The ragworm Hediste diversicolor (O. F. Müller, 1776) is a widespread species of coastal lagoons and estuaries from Morocco to Scandinavia. Population dynamics of H. diversicolor from the Atlantic coast of Morocco were studied in the Bou Regreg Estuary (Gillet, 1993), in the Souss Estuary (Aït Alla et al., 2006); in Spain, in the Bay of Cadiz (Arias & Drake, 1995); and in Portugal in the estuarine systems (Sprung, 1994; Fidalgo e Costa et al., 1998; Abrantes et al., 1999). In the North Atlantic Ocean, H. diversicolor was studied in the Severn Estuary (Mettam, 1979; Mettam et al., 1982); in the North Sea, in the Ythan Estuary, Scotland (Chambers & Milne, 1975); in North East England (Olive & Garwood, 1981); and in the North Norfolk (Nithart, 1998). H. diversicolor is a major link in food webs and of economic importance as bait for fishing in several European countries. This species was chosen because it has a key role in the functioning of estuaries, a major link in benthic food webs and through sediment reworking by bioturbation activity. In France, the population dynamics of H. diversicolor was first studied in the Loire Estuary (Gillet, 1990; Gillet & Torresani, 2002) and the bioturbation activity (Gillet et al., 2012). This is a preliminary work to a large scale research program on H. diversicolor in different estuaries with the PNETOX ‘National Program of Ecotoxicology’. In the framework of the French National Program of Ecotoxicology, environmental quality was assessed in the multi-polluted Seine Estuary and the comparatively clean Authie Estuary, France (2002-2004), by determining contaminant levels in water, sediments and the infaunal worm H. diversicolor (Durou et al., 2003; Amiard-Triquet et al., 2007; Gillet et al., 2008). A scientific project comes under the framework of the International network Nereis Park Experiment gathering 27 laboratories from all over the world. The experiments were carried out concurrently in spring 2007 using a common protocol to study the bioturbation activity of H. diversicolor (Gillet et al., 2012; Gilbert et al, in press).