Frecliving marine nematodes were sampled on two occasions from an extonsive grid of 20 stations in the Bohai Sca and its approaches. Differences within stations between sampling periods were small, resulting from small changes in abundance of dominant species. Differences between stations were significant, and were used to cluster stations into groups with similar species composition. These station groupings revealed a weak faunal gradient leading from the mouth of the Huanghe (Yellow River) to the Bohai Strait. Analyses relating faunal composition to environmental variables showed that there were significant differences in environmental variables between faunally-defined groups of stations. The variables most closely correlated with community structure were silt/clay and sand, depth, phacopigment concentrations below the sediment surface, organic content and arsenic. These reflect natural processes within the Bohai Sea. A suite of univariate measures were related to distance from the river mouth, with a major discontinuity about 120km into the Bohai Sea. Comparison of values of the biodiversity measures average taxonomic distinctness (△-) and variation in taxonomic distinctness (△+) suggest that the mciobenthos of the Bohai Sea as a whole is not under major pollution stress.