Meiofaunal Richness Research Articles

Ecological Responses of Meiofauna to a Saltier World—A Case Study in the Van Uc River Continuum (Vietnam) in the Dry Season

Increasing intensity of storms, typhoons, and sea level rise in conjunction with high water demand, especially for agriculture, in dry seasons in the Red River Delta may have led to seawater intruding deeper into the rivers’ estuaries. Given that losses of agricultural productivity and shortages of freshwater resources are projected, a reliable early warning of salinity invasion is, therefore, crucially needed. To evaluate the impact of salinity variations on riverine ecosystems, distribution patterns of meiofauna were examined at 20 stations along the Van Uc River continuum in the dry season. Meiofaunal richness indices were higher in the estuary and slightly decreased upriver. Nematoda was the most dominant taxon in salty stations, while Rotifera was more abundant in the less salty ones. A multiple variate analysis showed a strong interplay among salinity, nutrients, and pore water conductivity, which shaped the meiofaunal distribution. The inclusion of pore water salinity, nutrients, and meiofaunal community structure indicated a greater extent of the saline ecosystem in the estuary, posing a greater risk of freshwater salinization. Our results highlight the potential role of meiofauna as bioindicators but also call for a reformation of salinity assessment for better freshwater conservation and management.

Amazon River discharge impacts deep‐sea meiofauna

AbstractIn this study, we show that the deep‐sea meiofauna community at the Brazilian Equatorial Margin (BEM) is strongly influenced by the Amazon River. Our comparison across four deep ocean basins including Amazon, Pará‐Maranhão, Barreirinhas, and Ceará showed that the former supports a completely distinct meiofaunal community. Meiofaunal richness increased with increasing distance from the Amazon, reflecting changes in sediment proprieties among basins. Total phytopigment content at Amazon sediments was threefold higher than at other basins. The chlorophyll a/Phaeo mean ratio, however, was lower than 1, suggesting a predominant degraded bulk organic matter derived from the Amazon River discharge. Nematode assemblages from Amazon strongly differed from the other basins mostly due to higher genus richness, trophic diversity, and variations in the abundance of Sabatieria, which in turn led into higher dissimilarity values and turnover rate. Furthermore, the bathymetric distribution of nematode assemblages at Amazon and Ceará basins differed significantly among depth zones, especially due to the higher abundance and diversity at Amazon basin. Our findings show that the Amazon River plays a critical role in structuring and shaping the deep‐sea meiofauna and nematode biodiversity at the BEM. Increasing impacts on the Amazon rainforest will certainly affect the amount of freshwater discharge, and the quantity and quality of organic material transported to the Atlantic Ocean, which in turn will have effects on the deep‐sea communities.

Meiofaunal Community Spatial Distribution and Diversity as Indicators of Ecological Quality in the Bohai Sea, China

The Bohai Sea is a semi-enclosed marginal sea in the North West Pacific. Meiofauna samples were collected from 22 stations in the Bohai Sea to document the spatial distribution, structure, and diversity of the meiofaunal community and investigate the major factors influencing the community features. A total of 20 higher taxa of meiofauna were identified. The dominant group was Nematoda, accounting for 90.8% of the total meiofaunal abundance on average, followed by Copepoda, Bivalvia, Polychaeta, Kinorhyncha, and Ostracoda. Meiofaunal abundance ranged from 121 ± 89 ind (10 cm2)−1 to 3042 ± 1054 ind (10 cm2)−1. Diversity indices also varied among different stations, with a Margalef’s richness index (d) of 1.1–3.1, Shannon-Wiener diversity index (H′) of 0.7–1.8, and Pielou’s evenness index (J′) of 0.4–0.8. Meiofaunal abundance and diversity indices were significantly lower in the areas of Bohai Bay and adjacent to Laizhou Bay. The correlation analysis showed that meiofaunal abundance and diversity indices are closely linked to variations in sediment silt-clay content, medium grain size (MDΦ), and chlorophyll-a concentrations. The ecological quality status of most stations can be ranked from poor to moderate based on meiofaunal richness. According to the value of nematode to copepod ratio (Ne:Co ratio), most stations are uncontaminated, except seven stations are slightly or moderately contaminated. Both meiofaunal richness and Ne:Co ratio indicate the poor ecological quality of three stations adjacent to Laizhou Bay. The efficiency of the meiofauna communities as environmental indicators will be tested in a greater area in the future studies.

Meiofaunal Dynamics and Heterogeneity along Salinity and Trophic Gradients in a Mediterranean Transitional System

The spatiotemporal variation in meiofaunal assemblages were investigated for the first time in the Cabras Lagoon, the largest transitional system in the Sardinian Island (W-Mediterranean Sea). Two main environmental (salinity and trophic) gradients highlighted a significant separation of the three study sites across the lagoon, which were consistent through time. The environmental variability and habitat heterogeneity of the Cabras Lagoon influenced the meiofauna. In particular, salinity and dissolved oxygen, primarily, shaped the meiofaunal assemblage structure at the seaward site which was significantly different from both the riverine and the organically enriched sites. On the other hand, the trophic components (e.g., organic matter, Chlorophyll-a, and phaeopigments) and the different degrees of confinement and saprobity among sites were the secondary factors contributing mostly to the separation between the latter two sites. The lack of significant differences in the temporal comparison of the meiofaunal assemblage structure along with the very low contribution of temperature to the meiofaunal ordination indicated that this assemblage was more affected by spatial rather than by temporal variation. This pattern was also supported by significant differences between the three sites in several univariate measures, including total number of individuals, number of taxa, Pielou’s evenness, and the ratio between nematodes and copepods. Thus, the present study corroborates the hypothesis that meiofaunal organisms are good indicators of the spatial heterogeneity in transitional waters (TWs) and could have a greater species richness than that expected. Indeed, the Cabras Lagoon overall showed one of the highest meiofaunal richness values found from both Mediterranean and European TWs.

Biotic and abiotic factors affecting seasonal and spatial distribution of meiofauna and macrophytobenthos in transitional coastal waters

Benthic organisms are considered among the best bioindicators being closely associated to sediments in which many pollutants are stored. In this study, macrophytes and meiofauna have been investigated in a transitional area (Venice lagoon, Italy) characterized by numerous anthropogenic pressures. Macrophyte Quality Index and meiofaunal richness were used to assess Ecological Quality (EcoQ) status in line with Water Framework and Marine Strategy Framework Directives. Comparing the EcoQ classes, the results appeared consistent in 24 sites, whereas, in the remaining 5 ones, the values significantly diverged. These results could be related i) to the presence of the seagrass Cymodocea nodosa that could affect meiofaunal taxa with the production of tannins; ii) to the different time response of these communities to human impacts. This synergistic investigation has allowed an accurate description of the spatial and temporal changes of meiofauna through data on abiotic and biotic parameters characterizing the ecosystem trophic level.

Biodiversity and distribution of the meiofaunal community in the reef slopes of the Maldivian archipelago (Indian Ocean)

Marine biologists have progressively increased their consciousness of the importance of meiofauna for the benthic domain in both temperate and tropical regions. After the 1998 bleaching, Maldivian reefs (Indian Ocean) have been regarded as a vulnerable ecosystem that must be carefully monitored. Accordingly, an extensive investigation of meiofaunal distribution in the reef slopes of the Maldivian archipelago has been carried out, taking into account geographical position, type of habitat (inner vs. outer slope), inclination and depth gradient. Twenty-four taxa revealed the highest meiofaunal richness ever found in Maldivian reefs. Interestingly, Thermosbenacea and Syncarida were identified, which are two taxa that have only recently been documented in the marine ecosystem. Chaetognatha were also present, which is a group that was only considered to be planktonic until 2000, when they were also discovered in the benthos. The type of habitat, affected by different hydrodynamic conditions, was the main factor influencing the meiofaunal community's structure and diversity. In detail, the outer reefs were characterized by the highest level of diversity, confirming previous observations on the rate of coral reef growth and vitality and underlining the greater vulnerability of the inner slopes. In contrast, depth only significantly affected the community structure, but not its density or diversity. Accordingly, community structure seems to be more sensitive than abundance and diversity indices when it comes to detecting depth gradients. The 10° inclination of the inner slopes revealed the most different community structure and the greatest dominance of nematodes, leading to the lowest diversity levels.

Meiofaunal assemblages of the bay of Nisida and the environmental status of the Phlegraean area (Naples, Southern Italy)

Nisida is an islet of volcanic origin of the Phlegraean archipelago (Southern Italy) that has been included in the General Reserve of the Regional Park of Phlegraean Islands. The islet has been inaccessible both by land and by sea for a long time and, thus, has maintained its naturalistic value almost unchanged, in contrast with the close Bagnoli area, in which a steel industry has been active for several decades. An investigation was carried out in 2014–2015 at the bay of Nisida (Porto Paone). The main aims of our study were to document the structure of the meiofaunal assemblage, to identify the environmental factors that lead to its spatial and temporal variations, and to evaluate the ecological quality of this area, so bridging a gap in the scientific knowledge of Porto Paone. According to the diverse substrate typology and hydrodynamic regime, four stations were established to evaluate the meiofaunal assemblage over a period of one year. A high number of meiofaunal taxa (21) and a high biodiversity of meiofauna were recorded: the total meiofaunal density was higher in the eastern sector of the bay, where the effects of currents increase the abundance of temporary meiofauna in the sediment by increasing the supply of planktonic larvae of macrofauna (i.e., annelids, molluscs). PERMANOVA revealed significant differences of the assemblage structures at both the temporal and spatial scales. Summer conditions appeared to favor an increase of several taxa, which may be related to both an enhancement of the trophic sources, in turn promoting more trophic lifestyles, and to the biological cycles of individual taxa. Among the environmental variables, sediment variations, temperature, and chlorophyll-a (Chl-a) concentration appeared to be important in influencing the meiofaunal distribution. The results suggest that Porto Paone is characterized by a great richness (21 vs. 8 total taxa), especially if compared with the close, highly impacted area of Bagnoli. According to the current classification of environmental quality based on the meiofaunal richness, Porto Paone may be classified with a high ecological quality.

Meiofaunal Richness in Highly Acidic Hot Springs in Unzen-Amakusa National Park, Japan, Including the First Rediscovery Attempt for Mesotardigrada.

Extreme environments sometimes support surprisingly high meiofaunal diversity. We sampled runoff from the acidic hot springs of Unzen, Japan. This is the type locality of Thermozodium esakii Rahm, 1937, the only tardigrade in the class Mesotardigrada, which remains contentious in the absence of corroboration or supporting specimens. Our sampling revealed at least three species of arthropods, four rotifers, and five nematodes living in the hot (ca. 40°C) and acidic (ca. pH 2.5) water, but no tardigrades.

Persistent impacts to the deep soft-bottom benthos one year after the Deepwater Horizon event.

In fall 2010, several months after the Deepwater Horizon blowout was capped, zones of moderate and severe impacts to deep-sea, soft-bottom benthos were identified that together extended over an area of 172 km2 . A subset of stations sampled in 2010 was resampled in May and June 2011, 10 to 11 months after the event, to determine whether the identified adverse effects were persisting. The design compared 20 stations from the combined moderate and severe impact zone to 12 stations in the reference zone that were sampled in both years. There were no statistically significant differences in contaminant concentrations between the impact and nonimpact zones from 2010 to 2011, which indicates contaminants persisted after 1 y. Whereas there were some signs of recovery in 2011 (particularly for the meiofauna abundance and diversity), there was evidence of persistent, statistically significant impacts to both macrofauna and meiofauna community structure. Macrofaunal taxa richness and diversity in 2011 were still 22.8% and 35.9% less, respectively, in the entire impact zone than in the surrounding nonimpact area, and meiofaunal richness was 28.5% less in the entire impact zone than in the surrounding area. The persistence of significant biodiversity losses and community structure change nearly 1 y after the wellhead was capped indicates that full recovery had yet to have occurred in 2011. Integr Environ Assess Manag 2017;13:342-351. © 2016 SETAC.

Plant-animal diversity relationships in a rocky intertidal system depend on invertebrate body size and algal cover.

Considerable research has examined the influence of herbivores on the maintenance of plant diversity, but fewer studies have examined the reciprocal effect of plant diversity on the animals that use the plant community for food and shelter, particularly in marine systems. Several mechanisms could underlie such effects. Animal diversity and abundance could be increased by complementary use of different plants by different animals, or by an indirect effect of plant diversity on plant production that results in more total plant biomass in high plant-diversity communities. Alternatively, plant species identity could play a dominant role leading to sampling effects or no effect of diversity at all. We conducted a six-year field manipulation of the richness of rocky shore seaweeds in northern California and measured the effects of algal richness and identity on the invertebrate community, from meiofauna to macrofauna. We found that diverse algal communities hosted more species of both large and small invertebrates than the average algal monoculture but that the mechanisms underlying this pattern differed substantially for organisms of different size. More species of macrofauna occurred in the polycultures than in any of the monocultures, likely due to the greater total cover of algae produced in polycultures. Rare and common macrofaunal taxa responded to host plant species richness in opposite ways, with more occurrences of rare taxa and lower abundance of very common taxa in the polycultures. In contrast, meiofaunal richness in polycultures was no different than that of monocultures of finely branched species, leading to strong effects of algal identity. Our findings are similar to those from terrestrial systems in that the effects of plant diversity we observed were most related to the greater amount of habitat in polycultures as a result of overyielding in algal biomass. However, our findings differ from those in terrestrial systems in that the primary mechanisms for both richness and identity effects appear related to the value of plants as shelter from harsh abiotic conditions or predation rather than food, and in that animal body size altered the mechanisms underlying diversity effects.