Meiofaunal Abundance Research Articles

Effects of freshwater flow extremes on intertidal biota of a wet-dry tropical estuary

Freshwater flow into estuaries during periods of high rainfall is considered to enhance the biomass of primary producers, with positive effects propagating to higher trophic groups. We examined the effect of flow on chlorophyll a (chl a) concentrations and meiofaunal abundance on the intertidal mudflats in a wet-dry tropical estuary in the Norman River, northern Australia. Meiofaunal density and sediment chl a concentrations (microphytobenthos) were significantly reduced during 2 consecutive wet season floods (the first, a major flood; the second, minor). Additionally, a short-term study of primary productivity on the mudflats during the minor flood measured rates below detection limits. The effects of salinity and burial by sediment on chl a concentrations and meiofaunal abundance were examined experimentally. Both the sudden and prolonged changes in salinity and sediment movement, and subsequent sedimentation as a result of wet season floods were the likely causes of the reduced meiofaunal density, chl a concentrations and benthic primary production. In the short term, large floods in the wet-dry tropics appear to act more as a disturbance event than a subsidy for benthic estuarine biota, and any positive effects of the flood may not occur until flooding eases. Additionally, we propose that there is a transitional period between the typical wet and dry seasons in the wet-dry tropics, during which flood waters are dissipating and the initial impact of the flood has abated, and there are positive effects on meiofauna and microphytobenthos biomass.

The Impact on Bottom Sediments and Ostracods in the Khlong Thom River Mouth Following the 2004 Indian Ocean Tsunami

Fossil ostracods are a useful tool for identifying tsunamigenic sediments. However, the behavior of ostracod shells within the bottom tsunami sediments in Recent river mouths and estuaries is poorly understood. In this study, we analyzed bottom sediments and ostracod specimens taken from sites within the Khlong Thom River and sites adjacent to the Malacca Strait along the Malay Peninsula during three intervals—pre-tsunami, four months after the tsunami, and post-tsunami—to determine the impact of the 2004 Indian Ocean tsunami on the bottom sediments in the river mouths and estuaries. The broad distribution of the terrigenous plant material-bearing sediments in the Malacca Strait and the southern part of river mouth areas after the tsunami indicates that the sediments and the suspended materials deposited on bottoms were preserved for four months after the tsunami. However, no plant debris was recorded in the Malacca Strait, the southern part of the river mouth (RM), or junction areas between the river mouth and the estuary in 2008, suggesting that they had dispersed from the bottom during the three years and eight months after the tsunami. Of the bottom sediments taken four months after the tsunami, a few containing no plant debris were recorded in the northern and middle parts of RM, characterized by no ostracods or an abundance of adult and late juvenile instar specimens of Keijella reticulata. Based on these observations, we believe that small materials, such as plant debris and early juvenile instar ostracods, were transported from the bottom after the tsunami by the ordinary current. Previous investigations have captured changes in the abundance and density of meiofauna within a few days of a tsunami; therefore, the existence of some changes in ostracods that were able to recover during the four months may be considered, although there was no change in ostracod biofacies caused by the tsunami in the study area.

A preliminary comparative assessment of the meiofaunal communities of Maltese pocket sandy beaches

Whilst the macrofaunal communities of Maltese pocket sandy beaches have been extensively studied, the meiofaunal communities of the same beaches are virtually unknown. The main aims of the current study include the acquisition of preliminary data on the occurrence of meiofaunal higher taxa on Maltese pocket sandy beaches, the comparison between the Maltese beach meiofaunal communities with those on other Mediterranean sandy beaches and the assessment of the influence of a selected number of beach physical parameters on the same communities. Seven sandy beaches in the Maltese Islands were sampled during spring 2012, with sediment samples being collected at the Mean Sea Level (mediolittoral zone). Median grain size and sediment organic and water content were measured for each beach. A total of 13 higher meiofaunal taxa were recorded from the Maltese sandy beaches. The meiofaunal abundance ranged between 50 and 1392 individuals/10 cm2, whilst the number of meiofaunal higher taxa recorded at a single sampling station ranged between 5 and 10. Mean grain size and sorting coefficient appeared to have the highest influence on variations in Maltese meiofaunal communities. Based on conducted analysis it is suggested that inter-beach dispersal of meiofaunal propagules for Maltese beaches is restricted to short distances and does not operate over distances exceeding 5–10 km. This in turn results in some degree of compartmentalisation of the same assemblages. The meiofaunal assemblages recorded from the Maltese beaches exhibited comparable densities to those recorded on other Central Mediterranean sandy beaches and no significant differences in community structure at higher taxa level were observed.

Grazing effects on nematodes and other components of the periphyton at three depths in Lake Erken

The periphyton of stony hard substrates in the littoral zone of lakes is inhabited by an abundant and diverse algae and meiofauna assemblage that is regulated by grazing. The objective of our study was to examine the effect of macroinvertebrate grazers on periphytic algae and meiofaunal organisms at different depths in the littoral zone of Lake Erken (Sweden). To this end, a 2-factorial field experiment was carried out in which macrofaunal access to the periphyton was manipulated at 3 different water depths (30, 70, and 200 cm). Grazing effects on algal biomass varied among depths and were highest in both deeper zones. Compared to algal biomass, the abundance of meiofaunal organisms was less affected by grazing because macrograzers significantly reduced meiofauna only at the 200-cm depth. The organism mainly responsible for the depth-dependent differences in grazer effects was the snail Theodoxus fluviatilis, which dominated macrofaunal assemblage at depths where grazing effects were the strongest (70 and 200 cm). The abundance of T. fluviatilis was positively correlated with the proportions of reduced algal biomass and reduced meiofaunal abundance. Meiofaunal groups and individual nematode species responded differently to grazing, so our results further revealed that grazing macroinvertebrates affected the composition of the meiofaunal assemblage. However, meiofaunal and nematode assemblages differed more across depths than across grazing treatments, suggesting that other depth-related factors (e.g., hydrodynamics or light) also were important for structuring periphytic meiofaunal assemblages.

Biostimulation as an attractive technique to reduce phenanthrene toxicity for meiofauna and bacteria in lagoon sediment

A microcosm experiment was setup to examine (1) the effect of phenanthrene contamination on meiofauna and bacteria communities and (2) the effects of different bioremediation strategies on phenanthrene degradation and on the community structure of free-living marine nematodes. Sediments from Bizerte lagoon were contaminated with (100 mg kg(-1)) phenanthrene and effects were examined after 20 days. Biostimulation (addition of nitrogen and phosphorus fertilizer or mineral salt medium) and bioaugmentation (inoculation of a hydrocarbonoclastic bacterium) were used as bioremediation treatments. Bacterial biomass was estimated using flow cytometry. Meiofauna was counted and identified at the higher taxon level using a stereomicroscope. Nematodes, comprising approximately two thirds of total meiofauna abundance, were identified to genus or species. Phenanthrene contamination had a severe impact on bacteria and meiofauna abundances with a strong decrease of nematodes with a complete disappearance of polychaetes and copepods. Bioremediation counter balanced the toxic effects of phenanthrene since meiofauna and bacteria abundances were significantly higher (p < 0.01) than those observed in phenanthrene contamination. Up to 98 % of phenanthrene removal was observed. In response to phenanthrene contamination, the nematode species had different behavior: Daptonema fallax was eliminated in contaminated microcosms, suggesting that it is an intolerant species to phenanthrene; Neochromadora peocilosoma, Spirinia parasitifera, and Odontophora n. sp., which significantly (p < 0.05) increased in contaminated microcosms, could be considered as "opportunistic" species to phenanthrene whereas Anticoma acuminata and Calomicrolaimus honestus increased in the treatment combining biostimulation and bioaugmentation. Phenanthrene had a significant effect on meiofaunal and bacterial abundances (p < 0.05), with a strong reduction of density and change in the nematode communities. Biostimulation using mineral salt medium strongly enhanced phenanthrene removal, leading to a decrease of its toxicity. This finding opens exciting axes for the future use of biostimulation to reduce toxic effects of PAHs for meiofauna and bacteria in lagoon sediment.

Diversity and composition of macro- and meiofaunal carapace epibionts of the hawksbill sea turtle (Eretmochelys imbricata Linnaeus, 1822) in Atlantic waters

The presence of macro-epibionts on turtle carapaces is a well-known phenomenon, whereby carapaces are occupied by dynamic and fully functional epibiont communities. However, meiofaunal organisms have been largely ignored in turtle shell studies despite their omnipresence and higher abundances and diversity than the macrofauna. Epifauna from the hawksbill sea turtle Eretmochelys imbricata was investigated during summer 2010 with the aim to advance our knowledge on meiofaunal epibiont communities on turtle carapaces and gain insights into their interaction with settled macrofauna. Eighteen epibiont higher taxa were found (17 meiofauna, 5 macrofauna), 5 of which are common for macro- and meiofauna. Meiofauna was present on all turtle carapaces, but macrofauna occurred on only 8 out of 19 investigated carapaces, suggesting that carapace colonization by meiofauna precedes macrofauna recruitment. In addition, the macrofauna embedded on the carapaces increased the microhabitat complexity, favoring richer and more abundant meiofauna communities. The significant positive correlations between meiofauna and macrofauna taxa (up to 90 %) suggests the presence of mutual facilitating processes and indicates the positive effects between meio- and macrofaunal epibionts important for their recruitment and establishment. The hawksbill sea turtle carapaces were occupied by fully functional and active epifaunal communities, with adult and reproductive stages for most meiofaunal and macrofaunal taxa. Turtle carapaces can therefore be seen as a biological substrate that can serve as a platform for faunal dispersal, as has been observed for barnacles, enhancing the geographical distribution of several species through sea turtle migration. In addition to the main focus of this paper on meio- and macrofaunal epibiont communities, we provide an updated list of taxa found on carapaces of the hawksbill sea turtle and discuss the geographical scope and dispersion potential of some of these taxa.

The roles of biological interactions and pollutant contamination in shaping microbial benthic community structure

Biological interactions between metazoans and the microbial community play a major role in structuring food webs in aquatic sediments. Pollutants can also strongly affect the structure of meiofauna and microbial communities. This study aims investigating, in a non-contaminated sediment, the impact of meiofauna on bacteria facing contamination by a mixture of three PAHs (fluoranthene, phenanthrene and pyrene). Sediment microcosms were incubated in the presence or absence of meiofauna during 30days. Bioremediation treatments, nutrient amendment and addition of a hydrocarbon-degrading bacterium, were also tested to enhance PAH biodegradation. Results clearly show the important role of meiofauna as structuring factor for bacterial communities with significant changes observed in the molecular fingerprints. However, these structural changes were not concomitant with changes in biomass or function. PAH contamination had a severe impact on total meiofaunal abundance with a strong decrease of nematodes and the complete disappearance of polychaetes and copepods. In contrast, correspondence analysis, based on T-RFLP fingerprints, showed that contamination by PAH resulted in small shifts in microbial composition, with or without meiofauna, suggesting a relative tolerance of bacteria to the PAH cocktail. The PAH bioremediation treatments were highly efficient with more than 95% biodegradation. No significant difference was observed in presence or absence of meiofauna. Nutrient addition strongly enhanced bacterial and meiofaunal abundances as compared to control and contaminated microcosms, as well as inducing important changes in the bacterial community structure. Nutrients thus were the main structural factor in shaping bacterial community composition, while the role of meiofauna was less evident.

Meiofauna assemblages of the Condor Seamount (North-East Atlantic Ocean) and adjacent deep-sea sediments

Seamounts are currently considered hotspots of biodiversity and biomass for macro- and megabenthic taxa, but knowledge of meiofauna is still limited. Studies have revealed the existence of highly diverse meiofauna assemblages; however most data are mainly qualitative or focused only on specific groups, thus preventing comparisons among seamounts and with other deep-sea areas. This study, conducted on Condor Seamount (Azores, North-East Atlantic Ocean), describes variation in abundance, biomass, community structure and biodiversity of benthic meiofauna from five sites located on the Condor Seamount: and one site away from the seamount. While the summit of the seamount hosted the highest alpha biodiversity, the flanks and the bases showed a rich meiofauna assemblage in terms of abundance and biomass. The observed marked differences in grain size composition of sediments reflected the oceanographic conditions impacting different sectors of the Condor seamount, and could play an important role in the spatial distribution of different meiofaunal taxa. Trophic conditions (biochemical composition of organic matter) explained 78% of the variability in the meiofauna biomass pattern while sediment grain influenced the vertical distribution of meiofauna and only partially explained meiofaunal taxa composition. This study provides a further advancement in the knowledge of meiofaunal communities of seamounts. Only a deeper understanding of the whole benthic communities (including meiofauna) will allow to elaborate effective management and conservation tools for seamount ecosystems.

Temporal dynamics of shallow subtidal meiobenthos from a beach in Tenerife (Canary Islands, northeast Atlantic Ocean)

A shallow subtidal (3 m deep) meiofaunal assemblage in Los Abrigos Bay, Tenerife, Canary Islands was sampled during May 2000–April 2001. The main aims were to (1) find temporal variations in meiofaunal assemblage structure and overall abundance, as well as in the most abundant meiofaunal species throughout the study period, and (2) identify environmental variables (sedimentary composition, organic matter content, and total nitrogen) that better explain meiofaunal assemblage structure during the study year. The most abundant species were the nematodes Siphonolaimus sp. 2 and Catanema sp., which represented 46.2% of the overall meiofaunal abundances and varied significantly throughout the study duration. Overall meiofaunal abundance and the most abundant taxonomic groups (nematodes, copepods, and oligochaetes) showed significant temporal variations during the study period. Nematodes overwhelmingly dominated during the study period, ranging from 78% in May to 97.34% in February. Multivariate analyses showed seasonality inmeiofaunal community structure during the study year, with the lowest abundances in May.

CellTracker Green labelling vs. rose bengal staining: CTG wins by points in distinguishing living from dead anoxia-impacted copepods and nematodes

Abstract. Hypoxia and anoxia have become a key threat to shallow coastal seas. Much is known about their impact on macrofauna, less on meiofauna. In an attempt to shed more light on the latter group, in particular from a process-oriented view, we experimentally induced short-term anoxia (1 week) in the northern Adriatic Sea (Mediterranean) and examined the two most abundant meiofauna taxa – harpacticoid copepods and nematodes. Both taxa also represent different ends of the tolerance spectrum, with copepods being the most sensitive and nematodes among the most tolerant. We compared two methods: CellTracker Green (CTG) – new labelling approach for meiofauna – with the traditional rose bengal (RB) staining method. CTG binds to active enzymes and therefore colours live organisms only. The two methods show considerable differences in the number of living and dead individuals of both meiofauna taxa. Generally, RB will stain dead but not yet decomposed copepods and nematodes equally as it does live ones. Specifically, RB significantly overestimated the number of living copepods in all sediment layers in anoxic samples, but not in any normoxic samples. In contrast, for nematodes, the methods did not show such a clear difference between anoxia and normoxia. RB overestimated the number of living nematodes in the top sediment layer of normoxic samples, which implies an overestimation of the overall live nematofauna. For monitoring and biodiversity studies, the RB method might be sufficient, but for more precise quantification of community degradation, especially after an oxygen depletion event, CTG labelling is a better tool. Moreover, it clearly highlights the surviving species within the copepod or nematode community. As already accepted for foraminiferal research, we demonstrate that the CTG labelling is also valid for other meiofauna groups.

Non-Linear Interactions Determine the Impact of Sea-Level Rise on Estuarine Benthic Biodiversity and Ecosystem Processes

Sea-level rise induced by climate change may have significant impacts on the ecosystem functions and ecosystem services provided by intertidal sediment ecosystems. Accelerated sea-level rise is expected to lead to steeper beach slopes, coarser particle sizes and increased wave exposure, with consequent impacts on intertidal ecosystems. We examined the relationships between abundance, biomass, and community metabolism of benthic fauna with beach slope, particle size and exposure, using samples across a range of conditions from three different locations in the UK, to determine the significance of sediment particle size beach slope and wave exposure in affecting benthic fauna and ecosystem function in different ecological contexts. Our results show that abundance, biomass and oxygen consumption of intertidal macrofauna and meiofauna are affected significantly by interactions among sediment particle size, beach slope and wave exposure. For macrofauna on less sloping beaches, the effect of these physical constraints is mediated by the local context, although for meiofauna and for macrofauna on intermediate and steeper beaches, the effects of physical constraints dominate. Steeper beach slopes, coarser particle sizes and increased wave exposure generally result in decreases in abundance, biomass and oxygen consumption, but these relationships are complex and non-linear. Sea-level rise is likely to lead to changes in ecosystem structure with generally negative impacts on ecosystem functions and ecosystem services. However, the impacts of sea-level rise will also be affected by local ecological context, especially for less sloping beaches.

The influence of submarine groundwater discharges on subtidal meiofauna assemblages in south Portugal (Algarve)

Submarine groundwater discharges (SGD) have been documented as contributing to the biological productivity of coastal areas, through a bottom-up support to higher trophic levels. Nevertheless, the effects on the bottom levels of the coastal food web, namely the meiofauna, are still very poorly known. The “Olhos de Água” beach is the only area on the South coast of Portugal where submarine freshwater seepages have been identified. In this study, meiofauna assemblages in the area impacted by SGD were compared with the meiofauna from a similar area, but without SGD. Samples were taken in Spring and Summer 2011, under different hydrological regimes, aquifer recharge (after Winter) and dryness (after Spring), respectively. The major changes in the community were recorded at a seasonal level, with higher abundances and number of taxa in Spring, when compared to Summer. This may be explained by better sediment aeration during spring along with higher food availability from the sedimentation of spring phytoplankton blooms. Although no significant differences were detected by multivariate analysis on the meiofauna abundances between Control and Impact areas, pair-wise tests on the interactions between factors in number of taxa (S) and species richness (Margalef's d) suggested that the discharge of groundwater stimulated an increase in meiofauna diversity. Such effect can be observed between the meiofauna assemblages from impacted and control areas and also between periods with different discharge regimes (Spring and Summer) in the impacted area. These findings highlight the role that freshwater discharges from coastal aquifers have on meiofauna assemblages and suggest that SGD contribute to enhance the transfer of energy from the lower levels of the trophic web to upper levels.

Major consequences of an intense dense shelf water cascading event on deep-sea benthic trophic conditions and meiofaunal biodiversity

Abstract. Numerous submarine canyons around the world are preferential conduits for episodic dense shelf water cascading (DSWC), which quickly modifies physical and chemical ambient conditions while transporting large amounts of material towards the base of slope and basin. Observations conducted during the last 20 yr in the Lacaze-Duthiers and Cap de Creus canyons (Gulf of Lion, NW Mediterranean Sea) report several intense DSWC events. The effects of DSWC on deep-sea ecosystems are almost unknown. To investigate the effects of these episodic events, we analysed changes in the meiofaunal biodiversity inside and outside the canyon. Sediment samples were collected at depths varying from ca. 1000 to &gt; 2100 m in May 2004 (before a major event), April 2005 (during a major cascading event) and in October 2005, August 2006, April 2008 and April 2009 (after a major event). We report here that the late winter–early spring 2005 cascading led to a reduction of the organic matter contents in canyon floor sediments down to 1800 m depth, whereas surface sediments at about 2200 m depth showed an increase. Our findings suggest that the nutritional material removed from the shallower continental shelf, canyon floor and flanks, and also the adjacent open slope was rapidly transported to the deep margin. During the cascading event the meiofaunal abundance and biodiversity in the studied deep-sea sediments were significantly lower than after the event. Benthic assemblages during the cascading were significantly different from those in all other sampling periods in both the canyon and deep margin. After only six months from the cessation of the cascading, benthic assemblages in the impacted sediments were again similar to those observed in other sampling periods, thus illustrating a quick recovery. Since the present climate change is expected to increase the intensity and frequency of these episodic events, we anticipate that they will increasingly affect benthic bathyal ecosystems, which may eventually challenge their resilience.

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 159 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 nutri- ent 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 and harpacticoid copepods in different habitats of a Mediterranean seagrass meadow

This study investigated whether associated meiobenthic communities, especially harpacticoid copepods, differed amongst habitats. Five pre-defined habitats within and next to thePosidonia oceanicaseagrass meadow were sampled: living seagrass canopy leaves (LL), small (SMF) and large (LMF) macrophytodetritus fragment accumulations and sand, bare (BS) and covered (CS). The highest meiofauna abundances were recorded in the BS for the core sampled habitats (BS, CS, SMF and LMF) and in the LMF for seagrass material habitats (SMF, LMF and LL). Harpacticoid copepods were the most abundant taxon in all habitats. The assemblage composition at copepod family level showed two distinct habitats clusters: a leaf (LMF and LL) and a sediment cluster (BS, CS and SMF). Subsequently, stable isotope analyses were conducted to analyse the relationship between copepods and their potential food sources in seagrass material habitats. Based on δ13C isotopic analyses and SIAR mixing model, harpacticoid copepods relied for 70% on epiphytes and for 30% onP. oceanicaleaf material in the LMF and LL habitats.

Influence of the combined disposal of sewage and brine on meiofauna

Confluence of anthropogenic influences is common in coastal areas (e.g., disposal of different pollutants like industrial and domestic sewage, brine, etc.). In this study we assessed whether the combined disposal of domestic sewage and brine altered patterns in the abundance and assemblage structure of subtidal meiofauna inhabiting sandy seabeds. Samples were collected in May 2008 and January 2009 at varying distances (0, 15, and 30 m) from the discharge point. Meiofaunal abundances were consistently larger at 0 m (1663.05 ± 1076.86 ind 10 cm–2, mean ± standard error) than at 15 m (471.21 ± 307.97 ind 10 cm–2) and 30 m (316.50 ± 256.85 ind 10 cm–2) from the discharge outfall. This pattern was particularly accentuated for nematodes. Proximity to the discharge point also altered patterns in meiofaunal assemblage structure, though temporal shifts in the sedimentary composition also contributed to explain differences in the meiofaunal assemblage structure. As a result, meiofauna may be a reliable tool for monitoring studies of the combined disposal of sewage and brine as long as potential confounding factors (here temporal changes in grain size composition) are considered.

Effects of green macroalgal blooms on the meiofauna community structure in the Bay of Cádiz

The effect of macroalgal blooms on the abundance and community structure of intertidal sediment meiofauna was studied using an in situ enclosure experiments (Bay of Cádiz, Spain). Meiofaunal abundance (3500–41,000ind 10cm−2) was three to sevenfold higher in the presence of macroalgae. Nematoda were the dominant taxon both in Control (52–82%) and Macroalgae plots (92–96%), followed by Harpacticoida Copepoda and Ostracoda. Non-metric Multi-Dimensional Scaling (MDS) analysis clearly separated the meiofaunal community from Control and Macroalgae plots. Organic matter, organic carbon, total nitrogen, chlorophyll a and freeze-lysable inorganic nutrients were higher in Macroalgae plots, and were highly correlated with the horizontal MDS axis separating Control and Macroalgae meiofaunal communities. Meiofaunal abundance and taxonomic composition in the Bay of Cádiz seem to be bottom–up controlled either through a grazer system based on microphytobenthos in bare sediments or through a decomposer system in macroalgae affected sediments.

Hypoxic Meiobenthic Communities of the Istanbul Strait's (Bosporus) Outlet Area of the Black Sea

Meiobenthos abundance and distribution on the Black Sea shelf and the upper slope area off the Bosporus Strait outlet was studied along a depth transect from 75 to 300m water depth. This study represents the first detailed quantitative analysis of the structure and distribution of meiobenthos communities in the transition zone from oxic to anoxic conditions in the Bosporus outlet area of the Black Sea. Meiobenthos was present at all investigated depths and includes 21 taxa. Among these the Nematoda was the dominant taxon. The maximum of total meiobenthos was located at 75m, other peaks occured at 88 m, 103 m, 160 m, 250 m. At 300 water depth of 300 m the amount of the meiobenthos significantly decreased, while the abundance of such groups as the Ciliophora and Nematoda showed a relative increase in abundance extension. Essential taxonomic richness and abundance of meiofauna is observed in the sediment from the surface layer to 5 cm depth. These results suggest that some benthic eukaryotes can tolerate anoxic and sulfidic conditions. Further studies of this region’s fauna are needed to yield more information about the taxonomic composition of benthos in the transitional oxic/anoxic water masses of the Black Sea.

2005年夏季东太平洋中国多金属结核区小型底栖生物研究

Polymetallic nodules were discovered on the Pacific Ocean in 1891.They exist at the sediment surface,sometimes in upper layers of sediments,and cover more than 50% of the sea floor at Clarion-Clipperton fracture Zone(CCFZ) in the north Pacific.The huge economic value from nodule mining has brought to many research programs dedicated to resource evaluation and design of collecting tools in the 1970s.China has carried out surveys on polymetallic nodules and sediment in the CCFZ for many years.Since the late 1980s,China has already got 75000 km2 exclusive pioneer areas in COMRA′s contracted area.One of the potential impacts of nodule mining is the destruction of the fauna attached to the partial covering of surrounding epifauna by sediment blanketing.Meiofauna,the important components of benthic ecosystem,are considered to be energetically important in benthic food web.as they play a critical role in the recycling of nutrients.In order to manage and mitigate these impacts,we need to better understand the composition and the distribution of meiofauna and its relationship to the environment. A quantitative study was carried out on Dayang Yihao in July 2005.The meiofauna samples were collected from 12 stations in eastern and western sub-area at COMRA's contracted areas,Samples were collected using a multiple corer with four tubes of 9.5cm in diameter,and only undisturbed cores with clear overlying water were used.Thirteen benthic groups were found from the surveyed area,.The average density of meiofaunal were(104.4±20.48) ind/10cm2 and(40.26±25.84) ind/10cm2 in eastern and western sub-area,respectively.The average biomass of nematode were(5.25±0.99)(μg·Dry) /10cm2 and(1.68±0.77)(μg·Dry) /10cm2 in each sub-area.The analysis of spatial distribution has shown that the density of meiofauna and the biomass of nematode in eastern sub-area were substantially higher than that in western sub-area.Nematodes,copepods,polychaeta,and ostracoda were found to be the dominant taxa,and nematodes were the predominant one,constituting 93.13% and 91.36% of total density of meiofauna in eastern and western sub-area,respectively.The analysis of vertical distribution has shown that the density of meiofauna decreased with the depth in the sediment.The top 0—2cm layer of sediment accounted for over 75% of meiofauna.The proportion of meiofauna distributed in the deeper sediment was higher in eastern sub-area than that in western sub-area. In such an oligotrophic environment,low food supply may limit meiofaunal abundance,biomass,,and to a lesser extent species richness..In eastern sub-area,the average concentrations of chlorophyll a and phaeopigment in the top 6cm sediment were 0.004μg/cm2 and 0.169μg/cm2 respectively.In western sub-area,the average concentrations of chlorophyll a and phaeopigment in the top 6cm sediment were 0.002μg/cm2 and 0.082μg/cm2,respectively.There were significant positive relationships between chlorophyll a and phaeopigment in the surface sediment.The correlation between the meiofauna distribution and the environmental factors was investigated.The results indicated that(1) the density of the dominant groups(i.e.nematode,copepods,polychaetes) and the biomass of nematodes were significantly negatively correlated with the latitude and longitude;(2)but were significantly positively correlated with the amount of phaeopigment;(3) the biomass in the sediment had no significant impact on the density of meiofauna and their major groups,but was significantly positively correlated with the amount of phaeopigment;(4) the density of meiofauna,nematodes and polychaetes and the biomass of nematodes were significantly positive correlated with the amount of chlorophyll a;(5) the density of copepods has no sigifnicant correlation with the amount of chlorophyll a.

Meiobenthos in earthen ponds used for semi-intensive shrimp farming (New Caledonia, South Pacific)

We analysed the temporal variability of meiobenthic (meiofauna and protists) abundance and community structure in the sediments of two shrimp farms located in New Caledonia. In each farm, sediment samples were collected weekly from February to June 2006 at two ponds, and analysed for quantity and composition of sedimentary organic matter, meiofaunal abundance, taxa richness and community composition. Independently of the initial conditions, sedimentary contents of biopolymeric C and total phytopigment varied significantly during shrimp rearing, although not consistently in the two ponds. Changes in the quantity and biochemical composition of sedimentary organic matter were associated with changes in total meiofaunal abundance and taxa richness, as well as in total and rare (<1% of total abundance) meiobenthic community composition. We show that the slight eutrophication of the sediment during the shrimp rearing cycle determined significant effects on the meiofaunal community composition as well as on the relative importance of metazoan vs. protists abundance. The results of this study suggest that the study of meiobenthic communities represents a reliable descriptor of the environmental quality of shrimp farming ponds.