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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.