Search Results (85)

Gastrotrichs (Phylum Gastrotricha) are widespread and species-rich components of benthic and periphytic communities, where they are thought to contribute substantially to food-web functioning by linking the microbial loop to higher trophic levels through their feeding on detritus, bacteria, microalgae, and fungi, and serve as prey for larger animals. Despite the well-recognized role as primary consumers, their position as potential prey remains largely unresolved, with documented predators so far restricted to carnivorous protists. Here, we report the first documented case of metazoan predation on a freshwater gastrotrich, in which a cyclopoid copepod actively captures and partially consumes a chaetonotid species. The interaction was first detected under minimally disturbed conditions and subsequently replicated in controlled experimental settings. Predation was documented through in vivo video recordings and supported by species-level identification of both predator and prey. These findings expand the currently recognized trophic interactions involving freshwater gastrotrichs and provide new insight into their ecological role within aquatic food webs. Full article

Freshwater ostracods have considerable potential as indicators of environmental conditions, yet their ecology remains poorly documented in many large river floodplains of Southeast Europe. This study examines samples collected from ten aquatic habitats located along the Danube floodplain in Serbia’s Banat and Podunavlje regions. Monthly sampling was conducted over a twelve-month period (July 2023–June 2024), with concurrent measurements of water temperature, pH, dissolved oxygen, electrical conductivity, and turbidity. Ostracods were recorded at seven sites, yielding 19 taxa belonging to 13 genera and four families within all three non-marine superfamilies of Podocopida. Eight recorded taxa represent new additions to the Serbian fauna. Species richness was highest in semi-isolated floodplain habitats. Canonical correspondence analysis (CCA) showed that seasonal environmental variation, especially water temperature, turbidity, and conductivity, strongly structured assemblages. Hierarchical cluster analysis (UPGMA) grouped samples primarily by species composition, with seasonality exerting a strong secondary influence. Seasonal patterns revealed pronounced interspecific differences in temporal persistence and ecological tolerance of recorded species. Findings highlight the Danube floodplain’s role as a dispersal corridor, while also revealing that the river itself acts as a partial barrier, restricting faunal exchange to widespread, tolerant species. The results emphasize the importance of habitat heterogeneity and year-round sampling and support the integration of ostracods into long-term floodplain monitoring programs. Full article

Two new species of free-living marine nematodes were collected in the Yellow Sea, China, and they are described herein as Actinonema sinica sp. nov. and Comesoma zhangi sp. nov. Actinonema sinica sp. nov. is characterized by short cephalic setae; lateral differentiation consisting of a row of longitudinal sclerotized bars and beginning at the level of anterior third of the pharyngeal region; horn-shaped telamons; a curved rod-shaped gubernaculum; and an elongate conical tail with a smooth, pointed tip. Comesoma zhangi sp. nov. is characterized by long, thick cephalic setae, reaching up to 28 µm in length; a cup-shaped buccal cavity lacking a tooth and narrowing posteriorly with small projections; an amphidial fovea with two turns; slender, arcuate spicules 2.6 times the cloacal body diameter in length, lacking a proximal capitulum; a plate-like gubernaculum without apophysis; and the absence of precloacal supplements. Updated keys to the valid species of the genus Actinonema and the genus Comesoma are provided. A comparative morphological table of all currently accepted species of Comesoma is also provided. Full article

Meiofaunal assemblages are crucial components of benthic ecosystems, significantly contributing to organic matter cycling and energy transfer. However, baseline quantitative data from some upwelling systems remain limited. This study characterizes the abundance, vertical distribution, and secondary production of meiofauna at a coastal upwelling station off southern Peru (14°16′ S) for July 2006 (Neutral conditions) and May 2007 (moderate La Niña, LN), using four-replicated sediment cores sectioned into 0–1, 1–2, 2–5, and 5–10 cm layers. While Nematoda (families Desmodoridae, Chromadoridae, Monhysteridae, Oxystominidae, Comesomatidae) dominated the community (>79% in all layers, both years), the total taxonomic richness did not differ substantially between study periods nor across the sediment column for 2006 or for 2007. Total density (0–10 cm) fluctuated between 3916 ± 2202 Ind 10 cm⁻² in 2006 and 4203 ± 2274 Ind 10 cm⁻² in 2007, with non-significant changes. Biomass (µgC 10 cm⁻²) in 2006 ranged from 80 ± 24 in the 5–10 cm section to 455 ± 134 in the 2–5 cm section. The uppermost 0–1 cm layer showed 238 ± 155, while the 1–2 cm section reached 302 ± 69. In 2007, biomass was consistently higher in the surface layers, with maximum values in the 1–2 cm section (500 ± 534), followed by the 0–1 cm section (376 ± 34). Hierarchical clustering produced depth-ordered groups with high within-depth similarity (>80–90%). SIMPER results identified Desmodora, Comesomatidae, and Chromadoridae among the top contributors to within-depth similarity and to the dissimilarity observed between surface and subsurface assemblages. A depth-related gradient of community composition was detected, suggesting vertical habitat heterogeneity modulated by several environmental factors; however, PERMANOVA analysis residuals (96.73%) indicate a high variation not explained by ENSO phase, sediment section, or their interaction, suggesting other unmeasured factors explaining meiofaunal community structure. Meiofauna’s production ranged from 2.836 ± 0.049 gC m⁻² y⁻¹ in 2006 to 3.106 ± 1.566 gC m⁻² y⁻¹ in 2007. These findings expand the limited knowledge on meiofaunal abundance and metabolic demands in this ocean region, fostering future efforts for comparative analyses across latitudes, depth gradients, and oceanographic regimes. Full article

During a survey of the intertidal zone on the eastern coast of Jeju Island, Korea, a new species of free-living marine nematode belonging to the Selachinematidae (Chromadorida) family was discovered and described. Gammanema papillatum sp. nov. is morphologically most similar to G. lunatum and G. agglutinans, both recorded from New Zealand, by sharing a loop-shaped amphid in males, unlike the multispiral amphid typical of most congeners, and the presence of cuticular spines. It differs from G. lunatum in body length (1122–1366 µm vs. 754–1196 µm), a-ratio (21–23 vs. 13–15), shape of the supplementary organs (papilla-shaped vs. cup-shaped), and distance from the posterior-most supplement to the cloacal opening (58–63 µm vs. 18–32 µm). In terms of precloacal supplementary organ morphology, the new species also resembles Gammanema conicauda, as both are the only congeners with papilla-shaped precloacal supplementary organs. However, G. papillatum sp. nov. differs from G. conicauda by the number of supplementary organs (7–8 vs. 22), amphidial shape (loop-shaped vs. unispiral), and the presence of cuticular spines (absent in G. conicauda). Near full-length SSU and D2–D3 region LSU rDNA sequences were obtained for the new species. Molecular analyses revealed the lowest divergence from G. lunatum (SSU: 1.7%; LSU: 19.8%), with greater divergence from other congeners (SSU: 4.0–4.6%; LSU: 30.5–37.1%). This represents the second record of Gammanema from Korean waters and provides new insights into trait combinations that may help define a subgroup within the genus. Full article

Coastal waters are sensitive habitats that support high biodiversity and provide essential ecosystem goods. Changes in sedimentation regimes due to land-use and engineering activities in the coastal zone affect biodiversity and these habitats’ ecological value. This study aims to characterize the meiobenthic communities inhabiting the Zwin tidal lagoon, located on the border between Belgium and the Netherlands, and to evaluate to what extent the sedimentological characteristics and the quantity and composition of organic matter influence the composition and distribution of meiofauna. The meiobenthic community showed traits of a well-established population dominated by nematodes, followed by copepods + nauplii. Notably, meiofauna rapidly colonized the area after its opening to the sea in February 2019 (two years before sampling), showing that even very weak tidal currents were sufficient to suspend and transport these animals to the new environment. Our results suggest that the Zwin lagoon is a productive system with high food quality (i.e., PRT/CHO ≥ 1), predominantly of marine origin. Major structural differences in communities were related to the sedimentary environments at the investigated stations and estimations of the quantity of food. The present findings confirm that sedimentary dynamics and depositional processes, through their influence on sediment properties (e.g., grain size) and organic matter’s quantity and composition, shape meiofaunal communities and their vertical and horizontal distributions. Full article

Twenty-nine sediment samples were collected from Hurghada Bay, a highly impacted coastal area along the Northern Red Sea of Egypt, to evaluate environmental quality and human-induced effects on benthic ostracods. As potential bioindicators, benthic ostracods are highly responsive to environmental disturbances, with pollution leading to reduced abundance, lower diversity, and increased opportunistic taxa. To investigate the link between ostracod assemblages and sediment contamination, we measured the concentrations of eight heavy metals (Cu, Cd, Zn, Pb, As, Cr, Ni, and Mn) using inductively coupled plasma–atomic emission spectrometry (ICP-AES). Multivariate statistical analyses identified three distinct ostracod assemblages distributed across three station groups with varying pollution levels. Group I, associated with offshore stations, exhibited low to moderate heavy metal (HM) concentrations and high ostracod abundance and was dominated by Moosella striata, Hiltermannicythere rubrimaris, Ruggieria danielopoli, Neonesidea schulzi, and Paranesidea fracticorallcola, where the water depth and sand content are the main controlling factors. In contrast, Group II, corresponding to stations with the highest HMs and total organic matter (TOM), was dominated by pollution-tolerant species Jugosocythereis borchersi, Cyprideis torosa, Alocopocythere reticulata, and, to a lesser extent, Ghardaglaia triebeli, with reduced ostracod density and diversity. Group III, characterized by stations influenced by the mud-controlling factor, had the lowest HMs and was dominated by pollution-sensitive species Xestoleberis rhomboidei, Paranesidea fortificata, and Loxocorniculum ghardaquensis. These findings highlight the ecological risks posed by HM pollution and emphasize the urgent need for pollution mitigation strategies and continued monitoring to preserve the Red Sea’s benthic biodiversity. Full article

The cosmopolitan nematode Spirinia parasitifera has long been considered a single, morphologically variable species; however, mounting molecular evidence suggests that it represents a complex of cryptic taxa. In this study, we describe Spirinia koreana sp. nov., a new species collected from intertidal sediments of the Republic of Korea. The new species exhibits a high degree of morphological resemblance to both S. antipodea and S. parasitifera, with overlapping ranges in most morphological traits. While certain measurements, such as relatively shorter body length, more slender form (higher a ratio), moderately long tail length, and shorter spicule length differ from those in some described populations, no single morphological character alone reliably separates S. koreana from all previously reported specimens of S. parasitifera or S. antipodea. Nevertheless, molecular evidence from multiple genetic markers clearly supports its distinction as a separate species. Molecular data from mitochondrial COI, 18S rRNA, and 28S rRNA genes confirm the genetic distinctness of the Korean specimens from S. parasitifera and S. antipodea. Notably, S. koreana sp. nov. differs from other Spirinia species by 2.1–3.4% in 18S and up to 34.4% in 28S sequences, surpassing thresholds previously used to delimit marine nematode species. Our results emphasize the value of integrative taxonomy combining fine-scale morphology and multi-marker molecular data to uncover hidden diversity in meiofaunal nematodes. Full article

Meiofauna are frequently overlooked in biodiversity assessments, resulting in a lack of understanding regarding their current status, the potential impact of anthropogenic activities, and climate change. This study on the intertidal zone of the Small Beach of Ostend marks a new effort to characterize meiofaunal communities along the Belgian coast. Sampling was carried out on five separate occasions throughout the year, with abiotic data collected during each event. Collected specimens were sorted according to their taxonomic group, resulting in a retrieval of 1742 organisms. Among these, Platyhelminthes and Nematoda were most abundant. Through metabarcoding of the 18S ribosomal region, a biodiversity assessment was conducted, yielding a total of 106 Amplicon Sequence Variants (ASVs). After filtering out rare reads, 65 metazoan ASVs were retained: 18 representing Platyhelminthes, 16 Nematoda, 15 Copepoda, 12 Polychaeta, and 4 Acoela. Identification of the ASVs through blasting generated 23 unique species-level identifications. The highest species richness was observed among Proseriata and Nematoda, each comprising six different species. Additionally, four different species of Polychaeta and Copepoda, two species of Acoela, and one species of Rhabdocoela were identified. Compared to findings on similar beaches along the Belgian coast from about 40 years ago, the meiofaunal communities on this beach exhibit an overall low species richness. Finding fewer and other species might be linked to the potential impact of beach nourishments, human trampling, and climate change. However, confirming this hypothesis requires future research. Full article

The patterns of meiofaunal distribution in a submarine canyon and adjacent open-slope habitats at Campos Basin, southwest Atlantic, were investigated. A total of eight stations was sampled, four inside the Canyon Almirante Câmara and four on the adjacent open slope. These stations represented four isobaths (400, 700, 1000, 1300 m) and were sampled during two distinct periods (2008, 2009). At each station, three replicates were obtained and sectioned into layers of 0–2, 2–5 and 5–10 cm. Nematoda was the most abundant group in both habitats, comprising more than 85% of the total meiofauna in both sampling periods. The density and assemblage structure of the meiofauna showed high variability between the 400 m isobath and the other three isobaths in the canyon habitat. These results reinforce the roles of habitat heterogeneity and the availability of food sources as key factors strongly influencing the deep-sea meiofauna in the southwest Atlantic Ocean. Phytopigments were significantly correlated with the two major meiofaunal groups (Nematoda and Copepoda), as well as with total meiofaunal density, only in the canyon habitat. On the adjacent open slope, only copepods showed a significant correlation with sediment characteristics (mean grain size and carbonates), suggesting that distinct environmental factors influence the distribution of meiofauna in the two habitats. Full article

In the current research, we examined the effects of warfarin (W1 = 5 mg/L and W2 = 25 mg/L) and tinzaparin (T1 = 5 mg/L and T2 = 25 mg/L) on meiofauna using microcosms. These microcosms were intentionally contaminated with both anticoagulants for one month. The findings indicated that nematodes and amphipods demonstrated the greatest resistance to the two anticoagulants evaluated. Specifically, the number of amphipods increased after exposure to the treatment that included T2. Following the separate introduction of each drug, amphipods displayed a taxonomic restructuring, with a more significant impact observed from T2 and T2W1. Results were derived from multivariate analyses of a compilation of sensitive amphipod taxa in response to tinzaparin and warfarin. In contrast, different species were identified as positive indicators for tinzaparin. Ultimately, the similarity between the control amphipod replicates and those subjected to mixed anticoagulants (T1W1 and T2W2) suggests that warfarin may have reduced the toxicity of tinzaparin. Additionally, the computational study indicated that warfarin interacts with 4XNN and forms strong molecular interactions with several key residues, which contribute to the toxicokinetic characteristics observed in the empirical findings. Full article

The diversity of the species-rich copepod family Laophontidae T. Scott, 1905, is rarely investigated in China. Based on the recent collections from the coasts of the Yellow Sea in Shandong, two species of the genus Quinquelaophonte Wells, Hicks and Coull, 1982 were first reported from China, with one identified as new. The new species, Quinquelaophonte xinzhengi sp. nov., differs from other congeners by the following characteristics: female caudal ramus about 3.2 times as long as maximum width; P1 enp-2 bearing one claw and one minute seta; female P3 exp-3 with two inner setae, male P3 exp-3 with one inner seta; P4 exp-3 with one inner seta; and female P5 exopod bearing six setae. The COI genetic divergences between the new species and three closely related congeneric species all exceed 20% (21.5–22.3%), supporting their separate species status. Our samples of Q. enormis Kim, Nam and Lee, 2020, which are first found in China, show subtle differences with the original description of the type specimens from Korea on basis of maxilliped and P2 enp-1 with cuticular bulge subapically, female P3 and P4 without conspicuous morphological variation. This is also the first report of Quinquelaophonte from the China Seas. Full article

Tyre wear particles are a significant source of primary microplastics in the natural environment with the potential to accumulate in aquatic sediments, yet our understanding of the ecological impact of these particles is limited. Using mesocosms of estuarine sediment containing a model macrofauna community (Scrobicularia plana and Hediste diversicolor), meiofauna, and microphytobenthos, we investigated the impact of exposure to sedimentary tyre particles (0.2, 1, and 5% kg sediment(dw)⁻¹) upon meiofauna community structure, primary production, secondary production, and nutrient fluxes. Under the conditions (13 °C) and timescale (31 days) investigated, exposure to sedimentary tyre particles did not lead to any significant differences in nutrients for primary productivity, with limited impact on meiofaunal secondary productivity. An increase in Tanaidacea was observed in 1% and 5% tyre particle treatments, putatively due to reduced macrofaunal predation. Previous studies have highlighted the ecotoxicity of tyre wear particles. The limited impacts on meiofauna may be due to our experimental particles being too large for meiofauna to ingest or the timescale of the experiment being too short to witness changes at the community scale. Impacts from tyre particle leachates were likely limited due to dilution in the partial recirculation system. Leachate dilution will occur naturally in marine systems and should be a consideration in the design of future studies. Full article

Gastrotrichs (hairy bellies) are microscopic, acoelomate worms that live in freshwater and marine environments and represent one of the significant components of the meiobenthic communities. There are over 520 marine species, and several of them are also found in the Mediterranean Sea. However, data on the gastrotrich fauna from Tunisia is negligible, with nearly zero annotated records. We have initiated a series of investigations along the Tunisian shores to address this gap. Herein, we report data from four collecting sites on the northern Tunisian coastline. Sandy samples from 2 m water depth yielded 21 species, 11 in the order Macrodasyida and 10 in Chaetonotida. One chaetonotidan new to science is formally described, while morphometric data and photomicrographs are provided for all the others. Incidentally, we report on the longest gastrotrich ever found. Information about the microhabitat’s characteristics, including the water’s salinity and temperature and granulometric parameters of the sediment, are also reported. Finally, we provide information on Tunisian species previously discovered by our team and involved in phylogenetic studies for which morphological data and details about their findings have never been published. We explicitly address and correct the errors in GenBank concerning the attribution of gene sequences for these species. Full article

During a survey of marine biodiversity in the deep sea off northeastern Guam, two marine desmoscolecid nematodes belonging to the subgenus Tricoma were discovered. Tricoma (Tricoma) disparseta sp. nov. was described based on specimens collected from sponge and starfish habitats on a seamount at depths ranging from 1300 to 1500 m. Tricoma (Tricoma) disparseta sp. nov. is distinguished by having 59 to 62 main rings, 9 to 10 subdorsal setae, and 14 to 18 subventral setae on each side. Notable features include the differentiation in length and insertion between the subdorsal and subventral setae, as well as the amphid extending to the second or third main ring. Additionally, the spicules have a relatively small capitulum at the proximal end, while the gubernaculum is bent into a hooked shape. The specimen of T. (T.) longirostris observed in this study closely resembles previously reported specimens, characterized by 78 main rings, a long and narrow head shape, eight to nine subdorsal setae, 14 to 15 subventral setae, and a gubernaculum with a knobbed apophysis. Two Tricoma species from the Northwest Pacific Ocean are described in detail, and pictorial keys and comparative tables for species identification are provided for groups with 50 to 64 main rings. Full article