Free living marine nematodes from the Southern Bight of the North Sea. 3. Species of the Monoposthiidae, Filipjev, 1934

The intraspecific variations of Monoposthia mirabilis Schulz, 1932 are examined. Different morphotypes are present in different habitats. The morphological variation is correlated with an environmental gradient, i.e. the median grain size of the sand fraction. A new species of the Monoposthiidae, Nudora gourbaultae sp. nov., is described; it is characterized by the broadened first and second cuticular annule, the presence of 12 costae, two pre-anal cuticular modifications and the shape of the gubernaculum

The meiofauna distribution in correlation with environmental characteristics in 5 Mekong estuaries, Vietnam

Meiofauna assemblages in 5 estuaries of the Mekong river system (Cua Tieu, Cua Dai, Ba Lai, Co Chien and Dinh An) were sampled for community analysis in March 2009, the dry season. The objectives of this research were to provide the first base line survey of meiofauna assemblages in the 5 Mekong estuaries, and to understand how environmental characteristics affect the densities, diversity and structure of the meiofauna. In each estuary, three to four sampling stations were chosen along the salinity gradient from the river mouth to the fresh water part. Besides the meiofauna also sediment- and water column-related environmental characteristics were identified such as dissolved oxygen, pH, salinity, temperature, median grain size, density of coliform bacteria, nutrient and pigment concentrations. Twenty-three major taxa of meiofauna were recorded over the 19 sampling stations. Nematoda, Copepoda, Turbellaria and Oligochaeta dominated with varying densities, but without any clear correlation with the salinity gradient present along the estuaries. The densities of the meiofauna ranged from 105 to 3678 ind.10 cm-2 on average. Nematodes were always dominant with relative abundances ranging from 40-98% of the total meiofauna. Meiofauna densities were significantly correlated with sediment pigment concentrations but also other factors may play a role. Diversity showed a positive correlation with dissolved oxygen in the overlying water. The observed densities of the intertidal meiofauna in the Mekong delta are high compared to other estuaries worldwide

Discovery of Novocriniidae (Copepoda, Harpacticoida) from cold-water corals in the Porcupine Seabight (NE Atlantic), with description of a new species of <i>Atergopedia</i> Martínez Arbizu & Moura, 1998

The female of Atergopedia longicaudata sp. n. is described from dead cold-water coral fragments collected from the Porcupine Seabight (NE Atlantic). The new species is the fourth representative of the family Novocriniidae (Copepoda, Harpacticoida); it can be distinguished from its congeners by the elongate caudal rami and the ancestral armature on enp-3 of P1. Rediscovery of Atergopedia vetusta Martínez Arbizu & Moura, 1998, originally described from the Arctic Barents Sea, results in corrections to the species description. Archaeotisbe confluenta Kornev & Chertoprud, 2008 is transferred to the genus Atergopedia Martínez Arbizu & Moura, 1998, and Archaeotisbe Kornev & Chertoprud, 2008 is newly treated as a junior synonym of Atergopedia. Diagnoses (as ground patterns) for the two novocriniid genera (Atergopedia and Novocrinia Huys & Iliffe, 1998) are provided, and autapomorphies are indicated

Ecologie van de vrijlevende mariene nematoden van de Voordelta (zuidelijke bocht van de Noordzee)

This study forms part of a global research project, which aims to evaluate the effect of the Delta works on the ecosystem of the Dutch Delta. The Dutch Delta is the sublittoral region along the coast of the south of the Netherlands, from the Belgium border in the south to the Hoek van Holland in the north. Off shore, the area is arbitrary limited by the 10m depth line. From north to south, the Nieuwe Waterweg, the Haringvliet, Lake Grevelingen, the Eastern Scheldt and the Western Scheldt debouch into this part of the Southern Bight of the North Sea. As a result of the tidal currents and the thereon coupled transport of the sediments, a heterogenous pattern of banks and channels has evolved. The hydrodynamic regime and the bottom morphology have changed drastically since the start of the Delta works in the beginning of the sixties. Correlated to the changes of the abiotic environment, alterations of the biotic characteristics are expected. To investigate this, in the first place an inventarisation of the region is required. The present study deals with an important component of the marine benthic ecosystem: the free-living nematodes. Twenty sampling stations were selected, of which 8 are located in the channels, while the others are situated on the banks. Data of the abiotic environment were available for these locations. In total, the stations were sampled three times (Autumn '84, Spring '85 and Autumn '85), with the help of a Van Veen grip or a boxcorer. Apart from the inventarisation, it is tried to gain insight in the relationship between the structure of the nematode communities and the present abiotic environmental gradients. The Dutch Delta Region is characterized by large physical and chemical gradients which might be important for the determination of the structure of the nematode communities. The studied factors can be grouped as follows: -Hydrodvnamics: The highest current velocities (up to 120 cm/s) and fluctuations are measured in the channel of the Western Scheldt. In the mouth of the Eastern Scheldt, near the storm surge barrier, high velocities (up to 91 cm/s) exist as well. On the banks, the current velocities are always low (67 cm/s). -Sediment composition: the sediment mostly consists of well sorted fine sand (0.14- 0.37 mm), with only low percentages of gravel and silt. The finest sediments are found in the north, at the level of and above the Lake Grevelingen. The highest silt fractions (5 to 20 %) are present in the channels, while on the banks the level of this fraction never surmounts 5 %. In the Western Scheldt stations, temporal silt accumulations occur. Due to the fluctuations of the currents, these silt fractions may vary between 1 and 60 %. -Water quality: the highest chlorophyll-a values are found on the shallow banks. Low values are also associated with some of the deeper stations, mainly those situated at the level of the seawards offshoots of the channel of the Eastern Scheldt. The freshwater input in the Delta region only influences the salinity to a low degree. Only at the level of the sluices of the Haringvliet, the percentage of freshwater may be higher than 20 %. The density, diversity, species composition, trophic structure, biomass and production of the nematode communities has been studied. Density always appears to be correlated with the sediment composition. Highest densities are found in the silty and fine sandy stations. In the mouth of the Lake Grevelingen, the density is exceptionally high (almost 12000 N/10 cm²), this in comparison with the other silty and fine sandy regions (as found in the north of the Dutch Delta and in a part of the channel of the Eastern Scheldt; 2000 to 6000 N/10 cm²). Most likely, it is the natural organic enrichment of the lake Grevelingen which causes this spectacular increase. Shallowest stations are characterized by relatively low densities (80 to 300 N/10 cm²). Deeper stations (with high velocities and fluctuations of the currents; e.g. in the mouth o

Ecology and biogeography of free-living nematodes associated with chemosynthetic environments in the deep sea: A review

Background: Here, insight is provided into the present knowledge on free-living nematodes associated with chemosynthetic environments in the deep sea. It was investigated if the same trends of high standing stock, low diversity, and the dominance of a specialized fauna, as observed for macro-invertebrates, are also present in the nematodes in both vents and seeps.Methodology: This review is based on existing literature, in combination with integrated analysis of datasets, obtained through the Census of Marine Life program on Biogeography of Deep-Water Chemosynthetic Ecosystems (ChEss).Findings: Nematodes are often thriving in the sulphidic sediments of deep cold seeps, with standing stock values ocassionaly exceeding largely the numbers at background sites. Vents seem not characterized by elevated densities. Both chemosynthetic driven ecosystems are showing low nematode diversity, and high dominance of single species. Genera richness seems inversely correlated to vent and seep fluid emissions, associated with distinct habitat types. Deep-sea cold seeps and hydrothermal vents are, however, highly dissimilar in terms of community composition and dominant taxa. There is no unique affinity of particular nematode taxa with seeps or vents.Conclusions: It seems that shallow water relatives, rather than typical deep-sea taxa, have successfully colonized the reduced sediments of seeps at large water depth. For vents, the taxonomic similarity with adjacent regular sediments is much higher, supporting rather the importance of local adaptation, than that of long distance distribution. Likely the ephemeral nature of vents, its long distance offshore and the absence of pelagic transport mechanisms, have prevented so far the establishment of a successful and typical vent nematode fauna. Some future perspectives in meiofauna research are provided in order to get a more integrated picture of vent and seep biological processes, including all components of the marine ecosystem