Meiofaunal Abundance Research Articles

Colonization and development of stream communities across a 200-year gradient in Glacier Bay National Park, Alaska, U.S.A.

In May 1997, physical and biological variables were studied in 16 streams of different ages and contrasting stages of development following glacial recession in Glacier Bay National Park, southeast Alaska. The number of microcrustacean and macroinvertebrate taxa and juvenile fish abundance and diversity were significantly greater in older streams. Microcrustacean diversity was related to the amount of instream wood and percent pool habitat, while the number of macroinvertebrate taxa was related to bed stability, amount of instream wood, and percent pool habitat. The percent contribution of Ephemeroptera to stream benthic communities increased significantly with stream age and the amount of coarse benthic organic matter. Juvenile Dolly Varden (Salvelinus malma) were dominant in the younger streams, but juvenile coho salmon (Oncorhynchus kisutch) abundance was greater in older streams associated with increased pool habitat. Upstream lakes significantly influenced channel stability, percent Chironomidae, total macroinvertebrate and meiofaunal abundance, and percent fish cover. Stable isotope analyses indicated nitrogen enrichment from marine sources in macroinvertebrates and juvenile fish in older streams with established salmon runs. The findings are encapsulated in a conceptual summary of stream development that proposes stream assemblages to be determined by direct interactions with the terrestrial, marine, and lake ecosystems.

Colonization and development of stream communities across a 200-year gradient in Glacier Bay National Park, Alaska, U.S.A.

In May 1997, physical and biological variables were studied in 16 streams of different ages and contrasting stages of development following glacial recession in Glacier Bay National Park, southeast Alaska. The number of microcrustacean and macroinvertebrate taxa and juvenile fish abundance and diversity were significantly greater in older streams. Microcrustacean diversity was related to the amount of instream wood and percent pool habitat, while the number of macroinvertebrate taxa was related to bed stability, amount of instream wood, and percent pool habitat. The percent contribution of Ephemeroptera to stream benthic communities increased significantly with stream age and the amount of coarse benthic organic matter. Juvenile Dolly Varden (Salvelinus malma) were dominant in the younger streams, but juvenile coho salmon (Oncorhynchus kisutch) abundance was greater in older streams associated with increased pool habitat. Upstream lakes significantly influenced channel stability, percent Chironomidae, total macroinvertebrate and meiofaunal abundance, and percent fish cover. Stable isotope analyses indicated nitrogen enrichment from marine sources in macroinvertebrates and juvenile fish in older streams with established salmon runs. The findings are encapsulated in a conceptual summary of stream development that proposes stream assemblages to be determined by direct interactions with the terrestrial, marine, and lake ecosystems.

Response of benthic organisms to seasonal change of organic matter deposition in the bathyal Sagami Bay, central Japan

An interdisciplinary research project was carried out to understand seasonal carbon cycling in a deep-sea ecosystem in Sagami Bay, central Japan. Temporal changes in the chloroplastic pigment (CPE) concentration in the sediment, as well as the abundance, the biomass and the metabolic activity of benthic organisms were studied. CPE was detectable throughout the year, and its amount increased in the spring when a fluffy layer was observed on the surface of the sediment. Significant seasonal fluctuation of bacterial abundance was found, but the range was small, the maximal value being only 1.6 times larger than the minimal one. Metabolic activity did not show significant temporal difference. The abundance and biomass of metazoan meiofauna seemed to fluctuate seasonally, but ANOVA did not confirm it statistically. Our results suggest that if enough organic matter is supplied constantly, the deep-sea benthic community will be stable even though seasonality of organic matter flux associated with the spring bloom exists. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS seasonal change / meiobenthic abundance / bacterial abundance / metabolic activity / chloroplastic pigment concentration

Metazoan meiofauna of the deep Arabian Sea: standing stocks, size spectra and regional variability in relation to monsoon induced enhanced sedimentation regimes of particulate organic matter

Effects of monsoon-induced enhanced depositional regimes of particulate organic carbon (POC) on regional variability and distribution patterns and size spectra of metazoan meiofauna, particularly of nematodes, were investigated at five sites 3158–4414 m deep in the Arabian Sea. The sampling sites were subjected to different flux rates of POC. Total meiofaunal abundance ranged from 109 to 320 ind./10 cm 2. Nematodes were the numerically most abundant taxon, with a relative abundance of 82.5–88.7%, followed by copepods and ostracods. Mean individual nematode biomass ranged from 0.0272 to 0.1033 μgC, and Mean nematode population biomass varied between 0.0026 and 0.0133 mgC/10 cm 2. Mean nematode lengths ranged from 614.2 to 832.6 μm. The length distributions of nematodes at the different sites were typically skewed with the distributions extending into the longer size classes. At the sites with higher POC deposition rates, nematodes displayed deeper distributions in the sediment column (47.4–58.5% of nematodes in the top 1 cm layer of the sediment) in contrast to very shallow distributions at a site of low POC flux (75.1% of nematodes in the top 1 cm of the sediment). Regional variability of nematode biomass, size and vertical distribution was related to monsoon-driven gradients of POC- and chlorophyll a (chl. a) flux rates and bacterial biomass i.e. bioavailable organic carbon. This was in contrast to nematode abundance which did not correlate significantly with any of these environmental parameters. The differential pattern between biomass and abundance, distribution might be related to POC-dependent alterations in the species composition of the nematode assemblages at the different sites. The hypothesis of increased meiobenthic stocks due to monsoon-induced enhanced sedimentation could not be confirmed compared to data from other less productive oceanic regions. Nematode abundance and biomass in the Arabian Sea were similar to values obtained from the abyssal temperate NE-Atlantic.

Integrated abundance and biomass of sympagic meiofauna in Arctic and Antarctic pack ice

The abundance and biomass of sympagic meiofauna were studied during three cruises to the Antarctic and one summer expedition to the central Arctic Ocean. Ice samples were collected by ice coring and algal pigment concentrations and meiofauna abundances were determined for entire cores. Median meiofauna abundances for the expeditions ranged from 4.4 to 139.5 × 103 organisms m−2 in Antarctic sea ice and accounted for 40.6 × 103 organisms m−2 in Arctic multi-year sea ice. While most taxa (ciliates, foraminifers, turbellarians, crustaceans) were common in both Arctic and Antarctic sea ice, nematodes and rotifers occurred only in the Arctic. Based on the calculated biomass, the potential meiofauna ingestion rates were determined by applying an allometric model. For both hemispheres, daily and yearly potential ingestion rates were below the production values of the ice algal communities, pointing towards non-limited feeding conditions for ice meiofauna year-round.

Role of meiofauna in estuarine soft‐bottom habitats*

Meiofauna are ubiquitous in estuaries worldwide averaging 106 m−2. Abundance and species composition are controlled primarily by three physical factors: sediment particle size, temperature and salinity. While meiofauna are integral parts of estuarine food webs, the evidence that they are biologically controlled is equivocal. Top down (predation) control clearly does not regulate meiofaunal assemblages. Meiofauna reproduce so rapidly and are so abundant that predators cannot significantly reduce population size. Food quantity (bottom up control) also does not appear to limit meiofaunal abundance; there is little data on the effect of food quality. In estuarine sediments meiofauna: (i) facilitate biomineralization of organic matter and enhance nutrient regeneration; (ii) serve as food for a variety of higher trophic levels; and (iii) exhibit high sensitivity to anthropogenic inputs, making them excellent sentinels of estuarine pollution. Generally mineralization of organic matter is enhanced and bacterial production stimulated in the presence of meiofauna. Tannins from mangrove detritus in northern Queensland appear to inhibit meiofaunal abundance and therefore the role of meiofauna in breakdown of the leaves. Meiofauna, particularly copepods, are known foods for a variety of predators especially juvenile fish and the meiofaunal copepods are high in the essential fatty acids required by fish. The copepod’s fatty acid composition is like that of the microphytobenthos they eat; bacterial eaters (nematodes?) do not have the essential fatty acids necessary for fish. Most contaminants in estuaries reside in sediments, and meiofauna are intimately associated with sediments over their entire life‐cycle, thus they are increasingly being used as pollution sentinels. Australian estuarine meiofauna research has been concentrated in Queensland, the Hunter River estuarine system in New South Wales, and Victoria’s coastal lagoons. Studies in northern Queensland have primarily concentrated on the role of nematodes in mineralization of organic matter, whereas those from southern Queensland have concentrated on the role of meiofauna as food for fish and as bacterial grazers. The New South Wales studies have concentrated on the Hunter River estuary and on the structure and function of marine nematode communities. In Victoria, several fish have been shown to eat meiofauna. The Australian world of meiofaunal research has hardly been touched; there are innumerable opportunities for meiofaunal studies. In contaminated estuarine sediments reduced trophic coupling between meiofauna and juvenile fish is a basic ecological question of habitat suitability, but also a question with relevance to management of estuarine resources. Because meiofauna have short lifecycles, the effects of a contaminant on the entire life‐history can be assessed within a relatively short time. The use of modern molecular biology techniques to assess genetic diversity of meiofauna in contaminated vs uncontaminated sediments is a promising avenue for future research. Much of the important meiofaunal functions take place in very muddy substrata; thus, it is imperative to retain mudflats in estuaries.

Meiofauna distribution and mesoscale variability in two sites of the Ross Sea (Antarctica) with contrasting food supply

Meiofauna abundance, biomass and community structure were investigated in two comparable deep sites of the Ross Sea (Antarctica) characterized by different trophic and sediment characteristics. Site B (567 m depth, dominated by muddy sediments) and site C (439 m depth, characterized by the presence of calcareous debris and coarse sand) were located at increasing distance from the polynyas and were subject to different inputs of organic material to the seabed. Total meiofauna abundance ranged from 192.0 to 1191.2 ind. 10 cm−2, and total biomass varied between 9.5 and 50.3 μgC 10 cm−2. Meiofauna densities from the Ross Sea are, on average, 2–7 times lower than those reported from other similar deep polar regions and displayed significant differences between the sites. Nematodes dominated the samples at both sites, but their relative significance changed between the sites (80% at site B and 56% at site C), followed by copepods (1.6% and 35% at sites B and C, respectively). Meiofauna composition at site B appeared similar to that reported for deep-sea antarctic or temperate sediments, whereas the composition at site C was similar to that of coastal areas. On a macroscale, the different inputs of utilizable organic material at the two sites were reflected in meiofaunal distribution patterns, indicating that meiofaunal communities from the Ross Sea are dependent on particulate organic matter fluxes from the photic layer and are coupled to pelagic phenomena. Very low microscale variations (i.e. between replicates) in meiofauna density contrasted with large mesoscale variability, which was related to the concentration of the main food indicators (phytopigments, proteins, carbohydrates and lipids).

Effects of the SW Atlantic burrowing crab Chasmagnathus granulata on a Spartina salt marsh

In this work we evaluated the effect of the burrowing crab Chasmagnathus granulata on the soil quality and on the cordgrass Spartina densiflora in a SW Atlantic coastal lagoon (Argentina, 37°32'S. 57°19'W). Soil hardness and percolation rates were higher outside the crab inhabited area than inside, and soil profiles showed 2 different strata in areas without crabs. Crabs were associated with low soil water content, a higher variability in pH, and a homogeneous distribution of organic matter. Meiofaunal abundance was lower inside the area inhabited by crabs than outside. The water content of aboveground structures of S. densiflora was lower inside the crab populated areas. Leaf survival was lower inside the area inhabited by crabs than outside. In areas with new shoots (after burning by a brush fire) crabs depleted the aboveground plant structures. A caging experiment showed that crabs decreased leaf survival by herbivory. During the experiment, substrata was covered by sediment displaced by crabs, and the area showed less soil hardness and lower percolation rates than controls. Crabs decreased water content and organic matter on upper sediment layers. Meiofaunal abundance (arachnids and insects) was higher in control plots (without crabs) than in treatment plots. A field selection experiment showed that crabs decreased survival of young stems, but did not affect old stems. All this evidence suggests that C. granulata affects cordgrass production by herbivory on new shoots, and can change the physical characteristics of the environment, which may also indirectly affect S. densiflora production. Thus, the general belief that in Spartina marshes only a small proportion of primary production is consumed in situ may not apply to SW Atlantic Spartina marshes inhabited by crabs.

Role of Holocene beds of the stout razor clam Tagelus plebeius in structuring present benthic communities

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 185:213-228 (1999) - doi:10.3354/meps185213 Role of Holocene beds of the stout razor clam Tagelus plebeius in structuring present benthic communities Jorge Gutiérrez*, Oscar Iribarne Departamento de Biología (FCEyN), Universidad Nacional de Mar del Plata, CC 573 Correo Argentino Central, (7600) Mar del Plata, Argentina *E-mail: jlgutie@mdp.edu.ar ABSTRACT: Shell beds of the stout razor clam Tagelus plebeius in life position are common in the intertidal areas of several SW Atlantic estuaries (36° to 39° S). In this study we investigate the effect of this habitat structure on the benthic community, focusing on: (1) species which use this habitat as a refuge, (2) characteristics of the internal and external shell sediment and the abundance of macroinfauna and meiofauna in each one, (3) the effect of removing or introducing life-position shells on the abundance of macroinfaunal and meiofaunal organisms, (4) the effectiveness of shells as predator excluders and (5) sedimentary balance in shell beds and the role of superficial life-position shells. Eighteen macrofaunal species were encountered inhabiting the shell cavities; the amphipod Corophium insidiosum, the gastropod Heleobia australis and the polychaete Laeonereis acuta were the most abundant. Water and organic matter content were higher in the inner shell sediment than in the sediment sampled outside, but the distribution of phi-grain size values did not differ significantly between them. Except for nematodes, all the meiofaunal taxa and C. insidiosum showed higher abundance in the inner shell sediment. Removal of life-position shells in a shell bed negatively affected the abundance of C. insidiosum and the polychaete Heteromastus similis. Shell introduction in a mud flat had a positive effect on the abundance of almost all the taxa encountered. Two predator exclusion experiments indicate that these shells protect the fauna living within the shells and the underlying shell infauna from motile surface predators. Observations of shorebird feeding behavior showed that they rarely peck into the shell cavities. Daily measurements of the protruding length of shells demonstrated that these beds are exposed to erosive regimes, and shell removal in a shell assemblage destabilizes the sediment. The evidence suggests that superficial shells positively affect the diversity and abundance of organisms. KEY WORDS: Habitat structure · Shell beds · Physical ecosystem engineers · Positive effects · Taphonomic feedback · Benthos · Tagelus plebeius Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 185. Publication date: August 20, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Benthic activity in sediments of the northwestern Adriatic Sea: sediment oxygen consumption, macro- and meiofauna dynamics

Benthic activity was examined at three stations (18 m water depth) in the northwestern Adriatic Sea. Carbon mineralisation rates, as based on sediment oxygen consumption rates, ranged from 54 to 89 g C m −2 y −1. The relatively high carbon mineralisation rates, large macrofaunal biomass (9 to 16 g C m −2) and macrofaunal production (11 to 19 g C m −2 y −1) provide evidence of high organic-matter input and intense benthic–pelagic coupling. This is further supported by the high dominance of the suspension-feeding bivalve Corbula gibba, which accounts for 52 to 63% of the total annual macrofaunal biomass production. Although the infaunal distribution of total macrofauna showed a sharp decline in densities and biomass with depth into the sediment, different patterns within the dominant taxa were observed. Whilst the bivalve Corbula gibba and the amphipod Ampelisca sp. were restricted to the surface layer, other species such as the dominant bivalve Mysella sp. and the gastropod Hyala sp. were not confined to a specific depth level and the majority of the populations occurred deeper than 5 cm into the sediment. Bioturbation, based on the occurrence of macrofauna, extended to at least 20 cm. Nematodes and foraminifera together formed 80 to 90% of the meiofaunal community in the upper 5 cm of the sediment. Annual mean densities ranged from 3.40 to 6.07×10 6 ind. m −2. Maximum abundance of meiofauna was not encountered at the station where maximum macrofaunal activity was recorded, and this could reflect the negative effect of biological interaction on meiofaunal densities in areas that have a high food supply.

Annual course of sediment parameters and meiofauna on a sandy tidal flat in the wadden sea after the severe winter of 1995/96

Local abiotic and biotic data are presented from the Groninger Plate (a sandy tidal flat south of Spiekeroog Island) covering a period of one year (February 1996 — February 1997), which includes the coldest part of the ice winter of 1995/96 as well as the winter of 1996/97. The thickness of the visible oxidized layer revealed a clear seasonality. Regarding sandy sediments, values were generally low and ranged between 2.9 cm in winter and 0.9 cm in summer. Biotic and abiotic data are restricted to composition and abundance of meiofauna taxa, total organic carbon, Chl a and phaeopigments as well as temperature and salinity. A significant reduction of meiofaunal abundance, particularly of nematodes, in the top 2 cm was recorded in samples taken in sediments covered by ice, as compared to sediments without an ice cover. However, vertical distribution of meiofauna under ice cover showed that nematodes had migrated to deeper sediment layers. The meiofauna appeared to have overcome the stress of low temperatures and ice formation better than the macrofauna.

A quantitative survey of the benthic meiofauna in the Gulf Of Riga (eastern Baltic Sea), with special reference to the structure of nematode assemblages

Abstract The Gulf of Riga is relatively shallow and considered to be one of the most eutrophied areas in the Baltic Sea with an annual primary production estimated to 290 gCm-2 yr-1. Meiofauna sampling was carried out at 30 stations homogeneously spread over the Gulf of Riga, varying in depth and sediment structure. The average meiofauna abundance was 4800 ind/10 cm2, with a maximum of 17000 ind/10 cm2. Harpacticoid copepods were abundant all over the Gulf, averaging 425 ind/10 cm2. The highest number was found close to the mouth of the river Daugava, up to 1400 ind/10 cm2. Harpacticoids were significantly more abundant in sediments with medium organic content (loss on ignition (LOI) 5–10%) compared to sediments with low organic content (LOI 10%). Other major taxa were not correlated with sediment organic content. Altogether, 38 nematode spec...

The effect of experimentally increased near-bottom flow on metazoan meiofauna at a deep-sea site, with comparison data on macrofauna

It has been argued that strong near-bottom flows affect macrofauna and meiofauna in the deep sea, but the evidence comes largely from studies that compared sites separated geographically by hundreds to thousands of kilometers and in depth by hundreds of meters. In this paper, the results of the first experimental investigation of the effects of strong near-bottom flow on deep-sea metazoan meiofauna are presented. At a site (32° 27.581′ N, 127° 47.839′ W) at 583 m depth on the Fieberling Guyot summit plain, the submersible Alvin emplaced weirs designed to increase the near-bottom flow locally. After 6.5 weeks, sediments in the weirs and unmanipulated locations in the vicinity were sampled. The abundances of nematodes, harpacticoid copepods, ostracods, and kinorhynchs, considered collectively and as individual taxa, were significantly lower in the weir samples than in the background samples. Parallel responses were observed in total macrofaunal and mollusk abundances. Proportional declines in kinorhynchs and mollusks were observed as well. These results suggest that strong near-bottom flow can reduce the abundance of meiofauna and macrofauna in the deep sea and alter assemblage composition.

Grass shrimp Palaemonetes pugio predation on sediment- and stem-dwelling meiofauna:field and laboratory experiments

Field and laboratory experiments were conducted to clarify the predatory role of Palaemonetes pugio Holthius in salt-marsh benthic communities. Field experiments (cage enclosures using P. pugio as a predator) were conducted on unvegetated mudflat and vegetated-marsh sites. Neither sedimentor stem-dwelling meiofaunal abundances were significantly impacted. Laboratory experiments measured the functional response of P. pugio feeding on suspended harpacticoid coprpods. tested the efficiency of P. pugio feeding on harpacticoids in sediments, and measured the predation rate of P. pugio on stem-dwelling melofauna. Grass shrimp feeding rate on suspended copepods followed a type I1 functional response, increasing with increasing prey density to a maximum of 59 copepods h-'. When a sediment refuge was available, a 40% decline in the consumption of copepods by P pugio was noted; this decreased feeding efficiency may contribute to the lack of significant declines in meiofaunal abundances in field enclosures over unvegetated sediment. P, pugio proved to be a highly effective predator on the fauna of Spartina alterniflora stems, significantly reducing abundances of stem-associated meiofauna within 24 h and consuming an estimated 35 meiofauna h-' The greatest impact was exhibited on the lowest (0 to 6 cm) portion of the stems. These experiments suggest that laboratory experiments are an important aid to help interpret field experiments examining predation on meiofauna, and that Spartina stems, and their epiphytic algae and meiofauna, are important, but largely overlooked, resources in salt-marsh food webs.

Predation on meiofauna by juvenile spot Leiostomus xanthurus (Pisces) in contaminated sediments from Charleston Harbor, South Carolina, USA

Meiofauna are a major food source for estuarine juvenile fish despite the fact that meiofauna often live in close contact with sediment-associated contaminants. Although there is laboratory evidence that fish feeding on contaminated meiofauna can build up significant contaminant body burdens, whether or not fish predation on meiofauna is affected by sediment contamination in the field has not been well established. To answer thls question, the number and taxa of meiobenthic prey items consumed by fish were compared between contaminated and uncontaminated habitats. A model predator, luvenile spot Leiostomus xanthurus (Pisces) was allowed to feed on natural meiobenthic communities in experimental sediment microcosn~s. Significantly more meiofauna were observed in the uncontaminated reference site (1060 nematodes per 10 cm2, 177 copepods per 10 cm2) than in the contaminated site (278 nematodes per 10 cm2. 97.5 copepods per 10 cm2). Although harpacticoid copepods were found in the foreguts of spot from both contaminated (mean 22.1 prey per fish) and uncontaminated (mean 13.7 prey per fish) sediments, there were few, if any, significant reductions in meiofauna abundance due to predation. There were differences between contaminated and uncontaminated sediments in taxa eaten by spot, but these differences were most likely due to differences between the meiofauna communities from the 2 sites, not differences in fish feeding behavior. Despite the potential adverse effects of eating meiofauna from contaminated sediments, juvenile spot do not avoid them.

Meiobenthos distribution pattern in the tropical East Atlantic: indication for fractionated sedimentation of organic matter to the sea floor?

To test the extent to which sea surface productivity governs the distribution pattern of benthic organisms, meiobenthic standing stocks were investigated on the shelf, continental margin and the adjacent abyssal plains off the western African coast between Guinea (10°N) and Angola (18°S). The area of investigation is characterized by gradients in surface productivity due to spatially and seasonally varying coastal upwelling. Reflecting the dependency of deep-sea organisms on organic matter input from the euphotic zone, similar gradients ought to be expected within the benthos. Meiofaunal abundances and biomasses (including Foraminifera) from a total of 57 stations along 13 transects across the continental margin showed a fairly close correlation with sediment-bound chloroplastic pigment concentrations, indicating the sedimentation of particulate organic matter from phytoplankton production. However, certain discrepancies in faunal and pigment distribution patterns were found in regions apart from the centres of enhanced primary␣productivity, i.e. apart from the upwelling centres: whereas pigment concentrations in the sediments were still comparably high, meiofaunal numbers in those peripheral areas were generally lower. It is suggested that smaller/lighter phytodetritial matter, transported over long distances by subsurface currents and exposed to ongoing microbial degradation during its passage, probably does not have the same energy content as the relatively fast-sinking, larger phytodetritus aggregates (“marine snow”), which are found in centres of enhanced primary productivity and support extensive benthic stocks. Thus, meiobenthic abundances in relation to sediment-bound pigment concentrations on the western African continental margin may indicate fractionated sedimentation of organic matter to the sea floor.

Distribution and abundance of meiofauna in a Subtropical Coastal Lagoon in the south-eastern Gulf of California, Mexico

The composition and density of meiofauna in Ensenada del Pabellón Lagoon (south-eastern Gulf of California) was evaluated in terms of carbon and nitrogen content, and granulometry. Meiofauna density ranged from 50.0 to 2676.83 ind 10 cm −2. Nematodes, harpacticoid copepods and foraminiferans were the most abundant among the 18 taxa registered. The highest densities of meiofauna were related to high levels of nitrogen and carbon (up to 0.14 μmol N g −1 and to 3.17 μmol C g −1) in stations affected by agro-industrial drainages and characterized by muddy sediments and slow tidal currents. The lowest densities of meiofauna were observed in stations with sandy sediments of low carbon and nitrogen content, located further away distant from agro-industrial discharges. Statistical analyses showed that high carbon content had a positive effect on copepod, foraminiferan, ostracod and nematode densities whereas the effect of nitrogen content was positive only for nematodes.

Monitoring meiobenthos using cm-, m- and km-scales in the Southern Bight of the North Sea

Meiobenthos at the mouth of the Grevelingen and Oosterschelde Estuaries in the Southern Bight of the North Sea was monitored using meiobenthic abundance and nematode community structure. Hierarchical sampling included 54 subsamples nested within 18 cores within six stations within two transects. The spatial patterns of the meiofaunal populations and communities are presented in cm-scale (among subsamples), m-scale (among cores), km-scale (among stations) and 10 km-scale (between transects). The variance components analysis of meiofaunal abundances showed that km-scale and 10 km-scale represented 63–90% of total variance while m-scale and cm-scale provided only 10–37%. Different communities were found among stations rather than among cores or subsamples by detrended correspondence analysis ordination and clustering analysis. The main assemblage of meiofauna occurred at the km-scale. Nematode diversity was more powerful than meiofaunal abundance in detecting spatial variation at all scales. However, at least two replicates are required for monitoring when sampling using a 10 cm 2 subsampling core.

Developments in sampling the fauna of deep water-table aquifers

From 1993 to 1995, we tested four pressure pumps in the field, a centrifugal pump, an air-lift, an inertial pump, and a pneumatic pump, all of which could be used to remove groundwater invertebrates from deep water-table aquifers (i.e., with a groundwater table deeper than about 8 m below the ground surface). Changes in invertebrate abundance, relative abundance of taxa, and recovery of additional taxa during pumping were investigated to evaluate the sampling performance of the pumps. The centrifugal pump tested during this study damaged most macro-invertebrates to such an extent that they could not be identified. Therefore, it could be used only for the sampling of meiofauna. With the inertial and air-lift pumps, biological abundance decreased at the early stage of pumping and changes in the abundances of meiofauna and macrofauna were different. Because of this, these two sampling devices might be efficient in removing the invertebrates only in the immediate vicinity of the well and are, moreover, likely to generate preferential removal of taxa showing low resistance to displacement by the current. In contrast, the pneumatic pump was a powerful suction device capable of removing all the taxa without damaging them and appeared to be a promising pumping technique for the faunal sampling of deep water-table aquifers.

Black spots produced by buried macroalgae in intertidal sandy sediments of the Wadden Sea: Effects on the meiobenthos

The effects of buried decaying macroalgae on meiobenthos were examined in intertidal sandy sediments of the Wadden Sea of Lower Saxony. In situ experiments confirmed that one of the principal causes of the formation of reduced surface sediments or ‘black spots’ on the tidal flats is the increasing occurrence and subsequent decomposition of filamentous green algae ( Enteromorpha spp.) buried in the sediment. Five to fifteen days after algal material had been buried, the sediment surface turned black. The impact of these black spots on meiobenthos was dramatic: the changed chemical conditions in the sediment resulted in long and drastic reductions in meiofaunal abundance and number of taxa. A multi-dimensional scaling (MDS) analysis of data on meiobenthic abundances revealed that samples from black-spot areas were clearly separated from those of control and reference areas. Re-oxidized black spots showed recolonization by meiofaunal animals, with numbers of individuals and taxa similar to those of oxidized surface sediments. The use of abundances of members of higher meiobenthic taxa to monitor changes in the sediment's chemistry, especially those caused by biomass overload, is discussed.