Vertical Distribution Of Nematodes Research Articles

Contrasting macrobenthic activities differentially affect nematode density and diversity in a shallow subtidal marine sediment

By bioturbating and bio-irrigating the sea floor, macrobenthic organisms transport organic matter and oxygen from the surface to deeper layers, thereby extending the habitat suitable for smaller infauna. Next to these engineering activities, competition, disturbance and predation may also affect the spatial distribution of these smaller organisms. In a controlled laboratory experiment, we studied the effects of 3 functionally different macrobenthic species on the vertical distribution of nematodes. Abra alba, a suspension-deposit feeding bivalve reworking the sediment randomly, Lanice conchilega, a suspension-deposit feeding, tube-irrigating polychaete and Nephtys hombergii, a burrowing predatory polychaete, were added in single-species treatments to sediment from a coastal subtidal station in the Belgian part of the North Sea, sieved (1 mm) to remove macrofauna. After 14 d, the control treatment without macrobenthos was found to be detrimental to nematode density and diversity, which points to the importance of macrobenthic engineering to sustain the smaller components of the food web. Nematode densities were highest at the sediment surface in all treatments, but subsurface density peaks were observed in A. alba (to 3 cm depth) and L. conchilega (to 7 cm depth) microcosms. In the A. alba treatment, the dominant non-selective deposit feeders and the epistrate feeders shifted downwards probably to avoid disturbance and exploitative competition by the bivalve siphons at the surface, while they might have benefited from the faecal pellets deposited in the subsurface. In the L. conchilega treatment, the several dominant species were redistributed over depth layers, indicating polychaete-mediated habitat extension from surface into depth. Nematode communities seemed hardly affected by the presence of N. hombergii. These results reveal that functionally contrasting macrobenthic engineering effects shape nematode communities in different ways, which may maintain the role of nematodes in ecosystem functioning. The present study therefore highlights the need for conservation of macrobenthic functional diversity.

Factors Influencing the Vertical Distribution of Nematodes in Sediments

ABSTRACT The effects of oxygenation of sediment and the presence of macrobenthic organisms (gammarids, tubificids, and chironomid larvae) on the vertical distribution and species segregation of nematodes were studied in laboratory microcosms with freshwater sediment. The abundance of nematodes was positively affected by oxygenation, particularly in the deep sediment layers. Small nematodes increased in the deeper layers of oxygenated treatment. Macrobenthic animals did not influence abundance or vertical distribution of nematodes but had an impact on nematode community structure. The families Tobrilidae and Monhysteridae dominated the community. In the control treatments the monhysterids were abundant, whereas the importance of tobrilids increased in the treatments with macrobenthic animals.

Sediments hosting gas hydrate: oases for metazoan meiofauna

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 337:27-37 (2007) - doi:10.3354/meps337027 Sediments hosting gas hydrate: oases for metazoan meiofauna Stefan Sommer*, Erik Gutzmann, Olaf Pfannkuche Leibniz-Institut für Meereswissenschaften, IFM-GEOMAR, Wischhofstraße 1–3, 24148 Kiel, Germany *Email: ssommer@ifm-geomar.de ABSTRACT: The effect of methane seepage from sediments harbouring shallow gas hydrates on standing stocks and the distribution pattern of meiobenthic organisms, in particular Nematoda and Rotifera, was studied at about 800 m water depth at Hydrate Ridge, Cascadia subduction zone, off Oregon. The presence of shallow gas hydrates, buried only a few 10s of centimetres below the sediment surface, was indicated by extensive bacterial mats of chemosynthetic Beggiatoa sp. and clam fields of the bivalve mollusk Calyptogena spp. Mean abundances of meiobenthic organisms integrated over the upper 10 cm of the sediment were highest (1294 ind. 10 cm–2) at clam fields, closely followed by control sediments least affected by gas hydrates (1199 ind. 10 cm–2) and lowest in sediments covered with bacterial mats (762 ind. 10 cm–2). Average meiobenthic biomass was highest at the clam field site (262.2 µg C 10 cm–2), 210.4 µg C 10 cm–2 at the control site and very low in sediments covered with bacterial mats (61.4 µg C 10 cm–2). The dominant taxa of meiobenthic organisms at the investigated sites were nematodes and, unexpectedly, Rotifera that are almost unknown from the deep marine habitat. In terms of abundance, rotifera dominated the meiobenthic community in gas-hydrate-influenced sediments, while control sediments and deeper basins adjoined to Hydrate Ridge were dominated by nematodes. Nematodes were concentrated in the sediment surface at all sites, whereas rotifers were almost evenly distributed at all depths, with a slight preference for deeper sediment horizons. The horizontal as well as vertical distribution of nematodes and rotifers is likely to be determined by competition or predation, and by the high adaptive capability of rotifers to highly sulphidic and anoxic conditions. Estimates of meiobenthic carbon turnover in relation to the bulk organic carbon supply indicate that, in contrast to other meiobenthic communities in cold seep environments, the meiobenthos in the studied gas-hydrate-containing sediments do not benefit from the excess availability of organic carbon via the chemoautotrophic food web. This may be because, for most meiobenthic organisms (other than rotifers), tolerance mechanisms are overwhelmed by the deleterious environmental conditions of reduced oxygen availability and extremely high sulphide fluxes. KEY WORDS: Meiofauna · Nematoda · Rotifera · Gas hydrate · Carbon turnover · Hydrate Ridge · Cascadia subduction zone Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 337. Online publication date: May 14, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Effects of Copepods and Chironomids on the Abundance and Vertical Distribution of Nematodes in a Freshwater Sediment

ABSTRACT In the presence of copepods and chironomids the number of nematodes in a laboratory microcosm system was not influenced; however, the vertical distribution patterns in the sediment were influenced by the presence or absence of copepods and chironomids. The relative numbers of nematodes in 0–1 cm versus 1–5 cm sediment layer in copepod and copepod plus chironomid treatments were significantly higher than that for the controls. The vertical distribution of three dominant nematode species (Eumonhystera filiformis, Ethmolaimus pratensis and Tobrilus sp.) showed that the juveniles were more concentrated in the superficial sediment layer, whereas adults burrowed deeper into the sediment. Significant differences for the vertical distribution were found for adults of E. pratensis and for juveniles of E. filiformis and E. pratensis. Analysis of the macro- and meiozoobenthos of Lake Starnberger See indicated that nematode abundances were positively correlated with those of chironomids, oligochaetes, ostracods, and copepods.

Laboratory experiments on the infaunal activity of intertidal nematodes

The impact of oxygen on the vertical distribution of an intertidal nematode community was investigated in a manipulation experiment with sediments collected from the Oosterschelde (The Netherlands). The vertical distribution of nematodes was examined in response to sediment inversion in perspex cores with or without the presence of an air-flushed silicone tube introducing oxygen to the bottom sediment layer. Following an incubation of 1 week, peak densities of nematodes were recorded in the deep layers of the sediment in cores with subsurface oxygenation. In contrast, this concentration of nematodes was absent in the cores that lacked bottom oxygenation and the majority of the total assemblage was still located in anoxic sediment layers. This suggests that oxidised sediments with traces of oxygen represent favourable conditions for nematodes and indicates that these nematodes are tolerant to short-term anoxia and burial. Observations on the species level suggest that oxygenation, primarily through its direct impact on geochemical properties of the sediment, may be an important factor governing the subsurface activity of nematodes.

The macro- and micro-scale patchiness of meiobenthos associated with the Darwin Mounds (north-east Atlantic)

Meiobenthic community structure was investigated at different spatial scales (from 100 metres to centimetres) on and adjacent to a group of coral-topped sandy mounds in the bathyal north-east Atlantic (Darwin Mounds, Rockall Trough) and related to the environmental conditions in the area, mainly differences in sediment organic carbon content and presence of biogenic structures. Meiobenthos abundances were similar to those observed in other deep-sea sites, with nematodes representing at least 94% of the total community. The dominant nematode genera were Microlaimus, followed by Sabatieria, Richtersia, Rhynchonema and Trefusia, together with typical deep-sea genera (e.g. Halalaimus and Acantholaimus). Multivariate analysis of nematode generic relative abundances at the different stations indicated that there was no significant influence on distribution resulting from large scale topographic and biogeochemical conditions around the mounds. The same genera were associated with dead tests of the xenophyophore Syringammina fragilissima and in the surrounding sediments. The vertical distribution of nematodes on and adjacent to the mound showed some unusual features, as the deeper layers of the sediments were inhabited by stilbonematids. These genera harbour ectosymbiotic, chemoautotrophic bacteria and have not previously been recorded from the deep sea. The occurrence of stilbonematids in notable numbers in the subsurface layers of the sediments in the vicinity of the Darwin Mounds provides evidence for the occurrence of anoxic microenvironments.

Vertical distribution and feeding types of nematodes from Chetumal Bay, Quintana Roo, Mexico

The vertical distribution and feeding type of nematodes in sediments of Chetumal Bay, Mexico, were studied in five intertidal transects along the urbanized zone in June and December 1995. Sediments were collected with a PVC corer to 6-cm sediment depth and cut immediately into three equal 2-cm depth fractions. Nematode density varied from 7.4 × 103 to 5.3 × 105 m−2 in June and from 1.7 × 104 to 7.2 × 105 m−2 in December. In June, the epistrate feederPseudochromadora sp. was the most abundant in the deepest sediment fraction (4–6 cm), whereas epistrate feeders,Neotonchoides sp.,Desmodora sp., and the deposit feederBathylaimus australis were dominant in the top most sediment (0–2 cm). In December, deposit feeders,Desmolaimus zeelandicus, Parodontophora sp., and the epistrate feederOncholaimus oxyuris were the most abundant in the deepest sediment, whereasNeotonchoides sp. andPseudochromadora sp. dominated the first 2 cm of sediments. Highest nematode density was recorded in the uppermost sediment layer (0–2 cm). Feeding types showed different abundance among transects and between months. There was a seasonal change in vertical distribution of nematodes, with the highest abundance in the deepest sediment layer in December, possibly due to the effect of wind waves on sediments of Chetumal Bay. The trophic composition of the nematode fauna in Chetumal Bay showed a dominance of deposit feeders and epistrate feeders, most likely in response to organic enrichment that is typical of eutrophic environments.

Nematode communities of Lake Tana and other inland water bodies of Ethiopia

Free-living nematodes from littoral benthic sediments of four lakes, two rivers and a hot spring in Ethiopia are studied. Populations of nematodes encountered are identified to the species level. The general nematode (generic and species) composition of the lakes, rivers and hot spring are appraised by giving special emphasis to the nematodes from L. Tana, i.e. three sites where different environmental factors come into play were considered. Gelda is a site close to a river inlet (River Gelda), Gedero is a site exposed to strong wind action while Zegie is a secluded site protected by a land mass from any strong wind action. Nematode communities were identified using classification and ordination techniques. The identified communities are then characterised with respect to species composition, biomass, density, diversity, size structure, feeding type and maturity index. Also, the vertical distribution of nematodes is examined at the community and species level. An attempt has been made to associate these variations with the considered environmental factors viz. site, water depth, sediment depth, median grain size and percentage of mud in the sediment. Median grain size and percentage of mud varied over the three sites with the lowest grain size and the highest percentage of mud in Gelda. The incoming river is regarded responsible for the high mud content at this site. The composition of the nematode communities from the lakes, rivers and hot spring by and large was typically freshwater. The highest number of species (40 species) was recorded from L. Tana (a lake relatively intensively sampled) whereas the lowest number was recorded from the saline lake, Abiyata (2 species). Both species in the latter belong to the genus Monhystrella. The complete dominance of species of this genus in L. Abiyata and its presence in the saline lakes and hot spring is argued to be associated with their opportunistic nature and their high temperature dependency and their capacity to withstand high osmotic stress conditions. The role played by salinity in the distribution of nematodes in inland water bodies is considered vital. The occurrence of two species of the genus Udonchus in River Abbay where an outlet of a waste disposal scheme of a textile factory is situated, and their absence in any other site coupled with the habitual presence of one of the two species in mineral waters are used to argue that the genus may be an indicator of some kind of environmental (chemical ?) stress. Five nematode communities are identified in L. Tana, viz. Gelda at 0.5 m, Gelda at 1.5 m, Zegie at 0.5 m, Zegie at 1.5 m and Gedero. The vulnerability of Gedero to strong wind action is maintained to be the main reason for the absence of a significant difference in nematode community at the two water depths at this site. The presence of few dominant species characterised four of the five communities. Factors that account for differences in species composition and abundance are discussed. Local conditions are thought to be important in the different communities in L. Tana. A strategy in niche partitioning is suggested to be the main driving force behind the composition of few most dominant species which (in L. Tana and other reviewed lakes) invariably was a combination of a deposit feeder(s) and an omnivore/predator(s) species. In general, nematode diversity in L. Tana was comparable to that found in oligotrophic and mesotrophic freshwater lakes. Nematode diversity varied over the different communities

Nematode distribution in ocean margin sediments of the Goban Spur (northeast Atlantic) in relation to sediment geochemistry

Nematode density along a depth gradient (206–2760 m) in the northeastern Atlantic (Goban Spur) is linearly and positively related to organic matter mineralization in the sediment. It is estimated that nematodes contribute at most 13% to total carbon turnover, and this contribution decreases with water depth. The vertical distribution of nematodes in the sediment closely follows concentration vs depth profiles of total nitrogen in the sediment. Both nematodes and total nitrogen tend to be more concentrated towards the surface with increasing water depth. There is no indication that nematode vertical distribution is directly influenced by the oxygen penetration in the sediment. However, it is hypothesized that the sediment oxygen concentration can explain the relatively greater importance of smaller organisms in benthic communities with increasing water depth. The nitrogen vs sediment depth profiles are consistent with a greater impact of larger organisms on sediments at the shallow stations and decreased sediment mixing with increasing water depth.

Vertical distribution of benthic nematodes in an oligotrophic lake: seasonality, species and age segregation

The vertical distribution of nematodes up to 20 cm sediment depth was studied over a one-year period in the alpine, oligotrophic lake Konigssee. Ten water depths were examined, four of which correspond to the littoral (1 m, 2 m, 5 m, 10 m), three to the littoriprofundal (15 m, 20 m, 30 m) and three to the profundal (60 m, 120 m, 190 m). The sediment was devided into four layers (0–2 cm, 2–5 cm, 5–10 cm and 10–20 cm). (1) The highest proportion of nematodes was found in the top layer. Out of 45 263 nematodes, 89% were found in the first 5 cm of the sediment and only 1 % deeper than 10 cm. (2) The proportion of nematodes in the top layer increased along with water depth. Water depth was a better predictor of percentage of nematodes in the top layer than particle size or content of organic carbon in the sediment. (3) There were considerable differences among species in their vertical distribution in the sediment. (4) There was a significant trend for juveniles to occupy more superficial layers than adults across various species. (5) There are time related vertical preferences among adults and juveniles of several nematode species across the year, suggesting vertical migration in the sediment (e.g. Aphanolaimus aquaticus Daday, Eumonhystera longicaudatula Gerlach & Riemann, Tobrilus gracilis Bastian, Monhystera paludicola de Man, Ethmolaimus pratensis de Man and Ironus tenuicaudatus de Man). The factors determining the vertical variation in nematode abundance in freshwater systems across space and time are still unknown.

Spatial and Temporal Variation of the Nematofauna in Representative Soils of the Central Region of the Iberian Peninsula

The population dynamics of the nematofauna in cultivated lluvisoils in the Spanish Central Region were studied throughout the year and related to the development of the crop. The vertical distribution of nematodes in this soil type was related to the clay content in deep horizons, which affects the moisture characteristics in different levels. Both spatial and temporal changes were observed in the majority of nematode groups, which correlated with the moisture content and host plants present.

Vertical distribution of nematodes in arable soil under grass (Festuca pratensis) and barley (Hordeum distichum)

The connection between faunal composition and soil factors is discussed in this study on vertical distribution of soil nematodes under grass and barley. The investigation was undertaken on the field site of a Swedish integrated research project “Ecology of Arable Land. The Role of Organisms in Nitrogen Cycling”. Higher nematode number (7.6 × 106 m−2) and biomass (340 mg dry wt. m−2) were found under a 4-year-old grass ley than under barley (5.0 × 106 m−2; biomass, 136 mg dry wt. m−2). Plant feeders dominated under the grass ley (3.2 × 106 m−2 whereas under barley the bacterial feeders (2.4 × 106 m−2) were the most abundant feeding group. Number, biomass, mean individual size and various community parameters indicated a much better nutritive situation for the nematodes under grass than under barley. The vertical changes in the various parameters, including proportion of egg-carrying females, indicated an increasing food shortage for the nematode populations towards greater depths. In the top soil, predation could be an important factor in regulating nematode number.

Evidence that sediment type influences the horizontal and vertical distribution of nematodes at a deep-sea site

The relationship between sediment type and the nematode fauna was studied at the HEBBLE site (40°27′N, 62°20′W), which is at 4820 m depth on the Scotian Rise in the northeast Atlantic. Because of the hydrodynamic regime, the fine-grained, surficial sediments (brown mud) are eroded and redeposited several times per year, so the properties of brown mud can be expected to be relatively homogeneous, regardless of depth of burial. Brown mud accumulates in topographic lows, so although the 0–1 cm layer in our samples is brown mud, the 1–2 and 2–3 cm layers can be either brown mud or foraminiferan mud. Where both sediment types occur in a single horizontal plane (i.e. the 1–2 cm layer and the 2–3 cm layer), nematodes are more abundant in the brown mud than in the foraminiferan mud, and this pattern occurs across feeding and tail-morphology functional groups. In those samples in which brown mud occurs from 0 to 3 cm, nematodes do not differ significantly in abundance among the three depth layers, suggesting that the usual decrease in abundance with depth in the sediment is not simply a function of proximity to the sediment surface, but relates to a change in the quality of the sediment with depth. Further, in brown mud, nematodes tend to be more abundant in the 1–2 cm layer than in the 0–1 cm layer. At the HEBBLE site, there is reason to suspect that small organisms are at risk on the sediment surface. The unexpected nematode-abundance profile may occur for the same reason.

Studies on the interstitial animals in the Ishikari beach, Hokkaido, northern Japan-A preliminary report

General patterns of the microdistribution of some interstitial animal groups are described as a preliminary report from the studies on the interstitial fauna and the bionomics of harpacticoids, which have been carried out at the Ishikari beach on the Japan Sea coast of Hokkaido. The Ishikari beach is characterized by homogeneous medium fine sand and small tide. Vertical distribution of nematodes are examined in order to estimate the difference between the density as represented by the number of individuals per unit sample volume and that per unit pore water volume by using the method formerly elaborated by the author. Characteristics in the microdistribution of Hesionides arenaria (Polychaeta) and Hypsibius itoi (Tardigrada) and five species of Harpacticoida are discussed. Distribution range of Arenopontia ishikariana, that is the dominant species in this beach (the maximum density recorded 4045 individuals per 100 cc sand sample), is very wide both horizontally and vertically, extending from the foreshore to the backshore. Nodtiella sp. penetrate into the backshore a little above the ground water level. Arenosetella bidenta and Leptastacus japonicus occur within well wet sand of the foreshore, and do not penetrate into the backshore. Paraleptastacus unisetosus are restricted in deep layers of the backshore during the summer, but appear in the upper foreshore during a short period of the early spring. This change of the microdistribution of P, unisetosus suggests a seasonal migration.

The Distribution of Free-Living Nematodes in Relation to Salinity in the Middle and Upper Reaches of the River Blyth Estuary

The habitat of mud-dwelling estuarine nematodes consists essentially of an extremely complex mixture (Baver 1948) of inorganic and organic particles surrounded by interstitial water. Except when the mud dries out completely the body surface of a nematode in this habitat is continually in contact with the interstitial water. Exposure, salinity changes, and other characteristics of estuaries affect nematodes only in so far as they affect conditions in this water. The ecological factors peculiar to this habitat can be seen to be very different from those affecting nematodes living on rocky shores, intertidal seaweeds or marine beaches. The original work on the marine nematodes of this country is that of Bastian (1865). This was followed by a number of recordings and descriptions of new species made by Southern (1914) during the Clare Island survey. Since then the nematodes of the Plymouth area have been described by Schuurmans-Stekhoven (1935b) and by Wieser (1951, 1952) in two important works. In his latest paper Wieser studied the vertical distribution of nematodes inhabiting intertidal seaweeds, and although the detailed ecology of the species found in this habitat cannot be extrapolated to the present investigation, the species recordings and the general intertidal ecology of the nematodes studied have been useful for comparison. Moore (1931) and Mare (1942) have studied nematodes as a group, without distinguishing the species, during wider investigations on marine benthic communities, and Rees (1940) has dealt generally with intertidal nematodes. The work of Rees dealt with the horizontal and vertical distribution of nematodes found during a wider survey of the ecology of a mud flat in the Bristol Channel, but none was identified. His work has been used as the only available point of departure for the present investigation. The distribution of free-living nematodes in water of varying salinity has been the subject of much research in the Baltic and in certain areas of the Zuiderzee. An extensive literature exists for the Belgian coast, the North Sea coast of Germany and the Dutch coast, which is summarized in Schuurmans-Stekhoven (1935a) and more recently by Wieser (1951). In the Zuiderzee and the Baltic, rates of salinity change are much less rapid than those found in estuaries and the distribution of