Total Meiofauna Density Research Articles

Short-term microplastic effects on marine meiofauna abundance, diversity and community composition.

Due to the copious disposal of plastics, marine ecosystems receive a large part of this waste. Microplastics (MPs) are solid particles smaller than 5 millimeters in size. Among the plastic polymers, polystyrene (PS) is one of the most commonly used and discarded. Due to its density being greater than that of water, it accumulates in marine sediments, potentially affecting benthic communities. This study investigated the ingestion of MP and their effect on the meiofauna community of a sandy beach. Meiofauna are an important trophic link between the basal and higher trophic levels of sedimentary food webs and may therefore be substantially involved in trophic transfer of MP and their associated compounds. We incubated microcosms without addition of MP (controls) and treatments contaminated with PS MP (1-µm) in marine sediments at three nominal concentrations (103, 105, 107particles/mL), for nine days, and sampled for meiofauna with collections every three days. At each sampling time, meiofauna were collected, quantified and identified to higher-taxon level, and ingestion of MP was quantified under an epifluorescence microscope. Except for Tardigrada, all meiofauna taxa (Nematoda, turbellarians, Copepoda, Nauplii, Acari and Gastrotricha) ingested MP. Absorption was strongly dose dependent, being highest at 107 particles/mL, very low at 105 particles/mL and non-demonstrable at 103 particles/mL. Nematodes accumulated MP mainly in the intestine; MP abundance in the intestine increased with increasing incubation time. The total meiofauna density and species richness were significantly lower at the lowest MP concentration, while at the highest concentration these parameters were very similar to the control. In contrast, Shannon-Wiener diversity and evenness were greater in treatments with low MP concentration. However, these results should be interpreted with caution because of the low meiofauna abundances at the lower two MP concentrations. At the highest MP concentration, abundance, taxonomic diversity and community structure of a beach meiofauna community were not significantly affected, suggesting that MP effects on meiofauna are at most subtle. However, lower MP concentrations did cause substantial declines in abundance and diversity, in line with previous studies at the population and community level. While we can only speculate on the underlying mechanism(s) of this counterintuitive response, results suggest that further research is needed to better understand MP effects on marine benthic communities.

Recovery of meiofauna following a short-term disturbance on coral reefs

The present study experimentally determined the short-term effect of different trampling intensities on the phytal habitat and associated meiofauna, and assessed the recovery of these communities on a coral reef. The experiment was conducted within the protected area on the reef of Porto de Galinhas Beach, northeastern Brazil. Within three areas, 30 × 30 cm2 plots were subjected to different experimental trampling intensities: 0 (control), 32 (low intensity) and 79 (high intensity) footsteps applied during 3 consecutive days. Samples were taken before trampling started and then 1 day and 1, 2 and 3 months after the end of trampling. Multivariate and univariate analyses were used to test for changes in the phytal substrate, the densities of the main meiofaunal major taxa, and the diversity, comparing the trampling intensities and the time periods. The immediate impact of trampling negatively affected the phytal substrate, causing large reductions in sediment content, total substrate weight, and algal turf height. Trampling also drastically decreased the density of the associated meiofauna and modified the community structure. The major meiofauna groups showed different patterns of recovery during the first and second months. However, 3 months after trampling ended, no impact was found for densities of total meiofauna and for most major taxa, and no differences were observed in the community structure among all trampling intensities. Finally, the results for trampling susceptibility and resilience allowed us to extend the discussion to management strategies for the use of reef areas for recreation.

남극 킹조지섬 마리안소만의 중형저서동물 군집구조

The temporal dynamics of the meiofauna community in Marian Cove, King George Island, Antarctica were observed from March 7 to December 21 2007. Nine meiofauna taxa were found, with nematodes the most dominant group, making up 92.97% of the total meiofauna density, followed by harpacticoid copepods (3.18%). Meiofauna abundance ranged from 123 to 874 individuals per 10 <TEX>$cm^2$</TEX> (mean 464 inds.10 <TEX>$cm^{-2}$</TEX>), which is lower than that found in some polar and temperate regions. The lowest meiofauna abundance was found in the 26th April sample (III) and the highest meiofauna abundance was found in the March 23rd sample (II). There was no correlation between meiofauna abundance and season. The seasonal changes were likely caused by meltwater runoff, and there were the physical disturbances on the bottom sediment by huge iceberg. Biomass of meiofauna varied between 20.36 and 101.02 <TEX>${\mu}gC{\cdot}10\;cm^{-2}$</TEX>, and overall mean biomass was 54.17 <TEX>${\mu}gC{\cdot}10\;cm^{-2}$</TEX> during the study periods. More than 80% of meiofauna was concentrated in the upper 2 cm of the sediment, and density decreased with depth. The mean diversity index was 0.37, and the ratio between the abundance of nematodes: and harpacticoids (N/C) ratio ranged from 7.31 to 95.04 (mean 26.39). NMDS analysis divided the community into three groups: A (III, IV, V, VII, VIII), B (II, IX, XI, XII) and C (I, V, X). The results of ANOSIM and SIMPER analysis revealed significant differences in community structure among three groups and major contributed meiofauna taxon in grouping were nematodes and copepods. No significant correlations were observed between major meiofauna taxon and environmental factors. Thirteen species in 12 genera representing nine families of harpacicoids were recorded. Ancorabolidae was the most diverse family, and Heteropsyllidae was the most abundant. The correlation analysis between benthic harpacticoid copepods and environmental factors showed that some species were affected by water temperature, sediment temperature, salinity, chlorophyll a concentration, grain size of the sediments and heavy metal contents of the sediments. These data describe the usefulness of benthic harpacticoid copepods as biological indicator species in Antarctic regions.

Main meiofauna taxa as an indicator for assessing the spatial and seasonal impact of fish farming

The present study aimed to establish potential indicators of fish farming pollution in muddy substrate, by means of meiofauna, and to test whether the effect of the fish farm is more important to determine the meiofauna community than the seasonal environmental conditions. Sampling was performed in spring, after several months of light feeding, and in summer, at high food supply. Samples were collected in three directions at various distances from the floating cages. Harpacticoid copepods and kinorhynchs, whose abundance decreased under the cages, were put forward as indicator taxa. However, harpacticoid copepods were sensitive to fish farm only, while kinorhynchs showed responsiveness to fish farm and to seasonal environmental conditions. Total meiofauna density was dependent on season sensu stricto. The nMDS clearly showed a ‘cage community’ and ‘control community’ in both sampling occasions; therefore it is a good tool for impact assessment.

Spatial patterns of meiofauna and diversity of nematode species assemblages in the Uvea lagoon (Loyalty Islands, South Pacific)

Meiofauna assemblages were investigated at 15 stations on triplicated samples in the Uvea Atoll (Loyalty Islands) in relation to 9 selected environmental parameters. Spatial patterns and variability of meiofauna density were quantified according to location, macrofauna and nematode species assemblages. Meiofauna was dominated by ciliates and nematodes. Densities of total meiofauna and of most of the meiofauna taxa were significantly higher in the back reef North Pléiades stations than the leeward side of the Island. The highest correlation between biotic patterns and environmental parameters that best explains the pattern was with sediment thickness and to a lesser extent organic matter, C/N ratio and depth. One hundred and thirty-four nematode species were identified with four dominant species Chromadora macrolaimoides, an undescribed species of Bolbonema, Daptonema svalbardense and Prochromadorella septempapillata. Three significantly different nematode species assemblages were detected in two of the previously described macrofauna assemblages by cluster analysis and multidimensional scaling methods suggesting that nematodes are more sensible ecological indicators than macrofauna. Diversity indices based on dominance were not significantly different among the three nematode species assemblages but indices based on species richness and rarefaction were significantly higher leeward of Uvea Island. Estimates of total species richness showed no sign of stabilizing with sample size. However, rare species stabilized very quickly, whereas abundant species were added with increasing sampling coverage, indicating a high spatial variability of the local composition of nematodes.

심해 극한 환경에서의 중형저서동물 군집

The spatial patterns of meiobenthic communities in deep-sea sediment were examined. Sediment samples for analyzing of meiobenthic community structure were collected using a remote operated vehicle (ROV), multiple corer TV grab at 20 stations at five sites. In all, 15 meiofauna groups were recorded. Nematodes were the most abundant taxon. Benthic foraminiferans, harpacticoid copepods, polychaetes, and crustacean naupii were also dominant groups at all sites. The total meiofauna density at the study sites varied from 49 to 419 ind./. The maximum density was recorded at a site located in Challenger Deep in the Mariana trench where simple benthic foraminifera with organic walls flourish. These distinctive taxa seem to be characteristic of the deepest ocean depths. Active hydrothermal sediments contain up to 150 harpacticoid copepods per of sediment. In a inactive ridge sediments, devoid of macrofaunal organisms:, the abundance of harpacticoid copepods never exceeded 15 ind./. Multivariate analysis (multidimensional scaling) revealed significant differences in community structure among the three regions; near an active hydrothermal vent, in the deepest ocean depths and at typical deep-sea bed sites.

Muddy-bottom meiofauna responses to metal concentrations and organic enrichment in New Caledonia South-West Lagoon

The New Caledonia South-West Lagoon is subject to both major terrigenous and urban inputs associated with the development of the Nouméa city, which may affect its functioning. Environmental parameters, sediment biochemical characteristics, metal concentrations and benthic meiofauna were assessed to better characterize and unravel the effects of these two potential disturbances in muddy sediments. Seventeen stations were sampled along disturbance gradients within four bays located around the city of Nouméa and subject to different levels of anthropogenic and terrigenous inputs. Two cruises were carried out during July (dry season) and December 2002 (beginning of the rainy season). Spatial changes were much more important than temporal ones. Temporal changes were restricted to the biochemical characteristics of superficial sediment and more specifically to its labile organic fraction. Two groups of metals were identified based on their spatial distribution. The first was composed of Cr, Mn, Co and Ni, which mainly originate from the erosion of soils and mining activities. The second was composed of Zn, Cu and Pb, which mainly originate from urban activities. All sampled bays could be considered as potentially contaminated by one or more metals. Total meiofauna density correlated negatively with bulk descriptors of organic matter (during the December cruise) and positively with EHAA/THAA ratio (during both cruises). It did not correlate with Ni, Mn, Cr and Co but did correlate negatively with Cu and Pb during the December cruise. Our results suggest that the density of meiofauna in the South-West Lagoon is positively affected by the qualitative and negatively affected by the quantitative characteristics of sedimentary organic matter. This pattern differs drastically from what is usually observed in temperate ecosystems. This discrepancy may result from the importance of the inputs of refractory organic matter of terrestrial origin in the South-West Lagoon. Metals originating from soil erosion and mining have apparently no effect on total meiofauna, whereas some metals originating from urban activities may have a negative effect on total meiofauna at least during the beginning of the rainy season.

Influence of fine sediments on meiofauna colonization densities in artificial stream channels

Excessive fine sediments have been shown to adversely affect abundance and diversity of stream macroinvertebrates, but effects on meiofauna have been only minimally and indirectly assessed. We used 12 artificial channels in a 4 th order Ozark stream to investigate the influence of silt (particle diameter 63 μm to 2 mm) and gravel (particle diameter 2 to 16 mm) on meiofauna colonization. Four channels were filled with gravel, four with 1/2 gravel and 1/2 sand, and four with 1/3 gravel, 1/3 sand, and 1/3 topsoil, referred to as gravel, sand, and silt treatments, respectively. Substrate cores were taken from the natural and artificial channels for analysis of meiofauna (80 μm to 1 mm) and substrate composition. Rotifera, Copepoda, Chironomidae, Nematoda, Oligochaeta, and Mollusca (principally juvenile Corbicula fluminea) comprised the major meiofauna taxa. Total meiofauna density in the artificial channels differed significantly among treatments. Density was lower in the silt treatment than in gravel or sand treatments, but overall densities in the gravel and sand treatments did not differ. Responses to treatments varied among specific taxa; densities of rotifers, copepods, nematodes, and oligochaetes were lower in the silt than the gravel treatment, but chironomids and nematodes were equally abundant in gravel and sand treatments, while lower in the silt treatment. Total meiofauna density did not differ between the natural channel and the gravel treatment but was lower in the sand and silt treatments. Copepod density was higher in the gravel treatment, and nematode, oligochaete, and mollusk densities were lower for all three treatments compared to the natural channel. The lower density of total meiofauna associated with high concentrations of silt suggests that excessive silt reduces habitat space and/or quality for meiobenthic organisms, while a sand and gravel mix is suitable for some meiofauna taxa.

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.

Temporal dynamics of meiofauna communities in two small submountain carbonate streams with different grain size

The meiofauna community (especially nematodes, oligochaetes and chironomids) in the streambed surface of two small submountain carbonate streams (Krahenbach and Korsch, Germany) was investigated from April 1998 to March 1999. The Krahenbach stream is relatively sorted and fine-grained, while the Korsch stream is more heterogeneous and coarse-grained. The streams also differ in velocity, water level, conductivity, chloride concentration and organic content of sediment. Total meiofauna density reached a maximum value of 906 individuals per 102 cm in the Krahenbach and 3166 individuals per 102 cm in the Korsch. Rotifers were the most abundant group in the Krahenbach (52% of total fauna), whereas nematodes were dominant in the Korsch (63%). Meiofauna showed one abundance peak in the Korsch and two abundance peaks in the Krahenbach. In the Krahenbach, distinct seasonal patterns at family and species level occurred, whereas in the Korsch even at high taxonomic level only one abundance peak was observed. The most abundant nematode family in both streams were Monhysteridae, followed by Tobrilidae in the Krahenbach and by Tylenchidae in the Korsch. The dominant oligochaete family in both streams were Naididae (especially Chaetogaster langi (Bretscher, 1896) and Nais elinguis (O. F. Muller, 1773)), followed by Tubificidae. The most abundant chironomid genera in the Krahenbach were Stichtochironomus and Corynoneura. Prodiamesa olivacea (Meigen, 1818) was the dominant chironomid species in the Korsch. Deposit-feeding and detritus-feeding animals were numerically dominant in both streams. The increased mean abundance of Diplogasteridae, Rhabditidae, Tubificidae and N. elinguis in the Korsch compared to that in the Krahenbach indicates an organically enriched situation.

Benthic meiofauna responses to five forest harvest methods

Benthic meiofauna were collected from the pools of minute (0 order) streams in the Ouachita National Forest, Arkansas during March 21–23, 1996 to see if benthic communities responded to forest harvest methods in a similar manner as plankton communities collected two years prior. The study streams and their watersheds (2–6 ha) were located in 14–16 ha forest stands that were selected for comparability of stands. Five treatment stands were paired with adjacent undisturbed reference stands (10 total). Treatment stands were subjected to one of five harvest methods listed in order of decreasing severity of harvest disturbance to the stands: (1) clearcut; (2) pine seed-tree; (3) pine shelterwood; (4) pine-hardwood group selection; and (5) pine single-tree selection. The mean number of taxa per site was 14 with a range of 9–20 taxa including rotifers, copepods, nematodes, dipterans, ostracods and `other' meiofauna. Densities of total meiofauna (mean=2449 No. l −1) were significantly higher (p= 0.002) in treated sites. Highest densities occurred in single-tree and clearcut treatments. Rotifers were significantly more numerous at the single-tree treatments (p=0.03) and nematodes were significantly greater at the clearcut treatments (p=0.03). We conclude that benthic meiofauna in these headwater streams are sensitive to silviculture practices and that the impact of forest harvest persists for at least 2.5 years.

Meiofauna in intermittent streams differ among watersheds subjected to five methods of timber harvest

Meiofauna were collected from the pools of small (0 order) streams in the Ouachita National Forest, Arkansas to examine the impact of forest harvest methods. The study streams and their watersheds (2–6 ha) were located in 14–16 ha forest stands that were selected based on comparability of stands. Five treatment stands were paired with adjacent undisturbed reference stands (10 total). Treatment stands were subjected to one of five harvest methods, listed in order of decreasing severity of harvest disturbance to the stands: (1) clearcut; (2) pine seed-tree; (3) pine shelterwood; (4) pine-hardwood group selection; and (5) pine single-tree selection. Although the mean density of meiofauna collected in 22 l samples pumped from pools was low (1 No. l −1), significant differences were identified. Densities of total meiofauna, harpacticoid copepods, nauplii, ostracods and `other' meiofauna varied significantly by site and treatment (forest harvest). The highest densities of these taxa occurred at the single-tree treatment sites. Greater densities of meiofauna corresponded to greater diversity. The mean number of taxa per site was 11 with a range of 5–24. Rotifers, copepods, nematodes, ostracods and `other' meiofauna taxa were collected. The pattern of diversity of meiofauna at treatment sites from the least intensive (single-tree) to most intensive (clearcut) suggests a curve related to disturbance intensity.

The meiofauna community of two small German streams as indicator of pollution

In order to validate the results of biomarkerstudies as tools for the assessment of smallstreams, the meiofauna community and inparticular the nematodes of two small Germanstreams (Baden-Wurttemberg) were analysedduring 1998. One site of Krahenbach (AB)and three sites of Korsch (KA, KD, KE) weresampled in March, May, July and November. Thelimnological analysis indicates that two sitesof Korsch (KD, KA: polluted sites) weredistinctly enriched by inorganic and organicsubstances compared with KE and AB (unpollutedsites). In the Krahenbach, nematodes,chironomids, oligochaetes and tardigradesdominated the meiofauna community (92%),whereas in the Korsch nematodes andoligochaetes were dominant (93%). The totalmeiofauna density showed seasonal patterns inboth streams. Nematodes were the most abundantgroup at the four investigated locations. Themean abundance of nematodes ranged from 28individuals per 10 cm2 to 1205 individualsper 10 cm2 and at least 103 species wereidentified, belonging to 25 families. Nosubstantial difference occurred in thedistribution of nematode feeding-types at thepolluted and unpolluted sites. All communitieswere clearly dominated by bacteria-feedingnematodes with percentages ranging from 70% to75%. In order to assess the sediment quality,the nematode community of each sampling sitewas interpreted using the ratio ofSecernentea/Adenophorea as well as the MaturityIndex (MI). Both the percentage of Adenophoreaand the MI decreased towards the pollutedsites, detecting a more disturbed nematodecommunity at the polluted than unpollutedsites. However, there are nematode species(e.g. Tobrilus diversipapillatus) whichdo not fit in this assessment concept. In thisstudy the disturbance of the nematode communitywas related to eutrophication, rather than tothe effect of contaminants. In summary, thisinvestigation confirmed that meiofaunaorganisms and in particular nematodes aresuitable for the assessment of the sedimentquality of running waters.

Meiofauna response to a dynamic river plume front

The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g−1 for chlorophyll a and 1.2 to 17.7 μg g−1 for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g−1). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541 ind. 10 cm−2) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector, the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath, their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages.

Response of Meiofauna to Immediate Benthic Disturbance in the Central Indian Ocean Basin

Twenty-four stations (12 each, during pre- and postdisturbance studies) 5300 to 5330 m deep between 10°01' and 10°03'S latitude and between 75°59' and 76°02'E longitude were sampled to study the effect of benthic disturbance on the distribution of meiofauna in the Central Indian Ocean. Bottom-sampling was conducted with a box corer. Total meiofauna density ranged from 35 to 45 organisms per 10 cm2 of bottom area during the predisturbance period and 21 to 32 organisms per 10 cm2 during the postdisturbance period in the test and reference sites. Differences between pre- and postdisturbance study results were statistically significant (P < 0.05). Nematoda was the most abundant meta-zoan group, on an average representing >55% of the meiofaunal population. The abundance of nematodes and harpacticoid copepods as well as total meiofauna showed marked decreases during postdisturbance sampling. Vertical distribution of meiofauna in the sediment cores revealed that 75% to 90% of the metazoan population was confined to the top 2-cm layer of the sediment. Recolonization experiments suggest that harpacticoid copepods may take more time for recolonization than the nematodes and are more sensitive to the physical disturbance. These findings suggest that nematodes and harpacticoid copepods can be used as indicator organisms in recolonization experiments.

Seasonality, abundance, and microhabitat distribution of meiofauna from a Chickahominy River, Virginia tidal freshwater marsh

Meiofauna were sampled from intertidal pool and vegetative hummock microhabitats at a tidal freshwater marsh on the Chickahominy River, Virginia. Nematodes, ostracods, tardigrades, oligochaetes (Naididae), copepods (Harpacticoida and Cyclopoida), and the sabellid polychaete Manayunkia spp. were numerically dominant in monthly collections. Total meiofaunal densities ranged from 169 individuals 10 cm−2 (low marsh pools, April) to 13832 individuals 10 cm−2 (low marsh hummocks, September). Highest densities of total meiofauna were observed in August–September, coincident with recruitment of oligochaetes and Manyunkia spp. to low marsh hummocks. Nematodes were generally abundant in all seasons and represented 37% of total meiofauna collected. Nematode densities were significantly greater on hummocks (p=0.0001). Ostracods were significantly more abundant in pools, Greatest densities of ostracods were observed in May. Tardigrades were abundant November through March, and September. Significantly greater abundance of tardigrades was observed on hummocks. Harpacticoid copepods were abundant from December through April and cyclopoids were abundant from May through September (low marsh only).

Vertical Distribution of Meiobenthos in Bathyal Sediments of the Eastern Mediterranean Sea: Relationship with Labile Organic Matter and Bacterial Biomasses

Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep‐sea sediments.

Evidence of the passive deposition of meiofauna into fiddler crab burrows

Small-scale biogenic depressions are known to accumulate suspended particles from the water column. Fiddler crab Uca spp. burrows are prevalent depressions in salt marsh sediments and provide habitats for numerous meiofauna. This research investigated the distribution of meiofauna in fiddler crab burrows in a North Carolina salt marsh and examined the hypothesis that patterns of meiofauna abundance in these burrows are the result of passive accumulation of meiofauna. Burrow sediments contained higher densities of total meiofauna than ambient marsh sediments. The differential collection of meiofauna in large (1.6 cm diameter) vs. small (1.1 cm diameter) burrow mimics (test tubes) placed in the field over one tidal cycle suggested that (a) meiofauna are passively trapped in burrows and (b) burrow morphology may cause differential deposition into burrows. These findings were supported by observations of water flow patterns over large and small burrow mimics in a flume in which dye was entrained 0.5–3.5 cm into tubes. Entrainment of meiofauna appeared more likely at flow speeds of 4.3 than 2.5 or 8.7cm·s −1. Adult copepods, foraminifera, and adult and larval polychaetes were equally abundant in natural Uca burrows at all depths sampled. Nematodes, ostracods, juvenile copepods, copepod and noncopepod nauplii, and turbellarians were less abundant in deep (3–16 cm) than shallow (<3 cm) burrow sediments.