| Through field investigation,sampling and laboratory sorting analysis,the sediment samples collected from 13 stations in the central basin of the South China Sea in June 2020were studied,and got the relevant data of meiofauna and free-living nematodes.Thirteen stations isolated 14 small benthic meiofauna,including nematoda,copepoda,polychaeta and oligochaeta,with an average abundance 204.4±55.6 ind./10 cm~2 and average biomass 914.2±794.2μgdwt/10 cm~2.Free-living nematodes were the dominant group,accounting for 76.2%of the total abundance of meiofauna,followed by ostracoda(15.5%)and copepoda(4.2%).In vertical distribution,86.3%of meiofauna perched in 0–5 cm surface layer.The measured dry weight of free-living nematodes in this region were less than the empirical coefficient,the dry weight of free–living nematodes were 0.136±0.24μg/individual,and the mean biomass of nematodes were 21.2±3.8μgdwt/10 cm~2.Used IBM SPSS Statistics 22 to analyze and test the correlation between the abundance of free–living nematodes and the water depth of sampling points.The results showed that the abundance of free–living nematodes at each station in the survey area were negatively correlated with the water depth.The results of 13 stations showed that free–living nematodes had the highest dominance in the composition of feeding types in selective sediment feeders(1A),accounting for 39.5%,and scrapers or diatom feeders(2A)accounted for 38.5%.In terms of sex ratio,juveniles accounted for 56.5%of the total number of individuals in the community,and the ratio of female to male was 0.9:1.We used PRIMER 6 to calculate the diversity index of free-living nematodes at each station.The results showed that the species composition of free-living nematodes in the region were rich and the diversity were high compared with other sea areas or other regions in the South China Sea.The investigation on the environmental health of the surveyed sea area shows that the sediment environment in the central basin of the South China Sea was not polluted by organic matter.A total of 275 species or taxonomic entities of free–living marine nematodes belonging to 142 genera,39 families,10 orders and 2 classes.The dominant genera were Acantholaimus Allgen,1933,Halalaimus de Man,1888,Cervonema Wieser,1954 and Microlaimus de Man,1880.We discovered and described eight new species:Laimella multiamphida sp.nov.,Leptolaimus nanhaiensis sp.nov.,Leptolaimus paraquartus sp.nov.,Elzalia longicaudata sp.nov.,Minolaimus distalamphidus sp.nov.,Linhystera granda sp.nov.,Actinonema tabernus sp.nov.,Setoplectus minor sp.nov.and 5 new records:Greeffiella moppa Schrage,1972,Pararaeolaimus tetradenus Leduc,2017,Diplopeltoides anatolii(Voronov,1982)Tchesunov,1990,Diplolaimella thailandica Kito&Aryuthaka,1998 and Metadasynemella falciphalla Vitiello&Haspeslagh,1972. |
