| In order to study the effects of the southern Yellow Sea Cold Water Mass (YSCWM) on meiofauna especially for marine nematodes, the taxa composition, abundance, biomass of meiofauna and species composition, community structure and biodiversity of marine nematodes and their relationships with environmental variables were analyzed through the samples from 8 stations investigated by R/V "Dongfanghong II" in June and November,2013.The results showed that the average abundances of meiofauna were (900.8±365.6) ind./10 cm2 and (758.4±403.6) ind./10 cm2, and biomass were (886.9±308.2) μg/10 cm2 and (615.7±390.7) ±g/10 cm2 in June and November,2013, respectively. Results of ANOVA showed that no significant differences of meiofaunal abundance and biomass were detected among the 8 stations in these two study cruises. A total of 17 meiofaunal groups were identified. The most dominant taxonomic group was free-living marine nematodes, with a relative dominance of 88.5% in June and 94.0% in November. The following groups were also important, including benthic copepods, polychaetes, kinorhynchs and ostracods. Analysis of meiofaunal vertical distribution indicated that 92.5% and 95.4% of meiofauna distributed in the top 5 cm of the sediment in the two study cruises, while 59.1% of nematodes and 78.2% of copepods were found in the top 2 cm of the sediment. Correlation analysis among meiofaunal abundance and biomass, nematode and copepod abundance and environmental variables showed that meiofaunal abundance and biomass had significant negative correlation with bottom water temperature (BWT) and sediment silt-clay percentage (YT). Copepod abundance also had significant negative correlation with BWT and YT while it had significant positive correlation with sediment median diameter (Mdo). The results of BIOENV indicated that BWT, bottom water salinity (BWS), sediment water content (W), sediment chlorophyll-a (Chl-a) and phaeophorbide (Pha) contents were the most important factors to influence meiofaunal assemblages.In our study, a total of 75 species or taxa of free-living marine nematodes, belonging to 66 genera,25 families and 3 orders, were identified. In June, the average abundance of marine nematodes was (797.3±330.0) ind./10 cm2. A total of 68 marine nematode species were identified. The dominant species were Dorylaimopsis rabalaisi (27.46%), Spilophorella sp. (24.38%), Daptonema sp. (8.38%), Sabatieria sp. (7.31%). In November, the average abundance of marine nematodes was (712.8±376.5) ind./10 cm2. A total of 59 marine nematode species were identified. The dominant species were Spilophorella sp. (26.56%), Dorylaimopsis rabalaisi (22.05%), Parasphaerolaimus sp. (6.18%), Daptonema sp. (5.62%). CLUSTER analysis revealed four main types of nematode community (or station groups) in the sampling area. SIMPROF test showed that there were differences in the species composition of nematodes between the four communities, but no significant difference between each group. In terms of trophic structure, epigrowth feeders (2A) are dominant by species number and individuals number. The results of correlation analysis between biodiversity of marine nematodes and environmental factors showed that the Shannon-Wiener diversity index(H’) had significant negative correlation with the YT, organic matter (OM) and W, while the species richness index had significant or highly significant negative correlation with YT, OM and W (r=-0.682, P<0.01). Dominance index had significant or highly significant positive correlation with YT (r=0.517,P<0.05), OM and W. Pielou’s evenness index had no correlation with environmental factors. The results of BIOENV indicated that Pha, W, BWS, BWT were the most important factors to influence marine nematodes assemblages.In summary, there were no significant difference betweent the two seasons in abundance of meiofauna and marine nematodes in the study area. In the two seasons. there showed no differences in the number of nematode species and structure of nematode communites both of which were dominated by species of Dorylaimopsis rabalaisi and Spilophorella sp. just with different orders. In terms of trophic structure and age compositon. epigrowth feeders and juvenile were in dominant position in each season, respectively. |
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