Spatial organization of the macrobenthos in the Bou Regreg estuary, Moroccan Atlantic coast.

Spatial organization of the macrobenthos in the Bou Regreg estuary, Moroccan Atlantic coast. On the Moroccan Atlantic coast, the Bou Regreg estuary has been disrupted by many human activities since more than 30 years, in relation with the extension of Rabat and Sale cities on its strands and especially the installation upstream of a dam in 1974. The aims of this work, realized from March 1998 to January 1999, were to establish a first ecological assessment of the subtidal ecosystem of the estuary after the achievement of the dam, before the establishment of a large development of the area. The results of hydrological analyses showed an upstream shifting of salinity in comparison with the previous situation. Multivariate analyses showed three communities successively distributed from the sea to the upper part of the estuary. The hydrological factors expressed by the distance from the mouth of the estuary seem to be the main factors that controlled the three macrozoobenthic communities, from downstream to upstream respectively: (1) the Haustorius arenarius community, composed of two assemblages dominated respectively by Gastrosaccus spinifer and Solen marginatus; (2) the Cerastoderma edule community, characterized by a high species richness, dominated by tolerant species with opportunistic ones, indicating a strong organic matter impact; (3) the Scrobicularia plana community that characterizes estuarine environmental conditions. Biotic indices values, using ecological groups of macrofauna species, indicated that this estuary is globally unbalanced, excepted at the mouth part. A comparison with the situation before the construction of the dam in 1974 showed that the three main communities are still present, but that their structure and relative extension have been strongly modified.