Abstract: Organic matter input and processing was Studied in 2 contrasting sediments (Stn 115(FINE) and Stn 330(COARSE)) in the southern North Sea. The sediments are subjected to similar hydrodynamic conditions, but Stn 115(FINE) underlies a high turbidity zone, making it a fine, low-permeability sediment. Monthly data on chlorophyll a (chl a), delta C-13 and delta N-15 of particulate organic matter in the water column and sediment showed that the algal spring bloom deposition created a strong vertical gradient of sedimentary chl a at Stn 115(FINE). Macrobenthic biomass (78 +/- 60 g C m(-2), mean +/- SD) was dominated by suspension feeders, suggesting biological mediation of the organic matter input. In contrast, the offshore Stn 330(COARSE) is a coarse, high-permeability sediment in which chl a penetrated centimeters deep due to physically mediated input. The macrobenthic community, low in biomass (3.8 +/- 2.4 g C m(-2)), was dominated by mobile polychaetes and epibenthic amphipods, which is characteristic of physically disturbed sediments. Overall, sediment characteristics played an important but indirect role in the organic matter input and processing. At Stn 115(FINE) a large macrobenthic community developed that mediated the input of organic matter to the sediment through herbivore and predatory pathways. At Stn 330(COARSE) in contrast, organic matter input seemed to be dominated by physical processes. Overall, the fraction of algal carbon degraded in the sediment was higher at Stn 115(FINE) than at Stn 330(COARSE) indicating that the physical input at Stn 330(COARSE) was less efficient than the biological input at Stn 115(FINE).

Abstract: This study examines whether or not biogeographical and/or managerial divisions across the European seas can be validated using soft-bottom macrobenthic community data. The faunal groups used were: all macrobenthos groups, polychaetes, molluscs, crustaceans, echinoderms, sipunculans and the last 5 groups combined. In order to test the discriminating power of these groups, 3 criteria were used: (1) proximity, which refers to the expected closer faunal resemblance of adjacent. areas relative to more distant ones; (2) randomness, which in the present context is a measure of the degree to which the inventories of the various sectors, provinces or regions may in each case be considered as a random sample of the inventory of the next largest province or region in a hierarchy of geographic scales; and (3) differentiation, which provides a measure of the uniqueness of the pattern. Results show that only polychaetes fulfill all 3 criteria and that the only marine biogeographic system supported by the analyses is the one proposed by Longhurst (1998). Energy fluxes and other interactions, between the planktonic and benthic domains, acting over evolutionary time scales, can be associated with the multivariate pattern derived from the macrobenthos datasets. Third-stage multidimensional scaling ordination reveals that polychaetes produce a unique pattern when all systems are under consideration. Average island distance from the nearest coast, number of islands and the island surface area were the geographic variables best correlated with the community patterns produced by polychaetes. Biogeographic patterns suggest a vicariance model dominating over the founder-dispersal model except for the semi-closed regional seas, where a model substantially modified from the second option could be supported.

Abstract: To assess the role of macrofauna-mediated sediment changes on nematode community recovery, we examined the temporal development of macrobenthos, nematode communities and sediment properties following hypoxia in 16 m(2) replicated plots over a 6 mo period. Hypoxia drastically changed nematode community composition (i.e. reduced diversity and abundances of all dominant nematodes, except Odontophora spp.), but complete mortality, as was the case for the macrobenthos, did not occur. Macrofauna diversity recovered slowly, but community composition approached that of control communities after several months. In contrast, nematode diversity recovered to control values within 1 mo but, subsequently, decreased again; hence, no clear convergence towards the control community composition was apparent. This diversity decline and lack of community recovery was mainly attributed to abundance overshoots of the epistrate feeding nematodes Chromadora spp., Daptonema spp. and Ptycholaimellus ponticus in the treatments, which dominated the treatment community after 2 mo. Nematode community reassembling was strongly related to the coupled macrobenthos-environmental temporal development. The dynamics of 2 sediment characteristics, which were both mediated by the colonizing macrobenthos, are presented as possible determinant factors for this relationship: (1) low nematode post-settlement resuspension resulting from stable sediments at early macrofauna recovery stages and (2) enhanced nematode reproduction and settlement success in a dense microphytobenthos mat in relation to the temporal variation in macrobenthos grazing pressure and bioturbation. In conclusion, the strong relationships between macrobenthos recovery, environmental development and nematode community development after hypoxia highlight the importance of macrobenthos-sediment interactions in the recovery and structuring of nematode communities.

Abstract: In this paper, we investigated: (1) the predictability of different aspects of biodiversity, (2) the effect of spatial autocorrelation on the predictability and (3) the environmental variables affecting the biodiversity of free-living marine nematodes on the Belgian Continental Shelf. An extensive historical database of free-living marine nematodes was employed to model different aspects of biodiversity: species richness, evenness, and taxonomic diversity. Artificial neural networks (ANNs), often considered as �black boxes�, were applied as a modeling tool. Three methods were used to reveal these �black boxes� and to identify the contributions of each environmental variable to the diversity indices. Since spatial autocorrelation is known to introduce bias in spatial analyses, Moran�s I was used to test the spatial dependency of the diversity indices and the residuals of the model. The best predictions were made for evenness. Although species richness was quite accurately predicted as well, the residuals indicated a lack of performance of the model. Pure taxonomic diversity shows high spatial variability and is difficult to model. The biodiversity indices show a strong spatial dependency, opposed to the residuals of the models, indicating that the environmental variables explain the spatial variability of the diversity indices adequately. The most important environmental variables structuring evenness are clay and sand fraction, and the minimum annual total suspended matter. Species richness is also affected by the intensity of sand extraction and the amount of gravel of the sea bed. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: This study examines whether or not biogeographical and/or managerial divisions across the European seas can be validated using soft-bottom macrobenthic community data. The faunal groups used were: all macrobenthos groups, polychaetes, molluscs, crustaceans, echinoderms, sipunculans and the last 5 groups combined. In order to test the discriminating power of these groups, 3 criteria were used: (1) proximity, which refers to the expected closer faunal resemblance of adjacent. areas relative to more distant ones; (2) randomness, which in the present context is a measure of the degree to which the inventories of the various sectors, provinces or regions may in each case be considered as a random sample of the inventory of the next largest province or region in a hierarchy of geographic scales; and (3) differentiation, which provides a measure of the uniqueness of the pattern. Results show that only polychaetes fulfill all 3 criteria and that the only marine biogeographic system supported by the analyses is the one proposed by Longhurst (1998). Energy fluxes and other interactions, between the planktonic and benthic domains, acting over evolutionary time scales, can be associated with the multivariate pattern derived from the macrobenthos datasets. Third-stage multidimensional scaling ordination reveals that polychaetes produce a unique pattern when all systems are under consideration. Average island distance from the nearest coast, number of islands and the island surface area were the geographic variables best correlated with the community patterns produced by polychaetes. Biogeographic patterns suggest a vicariance model dominating over the founder-dispersal model except for the semi-closed regional seas, where a model substantially modified from the second option could be supported.

Abstract: The pan-European MacroBen database was used to compare the AZTI Marine Biotic Index (AMBI) and the Benthic Quality Index (BQI(ES)), 2 biotic indices which rely on 2 distinct assessments of species sensitivity/tolerance (i.e. AMBI EG and BQI E[S-50](0.05)) and which up to now have only been compared on restricted data sets. A total of 12409 stations were selected from the database. This subset (indicator database) was later divided into 4 marine and 1 estuarine subareas. We computed E(S-50)(0.05) in 643 taxa, which accounted for 91.8%, of the total abundances in the whole marine indicator database. AMBI EG and E(S-50)(0.05) correlated poorly, Marked heterogeneities in E(S-50)(0.05) between the marine and estuarine North Sea and between the 4 marine subareas suggest that sensitivity/tolerance levels vary among geographical areas, High values of AMBI were always associated with low values of BQI(ES), which underlines the coherence of these 2 indices in identifying stations with a bad ecological status (ES). Conversely, low values of AMBI were sometimes associated with low values of BQI(ES) resulting in the attribution of a good ES by AMBI and a bad ES by BQI(ES), This was caused by the dominance of species classified as sensitive by AMBI and tolerant by BQI(ES). Some of these species are known to be sensitive to natural disturbance, which highlights the tendency of BQI(ES) to automatically classify dominant species as tolerant. Both indices thus present weaknesses in their way of assessing sensitivity/tolerance levels (i.e. existence of a single sensitivity/tolerance list for AMBI and the tight relationship between dominance and tolerance for BQI(ES)). Future studies should focus on the (1) clarification of the sensitivity/tolerance levels of the species identified as problematic, and (2) assessment of the relationships between AMBI EG and E(S-50)(0.05) within and between combinations of geographical areas and habitats.

Abstract: Sediments of three different subtidal areas (15-705 m depth) of the Italian coasts (Manfredonia, Brindisi and Gallipoli) were investigated to study meiofauna and nematode composition. The nematodes were identified to the genus level and their abundances compared using multivariate analysis. Our data showed an evident depth gradient in meiofauna abundance: the shallowest sites had more diverse and abundant meiobenthic communities than the deeper ones. Nematodes were the dominant taxon (83-100%) at all sites, followed by Copepoda (0.5-8%). Sabatieria, Astomonema, Dorylaimopsis, Terschellingia and Daptonema were among the dominant nematode genera in the three areas. Nematode genus H� diversities were not Significantly dissimilar, though at community level some differences were detected among the study areas. The greatest differences were observed in the comparison of the communities from Manfredonia and Gallipoli. Furthermore, there was a difference between shallow (<200 m) and deep sites due to high differential abundances of common genera (i.e. Astomonema, Dorylaimopsis, Sabatieria and Terschellingia).

Abstract: We investigated meiobenthic community response (as density and vertical distribution) to the sedimentation of phytoplankton in 2 contrasting sites in the southern North Sea, one with fine grained sediment close to the coastline and another with highly permeable sediments. Meiobenthic densities and pigments in the water column and sediment were measured monthly from October 2002 until October 2003. Stable isotope C-13 and N-15 signatures were analysed in sediment particulate organic matter (POM), water suspended particulate matter (SPM) and in different meiobenthic taxa at 3 different times (prior, during and after spring bloom deposition) at 2 sediment depths (0 to 1 and 4 to 5 cm). Our aim was to determine whether sediment type affects the overall meiobenthic community response (densities and vertical distribution) and utilisation of freshly deposited phytoplankton as a food source. Variation in nematode response to the sedimentation event was evident and was related to the contrasting biogeochemical processes at the stations. In permeable sediments, the nematode response was rapid after phytoplankton deposition, while in the fine-grained station, nematode response (as density) was delayed. In general, meiobenthic C-13 signatures remained relatively constant over time and were not coupled with changes in water SPM and sediment POM. There was vertical variation in meiobenthic C-13 signatures in fine sediments. Nematodes belonging to the genera Sabatieria and Richtersia from the deeper sediment layer had isotope signatures similar to those of surface living nematodes, indicating migration of these genera to the surface to feed. In permeable sediments, such vertical differences were absent because of sediment biogeochemical properties. delta C-13 and delta N-15 values of copepods clearly indicated a chemoautotrophic food source within the fine-grained sediment, which has not been previously reported for these environments.

Abstract: The impact of dead discards, originating from beam trawl fishing on the nematode community from the Tagus estuary was investigated in terms of vertical distribution of the dominant nematode groups. Sediment cores were collected from a mud-flat from the Tagus estuary. Crangon crangon (Linnaeus, 1758) carcasses were added to the surface of the cores, simulating the settling of dead discards on the sediment. The vertical distribution of the dominant nematode groups was determined up to 4 cm deep at four different moments in time post deposition (0, 2, 4 and 6 h) and compared to control cores. The C. crangon addition to the sediment led to the formation of black spots and therefore oxygen depleted areas at the sediment surface. The Chromadora/Ptycholaimellus group, normally dominant at the surface layer, migrated downwards due to their high sensibility to toxic conditions. Sabatieria presented the opposite trend and became the dominant group at the surface layer. Since Sabatieria is tolerant to oxygen stressed conditions and high sulphide concentrations, we suggest that it migrated opportunistically towards an unoccupied niche. Daptonema, Metachromadora and Terschellingia did not show any vertical migration, reflecting their tolerance to anoxic and high sulphiclic conditions. Our study showed that an accumulation of dead discards at the sediment surface might therefore alter the nematode community vertical distribution. This effect is apparently closely related to toxic conditions in the sediment, induced by the deposition of C. crangon at the sediment surface. These alterations might be temporal and reflect an adaptation of the nematode community to dynamic intertidal environments. (C) 2008 Elsevier Ltd. All rights reserved.

Abstract: We investigated short-term changes (two years) in nematode communities (density, diversity, biomass and community composition) in an area on the Kwintebank (Belgian Continental Shelf) that was closed for sand extraction activities and compared these patterns to nematode community characteristics from another area on the Kwintebank were sand extraction was still ongoing. Six stations were sampled in 2003 and 2004 and nematode community composition and univariate measures of diversity were compared with values obtained during the extraction period and with a �pre-impact situation� sampled in 1978. Although nematode density, diversity and biomass did not change two years after cessation of the exploitation, nematode community composition did and was more stable than in the extracted site. This is attributed to the absence of continuous disturbances associated with the extraction activities such as the creation and filling up of dredge furrows. As a consequence of the typical life history traits of nematodes, recovery seems to follow different pathways when compared to macrobenthic recovery from the same impact. (C) 2008 Elsevier Ltd. All rights reserved.

Abstract: Meiobenthic uptake of C-13 labelled diatom Skeletonema costatum and Prymnesiophyte Phaeocystis was investigated in permeable and fine grained depositional sediments from the Southern Bight of the North Sea at different sediment horizons. Both the diatom and Phaeocystis-derived organic matter (OM) cascaded into meiobenthic biomass in low but similar percentages and label uptake was highest at the upper cm in both stations. Phaeocystis-derived CM might be as important as diatoms as a food source for the meiobenthos. Meiobenthic biomass in the coarse sediment was lower than in the fine sediment; however label uptake per unit of organism carbon was higher. This was explained as an adaptation to an environment where only low amounts of labile OM are present. In this station, the so-called �stout nematodes� (length to width ratio 15, [Vanaverbeke, J., Soetaert, K., Vincx, M. 2004a. Changes in morphometric characteristics of nematode communities during a spring phytoplankton bloom deposition. Mar. Ecol. Prog. Set. 273,139-146]) showed lower uptake compared to the slender nematodes. Therefore their previously reported opportunistic response to a pulsed food supply must rely then on their life-history characteristics. In finer sediments Sabatieria showed the highest uptake at the 1-3 cm layer, reflecting migration to the sediment-water interface to feed on freshly deposited labile OM. Richtersia C-13 uptake was fairly low, indicating the exploitation of another carbon source than the one derived from Skeletonema costatum or Phaeocystis. Enoploides presented the highest uptake, indicating that these predacious nematodes have another food source besides meiobenthic preys. Generally total uptake was low and not nearly sufficient to meet nematode carbon requirements. (C) 2008 Elsevier B.V. All rights reserved.

Abstract: The response of benthic bacterial community composition, diversity, and biomass to phytoplankton deposition was investigated in 2 different sediment horizons at 2 contrasting sites in the southern North Sea. Differences in bacterial community composition between stations were observed. Seasonal differences in bacterial community composition were significant and were stronger in fine sediments, probably related to stronger fluctuations in food availability. Variation in community composition over the vertical sediment profile was different for both stations. In coarser sediment, the difference was mostly due to the absence of certain operational taxonomic units (OTUs) at the surface, while in fine sediment, 2 distinct communities were present. A RELATE test revealed that bacterial community composition was influenced by the amount of labile organic matter (estimated through chl a concentration in the sediment). Diversity in terms of OTU richness and Shannon-Weaver diversity index was higher in finer grained sediments. In coarser sediments, diversity at the surface layer was lower, which might be related to stronger hydrodynamic pressure at this station. These differences were not observed at the other station. Seasonal changes in diversity were not detected at either station. Bacterial biomass was slightly higher in finer sediments and was not correlated with either chl a or temperature. Seasonal differences in bacterial biomass followed those observed for community composition, while no vertical differences were detected.

Abstract: We investigated the long-term effects of sand extraction activities on the nematode communities from the Kwintebank. Although changes in nematode community composition cannot be completely uncoupled from natural processes, we suggest that the morphological changes in the sandbank and physical disturbance associated with the dredging activities indeed affected nematode community composition. Nematode diversity did not change since the start of the extraction activities but nematode community composition changed significantly. The SIMPER routine identified predatory nematodes to be important for the within group similarity at the start of the exploitation, while similarity in 1997 and 2001 was determined by the contribution of deposit feeding nematodes. In addition, long nematodes, vulnerable to physical disturbance became less important. These changes are attributed to long term changes in sediment characteristics in combination with additional short-term disturbances by the creation and filling of dredge furrows which are related to the extraction activities. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract: 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.

Abstract: The response of nematode communities to the sedimentation of a spring phytoplankton bloom in a sandy, well-oxygenated sediment at a single station (station 330) in the Southern North Sea was investigated monthly from early March to July 1999. Both structural (nematode density, diversity, vertical distribution and community composition) and functional (feeding type distributions, number of species within feeding groups) characteristics showed considerable changes shortly after the arrival of fresh organic material at the sediment surface. The general increase in numerical densities and diversity was related to changes within the groups of selective deposit-feeding and epistrate-feeding nematodes. It is hypothesised that sedimentation and subsequent remineralisation of fresh organic matter during the spring phytoplankton bloom result in an increase of suitable food items (both living and dead). This, combined with the availability of oxygen, creates conditions in which many nematode species can co-exist. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Nematode body size was investigated in terms of body length, width and length/width (LA,V) ratios, before, during and shortly after a spring phytoplankton bloom deposition in a station in the southern North Sea (20 m depth). Sediments consisted of medium sand (median grain size: 333 pm) and were devoid of mud. Redox values in the upper 6 cm of the sediment were positive (>100 mV) throughout the sampling period. During the peak of the spring phytoplankton bloom in May 1999, several small-sized species (adult length <700 mum) emerged. Most prominent was the appearance of a �stout� nematode assemblage characterised by low L/W ratios. Most of these small nematode species were virtually absent before the peak blooming, and they decreased in abundance shortly after A deposition of phytoplankton to the seafloor. This indicates the opportunistic behaviour of these nematodes, which is consistent with their small length, enabling them to reach adulthood rapidly. The net rate of increase of the stout nematodes during the bloom was estimated as 6.4% d(-1). This is much larger than the estimated net rate of 1.5% d(-1) for the total nematode community. The species composition of the stout nematode assemblage differed from similar stout assemblages described for continental slope and deep-sea areas. In the southern North Sea, Epsilonematidae were dominant while members of the Desmoscolecidae were prominent in offshore deeper areas. Possibly these differences reflect the relatively strong hydrodynamic forces at the North Sea site. In contrast with their short temporal appearance at our coastal North Sea site, stout nematodes seem to be a consistent member of deep-sea nematode communities. We hypothesise that this is caused by the quality of organic matter reaching the seafloor, together with differences in sedimentology and temperature, influencing the duration of the presence of suitable food items for these nematodes.

Abstract: Macrobenthic zonation on sandy beaches has been studied widely, whereas meiobenthic/nematofaunal species richness and zonation patterns have received little attention. We investigated community structure, intertidal zonation of nematode species and feeding structure across a macrotidal, ultra-dissipative, sandy beach (De Panne, Belgium). A total of 88 free-living marine nematode species were recorded along transects. Average nematode densities increased from the upper beach (320 +/- 45 ind/10 cm(2)) towards the low-tidal level (2784 +/- 6 ind/10 cm(2)), which corresponds well to the better-known macrobenthic patterns on sandy beaches. While macrobenthic species richness usually increases towards the low-tidal level, nematode species richness reached highest values around the mid-tidal level (34 +/- 3 sp.). This can be explained by an optimal balance between time of submergence, oxygen supply and sediment stability. Multivariate analyses indicated four different nematode assemblages that reflect the tidal zonation patterns: the upper beach, the driftline, the middle beach association and the lower beach association. The assemblages were significantly different from each other although similarities tended to increase down the beach, indicating a more gradual transition between the mid-tidal and low-tidal assemblages. Non-selective deposit feeders dominated all zones except in the driftline, where epistratum feeders were dominant. Percentage of very fine sand and percentage of shell fragments provided the best granulometric variables in determining these assemblages. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Nematode biomass spectra (NBS) for different nematode communities - subject to different forms of stress and enrichment-from the Belgian continental shelf have been constructed and analysed. These analyses showed that non-normalised NBS yield better results for comparisons of nematode assemblages than normalised NBS (in which the biomass in a weight class is divided by its corresponding weight interval) since the ecologically relevant information is retained. Normalising the spectra caused elevated biomass values and peaks to disappear, introducing bias when interpreting the distribution of biomass over spectra. Cumulative nematode biomass spectra proved to be useful in evaluating statistical differences, using the slope of the regression line of the cumulative biomass to the nominal value of a log(2)-based size class. Interpreting Pareto-type graphs and regressions was not straightforward. We suggest a combined use of both NBS and the regression approach for the analysis of NBS. NBS and cumulative NBS constructed for nematode communities from undisturbed sediments proved to be conservative: no differences in size distribution were found for communities from different locations. Physical disturbance, introduced by sand extraction, did not affect the regression slopes of cumulative NBS. However, a shift in peak biomass values towards lower size classes was observed in the regular NBS. This was attributed to an alteration of the nematode communities due to the frequent physical disturbance of the sediments. At an oxygen-stressed site, we observed a single class biomass peak, due to the presence of a single nematode species well adapted to the impoverished sediment quality. Phytoplankton sedimentation during a spring bloom corresponded to shifts in peaks in NBS due to a change in age structure of the nematode communities. Biomass values probably increased as a result of a higher food supply to the benthos.

Abstract: The spatial heterogeneity of the nematode community on an intertidal flat (the Molenplaat) in the Westerschelde estuary (SW Netherlands) has been investigated. The extent to which macroscale (km) variability was more important than microscale (m) variability was tested. In addition, the importance of vertical distribution profile in the sediment in explaining the horizontal macroscale variability was evaluated. Differences in the structure of the community were analysed at a kilometre scale at three sites that differed in chemico-physical features. The differences in geochemical and physical conditions on a horizontal scale were reflected in species composition and trophic structure of the nematode communities, and to a much lesser extent in their total abundance and species diversity. Detailed investigation of vertical depth profiles showed more pronounced differences between environmentally divergent sites. Sediment granulometry appears to be important in controlling the fauna in the upper sediment layers. At depth, similar faunal assemblages were found irrespective of sediment granulometry, suggesting that other environmental features are more dominant. Vertically, nematode species showed depth distributions that were indicative of sediment characteristics related to the site-specific hydrodynamic regime. Pronounced vertical segregation of nematode species was observed within sandy sediment under strong hydrodynamic and food-stressed conditions. A surface-dwelling nematode community of large predatory enoplids was separated from a deposit feeding xyalid-microlaimid community in deeper sediment layers (beneath 2 cm). Causal factors for this segregation are thought to be species interactions, feeding strategies and/or physical disturbance. In the finest sediments, with high silt content, almost all nematode species were confined to the upper sediment layers (1.5 cm). A sharp decline in density and diversity with depth was observed. Key factors for this distribution pattern are possibly related to the limited oxygen penetration in surface layers and the occurrence of sulphide in deeper sediment layers. At intermediate hydrodynamic and granulometric conditions, a gradual shifting of nematode community was observed with depth, with dominant nematode species maxima present at specific depth layers. (C) 2003 Elsevier Ltd. All rights reserved.

Abstract: Macrocrustaceans and juvenile demersal fish were sampled in spring of 1997 in the surf zone of an exposed sandy beach on the Belgian coast. Three consecutive 24 h cycles were sampled to investigate tidal, diurnal and semi-lunar distribution patterns within the epibenthic community. Multivariate statistical techniques and 3-way ANOVA were used to evaluate the effects of the environmental variables measured. The most important variable correlated with the variation in epibenthic catch density was the state of the tide (ebb and flood), but light intensity (day and night) was also important. The individual catch density of several species differed significantly over the three 24 h cycles. Despite the strong turbulent conditions of the site studied, clear tidal (e.g. the brown shrimp Crangon crangon, juvenile plaice Pleuronectes platessa) and diurnal (e,g. juvenile sole Solea solea and clupeids, caught mainly during the night/day respectively) periodicities of many macrocrustacean and demersal fish species were observed. Nevertheless, the extremely turbulent conditions of the surf zone possibly affect the behaviour of many species (e.g. juvenile brown shrimp are not able to bury themselves as the water retreats). To investigate whether the high dynamics of the surf zone suppress the ability of juvenile plaice to actively search for food, stomach contents were analysed. Also, the interaction with potential prey was investigated: the hyperbenthic fauna was sampled simultaneously and macrobenthic data were available from the literature, Clearly, the Belgian sandy beaches are used as a feeding ground by I-group plaice, An opportunistic utilisation of available food resources is suggested. I-group plaice migrate high up the beach during the flood tide to profit from the rich macrobenthic intertidal area, while the 0-group feeds mainly on the most abundant hyper- and macrobenthic organisms from somewhat deeper water. The presence of the 0-group in the intertidal area is possibly linked to refuge for predators or influenced by the strong surf zone currents.

Abstract: Nematode assemblages from four subtidal sandbanks belonging to different sandbank systems on the Belgian Continental Shelf were investigated both in spring and fall. The assemblages were characterised by different species composition patterns on the different sandbanks. This is in contrast to results of earlier studies which showed that neither meiobenthic nor macrobenthic taxa differed among these sandbanks. Although the sediments on these sandbanks could all be classified as medium sands, the use of Multiple Discriminant Analysis (MDA) suggested that median grain size and the proportions of median sand and very fine sand were the variables explaining the difference in nematode community composition. These findings emphasise the strong relationship between the relative abundance of nematode species and sediment composition. The influence of sand extraction on these sandbanks resulted in coarsening of the sediment, which had a direct effect on the nematode species composition. Diversity was not affected, indicating that nematodes inhabiting highly dynamic environments are well adapted to physical disturbance. The diversity at sandbanks is not necessarily very different from the surrounding areas, since in more offshore parts of the Belgian Continental Shelf, clean and rather coarse sands prevail and the differences in sediment composition are not sufficient to induce large differences in diversity. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We provide an overview of the role of biological processes in the Benthic boundary layer (BBL) and in sediments on the cycling of particulate organic material in the Goban Spur area (Northeast Atlantic). The benthic fauna, sediment and BBL characteristics were studied along a transect ranging from 208 to 4460m water depth in different seasons over 3 years. Near-bottom flow velocities are high at the upper part of the slope (1000-1500m), and high numbers of filter-feeding taxa are found there such that organic carbon normally passing this area during high flow conditions is probably trapped, accumulated, and/or remineralised by the fauna. Overall metabolism in shelf and upper slope sediments is dominated by the macrofauna. More than half of the organic matter flux is respired by macrofauna, with a lower contribution of metazoan meiofauna (4%) and anoxic and suboxic bacterial mineralisation (21%); the remainder (23%) being channelled through nanobiota and oxic bacteria. By its feeding activity and movement, the macrofauna intensely reworks the sediments on the shelf and upper slope. Mixing intensity of bulk sediment and of organic matter are of comparable magnitude. The benthos of the lower slope and abyssal depth is dominated by the microbiota, both in terms of total biomass (> 90%) and carbon respiration (about 80%). The macrofauna (16%), meiofauna (4%) and megafauna (0.5%) only marginally contribute to total carbon respiration at depths below 1400m. Because large animals have a lower share in total metabolism, mixing of organic matter within the sediments is reduced by a factor of 5, whereas mixing of bulk sediment is one to two orders of magnitude lower than on the shelf. The food quality of organic matter in the sediments in the shallowest part of the Goban Spur transect is significantly higher than in sediments in the deeper parts. The residence time of mineralisable carbon is about 120 d on the shelf and compares well with the residence time of the biota. In the deepest station, the mean residence time of mineralisable carbon is more than 3000 d, an order of magnitude higher than that of biotic biomass. (C) 2001 Published by Elsevier Science Ltd.

Abstract: The Belgian Continental Shelf (BCS) is characterized by a set of isolated subtidal sandbank systems, which greatly increase the habitat heterogeneity of the area. The meiobenthos of these sandbanks was investigated during 1997 and 1998. In total, 10 sandbanks have been sampled, belonging to three different geographically isolated systems: the Flemish Banks, the Hinder Banks and the Zeeland Banks. No obvious differences in sedimentological characteristics between the sandbanks were found, but biologically some differences could be detected. The more offshore Hinder Banks had the most diverse meiobenthos, while the Flemish Banks harboured the lowest number of meiobenthic taxa. Seasonal and regional differences in terms of densities are a result of a coupling with the primary production in the water column, with October showing highest densities and the offshore Hinder Banks harbouring lowest densities. The meiobenthos on the sandbanks was less dense (450-500 ind. 10 cm(-2)) than that in the deeper channels between the sandbanks (1250-1600 ind. 10 cm(-2)). These differences were attributed to high hydrodynamic stress around the sandbanks, preventing phytoplankton from reaching the sandbanks. Moreover, higher current speed above the sediment increases the risk for the meiobenthos of being eroded or suspended during storms. Four different communities could be identified. These did not reflect the geographical position on the BCS but seem to be influenced by local differences in sedimentological characteristics within sandbanks and sandbank systems. These sedimentological differences influenced the taxon diversity as well. Sediment preferences for less abundant taxa were investigated in several ways, and results indicated that sediments with a median grain-size were poor in terms of densities and number of taxa, while coarser sediments were richer in taxon diversity. Sediments with a median grain-size between 300-450 mum were rich both in terms of diversity and density, while sediments with a median grain-size of >450 mum still showed high diversity, but lower densities. (C) 2000 Academic Press.

Abstract: Meio- and macrofauna density and biomass were estimated at the OMEX-transect across the continental slope of the Goban Spur at water depths ranging from 208 to 4460 m in the north-east Atlantic. A linear increase in the ratio between meio- and macrofauna densities with increasing water depth was found. At the continental shelf meiofauna densities were similar to 50 times higher than macrofauna densities, whereas in the abyss meiofauna densities were more than 1000 times higher. This change in ratio was due to a significant decrease in macrofauna densities with increasing water depth, whereas the meiofauna densities staved more or less at the same level. The ratio in biomass between meio- and macrofauna showed a dip at similar to 1000 m. At this depth macrofauna biomass was similar to 55 times higher than meiofauna biomass, whereas at similar to 4500m macrofauna biomass was only about three times higher. Macrofauna biomass was high at similar to 1000 m, due to the high mean individual weight of the macrofauna, whereas meiofauna biomass and mean individual weight were low at this depth. Meiofauna consisted of similar to 90% nematodes. Within the macrofaunal fraction (>0.5mm) a linear increase in the ratio between nematodes and macrofauna sensu stricto with depth was found. At the deepest station similar to 20% of the macrofaunal fraction were nematodes, at the shallowest station only similar to 2%. Thus, large nematodes became relatively more important with increasing water depth. Within the macrofauna a decrease in the abundance of filter- and surface deposit-feeders relative to the subsurface deposit-feeders with increasing water depth was observed, which may be related to a change in food input. As no decrease in mean individual weight with increasing water depth within either group could be observed, the change in meio:macrofauna ratios along the OMEX-transect merely reflects a change in taxonomic (functional) composition, rather than a change in size.

Abstract: 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 df 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 dan 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. (C) 1997 Elsevier Science Ltd.

Abstract: The meiobenthos along a depth transect of oligotrophic sediments in the Arctic Laptev Sea was studied. The meiobenthos followed the general trends reported from other studies: densities decreased with depth in relation to the more limited supply of degradable organic matter at greater depths. Although the sediments along the transect were poor in organic matter in comparison with the NE Atlantic, the densities fitted well with the meiobenthic densities reported from the latter area. It is suggested that the meiobenthos in the cold polar waters is adapted to this extreme environment by a rapid response to short food pulses to the sediments. Nematodes were identified up to genus level and assigned to trophic groups. A total of 32 families comprising 95 genera were found along the transect. The communities were dominated by deposit feeders whose importance increased with depth. Both TWINSPAN and CCA analyses revealed a community shift along the depth transect: a shelf community dominated by Microlaimus and Chromadora could be distinguished from a slope community dominated by Monhystera and Leptolaimus. Generic diversity decreased with depth.

Abstract: The metazoan meiobenthos along the continental slope of the Goban Spur (NE Atlantic) was studied in the framework of the OMEX-programme (EC-MAST II). Meiobenthic densities, the vertical distribution of the meiobenthos in the sediment, and the biomass and generic composition of the dominant group, the nematodes, were investigated at different water depths. The meiobenthic communities along the depth gradient of the continental slope followed the usual trends: the communities were dominated by nematodes, and meiobenthic densities, total nematode biomass, and mean individual nematode weight decreased with increasing water depth. The shelf station had significantly higher densities, rematode biomass and mean individual weight than the deeper stations. The nematode communities along the OMEX slope were divided into a �shelf break� community (206 m) and a �down slope� community (1034-2760 m), with the station at 670 m depth as a transition station. It is suggested that the changes in the nematode community composition along the slope of the Goban Spur are related to the amount of oxygen (and the presence/absence of an oxic mineralisation pathway) in the sediment. The meiobenthos tended to be more concentrated towards the sediment surface with increasing water depth.