This research was carried out in a bay situated to the east of Marseilles (Côtes de Provence, France). The infra- and circalittoral macrobenthos was studied over a period of 28 years. During this series of investigations, carried out in 1959 (1954-59)-1962-1972-1976 and 1982, the bay was subjected to violent anthropogenic pressures, aggravated by climatic change that lasted for several consecutive years. The anthropogenic factors include the extension of a harbour, the construction of a yacht harbour near the main harbour, the installation of two outfalls for untreated urban sewage, deposits in the circalittoral zone of material from dredging of the harbour, the indirect impact of a distant coastal river diverted into the sewage main of the city of Marseilles and finally several catastrophic forest fires (1190 ha burned). The major climatic alteration, which lasted for a period of eight years, involved a scarcity of NW winds (dry, cold) and an excess of E winds (warm, wet), often accompanied by heavy rainfall. The overall result of these factors was a phenomenon of prolonged disequilibrium affecting all the macrobenthic assemblages and their facies, caused by changes in the deep current pattern and in particular an increase in silting of the infra- and circalittoral bottom throughout the bay (mean value recorded: increase of 0.8% per year), accompanied by inputs of organic matter and the regression of the Posidonia oceanica (marine phanerogam) meadows from the lower limit upwards.