Benthic ecosystem changes associated with wastewater treatment at Marseille: Implications for the protection and restoration of the Mediterranean coastal shelf ecosystems

Since 1965, macrobenthic communities have been studied in the area surround ing the sewer outfall of Marseille, France. The polluted zone increased by a factor of 3 and the subnormal zone increased by a factor of 10 between 19 70 and 1980. After construction of a primary treatment plant in 1987, the m acrobenthos of the polluted zone decreased significantly in terms of number of individuals. This decrease was apparently caused by a reduction of orga nic matter discharged to the sea and was particularly notable near the disc harge. However, composition of communities began to change in 1992 to 1993. Benthic samples taken at depths of 35, 39, and 51 m in July 1994 and Janua ry 1995 indicated a recovery of parts of a polluted zone to a community res embling the subnormal zone. Most notable is the disappearance of species in dicative of the polluted zone at stations H3 and H4 and the decrease at sta tion 17 (nearest the outfall). Also, sentinel species of the subnormal zone and species characteristic of the unpolluted zone increased in number. The study demonstrated a complete change of communities at stations 17 and H4 between 1990 and 1994. Communities at these two stations, both near the sew er outfall, are characteristic of the subnormal zone. The community at stat ion H3 that belonged to the subnormal zone displayed a degree of structural stability. These changes in benthic populations indicated that constructio n of the primary treatment plant reduced contamination in the area and may lead to recovery of the benthos in this region.