Meiofauna of silty sediments in the coastal area of the North Adriatic,with special reference to sampling methods

At five coastal silty sediment stations ranging in depth from 8 to 30 m, the abundance and composition of meiofauna were investigated. Three methods of sampling were used, i.e. Pfleger corer, Van Veen grab and SCUBA divers. Four samples per station were taken. The mean density of total meiofauna was 660 ± 109 ind. 10 cm². The main meiofauna group was Nematoda, the second abundant was Copepoda, and third was Kinorhyncha. Statistical tests showed significant differences in meiofaunal abundance between corer and grab samples, and between corer and divers samples.Differences in meiofauna abundance between stations were found.     

Intertidal zone of Svalbard

The meiobenthos was sampled at 119 localities along 1,500 km of Svalbard shores in the summers 1988–1993. The principal taxa were determined from 5-cm-long sediment cores collected during low tide on soft sediment shores. The density ranged from 0 to > 10,000 ind/10 cm². Nematoda was the most common and abundant taxon. Nematoda and Turbellaria, along with Oligochaeta and Harpacticoida, were typical and the most frequent set of taxa. The occurrence of meiofaunal taxa was weakly correlated with geographical area; the local habitat characteristics were decisive. The most abundant meiobenthos, with mean abundance >900 ind/10 cm² and the biomass about 0.34 g dry wt per 1 m2, was found on the western coast of South Spitsbergen.     

The effect of oxidized material on the vertical distribution of freshwater benthic fauna

The vertical distribution of representatives of the benthic groups: Ostracoda, Nematoda, Oligochaeta, Harpacticoida, Cyclopoida, and Chironomidae was determined. All groups had their highest numbers and biomass in the first 2 cm. The downward extent of oxidized material affected the distribution by dispersing the biomass more as seen by the deeper occurrence of groups when the oxidized material increased. Both the nematodes and oligochaetes were found to inhabit the first reduced layer when the oxidized material was less than normal.     

Benthic meiofaunal density and community composition in the deep White Sea and their temporal variations

In spite of the fact that shallow-water meiobenthos of the White Sea is a relatively well studied, the information on meiobenthic fauna from the deepest part of this sea is still very scanty. This study represents the first major study of the meiobenthos from the deep White Sea. The composition of the meiobenthic community, density and vertical distribution was studied during four sampling occasions in the deepest part of the Kandalaksha Depression (White Sea) in July 1998, October 1998, May 1999 and November 1999. Samples were collected from a depth of 270?m with the aid of a multicorer. The total density of meiobenthos in 1998 was twice than in 1999 (on average, 2,356 and 1,464 ind./10?cm², respectively). The most abundant meiobenthic group was Foraminifera (59?%), followed by Nematoda (26?%) and Harpacticoida (7?%). These relative and absolute abundance values are comparable with the same depth interval in Arctic and temperate regions. The density of foraminiferans and nematodes was higher in the autumn and lower in the summer. This may be explained by the mass propagation of these animals in the autumn season: the density of juvenile nematodes and small-sized foraminiferans increased significantly in the 1- to 4-cm-deep sediment layers in autumn. The size range of the meiobenthos in the deepest part of the White Sea was also comparable to deep-sea meiobenthos (the 63–125 and 125–250?μm size classes were most dominant).     

Foraminifera and Nematoda community within the area of Ahnfeltia tobuchiensis field in Stark Strait (Peter the Great Bay of the Sea of Japan)

In August of 2006 in Stark Strait (in the Peter the Great Bay) Foraminifera and Nematoda communities were investigated at two stations: in bottom under a red alga Ahnfeltia tobuchiensis bed and on a site located outside of the bed. Bottom sediments at the stations are represented by sands of various silting extent. Foraminifera dominated at both stations, the second place by abundance was occupied by Nematoda. Extremely high population density of meiobenthos, 14278.9 ± 4623.1 thousand sp./m², was observed under the Ahnfeltia bed. The foraminifera percentage was 98.1%, which was probably connected with the mass development of diatom algae on Ahnfeltia. A high degree of domination of one Foraminifera species was recorded—Cribroelphidium frigidum. Nematoda constituted 1.5% with the prevalence of Comesomatidae family representatives. At the station situated outside of Ahnfeltia field mean population density of meiobenthos was an order lower—1731.8 ± 621.3 thousand sp./m². Foraminifera constituted 63.8% of the total meiobenthos density with Eggerella advena as the dominating species. Among Nematoda (12.5%) Paracanthonchus macrodon, Axonolaimus seticaudatus and Monoposthia latiannulata were dominant. Foraminifera and Nematoda community under Ahnfeltia bed, where bottom sediments are more silted, had low indices of species diversity and a high degree of domination.     

Benthic Invertebrates Associated with a Serpulid Polychaete Assemblage in a Temperate Estuary

Hydroides dianthus (Verrill), a serpulid polychaete which secretes calcareous tubes, provides microhabitats for a variety of benthic invertebrates in Delaware Bay. These microhabitats function as biologically generated refuges and physical heterogeneities for at least 54 species. Dominance was measured by the biological index value which yielded 12 taxa that comprised 90% by number of the serpulid assemblage. These taxa included seven polychaetes, two amphipods, Nematoda, Oligochaeta, and Harpacticoida. In addition to the refuges provided by the serpulids, it was concluded that this temperate serpulid assemblage was comparable in function but not scale to calcareous biogenic assemblages in lower latitudes.     

Meiofauna communities along a depth transect off Halley Bay (Weddell Sea-Antarctica)

Summary Meiofauna communities from 10 stations along a depth transect from approximately 500 to 2,000 m off the Halley Bay Station (Weddell Sea) are investigated. Representatives of about 30 smallsized taxa of higher category are found, most of them belonging to the meiofauna. Loricifera are recorded for the first time for the Southern Ocean. At one of the stations a maximum of 22 taxa occur, the mean number of taxa ranges from 7 to 16. Nematoda, Harpacticoida, Ostracoda, Polychaeta and Bivalvia are present at all sampling sites. Nematodes are always dominant representing more than 90% of the individuals per sample, followed by harpacticoids (3%) and kinorhynchs (1.2%). Important fractions of the meiofauna (an average of more than 50%) occur in strata below the top 0–1 cm layer. Maximal density is 3,800 individuals (10 cm^–2), the mean abundance per station ranges from 790 to 3,720 individuals (10 cm^–2) and the overall mean is 1,700 individuals (10 cm^–2). Multivariate analysis (TWINSPAN, Cluster analysis, DCA) discriminates between three communities which are correlated with depth and sediment characteristics: the near shelf-ice, the slope and the deep-sea communities.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Some recommendations for an accurate estimation of Lanice conchilega density based on tube counts

The tube building polychaete Lanice conchilega is a common and ecologically important species in intertidal and shallow subtidal sands. It builds a characteristic tube with ragged fringes and can retract rapidly into its tube to depths of more than 20 cm. Therefore, it is very difficult to sample L. conchilega individuals, especially with a Van Veen grab. Consequently, many studies have used tube counts as estimates of real densities. This study reports on some aspects to be considered when using tube counts as a density estimate of L. conchilega, based on intertidal and subtidal samples. Due to its accuracy and independence of sampling depth, the tube method is considered the prime method to estimate the density of L. conchilega. However, caution is needed when analyzing samples with fragile young individuals and samples from areas where temporary physical disturbance is likely to occur.     

Longitudinal patterns of invertebrates in the hyporheic zone of a glacial river

1. Longitudinal changes in physicochemical factors and the composition of the invertebrate community were examined in the hyporheic zone of a glacial river (Val Roseg, Switzerland) over a distance of 11 km from the glacier terminus. Multivariate analysis was used to determine the habitat preferences of taxa along an upstream‐downstream gradient of increasing temperature and groundwater contribution to river flow. 2. The hyporheos conformed to the longitudinal distribution model described for zoobenthic communities of glacial rivers in that taxonomic richness increased with distance from the glacier terminus. Spatial variation in taxonomic richness was best explained by temperature, the influence of groundwater, and the amount of organic matter. The overriding importance of these variables on the distribution of taxa was confirmed by the multivariate analysis. 3. The hyporheic zone contributed significantly to the overall biodiversity of the Roseg River. Whereas insect larvae were predominant in the benthos, hyporheic invertebrates were dominated by taxa belonging to the true groundwater fauna and the permanent hyporheos. Several permanently aquatic taxa (e.g. Nematoda, Ostracoda, Cyclopoida, Harpacticoida, Oligochaeta) appeared exclusively in the hyporheic zone or they extended farther upstream in the hyporheic layer than in the benthic layer. Leuctridae, Nemouridae, and Heptageniidae colonised hyporheic sediments where maximum water temperature was only 4 °C. 4. Despite strong seasonal changes in river discharge and physicochemistry in hyporheic water, the density and distribution of the hyporheos varied little over time. 5. Taxonomic richness increased markedly in the downstream part of a floodplain reach with an extensive upwelling zone. Upwelling groundwater not only maintained a permanent flow of water but also created several species‐rich habitats that added many species to the community of the main channel.     

On the abundance and activity pattern of zoobenthos inhabiting a tropical reef area,Cebu, Philippines

A benthic faunal study was carried out in the tidal area of Mactan Island (Cebu, Philippines). The area was subdivided along a transect from the beach to the reef according to benthic assemblages. The sediments are largely composed of calcareous skeletal remains of the indigenous biota and surrounding calcareous rocks. The content of protein and carbohydrates of the sediment was estimated, providing an approximation of organic matter in terms of feeding efficiency. Total number of zoobenthos, both as regards the sediment samples and as to the epifaunal communities associated with seaweeds, is rather uniformly distributed justifying the 95% confidence level (P>0.05). Distinct differences are apparent in abundance values of individual taxa. Although the study area showed the expected distribution pattern, with dominance of Nematoda (39%) living in sediment and Harpacticoida (36–66%) dwelling on Thalassia and algae, Polychaeta reveal a dominant attraction to both these habitats. The reasons for this phenomenon are discussed in relation to the absolute lack of macrofaunal predators The zoobenthos adjust their distribution and activity to fluctuating conditions of the environment. Light is mainly suggested as stimulating diel migration activities of the benthic fauna, moving upwards from the sediment to the algae and Thalassia during daytime. In a field experiment the zoobenthos was investigated for digestion activity over a diurnal cycle. The results reveal that feeding activity of zoobenthos follows a diel cycle showing maximum activity during the morning and evening obviously influenced by changes of light.     

Chironomid pupal exuviae and larvae of two storage reservoirs in The Netherlands

For three years chironomid larvae were collected bimonthly with a grab sampler in two deep storage reservoirs in The Netherlands. Chironomid pupal exuviae were collected monthly, from April to November, with a handnet. Net samples yielded more taxa than grab samples. The taxa found in net samples originated from more habitats, than taxa found in grab samples. The relative contribution of Orthocladiinae was much larger in net samples. Based on the results obtained in the two reservoirs, some advantages and disadvantages of both sampling methods are discussed.     

An 18S ribosomal DNA barcode for the study of Isomermis lairdi, a parasite of the blackfly Simulium damnosum s.l.

The mermithid parasite, Isomermis lairdi Mondet, Poinar & Bernadou (Nematoda: Mermithidae), is known to have a major impact on populations of Simulium damnosum s.l . Theobald (Diptera: Simuliidae) and on their efficiency as vectors of Onchocerca volvulus (Leuckart) (Nematoda: Filarioidea). However, the value of I. lairdi and other mermithid parasites as potential means of integrated vector control has not been fully realized. This is partly because traditional taxonomic approaches have been insufficient for describing and analysing important aspects of their biology and host range. In total, rDNA barcode sequences have been obtained from over 70 I. lairdi mermithids found parasitizing S. damnosum s.l . larvae in three different rivers. No two sequences were found to vary by more than 0.5%, and cytospecies identification of mermithid hosts revealed that I. lairdi with identical rDNA barcodes can parasitize multiple cytoforms of the S. damnosum complex, including S. squamosum (Enderlein). Phylogenetic analysis using a partial sequence from the 18S ribosomal DNA barcode, grouped I. lairdi in a monophyletic group with Gastromermis viridis Welch (Nematoda: Mermithidae) and Isomermis wisconsinensis Welch (Nematoda: Mermithidae).     

The benthic communities of the saline lakes Abijata and Shala (Ethiopia)

Lake Abijata lies in a shallow depression (maximum depth 8–9.5 m); the water is green with phytoplankton and it supports large fish and bird communities. Lake Shala lies in a deep caldera (maximum depth reputedly 260 m); phytoplankton is sparse and fish and bird communities scanty.Lakes Abijata and Shala, sampled in January, 1985, had conductivities of 14 000 and 21 000 microSiemens cm^-1 at 25 °C respectively, mainly due to high sodium, carbonate and chloride ions. Calcium concentrations are very low.The benthic fauna was studied with an Ekman grab to a depth of 8.5 m in Abijata and 15.5 m in Shala and was found to be dense in both lakes but varying greatly in composition at different depths. In Abijata the benthos consisted mainly of Ostracoda and Chironomidae, and in Shala mainly of Tubificidae, Ostracoda and Chironomidae. There were very few Nematoda. No true halophilic species were found but the community consisted of euryhaline forms found also in non-saline waters. Predatory invertebrates were absent and many of the dominant species, notably of the Chironomidae, were different from those of non-saline lakes nearby.     

Benthic meiofauna assemblage structure of headwater streams: density and distribution of taxa relative to substrate size

Permanent meiofauna taxa and portions of the population of other invertebrates that are temporarily in the meiofauna size class are often precluded from stream studies and assessments. This study was designed to determine the identity, density, and distribution of major meiofauna taxa relative to substrate size in a set of similar headwater streams. Using a coring technique, meiofauna (80 μm–1 mm) and substrate samples were collected from 11 Ozark headwater streams in the Boston Mountain ecoregion of Arkansas, USA. Mean meiofauna density among streams was 1739 ± 436 organisms per l. Permanent meiofauna taxa (Copepoda, Cladocera, Ostracoda, Rotifera, Nematoda, Hydrachnida, and Tardigrada) comprised 22.5% of the organisms collected with a mean density of 394 ± 233 organisms per l; temporary meiofauna taxa (Oligochaeta, Turbellaria, Hydroidea, Chironomidae, Ephemeroptera, and other insects) comprised the remainder with a density of 1346 ± 308 organisms per l. Chironomidae was the most numerous temporary meiofauna taxon, and Hydrachnida was the most numerous permanent taxon. Streams were found to differ significantly in substrate composition and densities of major taxonomic categories. Substrate size was found to predict densities for most of these taxonomic categories. Meiofauna patchiness was reflected in high variability within streams. Canonical correspondence analysis revealed positive associations between Copepoda and Nematoda and silt, and between Copepoda, Nematoda, and Rotifera and fine sand. Hydrachnida and Rotifera were negatively associated with silt and coarse sand, respectively. The potential value of inclusion of meiofauna in stream environmental assessments is discussed.     

Novelty in phylogeny of gastrotricha: evidence from 18S rRNA gene

Gastrotricha form a phylum which is crucial for defining the origin of pseudocoelomates, in that they share a number of characters with Rotifera and Nematoda but also with acoelomates, and even the evolutionary relationships within the phylum are anything but defined. For this reason the first extensive molecular data on Gastrotricha from the 18S rRNA sequences of both orders have been obtained and analyzed. Sequence analyses show that the phylum Gastrotricha is strictly monophyletic along an evolutionary line quite distinct from that of both Rotifera and Nematoda. A new view of the evolutionary history of the phylum Gastrotricha is put forward, in which Chaetonotida, and not Macrodasyida, are the most primitive forms of the group, contrary to the commonly held view. A polyphyletic origin of aschelminthes is supported, and the misleading term pseudocoelomates should be discarded.     

First description of the male and new data on the female ofCristitectus congeri Petter, 1970 (Nematoda: Cystidicolidae)

The male ofCristitectus congeri Petter, 1970 (Nematoda: Cystidicolidae) is described and figured. The female's measurements are reported, and some anatomical characteristics are illustrated. Specimens were obtained from stomachs ofConger conger (L.) from off northwest Spain.     

三峡水库初次蓄水后干流库区桡足类的纵向分布与季节变化

作为大型水利工程, 三峡水库于2003年6月开始蓄水, 蓄水后库区水环境发生了变化。为了了解三峡水库水生态系统的演替规律, 同时为环境保护、渔业资源开发利用以及水环境管理提供理论基础, 我们对三峡水库第一阶段蓄水后桡足类的季节变化和空间分布进行了周年季节性研究。在三峡库区江津至茅坪的10个断面共采集到8种桡足类, 其中哲水蚤目2种、猛水蚤目1种、剑水蚤目5种, 北碚中剑水蚤(Mesocyclops pehpeiensis)、广布中剑水蚤(M. leuckarti)和汤匙华哲水蚤(Sinocalanus dorrii)分布较广。各样点种类数差异不大, 但组成上却有不同。桡足类种类组成、空间分布和密度具有明显的季节变化特征, 此外密度在水库的纵轴上也表现出明显的梯度分布, 越近大坝密度越高。     

Composition and distribution of meiofauna,including nematode genera,in two contrasting Arctic beaches

The meiofauna of two tidal beaches, one exposed and one more sheltered, on Bjornoya (Bear Island) was investigated in summer 2000. Both meiofaunal densities and composition seem to be controlled by physical properties of the sediment, which in turn are controlled by exposure. The moderately and poorly sorted sediments in the sheltered beach were more abundant in terms of meiofaunal densities than the well sorted sediments in the exposed beach (254–481 individuals in 10 cm² vs 7–269 individuals in 10 cm², respectively). In total, seven higher meiofaunal taxa were found. Turbellaria were the numerically dominant taxon in the exposed beach. In the sheltered beach, Turbellaria also dominated, followed by Nematoda and Harpacticoida. The vertical distribution of the meiofauna was in accordance with what has been reported from other intertidal beaches. Nematoda were studied in detail and their densities ranged over 0.7–7.7 individuals in 10 cm² in the exposed beach and 2.7–186.0 individuals in 10 cm² in the sheltered beach. Nematodes were identified to genus level and a total of eight nematode genera were found. Sediment community respiration, measured as oxygen consumption, ranged between 2.3 cm³ O₂ m^–2 h^–1 in the exposed beach and 7.3 cm³ O₂ m^–2 h^–1 in the sheltered beach (respectively, the equivalent of 24 mg and 75 mg of organic carbon metabolised per day). Values from the sheltered site are within the range of results registered in much warmer localities.     

Seasonal variation and longitudinal distribution of copepods in the main river area of the Three Gorges Reservoir

The ecosystem of the Three Gorges in the Yangtze River was changed into an artificial lake (res-ervoir) ecosystem after impoundment in June 2003. We surveyed the seasonal variation and spatial distribution of copepods from April 2004 to January 2005 in order to provide data for clarifying the successional pattern of the ecosystem. From Jiangjin to Maoping, eight copepod species were collected and classified into Calanoida (2), Harpacticoida (1), and Cyclopoida (5). Among them, Mesocyclops pehpeiensis, M. leuckarti and Sinocalanus dorrii had a relatively wide distribution. No distinct dif-ference in species number was found among the sampling sites, but the species composition was different. Species composition, distribution and density of copepods showed significant seasonal variations. In addition, cope-pod density showed an obvious gradient with the distance from the reservoir dam: the nearer to the dam, the denser the copepods.