate the ecological status of tropical estuaries subjected to different human activities, aiming to advance and improve the knowledge about the usefulness of functional attributes as indicators of environmental quality. Three approaches were compared: functional diversity indexes, single trait, and multi traits using the Biological Traits Analysis. The RLQ + fourth-corner combined method was used to identify relationships among functional traits, inorganic nutrients, and metals concentrations. Lower values of FDiv, FSpe, and FOri indicate a convergence of functions, characterizing impacted conditions. A dominant set of traits was related to disturbance, mainly inorganic nutrient enrichment. All the approaches allowed for the detection of disturbed conditions, however, multi traits was the most sensitive one.

The response of meiobenthinc sediment-dwelling nematodes to pyrene: Results from open microcosms, toxicokinetics and in silico molecular interactions

An experiment conducted with 'open microcosm' made by connected sedimentary compartments with different qualities was for 30 days to evaluate the migratory behaviour of nematodes as induced by exposure to pyrene. The nematofauna was collected along with sediment from a reference site in Bizerte lagoon. Following one week acclimatization period, the populated sediments were topped with azoic sediments, with a pyrene concentration of 150 μg kg^-1. The concentration of pyrene from sediments was measured on a weekly basis. A stable status of nematode assemblages was reached between the upper and lower compartments in each microcosm, whatever the treatment type. An upward exploratory phase was observed during the first two weeks within the assemblages, possibly induced by the repellent chemodetection of pyrene. This observation was confirmed by the toxicokinetic properties and molecular interactions of pyrene with the germ-line development Protein 3 and sex-determining protein of Caenorhabditis elegans as nematode model.

The exposure to polyvinyl chloride microplastics and chrysene induces multiple changes in the structure and functionality of marine meiobenthic communities

The effects of microplastics and sorbed polycyclic aromatic hydrocarbons at community levels were rarely assessed in laboratory experiments, despite their obvious advantage in reflecting better the natural conditions compared to traditionally single species-focused toxicological experiments. In the current study, the multifaceted effects of polyvinyl chloride and chrysene, acting alone or combined, on general marine meiobenthos, but with a special focus on free-living marine nematode communities were tested in a laboratory experiment carried in microcosms. The meiobenthos was exposed to two polyvinyl chloride (5 and 10 mg.kg^-1 Dry Weight 'DW') and chrysene (37.5 and 75 ng.g^-1 DW) concentrations, respectively, as well as to a mixture of both compounds, for 30 days. The results highlighted a significant decrease in the abundance of all meiobenthic generic groups, including nematodes, directly with increasing dosages of these compounds when added alone. The addition of chrysene adheres to microplastics, making the sediment matrix glueyer, hence inducing greater mortality among generic meiobenthic groups. Moreover, the nematofauna went through a strong restructuring phase following the exposure to both compounds when added alone, leading to the disappearance of sensitive nematodes and their replacement with tolerant taxa. However, the similarity in nematofauna composition between control and polyvinyl chloride and chrysene mixtures suggests that the toxicity of the latter could be attenuated by its physical bonding to the former pollutant. Other changes in the functional traits within the nematode communities were a decline in the fertility of females and an increase of the pharyngeal pumping power following exposure to both pollutants for the dominant species. The latter results were also supported by additional toxicokinetics analyses and in silico modeling.

Taxonomic and functional nematode diversity in Maldivian coral degradation zones: patterns across reef typologies and depths

The intensification of dredging and infilling activities in lagoons and on coral reefs are common practices in the Maldivian archipelago, and these activities alter the biodiversity of the bioconstructors and the functioning of the ecosystem. The alteration of environmental factors can also affect inconspicuous fauna, such as free-living nematodes. The implications of a reduction in biodiversity may transcend decreased taxonomic diversity, resulting in changes in functional diversity and redundancy; however, how the environmental conditions and human pressure affects the functionality of nematodes in Maldivian coral degradation zones (CDZs) remain poorly understood. In this paper, we examined changes in the taxonomic and functional diversity and the functional redundancy in nematode communities regarding the geographic location (atolls with various levels of human pressure), the exposure and topography of the reef (lagoon and ocean), the slope of the reef, and the depth. The functional diversity and redundancy were evaluated by considering two main biological traits of nematodes: i) the trophic strategy, and ii) the life strategy. The extremely high number of nematode genera observed in the Maldives is supported by the high complexity of the carbonate sediments. The reef exposure and depth were the most relevant environmental factors that influenced the taxonomic and functional diversity. The functional diversity, according to the trophic strategies, mirrored the taxonomic diversity because the adaptive plasticity of nematode buccal cavity structures is closely associated with the high biodiversity of the phylum. The high abundance of k-strategists in ocean reefs may indicate a higher ecological quality when compared to lagoon reefs; however, the absence of significant differences in life strategy functional diversity and functional redundancy indicates that a recovery process is underway. Analyses of nematode communities should be combined with standard investigations of reef bioconstructors during monitoring activities to assess the vulnerability of CDZ systems to future disturbances and facilitate the adoption of the most appropriate preventative actions.

Simple Is the Best: An Alternative Method for the Analysis of Free-Living Nematode Assemblage Structure

An alternative approach to notice changes of the nematode community structure was evaluated in five study cases in the Mediterranean Sea. In detail, we suggested a combination of morpho-functional traits (i.e., amphid, cuticle, buccal cavity, and tail shape) as an alternative to the taxonomic identification of nematodes. The results clearly demonstrated that the matrixes made using the trait code numbers perfectly mirror the changes of the nematode community structure at the genus level. The combination of the morpho-functional traits more frequently observed in areas under human pressure were ascribable to genera belonging to Xyalidae, Linhomoeidae and Chromadoridae families. This approach might greatly speed the analyses of nematode fauna in biomonitoring programs and might also be adopted for other meiobenthic organisms that may be categorized in functional groups opening new perspectives in the ecological assessment of meiofauna.

Effects of benzo(a)pyrene on meiobenthic assemblage and biochemical biomarkers in an Oncholaimus campylocercoides (Nematoda) microcosm

A microcosm experiment was carried out to determine how benzo(a)pyrene (BaP) may affect marine meiofauna community, with a main emphasis on nematode structure and functional traits. Three increasing concentrations of BaP (i.e. 100, 200 and 300 ng/l, respectively) were used for 30 days. The results revealed a gradual decrease in the abundance of all meiobenthic groups (i.e. nematodes, copepods, amphipods, polychaetes and oligochaetes), except for isopods. Starting at concentrations of 200 and 300 ng/l BaP, respectively, significant changes were observed at community level. At taxonomic level, the nematode communities were dominated at the start of the experiment and also after being exposed or not to BaP by Odontophora villoti, explicable through its high ecologic ubiquity and the presence of well-developed chemosensory organs (i.e. amphids), which potentially increased the avoidance reaction following exposure to this hydrocarbon. Moreover, changes in the activity of several biochemical biomarkers (i.e. catalase 'CAT', gluthatione S-transferase 'GST', and ethoxyresorufin-O-deethylase 'EROD') were observed in the nematode species Oncholaimus campylocercoides, paralleled by significant decreases in CAT activity for non-gravid females compared to controls at concentrations of 25 ng/l BaP and associated with significant increase in GST and EROD activities for both types of individuals.

Diuron environmental levels effects on marine nematodes: Assessment of ecological indices, taxonomic diversity, and functional traits

Coastal marine systems are the most sensitive zones to emerging pollutants. The present study aims to investigate the effect of Diuron on the meiofaunal assemblages, collected from the Bizerte channel (Tunisia). Microcosm experiments were set up using four increasing Diuron concentrations [D1 (10 ng g^-1 dry weight (DW)), D2 (50 ng g^-1 DW), D3 (250 ng g^-1 DW) and (1250 ng g^-1 DW)] compared to non-contaminated sediments (controls) and all plots were incubated for 30 days. Our results show that Diuron-supplemented sediments provoked the significant decrease of meiofaunal abundance as well as a change in nematodes' diversity and structure composition. All univariate indices, as well as the cumulative k-dominance, were lower in the Diuron than the control plot. Additionally, the ordination of treatments according to the two-dimensional nMDS plots analysis showed a clear structural separation of the Diuron treated replicates from the controls based on the functional groups lists. These current data emphasize the utility of the use of biological traits in the detection of disturbances in the aquatic biotope.

Toxicity of synthetic Endocrine Disrupting Compounds on meiofauna: Estradiol benzoate as a case study

An experimental study was carried out to determine the effects of the enrichment of sediments by endocrine perturbators on free-living nematodes from the Ghar El Melh lagoon, Tunisia. For 30 days, four concentrations of Estradiol Benzoate (hereafter EB) (0.43, 4.3, 8.6 and 12.9 ng l^-1). The average nematode abundances showed a significant increase after the introduction of EB in their close environment. In contrast, the taxonomic examination has shown a decrease in species diversity of nematodes. The ordination of treatments according to the nMDS showed a clear structural separation of the enriched replicates with EB from controls based on species lists, in particular for concentrations EB3 and EB4. Indeed, under such conditions, the nematofauna exhibited a more remarkable presence of a new record for Science Theristus n. sp. and a decrease in relative abundances of Paracomesoma dubium. On feeding level, a predominance of non-selective deposit-feeders and a decline in proportions of epistrate feeders and carnivorous omnivores was observed with increasing concentrations of EB. Furthermore, in treated replicates with EB, females discernibly showed an increase compared to controls. Overall, EB affect significantly features of meiobenthic nematodes starting from the concentration of 4.3 ng l^-1.

Toxicity of hydroxychloroquine, a potential treatment for COVID-19, on free-living marine nematodes

On March 2020, hydroxychloroquine (HCQ) was recommended as a treatment for COVID-19 high risk patients. Following the massive and widespread use of HCQ worldwide, a discernible high quantity is anticipated to end-up through the sewage systems in marine coastal areas. A closed microcosm study was undertaken herein for 30 days where meiobenthic nematodes were exposed to a range of HCQ concentrations (3.162, 31.62 and 63.24 μg.ml^-1). After one month of exposure in HCQ, the total abundances and Shannon-Wiener index of the assemblages decreased, whereas the individual mass and the Trophic Diversity Index increased at the highest concentrations. Overall, a numerical negative impact was observed for the epistrate feeders and non-selective deposit feeders, however, this benefited to the omnivores-carnivores, and particularly to the Oncholaimids. Such responses of the nematodes 2B and the corresponding taxa are bioindicative of current- or post-COVID-19 crisis risks in relation with the bioaccumulation of HCQ in seafood.

Using meiobenthic taxa, nematofauna biological traits, and bacterial abundance to assess the effects of the polybrominated diphenyl ethers compound: Case study of tetrabromo diphenyl ether BDE-47

Trophic web structuring in aquatic sediments is dependent on the biological interactions between metazoans and microbial communities. The presence of pollutants in these biotas can therefore impact the meiofauna structure via the modification of the microbial communities. The current study examined in a laboratory bioassay the response of meiobenthic communities, particularly marine nematode taxa from the Bizerte Lagoon to the effect of the most detected polybrominated diphenyl ether in this aquatic environment, BDE-47. Four doses [D1 (2.5 ppb Dry weight (DW)), D2 (25 ppb DW), D3 (50 ppb DW), and D4 (100 ppb DW)] were gradually applied and sediment microcosms were incubated for 30 days in the presence or absence of meiofauna. Our results show that BDE-47-enriched sediments decreased the meiofaunal taxa and bacterial abundance. A lower taxonomic diversity of the nematodes' general structure was observed with all doses used. The numerical analysis of the two dimensional (2D) non-metric multidimensional scaling (nMDS) plots and the evolution of the relative abundances of each functional group of nematode genus assemblages revealed that the abundance of all biological traits was modified. Nevertheless, only three of the functional traits, adult length, feeding group, and amphid shape, showed a clear difference between the control and the treated microcosms. The similarity percentage analysis (SIMPER) revealed that the average dissimilarity between nematode genera communities and biological traits increased with BDE-47-enriched sediments. The nMDS second-stage ordination of inter-matrix rank correlations for matrices including genera and biological traits showed that the amphid shape was the functional trait closest to the generic distribution. Finally, the Principal Component Analysis (PCA) for the nematode biological traits and bacteria indicated a positive correlation of these microbes with the functional groups [1A, Cr, and ef], and a negative correlation only with the "cla"-type tail shape.

Do presence of gray shrimp Crangon crangon larvae influence meiobenthic features? Assessment with a focus on traits of nematodes

In this study, a microcosm experiment was conducted for 30 days to assess the impact of the presence of juvenile gray shrimp Crangon crangon on meiofauna. The results suggested that juvenile shrimp had a significant negative impact on the abundance of nematodes and copepods, but no effect on polychaetes. Moreover, nematodes showed a significant decline in individual weight. The collected nematodes were taxonomically identified and assigned to five functional traits: shapes of the tail and amphid, life history, feeding types, and adult length. The nematode traits were affected by the number of shrimp introduced, and descriptors followed normal or inversed bell-shaped curves. When no shrimp were present, the nematofauna had a higher species richness compared with treatments of 4, 8, and 12 shrimp. Bell-shaped curve patterns were common in relation to the two phases of feeding for C. crangon. During the first phase, C. crangon consumed the nematode species Oncholaimus campylocercoides; thereafter, shrimp fed mostly on the nematode Anticoma eberthi and copepods.

Nematode traits after separate and simultaneous exposure to Polycyclic Aromatic Hydrocarbons (anthracene, pyrene and benzo[a]pyrene) in closed and open microcosms

The majority of experimental studies carried out to date, regarding the effects of pollutants on meiofauna have been conducted by means of closed systems, and rarely using open ones. The current work explored the impact of three Polycyclic Aromatic Hydrocarbons (PAHs), anthracene, pyrene and benzo[a]pyrene, applied alone or combined, on meiobenthic nematodes using both systems. The results revealed that single PAHs impacted the nematofauna similarly in closed or open systems with a higher toxicity observed for benzo[a]pyrene. However, the closed microcosms contaminated with PAHs became organically enriched, resulting in more non-selective deposit feeders and omnivores-carnivores. Taxonomic and functional effects related to combinations of PAHs were close to those of individual treatments in closed systems, however, for open ones, the outcomes were different. The caudal morphology influenced the response of taxa during their avoidance/endurance of hydrocarbons in open systems where the effects of PAHs mixtures appeared not only additive but also synergetic. Based on the results of the study, the use of open systems is preferred to closed ones as the research outcomes were more accurate and representing better conditions prevailing in nature.

Restructuring of a meiobenthic assemblage after sediment contamination with an antibacterial compound: Case study of ciprofloxacin

A microcosm experiment was conducted to evaluate the impacts of the fluoroquinolone antibiotic ciprofloxacin on meiobenthic taxa abundance, nematode genus structure, and functional trait parameters. Sediment samples were experimentally enriched with four different doses of ciprofloxacin [D1 (50 ppm Dry weight 'DW'), D2 (100 ppm DW), D3 (200 ppm DW), and D4 (500 ppm DW)] and were then compared with non-enriched sediments (controls). After one month of exposure, the data showed that ciprofloxacin had altered the meiofaunal taxa abundance. A change in the structure of nematofaunal genera was observed, particularly with the highest dose (D4), which was characterized by the lowest taxonomic diversity. The SIMPER analysis revealed that the average dissimilarity between nematode communities increased with increasing doses of ciprofloxacin. Two dimensional (2D) non-metric multidimensional scaling (nMDS) plots and relative abundances of functional groups of nematode genus assemblages revealed that all functional trait abundances were affected, particularly with the highest dose. However, only the amphid shape and feeding group functions showed a clear distribution separation between the control and ciprofloxacin treatments. The nMDS second-stage ordination of inter-matrix rank correlations for matrices including genus and functional traits showed that the tail shape was the closest functional trait to the generic distribution. Thus, only the curves of cumulative dominance related to the tail shape mirrored discernibly the sedimentary concentrations in ciprofloxacin.

The individual and combined effects of cadmium, polyvinyl chloride (PVC) microplastics and their polyalkylamines modified forms on meiobenthic features in a microcosm

A microcosm experiment was carried out to study the ecotoxicity and interactions between heavy metals and polyvinyl chloride microplastics. Fifteen treatments were tested and results were examined after one month. In details, this work aims to study the ecotoxicological effects of cadmium (10 and 20 mg kg^-1 Dry Weight DW), polyvinyl chloride (PVC) and its modified forms; PVC-DETA (PD) and PVC-TETA (PT) (20 and 40 mg kg^-1 DW), separately and in mixtures, on meiofauna from Bizerte lagoon (NE Tunisia) with focus on nematode features. The results obtained showed that individual treatments were toxic for meiofauna and particularly for free-living nematodes. No clear trends characterized the numerical responses but significant reductions were observed for diversity indices. Moreover, the binary combinations of contaminants have a lesser toxic effect compared to their individual effects. This effect could be related to the high-capacity chelating ability of PVC and its polymers against cadmium.

Ecotoxic response of nematodes to ivermectin, a potential anti-COVID-19 drug treatment

At the end of March 2020, ivermectin was confirmed as a drug for COVID-19 treatment. A significant amount of ivermectin could deposit into sediments of the semi-closed Mediterranean Sea, where three European COVID-19 epicenters are located: Italy, Spain, and France. Meiobenthic nematodes were exposed to three ivermectin doses (1.8 ng.g^-1, 9 ng.g^-1, and 18 ng.g^-1) for 10 days. Ivermectin caused a great reduction in abundance. However, the diversity indices decreased only at high doses. Ivermectin disadvantaged the 1B-Cr-Id functional type (non-selective deposit feeders and nematodes with circular or indistinct amphids) and benefited the 2A-REL-Sp type (epistrate feeders and nematodes with rounded or elongated loop amphids). Thus, Trophic Diversity and Amphideal Diversity index values increased with sedimentary ivermectin enrichment. Large amphideal foveas were more efficient for 2A-REL-Sp nematodes to avoid ivermectin. The responses of the functional type 2A-REL-Sp and corresponding taxa predict post-COVID-19 environmental concerns and the bioaccumulation of ivermectin in seafoods.

Toxicity of a chromium-enriched superfood, Spirulina platensis, assessed by taxonomic and morpho-functional diversity of marine meiofauna

A laboratory bioassay was conducted to investigate the ecotoxicity of a chromium-enriched superfood, Spirulina platensis, on the meiofauna collected from the Ghar El Melh lagoon, Tunisia. After 1 month of exposure, the abundances of meiobenthic taxa and the taxonomic and morpho-functional diversity of nematodes showed significant differences between the Spirulina and Spirulina + chromium groups. The nematodes were more tolerant of all types of stressors compared to harpacticoids, polychaetes, and oligochaetes, and the lowest taxonomic and morpho-functional diversity of nematodes was observed in the highest sedimentary concentration of S. platensis (50% DW). The mixed treatments may have been richer in micro-habitats and subject to low selective pressure, thereby hosting nematodes with a wide range of adaptations. The responses of the nematode species differed depending on their functional traits. Spirulina enriched with chromium induced two responses for the same feeding group: high toxicity for Daptonema fallax and low toxicity for two Theristus species (T. flevensis and T. modicus). The ecotoxicity of the Spirulina/chromium mixtures were lower than that of Spirulina alone, suggesting mutual neutralization between these two elements. The association between functional traits and taxonomic diversity showed that the effects of the mixtures were not additive and that one of the stressors camouflaged the effect of the other. Our findings should encourage the commercialization of chromium-enriched S. platensis owing to its lower ecotoxicity than Spirulina alone.

The Influential Role of the Habitat on the Diversity Patterns of Free-Living Aquatic Nematode Assemblages in the Cuban Archipelago

Free living nematodes are the most abundant and diverse metazoans in aquatic sediments. We used a framework of habitat types to reveal quantitative patterns in species richness (SR), β-diversity, and biological traits (BT). Meiofauna was quantitatively collected from 60 sites within nine habitat types and 24,736 nematodes were identified to species level. We reported a regional richness of 410 ± 12 species for the Cuban archipelago; however, caves and deep waters need to be sampled more intensively. Relationships between SR and abundance supported the dynamic equilibrium model with habitats ordered across gradients of resource availability and physical disturbance. Seagrass meadows were the most specious and freshwater/anchihaline caves the least diverse habitats. Differences in β-diversity likely were due to habitat heterogeneity and limitations for dispersal. The assemblage composition was unique in some habitats likely reflecting the effects of habitat filtering. However, coastal habitats shared many species reflecting high connectivity and dispersal capability of nematodes due to hydrodynamics. The BTs “life strategy”, “trophic group”, and “tail shape” reflected ecological adaptations; but “amphidial fovea” and “cuticle”, likely reflected phylogenetic signatures from families/genera living in different habitats. Habitat type played an influential role in the diversity patterns of aquatic nematodes from taxonomic and functional points of view.

Salinity drives meiofaunal community structure dynamics across the Baltic ecosystem

Coastal benthic biodiversity is under increased pressure from climate change, eutrophication, hypoxia, and changes in salinity due to increase in river runoff. The Baltic Sea is a large brackish system characterized by steep environmental gradients that experiences all of the mentioned stressors. As such it provides an ideal model system for studying the impact of on‐going and future climate change on biodiversity and function of benthic ecosystems. Meiofauna (animals < 1 mm) are abundant in sediment and are still largely unexplored even though they are known to regulate organic matter degradation and nutrient cycling. In this study, benthic meiofaunal community structure was analysed along a salinity gradient in the Baltic Sea proper using high‐throughput sequencing. Our results demonstrate that areas with higher salinity have a higher biodiversity, and salinity is probably the main driver influencing meiofauna diversity and community composition. Furthermore, in the more diverse and saline environments a larger amount of nematode genera classified as predators prevailed, and meiofauna‐macrofauna associations were more prominent. These findings show that in the Baltic Sea, a decrease in salinity resulting from accelerated climate change will probably lead to decreased benthic biodiversity, and cause profound changes in benthic communities, with potential consequences for ecosystem stability, functions and services.

Effects of Yellow Sea Cold Water Mass on marine nematodes based on biological trait analysis

The Yellow Sea Cold Water Mass (YSCWM) is a seasonal hydrological phenomenon with significant effects on benthic animals. Based on a range of biological traits, including feeding type, tail shape, adult body length, body shape and life history (c-p value), the biological trait analysis (BTA) of marine nematodes in the southern Yellow Sea was studied in June 2003 (summer) and January 2004 (winter) in order to reveal the effects of YSCWM on benthic animals. In terms of biological traits composition of marine nematode assemblages, results of ANOSIM showed that there were no significant differences among sites inside the YSCMW area. However, for spatial distribution, marine nematode assemblages showed significant differences between sites inside and outside of the YSCWM area in terms of body shape, as there was higher percentage of nematodes with slender body shape while lower percentage with stout and long thin body shape at the sites inside the YSCWM area. Results of BIOENV analysis showed that water depth and sediment silt-clay percentage were the most important factors contributed to the differences of biological traits of marine nematode assemblages in summer, while sediment phaeophorbide content best explained the differences of marine nematode assemblages in winter. The existence of the YSCWM may provide a stable environment for marine nematode assemblages, keeping them in a continuous state during the seasonal changes. The higher percentage of nematodes with slender body may be the response to the YSCWM.