Non-selective Deposit Feeders Research Articles

Biological traits and functional diversity of free-living nematode assemblages along a water-depth gradient in the northwestern of Gulf of Mexico

This study analyzed the biological traits (BTs) and functional diversity (FD) of free-living nematodes in the northwestern of Gulf of Mexico. We collected sediment samples at 27 sites at a depth gradient from 44 to 3466 m. The nematodes were identified at species level and classified in five groups of BTs: feeding type, amphid shape, tail shape, body shape, and body length. We determined the FD based on the combination of BTs through a functional dendrogram, using the total length of the branch as a measure of functional diversity. Salinity, pH, and dissolved oxygen were measured in each site, as well as the sediment composition and percentage of organic carbon (OC). A total of 1673 nematodes were identified, belonging to 35 families, 96 genera, and 153 species. The number of species varied along water depth (1–60 species). The more abundant BTs were the non-selective deposit feeders (49 %), amphid spiral shape (55 %), clavate conical cylindrical tail (52 %), sizes 1000–1500 μm (51 %), and body shape slender (97 %). The most common combination of traits was non-selective deposit feeders, spiral amphid, clavate conical cylindrical tail, slender shape, and sizes < 1500 μm. The changes of BTs with increasing depth were more evident in the feeding types and amphid shape. The FD fluctuated between sites (0.42–0.99) and was significantly correlated with the number of species, suggesting that taxonomic and functional diversity have similar responses to environmental variables. The FD was significantly influenced only by the percentage of sands. Our data provide valuable information that can be used in subsequent studies and benthos monitoring.

Re-discovering macerating Posidonia oceanica bottoms: Characterization of meiofaunal community inhabiting a peculiar Mediterranean habitat

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.

Chronic contamination in the southern Gulf of Mexico coastal zone, as evidenced by meiofauna biological traits

Meiofauna is a good pollution indicator that reflects the ecological status of sediments and their linkages with overlying communities. However, long-term monitoring of this fauna is a developing research activity in most marine ecosystems. This study assessed seasonal spatial and temporal changes in meiofauna composition, abundance, and biological traits in the southern Gulf of Mexico sublittoral zone. We examined two questions: How do the meiofauna attributes vary spatially and seasonally? Which contaminants correlate with the distribution of meiofauna biological traits? We analysed sediment characteristics, metals, hydrocarbons, and meiofauna data collected at shallow coastal sites (<10 m) during eight annual surveys (2005–2020). Organic contamination increased when natural disturbances occurred, mainly in the dry season, decreasing the number of nematode taxa and increasing their abundance. During the eight yearly sampling events, nematodes, harpacticoid copepods, and polychaetes varied according to the sedimentary gradient. Chronic contamination (aromatic compounds, Cr, V, Cd, Cr) covaried with meiofauna biological traits. Our results point out meiofauna taxa (e.g., Anoplostoma, Halalaimus, Monhystera, harpacticoid copepods, saccocirrid polychaetes) as bioindicators of resilient and disturbed sites for terrigenous and transitional sediments, while in carbonate sediments dominated sensitive species. Resilient sites were exposed to the Grijalva-Usumacinta river discharges and the oil industry. Tolerant and opportunistic taxa such as the nematodes Anoplostoma and Xyala were classified as colonisers and non-selective deposit feeders. Conversely, sensitive taxa such as Halalaimus and harpacticoid copepods were semelparous, carnivorous, and persisters.

Meiobenthos and ocean acidification: Effects on meiobenthic communities inhabiting Mediterranean cold shallow CO2-vents

Ocean acidification is causing major changes in marine ecosystems, with varying levels of impact, depending both on the habitat and the studied organisms. Here, we investigated for the first time the meiobenthos and nematode fauna inhabiting the sediments around Castello Aragonese (Ischia, Italy), characterized by variable pH values due to coastal volcanic CO2 venting. In this scenario, nematode functional diversity changed according to different pH levels and grain size: maturity index was higher at most acidic stations and trophic composition spanned from the dominance of predators in the acidic stations, to the high abundance of non-selective deposit feeders and epistrate feeders in the ambient-pH stations. Overall, the present study revealed a relatively high tolerance of meiobenthos and nematodes to lower pH conditions. However, an in-depth analysis of nematode fauna showed differences in their assemblages at different pH levels with few nematode genera rather adapted to the extreme environmental conditions at the acidic stations.

Unveiling the meiobenthic community structure of Prydz Bay, Antarctica during austral summer

Meiobenthos are bottom-dwelling aquatic invertebrates having a size range of 63–500 μm. They play a pivotal role in ecosystem functioning, biogeochemical and trophic nutrient cycling. Due to the presence of Antarctic Circumpolar Current and steep gradient in nutrients and temperature, many taxa of the Southern Ocean (SO) show diverse biodiversity patterns in comparison to other deep sea areas of the world. Over the years, several Indian SO Expeditions have been carried out in the Indian sector of SO (ISSO), but this is a pioneer attempt to unveil the meiobenthic community structure and their functional diversity pattern from Prydz Bay (Indian sector of Southern Ocean), Antarctica. Meiobenthic community structures were investigated in eight different sampling sites along with their vertical profiling from the Prydz Bay during the austral summer 2020. Total meiofaunal abundance ranged from 24 to 521 indv. 10 cm-2, with the highest abundance recorded at station 23 and the lowest at station 9. A total of 9 meiobenthic taxa were found from this eco-region, with the highest percentage being the free-living marine nematodes as metazoan taxa. A total of 86 free-living nematode species were identified, where Sabatieria was the most common genus and represented by eleven species. Several univariate and multivariate analyses deciphered a distinct spatial variation in the meiobenthic community structure. Sediment texture and depth were the most significant environmental variables in shaping nematode assemblages. Biological Trait Analysis was performed using a total of 24 traits in 5 categories to unravel the functional diversity of free-living marine nematodes. The most dominant morphotypes were slender body shape, conical tail shape, dotted cuticle pattern, and non-selective deposit feeders with colonizing abilities of 2 (c–p score 2, in a scale from 1 to 5). Maturity Index (MI) and Index of Trophic Diversity (ITD) were highest in stations 15 and 32, respectively. RLQ approach with fourth-corner analysis was used to decipher the relationship between traits and environmental parameters. The RLQ analysis revealed the positive association of non-selective deposit feeder and slender body-shaped nematodes with higher water depth. The characterization of meiobenthic (especially nematode) communities in the context of taxonomic and functional attributes could help to evaluate the ecological status of ISSO. Further long term monitoring is also needed to get a comprehensive idea about their role in benthic ecosystem functioning in the milieu of global climate change.

Effects of the ridge‐and‐runnel system on macrofaunal spatial distribution on a macrotidal sandy beach in the Brazilian Amazon coast

AbstractRidge‐and‐runnel systems are common morphological features across the intertidal zone of dissipative macrotidal beaches. However, these systems have often been overlooked by macrofaunal zonation studies. The present study investigated the effects of this system on the spatial distribution of the macrofaunal community on an Amazonian macrotidal sandy beach. Samples (macrobenthos and sediments) were collected at seven equidistant levels (50 m apart) from the high tide water mark to the swash zone, in two different areas: (1) with and (2) without ridge‐and‐runnel systems. The results showed a significant increase in macrofaunal abundance and richness in area with runnels, associated with muddier sediment and higher organic content. The macrofauna in the runnels, both in upper‐intertidal and lower‐intertidal zones, had higher density and richness than that in the sandbars. There was no difference between tidal levels in area 2, although we observed an increasing tendency of abundance and richness towards the low tide line. Taxonomic composition and trophic groups also differed between areas, with predominance of species that are typical of sandy‐mud substrate and higher participation of nonselective deposit feeders in area 1. Predatory species typical of sandy substrates prevailed in area 2. These findings add knowledge to sandy beach ecology and indicate the importance of including aspects of habitat complexity in both across‐ and alongshore macrofaunal distribution studies.

Free-living nematode assemblages along a water-depth gradient in the Perdido belt, northwestern Gulf of Mexico

This study investigated nematode assemblages in the Perdido belt, northwestern Gulf of Mexico (GoM) in terms of species composition, distribution, density, and diversity. We examined 27 sediment samples collected at depths of 44-3466 m. The nematodes were identified at the lowest level possible and classified into four trophic groups based on their buccal cavity. Additionally, their sex and stage of life were determined. The sediment composition was determined, as well as the percentage of organic carbon (OC). The density per site fluctuated between 0.02 and 13.30 ind/10 cm2. A total of 1768 nematodes were identified, belonging to 9 orders, 35 families, 96 genera, and 153 species, of which 9 genera and 15 species are new records for the GoM. The families Xyalidae and Comesomatidae were the most diverse genera (9 and 8, respectively). Sabatieria sp. 1 was the most abundant and widely distributed species. The number of species varied at different depths (range 1-60 species) and Pielou evenness (0.7-1). Most of the organisms collected were adult females. The non-selective deposit feeders were the most abundant (49%), followed by epigrowth feeders (20%). Most of the sites consisted of sand (range 10.1-70.2%). The percentage of OC varied at different depths (0.1-1.4%). No significant correlation was found between species richness and depth. The species composition changes with depth, density and most of the trophic groups tend to decrease with increasing depth. The dominant species are more related to the percentage of sands and silts than to clays and OC.

Nematode functional traits and community structure change from river to the terrestrial border in Segara Anakan Mangrove, Indonesia

Abstract. Maharning AR, Ardli ER, Prabowo RE. 2023. Nematode functional traits and community structure change from river to the terrestrial border in Segara Anakan Mangrove, Indonesia. Biodiversitas 24: 2434-2446. We intended to explore the spatial distribution of nematode functional traits and community structure in Segara Anakan Mangrove, Indonesia. Samples were retrieved from 14 stations, extending from the river to the area adjacent to terrestrial forest. We used taxonomic and functional trait identification, covering body shape, length, tail shape, feeding type, and life history as independent traits, and combined traits by collecting traits describing individual nematodes. The principal component analysis suggested that predatory or omnivorous or long-size nematodes mainly inhabited stations adjacent to the terrestrial forest but were unclear for the mid-stations. There were 29 combined traits and 38 genera of nematodes observed. The detrended correspondence analysis revealed that nematode compositional changes from the river to the terrestrial adjacent area were clearer for the combined traits and nematode genera. Seven combined traits and 12 genera inhabited only the particular stations of the study site. The common nematodes were slender, 1-2 mm long, elongated filiform tails, non-selective deposit feeders, and very tolerant to pollutants, which lived in almost all stations (92.86%). The genus relative abundance (&gt;10%) included Anoplostoma, Eubostrichus, and Chromadorina. The results suggest that distance from the river might regulate the habitability of nematodes, in which nematode functional traits play roles.

Variations of Free-Living Marine Nematode’s Taxonomic Structure and Functional Traits in Contrasting Sandy Beach Habitats

In the present study, two temperate sandy beaches, which were located on the coast of different seas with different hydrological states, were selected to investigate the variations and drivers of the taxonomic structure and functional traits of the free-living marine nematode. According to the present study, Xyalidae and Chromadoridae were widely observed in both locations, but the species composition and functional traits were not completely the same. In fine sands, non-selective deposit feeders or colonizers (nematodes with c-p = 2) were far more quantitatively than other functional traits, suggesting a relatively restricted range of functional traits. The increased microhabitat heterogeneity in coarse sands can support species with more diverse functional traits. Chl-a was the most prominent variable that significantly related to nematode species composition and functional traits at XB sites. Nematode data were closely related to temperature or temperature-related environmental factors, such as DO and salinity, at GB sites.

Monitoring the anthropogenic impacts in Admiralty Bay using meiofauna community as indicators (King George Island, Antarctica).

Activities at the Brazilian Antarctic Station (EACF) may cause damage to surrounding environment. Meiofauna was used to evaluate this impact. One area possibly impacted by the stations' presence (CF) and a reference area (BP) were compared. Sediment samples for meiofauna and environmental variables were obtained in two periods, at two sites and depths in each area. Densities were higher at 20-30m and nematodes were the dominant taxa (90%). Nematode densities ranged from 1,278±599 (BP1 50-60m) to 16,021±12,298 ind.10 cm-² (BP2 20-30m). A total of 68 genera were found. Sample richness ranged from 8 to 26 and diversity from 1.4 to 3.6 bits/ind, both being higher at BP 50-60m, where dominance of epistrate feeders was lower. Selective and non-selective deposit feeders were codominant with similar proportions. Maturity index was high and constant between samples. Aponema, Sabatieria, Daptonema, Dichromadora and Halalaimus were dominant, with higher densities at 20-30m. In contrast, Actinonema, Molgolaimus, Oxystomina and Marylynnia were more abundant at 50-60m. Differences in meiofauna community were found mainly between depths, but not between sites or periods, suggesting no anthropogenic impact. Nevertheless, lower Nematoda diversities and maturity index at 50-60m in CF when compared to BP may indicate a possible anthropogenic effect near EACF.

Disentangling the Effect of Seasonal Dynamics on Meiobenthic Community Structure From River Matla of Sundarbans Estuarine System, India

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

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.

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.

FAUNA OF FREELIVING NEMATODES IN THE UKRAINIAN PART OF THE DANUBE RIVER MOUTH AREA IN THE MODERN PERIOD

Problem. The Problem links with variability of modern state environmental condition of the Danube river mouth area and the whole Black sea system as well. Thus the taxonomic diversity and quantitative development of free-living nematodes (the dominant component of meiobenthos) is under the euthrophication press because of directly Danube water input. Among the benthic organisms, only meiobenthos can react very quickly to changes in hydrochemical and hydrological parameters. Due to their small size and short-cycle development, they are the first to respond to deteriorating environmental conditions.The purpose is to identify the species composition and quantitative indicators of free-living nematodes of the meiobenthos in different parts in the Danube mouth area in modern period.Materials and methods. The data of long-term monitoring of meiobenthos in the Ukrainian part of the Danube mouth area located under the direct technogenic influence (dumping and shipping way construction), carried out by the Institute of Marine Biology of the National Academy of Sciences of Ukraine during from November 2004 to November 2019, were used.Main results of the research. The fauna of nematodes is represented by 69 species of 37 genera, 18 families and 6 orders. The orders Monhysterida and Enoplida dominate by the number of species. The increase in the number of species in each of the orders from the river mouth to the open sea was observed. The predominant trophic group is non-selective deposit feeders (1B). The distribution of quantitative indicators of the density of nematodes in different areas varies within significant limits: from 1000 ind.∙m-2 up to 682 500 ind.∙m-2. (average – 119 474 ind.∙m-2). The biomass varied from 1.3 mg∙m-2 to 425.4 mg∙m-2 (average – 57.4 mg∙m-2).Conclusions. The quantity changes of fauna of nematodes in the Ukrainian part of the Danube mouth area depends on the influence of naturally changing environmental conditions, as well as on the technogenic load. Keywords: meiobenthos; nematodes; species diversity; Ukrainian part of the Danube mouth area.

High throughput shotgun sequencing of eRNA reveals taxonomic and derived functional shifts across a benthic productivity gradient.

Benthic macrofauna is regularly used in monitoring programmes, however the vast majority of benthic eukaryotic biodiversity lies mostly in microscopic organisms, such as meiofauna (invertebrates<1mm) and protists, that rapidly responds to environmental change. These communities have traditionally been hard to sample and handle in the laboratory, but DNA sequencing has made such work less time consuming. While DNA sequencing captures both alive and dead organisms, environmental RNA (eRNA) better targets living organisms or organisms of recent origin in the environment. Here, we assessed the biodiversity of three known bioindicator microeukaryote groups (nematodes, foraminifera, and ciliates) in sediment samples collected at seven coastal sites along an organic carbon (OC) gradient. We aimed to investigate if eRNA shotgun sequencing can be used to simultaneously detect differences in (i) biodiversity of multiple microeukaryotic communities; and (ii) functional feeding traits of nematodes. Results showed that biodiversity was lower for nematodes and foraminifera in high OC (6.2%-6.9%), when compared to low OC sediments (1.2%-2.8%). Dissimilarity in community composition increased for all three groups between Low OC and High OC, as well as the classified feeding type of nematode genera (with more nonselective deposit feeders in high OC sediment). High relative abundant genera included nematode Sabatieria and foraminifera Elphidium in high OC, and Cryptocaryon-like ciliates in low OC sediments. Considering that future sequencing technologies are likely to decrease in cost, the use of eRNA shotgun sequencing to assess biodiversity of benthic microeukaryotes could be a powerful tool in recurring monitoring programmes.

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

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

Species and Functional Diversity of Deep-Sea Nematodes in a High Energy Submarine Canyon

Gaoping Submarine Canyon (GPSC) off southwestern Taiwan is a high energy canyon connected to a small mountain river with extremely high sediment load (~10 kt km-2 y-1). Due to heavy seasonal precipitation (>3000 mm y-1) and high tectonic activity in the region, the GPSC is known for active sediment transport processes and associated submarine geohazards (e.g., submarine cable breaks). More importantly, strong internal tides have been recorded in the GPSC to drive head-ward, bottom-intensified currents, which result in sediment erosion and resuspension in response to the tidal cycles. To understand the effects of extreme physical conditions on marine nematodes, we sampled the surface sediments along the thalweg of upper GPSC and adjacent slope (200-1100 m) using a multicorer in the summer and fall of 2015. We found that the nematode species, functional, trophic diversity and maturity dropped significantly in the GPSC as compared with slope communities, but the nematode abundances were not affected by the adverse conditions in the canyon. The non-selective deposit-feeding, fast colonizing nematodes (e.g., Sabatieria, Daptonema, Axonolaimus, and Metadesmolaimus) dominated the canyon seafloor. In contrast, other species of non-selective deposit feeders (Setosabatieria and Elzalia), epigrowth feeders (Craspodema), omnivores/predators (Paramesacanthion), and other species constituted the diverse nematode assemblages on the slope. We found that the strong bottom currents in the GPSC may depress the local nematode diversity by removing the organic-rich, fine-grained sediments; therefore, only the resilient or fast recovering nematode species could survive and prevail. The high species turnover with depth and between the canyon and slope habitats demonstrates that strong environmental filtering processes were the primary mechanism shaping the nematode community assembly off SW Taiwan. Between the canyon and slope, a considerable contribution of nestedness pattern also indicates some degree of local extinction and dispersal limitation in the dynamic GPSC.

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.

Effects of an experimental oil spill on the structure and function of benthic assemblages with different history of exposure to oil perturbation

The present study compared the short-term effects of a diesel oil spill on the strucure and function of nematode and macrobenthic assemblages between tidal flats with different history of exposure to oil perturbation. A manipulative field experiment was conducted, where oil exposed treatments were contrasted with controls, during four successive times, two before and two after the oil spills. During the oil spill the death and the presence of diverse debilitated macrofaunal organisms were observed in the oil treatments. However, 24 h later no significant changes were identified, suggesting that the impacted plots were quickly recolonized. Nematode assemblages showed a decrease in overall density and an increase of r-strategist traits such as non-selective deposit feeders and colonizers at perturbed treatments from one of the historically non-perturbed tidal flats. We discuss the mechanisms responsible by distinctive patterns of response observed between the two benthic components.