Litter decomposition, a fundamental process of nutrient cycling and energy flow in freshwater ecosystems, is driven by a diverse array of decomposers. As an important component of the heterotrophic food web, meiofauna can provide a trophic link between leaf-associated microbes (i.e., bacteria and fungi)/plant detritus and macroinvertebrates, though their contribution to litter decomposition is not well understood. To investigate the role of different decomposer communities in litter decomposition, especially meiofauna, we compared the litter decomposition of three leaf species with different lignin to nitrogen ratios in litter bags with different mesh sizes (0.05, 0.25, and 2 mm) in a forested stream, in China for 78 days. The meiofauna significantly enhanced the decomposition of leaves of high-and medium- quality, while decreasing (negative effect) or increasing (positive effect) the fungal biomass and diversity. Macrofauna and meiofauna together contributed to the decomposition of low-quality leaf species. The presence of meiofauna and macrofauna triggered different aspects of the microbial community, with their effects on litter decomposition varying as a function of leaf quality. This study reveals that the meiofauna increased the trophic complexity and modulated their interactions with microbes, highlighting the important yet underestimated role of meiofauna in detritus-based ecosystems.

Meiofauna particularly marine nematodes around the Caiwei Guyot in the northwest Pacific Ocean and a Polymetallic Nodule Field in the northeast Pacific Ocean were studied. Due to the geographic structure, the Caiwei Guyot and the Polymetallic Nodule Field had different environmental characteristics. Meiofaunal abundances around the Guyot area ranged from 9.18 to 25.59 ind./10 cm2, which were much lower than those in the Polymetallic Nodule Field. Marine nematode was the most dominant group. A total of 123 species, belonging to 74 genera and 29 families were found. Xyalidae (21.43%), Cyatholaimidae (9.82%), Linhomoeidae (8.03%) were the dominant families. The values of species number, Margalef\'s species richness and Shannon-Wiener diversity index ranged from 15 to 62, 4.75 to 12.84 and 2.58 to 3.93, respectively. The combination of water depth, silt-clay content and chlorophyll-a concentration can best explain the differences of nematode community. This study provides a baseline for deep-sea meiofauna distribution.

Artificial reefs are widely deployed for fishery enhancement and marine conservation. A comprehensive assessment on the effects of artificial reefs could minimize the negative consequence of blindly developing artificial reefs. We examined the meiofaunal community and benthic environment adjacent to and <5 m from artificial reefs in Xiangyun Bay, Bohai Sea, China. We found the highest total meiofaunal abundance beside the artificial reef. Shannon-Wiener and Pielou indexes had no significant difference among different distances from the artificial reefs. The presence of artificial reefs impeded the surrounding flow and provided additional substrate for bivalves and kelps, which could cause finer sediment and organic enrichment around it. Sediment grain size and total organic matter were the most important parameters influencing the meiofauna. We suggest that the shape, material, configuration and location of artificial reefs should be related with a specific goal to avoid mindless proliferation.

The Yellow Sea Cold Water Mass (YSCWM) is a seasonal hydrological phenomenon with significant effects on benthic animals. Based on a range of biological traits, including feeding type, tail shape, adult body length, body shape and life history (c-p value), the biological trait analysis (BTA) of marine nematodes in the southern Yellow Sea was studied in June 2003 (summer) and January 2004 (winter) in order to reveal the effects of YSCWM on benthic animals. In terms of biological traits composition of marine nematode assemblages, results of ANOSIM showed that there were no significant differences among sites inside the YSCMW area. However, for spatial distribution, marine nematode assemblages showed significant differences between sites inside and outside of the YSCWM area in terms of body shape, as there was higher percentage of nematodes with slender body shape while lower percentage with stout and long thin body shape at the sites inside the YSCWM area. Results of BIOENV analysis showed that water depth and sediment silt-clay percentage were the most important factors contributed to the differences of biological traits of marine nematode assemblages in summer, while sediment phaeophorbide content best explained the differences of marine nematode assemblages in winter. The existence of the YSCWM may provide a stable environment for marine nematode assemblages, keeping them in a continuous state during the seasonal changes. The higher percentage of nematodes with slender body may be the response to the YSCWM.

In order to reveal the spatio-temporal distribution of meiofaunal assemblages and its relationship with environmental factors in semi-enclosed bay habitats, meiofaunal and sediment samples were collected in February (winter), May (spring), August (summer) and November (autumn) 2014 in Jiaozhou Bay, China. A total of 20 meiofaunal taxa were identified. The most dominant group was free-living marine nematode, followed by benthic copepod. During the four sampling seasons, the values of meiofaunal average abundance were (912.3 ± 603.1), (1576.4 ± 659.5), (1074.6 ± 417.6), (2152.4 ± 1062.3) ind./10 cm2 while those of biomass were (575.0 ± 398.5), (874.3 ± 518.4), (617.9 ± 337.8), (1203.6 ± 719.6) μg dwt/10 cm2, respectively. In terms of vertical distribution, meiofauna were mainly found in the (0-2) cm sediment layer (59.92%), followed by (2-5) cm layer (28.25%) and (5-8) cm layer (11.82%). Results of correlation analysis showed that bottom water temperature was the main factor influencing meiofaunal distribution and food source (sediment organic matter content) was the main factor influencing meiofaunal assemblages.

Deep-sea hydrothermal vent fields are among the most extreme habitats on Earth. Major research interests in these ecosystems have focused on the anomalous macrofauna, which are nourished by chemoautotrophic bacterial endosymbionts. In contrast, the meiofauna is largely overlooked in this chemosynthetic environment. The present study describes a new species, Thomontocypris shimanagai sp. nov. (Crustacea: Ostracoda), which was collected from the surface of colonies of neoverrucid barnacles and paralvinellid worms on the chimneys at the Myojin-sho submarine caldera. This is the first discovery of an ostracode from deep-sea hydrothermal vent environments in the western Pacific region. In addition to the species description, we discuss three aspects: 1) adaptation, 2) endemism, and 3) dispersal strategy of the hydrothermal vent ostracodes. Regarding these aspects, we conclude the following: 1) the new species may feed on sloughed-off tissues, mucus secretions, or fecal pellets of sessile organisms, rather than depend on chemoautotrophic bacteria as symbionts for energy; 2) as has been pointed out by other studies, Thomontocypris does not likely represent a vent-specific genus; however, this new species is considered to be endemic at the species level, as it has not been found outside of the type locality; and 3) this new species may have migrated from adjacent deep-sea chemosynthesis-based habitats, such as hydrothermal vents, with wood falls potentially having acted as stepping stones.

The link between biodiversity and ecosystem functioning (BEF) over long temporal scales is poorly understood. Here, we investigate biological monitoring and palaeoecological records on decadal, centennial and millennial time scales from a BEF framework by using deep sea, soft-sediment environments as a test bed. Results generally show positive BEF relationships, in agreement with BEF studies based on present-day spatial analyses and short-term manipulative experiments. However, the deep-sea BEF relationship is much noisier across longer time scales compared with modern observational studies. We also demonstrate with palaeoecological time-series data that a larger species pool does not enhance ecosystem stability through time, whereas higher abundance as an indicator of higher ecosystem functioning may enhance ecosystem stability. These results suggest that BEF relationships are potentially time scale-dependent. Environmental impacts on biodiversity and ecosystem functioning may be much stronger than biodiversity impacts on ecosystem functioning at long, decadal-millennial, time scales. Longer time scale perspectives, including palaeoecological and ecosystem monitoring data, are critical for predicting future BEF relationships on a rapidly changing planet.

In order to assess marine sediment quality of a semi-enclosed bay, sediment and meiofaunal samples were analyzed at 35 stations in coastal waters of Bohai Bay, China. Concentrations of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, Co and Mn) in sediment were measured and the Hakanson potential ecological risk index coupled with the ratio of nematodes to copepods (N/C ratio) was used. Results showed that the concentration of Mn was the highest while Cd was the main risk contributor. The Hakanson potential ecological risk index indicated that all pollutants posed low risks in the study area. However, the N/C ratio exhibited different results compared with Hakanson potential ecological risk index. BIOENV analysis identified the concentration of Ni and sediment grain size as the most important environmental variables influencing meiofaunal assemblages. The present study indicated that, in marine sediment quality assessments, meiofaunal assemblages should be involved besides pollutant concentrations.

The accuracy and applicability of the Nematode/Copepod index (N/C) in monitoring the effects of environmental disturbances is controversial. In this study, we used an integrated approach that includes both meiofauna and the sedimentary environment to demonstrate a tourism-induced disturbance gradient among sampled beaches. We also analysed the relationships between meiofauna and environmental factors. The results showed that disturbed beaches were characterised by high values of meiofauna abundance, chlorophyll a content, total organic carbon content and N/C but lower levels of dissolved oxygen. The chlorophyll a and dissolved oxygen contents were found to be the most important factors for explaining the disturbance gradient amongst the beaches. The N/C index had a positive relationship with chlorophyll a and a negative relationship with dissolved oxygen. There was no significant relationship between N/C index and total organic carbon content.