Multidisciplinary study to monitor consequences of pollution on intertidal benthic ecosystems (Hauts de France, English Channel, France): Comparison with natural areas.

The intertidal areas of the Hauts-de-France (English Channel - France) stand out for the occurrence of fragile ecosystems that are exposed to natural and human-induced stress. Over the last two centuries, the northern part of this region has experienced a strong human pressure, with the settlement of numerous activities (i.e., metallurgic factories, harbors, embankments). On the contrary, the southern part includes mostly natural areas. The whole region is influenced by a macrotidal regime. A multidisciplinary approach based on sedimentological (grain-size), geochemical (trace metals, biomarkers) and biological (foraminifera) proxies was used to unravel the contrasting environmental conditions in the Hauts-de-France. Three foraminiferal-types communities, which reflect different ecological characteristics at regional scale, were identified: 1) estuarine macrotidal assemblages (Haynesina germanica associated to Elphidiidae) in low impacted estuaries; 2) industrial-perturbed assemblages (H. germanica and Cribroelphidium excavatum) in harbor areas; and 3) infaunal-dominant assemblages (Bolivina variabilis and B. pseudoplicata) in embankment areas. The outcomes of this study show that a multiproxy procedure needs to be adopted for properly characterizing intertidal ecosystems, where human impacts and natural stresses overlap and are hard to disentangle.