Meiofaunal colonization of azoic estuarine sediment in Louisiana: Mechanisms of dispersal1

Two mechanisms of muddy-bottom meiofaunal dispersal, waterborne suspended transport and holobenthic infaunal immigration, were compared as to their rate and effectiveness in mediating community reestablishment after small-scale defaunation. Colonizing meiofauna were quantitatively sampled in winter and summer from 16 replicates of two azoic sediment chamber designs on 2 and 29 days postplacement. The chambers were ≈ 3750 cm³; one design allowed colonization via suspended movement through an open top, while the other design permitted entry only by infaunal crawling through subsurface open sides. After 48 h, mean harpacticoid copepod and naupliar densities in sediment chambers open to colonization exclusively by meiofauna in suspended transport were not significantly different from background sediment densities. Sediment chambers allowing colonization exclusively via infaunal immigration through the sediment, however, contained copepod and naupliar densities that were significantly less than densities in background sediments and suspension-colonized chambers. In contrast, nematode densities in both suspension- and infaunally colonized chambers were significantly less than in background sediments, but densities were not significantly different between the chamber treatments. Thus for a small-scale defaunation, copepods most rapidly and completely recolonize sediments via suspended transport. Nematode dispersal occurs equally well via suspended or infaunal movement; however nematodes never seemed to utilize the chambers fully because densities did not reach background levels even after 29 days.     

Field manipulations of tidal flushing,light exposure and natant macrofauna in a Louisiana salt marsh: Effects on the meiofauna

Field manipulative experiments were used to investigate some of the potential regulating factors of the meiofauna of a Louisiana salt marsh. Effects of various combinations of marsh grass clipping, exclusion of natant macrofauna, and tidal flushing on nematode, polychaete, and copepod density, as well as copepod species composition, were determined. Edaphic chlorophyll a was measured simultaneously. Grass clipping consistently affected the meiobenthic copepod assemblage; diversity and evenness dropped by Day 29 when Nitocra lacustris (Schmankevitsch) became dominant. Nematode density relative to controls was lower by Day 29 in clipped plots. N. lacustris abundance increased relative to controls in clipped plots enclosed by a solid Plexiglas box. Nematode density was negatively correlated with chlorophyll a content. No simple explanation of these patterns is possible; concomitant changes in microflora coupled with associated changes in the physical/biological environment of meiofauna must be responsible. Exclusion of only natant macrofauna (fish, shrimp, crabs) had no influence on meiofauna contrary to findings in other marshes. Dense grass cover and short, irregular tidal inundation may normally restrict intertidal grazing in Louisiana marshes.     

Community structure and functional roles of meiofauna in the North Sea

Knowiedge on community structure of North Sea meiofauna has greatly increased recently. A quasisynoptic picture of meiofauna densities and copepod community structure from 171 stations of the southern North Sea, sampled in April–May 1986, has been obtained during the North Sea Benthos Survey. Latitudinal patterns in meiofauna abundance and copepod weight, abundance and diversity exist in an area between 51°30′N and 58°30′N. Using TWINSPAN-classification five major groups of copepod species can be recognized which are related to sediment type, latitude and depth. The part of the meiofauna in total benthic energy flow, their role in the benthic food web and in biogeochemical cycles is discussed based on existing literature. There are still considerable gaps in knowledge and the field is not progressing rapidly. Publication no. 599 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

Diel and seasonal vertical distribution of meiobenthic copepods in muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay)

The vertical distribution of meiobenthic copepods was investigated within muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay, France). The aim of the study was to determine if in muddy sediments, as previously established in sandy sediments, meiobenthic copepods migrate vertically according to the seasons or diel periods. Two experimental approaches were used, viz: a three-season comparison was made of the diel vertical distribution of the harpacticoid Canuella perplexa T. & A. Scott (1893) and secondly the depth distribution of a meiobenthic copepod assemblage was followed for a 24 h period, in shallow water subtidal locations. The harpacticoid C. perplexa vertically migrated through the top three centimeters of the sediment, showing diel and seasonal variations in depth distribution. The differential vertical distributions shown by the dominant meiobenthic populations suggest that emergence into the water column may mainly concern surface dwelling copepods. The physical and biological factors affecting seasonal and diel changes in the copepod assemblage of the fish ponds are discussed.     

Abundance and colonization potential of artificial hard substrate-associated meiofauna

Meiofauna are known to live on hard substrates in association with periphytic and epiphytic algae and attached epibiota; however, the abundance, diversity and colonizing abilities of hard-substrate meiofauna have been poorly documented. We quantified meiofauna living on microalgal-covered pilings associated with a wood pier in a shallow (<2 m deep) estuarine embayment with the use of a suction sampler, and compared colonization of pier-piling and sediment-dwelling meiofauna onto collectors that capture suspended meiofauna from the water column. Collectors were small mesh pads (159 cm³) suspended at mid-water depth, and their size and structural complexity were similar to floating or drifting masses of macroalgae that may be colonized by meiofauna. Sediment was collected by coring, and copepod (to species) and nematode (to genera) colonists on mesh pads were compared with pier-piling and sediment communities. Abundance of total meiofauna averaged 124±13.6 (S.E.) on pier pilings, compared to 2092±274.6 individuals 10 cm⁻² in surrounding sediment. Phytal copepods (free-living copepods with prehensile first legs and dorsoventrally and laterally compressed body forms) and copepod nauplii dominated pier-piling collections, but nematodes were dominant on faunal collectors and in sediment. Phytal copepods also were abundant on faunal collectors but were rare in sediments. Copepod and nematode diversities were similar, but species composition was largely nonoverlapping, in pier pilings and sediments. Net recruitment of meiofauna to faunal collectors averaged about 900 individuals collector⁻¹ day⁻¹ during the 1-week experiment. Nematode and copepod colonists on faunal collectors were both much more similar to pier-piling than to sediment assemblages. These data suggest that meiofauna are abundant and diverse on algal-covered pier pilings, and they may become more important to marine ecology as artificial hard substrates increase with increasing urbanization. Furthermore, pier-piling meiofauna appear to readily migrate into the water column and probably contribute to a rapidly dispersing pool of meiofauna in estuaries.     

Tube-dwelling Meiofauna in Marine Sediments

Tube-dwelling has been recognized previously as a life-style for several meiobenthic species, but behavioural observation of living specimens has rarely been reported. The extent to which tube-building and tube-dwelling occurs within meiofauna, and how they have influenced evolutionary and ecological processes as well as morphology within these organisms, is relatively unknown but potentially of great significance. In addition to direct observation of tube-building and the occurence of tubes in natural habitats, the internal anatomy associated with tube-building in two nematode species (Ptycholaimellus jacobi, P. ponticus) and one harpacticoid copepod species (Stenhelia palustris) is the focus of this study. Special attention is given to the secretory products, glands, and their association with secretory pores. Also, the role of meiobenthic tube-dwelling activities in relationship to their environment is extensive discussed.     

Effects of leaf litter addition on meiofaunal colonization of azoic sediments in a subtropical mangrove in Hong Kong

The responses of major meiofaunal taxa and nematode species assemblage to the decaying leaf litter of the mangrove Kandelia candel were investigated through a field colonization experiment in subtropical Hong Kong. Sixty-four replicate azoic and organic-free sediment cores were treated with leaf litter additions of 0x, 0.5x, 1x and 2x natural sediment organic concentration, respectively, and retrieved 1, 10, 30 and 60 days post-placement. Replicate cores of ambient sediment were also taken at each sampling date to provide baseline information. Results of ANOVAs suggested that either different meiofaunal taxa responded to the leaf litter in different ways or the response of the same taxon changed over decomposition time. Multivariate ordination performed on nematodes revealed an alteration in community structure after 10, 30 and 60 days between controls and treatments. This alteration was attributed to some deposit feeding nematodes, particularly a bacterivorous species, Diplolaimella sp., which bloomed in all the cores treated with leaf litter, testifying to the important role such meiofauna plays in the process of detritus decomposition.     

Diversity and community structure of harpacticoid copepods associated with cold-water coral substrates in the Porcupine Seabight (North-East Atlantic)

The influence of microhabitat type on the diversity and community structure of the harpacticoid copepod fauna associated with a cold-water coral degradation zone was investigated in the Porcupine Seabight (North-East Atlantic). Three substrate types were distinguished: dead fragments of the cold-water coral Lophelia pertusa, skeletons of the glass sponge Aphrocallistes bocagei and the underlying sediment. At the family level, it appears that coral fragments and underlying sediment do not harbour distinctly different assemblages, with Ectinosomatidae, Ameiridae, Pseudotachidiidae, Argestidae and Miraciidae as most abundant. Conclusions on assemblage structure and diversity of the sponge skeletons are limited as only two samples were available. Similarity analysis at species level showed a strong variation in the sediment samples, which did not harbour a distinctly different assemblage in opposition to the coral and sponge samples. Several factors (sediment infill on the hard substrates, mobility of the copepods, limited sample sizes) are proposed to explain this apparent lack of a distinct difference between the microhabitats. Coral fragments and sediment were both characterised by high species diversity and low species dominance, which might indicate that copepod diversity is not substantially influenced by hydrodynamical stress. The additive partitioning of species diversity showed that by adding locations species richness was greatly enhanced. The harpacticoid community in the cold-water coral degradation zone is highly diverse and includes 157 species, 62 genera and 19 families. Information from neighbouring soft-bottom regions is necessary to assess whether total species diversity is increased by the presence of these complex habitat-providing substrates.     

Effects of flow on meiofauna colonization in artificial streams and reference sites within the Illinois River, Arkansas

Despite frequent disturbances from flow, stream meiofauna form diverse and abundant assemblages suggesting that they are resistant and/or resilient to flow disturbances. Stream flow profoundly influences benthic invertebrate communities but these effects remain poorly understood. We examined the influence of flow on meiofauna colonization at small spatial scales (2–3 m) using artificial streams in conjunction with similar sites (flow, depth, substrates) in the reference stream (Illinois River, Arkansas). Colonization of meiofauna was found to be rapid and generally increased with flow rates examined (1–2, 6–7, and 11–12 cm s⁻¹). Six of the 10 most abundant taxa successfully completed colonization in artificial channels (equaled or exceeded reference benthic densities) within 5 days. Benthic meiofauna were more abundant in fast flows in artificial channels and in fast and slow flows in reference stream sites. A diverse assemblage of meiofauna was collected from the plankton which was dominated by rotifers, copepods (mostly nauplii), dipterans, and cladocerans. Densities of drifting meiofauna (potential colonists of the benthos) were low (5 no. l⁻¹) and similar among artificial channels and reference sites regardless of flow rates (F _1,18 = 2.19, p = 0.1407). Although densities were low, the numbers of drifting meiofauna were more than sufficient to colonize the benthos. Less than 0.65% of the drifting meiofauna were needed to colonize the substrates of artificial streams. The benthic assemblage paralleled that of the plankton, consisting mainly of rotifers, copepods (mainly nauplii), and dipterans. Evidence for active control over dispersal was observed as meiofauna densities varied between the plankton and benthos over the diel cycle (F _1,18 = 6.02, p = 0.0001 and F _1,18 = 9.88, p = 0.006, respectively). Rotifers, copepods, and nematodes were more abundant in the plankton during the day and in the substrates at night. These results suggest that meiofauna assemblages can change rapidly in response to alterations of habitat patches by disturbance.     

Quantitative distribution of meiobenthos and the structure of the free-living nematode community of the mangrove intertidal zone in Nha Trang bay (Vietnam) in the South China Sea

Meiobenthic studies were performed in an intertidal area in the Be River estuary (Nha Trang Bay, Vietnam). The study area is an area of riverine-type mangroves that have been heavily damaged by human impacts, including timber cutting and waste. Three biotopes are situated in the middle intertidal zone: a fringe of Rhizophora stylosa, a bush area composed of Avicennia aff. alba behind it, and muddy sand with fiddler crabs (Uca spp.), which is free of mangrove plants. Three replicate samples of meiobenthos were collected in each biotope and each sample was subdivided into two layers: 0–1 and 1–4 cm. The abundance of metazoan meiobenthos varied from 735 specimens/10 cm² in the Uca spp. biotope to 244 specimens/10 cm² beneath the Rhizophora trees. Six taxonomic groups of high rank were found among the meiofauna: Nematoda, Copepoda (Harpacticoida), Oligochaeta, Turbellaria, Kinorhyncha, and Foraminifera (Allogromiida). The spatial variability of meiobenthos and its key taxa was estimated and the spatial distribution patterns of free-living nematode species were described. About 90% of the total meiobenthos inhabited the upper 0–1 cm of the sediments. Nematodes constituted 90–95% of all meiobenthic organisms in the samples. A total of 48 species of free-living nematodes were found in the investigated mangrove intertidal area. In terms of species composition and set of dominants, the nematode community is comprised of three local assemblages: one of them inhabits the uppermost centimeter in the Uca and Avicennia biocenoses; the second assemblage occupies the upper sediment layer in the Rhizophora stand; a less abundant but specific assemblage of several nematode species occurs in the subsurface sediments at all three sites.     

Effects of paint-derived tributyltin on structure of estuarine nematode assemblages in experimental microcosms

A microcosm experiment was designed to evaluate the effects of different levels of paint-derived tributyltin (TBT), and different modes of exposure, on the diversity, feeding mode and assemblage structure of estuarine nematodes. Estuarine meiofauna were exposed to two types of treatments (mixture and deposit), containing uncontaminated sediment and sediment spiked with paint-derived TBT at 1 and 10 mg kg⁻¹ for a duration of 4 and 8 weeks. In the mixture treatments, meiofauna assemblages were incubated in clean and contaminated sediments. In the deposit treatments meiofauna assemblages were exposed to the deposition of clean and contaminated sediments simulating the disposal of TBT-contaminated dredged material at sea. Effects of TBT on nematode species are likely to occur by (a) the uptake of leached TBT from the sediment pore water through their permeable cuticle, resulting in decreased diversity and increased changes in assemblage structure with increasing levels of TBT contamination, and (b) direct ingestion of paint-particles with food, resulting in a significant decline of nonselective deposit feeders in contaminated sediments. The numbers of many species differed greatly between mixture and deposit treatments. Results from multivariate analyses showed an immediate and dominant effect of burial on most nematode species in the deposit treatments compared to the longer-term effect of TBT contamination. The survival rates of nematode species in the top layer of these sediments depended on their ability to withstand TBT contamination as well as their potential to migrate, survive and reproduce in the deposit. This study unambiguously showed that the response of nematode species depended not only on the level of TBT contamination but also on the duration and mode of exposure to contaminated sediment, which should be taken into account when assessing the effects of TBT on aquatic communities.     

Harpacticoid copepods associated with the seagrass Halophila ovalis in the Ashtamudi Estuary,south-west coast of India

A temporal study of harpacticoid copepod populations associated with the seagrass Halophila ovalis was undertaken in the Ashtamudi Estuary, south-west coast of India. A total of 19 species representing 8 families was recorded in this assemblage. Harpacticoids formed 7.52% of the total phytal meiofauna. At the species level, harpacticoids exhibit parallel assemblages with phytal zones, found in other localities.     

Post-release survival of oiled, cleaned seabirds in North America

The number of days between ringing and recovery of oiled, cleaned and released seabirds was extremely low, usually a matter of a few days or weeks, and for three species was 5–100 times lower than for non-oiled birds. For oiled, cleaned Guillemots Una aalge , postrelease life expectancy was 9.6 days and long-term recovery rates were 10–20% of those of non-oiled birds. Measures of survival were not greater for oiled birds treated in recent years with modern methods. The cost and effectiveness of rehabilitation efforts for oiled seabirds need to be reexamined in the light of results showing low post-release survival.     

Experimental investigations of benthic reentry by migrating meiobenthic copepods

The resettlement behavior of meiobenthic copepods, which actively migrated from sediments in a seagrass bed, was investigated in a shallow subtidal area in Tampa Bay, Florida, U.S.A. Experimental studies were conducted to determine whether meiobenthic copepods after emerging from sediments at sunset reenter the sedimentary substratum or select other subhabitats, water and seagrass blades. Migrating copepods were collected with emergence traps and transferred to experimental aquaria in the field which contained sediment, seagrass-blade and water treatments. Settlement into each type of treatment was measured in separate 2-h and 9-h experiments. Differences in densities of copepod taxa retrieved from emergence traps and introduced into experimental aquaria were recorded as were differing relative proportions of each copepod species returning to the substratum treatments. Settlement patterns of total copepods and three dominant copepod species, Zausodes arenicolus, Halicyclops sp. and Robertsonia hamata, departed from those expected by chance. The populations of R. hamata and Halicyclops sp. which settled were generally skewed towards males and a close matching of males and copepodites within treatment dishes was evident. Similar to nighttime-emergence patterns, timing and magnitude of postmigration reentry differs among copepod taxa and such reentry may be linked to reproductive events. Complex behavioral processes previously noted for fish and macrofaunal organisms in seagrass beds may also be important in recruitment and reassortment of meiobenthic copepods.     

Composition,distribution and biomass of meiobenthos in the Oosterschelde estuary (SW Netherlands)

Meiofauna composition, abundance, biomass, distribution and diversity were investigated for 31 stations in summer. The sampling covered the whole Oosterschelde and comparisons between the subtidal — intertidal and between the western-central — eastern compartment were made.Meiofauna had a community density ranging between 200 and 17 500 ind 10 cm^–2, corresponding to a dry weight of 0.2 and 8.4 gm^–2. Abundance ranged between 130 and 17 200 ind 10 cm^–2 for nematodes and between 10 and 1600 ind 10 cm^–2 for copepods. Dry weight biomass of these taxa was between 0.5–7.0 gm^–2 and 0.008–0.3 gm^–2 for nematodes and copepods respectively.The meiofauna was strongly dominated by the nematodes (36–99%), who's abundance, biomass and diversity were significantly higher intertidally than subtidally and significantly higher in the eastern part than in the western part. High numbers were positively correlated with the percentage silt and negatively with the median grain size of the sand fraction. The abundance and diversity of the copepods were highest in the subtidal, but their biomass showed an inverse trend being highest on the tidal flats.The taxa diversity of the meiofauna community and species diversity of both the nematodes and the copepods were higher in subtidal stations than on tidal flats. In the subtidal, the meiofauna and copepod diversity decreased from west to east, whereas nematode diversity increased.The vertical profile clearly reflected the sediment characteristics and could be explained by local hydrodynamic conditions.Seasonal variation was pronounced for the different taxa with peak abundance in spring, summer or autumn and minimum abundance in winter.Changes in tidal amplitude and current velocity enhanced by the storm-surge barrier will alter the meiofauna community structure. As a result meiofauna will become more important in terms of density and biomass, mainly due to increasing numbers of nematodes, increasing bioturbation, nutrient mineralisation and sustaining bacterial growth. A general decrease in meiofauna diversity is predicted. The number of copepods is expected to decrease and interstitial species will be replaced by epibenthic species, the latter being more important in terms of biomass and as food for the epibenthic macrofauna and fishes.     

The importance of turbellarians in the marine meiobenthos: a review

Recent data and opinions on meiofaunal ecology are briefly reviewed; and from scattered data, the place of turbellarians in the meiobenthic community is discussed. Turbellarian diversity, density, and biomass are higher in sandy habitats than in muddy bottoms. In sand, turbellarian diversity is of the same magnitude as that of other important meiofaunal taxa, while densities range between 7–25% of the total meiofauna. Mean individual turbellarian dry weight seems to be four times that of nematodes and in sandy habitats turbellarian biomass may be equal to or excede that of nematodes. Most turbellarian species may be considered as predators and in this respect may take the place occupied by macrofaunal species in muddy sediments. mens.

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Meiobenthos of hypersaline tropical mangrove sediment in relation to spring tide inundation

Tropical intertidal sediments often contain porewater of relatively high salinity, especially in areas exposed to longer periods without seawater inundation and high evaporation. Such an area exists on the west coast of Zanzibar: a high intertidal mangrove plateau, flooded only during spring high tides, with sediment porewater salinities commonly exceeding 100 ppt. A field survey was conducted in this area to examine variations in population density of major meiofaunal taxa and the assemblage structure of free-living marine nematodes during spring-neap tidal cycles. Samples were taken on seven occasions for two months, starting from the end of the rainy season. Porewater salinity remained high throughout the sampling period, ranging from 89 to 160 ppt. Neither spring tide inundation nor heavy rains lowered the salinity markedly. The meiofauna consisted only of four taxa, present on all sampling occasions: nematodes, harpacticoid copepods, plathyhelminthes and chironomids. Densities in surface sediments (0–5 cm) were low compared to other mangrove areas, ranging from 271 to 656 animals 10 cm^-2 with nematodes dominant on all sampling occasions (58–87%). Density fluctuations could not be explained by the effects of spring tide inundation, but the meiofauna showed significant correlations with grain size and organic material. Despite the wide range of salinity, only the numbers of chironomids were negatively correlated with increased salinity. Nematode species diversity was low in all samples, although altogether 28 species were recorded in the samples. Four species occurred in more than 50% of the samples (Microlaimus sp. (100%), Metalinhomoeus sp. (76%), Daptonema sp.l (56%), Chromadorina sp. (56%)) while 12 species were found only in one or two samples. Multidimensional scaling ordination (MDS) of the nematode species abundance data indicated little effects of spring tide inundation on the assemblage structure, but rather a successive change from wet to dry season with a reduction in species diversity and increased numbers of the dominant nematode species Microlaimus sp.     

On the Vertical Distribution of the Metazoan Meiofauna in Shelf Break and Upper Slope Habitats of the NE Atlantic

The metazoan meiofauna of nine stations in shelf break and upper slope areas (70 to 1500 m water depth) of the N.E. Atlantic were investigated in order to assess which environmental factors are important in the control of densities and sediment profiles. Total meiofaunal densities (ranging between 368 and 1523 ind/10 cm²) were correlated with bacterial densities, an important food source for meiofauna. However, considering sediment vertical distribution profiles, the relative importance of both food and oxygen on the meiofauna became obvious. A combination of both bacterial densities and oxygen supply could explain about 95% of the variability in the vertical profiles of the meiofauna densities. Meiofauna numbers increase in proportion to food availability in the surface sediment layers, but this relationship breaks down in deeper sediment layers where the oxygen supply is often limiting, particularly in fine sediments.     

Mussel beds — amensalism or amelioration for intertidal fauna?

The faunal assemblages of a mussel bed (Mytilus edulis L.) and ambient sandflat were compared to study how a bioherm of suspension feeding organisms affects benthic communities in a tidal flat. During a survey of mussel beds in the Wadden Sea at the island of Sylt (North Sea), a total of 52 macrofaunal species and 44 meiobenthic plathelminth species were detected. They occupied different microhabitats in the mussel bed. 56% of the macrofauna species were dwelling in the sediment beneath the mussels and 42% were epibenthic or epiphytic. The latter were restricted in their occurrence to the mussel bed. Along a transect from the sandflat to the mussel bed the mean species densities of macrofauna did not differ significantly, while abundances were significantly lower in the mussel bed than in the sandflat. The composition of the assemblages shifted from a dominance of Polychaeta in the sandflat to Oligochaeta in the mussel bed. Surface filter-feeding polychaetes of the sandflat (Tharyx marioni) were displaced by deposit feeding polychaetes under the mussel cover (Capitella capitata, Heteromastus filiformis). The total meiobenthic density was lower and single taxa (Ostracoda, Plathelminthes, Nematoda) were significantly less abundant in the mud of the mussel bed. The plathelminth assemblage was dominated by grazing species (Archaphanostoma agile), and differed in community structure from a sandflat aseemblage. An amensalistic relationship was found between the suspension-feeding mussels and suspension-feeding infauna, while deposit-feeders were enhanced. The presence of epibenthic microhabitats results in a variety of trophic groups co-occurring in a mussel bed. This is hypothesized as trophic group amelioration and described as an attribute of heterotrophic reefs.     

Effects of organic enrichment on meiofaunal abundance and community structure in sublittoral soft sediments

In experimental mesocosms established at Solbergstrand, Oslofjord, Norway, organic enrichment was effected by the addition of powdered Ascophyllum nodosum (L.) Le Jol., in quantities equivalent to 50gC·m^?2 and 200gC·m^?2, to boxes of sublittoral soft sediment. After 56 days, the structure of the meiofaunal communities in these treatments was compared with that of the control boxes. At this time the meiofaunal communites at each level of organic enrichment were markedly different from each other and from that in the control sediment. The responses of the two major components of the meiofauna, however, were different. Although the abundance of nematodes was slightly reduced in the high dose treatment this was not accompanied by detectable changes in community structure. Harpacticoid copepods, on the other hand, increased significantly in abundance in the treatment boxes and showed a general trend towards increased dominance and decreased diversity with increasing levels of organic enrichment, although in the low dose treatment there was also an increase in the number of species present. It is also shown that the nematode/copepod ratio is unreliable as a biomonitoring tool and it is suggested that the differential responses in community structure between the nematode and copepod components of the meiofauna might be a better indication of stress at the community level.