Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem

Summary The muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×10⁶ individuals per m² and ash free dry weight of 2.9 g/m² during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 10⁶ individuals per m². This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.     

Panicum maximum (Jacq.) density effect upon macrofauna structure in sediments of pilot-scale vertical flow constructed wetlands treating domestic wastewater

Plant density may have an impact on macrofauna structure in constructed wetlands (CW). In this study, Panicum maximum density effect on macrofauna structure in pilot-scale vertical flow CW treating domestic wastewater was estimated. Two beds were planted with P. maximum at 10 roots/m² (low density) and two others at 20 roots/m² (high density). Two unplanted beds were used as controls. After six months of wastewater treatment, macrofauna was collected by taking five cores of sediment samples at the corners and the centre of each bed following three layers in the vertical profile. Plant density seems not to impact significantly the CW performance. However, the plant density of 10 roots/m² (low density) provided higher wastewater treatment efficiency. Concerning macrofauna, 11 taxa belonging to 6 classes and 11 orders were collected. Macrofauna was significantly more diversified in the planted beds than in the control. But the two plant densities investigated do not show significant difference between macrofauna diversity of the planted beds. Macrofauna abundance was two- and three-fold higher, respectively, in the planted beds at high and low densities than in the controls. From the upper surface to the bottom of the beds, macrofauna diversity and abundance decreased, and were heavily dominated by Annelida.     

Effect of detritus supply on trophic relationships within experimental benthic food webs. II. Microbial responses,fate and composition of decomposing detritus

The dynamics of bacterial, protozoan and fungal populations were examined in a long-term (40–55 wk) microcosm experiment designed to assess the effects of detritus supply on meiofauna-polychaete (Capitella capitata (Type I) Fabricius) interactions. Bacterial and protozoan numbers and bacterial growth rates were inversely correlated with population fluctuations of the polychaete at low (50 mg N · m^?2 · day ^?1) detritus supply, but did not correlate with fluctuating polychaete densities at two higher (100 and 150 mg N · m^?2 · day^?1) ration levels of detritus. Bacterial and protozoan numbers and bacterial growth rates did not correlate with standing amounts of detritus or with fungi or meiofauna at any of the detritus rations. Fungi were associated primarily with aggregates of detritus particles and fecal pellets produced by C. capitata.Labile (fiber-free) organic matter did not correlate with microbes or meiofauna, but was inversely correlated with population fluctuations of the polychaete C. capitata at all three ration levels of detritus. Polychaete fecal pellets accounted for most of the refractory matter in the tanks with C. capitata and did not accumulate in the sediments, suggesting that fecal pellets were continually being produced, broken apart and decomposed.Our experiments suggest that contradictions in previous studies on the effects of macroconsumers on microbes, especially bacteria, can be explained as a failure to consider the effects of detritus supply on microbial growth rates.     

Distribution patterns of micro- and meso-zooplankton communities in sea ice regions of Lützow-Holm Bay, East Antarctica

In the Southern Ocean, zooplankton research has focused on krill and macro-zooplankton despite the high densities of micro- and meso-zooplankton. We investigated their community structure in relation to different sea ice conditions around Japan’s Syowa Station in Lützow-Holm Bay, in the summers of 2011 and 2012. Zooplankton samples were collected using vertical hauls (0–150 m), with a closing net of 100-μm mesh size. The results of cluster analysis showed that the communities in this region were separated into fast ice, pack ice, and open ocean fauna. The fast ice fauna had lower zooplankton abundance (393.8–958.9 inds. m^?3) and was dominated by cyclopoid copepods of Oncaea spp. (54.9–74.8 %) and Oithona similis (6.6–19.9 %). Deep-water calanoid copepods were also found at the fast ice stations. Pack ice and open ocean fauna had higher zooplankton abundance (943.6–2,639.8 inds. m^?3) and were characterized by a high density of foraminiferans in both years (6.6–61.9 %). Their test size distribution indicated that these organisms were possibly released from melting sea ice. The pteropod Limacina spp. was a major contributor to total abundance of zooplankton in the open ocean zone in 2012 (26.4 %). The physical and/or biological changes between 2 years may affect the abundance and distribution of the dominant zooplankton taxa such as cyclopoid copepods, foraminiferans, and pteropods. Information on the relationships between the different species associated with sea ice will help to infer the possible future impacts of climate change on the sea ice regions.     

象山港国华宁海电厂附近海域小型底栖动物的群落结构

于2008年夏季(6月)和冬季(12月),在象山港国华宁海电厂沿排水口右侧、从近到远相隔500m设立三个断面A、B、C,并对小型底栖动物丰度及其群落结构变化进行调查研究,结果表明:共鉴定出10个小型底栖动物类群,平均丰度达9407.9inds/10cm².从类群上看,自由生活海洋线虫占总丰度的62.3%,介形类占第二位,为19.3%.ANOSIM分析结果显示小型底栖动物季节间的丰度存在明显差异(p<0.05),夏季平均丰度(8055.3±1282.9inds/10cm²)比冬季(2141.1±614.2inds/10cm²)约高出3倍.冬季不同断面间的丰度无显著差异,但夏季断面间差异显著(p<0.05),尤其在排水口附近的A断面丰度最低,为1002.8inds/10cm².SIMPER分析结果显示海洋线虫、介形类、腹足类、涡虫、桡足类是各断面之间非相似的关键类群,这些类群的迁移指示电厂温排水已导致排水口附近海域小型底栖群落结构不稳定,不仅水平分布有差异,垂直分布也明显不同.     

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.     

Structuring factors in a marine soft bottom community during eutrophication—an experiment with radio-labelled phytodetritus

The quantitative development and uptake of radio-labelled phytodetritus in benthic macro- and meiofauna was studied in a 5-month experiment in two mesocosms, one of which received a single large nutrient (N and P) addition, while the other served as control. In reponse to the 12-fold increase in phytoplankton biomass noted after 2 weeks and the resulting enhanced accumulation of fresh phytodetritus, the abundance and biomass of the polychaetes Mediomastus ambiseta and Polydora ligni and the mud anemone Cerianthiopsis americanus increased significantly in the enriched tank. The abundances of P. ligni and M. ambiseta increased 37-fold and 12-fold, respectively, within the first two months of the experiment. No other macrofaunal or meiofaunal taxa showed any consistent positive quantitative response to the increased input of phytodetritus. In the control tank no considerable change in the benthic community structure was noted. The measurements of radio-label uptake within the benthic fauna showed that the quantitatively most successful species utilized fresh phytodetritus highly. However, a high degree of utilization of fresh detritus was also shown by taxa that did not respond quantitatively within the 5 month of the experiment, and almost all taxa showed a preference for fresh detritus over older organic material. Within the benthic meiofauna, kinorhynchs and especially foraminiferans showed a remarkably low preference for fresh detritus. A budget calculation comparing the total amounts of labelled organic carbon bound in animal tissue and in the sediment indicated that at any time at least 75% of this carbon was available for assimilation by deposit feeders. These results suggest that factors other than the availability of food, such as competition for space by a few opportunistic macrofauna species, limited the response of other species within this benthic community to the increased input of phytodetritus.     

Nahrung und Freßverhalten bei Sedimentfressern dargestellt am Beispiel von Sipunculiden und Holothurien

Using a Phillipson microbomb calorimeter, the energy values of the “infauna-substrate-feeders”Sipunculus nudus andPhascolosoma vulgare and the nutritive value of their food substrate were determined. Calorific measurements were made of the total food substrate, of meiofauna organisms living in it and of fecal pellets from other invertebrate animals which are an important part in the food supply. Analyses of the gut content of the sipunculids and their feces were compared with the surrounding sediment. The total sediment had an ash content of about 97%, and an energy content of approximately 0.14 cal mg^?1 dry weight; this is equivalent to 165 kcal m^?2. For the meiofauna in this substrate a biomass of 800 mg dry weight was calculated. Using calorific determinations of important meiofauna groups (nematodes 5274 kcal kg^?1, ostracods 5884 and 6000 kcal kg^?1), one square meter of the sediment surface — the sipunculid food source — yielded a caloric content of 3.78 kcal for the meiofauna, which means a contribution of 2.3% to the total food substrate. The largest part of the calorific contents is by far provided by fecal pellets with 0.6 cal mg^?1 dry weight or 150 kcal m^?2; this accounts for 92% of the total calorific content of the food substrate. Peritrophic membranes and attached microorganisms may be responsible for this spectacularly high value. Coprophagy plays an important role. The rest of the total value was contributed by particulate and dissolved detritus as well as protozoans with a calculated sum of 10 kcal m^?2 or 6%. Food uptake is selective with regard to small sediment grain sizes. The amount of meiofauna in the gut is 80 times lower than in the surrounding environment, the energy content in the anterior gut 10 times higher. The energy loss inS. nudus from the anterior gut to the middle gut is more than 70%, to the posterior gut a further loss of 19% was observed. Calorific measurements in the feces were no longer possible. The utilization of food appears to be almost 100%. A correlation between ash content and the quantity of the sand grain-size fraction 37–125 μm and the calorific content is shown. The meiofauna does not represent a significant part of the total food structure, but it is taken up and utilized as food by the sediment feeding macrofauna.     

Microalgal–meiofaunal interactions in a sublittoral site of the Gulf of Trieste (northern Adriatic Sea, Italy): A three-year study

Monthly sediment sampling was carried out from February 1999 to December 2001 at a 21-m deep station. Benthic diatom biomass and meiobenthic abundance were estimated together with abiotic parameters (PAR irradiance, temperature, salinity and dissolved oxygen). During the three-year study average microphytobenthic abundance (ABU) and biomass (BIOM) were 4.7 ± 2.6 × 10⁴ cell cm^− 3 and 14.3 ± 8.1 µg C cm^− 3, respectively, while the mean meiofaunal abundance was 923 ± 210 ind 10 cm^− 2. The microphytobenthic community was mainly composed of Bacillariophyceae (99.3%) with a smaller percentage of phytoflagellates (0.7%). Among diatoms 39 genera were observed with a total of 110 taxa and 100 species. The main benthic diatom genera were Navicula, Paralia, Nitzschia and Diploneis. A total of 18 meiobenthic taxa were detected: 7 taxa belonged to permanent meiofauna (Nematoda, Copepoda Harpacticoida and their nauplius stages, Kinorhyncha, Turbellaria, Gastrotricha, Ostracoda and Acarina). The remaining 11 taxa belonged to temporary meiofauna (juvenile macrofauna: Polychaeta, Cumacea, Amphipoda, Isopoda, Nemertea, Decapoda, Sipunculida, Ophiurida, Gastropoda, Bivalvia and Cnidaria). Positive correlations between PAR and the biomass of the major diatom genera were revealed. Temperature did not seem to influence the microphytobenthic community as a whole, although we found statistically significant correlation between temperature and the genera Nitzschia and Amphora. Salinity showed significant positive correlation only with the genus Pleurosigma, in contrast, dissolved oxygen did not seem to affect the microalgal community. The major meiofaunal taxa were not correlated with abiotic variables, but were positively correlated with most diatom genera. Paralia was negatively correlated with the three main meiofaunal taxa. The three-point moving average applied to our biotic data allowed us to better the signal without the background noise which hid the actual variations of the studied communities. Applying the three-point moving average to the main taxa, it resulted that microphyto- and meiobenthos were in phase. The principal component analysis (PCA), constructed considering both biotic and abiotic variables, accounted for 58% of the total variance. PC1 axis explained 39.74% of the total variance and was correlated with Navicula, Diploneis and Nitzschia. PC2 axis explained 18.40% of the remaining variance and was correlated with Copepoda, Paralia and PAR. In contrast to 1999 and 2001, a mucilage event occurred in 2000, which resulted in the formation of a false bottom and a decrease in the abundance of microphyto- and meiobenthos.     

Biomass and abundance of macrofauna in intertidal sediments of Königshafen in the northern Wadden Sea

Intertidal sediments of Königshafen (Island of Sylt, North Sea) were sieved for mesofauna (>0.25 mm) and macrofauna (>1 mm) in spring and autumn 1990. Although sediments are coarser than in other parts of the Wadden Sea, the macrobenthic fauna was very similar but with a tendency towards higher species density, abundance and biomass. Taking into account the areal size of sandy flats, seagrass beds, mud flats and mussel beds, the average biomass is calculated to be 65 g ash-free dry weight m^?2 The lugwormArenicola marina dominates the biomass (28%), followed by the bivalvesMytilus edulis (21%),Mya areanaria (16%),Cerastoderma edule (10%) and the mudsnailHydrobia ulvae (9%). While spring and autumn biomass are almost alike, abundance is highly variable and entirely dominated byH. ulvae. Mesofauna is mainly composed of oligochaetes, small and juvenile polychaetes. Abundance is similar to that of macrofauna, while biomass is only about 1 g m^?2. Macrophyte biomass amounted to 9% of that macrofauna. In the course of the centurym mussel beds expanded while muddy areas declined. The concomitant effects on biomass presumably compensated each other.     

Macrofauna on flood delta shoals in the Wadden Sea with an underground association between the lugwormArenicola marina and the amphipodUrothoe poseidonis

Living conditions for macrofauna on flood delta shoals are determined by surf, strong currents and sediment mobility. Thus, a unique assemblage of invertebrate species colonize these far off-shore, low intertidal flats. We here describe the macrobenthic fauna of emerging shoals in the Wadden Sea between the islands of Römö and Sylt. Besides ubiquitous macroinvertebrates of the intertidal zone and species which attain their main distribution in the subtidal zone, the flood delta shoals are characterized by organisms adapted to live in these highly unstable sediments, like the polychaetesSpio martinensis, Streptosyllis websteri, Magelona mirabilis, Psammodrilus balanoglossoides, the pericarid crustaceansCumopsis goodsiri, Tanaissus lilljeborgi, Bathyporeia sarsi and a few others. Average abundance (1440 m^?2 of ind >1 mm) and biomass (12.9 g AFDW m^?2) were low compared to other intertidal habitats in the Wadden Sea. Biomass was dominated by largesized individuals of the lugwormArenicola marina. The U-shaped burrows of these polychaetes were inhabited by high numbers ofUrothoe poseidonis. Maximum densities of these amphipods occurred in the deepest parts of the burrows. Sampling at approximately montly intervals revealed no apparent seasonality ofU. poseidonis abundance. Together with smallCapitella capitata, these amphipods constitute a deep-dwelling component of the macrofauna associated with lugworms, which is separated from all other macrofauna living at the sediment surface. As a response to rising sea level and increasing tidal ranges, we expect the unstable sandy shoals, inhabited by numerousSpio martinensis andUrothoe poseidonis, to expand within the Wadden Sea at the cost of stable sandy flats with abundant macrofauna.     

The effect of macrofauna,meiofauna and microfauna on the degradation of Spartina maritima detritus from a salt marsh area

Decomposition of salt marsh plants results from physical, chemical and biological processes including abiotic and biotic fragmentation, microbial decay and chemical transformation. According to literature data, only a few species have the ability to feed directly on living plant material, so fungi and bacteria seem to be the principal competitors for the organic substrates. Nevertheless, by consuming bacteria, protists and fungi associated to the detritus, macrofauna and meiofauna recycle the incorporated nutrients. Moreover, this nutrient regeneration may be seen as an effective factor in maintaining and stimulating bacterial production. In fact, it is well known that many detritus feeding species have very low assimilation efficiencies. The objective of the present study was to compare the nutrient mass balance of carbon; nitrogen and phosphorus in Spartina maritima covered areas and bare bottom sediment, with and without contribution of macrofauna, meiofauna and microbial populations. Nutrients mass balance was studied taking into account the initial and final nutrient concentrations in the sediment, water and plant material. Faunal activity was measured as a function of remineralised carbon, nitrogen and phosphorus. The experimental set-up included sixteen sub-experiments, which varied with respect to type of fauna, plant biomass and oxic status. Each sub-experiment was performed in small glass containers (3 L) containing about 900 g wwt sediment and 2.5 L estuarine water. Plant material, cut from intact plants, sediment cores and estuarine water were brought from the southern arm of the Mondego estuary (Portugal). The results showed that although the bacterial activity was responsible for the Spartina maritima degradation, the presence of meiofauna and macrofauna significantly enhanced the process. Moreover, the presence of Spartina maritima positively affected the mineralisation of the sediment carbon and nitrogen, especially when the three faunal components were present, and denitrification rates were highest in the presence of the macrofauna and meiofauna. The present study suggests that macrofauna and meiofauna have an important role on the ecosystem nutrient flux and that fauna might function as a sink for excess nutrients, that otherwise could be exported to the coastal waters.     

Seasonal changes in the distribution and abundance of benthic invertebrates in six headwater streams in central Florida

Seasonal variations in invertebrate assemblages at two sites (upstream and downstream) on six central Florida headwater streams were compared by sampling at quarterly intervals with core and dip net samplers. Two of the streams were reclaimed following phosphate mining (～6 yr prior to this study), two received runoff from mined lands, and two were disturbed by agriculture and/or residential developments. Physical and chemical characteristics of the reclaimed streams differed markedly from those of the non-reclaimed streams; principal differences between the streams were in current velocity, percent organic matter (POM), Mn, conductivity and alkalinity. Annual mean densities of meiofauna and smaller macrofauna for the 12 stream sites ranged from 20?896 to 175?212 m^?2 and the mean for all sites was 56?492 m^?2. The reclaimed streams and one of the streams influenced by agriculture had annual means of less than 40?000 m^?2, 3- to 5-fold lower than the other streams. Fall and winter core densities were ～2.4-fold greater than those for spring or summer when drought and low dissolved oxygen prevailed. Meiofauna comprised 68–91% of the core sample invertebrates in reclaimed streams but only 43–62% in the non-reclaimed streams; principal functional groups were: gathering collectors – 61.5%, predators – 19.3% and filtering collectors – 15%. The taxonomic composition of the reclaimed streams was predominated by crustaceans (60–71%) while chironomids and annelids were more abundant (71–92%) in the non-reclaimed streams. Dip net sampling added 21 larger macrofauna species (Odonata, Hemiptera and Coleoptera) to our list of taxa, producing a total of 209 species. Species richness and diversity (H′ and N ₂) indices were lower in the reclaimed streams, but evenness was more variable. The Czekanowski–Dice–Sørensen similarity index showed that the reclaimed stream sites were quite similar to each other, but differed markedly from the other stream types; there was large variation both within and between seasons. For central Florida headwater streams, drought appears to have a larger influence on invertebrates than the type of land use, however this relationship should be confirmed using streams of similar hydrology.     

Long-term nutrient enrichment elicits a weak density response by saltmarsh meiofauna

The effect of chronic nutrient enrichment on benthic meiofauna was examined in a whole-ecosystem experiment conducted in salt marshes in the Plum Island watershed of northeastern Massachusetts, USA. We compared abundances of total meiofauna, nematodes, copepods, ostracods, and annelids including Manayunkia aestuarina, in fertilized (where N and P was increased 15× in incoming tidal water throughout each growing season for 6 years) and reference marsh creeks to test for bottom-up responses. Although some responses to nutrient enrichment were evident, results did not match our expectations of strong increases in abundance. Variation in abundance between nutrient-enriched and reference creeks was detected in all three subhabitats but responses were inconsistent and variable over time, suggesting that natural variability was greater than variation induced by fertilization. Our results showed an overall weak negative correlation between meiofauna abundance and benthic microalgae (BMA) biomass partly because the BMA response to nutrient enrichment was relatively small and perhaps limited by grazing macrofauna and nekton. Our results suggest a better mechanistic understanding of the relationship between BMA and meiofaunal abundance is needed to fully understand how nutrient enrichment affects meiofauna.     

Meiofauna sediment relations in leeward slope turf algae of Heron Island reef

As part of studies investigating the influence of grazers on reef meiofauna, we assessed the density, composition and richness of meiofauna (retained on a 100-μm sieve) on the leeward reef slope of Heron Reef, GBR, Australia using an airlift vacuum sampling device. Estimates of meiofauna densities ranged between 40 individuals 10 cm⁻² and 290 individuals 10 cm⁻², which is considerably lower than many estimates from carbonate sediments and hard substrates from other reefs and marine habitats. The 17 taxa of meiofauna were dominated by harpacticoid copepods (40%) and nematodes (32%). Varying sediment load within algal turfs explained 37% of variation of meiofauna density. A model is proposed in which increased shelter afforded by high living coral cover reduces meiofaunal losses from grazing and increases sediment loads, balanced by areas of low coral cover in which sedimentation rates are lower and grazing rates higher. At none of the four sites did major differences in abundance occur between November and March sampling events. Together these observations suggest that epilithic meiofaunal communities are generally spatially and temporally predictable at small scales in this reef system, indicating that their ecological services are similarly conservative. Handling editor: I. Nagelkerken     

Intertidal zone of Svalbard 3. Littoral of a subarctic, oceanic island: Bjornoya

Twenty-two stations in the intertidal and shallow sublittoral of Bjornoya (74 °N, 19 °E) were studied in August 1994 revealing a large and diverse standing crop of macro-algae (16 species) and littoral macrofauna (at least 17 species). In most places the biomass of littoral macroorganisms exceeded 100 g ww/m². In the shallow sublittoral, between 2 and 20 m, 45 animal taxa and 23 algae species were collected. Littoral coarse sand meiofauna was dominated by Turbellaria, while, on algae, Halacaridae and Harpacticoida predominated. Meiofauna densities ranged from 0 to 169 ind./10 cm² and biomass from 0 to 0.4 g dw/m². The abundance of littoral species and their zoogeographic origin resemble that of Spitsbergen more than that of the northern Scandinavian coast, although both are of equal distance from Bjornoya. The first record of the boreal bivalve Mytilus edulis from the island is presented. Another striking feature was the presence of the arctic amphipod Gammarus setosus and the absence of its boreal sibling species G.oceanicus. Received: 19 March 1996 / Accepted: 1 December 1996     

Soil microarthropods and macrofauna in monsoon tropical forests of Cat Tien and Bi Dup-Nui Ba National Parks,southern Vietnam

The abundance, biomass, vertical distribution, and taxonomic composition of soil invertebrates (springtails, macrofauna, and termites) were studied in forest formations differing in edaphic and climatic conditions: lowland forests dominated by Lagerstroemia spp. or Dipterocarpus spp. in the Cat Tien National Park and in a mountain pine (Pinus kesiya) forest on the Da Lat Plateau, southern Vietnam. In the lowland forests, springtails had a relatively low density (10000–12000 ind./m²), but their diversity was high (41–43 species in each forest). The density of large soil invertebrates (without ants and termites) reached 500–700 ind./m² at a biomass of approximately 30 g/m² (with earthworms accounting for up to 230 ind./m² and 19–28 g/m²). Among termites, species of the genera Macrotermes and Odontotermes were dominant. Their total biomass in some areas exceeded 15–20 g/m². In the mountain pine forest, the total biomass of soil macrofauna was approximately 11 g/m², the abundance and diversity of springtails were low (7500 ind./m², 28 species), and wood-destroying species of the genera Schedorhinotermes sp. and Coptotermes sp. dominated among termites.     

Horizontal and vertical distribution of meiofauna on sandy beaches of the North Sea (The Netherlands, Belgium, France)

Sandy intertidal zones were analysed for the presence of meiofauna. The material was collected on six macro-tidal sandy beaches along the North Sea (The Netherlands, France, Belgium), in order to analyse the vertical and horizontal meiofaunal distribution patterns. Eleven higher meiofauna taxa (one represented by larval stage—Copepoda nauplii) were recorded. The maximum total meiofauna abundance was observed on the Dutch beach (4,295±911 ind. 10 cm⁻²) in the Westerschelde estuary, while the lowest values (361±128 ind. 10 cm⁻²) were recorded in France at the Audresselles beach. Meiofauna of the different localities consisted mainly of nematodes, harpacticoids and turbellarians. Nematodes numerically dominated all sampled stations, comprising more than 45% of the total meiofauna density. Meiofauna was mainly concentrated at the sand surface with about 70% present in the uppermost 5 cm. Meiofauna occurred across the entire intertidal zone. A clear zonation pattern in the distribution of meiofauna taxa across the beaches was observed. The present work suggests that designation of exposed sandy beaches as physically controlled (McLachlan 1988) does not explain their biological variability.     

The faunal role in the degradation of the common intertidal salt marsh plant <Emphasis Type="Italic">Scirpus maritimus</Emphasis>

The aim of this work was to evaluate the role of different environmental conditions (oxic and anoxic), and the presence of macrofauna and/or meiofauna during the different steps of Scirpus maritimus L. decomposition/mineralization under controlled laboratory conditions. The results showed no significant differences between the anaerobic and the aerobic degradation of plant material, under the presence of bacteria or meiofauna. Nevertheless, under anoxic conditions sediment mineralization was enhanced, with an increase concentration of phosphorus and ammonium in the water phase. Concerning the presence of fauna, results show that, although bacterial activity was responsible for 70% of the S. maritimus leaves degradation, the presence of macrofauna together with meiofauna enhanced the leaves mineralization up to 90%. Moreover, the presence of macrofauna together with meiofauna significantly affected the decomposition of phosphorus and of nitrogen, as well as the leaves lesser labile structural parts, by increasing the mineralization of plant carbon, and raised the nutrient turnover within the system.The present study reinforces the functional link between fauna levels on the nutrient dynamics in salt marshes ecosystems, namely at the vegetation detritus/water column interface. Handling editor: S. M. Thomaz     

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.