Data on density, diversity and species number of harpacticoids and nematodes from a 3 m deep station in Lake Grevelingen are reported over the period 1975-1980. Vertical distribution of both copepod and nematodes densities are added. Over the 6 years period 95 species of nematodes and 26 species of harpacticoids have been identified. Neither diversity nor species number of harpacticoids changed significantly over the period. Nematode diversity and species number showed considerable changes, and especially the species composition evolved drastically over the years. The changes in feeding types among nematodes are discussed. Densities of both copepods and nematodes changed substantially over the 6 years period. Concurrent with a significant rise of the redox discontinuity layer from more than 20 cm sediment depth to less than 5 cm, the interstitial copepod fauna disappeared almost completely. The changes in vertical distribution of nematode densities were less pronounced though substantial.