Colonization experiments, carried out over a 32-week period at 63 m water depth in the Oslofjord, Norway, have shown that sediment Cu-concentrations of >900 ppm cause a change in the living (stained) foraminiferal community structure as compared to control values of 70 ppm. The changes, which are revealed through multivariate statistical analyses (MDS-ordination and ANOSIM tests) of the different treatment assemblages, are reflected by increased equitability and reduced abundances in treatments with high (967-977 ppm) and very high (1761-2424 ppm) Cu-concentrations. At the species level, a significant negative effect of the Cu-enrichment could be observed only for Stainforthia fusiformis and Bolivinellina pseudopunctata. There was no significant decrease in the number of species with increasing sediment Cu-enrichment. This indicates that not even sediment [Cu] > 2000 ppm had a severe negative impact on the foraminiferal species ability to colonize. One prominent effect of the Cu-contamination is that, at concentrations higher than about 900 ppm, the opportunistic and dominant S. fusiformis developed an increasingly patchy distribution pattern. Cu-contaminated sediments alone do not seem to promote development of deformed hard-shelled foraminiferal tests beyond the normal range.